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Discussion Starter #1
Still cant figure out why my car leaves so soft....to bring you up to speed: car is a full chassis 2650 lb ride...598 C-head..5700 stall convertor...powerslide 1.80 straight cut..4.11 rear...33 inch tall tire 105 inch run out. timing currently set at 34 degrees...degreed cam 114 came in closer to 115 installed straight up. I figured this this thing would pull like mad out of the hole...not the case. 4600 off the brake the best 60ft i got was a 1.29. after a 100 feet it pulls like crazy and has run a best of 8.49 at 163mph. Thought maybe it was convertor..talked to Art at Coan and he thinks the convertor is right where it should be after the shift and thinks the car may need more gear. Would switching from 4.11's to 4.29 or even 4.56 pick up the low end that much? Keep in mind i dont want to go through the traps at 8000rpm. Could it be a timing issue? advance cam? I want this thing to leave like a banshee...if it doesnt even want to pull the front wheels i might as well lighten it up 30lbs and take the wheelie bars off :(
 

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i think 4.56 would be about right for a 33 inch tire. I'm running 4.57 with a 31 in tall tire and 60' 1.32-1.36 in a low 10 sec 3000 lbs back half car at the traps I'm at 7200 . what kind of rpm are you seeing at the traps?
 

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Have you tried leaving the line at full boogie on the converter? I chip mine down to maybe 5500 from 6000 or so sometimes but leaving at 4600 on a 5700 converter has to kill some hit.

I have run 1.20 at 60 on an 8.21, 165 pass with 3.89 gears, 1.96 glide and 32 X 16 goodyears. crosses the line at 7200 or so.

dkp
 

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Discussion Starter #4
never came off the convertor that high...4600 max..would it be ok to leave that high? 3.89 gear and 7100 at the stripe...4.57 would really be crankin...I had been shifting at 6700 and crossing at 7000 then when i shifted at 7000 it crossed around 68-6900 area.
 

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Jed,
Had the same problem with our 557... had the cam straight up, but once we advanced it 3 degrees it would carry the fronts 6 to 8inches high for 15 to 20ft.
you might try it & see if it will help, it sure helped ours.

good luck, you'll get it.
 

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What do you shift at?

What do you go thru the traps at?.

Appears it could use more gear as others have mentioned. Converter could be slightly tight if its rated for more than 1200-1500 rpms under your shift point.
 

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I'm with Dean on this , turn off the two step and let er lean on the convertor. I'm thinkin at 4700 you might be below the rpm required to let the engine perform, but turning off the launch limiter is cheaper and easier than a convertor change. You will know if your heading in the right direction. I'm guessing a motor like that would love a 5500-6000 convertor with a glide and 4:30 gear, maybe 4:11 cause you got. Probably a silly question, but do you have jet extensions in the rear bowl?
 

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Discussion Starter #10
Lots of great replies definately gonna try them all...i think my first step will be the timing. Is it difficult to advance the cam? i figure maybe just two degrees to see what it does. How will i know if i have enough clearance without a clay test ? :( dont really want to smash valves at 100 bucks a piece. If i just advance it two degrees where will that put the total timing if its at 34 degrees now? and yes on the jet extensions...its a pro systems carb
 

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I agree it needs a gear change. A 4:56 at a minimum. Get some torque to the ground and let the motor work up where its happy.
 

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Discussion Starter #12
This set up has a danny bee that i installed straight up...im not a master with the degree wheel but i must have checked it four times and it came out to 115 instead of 114 like the cam card stated. Does that mean im already one degree retarded? should i advance the cam 2 degrees and see what happens?
 

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Mine leave just as hard with the chip pulled flat on the wood or on a 3000 chip...............I doubt raising the leave rpm on the chip will help any, and it really shouldn't

Sounds like its a combo of things, converter too tight or wrong, could use a tad more gear, cam timing off a bit.

For sure get after the Danny Bee and try advancing the cam.
 

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more gear would help but i'd advance the cam.your not turnen it very hard,IMO,so you have a very small window of good HP.move the cam 2*and see how it does.
 

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turn it up

Jed - my car is 3,000 lbs - with my 598 C head deal on Methanol - running at around 8,000' DA I get 60's around the same as yours. Mine stalls at about 5800 and I have it chipped at 5700. I run a 33" tire with 4:11's - cross at about 7k even - around [email protected]+. best pass ever here in really good air - 1.25 60' 8.71 @ 156. Chipping down the launch to around 4800 will knock a couple of hundreths off my 60'.

Kurt
 

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I was thinking more 1/8 mile , but that engine is gonna have to be turned some rpm unless its got a grandma cam shaft in it. I turn my 562 p-51 engine 7400 in the 1/8 and its got little ports compared to c heads.
 

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Discussion Starter #19
Its not a huge cam by any means its under 800 lift...what gear do you run ky? how hard out of the hole do you come out and shift? finish rpm? just curious thats a serious ground pounder you have there...whats it weigh?
 

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The car weighs 2400 lbs w driver
Most of the time I run 4:86 gears with a 105 "tire , but I have ran 4:30 and back and forth. The car will run faster with 4.86 gears and I wish I could find a big pinion 5:14 gear set I would try them.

The car likes more launch rpm with the 4:30's (6000rpm chip) and will also et quicker with a higher chip with the 4:86 , but it is not near as sensitive to launch rpm with the 4:86 gears. I shift at 7200.

I don't know if you have dynoed your engine or not but that would tell you what you need to know.

The next issue you get into is what the chassis likes , at some point you have got to slip the tires a bit on the launch (wheel speed)

The gear ratio combined with the tire diameter places a load on the converter, a 4.10 gear will place a lot more load on the converter in high gear than a 4:86 , when you factor in your 1/8 mile speed you are also getting an aero dynamic force playing against your converter also , that is why a lower gear will not always rpm more at the traps.

The big thing with gear ratio is you can not multiply hp it is going to stay the same , but you can multiply torque to the rear wheels. More torque all the way down the track , more power strokes what is accelerating the car.

The car will not slow down until your rpm reaches over the hp peak and the rpms will go flat or quit climbing.
 
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