Thread: what do you guy think the highest compresson i can run on pump gas

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When you index spark plugs, you use special washers so the open part of the plugs are facing in the same direction to aid in igniting the charge more efficiently. Drag racers do it because they are looking for every possible hp, but it is not necessary on a mild street engine. 32 degrees refers to the total amount of timing advance. If your distributor has 24 degrees advance built into it, then if you use a timing light to set your timing to the 8 degrees BTDC mark on the cam cover, you will have 32 degrees total advance. The new fastburn chamber designs make more power with less timing--GM's ZZ4 crate engines are set to 32 degrees. It is common for the older style chambers to make more power with more advance--say 36 degrees, but it depends a lot on the cam specs.

Frank, indexing the plugs means placing the gap of the plug facing the center of the combustion chamber or towards the exhaust valve, depending on whom you're talking to. It allows optimized flame propogation (the travel of the flame kernel across the chamber after the plug fires) and equalizes the process in all cylinders for increased power and smoothness. It won't make a world-shattering difference, maybe on the order of 1-2%, but every little bit helps.

32 degrees means the total initial and centrifugal ignition timing advance. Maximum cylinder pressure is generated somewhere between 12 and 15 crankshaft degrees after top dead center after the plug has fired off the mixture. It takes time for the flame kernel to cross the chamber and ignite all the fuel/air mixture, so we must fire the plug before the piston gets to top dead center to give the mixture time to burn and produce maximum pressure after top dead center to push the piston down on the power stroke. On a small block chevy, we would normally use around 12 degrees initial timing at the crank and 22 to 24 degrees centrifugal advance in the distributor for a total of 34 to 36 degrees, depending on the combustion chamber design. Some current heads are being produced with extremely efficient chambers and will require less ignition timing advance than some of the older, less efficient designs.

http://www.advanceautoparts.com/engl...0001001sp.asp#
http://www.fordmuscle.com/archives/2000/07/indexplugs/
http://store.summitracing.com/egnsea...g+washers&x=22

SORRY RUMRUMM, I DIDN'T SEE PAGE 2 BEFORE I ANSWERED.
WE SAID THE SAME THING THOUGH, AND THAT'S A GOOD THING.

No problem, Richard. Good explanation.

I'd always heard that if you kept it below 9:1 you are fine.

Judging from the previous replies, i think I'm right.

thanks for the help

jmo but this question can't be answered!!!!!! every engine, head, static comp,cam will make it different.. no one can give a 100% answer to this with every little detail of the engine even with that it very hard to know...

You are right about that. What you can safely run for compression is dependent on what you choose for engine components. My 383 has 10.6:1 static compression, and it runs fine on 92 octane. But I built it knowing that with aluminum heads and a CC Magnum 280 cam, I could run under 8.5:1 DCR which is the edge for pump gas. I originally wanted to run a CC XE274, but it made the DCR too high. Because the intake valve on the Magnum 280 closes 3 degrees later (66) than the XE274 (63), the DCR was lower and within pump gas range.

Ive got a 555ci N/A 802hp that I run on 91 pump gas at 10.50-1 compression.