My missing MPH has returned
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
My missing MPH has returned
Back in Oct/Nov last year I had a thread going here looking for theories about where 2 mph went on my last run on the track last year. I dropped from 110.5 to 108.5 with no apparent cause. After checking the engine, I pulled the trans and converter out, suspecting the converter. Sent it to Transmission Specialties. They cut it open, found nothing wrong, put in new bearings, welded up and returned it. I took my TH350 trans to Sepanic Racing Transmissions in Moosic PA. Jack took the trans apart and found evidence of slipping high gear clutches. He explained that the previous rebuilder didn't correctly perform the needed mod to prevent this. He did a full rebuild. I reinstalled everything, along with new 1/2 shafts and U joints. The car felt good on the street but I hadn't gotten to the track till today. Just test & tune today. I made 2 runs, both 12.40 at 110+mph, so the high gear clutch fix apparently cured the problem.
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
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Sweeeet! That will do it!
So what did he do for high gear? On T-400's I'd leave the center lip seal out of the drum so it applied pressure to the whole piston instead of just part of it in reverse and the other part in high. Slammed into reverse pretty hard...but that sucker never slipped in high gear with 2 stages of N2O feeding into it on top of a healthy Big block!
JIM
So what did he do for high gear? On T-400's I'd leave the center lip seal out of the drum so it applied pressure to the whole piston instead of just part of it in reverse and the other part in high. Slammed into reverse pretty hard...but that sucker never slipped in high gear with 2 stages of N2O feeding into it on top of a healthy Big block!
JIM
Race Director
Joined: Dec 1999
Posts: 11,094
Likes: 990
From: Sierra Foothills CA
Back in Oct/Nov last year I had a thread going here looking for theories about where 2 mph went on my last run on the track last year. I dropped from 110.5 to 108.5 with no apparent cause. After checking the engine, I pulled the trans and converter out, suspecting the converter. Sent it to Transmission Specialties. They cut it open, found nothing wrong, put in new bearings, welded up and returned it. I took my TH350 trans to Sepanic Racing Transmissions in Moosic PA. Jack took the trans apart and found evidence of slipping high gear clutches. He explained that the previous rebuilder didn't correctly perform the needed mod to prevent this. He did a full rebuild. I reinstalled everything, along with new 1/2 shafts and U joints. The car felt good on the street but I hadn't gotten to the track till today. Just test & tune today. I made 2 runs, both 12.40 at 110+mph, so the high gear clutch fix apparently cured the problem.
I won't make it to the strip this year but I just found out I'll be making some passes at our local airport for a Father's Day event. In the past it's been cars vs. airplanes but this year it looks like it'll be good old fashioned drag racing. Practice runs on Thurs. & Fri. with a Mustang GT500, a Camaro with nitrous, and a couple old school gassers. No idea how well any of them will get down the track....uhhhh, runway- but I'll know more when we're done playing Thursday. I may be the slowest guy out there but whatever the case it should be fun.
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
Thanks for the responses guys.
Jim - My understanding of the fix was that there are 2 changes they do to increase fluid pressure on the hi gear clutches to prevent slippage. One of them is to restrict a bypass. That was not done in mine originally. My trans lived that way for quite a while since I'm only putting about 400 hp through it. So far so good.
Les - Good luck on that air strip. Could be a little tough traction-wise. I don't imagine they will be prepping it.
Jim - My understanding of the fix was that there are 2 changes they do to increase fluid pressure on the hi gear clutches to prevent slippage. One of them is to restrict a bypass. That was not done in mine originally. My trans lived that way for quite a while since I'm only putting about 400 hp through it. So far so good.
Les - Good luck on that air strip. Could be a little tough traction-wise. I don't imagine they will be prepping it.
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
Thanks. Just for curiosity sake while I was on the DA calculator site, I entered my timeslip numbers from Sunday into the correction factor. I think this adjusts the numbers to correspond to a DA of zero. The corrected ET was 12.003. Close to 11 seconds in terms of corrected data, but nothing really counts unless its actually on the timeslip.
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Instructor
Joined: Oct 2014
Posts: 143
Likes: 24
From: Prince George BC
Good news you found your lost 2 mph . I could also say I have a 12 second car with 13.1 and 105 mph . Until I see that time slip it is still a 13.1 . Still having fun no matter what time slip says 
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
That 105 mph should get you into the 12s. I'm still thinking its camshaft or torque converter holding back your launch. Not easy fixes, I understand. Just food for thought.
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
Very impressive times! Can you share what the specs are on your car? Hp/tq read grear. I haven't ran mine at the track yet since building it last year. I have just over 1000 miles with no problems so far. Except for the tach. That's next. My engine is a 383 that dynoed at 496.4 hp with 468 tq. Trans is a 700r4 built for 650 hp 3000 stall and rear gear 3:70.
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
Very impressive times! Can you share what the specs are on your car? Hp/tq read grear. I haven't ran mine at the track yet since building it last year. I have just over 1000 miles with no problems so far. Except for the tach. That's next. My engine is a 383 that dynoed at 496.4 hp with 468 tq. Trans is a 700r4 built for 650 hp 3000 stall and rear gear 3:70.
Melting Slicks
Joined: Jul 2006
Posts: 2,282
Likes: 483
From: Salmon Arm, BC
I don't know my hp/torque numbers but I'm sure they're much less than yours. I have 3.73 gears, TH350, 3000 stall. Engine is a 383, ported Vortec heads, 225/232 duration hyd. roller cam, 9.7:1 compression, Qjet carb, 1 5/8 headers, 2.5 inch exhaust. I use drag radials at the track - that will be critical for you. BTW - I have run 12.15 in real good air. That's after a lot of trial and error.
I'm most likely going to get some sticky tires to help with the spinning off the line, and am wondering if you have beefed up your driveline at all or if it's still stock?
I'll be putting a drive shaft hoop on, and a line lock to help warm the tires.
Team Owner
Joined: Jun 2001
Posts: 43,136
Likes: 155
From: Thomson Georgia
Trans is a 700r4 built for 650 hp 3000 stall and rear gear 3:70.[/QUOTE]
Nice Tranny gear set-up! I have the same.
Your numbers are Very impressive and it sounds like there is even more room to improve
Nice Tranny gear set-up! I have the same.
Your numbers are Very impressive and it sounds like there is even more room to improve
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
I have to say I always look forward to reading your posts, as our cars are quite similar performance wise, and we both run vortec heads.
I'm most likely going to get some sticky tires to help with the spinning off the line, and am wondering if you have beefed up your driveline at all or if it's still stock?
I'll be putting a drive shaft hoop on, and a line lock to help warm the tires.
I'm most likely going to get some sticky tires to help with the spinning off the line, and am wondering if you have beefed up your driveline at all or if it's still stock?
I'll be putting a drive shaft hoop on, and a line lock to help warm the tires.
As for beefing up the drivetrain - I have a GOOD torque converter. Originally had a B&M and broke that. Trans is redone by Sepanic as a street/strip unit. Shifts automatically - even on the track. Spicer solid U joints, all six. I had stock 1/2 shafts, no problems, but I replaced them recently with new ones from Fort Wayne Clutch. They come with the flange and u joints installed. I have Drag Vette billet caps replacing the u bolts on the inner u joints. The rear itself was rebuilt by Bairs with Strange 3.73 gears. Overall, not very exotic, but I have 241 runs on the car now, starting at 14.0 and working down and I've always been able to drive it home. But really, my goal is consistency since I enjoy bracket racing.
Post up your results when you get to the track.
Last edited by BKbroiler; Jun 15, 2016 at 09:06 PM.
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
I don't know my hp/torque numbers but I'm sure they're much less than yours. I have 3.73 gears, TH350, 3000 stall. Engine is a 383, ported Vortec heads, 225/232 duration hyd. roller cam, 9.7:1 compression, Qjet carb, 1 5/8 headers, 2.5 inch exhaust. I use drag radials at the track - that will be critical for you. BTW - I have run 12.15 in real good air. That's after a lot of trial and error.
Melting Slicks
Joined: Jul 2006
Posts: 2,282
Likes: 483
From: Salmon Arm, BC
Well..... I did get to the track a couple of weeks ago, first time in 37 years.
I did 9 runs, and the best I could do was a 13.80 @105.
Most were in the low 14' due to missed shifts (2nd to 5th and back to third on three occasions
), spinning off the line, or general lack of skill....
Had lots of fun though
I did 9 runs, and the best I could do was a 13.80 @105.
Most were in the low 14' due to missed shifts (2nd to 5th and back to third on three occasions
), spinning off the line, or general lack of skill....Had lots of fun though
Thread Starter
Le Mans Master
Joined: May 2002
Posts: 5,084
Likes: 786
From: Lebanon Township New Jersey
Well..... I did get to the track a couple of weeks ago, first time in 37 years.
I did 9 runs, and the best I could do was a 13.80 @105.
Most were in the low 14' due to missed shifts (2nd to 5th and back to third on three occasions ), spinning off the line, or general lack of skill....
Had lots of fun though
I did 9 runs, and the best I could do was a 13.80 @105.
Most were in the low 14' due to missed shifts (2nd to 5th and back to third on three occasions
), spinning off the line, or general lack of skill....Had lots of fun though