Technical > Matt Shaff's Engine Shop

Compression Ration SBC Mild Blown

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dusterdave173:
Cool! Why I am on here   thanks to everyone!

Draw 3D:
I agree with dreracecar, on my SBC, I have 11:1 compression, spinning the blower 10% over with 30° timing in the mag for my mild setup.

Paul New:

--- Quote from: dreracecar on February 25, 2015, 08:49:14 AM ---20* NO frickin way

  Alcohol burns as a liquid not a vapor like gas, thus it fires off when conditions are right AND changes fireing as conditions change---- thats why you run a magneto because of the long spark duration, so that the spart will be around during those changes.

10+ CR gives you that needed kick to get things going before the blower comes in. Alc is extreemly hard to pre ignite (detonation) Anything less ( in reletive numbers)and you are just making a pig out of it.

On a cold motor if you had 20* of timing, you would prob fire of the cyl at 14/15 deg btdc and warmed up only have 20* in it??. Minimum I would start with is 29/30* at anywhere below 2000' corrected and 1* per 1000' after that

 Its all about makeing the motor happy. The same engine I run, many years ago, because of class index, I ran 5 over on the blower, 29* of lead,and thru a lot of fuel at it (fat) to slow down to 7.60 and the motor was not happy about it. Now because of 7.0pro, I run 18 over, 34*lead, and trim the fuel back and use a high speed, now the motor runs clean and is happy (same spark plugs all year and 15 passes before I change oil)and still not even near a tune-up range that will start hurting parts.

 The amount of blower boost/overdrive is what makes the combo mild, but basic motor/fuel princibles must be adheared to first and foremost

--- End quote ---

Ditto DRE statement.

I have run 10-1 all the way up to 11.4-1 in my blown alky SBC's timing anywhere from 25° to 34° depending on the combo and cylinder heads used. I typically run 30° and around 24lbs of boost

Frontenginedragsters:
I beg the courts forgiveness.
I wasn't thinking clearly.
it won't happen again.

Matt

George:

--- Quote from: Frontenginedragsters on February 27, 2015, 08:56:08 AM ---I beg the courts forgiveness.
I wasn't thinking clearly.
it won't happen again.

Matt

--- End quote ---

20 lashes !!!! ;)

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