What cams for a fast street short stroke 2.3 at 10.5:1?

[RobFrost]

I'm putting 96mm AE 10.5:1 pistons into a 2.2E and I was wondering what cams are ideal for a redline in the 7,000s. I'll be using standard valvetrain which I presume will limit me to no more than say 7,500 rpm I guess.

I've mildly ported the heads and stacks about 2mm and aim to keep the MFI if I can get the right space cams made.

Twin plug is on the table if it's needed. By which I mean, I am unwilling to make any compromise in order to avoid twin plug.

I want it to be relatively usable for daily driving but for the revs to go all the way up.

I guess key questions are;

• what's the optimal amount of overlap for this CR / head combination to get the maximum fuel in while easing any detonation issues at high throttle low revs?
• how much lift can I get away with, with these pistons?
• what's the ramp limit with stock valvetrain?

I was initially thinking of a mod solex cam but more lately I've been contemplating whether that will rev as high as I want.

[Geneulm]

Ok. I will bite:

Build for 7800 redline. You can go more with a short stroke but it's a single overhead cam motor iit will be tough to get more power especially w a street cam.

Try to get around 10:1 compression. Wouldn't want to go higher. Gas isn't want it used to be.

Porting to 36mm

Cam: some sort of mod s (ge, dc 40 to 60
Range. Cam Dr can chime in here.

Def twin plug.

Plenty of adjustment room w S space cam. Might even be with an E space cam I just haven't tried it.

This is all within proven recipes/factory equipment limits.

[Rosco_NZ]

Do you mean 86mm pistons? 96mm going to be difficult with 92mm case spigots. 2.7 7R spigots are 97mm.

[Rosco_NZ]

I’ve heard mod Solex is the cam for 2.3-2.5 engines.

[stownsen914]

Solex is known as a good street sport cam, but is milder than factory S. Factory S cam achieved peak hp in the 6500 RPM range in the 2.4 S and 2.7 RS, for comparison, so I'd imagine Solex would peak a little lower. It sounds like OP is looking for something sportier. I'm sure folks will chime in with their experiences, but something like DC40 might be a nice option.

[Henry Schmidt]

10.5:1 is a ridiculous goal with a short stroke MFI street engine.
Any cam that would create enough mid-range performance would also generate way too much dynamic compression for any reasonable fuel situation.
With a short stroke engine, the piston dome would have to be pronounced, creating two distinct/separate flame fronts and detonation scenarios of infinite challenges.
Think seriously about 9.5:1, In these MFI engines, maximizing compression doesn't yield enough performance to justified the ignition struggles. Low compression and higher ignition will return the snap you get from higher compression numbers.
2.3 66/86 is what I think you're contemplating.
Mod S is one of my favorite cams but they are pretty much done at 6500 RPM.
I've built this engine engine a few times and it has a potential to return around 200 hp. Drop in a little more aggressive cam like a DC 80 [even 10:1] and thing come alive on top [7600rpm] but you lose a lot under 4500.

[Chris78]

Is the above true if twinplug?

[RobFrost]

Originally Posted by Rosco_NZ

Do you mean 86mm pistons? 96mm going to be difficult with 92mm case spigots. 2.7 7R spigots are 97mm.

yeah, my bad 86mm.

[RobFrost]

Originally Posted by Henry Schmidt

10.5:1 is a ridiculous goal with a short stroke MFI street engine.
Any cam that would create enough mid-range performance would also generate way too much dynamic compression for any reasonable fuel situation.
With a short stroke engine, the piston dome would have to be pronounced, creating two distinct/separate flame fronts and detonation scenarios of infinite challenges.
Think seriously about 9.5:1, In these MFI engines, maximizing compression doesn't yield enough performance to justified the ignition struggles. Low compression and higher ignition will return the snap you get from higher compression numbers.
2.3 66/86 is what I think you're contemplating.
Mod S is one of my favorite cams but they are pretty much done at 6500 RPM.
I've built this engine engine a few times and it has a potential to return around 200 hp. Drop in a little more aggressive cam like a DC 80 [even 10:1] and thing come alive on top [7600rpm] but you lose a lot under 4500.

Thanks Henry. Just to reiterate the comment above - is what you put still true with twin plug? Also, I'm happy to step up the overlap a bit and lose some compression low down because I'll be gaining a bit of low end power due to compression and cc. Also worth a mention, i'm in the UK and I think we have slightly better fuel than you guys. Our super unleaded is 97/98 RON and universally available.

[Henry Schmidt]

Originally Posted by RobFrost

Thanks Henry. Just to reiterate the comment above - is what you put still true with twin plug? Also, I'm happy to step up the overlap a bit and lose some compression low down because I'll be gaining a bit of low end power due to compression and cc. Also worth a mention, i'm in the UK and I think we have slightly better fuel than you guys. Our super unleaded is 97/98 RON and universally available.

yes

[targa72e]

I posted Dyno results from several engines I built (2.4-2.7). Cams were E or MOD S. All were in the same car on the same dyno. Good comparison of cams.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

john

[RobFrost]

I wonder will the DC80 be okay with 10.5:1 or better with lower like 10:1? In terms of compromises, a peppy engine is more important to me than being streetable - although I would aim to use it almost daily. As I already have a standard 2.2 T engine for being sensible.

[RobFrost]

Originally Posted by targa72e

I posted Dyno results from several engines I built (2.4-2.7). Cams were E or MOD S. All were in the same car on the same dyno. Good comparison of cams.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

john

Thanks. That's useful, partly because it show me the power dying off at lower revs than I'd ideally like.

[stownsen914]

I have an Elgin 310-296 on 100 lobe centers (very similar to GE80 and DC80) in a 2.7L race engine. I'm pretty tolerant of finicky cars/engines for the sake of my gearhead hobby, but I can't imagine driving a car powered by that engine on the street. The power comes on above 5000 and makes power to 7500. In my car it spends 98% or its time in that range.

[Henry Schmidt]

Originally Posted by RobFrost

I wonder will the DC80 be okay with 10.5:1 or better with lower like 10:1? In terms of compromises, a peppy engine is more important to me than being streetable - although I would aim to use it almost daily. As I already have a standard 2.2 T engine for being sensible.

The key to running huge cams in compromised situations is a dance between compression, ignition timing, and cam timing. To make horse power with a small motor you have to spin it. It's an air pump and you have to pump air. That simple.
As counter intuitive as it sounds, in running huge cams in these "street" applications I have found the formula to be, lower compression [9.5:1], advanced cam timing [piston clearance is critical] and aggressive ignition timing [30-34 twin plug]. Now all you have to do is find some CO tuning numbers and you're good to go.

Years ago I built a 2.8SS, Slide valve, twin plug street engine with RSR Sprint cams [arguably an ugly street cam] that was in a car called the "Red Sled". Randy Wells wrote an Excellence article about the car and was amazed at how civilized it was until you pushed the throttle in anger. These principles were incorporated in that build.
The Excellence article was from Oct 2011 "Sliders An early 911 with SoCal hot-rod style."

You may have remembered this engine from the cover of Wayne's engine rebuild book.

[stownsen914]

Thanks for sharing some of the secret sauce, Henry.

[Henry Schmidt]

Originally Posted by stownsen914

Thanks for sharing some of the secret sauce, Henry.

No secret sauce. In the early days we didn't have cam guys creating all these unique application products. Master were limited. That left us trying to find ways that allowed us to use what we had. Best options possible? I don't even know what that means.
We just had fun trying to make this stone aged technology fly.