How much compression is to much?

Marlboro_Man · Sep 3, 2006

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:

Dayzed50 · Sep 3, 2006

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.

R2D2 · Sep 3, 2006

toyota prius 13:1 camaro 12:1 its all in the cam, use an off the shelf grind 10.5 or so

86bluecobra · Sep 3, 2006

For street use it is a safe rule not to go above 11.5 to 1.

JChalfan · Sep 3, 2006

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

85_SS_302_Coupe · Sep 3, 2006

I've always heard that 10:1 is the most you wanna run on pump gas of any octane because of discrepensies in the actual octane that you might come accross.

Marlboro_Man · Sep 3, 2006

So even with a custom grind cam you guys think 12.1 is to much?

Now what about when we start talking about nitrous in the combo?

R2D2 · Sep 3, 2006

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

85_SS_302_Coupe · Sep 3, 2006

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.

Grn92LX · Sep 3, 2006

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!

11.045:1 here with my little pump gas street terror not one single issue..

N8Miller · Sep 3, 2006

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.

bluevenom867 · Sep 3, 2006

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.

5spd GT · Sep 4, 2006

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!

Marlboro_Man · Sep 4, 2006

The car isn't my DD, It's more of a weekend warrior.

So I think 11.0.1 with a custom cam is what I should shoot for, RIGHT?

gcwh02 · Sep 4, 2006

Marlboro_Man said:
So even with a custom grind cam you guys think 12.1 is to much?

Now what about when we start talking about nitrous in the combo?

I run 12:1 on pump gas, timing at 10. No detonation

willys1 · Sep 4, 2006

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

5spd GT · Sep 5, 2006

I'm talking 5.0L willys1

Piston design, head combustion chamber shapes, and this and that are all different than the better vette...

bluevenom867 · Sep 5, 2006

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.

How much compression is to much?

Marlboro_Man

Member

Dayzed50

R2D2

86bluecobra

Advanced Member

JChalfan

Member

85_SS_302_Coupe

it sucks (I know) to be on the receiving end

Marlboro_Man

Member

R2D2

85_SS_302_Coupe

it sucks (I know) to be on the receiving end

Grn92LX

Fidanza Man!

N8Miller

I need NOS....make it 2 of the big ones

bluevenom867

I will have images of molesting stuffed animals in

5spd GT

"the 5.0 owns all"

Marlboro_Man

Member

gcwh02

New Member

willys1

Active Member

5spd GT

"the 5.0 owns all"

bluevenom867

I will have images of molesting stuffed animals in

Similar threads

How much compression is to much?

Member

R2D2

Advanced Member

Member

it sucks (I know) to be on the receiving end

Member

R2D2

it sucks (I know) to be on the receiving end

Fidanza Man!

I need NOS....make it 2 of the big ones

I will have images of molesting stuffed animals in

"the 5.0 owns all"

Member

New Member

Active Member

"the 5.0 owns all"

I will have images of molesting stuffed animals in

Similar threads

Privacy & Transparency

Privacy & Transparency