BY ENGINE/4age/enginemods
From AE86 Driving Club FAQ
The Modified 4AGE Page
In these pages, I talk about the various mods needed to take the Toyota 4AGE 1600cc engine from as low as 115hp all the way up to 240hp in 10hp increments, and beyond with turbos.
To start with, there are basically four types of 4AGE engine - - The 'big port' TVIS head version. - The 'small port' non-TVIS version. - The 20 valve versions. - The supercharged versions.
Writing a page like this is rather difficult, to say the least! The number of variations with all of the 4AGE's around the world, the number of different installations in people's own cars, etc, make the job of giving accurate estimations to how much power you're going to get if you do this and that a best guess effort. Never the less, I'll give it a go, based on my own hands-on experience, and also dealing with many, many emails, phone calls, and other conversations with drivers & engineers around the world. I'll also be using data from a 'software dyno' program that I have, and it has proven to be quite accurate in predicting trends in power up/down when changing cams, etc. It's also important to realise that you must read from 'top to bottom', as I'll only be detailing the mods for each power increment, and not repeat those mods in later (higher) increments. Equally important is to read the 'other stuff' paragraph, as it contains vital information to increasing the power of the 4AGE. (And other engines) I have also included a photos section that has many of the topics that I talk about on this page, so for example where I talk about a cheap Weber inlet manifold I have a picture of it in the photos section.
Contents |
4AGE
115hp - 134hp
This is the sort of horsepower that standard 4AGE's have around the world. The Air Flow Meter (AFM) TVIS versions make 115hp and are commonly found in the US & other countries. The Manifold Absolute Pressure (MAP) sensor TVIS versions, which are slightly more common, make 127hp. They are commonly found in Japan, Australia, and New Zealand. Both these types are found in the AE-82, AE-86, etc Corolla's, and have the large size inlet ports. The AE-92 Corolla's 4AGE has no TVIS, small inlet ports, and makes 134hp with a MAP sensor. For more information on all these engines, take a look at my Standard 4AGE page. Some points to note - - The 'small port' and 'big port' computers are occasionally interchangeable, but will rarely increase or decrease the power output of the engine. - The AFM and MAP type computers are not interchangeable, unless you also change the rest of the wiring loom to suit. - Since all the MAP sensed engines have much the same amount of power and torque, it is not worth changing the engine (to, say, a small port version) to try to get more power. There are more effective ways of spending your money.
140hp - 150hp
Bolt-on external mods are all that is needed for this much extra power. Simple mods, such as a free flowing exhaust and cold air inlet pod will give you a few more HP. Synthetic engine oil will also give you a few more HP over conventional mineral oils. By doing all of these things you'll gain a good 10hp or so over a standard engine, but anything more than that and you'll need to start digging around under the cam covers ... Towards the 150hp mark, you'll need to go for cams of around the 256° duration. If timed properly, they'll idle and run just like a pair of standard cams. Aftermarket 'chips' for the factory computer will also help the power output, but they vary greatly in quality and results - Do your homework before buying!
150hp - 160hp
The standard cam timing is 240° duration, from seat-to-seat, and this is typical for a modern road going twin cam engine. A pair of 256° cams and the mods mentioned in the 140hp - 150hp paragraph will get you around 150hp if everything else is right, but to get much more you'll certainly need bigger cams, around the 264° mark. This size cam is the upper limit of the cam duration that you can use with the factory computer, as they need a decent inlet manifold vacuum to sense to work properly. The AFM versions may be a little better off, but I've had no information on this. You won't get 160hp with the factory computer, however, and so you'll need to spend a few dollars on an aftermarket system. I highly recommend getting a programmable system rather than a new 'chip' or a simple 'add-on' for the factory computer, as if you want more power later on then you won't be limited to whatever the chip/add-on has already programmed. Once you have an aftermarket computer, you can run pretty much any size camshafts that you like, with little penalty, so to ensure that you end up with the power more like 160hp, you should run 272° cams. Note that with cams larger than about the 260° mark you will actually benefit from removing the TVIS, if fitted. The TVIS, when used with cams smaller than about that duration, will give you more low end ( < 4,400rpm) power, but this effect disappears with the bigger cams.
150hp - 160hp is also the point at which you'll need to get some work on the head. Fortunately, there's not a lot to be done and if you've got the head off then it's worthwhile spending a little more time and effort to make the mods to allow the head to flow up to ~180hp - 190hp. There are four areas that need attention on the 4AGE heads - The area just above the valve seats, the combustion chamber, and the ports themselves, and the valves & seats. - The area above the valve seats are a little too parallel, and should be narrowed up a little to create a bit of a venturi effect. - The combustion chamber has numerous sharp edges that need to be smoothed off, to eliminate pre-ignition, etc. - The inlet and exhaust ports are quite good standard, but they are a little too big on the big port heads and a little too small on the small port heads. The small port head is easy to make a bit larger, but making the big port smaller is quite difficult, so don't try it - Just clean up all the nasty little bumps & casting marks in the head instead. - The valves & seats benefit greatly from a good three or even five angle cutting job. Please read my Engine pages for more information on porting, etc. Note that a lot of engine shops leave the ports with a near-mirror finish and the port dividers almost razor sharp - This is the wrong thing to do!
160hp - 170hp
Starting to make serious power now! You can pretty much forget about passing any emissions laws you may have in your country ... ;) You'll be needing cams of at least 288° duration, and will also have to start looking at modifying the bottom end. It's also getting near the end of what the standard inlet manifold can do, so this is around the point where things start getting expensive. All the head work that you've done in the previous paragraph will cover you for this amount of power, so, to improve on 150hp - 160hp you'll need to raise the compression of the engine. There's two ways of doing this - by shaving the head or getting new pistons. The stock pistons are good for 160hp no worries, but much past that I'd recommend using good aftermarket units, such as Wisco's. You'll be needing a compression ratio of at least 10.5:1, and with 96 octane fuel you can run up to about 11:1 compression without worrying too much about pinging. The stock con-rod bolts are good for up to about 170hp, but past that you should replace them with the best you can get, such as ARP or small block Chevy. (I mean, if you're going to replace them you may as well do a good job!) You'll also need to be able to rev the engine to 8,000rpm, and maybe even 8,500rpm.
The inlet manifold is a bit of a problem, but if you're sneaky then you can make a twin Weber style manifold with throttle bodies quite cheaply. (ie, for around Aus$150, whereas buying all the gear to do the same job 'off the shelf' could easily cost over Aus$1200!) What I did was to buy a section of alloy plate ~8mm thick and another bit of thick-wall alloy tube 52mm dia. I cut the alloy to make the flanges of the Weber base and the cylinder head base. I then cut the 52mm tube to the right length (four times) and partly crushed one end so it matched the shape of the inlet ports. I then spent a few days cleaning it all up so the parts fitted each other neatly, then got them MIG welded up. And then spend another few hours filing away at the welds to smooth & blend it all again. I then ran a milling machine over both flanges to make sure that they'd seal up against the straight edge of the head and throttle bodies. For the throttle bodies (typically Aus$400+ each) I simply have used a pair of 'dead' Dellorto 45mm carbies. I have removed all of the internals so that only the throttle butterflys remain, thus making them cheap TB's. All that being said, it may be easier to simply use something like a pair of 45mm Webers, but I highly recommend the use of electronic fuel injection over any carburettors anytime, because of the ability to control the fuel scheduling far more accurately & consistently than you possibly can with any carby.
A quick note - the 4AGE that I have in my AE-86 Sprinter has 288° cams, an aftermarket computer, 10.5:1 compression, and a small amount of head work done. It makes about 160hp with a completely stock bottom end. It runs to 8,500rpm without any worries. (so far!)
170hp - 180hp
Still not any huge differences between the big and small port engines here. Not a lot more work required to get the extra 10hp from the engine now; just slightly bigger cams really. I'd recommend 288 to 304° duration.
180hp - 190hp
Definitely 304° cams, and you'll have to start paying attention to tuning the inlet manifold length, if you haven't done so already. This is also getting to the limit of what a lightly ported small port head can manage.
190hp - 200hp
Getting towards the upper limit of 304° cams, and you'll also need to have the compression up to a good 11:1. 200hp is about the limit for a small port head, no matter what the porting, so from here on the big port is the way to go. Another area that has pretty much reached its limit is the stock valves - Past 200hp you'll be needing the big valve kit. More on that next paragraph. The standard exhaust manifold has also reached its limit, so 200hp is about as far as you can go with an engine that still retains a large amount of standard parts. It will need to be revved to around 9,000rpm to get 200hp, though if built properly the engine will still be able to be driven on the road.
200hp - 220hp
Past 200hp is where the 4AGE becomes a much more serious engine, and so it requires a much greater attention to detail. It's the point at which you have to start spending a lot more money, for ever decreasing results. But, if you want the extra power then you gotta spend the dollars ... The reason I've taken the jump from 200hp to 220hp is that there's not a lot of people that make 4AGE's of around this amount of power, hence I don't have a lot of information as such. I've found that past about the 180hp mark, it's the pure racers that do their best to get over 200hp, and so there's a bit of a gap. The other reason I seem to have skimped over the 170hp - 180hp - 190hp - 200hp sections is that once the head work is done, it's really cam changes that make a lot of difference. You get a little bit here and there with compression ratio's, etc, but there's really not a lot of work to be done to get that jump from about 170hp up to around 200hp. Cams up around the 310° mark, with 0.360"/9.1mm lift are needed. You'll also have to start thinking about getting some 'shim under' buckets, which have the valve clearance adjusting shims as a small 13mm pellet shim, rather than the 25mm dia shim that sits on top of the cam buckets. This is because with cams bigger than the low 300's and roughly 8mm lift, the 'shim over' buckets will occasionally catch the edge of the shim with the top of the lobe of the cam and spit it out the side, thus RAPIDLY destroying the bucket and most likely a fair chunk of head in the next few milliseconds. The shim under kits can be obtained from TRD at hideous expense, or from other racing shops for (merely!) large amounts of money. The big valve sets are equally as expensive, but again I know of a way that can reduce costs. I have found that the valves from a 7MGTE Supra engine should be identical to the TRD big valve kit, for a fraction of the cost. They are 2mm larger than the 4AGE valves, and should not be fitted if the engine makes less than about 200hp because you will LOSE power. The other problem with the 7MGTE valves is that they're about 2mm shorter than the 4AGE ones, so much thicker shims are needed. With shim-over buckets this is an ugly thing, but I guess it's possible with shim-under type buckets. There are two crankshafts available for the 4AGE, the 'small' one which has the big end journals of 40mm dia, and the 'big' crank which has 42mm big ends. The big crank weighs about 700grams more than the small crank, (~11kgs Vs ~11.7kgs) and up to about 200hp - 220hp it is stronger, but in practice there is little difference between the two cranks. This changes with more than that amount of power though ... The factory exhaust manifold, which was good up to about 200hp, now must be replaced with a good set of aftermarket extractors. By good, I mean that they must fulfill a few criteria to make them good rather than merely average - - The four pipes MUST be equal length, to within less than 1/4"/6mm. - The four pipes must NOT have any crushed bends in them anywhere at all. - The four pipes must go into the collector in the same sequence as the firing order of the engine, ie, 1-3-4-2. Many of them simple put the pipes into the collector in any order that's convenient, but these sort make less power than a good set. - The collector must be around the 60mm dia mark. Many aftermarket extractors have 50mm collectors, and this is not large enough to make big HP.
220hp - 240hp
Save yourself a lot of time and money, and just pop out and buy a slightly used Formula Atlantic engine! But seriously, this is really big boys territory, and although it's readily achievable it can get rather expensive indeed. Up to about 220hp, you should use the small crank in preference to the big one, because the larger bearing journals create more friction due to the larger diameter (42mm Vs 40mm) having a greater radial speed for the same engine rpm's. You need to run up to and in some cases beyond 10,000rpm, so it's a careful balancing act between strength and friction and inertia. Certainly to get the higher end of the power range you need to run a forged steel crank, and they are rather rare and rather expensive. I'd be happy to run the stock con-rods (with ARP bolts, as mentioned before) up to about 220hp, but for sure past that a good set of something like Carillo's, Cunningham, or Crower rods are required. They must be made so that they weigh a good 10% less than the stock rods, to reduce the reciprocating internal weight. Wisco pistons are also past their useful limit, and so high quality (and price, of course) pistons such as Mahle must be used. The oil pump is a major risk as the revs rise into the five digit area, and the solution for that is to buy an expensive TRD unit. FWIW, the stock pumps tend to split the driven gear across their widest part at very high revs, and so shred the oil pump assembly when they let go. Cams around the 320° duration mark, with .400"/10.1mm lift are needed. They will make little power below about 6,000rpm. Dry sumping is also virtually a requirement, as if it's done properly then the engine will make a bit more power than what it otherwise would wet sumped. The wet sump system will also have trouble keeping the oil under control at the revs the engine needs to run to.
240hp - 300hp
If I had a huge bucket of money and a lot of time, I reckon that I could get 260hp or so from a 4AGE. Most likely more. What I'd do is to make a shorter stroke crank, sleeve the bores to get the largest pistons possible in, to try to keep the capacity around the 1600cc mark. I'd get a set of titanium con-rods. I'd develop or maybe buy a set of pneumatic valve springs, so I could run the engine to 15,000rpm, or more if possible. Or, I could just get a fairly stock 4AGE, decompress it down to about 8.5:1 and turbo the thing .... and probably get even more power anyway for a fraction of the cost. Ok, seriously, the best way to make a grunter turbo (4AGTE?) engine would be to simply buy a 4AGZE, sell the supercharger and manifolds, then with the money gained from that sale buy a ball-bearing turbo and a RWD AE-86 inlet manifold. Buy some mandrel bends from an exhaust shop to make up a turbo exhaust manifold, and either try to use the factory 4AGZE computer or save a lot of time & hassles and buy a good programmable aftermarket computer. Using my trusty software dyno program, I reckon a fairly small amount of boost - about 14psi - will give you just on 300hp. You'd need a reasonable intercooler, but they're are quite common these days. I figured slightly bigger cams than standard, around the 260° mark.
300hp - 400hp
To get more than 300hp requires a bit more work, much like the 220hp+ n/a 4AGE's. The same forged crank, aftermarket con-rods, some low compression pistons ('bout 8.0:1), big valves and shim under buckets. On top of those costs there is also a turbo and manifolds required. (I doubt if the factory RWD manifold would be good enough, and so a decent one would have to be hand made. Not difficult as such, but time consuming) Going back to my trusty software dyno, I come up with figures of only 20psi boost to make up around 400hp. If you could get the engine to hang together with 30psi boost, you're looking at a touch over 500hp!! To get more than that, for example, I know is possible because of the Formula One turbo engines of the late 1980's made well over 1,000hp from 1500cc's. I wouldn't suggest that it's remotely possible from anything like a 4AGE based on anything I mentioned above, but ... ;)
4AGE 20 valve engines
I have never worked on a 20v, but to a large degree an engine is an engine is an engine. The only hassle is that they have three inlet valves, and so some of the usual rules don't work. Toyota advertise them as being 162hp (165ps) for the first version, and 167hp (170ps) for the second and last version. FWIW, the first version has a silver cam cover and an AFM sensor, while the later one has a black top and a MAP sensor. One thing to note is that Toyota are telling fibs when they state the power output of the 20 valve engines - on all of the dyno reports I've ever heard of them, they only make around the 145hp - 150hp mark. So, I guess, possibly the easiest way to get a 4AGE from the stock 115hp - 134hp up to about 150hp is to simply fit a 20 valve engine. The only hassle with doing this is that with a RWD car, such as the AE-86, the distributor on the back of the head of the 20v will either require a hole cut in the firewall or a crank trigger system fitted.
From what I've seen of them, there's not a huge amount to be done except for a good clean up of the ports (remove casting flashes, etc), and a multi-angle valve seat job. The alignment between the inlet manifold and inlet port is rather bad and some good improvements can be made there, as can the area just above the inlet valve seats as they have a very nasty machining mark from the factory. Everything past that is purely bigger and bigger camshafts to get more power, and I believe that again when you come up to the 200hp mark you have to start changing the internals for stronger and lighter units. This again comes from a combination of increased power, but mainly the increased revs needed to pump enough air to make big power figures. FWIW, the bottom end of the 20v is much the same as the small port 16v 4AGE, but the pistons are different on both types and so cannot be swapped over. (So when I get people asking if they can simply pop a 20v head onto a 16v block, the answer is a qualified 'maybe'! :) Yes, you can as it'll bolt straight up ok, but No, because the pistons don't have the cut-outs for the valves in the right places. They're a non-interference type head and so the valves won't hit the pistons anyway, but it's still a good idea to get the correct pistons for it.) The most power I've ever heard of in any 20v 4AGE is about 215hp, or nearly 30hp less than a good 16v 4AGE.
4AGZE
145hp - 165hp
The earliest 4AGZE has 145hp, and there's basically three ways to get more power from them - by either simply fitting a later version that already makes 165hp, or by fitting the engine with the bigger crank pulley (that spins the supercharger faster, thus making more boost at less revs) from someone such as HKS or Cusco. The third way is to 'hot up' the engine, in much the same way as you would with a naturally aspirated engine, ie, bigger cams, ports, etc. The thing to remember is that you are limited in revs by the maximum speed of the supercharger, which really doesn't like being spun at more than about 10,000rpm. The reason for this is the tips speed of the rotors gets too high, and they will start to melt the teflon seals. So, you're limited to about 8,000rpm engine speed (the supercharger is run at 1.25 times the engine speed standard, and even faster with the NEVO, HKS, etc, pulleys) which means that whatever you do it must make the engine flow more air at stock sort of revs. This means that to get another 20hp or so from a 145hp 4AGE then a good clean-up of the inlet manifold & head, and perhaps some larger cams (256°) should easily give you that 20hp that you want. A larger intercooler and far more efficient air ducting (it could hardly be worse in the factory installation!) in & out will also help a lot.
165hp - 185hp
Again, the easiest way to get 185hp from a 165hp 4AGZE engine is to simply fit it with the bigger pulley, and maybe some minor mods to clean up any inlet and exhaust restrictions. Towards the high end of this power scale, I believe that the inlet manifold is a big restriction, as the supercharger dumps its air into a single point in the inlet manifold, which then divides the air up into four runner, one into each cylinder. The problem is that three out of the four runners enter the head at angles far from straight, and so the sharp angle at the junction will cause unwanted turbulence. (FWIW, the #1 cylinder's runner comes in at a ridiculous angle!) So, I'd say that if the time and effort was spent on making a decent inlet manifold (or perhaps just fitting a RWD AE-86 type manifold, perhaps) then the vast majority of that extra 20hp would come quite freely. Larger cams, as in the 264°'s mentioned before will help a lot, but also as with the 4AGE anything much more than that and the factory computer will have trouble sensing inlet vacuum. You can of course run an aftermarket computer that uses throttle position rather than using the MAP sensor, but the success rate of aftermarket computers with 4AGZE's is not great - Persistence will win the day, but I would strongly suggest that whatever computer you look at getting has at least these features - throttle/MAP blending, an external on/off output which is controlled by MAP and/or throttle position, and oxygen sensor closed loop feedback.
185hp +
The best 4AGZE I've ever heard of is supposed to make up around 200hp, and I believe that the chap in question has done all of the above mods to get that much. I think that a good way to help the power output would be to fit the engine with a 1GGZE supercharger, which is about 17% larger in volume and so can be spun slower to pump the same amount of air at the same revs - This means that the engine will suffer a little less power loss that what it otherwise would with the smaller supercharger. This power loss that I'm talking about is the power that the engine needs to spin the supercharger over at high revs. It increases rapidly as the revs build up, and so anything you can do to decrease that loss will help a lot. This is the problem with supercharged engines - They suffer from rapidly decreasing increments in improvement due to the cost of spinning that blower over ... So, the trick it to set a target revs in your mind, say 7,000rpm, and make the engine pass as much air as possible around that revs. Again, all the same tricks as mentioned in the above paragraphs is the way to go.
Bill Sherwood
Other stuff that's important
Cam timing
On the preceding page, I've talked about such-and-such a camshaft duration, but I didn't mention the actual timing of the cam that should be used. Everyone talks about having a cam of, say, 304°, but the one thing that's very important that they're missing out on is just where to put the 'top of the lobe', as this is the real trick to getting the best power out of your cams & engine. And fortunately, it's dead easy to do! The one simple rule that you have to follow is this - For cams with a duration of under about 270°, you want the cam lobes to be at about 110-110, and above about 270° have the lobe centres at about 100-100. (note that this is a general rule, and each engine will require fine tuning to get the last little bit out of it, but the actual figures will almost invariably be to within 2° or maybe 3° of those numbers, eg, 100-100 may up ending being 98-102, and 110-110 being 108-113)
So what do I mean by 110-110 and 100-100? Again, quite simple to do - With the engine at Top Dead Centre (TDC) #1 or #4 cylinder, and what you are looking for is to have the inlet cam lobes for #1 cylinder just starting to open, ie, the cam lobes on #1 cylinder must be pointing towards each other. If you wind the crank over 110° in the forwards direction, then the inlet valves should be fully open. This is checked by means of a dial vernier gauge, which can accurately and repeatably measure valve lifts to less than 0.001". To check the exhaust timing, simply wind the engine backwards from TDC #1 by 110° (or 100° as the case may be) If you haven't done cam timing like this before it may seem a tad difficult, but it only takes a few tools, a bit of patience, and some time. Note that it must be done as accurately as possible, because a 'degree or two here or there' just isn't good enough!
To get accurate cam timing like this can be done with standard cam wheels, modified by drilling new holes in the right spot after the new timing has been determined. Shown in the pictures below is the other two methods used to give adjustable cam timing, one of which is vernier adjusters and the other slotted cam wheels. Both are pretty easy to make, but only the slotted type can be adjusted with super-fine accuracy. (The vernier type has, say, ten holes drilled in the camshaft front flange and nine hole in the cam wheel. As you turn the cam wheel and cam around each other, the holes line up in different places so you can often find such an alignment very close to where you want the cam to be. But with the slotted type you can get the timing absolutely spot on. The slotted type are easy to make if you have access to a lathe, but they can also be bought for a reasonable price)
Another important thing to note is that the closer to 100-100 timing you get, the less and less inlet manifold vacuum you'll be getting, to the more likely the standard computer (and aftermarket, for that matter) will be unable to sense that vacuum properly, thus making the engine run badly and use too much fuel. The other effect is that the engine will start to idle roughly, compared to the 110-110 timing. (see later paragraphs on flywheel inertia and inlet manifold for further info on this, however) As an example of how a 4AGE idles with 100-100 cam timing, 288° cams, and a stock inlet manifold, have a listen to my AE-86 . Like a rotary, huh? :)
Flywheel inertia
Another important factor to getting good performance in a 4AGE, and any engine in fact, is to reduce the inertia of the engine by as much as possible. This of course means reducing the weight of everything that rotates or goes up & down. This is one of the main reasons why good pistons, con-rods, etc, cost a lot of money - They are made of better metal, made stronger, and weigh less. They also aren't a mass production part like the rest of your engine, so they will cost more per unit anyway. They are also worth it! Possibly the best value for the price you pay is a lightweight flywheel, as they affect the ability of the engine to pick (and lose) revs rather dramatically. It's effectively free power, even though it doesn't affect the actual power of the engine at all, ie, if you put two engines on dynos, one with a lightweight flywheel and the other stock, then they'll make the same power. Put the two in cars and go drag racing, the one with the lightweight flywheel will win every time. The 4AGE is no different, of course, and you can run a flywheel down to about 4.7kgs no worries on the road. I have a 3kg one in my AE-86 and it's fairly liveable ... ;) It's often said that a lightweight flywheel will also cause the engine to idle roughly, but this is more likely to be something else out of tune. (Eg, my racing car with it's 2.5kg flywheel idles dead smooth, and when I went from the stock 7kg one to the 3kg one in my AE-86 I didn't notice any difference) That something else, in the case of the 4AGE, is most likely to be a combination of cam timing and the inlet manifold. More on this later.
Crank and con-rod sizes
There are basically two sizes with the 4AGE's, and they can be divided up into the ones that the small and big port engines use. (Note that the 20v and the 4AGZE all use the 'big' crank & rods) Both types are fine to use up to about 200hp, but after that the big crank & rods are less likely to give trouble. For high revving engines though, the small crank will 'give' more power at those high revs due to causing less friction. (smaller crank journals causing less drag, etc) If you've got a high revving engine that makes more than 200hp, you should give serious thought to getting one of those hard-to-get forged cranks, which are of the 'small' dimensions. You have to live with whatever size con-rods that go with the crank, but the weight of them can be reduced a tiny bit by very careful grinding of the cap and taking the casting flashes off the little ends. The standard rod bolts are good for up to about 180hp, but past that a good set of ARP, etc, are required.
Oils
The oil you use in the 4AGE will also affect its performance, though you won't really notice much difference on the road. The only oil you should use is a full synthetic, such as Mobil One 10W-50 or the like. If you're in a country where the temperature isn't too high and you want that last little bit out of the engine, then I recommend Shell Helix Ultra 0W-40, which can give you an additional 5hp or so over any mineral oil. The only hassle with that oil is that it gets very 'thin' when hot, so it must be kept to a reasonable temperature by using an oil cooler, or if in a road car by not running flat out all the time. (give the engine a break for 30 mins from running flat out by driving slowly) To give you an example how much difference they can make, I used to use a synthetic oil for regular driving, but when I ran my car in an event at a race track I decided to run a good racing mineral oil (another really dumb thing I've done ...) and much to my surprise it wouldn't start on the morning of the race day, because it wouldn't spin over over fast enough. Luckily I had parked it on a hill and so I could roll start the car. Note that part of that problem was that my starter motor was a little tired, but this is typical of 4AGE starters anyway.
Bearings
A lot of the current bearing kits for the 4AGE have the main crank bearing shells with only one half being grooved and the other flat. This is not good, as the oil flow at high revs will suffer, and the con-rods may run out of oil. Not good! The grooved ones are the only way to go as they ensure a constant supply of oil. If the bearing kit that you get from your local supplier is like that, then either don't accept the kit or get two of them to make one good one.
Fuel injectors
In my RWD 4AGE I run the stock injectors with stock fuel pressure, and when the engine was making 160hp the injectors still had more than enough flow to run richer than what I needed, but they're very close to their limit and to go any further I would need to use either more fuel pressure or bigger injectors. Copied from my Stock 4AGE page, here is the injector sizes for the (Japanese sourced) 4AGE - TVIS big port 182cc/min Small port 235cc/min 4AGZE 365cc/min 20v 295cc/min From this chart, you can see that there are injectors that're big enough for rather large amounts of power. Note that the 20v's injectors are physically quite different to the other engine's ones, (sthey are side-feed injectors, rather than the top-feed that conventional injectors are) and so they cannot be swapped over without some modifying of the fuel rail, etc.
Ignition control
As soon as you get away from using the factory computer with the 4AGE, you will have to find a way to control the spark advance, as the factory distributor has no mechanical advance mechanism at all - The computer does it all. The distributor has two 'trigger' wheels inside it, one for the computer to sense the rpm of the engine and the other for sensing when a piston is at TDC. The cheap & nasty way to make the dizzy work without the factory computer is to simply hook up an ignitor module (eg, Bosch) and then run the engine without any spark advance. Speaking from about 70,000km experience of this, it's really not big deal - The only hassle is that the engine can be a little hard to start when cold or very hot. Another solution is to fit the engine with an electronic dizzy out of a 4K-E, as they have an electronic 'reluctor' like the 4AGE dizzy, but also have mechanical spark advance. They require a small adapter plate to be machined up, but it doesn't look very difficult to do from what I've seen. I have also seen a small black box, when I was living in New Zealand, that hooks up to the 4AGE dizzy that controls the spark as if it had regular spark advance. Unfortunately, I can't remember the name of the box in question, but it was about NZ$400, or about Aus$300, or US$200. A friend of mine has one, Liam Venter , and so he should be able to tell you more about it and how it works. Yet another way to control the spark, even on a heavily modified engine, is to use the factory computer in parallel with whatever you have controlling the fuel already. All you have to do is run the tacho trigger and power to the factory computer and run the right output wires from it to the factory dizzy and it should control the spark in much the same fashion as a stock engine does. (not sure if the factory computer uses MAP sense to modify the spark advance output or not, but it'll still work ok, and certainly be better than nothing in any case) The best way to control the spark on a modified 4AGE, however, is to use a good aftermarket computer, such as a Motec, Haltec, Autronic, etc. They all have very customisable maps to accurately control the spark advance, and so can be made to give the best possible power at all times. The other methods mentioned above are quite simplistic by comparison, but are fine for road use anyway. A full race engine requires the best possible method available, so there is need to be able to control the spark on the odd occasion by even knowing which gear the car is in ...
Inlet manifold
The standard inlet manifold is adequate, but pretty far from being good by any stretch of the imagination. I know from one particular race engineer that it's possible to get 190hp from a RWD manifold, but I think that for us mere mortals more like 170hp or so is more practical. (naturally aspirated, of course) What I'd really like to say though is that if you have the slightest chance of throwing the factory manifold away and using a decent twin Weber style manifold then do it right away! There are a couple of reasons for doing so - - Since you'll have to be running an aftermarket computer anyway, you won't have any troubles with the complete lack of a decent inlet vacuum to sense off. The only way to go is to use a throttle position only type computer, which schedules the fuel by sensing a combination of TPS (Throttle Position Sensor), RPM, water temperature, and air temperature. - The airflow into the inlet ports will be a LOT better, as it'll be even for each cylinder instead of having different amounts, as the factory manifold has. - The engine will idle like 'normal' engine does, ie, smooth! Yep, I've found out that if you use a factory manifold with anything bigger that about a 260° odd cam, then it'll start to idle roughly. By simply using a twin Weber style manifold, the engine will go back to being smooth idler. I'm not totally sure why this is the case, but I think it's due to the plenum chamber in the factory manifold, and the single throttle body affecting the airflow into the engine. (Quick note as I'm doing a site update: I did this mod on my own 4AGE in November 2001 and yes, it really does make the engine idle a LOT smoother. Even with the 288° cams it idles much like a stock engine)
Some people spend a fair few dollars on fitting the factory manifold with a bigger throttle, to try to increase the amount of air going into the engine. This is a total waste of money as far as I can see, as I have a dyno report on a engine that has had that mods done and there was a 1hp - 2hp improvement. This is more likely to be dyno error that any actual increase in power as such. The factory TB is 55mm in diameter, and while it may not seem to be that large remember that the engine only has one cylinder sucking at a time, so a 55mm hole is actually quite large. FWIW, a typical twin Weber 45mm set-up for a big HP 4AGE would have something like 40mm chokes for each cylinder, which is obviously a lot smaller (~53% the area) than the 55mm TB.
TVIS
The Toyota Variable InductionSystem is designed to, and really does, improve the power of a stock engine at low revs. From experience with talking with people around the world, it's best left in the 4AGE with cams smaller than about the 270° size. Past that size, however, the engine will make more torque by removing all the TVIS butterflys, the butterfly pivot shaft, and then block up the remaining holes to the outside world with a good sealer, such as Devcon. See the next page for a diagram on the TVIS manifold.
Webers & other carbies
Twin Weber kits for the 4AGE are readily available around the world, and they vary in price quite a bit. As described on the first page, it is not too difficult to make a twin Weber style manifold at home, and it'll cost very little. Buying second hand Webers can be a little risky, and if there's any doubt at all they should be rebuilt with any worn parts (often the needle & seat, for example) replaced. Any purchased Webers will also most likely have to be re-jetted to work properly with your 4AGE, and if buying them new you should be able to buy the carby with the jets you want. If second hand, they also most likely need to be re-jetted. So what jets & emulsion tubes, etc to get? Well, it's a bit hard to guess because there are that many different possibilities that could be needed for all the different 4AGE's, it's pointless trying. But typically they would use something like 145 main jets, 200 air correction jets, F16 emulsion tubes, and 36mm chokes. That's a start ... ;) Apart from the usual Webers, there is also Dellorto's and a couple of types of Mikuni carby that're a straight bolt-on in place of Webers. All three types have their own plusses & minuses - cost, availability, etc - but Webers are usually the easiest to get bits & pieces for. They are not necessarily the most tuneable or the best, however. Another possible carby to use is the flat slide Mikuni's, which are quite popular in Japan, but are rather expensive. (Though you can get lucky hunting around the motorbike wreckers) One final word on carbies though - If you have a choice of using a reasonable programmable EFI computer or any brand of carburettor, then in every case use the injection gear, as you'll have far superior tuneability and reliability. Also - if using EFI then make sure to also use a good swirl pot and second fuel pump to ensure that the engine gets a good fuel supply at all times.
THIS ARTICLE WRITTEN BY: Bill Sherwood
