what kind of compression do you run?

jerry S · Mar 25, 2004

The shop building my engine proposed a 11.5:1 CR when I told them that 98 octane gas is the standard here in Europe for high octane. Then I accidentially discovered that our 98 is more like US 94 octane. At that point, I suggested that they take it down a notch. I am told that I can run 10.5:1 on 94 and not have any problems. Further to this, they say that my engine will be able to accomodate a blower in the future if I keep it to no more than 5 lbs of boost. I don't want to be pushing the envelop here. Does anyone here have experience running 10 or 10.5:1 and would you concur with the assessment offered by my shop?

HistoricMustang · Mar 25, 2004

I run a 10.5 to 1 and use minimun of 92 to 93 octane. At the track I jump to a minimum of 100 octane.

I also chose to go a little low on the compression to help the motor last in the 3 hour Enduro races.

HistoricMustang
www.historicmustang.com

Mosse · Mar 25, 2004

I run Europes std 98 gas (lower one here in Finland 95, as prob for you also)

I have -69 351W with no probs with 10,5 compression. It depends also of the cam you have and degree of ignition.. So, I think youll be fine with 10,5... But the Blower part doesn´t sound so good? Even with centrifugal I´d stay around 9:1.

dolfan87 · Mar 25, 2004

10.5:1 is pushing it for a blower. You could do it, but wouldn't it make more sense to build a 9.0:1 engine, and then add the super charger? Even if you plan on waiting for the blower, you could live with the 9:1 in the mean time.

Just my .02 cents

87

LMan · Mar 25, 2004

I would be conservative and NOT run a blower at CRs above 10:1

I run 10.5:1, 93 octane, no issues.

slapper · Mar 25, 2004

10.5 :1 is too much for a blower, unless you want to be a slave to ADI alcohol injection, and intercooling. To spend the $$ and only realize 5 lbs boost is not really worth it.
I also agree that you lower the CR.
I'm running 8.8:1 CR and 10lbs of boost on 92 octane-- no issues

GT2K · Mar 25, 2004

You can make your own octane boost with a trip to Home Depot, this is not a joke and is proven scientifically. I myself have done it for the last year and it works well. I can provide further details but I'm really "just an instigating $#%&*@#" according Leghump67

Sicarius428 · Mar 25, 2004

I run 10.6:1 in my engine on 91(highest I can get in California) with some additive. A blower is going to be close with that compression and probably not worth the gains for only 5 psi. If you want to go the blower route get 9:1 compression. That is much better suited for supercharers. If you are going naturally asperated anything above 10:1 is where you want to be. You have to decide which way you want your engine to get its power and then decide on how you need to build it.
Kevin

slapper · Mar 25, 2004

GT2K said:
You can make your own octane boost with a trip to Home Depot, this is not a joke and is proven scientifically. I myself have done it for the last year and it works well.

I've ran a few mixes of tolulene with 92 octane, but it seemed that the ratio, be it 10:1 or higher had to be THOROUGHLY mixed, so just pouring it in a tank I didn't think was the best method.
Turco seemed to be much easier to work with and more consistant.

thehueypilot · Mar 25, 2004

I run 11:1 and with 5 degrees of initial timing, 800 rpm I can run 93 octane with zero pinging & "run-on" on the street. For race day I add 108 octane and advance the timing to 15 degrees with a happy motor.

brianj5600 · Mar 25, 2004

8.8 for me with a turbo on the way. If I was only going to run 5lbs of boost, I would use the 2g's for the blower to build a better n/a motor. A blower is not worth it for 5lbs.

12sec67 · Mar 25, 2004

10.5:1 roller 306 w/ flat tops and shaved 58cc RPM heads.

91 calif (76,chevron only) gas for the street and 103 VP unleaded for the track

fastcoupe68 · Mar 25, 2004

with aluminum heads you can always get away with a little more comp I built a 11.1 comp 351 and the customer ran sunoco 94 and never had a problem. You should be fine with your comp ratio at 10.5 w alum heads.

D.Hearne · Mar 25, 2004

Gosh, I feel funny running a 10.25 to 1 ratio on 87 octane Wally world gas. Motor in my 68 Merc runs fine on it mixed every other tank with CD2 lead substitute. It's a std bore, stock piston, Crane 272 degree Energizer cammed 390 with 12 degrees initial timing ( stock dist. with Pertronix)

GT2K · Mar 25, 2004

slapper said:
I've ran a few mixes of tolulene with 92 octane, but it seemed that the ratio, be it 10:1 or higher had to be THOROUGHLY mixed, so just pouring it in a tank I didn't think was the best method.
Turco seemed to be much easier to work with and more consistant.

I actually mix it all in the fuel can with some Marvel's Mystery Oil too. Gotta check but I think I was actually running Xylene. You do have to mix it good though, I agree with you there. I'm nearly 11 to 1 myself. Next motor will go the other way for the charger

ddonaca351 · Mar 26, 2004

I run 10.6 in my Cleveland, and it seems to be ok. I have a pretty good cam though to bleed off cylinder pressure at low rpms: 236 @ 50 and .562
As long as you have some cam and some converter, it should be ok.

DD-

what kind of compression do you run?

jerry S

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