Board Logo

HELP WITH COMP RATIO
RodPenrose - July 4th, 2012 at 06:59 PM

I am going to build another engine for my circuit car to use at Valla this year and would like to know how much compression you have used with the 98 octane fuel . I have some exotic fuel , but I want to stay with the V power as the fuel . I will be using a new set of Comp Eliminator heads that were the last set of heads ever ported by the late Dean Lowrey . These have 43.5cc in the chambers and I would like to run around .040/.050 deck height . I have used 11.90:1 before in a drag racing engine and it was pinging as I drove it up the return road . Please let me hear your options , ROD.

colin - July 4th, 2012 at 07:24 PM

My little 1916cc hillclimber was set at 11.3-1 and never pinged.
I was using 98octane BP Ultimate.
If your using a long duration cam it will bleed a little comp out. Also backing the timing down will help.
Thanks for the pistons you supplied Larry.:tu:

Cheers Col

Craig Torrens - July 4th, 2012 at 08:51 PM

yep, depends on the cam you're using :tu:

like Colin, I've run low 11's on 98 without pinging.

BiX - July 5th, 2012 at 10:37 AM

Mine runs low 11 on 98 octane. Flush the tank normally every few monhts if it hasn't been driven to keep it fresh.

Sides - July 5th, 2012 at 11:00 AM

My 1915 with 044's am running 11:1 with an FK87 - no worries at all on Caltex 98.

:tu:

Craig Torrens - July 5th, 2012 at 11:54 AM

Quote:
Originally posted by BiX
Mine runs low 11 on 98 octane. Flush the tank normally every few monhts if it hasn't been driven to keep it fresh.


Good point, fuel octane drops off after about 3-4 weeks in the tank.

RodPenrose - July 6th, 2012 at 08:48 AM

Thanks guy's for your imput . I have taken this all on board and with the restricted cooling of the comp elimimators I have made a decision based on your engines . I have had the barrels machined and will end up with a .048 deck and a comp of 11.26 . I will now start a post in the circuit racing section about the new engine for Valla , ROD.

BiX - July 6th, 2012 at 12:43 PM

Rod the other thing to think about is treatments for the engine. Everybody has their opinion, but I have used (at engine builders advice) various ceramic coatings on the engine, Inlcuding heat dissapaiting coatings on the fins (barrels and heads), low friction on skirts, heat retaining on the inside of barrels, chambers, piston top, valves and exhaust ports. Never done a back to back run with and without these, but in theory they should help stop heap build up and potentail detonation.

JVLRacing - July 6th, 2012 at 03:36 PM

Quote:
Originally posted by BiX
Rod the other thing to think about is treatments for the engine. Everybody has their opinion, but I have used (at engine builders advice) various ceramic coatings on the engine, Inlcuding heat dissapaiting coatings on the fins (barrels and heads), low friction on skirts, heat retaining on the inside of barrels, chambers, piston top, valves and exhaust ports. Never done a back to back run with and without these, but in theory they should help stop heap build up and potentail detonation.


BINGO:cool: very much agree

bigrudi - July 6th, 2012 at 06:59 PM

Have done back to back on coatings, but have good cooling set up to start of with, tried it on valves piston tops inside of chambers no noticeable variation in hp or temps . 11.1comp sounds good to me but make sure the fuel is fresh easy to hurt it with stale fuel .

matberry - July 6th, 2012 at 08:15 PM

x2 on coatings, my engines are generally street driven so I prefer lower CR's