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post #1 of 4 (permalink) Old 06-01-2014, 07:09 AM Thread Starter
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408W 750HP - what size jets?

Hi- i have a 408W. 750HP 76/84 jets.AFR205.. solid roller .616/.622... hooker super comps.. full 3" x pipe exhaust.. 34 timing. 3.0 8" rearend (i know ... dont say anything)

Dyno results showed i was too rich 11.67: 1 a/f ratio. This was at 5200 and above. Can someone recommend possible different jet sizes for me..

It started smokin bad at close to 6000. Come to find out after / during the pull #1 intake rocker arm came off too...maybe this caused the smoke??? I couldnt tell it came off during run. It was too loud

Any advice on jet sizes would be appreciated.
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post #2 of 4 (permalink) Old 06-09-2014, 08:09 PM
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Re: 408W 750HP - what size jets?

I am no carb guru but a couple of things come to mind..If it was at a higher rpm when it went rich I would suspect the secondaries being rich so maybe try going down a couple of sizes there..Also I am not sure what actual size the 750HP is but if its like the 950HP its much smaller than its name sake..The 950HP is more like 830ish CFM..If the 750 is sized similarly it may be on the small side for your 408 depending on the rest of your combo and what you are doing with it..

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post #3 of 4 (permalink) Old 06-09-2014, 08:19 PM Thread Starter
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Re: 408W 750HP - what size jets?

I was told to go down a couple sizes indeed. That was before we knew my rocker arm came off... Unfortunately - i dont know how to tell if a carb is too small. I do know the 750 hp i have right now is perfect for the street. I havent taken it to the track yet. THX for your help
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post #4 of 4 (permalink) Old 06-10-2014, 02:43 AM
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Re: 408W 750HP - what size jets?

Losing the intake valve operation will cause heavy smoke as it sucks against a closed valve, pulling oil past the rings into the chamber and out into the exhaust.

To know if a street/strip carb is too small for full-rpm flow, measure your current atmospheric pressure. Then read manifold pressure (vacuum) at torque peak and at HP peak. If the pressure drop at peak HP is more than double the pressure drop at TQ peak, you're choking it excessively.

If this were an all-out race-only engine, the spread may be smaller, but even there too large can slow you down if you lose average torque. This also does not apply to EFI, where vacuum is not necessary for fuel flow, and atomization to some degree.


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