square jetting a t ram

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mopardave
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square jetting a t ram

Post by mopardave »

Been trying to run 4 pv's in a twin 650 tunnel ram set up using .056 PVCR's and .070 main jets. I want to try square jetted no pv's. How much main jet should i start with?
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Re: square jetting a t ram

Post by Walter R. Malik »

mopardave wrote: Tue Nov 03, 2020 5:28 pm Been trying to run 4 pv's in a twin 650 tunnel ram set up using .056 PVCR's and .070 main jets. I want to try square jetted no pv's. How much main jet should i start with?
That is an OK place to begin however, in an actual drag vehicle, the very front will want to be a jet size or two richer and the very rear a jet size or two leaner.
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Re: square jetting a t ram

Post by mopardave »

My carbs set sideways.
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Re: square jetting a t ram

Post by F-BIRD'88 »

Assuming that the jetting is right now.
Calc the AREA OF the .056" hole and the .070" hole.. add together.. now calc this new combined AREA into a new jet diameter...
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Re: square jetting a t ram

Post by F-BIRD'88 »

Look up what holley jet # has a .090" hole.
The right jet FLOW will be +/- 2 jet #'s..

(Assuming the carbs are jetted correct now.)
Better to error on the rich side to start tuning.
Do not depend on a AFR to find best WOT actual car performance. Give it the jets it wants to go fast.

I would start with #82 and work/tune down from there.
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Re: square jetting a t ram

Post by rustbucket79 »

I would think it will settle out around +4 the current jets you currently have assuming you’re running larger secondary jets now. You might need to stagger jet (small pri big sec) to prevent rich cruise yet still hit target AFR at WOT.
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Re: square jetting a t ram

Post by mopardave »

ok, i have a jet flow chart and i can calculate. carbs set sideways and have .070 BLP jets in all corners. a .070 in a BLP jet is a .070 in a Holley jet.
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Re: square jetting a t ram

Post by ClassAct »

I’m not sure what eliminating the power valves in the primaries is going to do, but make it pig rich at a cruise.

I would eliminate the PV in the secondaries, fix the cruise jetting on the primaries and then get WOT correct with the primary PVCR and secondary main jets.

I can’t think of a single reason to not run a PV on the primary side, especially on something driven on the street.
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Re: square jetting a t ram

Post by F-BIRD'88 »

ClassAct wrote: Wed Nov 04, 2020 10:40 am I’m not sure what eliminating the power valves in the primaries is going to do, but make it pig rich at a cruise.

I would eliminate the PV in the secondaries, fix the cruise jetting on the primaries and then get WOT correct with the primary PVCR and secondary main jets.

I can’t think of a single reason to not run a PV on the primary side, especially on something driven on the street.
Agree.... Other than as a jet tuning exercise for best WOT drag test racing ONLY,,, why would you want to eliminate the primary power valves?
Street use is going to want PV's.

Also , jet it to run the best 1/4 mi ET and MPH. give it the fuel it wants to run fast, not some predemined "optimum" feel good AFR guage reading @WOT.
The AFR guage is AT best a "you are too lean" warning device for WOT jet tuning.
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Re: square jetting a t ram

Post by mopardave »

Thanks for the info on that. The carbs are custom built by Dom@Thumpercarbs. He uses the same size carbs on his 470 with no pv's and says it runs very good on the street this way. Does not run pig fat. I just want to give it a try. I have a drawer full of pv's and and always go back if need be. He uses a 85 BLP jet squared in his 470 which i believe is a 80 holley jet.
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Re: square jetting a t ram

Post by jmarkaudio »

Are they billet or cast Holley carbs? Choke tower or no? 76 Holley jet would be a starting point for stock zinc with the choke tower.
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Re: square jetting a t ram

Post by mopardave »

Billet BLP main body. No chock tower.
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Re: square jetting a t ram

Post by Gotzy »

jmarkaudio wrote: Fri Nov 06, 2020 9:16 am Are they billet or cast Holley carbs? Choke tower or no? 76 Holley jet would be a starting point for stock zinc with the choke tower.
Out of interest, what would the removal of a choke tower change that would require jet tuning please?
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Re: square jetting a t ram

Post by jmarkaudio »

Probably not much if any, billet bodies can vary if the Venturi size is different.
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