mph to low maybe wrong gears?

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Duster Drag Car

Duster Drag Car

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secound test and tune was solid and impoved times, but mph are low best time was 11.3 @ 102 mph and 11.47 @109. Im running 4.30 gears wondering if i should have went with 4.56 or 4.88 gears or even have left the 5.13s in it, gonna swap carbs with another 850 i have, gonna try 82 primary and 88 secoundaries and power valve plugs also gonna tune for n20 got to get this pig in the 10s.
 
I'm very very far from an expert. But I was under the impression basically the higher gear numbers (lower ratio) would produce lower top end speed/more acceleration? I'm SURE you know more than me. Et's are nice I would have thought you'd have a higher top speed to get there. But hey I've never been down the track so I can't say anything from experience. I'll be following here from the stands watching your runs :)
 
Post up a couple slip with all incrementals.

It's likely a tune up/fuel delivery/converter issue.

It's got to be laying over, stop pulling? If you have PV plugs in in it with that jetting, I bet it was surging in high gear. No PV's and a 4781 carb, I'd have at least 88 squared jetting in it! Don't know what you have for idle and in gear vacuum, but I'd put a 3.5-4.5 PV in the primary and see if it picks up... I think this is the major part of your issue.

Where does it stop pulling and what RPM are you going through the lights. Might have a bad converter in it. It's a good 10-15mph slow for the ET. I'd expect it to be running in the 117-118 range with that 11.30 ET

Go to a site like Wallace and look what the engine RPM should be for a tire size/gear ratio for those MPH and compare to what you saw. If the engine is revving way above the expected number, you may have some BIG slip in the converter.

Make sure all timing parameters are correct.
 
crackedback said:
Post up a couple slip with all incrementals.

It's likely a tune up/fuel delivery/converter issue.

It's got to be laying over, stop pulling? If you have PV plugs in in it with that jetting, I bet it was surging in high gear. No PV's and a 4781 carb, I'd have at least 88 squared jetting in it! Don't know what you have for idle and in gear vacuum, but I'd put a 3.5-4.5 PV in the primary and see if it picks up... I think this is the major part of your issue.

Where does it stop pulling and what RPM are you going through the lights. Might have a bad converter in it. It's a good 10-15mph slow for the ET. I'd expect it to be running in the 117-118 range with that 11.30 ET

Go to a site like Wallace and look what the engine RPM should be for a tire size/gear ratio for those MPH and compare to what you saw. If the engine is revving way above the expected number, you may have some BIG slip in the converter.

Make sure all timing parameters are correct.
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the carb i was running has 76-76 jets and pv plugs im gonna swap to another 850 i have maybe ill try your combo 88 squared 3.5-4.5 pv ,do you run that combo in a similar set up to mine, converter doesnt have much stall but doesnt seem to slip i had it rebuilt, its a good billet front unit with a anti ballooning plate and a good stater bearing i think its called.she runs like a bat out of hell for 900 ft then yes the surge and i played with the fuel pressure fom 5.5 - 8.5 psi, converter is 9.5 im sure a big dollar 8 inch would help maybe next year.
 
88 squared was IF you are currently running an 850 with NO PV's...

If you pull the PV out, step up the jetting 6-8 sizes.

DO NOT put the jetting square with the secondary and run a primary side PV. Only time the jetting should be squared is if you are running PV's on both ends or not.

I have no clue what you are currently running, you mention an 850. Go here and look up what the carb started out with for jetting and start there. If running a spacer, step up jetting 2 sizes front and rear from where the listing says it came stock with.

[ame]http://www.holley.com/data/TechService/Technical/Carb%20Numerical%20Listing.pdf[/ame]
 
I see on a previous post you have 29.5x11.5x15.....that and a 4.30 should work great for a BB...

you should be at least 117-118 mph,,,,,,
 
Duster Drag Car said:
the carb i was running has 76-76 jets and pv plugs im gonna swap to another 850 i have maybe ill try your combo 88 squared 3.5-4.5 pv ,do you run that combo in a similar set up to mine, converter doesnt have much stall but doesnt seem to slip i had it rebuilt, its a good billet front unit with a anti ballooning plate and a good stater bearing i think its called.she runs like a bat out of hell for 900 ft then yes the surge and i played with the fuel pressure fom 5.5 - 8.5 psi, converter is 9.5 im sure a big dollar 8 inch would help maybe next year.
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damn my 850 4781 was running 80s front and rear with pvs.that 76 squared has got tobe way lean with no pvs in there....
 
70aarcuda said:
I see on a previous post you have 29.5x11.5x15.....that and a 4.30 should work great for a BB...

you should be at least 117-118 mph,,,,,,
Click to expand...

What was your rpm going through the traps? sounds like a fuel problem to me.what kind of fuel pump etc set up do you have? i think your gear is fine. i run 125 in the 1/4 with a 4.30 gear and a 28 inch tall M/T 275/60/15 drag radial. now i think my car would be faster with a set of 4.10, but when i get my duster going i am going to a set of the M/T 29.5x11.5x15 slick like the op has. OK a question for the op what size and back spacing rear wheel are you running on your duster?
 
Today my friend with 383 in a 75 Duster ran 11.30,s at 117mph.He has a 30 inch tire with 4.56 gears.Myself I run a 29x11.5x15 with 4.30 and ran [email protected],m thinking your slip says 112mph maybe?
 
put another 850 together today with parts from the three carbs i have, new set up is 80 primary 84 secoudary both pv pluged 37 squirters ill see what happens at 7.5 psi fuel pressure
 
Duster Drag Car said:
slip says 1.545 60 4.434 330 6.923 660 9.179 1000 11.307 1320 102.21 mph
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what was your 1/8 mph and your 1000 ft mph if it shows it? also you are running it all the way through the 1/4? its going to be a great car once you get it tuned right. member 75dartsport ran 10.50 at 124/125 in the 1/4 with his duster and a 850 holley dp so i know it can be done. just don't give up and keep tuning till you get there. Mopar65
 
Hope you don't kill the engine before figuring out why it's not pulling.

Good luck because IMO, You're WAY off!
 
new plan is new neoprine floats 84 primary 88 secoundary with notched float, jet extensions primary pv pluged and no secoundary pv
 
dude,check your idle vacume in gear cut in half then use that 84 88 jetting with the correct power valves.or at least put in 90s square.if your totally against useing power valves.....
 
oldkimmer said:
..........Hey Rob, do u think this explosion will be = to the big bang theory..........kim.....
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Bazinga.jpg


I don't know...

I do know I wouldn't run any of the jetting packages that the OP has posted. IMO, the last one is still ~10 steps in total lean. I made my suggestion based on it being a 4781 model. I bet it was in excess of 50HP short on power with the current jetting. Surging, no power in high gear, lucky it didn't barf on itself. Maybe that would have been a good thing that it just shut off.

4781? I'll stick with run 80-82 with a PV or 88-90 without. That should be in the ballpark, not sitting in the parking lot. It may want more jet, just have to run it to find out. Wouldn't be surprised if it picked up 5 tenths with the right jetting.

It went 6.92, roughly same ET as the Car Craft 480hp stroker engine in a 3350# car. MPH more or less than 96?

I guess on the positive side, it will maybe pull to 1100 feet now. :)
 
crackedback said:
Bazinga.jpg


I don't know...

I do know I wouldn't run any of the jetting packages that the OP has posted. IMO, the last one is still ~10 steps in total lean. I made my suggestion based on it being a 4781 model. I bet it was in excess of 50HP short on power with the current jetting. Surging, no power in high gear, lucky it didn't barf on itself. Maybe that would have been a good thing that it just shut off.

4781? I'll stick with run 80-82 with a PV or 88-90 without. That should be in the ballpark, not sitting in the parking lot. It may want more jet, just have to run it to find out. Wouldn't be surprised if it picked up 5 tenths with the right jetting.

It went 6.92, roughly same ET as the Car Craft 480hp stroker engine in a 3350# car. MPH more or less than 96?

I guess on the positive side, it will maybe pull to 1100 feet now. :)
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i'm of the same opinion as you...whats up with pulling out the power valves,my carb i just got was the same way.the guy said it did not run right on his 427 chevelle.had stock jetting and powervalve plugs.i put in 4.5 power valves and put it on and it runs great esp at full throttle.
 
Duster Drag Car said:
slip says 1.545 60 4.434 330 6.923 660 9.179 1000 11.307 1320 102.21 mph
Click to expand...

It looks like you car is running great through the 1/8 mile...that 1/8 mile time equates to a 10.90 pass in the 1/4 mile. The things I would look at:

1. What fuel pump (might not be big enough)?
2. Clogged fuel filter?
3. Jetting, like Crackedback was saying, 76's sounds pretty lean...for what it's worth my small block uses WAY more jet than that (84-92 with PV).

I think you have a fuel delivery problem, not a gear problem...those gears sound perfect for a 1/4 mile car with a 29" tire. Also, I would not bother chasing the converter "issue" unless it is slipping real bad (like if you were turning 6800rpm at the stripe at 102mph...that would be a converter problem). Start by fixing the fuel problem, then if you want to fine tune it with a better converter go for it.

Still, not to bad for the only the second time out. Just be careful to get this fixed before it damages the motor.
 
Roger - please give me a call or stop by with the original carb... As they noted - you're way off and I can explain a bit of it and hand you a carb that's closer to what you need.
It's not the gearing. Get it running right, then calculate the slip in that convertor and I think you'll find the issue.
 
new set up primary 88 jets 4.5 power valve secoundary 92 jets with extensions pv pluged stay tuned for et in the 10s!
 
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