View Full Version : [b]High Compression Pistons[/b]

2nd June 2003, 08:56 PM
I'm in the process of building the engine for my 82 Zagato and wondered if anyone has had any luck building one of these motors using higher (9.8:1 or 10.1:1) pistons (from Chris Obert).

The 10.1:1 pistons have a raised dome of about 8 mm, so obviously I'm concerned about valve interferance. I'm also concerned about putting the effort in versus the returns on a fuel injected car.

Thanks for your insight and advice.

3rd June 2003, 01:15 AM
The 10.1:1 pistons will work just fine provided you have not milled the head more than .010". A slight retard in ignition timing(3-5deg) will be required. This should result in 125-130bhp in a 2L FI engine with no other modifications. If you plan on more agressive cams, then 130lb/hour injectors will be needed. Craig

3rd June 2003, 09:48 AM
I believe you WILL have valve interference, and will also need to cut the pistons for the valves, guess it depends on what pistons you are using.
FI vs. Carbs is not an issue re: compression. It is an issue re: cams.
the reson for this is that upping the compression doesn't dramatically increase the volumetric efficiency of the motor the way cams do. So the FI doesn't end up starving it. You may find FI to be preferable for HC because of the increased latent heat of vaporization provided by the finer atomization of the fuel vs. carbs should help to act as a hedge against detonation.
My .02


3rd June 2003, 11:23 PM
The only high compression pistons I ever came across for the TC that had insuficiant valve cutouts were FAZA 12.4:1. All of the 10:1 pistons I have tried (and that's a lot) had more than enough clearance even with very high lift cams. My 10.5:1 B Coupe runs on Pump Premium no problem, even with carbs. Craig

4th June 2003, 09:44 AM
You are still using a 2L head using stock valves then?

4th June 2003, 10:31 AM
At the present time, I'm planning on using a standard head (I haven't checked to see if it has been skimmed) and standard valves. I am going to have the head ported and polished to match my header.