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supermx96 05-29-2013 10:29 PM

carb jeting question
 
I have a question about my carb jeting on my engine setup,
engine is 468ci gen 6, 8:1 comp ratio, Edelbrock alum ported head, hyd roller camshaft, b&m 250 blower @ 5.5 - 6 boost, twin QFT 850 marine blower carb boost ref, run it at 5500-5600 rpm. With that to achive an AFR at 11 WOT and a AFR at 12 at 3000 rpm i need to jet the primary to #77 with 4.5 power valve and the secondary have jet #106 so does it have any problem to run them with a big diference between the pri and sec jet size?

At 3500 rpm the power valve is open due to 0 vacuum and that rpm is my cruising speed and the AFR drop at 11, i know that is a rich mixture for cruising but i dont know what i can do to make the cruise speed leaner without afect the WOT AFR too much because i have already some big jet in the secondary.

supermx96 05-30-2013 10:47 PM

Any thought on that??

FIXX 05-31-2013 01:32 AM

? do you have a powervalve in the secondary circuit?

supermx96 05-31-2013 06:27 AM


Originally Posted by FIXX (Post 3934379)
? do you have a powervalve in the secondary circuit?

No power valve in the secondary, comme new with # 78 and 4.5 power valve pri and 88 sec no power valve.

vintage chromoly 05-31-2013 11:49 AM

You should have some vacuum at 3500 rpm's.

Your power valve should open when you first open the throttle plates and you have no airflow yet. (No vacuum). Once cruising at 3500 you should have 10 inches or so, depending on the cam.

supermx96 05-31-2013 08:10 PM


Originally Posted by vintage chromoly (Post 3934635)
You should have some vacuum at 3500 rpm's.

Your power valve should open when you first open the throttle plates and you have no airflow yet. (No vacuum). Once cruising at 3500 you should have 10 inches or so, depending on the cam.

No vacuum and no boost at 3500 rpm probably because of the blower spining and the load this is in a Scarab 29 single engine.


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