20 Valve Blacktop Race Engine

[Trekka273]

I have a 20 Valve Blacktop that I am planning to build up for use in an off road racing buggy.

I am looking at changing the following:

272 degree/9mm lift TODA Intake Cam
264 degree/9mm lift TODA Exhaust Cam
Adjustable Cam pulleys
Toda 82mm Pistons
Head porting

For the rules of the class this engine will be used in, I can not go over 1650cc, not turbo/supercharger and it would be using premium unleaded fuel. I will be using an aftermarket ECU, more than likely a Motec.

Due to the nature of the racing I am looking for good torque and obviously an increase in overall power from standard.

Can people here give me their opinions on this setup and if they think that this would be suitable or if I should change some of the above parts. The part that worries me the most is making the right choice of cam....

Thanks for your help.

[DigitalPho3nix]

Welcome to the Forums!

What sort of off road racing is it? Will it involve sustained periods at full throttle, or will you be using the entire band of revs?

If you are at full throttle, then you's want most of your power to come at high rpm. For this, you will want big duration cams. But offroad (wheelspin), I would think an imposed rpm limit would be useful to help prolong the life of your engine.

If you are modulating the throttle, go for some smaller cams. The ones you suggest are possibly ideal. This will spread the powerband over a larger range.

[Starfire]

For a race engine those cams are fairly mild - they would probably be well suited to a hotter street engine.

I would be looking at about 320 degrees with as much lift as possible. They would run like a bitch unless you are at WOT though.

[Trekka273]

Thanks for the replies guys.

I think the 320 degree cams would be way too much. There are sections of the races where you are WOT for long periods of time, however the mofrity of the tracks are in and out of trees, lots of corners, etc so I don't want an engine that heaps of power but in a very narrow powerband betwen 8000-9000 RPM. I want it to pull well from mid range (say 4000 RPM) through to a rev limit of around 9000 RPM on the shift light (maybe rev limit it at 9500 RPM).

I have read that having the duration of the exhaust cam smaller than the intake cam aids in producing torque. Is this correct, or would I be better with a 272 on the intake and exhaust (or a 288?).

[oldcorollas]

For a race engine those cams are fairly mild - they would probably be well suited to a hotter street engine.
I would be looking at about 320 degrees with as much lift as possible. They would run like a bitch unless you are at WOT though.

perhaps if you want to run at 11000rpm

your goal is reasonable tho i would suggets to PM Takai and check with his setup and where his power band is.

your cam choice is pretty close (as you know ), but i'm not totally sure of the staggering effect ont he 4A... it has been mentioned a while ago tho.... sucks for you that swapping intake and exhaust cams is not possible (like the 16V), but the principal is the same, so if you can check out what others are running... heaps of people run cams around that size (on teh interweb)..

as for idea of larger cam.. it depends which is more restrictive, intake or exhaust... and the overlap will also be critical since you are loking for good pull down low(ish)
etc etc

don' get 300's

[takai]

Actually stu, you cant swap intake and exhaust cams on the 16v. Not unless you have a crank trigger or teeth machined into the exhaust cam.

Anyway, the cams you have there are pretty mild. Im making 130rwhp on a completely stock bottom end and mildly cleaned up top end with stock valves. I am running quad throttles and HKS valve springs along with some Group A cams (308*/9.1mm). It appears that one of the cheapest methods of getting power out of the 4A is to shovel air in faster, or more importantly out again. The exhaust valves and bowls are a bit small from what i can see to support decent HP, and software dynos seem to suggest this too.

You may want to look into oversized valves of some sort rather than going massively high in the cams. Ill assume that you would want a torque curve similar to a rally car, in which case the upper limit will probably be around the 272* or 284* mark. You want HUGE lift though, and fairly sharp ramp rates to make use of that lift as well as possible.

Ben Wilson would probably be better to speak to rather than me, as he has done more development on rally cars. My engine setup is quite peaky although you can feel the shove in the back when it comes on cam at about 4500-5000rpm. Oh yeah, and ignore the 320* cams as youll just get massive wheelspin at WOT while on dirt, and constantly be changing gears. That sort of cam is brilliant for circuit racing though

[Trekka273]

Once again, thanks for the tips guys.

I have had a little bit of a look at some oversize valves that a guy in the states sells, along with valve springs and retainers. These are 1mm oversize and are undercut for higher flow. I think it is from .dot Racing from memory. These were designed for the silvertop, so they are currently checking if they will all fit in the blacktop. I might get a set of them, but along with everything else I want on the engine they may have to wait.

As suggested, I am looking for a torque cruve similar to a rally car. THe guy from TODA in Australia suggested a 284 intake and 272 exhaust, but then others have said that that would produce the power too high in the range. Ideally I want it to pull from as low as possible and still have top end (doesn't everyone!!) but I guess I don't really want the power to only kick in at 5500 or 6000 RPM, as it would leave me with a narrow powerband. I would like it to have good pull from say 4000-4500 and then really kick in around the 5500RPM mark. Is 9mm lift too little, or should it be ok with that?

[oldcorollas]

Actually stu, you cant swap intake and exhaust cams on the 16v. Not unless you have a crank trigger or teeth machined into the exhaust cam.

sorry, i was thinking you would buy both with the gears on and then swap

[Celica RA45]

if you have the black top why dont you just start with a std motor and factory ecu and see what that is like 1st, it has vvt will make power to 7800 redline at 8200 ,and use this as a base line 1st ,then go for the build up

[Trekka273]

I have previously run with a near-standard silvertop running a Motec M4Pro and liked this engine a lot. It was very nice to drive and had a lot of power. It had a fair bit of porting work done but ran standard cams, pistons, etc. Since that time, the competition level has increased (I have been out of the racing for about 4 or 5 years), so to be comeptitive I want more than the standard motor offers.
This isn't an engine that I will have finished in a month or so, it is more of a project engine that I want to build up, hook up a Motec (not sure which one yet, suggestions here would be appreciated) and put it on an engine dyno so that the correct tuning can be done with the adjustable cam pulleys, etc.

[Trekka273]

Just thinking, would there be a big performance difference between 82mm TODA pistons and standard Toyota 82mm pistions?
Obviously the compression ration would be slightly lower with the standard Toyota piston, but that can be made up in other way if required. Is there a lot of difference in weight?
I can get genuine Toyota oversize pistons for $95 each (with no rings), which is a lot cheaper then the TODA pistons. So is the price difference really worth it for this project?

[oldcorollas]

depends on the weight and strength.
lighter = less power loss
stronger = reliability.

[Celica RA45]

you can get forged pistons made up in melb about 1200 a set with pins and rings and you can have any comp you like also you will have to fly cut the valve reliefs abit deeper as well

[Trekka273]

We had some pistons made in Melbourne for a previous motor (Suzuki GTI) and they were fantastic pistons, but $1200 is still alot of money when I can get oversize Toyota's for approximately $600.

I don't mind paying the money if they are going to make a good difference to the motor (although it will put the build of the engine back while I save for them), but I don't want to spend double the money if it isn't going to be worthwhile.

[off-road]

What gearbox are you using? Most transaxles are going to hate 9000 rpm.