4age carb'd

[driftae71]

hey all... onto yet another good idea for ae71... 4age carb'd... idea was to have a gze bottom end for strength and reliability and then 20v head with quad motorbike carbs and trumpets... havent done much research into it so any information or opinions on the idea would be great... :y:

[Mad RS]

Don't bother with a GZE bottom end. They are lower compression than a 4age and a bit heavier to handle boost. You want higher compression and a lighter internals for better RPM and top end in a NA engine. What you want to find is a 7 rib bottom end (ie a 100Kw). Adding the 20v head is a nice idea but a 4age 16v 100Kw with nicely setup 40mm Webbers, Del'Ortoes or Solex's would do the job fine. If you do go carb learn how to tune them as they do fall out of tune every few months or so.

[kaibeecee]

smallport bottom end is basically a 20v big end anyway.

solex, minkuni etc. are good, as said, 40-43mm is the go. you will need an adapter block to fit it

carbing a 20v head is not worth it, just run with AFM or MAP with the throttle bodies, cheaper, more effective.

[PuGZoR]

Since I was the one who introduced this idea to nate, might just add in what my thinking was. Please guys, if someone can correct me on this stuff, do so.

Basically NA/Carb has the following advantages over EFI:

Less wiring as most carb systems are mechanically driven.
In turn this means less can go wrong (bad connections, sensors breaking, etc).
Easier to tune at home (don't need to know maps, etc, all you need is a couple of screwdrivers and some patience).
Better reliability for fuel when mixed with a couple of good pumps (no injectors to fail, as long as you have big enough jets on the carbs and a decent tune, it won't lean out).
Nice noise and response (obviously this is comparable to a lot of good EFI systems though).
A bit different from the norm.
Nate and I have friends that are bike mechs by trade so we can get our hands on some pretty sweet carbs if need be, and further more the forementioned friends can teach us how to tune them properly, etc.

I only came up with the idea because I love working on my old holdens cause their engine bays are so fkn easy to get around in, due to the carb setup. I'm a novice and with only one mate helping, did a whole engine transfer in one weekend. Things you'd need to look out for are carbs that actually are easy to tune, and keep their tune (SU's are notorious for being annoying). Other than that, there aren't many real disadvantages compared to EFI, especially when you plan on modifying a lot...

Once again, someone shoot me down if I'm wrong here.

[kaibeecee]

dont get me wrong, i love carbs but it is easier in theory, but in reality turns out to be a very tedious and expensive task.

required is

adapter plate - $$$ and patience to buy off yahoo japan, or $$$$ to get engineered/made unless you have a tig and the billet to do it.

decent fuel lines/pumps - $$$$ walbro or similar i've found are the best, as said you want surge protection down pat

the main disadvantage is upon cold start, fuel lines the walls of the carb and can cause issues on cold starts with misfires etc

also, they take time to perfect, you wont be able to achieve as precise tune as with efi/quad

as far as fitment, i think some CBR carburetors are the correct size for 4AGs.

[Hen is a total nutcase]

I like the idea, and think it could be fun. But it really doesn't have any advantages short of the sound and the "difference" factor. There is a little less wiring, but it's balanced out by much more customness and less support.

And Pugzor, the reliability issue isn't an advantage for carbs. If you do proper wiring (solder/crimp and heatshrink) then you wont have any trouble. I think the extra mechanicals on a carb setup would be more likely to fail than the factory EFI sensors, injectors and other gear. As for fuel metering, again I think a carb is far more likely to go out of tune, have something rattle loose or get blocked jets or jammed floats than have an injector fail.

Manifolds for 45mm Webers are available new from Redline for around $220. Another issue you'll run into is controlling ignition advance. You either need a stand alone ignition computer or adapt a dizzy with vacuum advance.

And finally, FFS the only difference between a late GZE and silvertop bottom end is the pistons and rings. Everything else is identical. Same goes for earlier GZE bottom end and 100kw bottom end. If you want a 20V head, just use an entire 20V. I *think* Weber bolt pattern is similar to 20V quads, so you may be able to reuse the factory manifold. If you use a GE, just get an off the shelf manifold to suit.

Hen

[PuGZoR]

I suppose it depends how you look at things. If you buy a car with original running gear (import or not) that's EFI, there are things like sensors and wiring that just corrode over time. When dealing with a new EFI system and a new Carb system, yeah, I'd agree. Sorry, should have stated the comparison more fairly.

I guess the main difference would be personal preference if anything. Are you keen to do your own map tuning, or would you prefer to tune carbs? That's the main question I think... Agree with me on that one Hen?

[riojin]

i like 4age carbie idea simply cause of the sound. they sound 10x better than an efi version. but then again you can just quad throttle body up and you get a nice induction sound too

[grassworkzgarage]

dont bother mate your wasting ya time with carbs, if you aint got people in the know to help you, then time spent on the dyno will add up big $$$
plus if you aint racing then you should stick wif efi

[PuGZoR]

If you read my post you'd know that nate does know people. He does intend on spending time on track, and is intending to have a pretty serious engine.

I think most people here have the wrong thinking about carbs. Yeah they do need tune-ups compared to EFI, however (with most types of carbs anyway, I know SU's were notorious for this), it's not like they rattle loose and you need to retune them every time you go more than 100m. Having said that, carbs are only as good as the tuner, but if you're willing to take the time, learn the ins and outs of the carbies, do experimentation, I've seen with my own eyes that the results can be pretty good, and is a viable option for someone who does intend to make frequent modifications, as opposed to aiming for one setup and maintaining that.

I don't think nate's looking at a carb vs EFI thing here, but more of if there are any great bottlenecks to carbin' a 4AG.

BTW: Setup seems to be around same cost as a decent EFI system (considering he's starting with a KE70/AE71 (it'll be his second, he hasn't found the shell yet though)), however since he's doing his apprenticeship in mech, I assume he's willing to actually learn the carb he goes with. I still reckon it'd be cheaper, maybe a bit more hasstle but nothing nate wouldn't be willing to go with. Mind you I've bought up a full EFI system for my turbo '86 and the costs are fairly substantial if you want to do it "properly", having said that though the minimum requirements for a turbo setup are a fair bit more than what you'd need for an NA setup.