Compression ratio - european school vs. US school

[181]

This is my last topic regarding CR I promise :-)

I´m still solving CR and deck height dillema on my new 82x94 engine and i noticed that performance engines in Europe are generally using some higher CR then US engines in the same category. Is this due to lower quality fuel available in US?

My CR is 10:1 after first mockup and that is with 0.06" deck height (that is approx.1.5mm) and 53 cc chamber. Is that on the high side for FK8 cam and 42x37.5 043 heads ported by Steve Tims? My crank is forged 4340, I use H-beams and pistons are flat top Mahles.
I have 91RON, 95RON (this is american 91MON fuel), 98RON (this is american 94MON fuel)and even a 100RON fuel available (this is american 96MON fuel).

My engine won´t be a daily driver, more of a weekend warrior vehicle. Will the engine live happily with 10:1 CR or should I sacrifice some of my deck height and put my CR down to 9.5:1 with 0.08 deck (2mm deck in metric speak)? I can´t touch the chambers anymore.

Thanks,
Jan

[andy M.]

jan,

with the 10-1 comp. ratio and 100 octane gas you should be fine, my light-ish weight street car uses 97 with a 11.5 - 1 comp runs great and does not get hot, admittedly i do have an external cooler and fan but thats about it.

andy

[Lids]

compression and fuel type will have a major effect on detonation, it is vital that the timing etc is also spot on.  A High CR will increase the heat in the head, so its important that its cooled properly as well

[181]

well my engine will feature doghouse shroud with all stock VW tins, including sled tins and industrial tins to shield the exhaust heat from heads, and external aluminium oil cooler. Heads are cleaned so they have no casting flesh between fins. Car is very light (181 aka Thing).

[richie]

It also has alot to do with outside air temp,most of us in europe never get to see the temps that alot of USA has which will affect what you can get away with,particularly on a weekend warrior type of car,your 10/1 with VW casting heads with be fine,the 98ron would be my choice but you can tune to the 95 or the 100 without problems

cheers richie

[181]

great, thanks a lot