Need advise on 2.2L rebuild to Race 2.4L

[Plavan]

I plan on rebuilding my 2.2 into a 2.4 race motor. I have Waynes book and he gives three examples of the 2.2 motor upgrades. I plan on going with a 2.4/2.7 crank. Does J&E sell high compression 2.2 pistons? On my Dad's 2.0L race motor he has the 906 piston from J&E 10.3:1 comp. I am looking for the same compression ratio, or a little higher
With the rules of our race group I can go .60 overbore. Would that now be considered a 2.5L? 85mm in stead of 84mm pistons?
This is a race motor so it will only see race gas.
Any suggestions?

[Wayne 962]

JE makes good replacement pistons, and they can basically customize anything that you want, and be able to dial-in your compression ratio.

I'm not sure if they can do a custom .60 overbore piston thought - you'd have to ask them...

-Wayne

[awis321]

Wayne, along the same line, what kind of HP/torque can be expected from a 2.2L => 2.4L? I apologize if it's mentioned in the book, been skipping around looking at all the PICs.

[TimT]

JE makes a 85mm piston in 9.8:1 and 10.5:1 cr. You can also get higher cr's if you supply JE the deck height, the cylinder head volume,valve dia's etc. They will then custom make a piston for yuou..Dont know the difference in cost between the off the shelf JE pistons and the custom ones.

[jluetjen]

In 1971 Porsche had an ST motor like this (B&S: 86.7 x 70.4, 10.3:1, MFI or Weber 46's) which put out about 270 HP at 8000 RPM and 192 lb-ft at 5300 RPM using 906 cams.

If you can match the factory you're most likely doing pretty well. If you can beat it I'd say that you've done a really good job!

[snowman]

Johns 270 Hp sounds about right to me. I would also suggest Carillo rods for this. OR if you can get them the Porsche Ti rods. The best valve springs are required, Ti retainers help. Must use 110 octane race gas of course. All the cooling tricks are REQUIRED.

[Wayne 962]

I'd be really surprised if you can get 270 out of a 2.4 engine running on pump gas...

-Wayne

[jluetjen]

Wayne;
Isn't that what twin-plugs are for? Not that they create more HP, but they do allow less ignition advance to be used thus allowing non-race fuel to be used without detonation. At least that is how I understand it, but it wouldn't be the first time that I've got it wrong.

[911pcars]

Compared to a single plug ignition, twin plugs should allow you to use a higher compression ratio as well as increased spark advance without detonation (within reason). The higher compression will provide more power via increased VE. A high lift, longer duration cam will partially offset the increase C.R. due to charge loss through the intake/exh. ports.

You can realize more horsepower if you can spin the engine faster. That's one reason why F1 engines can get 800+ HP out of their 3 liter (?) engines @ 18,000 rpm.

Sherwood Lee
http://members.rennlist.org/911pcars

[BK911]

Sherwood!

Could you please elaborate on,

"The higher compression will provide more power via increased VE."

Thanks!
BK

[911pcars]

BK,
I'm glad you posed the question. The correct term is not VE (volumetric efficiency) which is more related to the efficiency of moving air/fuel in and out of the cylinder. It's more related to thermal efficiency. Increasing the compression ratio increases the BMEP (brake mean effective pressure) of the resultant combustion process. This increases the pressure applied to the piston(s); i.e. more torque and horsepower.

I hope this is more accurate.

Sherwood

[snowman]

Wayne,

The poster stated that the engine would only run on race gas in his original post.

[awis321]

Wayne, sorry to beat this topic to death...

In going over your 'Top Engine Picks' for a 2.2 case (I'm starting with a 71 2.2T), I'm assuming you're ranking the upgrades as such:

1) 2.2 -> 2.4 (10:1)
2) 2.2L S-Spec (9.8:1)
3) 2.4S w/ 2.2 (9.6:1)

Where would option 3 with Solex cams fit in the mix? Assuming all parts are within spec, is it a straight bolt-on upgrade?

Looking for a street engine with stump pulling torque--or as much as a 901 tranny will handle--that'll run mostly on pump 93 octane. Like the the simplicity of the small displacement engines but 3.x upgrades seem more economical.

-Dennis

[jluetjen]

My $0.02 -- If you want "stump pulling torque" then there is no substitute for cubic centimeters. There is a very strong coorelation between capacity and torque. If you want it at lower revs, then you need capacity even more. Get the biggest engine that you can find and run something like a T cam -- certainly no wilder then an Early E/Solex. If you can get a later E cam, it gives away a little top end HP for more low rev flexibility compared to the early E/Solex cam.

If you want "race car" performance and an engine that rev's to 7000 RPM and beyond, then the mildest cam that you'd want to consider is an E cam. S's, GE40's and GE60's will make more torque then an E, but you will need to spin the motor to 5000 RPM and above to get it. The smaller engines are a little easier to build to survive those revs because the stroke is shorter and everything is lighter in general. Below 5000 RPM the S type cams will be beat by T's and E's. Basically the Early E/Solex cam is pretty much in the middle of the cam spectrum.

BTW - 901's transaxles don't mind HP, but too much torque will overstress 1st gear unless you are careful.

[awis321]

John, thanks for the input.

-Dennis

[Wayne 962]

There might be an error in some of those CR numbers - I just asked Bruce Anderson about them, and the 2.4S with 2.2S pistons might be more like 10.5:1 or so, not the 9.6. I'm looking into this...

270HP on a 2.4 would be quite a bit more than 100HP per liter, which is tough to do on small engines without any forced induction. It can be done, but probably only by increasing the rev-limit to very high levels. Not too practical for an upgrade to a standard 911 engine. The 2.7RS put out about 210 with a 2.7 displacement.

John is right about the 'S' cams having their powerband in the upper range. However, as displacement increases, this changes, and the 'S' cams lose their peakiness. 'S' cams on a 3.2 or 3.5 is a great combination with loads of low-end torque and lots of high end power. There's a section on this in the new book too...

-Wayne

[jluetjen]

I agree with Wayne that a big engine can overcome any "off-cam" weakness of radical cams like an S cam. While the engine will still be "weak" compared to it's on-cam strength, a weak 3.2 or 3.5 still makes more torque then a 2.0E or T at the same rev range.

Thus originated the maxim: There is no substitute for cubic inches (unless the rules forbid it!)