How much compression is to much?

For a 306 combo, How much compression could i get away with running 93 octane?

Setup would be something like...

fresh 306
Stock crank
Stock Rods
New forged pistons
New rings
New bearings
E-cam
Cobra Intake with lower port matched to heads (or gasket)
New world senior heads (gasket matched and "cleaned up")
1.7rr
1 5/8 LT's


(the rest of the **** in my sig)



Just wondering!
:SNSign:
 
  • Sponsors (?)


I've seen some setups running in excess of 11.5:1 on 93octane, though I can't say I'd recommend it. 10.5:1 is safe. Maybe someone has some tips on reliably running more. Timing is the killer when you start reaching these heights, so if you go that high make sure you creep up slowly on your timing increases. Detonation kills.
 
sbftech said:
toyota prius 13:1 camaro 12:1 its all in the cam, use an off the shelf grind 10.5 or so

I was under the impression that combustion chamber design also had a big effect on how much compression you can run with pump gas. Dunno for sure, but personally I wouldn't go much over 10:1 to be safe.

Jeff
 
sbftech said:
Run what yu guys wanna run, I run 11.5:1 on 93 pump gas. As for ntrous, the more compression the better


Yeah i'm just going by word of mouth. My buddy runs 10.5:1 on his stroker but every now and then if he gets gas at the cheap places like quicky marts and stuff, he'll get a ping, and that's with a professional tune.
 
I have not sat down and figured my compression out, but its prolly in the 10.5:1 ratio. i run 92-94 ocatane.
with a custom cam, 12.0 or higher is permissable. with nitrous, on the street, i wouldnt go any higher than 13.0 due to the fact that your prolly only gonna use it once and a while.
 
sbftech said:
toyota prius 13:1 camaro 12:1 its all in the cam, use an off the shelf grind 10.5 or so

Yup,I know the local crab builder/braket racer can run his 13.3:1 on 93 pump.Now its not a street car,its a striped down Vega,back-halfed 4 link car with a tunnel rammed (2 2bbls) sbc,that wiegths probably only 2500 with driver,so not alot of load.I believe he is runing iron heads though.

Normaly he will run racing fuel and spray 350hp shot or so,goes into a 5.60-70 1/8 mile.One of the most consistant nitrous bracket cars I have seen.

But it shows its possable with the old school v8's and not blow them up.Or you can take a que from Engine Masters Challenge,and see just how much power you can get out of 91 octane,though there normally on the brink if not through out the run,on detonation.Certainly not drive able.
 
I'd like to see anyone running 11:1 or more on a daily driver. Anyone?

Cam design plays a lot in it, due to dynamic compression. The stiffer compression happens once the intake valve closes...aka valve timing.

More compression causes higher heat. Grn92lx has posted about that issue in his car before.

Pinging can become a problem as well, pre-igniting the fuel.

I would keep it 10.5:1 just to be safe. More can be had...and less can be had.

Good Luck!
 
5spd GT said:
I'd like to see anyone running 11:1 or more on a daily driver. Anyone?

Cam design plays a lot in it, due to dynamic compression. The stiffer compression happens once the intake valve closes...aka valve timing.

More compression causes higher heat. Grn92lx has posted about that issue in his car before.

Pinging can become a problem as well, pre-igniting the fuel.

I would keep it 10.5:1 just to be safe. More can be had...and less can be had.

Good Luck!
The new Vette is 11:1 :D
 
Temp plays a big part in this,you can run more if you can keep the motor cooler. The heads especialy....thats why the Vette has reverse flow cooling. BUT a good normal cooling set-up can work almost as well,it just requires a little more flow and volume.

Big alum. radiator and a high flow pump (you can use a booster if you got an electric,though it might work TOO well...or burn the bump up,either one lol),low temp thermostats,ect.