I am putting together a 2.8L with 10.3:1 pistons, s cams, MFI, twin-plugged, and probably crankfire ignition. I had assumed after talking with some of my buddies that I would be able to run this setup on 91 octane pump gas for street driving, however, I called Andial and mentioned the CR to them and the response was "We never use over 9.8:1 for street engines". This got me thinking...Is 10.3:1 too high for our CA pi##water gas, or am I OK?
Thanks in advance for any sage advice.

 

check out what compression the Honda S2000 runs...

 

Danno,
I know about high compression in newer cars...my C2S runs 11.3:1, but that is with electronic knock sensors, and other marvels of modern engineering. This engine will have none of that, so the CR must necessarily have a built in safety margin.

 

Steve,

10.3:1 is the ratio used in the European model 911sc in '83, I believe. Several guys in the POC run the same compression and use 91 octane pump fuel and I have not heard of any problems with the 3.0 liter engine. There was a recent thread on the availablity of higher octane gas from selected 76 stations and if I recall you can search for a station with race fuel in your neighborhood at www.union76.com, if you would rather be safe than sorry.

good luck !

 

Steve,
Sorry, the correct link is www.76.com

 

Steve,

BTW, I forgot to mention the fact that if you go with a crankfire ignition you can adjust the timing accordingly depending on the octane rating of the fuel. With the Electromotive setup you can set the initial timing, then also at 3000 rpm and 8000 rpm which has a linear advance.
Hope this helps!

 

Howard,


I switched the fuel injection on my 928 from CIS to the Electromotive stage II engine management system. What power gains have you seen from the conversion on your car?


I also upgraded to an Extrued Honed euro s intake and I'm in the process of installing the engine management system. Was it difficult to program? Are there any precautions when setting-up the system?


Jim Nowak

 

Howard,
Thanks for the link and reasurrance. I figured I would be OK since twin-plugging, but just wanted to be sure I wasn't making a mistake at the expen$e of my new engine.
I think the crankfire system will make setting the timing much easier and safer.

 

There are also aftermarket ignition systems with knock-sensors that will do automatic retard on sensing knock.

 

Jim,

I'm using the HPX unit, for help with the Tech II unit contact Richard Clewett at Clewett Engineering, he is the local distributor/tech support person for Electromotive. Contact him at www.clewett.com

good luck !

 

I have a grey market '86 Carrera with the euro motor. It runs 10.5 compression ratio.

I have no problems at all with the CA cat-**** octane fuel.

Not sure if that helps you, because my car obviously has an electronic ignition...

If you feel like driving up to Sears Point every time you want to fill up your tank, you can get 107 at the pump!

Good luck,

Dean

 

Did you measure compression ratio when you built engine? You have to shim the 2.8 RSR piston set if you run with street (non 2.8 RSR) heads or CR will be around 12:1. That will definitely not work with 91 octane even if twin plug. If twin plugged and truly 10.3:1 you will probably be ok if no more that 30 deg advance total. I would shim to 10:1 to be sure though.

 

Hi:

I would offer that you'll play hell shimming these 92mm cylinders up far enough to get a real 10.5:1 with the 67cc street heads. If you get close, you can have:

1) Too much deck height and this creates the perfect conditions for detonation.

2)Timing chains that do not fit. Sometimes you need to make chain box spacers and use smaller idler sprockets since the heads/cams sit further away from the crank.

Every case is a little different and if your heads have been surfaced (normally done during a valve job), this exacerbates the situation. Be sure and measure deck height in every cylinder and not just # 1 and # 4.

Lastly, and far far more importantly,...........never, ever use 30 deg of total timing in any twin-plug motor otherwise you will buy new P/C's in very short order.

Single plug motors get 34-36 deg total advance.

Twin-plug motors get 26-28 deg total advance.

Turbo twin-plug motors get 25-27 deg total advance.

Rules to live by and gentle on your pocket book,... .

 

Boy did I justifiably get myself in trouble. Shouldn't post unless you have actual personal experience. I have only talked with people who have shimmed the 2.8 P/C kit around 1mm and don't know what CR they actully came up with. 30 deg is a lot of advance, wasn't thinking when I wrote, although I did run this much advance with a 10:1 twin plug on unleaded 92 octane a long time without problems, lucky I guess.