what kind of compression do you run?

[jerry S]

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]

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]

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]

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]

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

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

 

[slapper]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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-