4 barrel jetting?
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4 barrel jetting?
Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.
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Re: 4 barrel jetting?
More info needed. If you have a powervalve in front you might try 2 sizes larger Presumming no PV in rear I would leave it alone Need way more info and will try to help.
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Re: 4 barrel jetting?
What cid motor are we taking about here?
That 72 primary sounds lean to me, or at least the primary to secondary spread sounds too big!
Is the Carb a model with 4 idle circuits?
Open header?
That 72 primary sounds lean to me, or at least the primary to secondary spread sounds too big!
Is the Carb a model with 4 idle circuits?
Open header?
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Re: 4 barrel jetting?
355, 9.5:1 pump gas(91)
Bowtie Vortec large runner head, 215-225cc(was bought this way so unsure of if its a early 371c head or later after they made runner changes.
raised runner chevy bowtie intake, plan to sell both heads and intake after race season however, Im aware they are wrong for the combo.
3000-7000 rpm range custom 4/7 comp cam 252/255 108L advanced 4 degrees. just 1 3/4" headers 3.5 collector
3.48 stroke
6.125 rod, unsure of what piston it has.
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Bowtie Vortec large runner head, 215-225cc(was bought this way so unsure of if its a early 371c head or later after they made runner changes.
raised runner chevy bowtie intake, plan to sell both heads and intake after race season however, Im aware they are wrong for the combo.
3000-7000 rpm range custom 4/7 comp cam 252/255 108L advanced 4 degrees. just 1 3/4" headers 3.5 collector
3.48 stroke
6.125 rod, unsure of what piston it has.
,
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Re: 4 barrel jetting?
I would jet up equally on both front and back. Start with 2 sizes. To keep balance. It will tell you if it likes it. The slight stumble could be from needing more jet too. If plugs are white, it likely needs more fuel.88bluestar wrote: ↑Tue Sep 04, 2018 7:58 pm Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.
Re: 4 barrel jetting?
Don't be fooled by unleaded pump gas. Plug porcelain nose should look they came out of the box for street use. Any color if any should be deep in the shell. They can be light gray for drag racing. Cure your off idle stumble with the pump cams and squirters.
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Re: 4 barrel jetting?
1st up is your fuel supply system able to deliver what your engine will need? Fuel flow test thru N&S's?
Craig.
Re: 4 barrel jetting?
Especially with a carb of unknown history, I like to disconnect the secondaries, optimize the tune on the primaries then reconnect and fine-tune with only the secondary jets. I've seen as much as a 15 HP gain with no change in AFR by going richer on one end and leaner on the other.88bluestar wrote: ↑Tue Sep 04, 2018 7:58 pm Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: 4 barrel jetting?
http://www.quickfueltechnology.com.au/c ... s-AUST.pdf Check out the what some of QF standard jetting are.