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Auto cross 2.3l with small turbo...cams?

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aaronmatusz

15+ Year Contributor
118
2
May 24, 2005
new london, Wisconsin
Hello all,
I just dropped a 2.3L stroker in my car and am curious about cam choices.

My setup:
2.3L stroker, 8.5:1 pistons, 2G head, +1mm valves, bee hive springs, port matched 2G intake manifold, BC stage II cams (like 272), adjustable cam wheels, HTA68 turbo. <= notice shrimpy turbo!

What I'm looking for:
The ultimate auto-X car.
Full boost at very low revs (2500rpm?), lots of torque, peak power at 5000-5500RPM. I fully expect to loose nearly a hundred horse power at redline compared to whatever peak power turns out to be.

I really don't know what's out there in these modern times... though I did spy FP1x cams from (duh) Forced Performance...those look kinda neat. Anything else out there?
 
Stock cams with adjustable cam gears. This will allow you to adjust the powerband as necessary...if you want more torque for short-shifting in Autocross, you can adjust the cams quickly and easily, then set the back for street driving.

This cam adjustment legend was taken from a Honda site; bear in mind our crank rotates the opposite direction of the photo:


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  • Wider lobe separation angle produces more midrange torque but with a loss of upper rpm and peak torque.

  • Narrower lobe separation angle produces more high rpm range and peak torque but with a loss of midrange.

  • Less lobe separation angle increases intake and exhaust valve opening overlap which creates more scavenging and a stronger upper rpm powerband. Less lobe separation angle (or more cam overlap) is better for a racing engine than a high performance street engine. The idle suffers as you add more overlap since there's not enough vacuum at idle rpm.


Now keep in mind that you are by no means adding performance cams by bolting on adjustable cam gears. This will give you the ability to adjust the overlap of the stock cams only- you are not adding duration to the cam cycle as you would with aftermarket cams.
 
You'll need a small turbo (like a 16g or equivalent) to remain competitive. Once you throw a boost controller on the car you'll be placed in the unlimited class and likely will never be competitive, so try not to use one. If you run aftermarket cams, same deal, though looking at your mods you might already be in unlimited. If you just want to have fun, don't worry about it.

I'd stick with a 16g for autocross myself - maybe an Evo X turbo or dual ball bearing GT28R, maybe a dual ball bearing 50 trim but that might even be too laggy for autox.
 
I really like the idea of a GT28R...I might do that later. Right now I'm running an FP HTA68 which I'm told is like a refined Evo III 16G. Does that qualify (to your way of thinking) as a small turbo?

I never thought any body would suggest stock cams for a stroker but heck, I still have 'em so may as well try it.

And then there's Kelford cams....never heard of those guys. I'll do some more research.
 
The relevance of my post may be limited as I do not yet have a stroker.

My current setup is on a 'Far too small' T28 on a 2.0 block with 264/264 cams. The little 28 is run wide open and does produce the meat of my power in the 4-6k range. I produce peak boost at 2500 wide open with no noticable turbo lag coming out of just about any corner.

yes, the power-band falls off up top. no denying that. However after co-driving a similar but 18g equipped car I noted that the trade off in top end power and speed seems to be well worth the torque needed to get out of the hole. though the 18g equipped car had greater grip and bigger top end power, the times in my own car were quicker.(far from a scientific comparison but still.. )

The point is I am running a small turbo and an undersized intercooler well outside of their efficiency ranges for a 90second lap just so i can get out of the hole with a big punch and not suffer from mid corner lag. It seems to work for me, between laps I can spray down the outside of the intercooler to battle heat soak and most classes for pump gas allow watter injection (not meth beacuse thats a fuel).

on the cam choice, always the gut reaction for new stroker guys is to think big engine, big flow numbers, big cams. but remember where you now make your power is not in the high rpms... I might say those 272's you have would be about right. if you wanted grab a single 264 cam and try out the combo, seems worth a dyno session for the price. also you may wish to do additional research on tuning Turbo cars with cam gears. in general more overlap does not pay dividends with turbo cars because of effect it has on turbo spool. even if you had a heavy cam on a Turbo autox car it should have little overlap and idle pretty much like stock.

so what I am trying to say is you are on the right track with your 'undersized' turbo, and probably right on with your cam choices if they are degreed correctly. So... how does it work for you? have you run this setup, or is it still being put together?

I'll be watching this thread as I have a 100mm crank sitting in the corner begging me to tear down the spare block and get to it already.
 
What you also have to keep in mind in all of this is your intake manifold. More aggressive cams make more power on the top end, but much of that will be wasted on a stock intake manifold, especially the 2g manifold. You'd probably end up getting more out of a 264/264 cam set with this set up - maybe a 264/272 combo, so that you'll have more power in the mid range instead of having most of it available on the upper end, where you might limit your range. No sense in going with more aggressive cams than that with that manifold, a smaller turbo, a lower revving stroker, and goals of autocrossing.
 
Here is the current dyno graph for the above stated stroker.

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The 2G head and intake manifold was chosen to keep gas velocity up at lower revs much like a Cyclone manifold does... I don't remember why my shop steered me away from my old Cyclone setup *shrugs*.

I should mention that the car had boost creep issues during this tuning session. I think the Dejon big SMIC would've been maxed out at 16PSI with this setup on pump gas (I like pump gas, It's cheap!), but boost climbed another 4PSI.

So what you're REALLY seeing is a hack tune (lots of timing pulled and very rich AFR) to keep the motor from blowing up.

Right this minute, the turbo is at the shop getting a more aggressive waste gate port job for use with my Tial MVS.

BTW, the FP HTA68 comes with a big 16G turbine housing... I traded it for an EIII16G turbine housing as I was assured it would flow better. Now I can't help but think that it might flow too well.

This is good stuff guys, everyone seems to understand what I'm after: Careful consideration of the parts list to make sure the whole works isn't fighting itself.
 
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If it was me, same setup but 9.0cr, stock cams, Big 16G, Hyundai G4CP IM, and experiment with a 41mm restricter.
 
runners are a bit shorter and plenum slightly bigger than the 2G IM, the ports need to be gasket match tho
 
I'm guessing that the Hyundai G4CP intake manifold would go great with my setup if I wanted to make it breathe better at somewhat higher revs...in fact it's too easy of a mod to ignore: I'm gonna buy one and try it even though it might be the wrong direction.

Well, 'till next season. I'm going to Japan for six months.
 
Let me know when your back around and not too busy...id like to see the new setup....
 
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