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Author Topic:   Holley Jetting
Flanndad
Member
posted June 09, 2003 07:01 AM
I'm running a 406 chevy with 12.5 to 1 conpression.
Currently running 110 octane fuel.
Carb is a 4779 holley stock jetting say's 70 front and 80 rear.
I set it up with 72 front 80 rear, with a 6.5 power valve.
I dropped a valve and trashed the first motor.
Question is this enough jetting for high octane fuel or not.


KPLugnut
Member
posted June 09, 2003 08:16 AM
Although air quality (temp, density, moisture content, etc) has a lot to do with final jetting, that should put you in the ballpark for that application (72/80). Was the motor heating up or showing obvious signs of being overly lean before the valve failure?
That fuel and compression combination is a common setup and we've had numerous carbs in the past run just fine with jetting in that vicinity. Of course, this also assumes the carb has not been modified by someone (air bleeds, venturi/throttle bore, etc).

Hope that helps,
KP


Flanndad
Member
posted June 09, 2003 09:15 AM
When the motor would idle, 170 to 175 would be top temp, but that was mid April in Michigan, I raced it the last week in April and the First in May, I don't believe it got above 185.

The carb is basically stock, with the exception of a Barry Grant rebuilt kit, and a larger squirter in the rear side of the carb.

KPLugnut
Member
posted June 09, 2003 11:35 AM
Then that jetting will be fine. Ultra cold air temps, tho, might have made it a bit on the lean side (since you were in the north where it does get cold), but I doubt it was lean enough to be the cause of any engine trouble. The jetting and assumed air quality this time of year will be pretty darn close, now.

Hope that helps.
KP


rocket36
Member
posted June 11, 2003 12:33 AM
detonation is the biggest killer of all engines. inspect all the parts from the engine to see if there is any sign.
definitely the cold weather will cause air to be very dense and lean "normal mixture" out I have melted an engine because of this.


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