refresh951

EVO - 8.8 CR

STI 8.2 CR

These with smaller bores and better structural head designs.

Listen, I understand there are no hard and fast rules and every engine build is different but our motors are weak at the head. This is a fact. That should be a serious consideration in a big power build even for the street. It is especially true of the 8V head.

V2Rocket

i think the ROW cars had so much more power from the tune and lack of cat, plus the compression bump.

the 1988 "world" engine with 10.2cr had +5hp versus the 1987 with 9.5cr (152 vs 147)

so +0.7cr was worth 5hp, including the revised tuning requiring premium gas.

at 1bar boost that would maybe mean +10hp, but you could get that at 1.07 bar instead

Raceboy

What are you trying to prove me? Like I already said, you build your engines the way you like and I build mine.
I was just talking about my experience from real life and what I have found most enjoyable over the years by building engines and trying them in real life, not looking at others dyno charts and calculating stuff and at the same time NOT driving and having fun.

Lol, and ginvin a Subaru WRX as an example? These engines blow up their 3rd cylinder pistons even without giving it more boost. If they have not torn apart their 2nd gear of teeth that is

Voith

How many races against gt3rs and such have you won with your street car?

Fun and enjoyable is fine but vw bug is fun and e36 328 is enjoyable, I want FAST.

Raceboy

Didn't you read? I was talking about street cars. And I raced 997 GT3 RS in my 2.5 16v on a straight line lol @ 1.1 bars, not a competition from a rolling start at 2nd gear. He I mean.
With my street car I don't race on the track. For track I have my 931 Gulf racecar.

And Voith, why are you building a 16v engine now? I remember you said they will crack the head in no time even with stock power, no? You should have stayed with 8V head and 6:1 CR.

Voith

Seaech the list for thread names that contain "won again" and admire the receipe for street car that dominates 400k€ cars on the track.

One has to challenge his fears so why not. If I wont like it I can swap back to 2.7 head and get somewhere near 6:1

Tom M'Guinn

How did I miss this thread!? Great discussion. I relate to the old saying about "the more you learn, the less you think you know" or something like that... There are so many moving variables (boost, cams, timing, combustion shape, charge temps, exhaust, turbo, fuel, etc.), and so much physics that flies over my head, it's wise for me to remain in study mode

My motor is 104x88 8v with 9:1 static compression, and I have struggled with knock. It makes nice power and has a street-friendly grunt at low end, but fighting the knock is a chore. After lots of HG's, the ignition is now quite low at WOT -- maybe half of what Patrick posted -- plus I only use 100 octane or E85, a stock 951 cam, cold plugs, knock and EGT monitoring, plus water injection. Together, those things have kept the head in place for the last couple of years, but it's a constant battle at high boost. I've never tested the back pressure, but will do that soon and report back. My turbo is a Vitesse "stage 5" and probably happier at lower boost than I run, so I'll be interested to see its BP. It may be that my BP and CR are conspiring to make my motor extra knocky. I tried three different more aggressive cams and they all increased knock to some extent, so I've been running the stock cam and don't honestly notice the difference, other than it's much easier to start in the morning.

When the 930 was first shipped to the US in 1976, it came with 6.5:1 static compression (and no intercooler), so there is/was certainly a school of thought in favor of low compression high boost... I'm building a new motor now and it will be 8:1...

Raceboy

What one considers as a street car may differ from that of another..

I have been building and tracking Porsches for nearly 20 years, plus tuned ECU's of lots of other cars so I consider myself to know at least something. And so far things have worked out for me well.
My 931 is plenty fast, at least faster than those cars that sit in the garge for years, waiting for completion

Duke

Well the 2.7l 8v engine has 4hp more than the 2.5l 8v. So maybe we all should stop building big displacement engines as 0.2l is only worth 4 hp...

Point is - be careful what data you use to prove a point.

Dave W.

Hi Tom,
I didn't know you have a 3 liter. You are far too humble at the meets! How much boost do you run?

I'm seeing two different paths in this thread; 1. high boost/low comp=power! and 2. high comp/low boost=responsive! Of course, both methods can be fun depending on your definition of fun. It's nice that we have many options so we can each build our car any way we like.

On my personal car I decided to use more displacement, 8.6:1 comp, E85 and ~18 psi. It's my daily driver so I wanted instant response, minimal lag, while ultimate HP was not a priority. I'm very happy with the results and would do it again if given the choice. I already have a 620hp, 2600 pounds, AWD racecar so if I want to go really fast I can simply jump in my other car for a quick blast. and I do mean 'quick' since it's not very comfortable.

The 1976 930 had extremely primitive engine management, so it was necessary to use low compression to keep the engine alive. I wouldn't use it as a good example of how to build an engine today. Since then there have been many advances like knock sensors, improved sensor accuracy, advancements in fuel injection, advancements in electronic ignition. These all have raise the limits of safety while enabling higher HP. I'd encourage anyone to take advantage of modern engine management and modern components when planning a build.

Tom M'Guinn

Thank you. Right back at ya! I thought we had talked about that, but in hindsight I was probably just peppering you with questions about your own build and never mentioned mine. I was actually the guy that started the 3 liter registry sticky at the top of this forum, and used to maintain the list before IB eliminated the ability to edit old posts

See some details about my motor in these threads:

https://rennlist.com/forums/944-turb...ding-blog.html

https://rennlist.com/forums/944-turb...e-3-liter.html

https://rennlist.com/forums/944-turb...493-498-a.html

333pg333

Well we had some success on the weekend in terms of results but the head is still lifting. Somewhat less, but still not a good thing. I think to make this particular motor work more efficiently we either have to move to a smaller turbo to get more response and have a bit less peak hp, or move to a larger turbo and possibly shorter runner intake and then make more power but have a peakier motor. None of these are really a suitable option for us.

As an aside, there were a few of those Subaru BRZ's running around the event on the weekend. One of them was pumping out 300kw's to the wheels (400whp) at 17psi from a 2ltr motor. He said that the stock versions of these motors are running 12:5.1 c/r and these guys reduced this to iirc 11:8.1 for the turbo application.

Voith

On rocket fuel?

333pg333

E85...so kinda... :-)

Voith

Makes more sense I guess.. Pump gas would re classify that engine to cluster bomb


Interesting article in favor of high cr http://www.hotrod.com/events/coverag...power-squeeze/