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950 HP jet size for street

25K views 31 replies 19 participants last post by  mrpaticular 
#1 ·
What are you guys running for jets in your 950 hp for street strip? I have 80's in the front and 89's in the rear with factory power valves front and rear. I am killing plugs and it is pig rich.

I have run my best ever et with these, but it is not worth l
killing the plugs. I am running NGK R5671-7's on the street and spray a 200 shot with NGK R5671-8 on the bottle.

Dart Pro 1 325's on a pumnp gas 462 if it matters.

Thanks!
 
#3 ·
i dont know what cam your running but that might be why your fouling plugs if the power valves are open while your cruising. i run 77 primary jets with a 3.5 power valve. and 86 secondary with no power valve and my plugs are last years. i think you'll need to be around 76 to 77 jets to run clean. and if you have very much cam the power valve is the big problem stock ones are 6.5 .hope this helps
 
#6 ·
If you have a power valve in the front and the rear. The jets should be about the same size. The jetting you have should be right for just a power valve in the front and the back one blocked off.
 
#7 ·
in summer air and especially street driving i can't see why the stock 78 square jetting wouldnt work for you

btw,your power valve size should be 50% of the vacuum at idle reading.

the way it's jetted now for racing doesn't seem right even though you've have your best times with it

could be a weak fuel system for you to have to use that much jet,kind of just a band-aid
 
#12 ·
Bob's advice is prob a great start.
Just for reference - I run 85/90 with rear pv blocked , this is where it flowed best @ the carb shop on a bench .It seems a little rich still. I think Bobs #'s are real cose to where I will end up.
 
#9 ·
Thanks for the replys guys. I will check the size the the P/V's tonight and likely plug the rear as suggested and reduce the jet sizes. As far as fuel is concerned, I run a Manga Fuel 500 pump and filter
-10 line to the reg and two -6's to the carb.

I'd like to run True Street near here at Z-Max on Saturday and I do not want to fowl plugs on the cruise.
 
#11 ·
I had 2 Holley 950HP's, both ran phenomenal, but very rich at cruise. They ran something like 10.8 AFR. I tried everything in the world to lean it out, and all it did was screw-up the throttle response. Ended up with a Prosystems 950HP that ran like the Holley but gave a cleaner cruise.

Is yours newer or older?
 
#14 ·
JMHO, the Dart Pro One heads have terrible low RPM response. Flow great at higher RPM / higher CFM demands, but poor at cruise. Went through the same thing. You run 325's on a 462" motor, I run 310's on a 469" motor. Kept jetting up to get it to cruise, them went fat at WOT. Switched to a BG 800 annular. Completely different motor with the annular. Not advocating it, just stating a personal experience. Only carb that I had that was close was the 750HP street which is really the 950HP with the smaller baseplate and street jetting. I would try a smaller carb w/ down legs or an annular booster carb.
 
#16 ·
It's too late for the NMCA this weekend, but i may end up sending this thing to Pro Systems. Brutal gas mileage (less than 50 percent of a buddy who has a regular 850) , it kills plugs and unless the plugs are new is usually hard starting.

Maybe I'm getting old, time for fuel injection??????
 
#20 ·
Exactly and seeing a rich condition by looking at a spark plug and or looking at what's coming out the the exhaust tells you absolutely nothing about where In the rpm range it's fat nor what circuit needs adjustment . A quality 200 dollar o2 afr set up takes all the guess work out of it .
Or you just keep throwing darts at the board blindfolded or just keep spending money on different carbs . Answer : buy the o2 afr set up and learn how to tune the carb
 
#19 ·
I have to add PV's DO NOT effect idle they compliment the main jet under load, thats why it was called an economizer valve years ago. measure your cruise vacuum and go from there. that whole half of idle reading is WRONG. L-78/L-72/LS-6 ran 10.5/8.5 from factory, you can clean up and drop down your jetting with the a valve that opens sooner.
 
#21 ·
Right and the PV doesn't necessarily open at all if your easing into the throttle all the way over 100 mph. The pv opens at a vacuum point as stamped on the pv so if it's a 4.5 pv it's not gonna ever open untill manifold vacuum hits 4.5.
It opens to make up for the huge drop in vacuum when the throttle is wacked.
.again...if your anything this side of a smokey yunick or the like then you might as well bite the big duece bullet and spend 200 on the 02 afr set up.
 
#25 ·
I hope figured it out. He's had almost 12 years to work on it.
 
#31 ·
If hes fat upstairs he needs to increase high speed air bleeds. If hes fat down low or anywhere in between it can be any number of different causes and fixes . Without an afr set up its hit and miss poke and hope
 
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