questions about cams...

[zed x]

hi
have a few questions about cams. i have a silvertop 20v in my ae86 btw :)

#1 is genrally the rule of thumb the bigger the cam the more it needs to rev to make its power?

#2 how much do cams go for genrally and do they come up for sale 2nd hand that often?

#3 do all cams sacrafise power somewhere to make more power somewhere else in the rev range?

#4 is this the next mod i should be doing to make more hp considering i have a silvertop runing off a mircotech?
looking forward to see what u guys have to say.,..

[86adz]

#1 by bigger cams i take u mean longer duration more lift can be beneficial too but if it gets too excessive u can find urself having to use shim under buckets also replacing valve springs goes hand in hand with bigger cams. power will increase and generally as you say more up in the rev range but exactly where the power is and its range can vary a bit with ur timing. a few variables to play with

#2 cams are around 300-400 bucks each and yes you do occasionally see 2nd handies for sale

#3 depending on how much larger you go will change how "drivable" ur car is for example if its a daily, large cams can (but not always) be a pain in the neck at low revs (stop start driving) basically your bottom end power increase will be negligible

#4 aftermarket ecu will help in improving power but its gains are probably not worth it unless ur running huge cams like >290 degree, havent experimented with ecus a lot but I'm sure some other people on here have and will give u some good info.

[zed x]

ok so all aftermarket cams will need upgraded valve springs?

what are some cams people are running in there 20valves and whats it like...?

[Jonny Rochester]

If you have a 20valve, and you are certain you are not going to turbo it, and you want more power... then you need different camshafts. You allmost certainly will need:

-different camshafts
-programable computer
-adjustable cam gears

And most likely you will want:
-upgraded valve springs
-upgraded conrods or rod bolts

And if you have the money:
-high comp pistons
-metal head gasket
-porting
-full motor balance
-elaborate exhaust system

But will also spend money on:
-another 20valve after putting hole in block
-dyno tuning
-gaskets, timing belt, seats, bolts, silicon etc...

I havn't done this, just a guess.

[Jonny Rochester]

For the 20valve, camshafts are available off the shelf from Toda in Japan, or Kelford in NZ. There are a few grinds available, people try different combinations, so no one knows what is "best". If you use high lift cams, or want to rev it hard, you will need uprated valve spings to stop valve float. Toda and Kelford sell the springs also. Toda sell the nicest looking cam gears.

The number of settings are infinite. You choose duration on each cam, lift on each cam, and lobe center angle (adjusted with cam gears) on each cam. In addition, you also choose your ignition graph to make power. Racers sometimes keep all this secret. But I can easliy give you ballpark figures for a good setup.

Get cams about 288 or 300 or 305 degrees duration.

The 20valve already has shim under bucket. You may need some different shims to set it up.

You may need a race engine mechanic/tuner to put it together and tune.

[af300e]

Johnny, is there an issue with big lift cams and the 5th valve lobes fouling on the plug tubes?

[zed x]

<div class='quotetop'>QUOTE (Jonny Rochester @ Jul 30 2008, 10:19 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=569107)</div>
If you have a 20valve, and you are certain you are not going to turbo it, and you want more power... then you need different camshafts. You allmost certainly will need:

-different camshafts
-programable computer
-adjustable cam gears

And most likely you will want:
-upgraded valve springs
-upgraded conrods or rod bolts

And if you have the money:
-high comp pistons
-metal head gasket
-porting
-full motor balance
-elaborate exhaust system

But will also spend money on:
-another 20valve after putting hole in block
-dyno tuning
-gaskets, timing belt, seats, bolts, silicon etc...

I havn't done this, just a guess.[/b]


farrrrk... well ive already got the computer so thats 1 thing haha

um well basically i was wanting to get some cams and cam gears to put in without having to upgrade valve springs or conrods.. then take it to the dyno get it tuned and yeah...
I'm not after ridiculous cams. jsut something to booost the power up a bit...

[Jonny Rochester]

Cams with a normal or medium lift will be better for endurance racing. Cams with high lift will have more peak power, but may not last as long as the lobe could wear out, or they could drive the valve springs too hard or something... and break a valve spring? Not sure.

Cams with more duration will be better for high rpm, at the expense or low rpm torque and idle. But this can also be adjusted with overlap and lobe centre, adjusted with cam gears.

My rough setup and prediction:
intake 304 degrees
exhaust 290 degrees
intake 102 degrees lobe centre
exhaust 105 degrees lobe centre
aftermarket conrods
toda valve springs
rev to 9000rpm
200hp at motor

Just a hyperthetical... Feel free to comment.

[Jonny Rochester]

I havn't done all this yet so I can't answer more questions. I have got some parts.

In secret, I plan to just use a silvertop with some wild cams and uprated springs, Toda cam gears. Then tune that as is and see when it breaks. Please don't tell anyone.

[Jonny Rochester]

Just another point. Before it goes near a dyno, it will need alot of time with valve clearances being set, then time with the degree wheel and cam gears. There is not enough time to play with cam gears on the dyno, not generaly. (Unless you work out a few setups and mark the possitions). You will spend all your dyno time adjusting fuel anyhow, and then ignition.

[zed x]

yeah well I'm not to keen on aggresive cams such as the ones mentioned above as i feel my car alread has enough go up top and i wanted a lil more down low/in the mid range (also i can't jsut get away with putting some in with some cam gears and leaving at that)

which leaves the 'medium' lift cams... but my concerns with these are would these cams make much noticabe difference and would i still have to replace valve springs and conrods etc for these cams as well

[Jonny Rochester]

OK, so your engine already has enough go up top? Then what you really want is a lower ratio diff, and be prepared to row the car around with the gear stick. That, or a supercharger.

Big cams can make it feel like you have more torque down low, but you don't really. It just feels like that because the engine is already idling at 1500 or 2000rpm, so it gets on song a bit quicker. Rather than idling at 600 and needing to rev to 2000 before you make power.

[Jonny Rochester]

I would say get the valve springs and conrods if your keen on 9000rpm to make power (even if it means a new motor every now and then). But if you never go over 8200rpm, the stock parts should be fine.

(All just a guess, from what I read).

[SpotterOne]

You should find that the "lumpy cam" effect is very well hidden by your ITB's. I have some fairly serious sticks in mine, and it idles just fine at 900RPM.

I don't think I've read anything in the above that is really incorrect, except that there is a little financial strangeness with cams.

$550 gets you cams that give 10HP
$550 can also get you cams that give 20HP
$550 will also get you cams that give 30HP

Point is, if youre going to spend the money, why not take the horsepower? Its only a matter of specifying the correct grind.....

You will need all those other bits that everyone else mentioned. Cam gears are essential as is a good engine builder to dial your cams, and a good tuner to fuel accordingly.

There is a limit to stock valve springs, but they are relatively cheap anyway.

I'd get even bigger cams, but I can't be bothered with underbucket shims.

[zed x]

hmm well basically I'm wanting more power from 4.5k through to 6.. and any more power boind that is a bonus

i guess i should ask when do cams start 'doing there thing' would i see a difference in power at these revs or are they puerly for making more power up around 8k

[SpotterOne]

Mine used to start pulling from about 4.5k, which incidentally is where the fuel spike was on the map. There was a real surge as you went through about 4.5k.

Now that I have made longer trumpets, it just pulls all the way from the bottom. Best mod I've done so far!

[zed x]

<div class='quotetop'>QUOTE (SpotterOne @ Jul 30 2008, 11:26 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=569155)</div>
You should find that the "lumpy cam" effect is very well hidden by your ITB's. I have some fairly serious sticks in mine, and it idles just fine at 900RPM.

I don't think I've read anything in the above that is really incorrect, except that there is a little financial strangeness with cams.

$550 gets you cams that give 10HP
$550 can also get you cams that give 20HP
$550 will also get you cams that give 30HP

Point is, if youre going to spend the money, why not take the horsepower? Its only a matter of specifying the correct grind.....

You will need all those other bits that everyone else mentioned. Cam gears are essential as is a good engine builder to dial your cams, and a good tuner to fuel accordingly.

There is a limit to stock valve springs, but they are relatively cheap anyway.

I'd get even bigger cams, but I can't be bothered with underbucket shims.[/b]

yeah i see ya point. well whhat size cams can i get b4 i need to start worrying about underbucket shims, stonger internals etc

[riojin]

timing setup aswell as duration will effect the power output.



know that a standard 20v has 250 degrees cams in already with approx 8mm of lift. (quite high for stock cams). for any noticable difference you should get atleast 264 cams with 9mm lift. i personally would suggest 272 with 9mm lift intake, 288 9mm lift exhaust.




heres a simple paint diagram to help me explain how higher duration and/or higher lift cams work

[attachment=29155:cams.jpg]
(this is by no means a perfect diagram)

y axis is power output, x axis is amount of revs

purple is rev limit from stock cams

pink is rev range with longer duration cams in place

blue x axis is when higher lift cams are in place


so you can read the graph these ways.

1. put in higher duration cams and use the black graph and pink rev range
2. put in higher lift use the blue graph and have the purple rev range
3. put in both and use the blue graph and pink rev range



to simply put it-
higher lift = more power because of more fuel flowing through the system
longer duration = higher rev range but will sacrafice low down revs (meaning you will not make any power below a certain rev range)







since you want more low-mid range you can do a few things (these are ranked in order of easiest to do/lowest gains to hardest to do/most gain)

1. change the way you drive. if you don't like how it performs at low revs don't use them, rev your car to 3000rpm and then let the clutch out (slowly unless you want wheel spin)
2. change the cam timing to give you more down low (but you will sacrafice top end) [also theres not much you can do here if you retain vvt)
3. get some different exhaust headers. 4-2-1 are the way to go for more low-mid range (again sacrafice top end)
4. longer trumpets=more low down (again sacrafice top end) [shorter trumpets=more up top]
5. raise the displacement (use a 7a block or stoker kit and again sacrafice top end)


read this

http://www.billzilla.org/4agmods.htm

and choose how much power you want and find out how much you will have to do to get it.

[SpotterOne]

^^^ well said.

My cams are 308 degrees duration and 9mm lift.

[zed x]

thhanks heaps for all the posts guys.. the diagram made alot of sence..
well by the sounds of it i want cams with a greater lift, but not so much of a longer duration - maby 1 more mm lift then standered but far greater lift

the cams spotterone has sound like what i need.

[zed x]

althought stronger conrods etc will definately be needed for these cams yeah?
what other mods do u have to your engine spotterone?

[rthy]

silvertop rods are fine for 8500 from people who have raced with them

[SpotterOne]

<div class='quotetop'>QUOTE (#109 @ Jul 30 2008, 11:56 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=569175)</div>
althought stronger conrods etc will definately be needed for these cams yeah?
what other mods do u have to your engine spotterone?[/b]

It's easier to ask "what mods haven't been done to your engine"!!!

I could answer that with underbucket shims and oversized valves.

I had those cams running with standard 16v BIGPORT rods and pistons, though somewhat unsuccessfully. When you shave enough of your head and block to get good compression ratio's, the valves will touch the outside of the piston flycut. They don't bottom out on the piston, they just hit right on the outer edge. The engine actually ran fine for quite a while, and a leakdown test showed that the valves were still sealing, but its not ideal.

That didn't stop the engine anyway. It wound up being a broken ring land that stopped it, which I'm fairly certain only happened because the pistons have had a hard life, and I'm making good horsepower.

As Sam says, the 20v and 16v smallport rods should be fine up to about 8500RPM and lots of HP. Personally, I like to keep my rev limiter down to 8100RPM with a 100 rev softcut because I hit it so often on a racetrack. I must install a shiftlight one of these days!

Having said all that, I'm putting spool conrods, ARP Rod bolts and Forged pistons in my new motor. I can't be bothered pulling it apart again, so this time I'm doing it properly.

[zed x]

hmmm ok
well i think ill jsut keep my redline down set it at 8ish and hope my engine don't break

sooo where do i get cams from and whats involved in installing them

[SpotterOne]

<div class='quotetop'>QUOTE (#109 @ Jul 31 2008, 11:09 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=569649)</div>
sooo where do i get cams from and whats involved in installing them[/b]

I assume you would get the cams from any reputable cam supplier. I make an assumption because mine is a 16v. I got mine from Wade Cams.

You will need the following:

adjustable cam gears.
a pile of shims to re-shim your valves. Quite often bigger shims are required.
someone to "dial-in" your cams (or do it yourself if you have the gear and skills)
retune of your ecu

It is good insurance to fit a new cambelt

Its certainly worthwhile getting a cambelt kit that has the tensioner bearing in it.

Not cheap if you do it properly. I did all the work myself, so I saved a bundle. I would estimate something in the region of $1500 - $2500 for all that to be done for you.