Who hits OD during there run?
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BEATAV8
The Engine Whisperer
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- Feb 14, 2002
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Keeping it in 3rd gear is the way to go.
Most anybody running high twelves could potentially grab 4th at the big end of the 1/4 mile.
Keeping it in 3rd and letting 'er wind out will improve the MPH considerably.
But watch those revs though!
Most anybody running high twelves could potentially grab 4th at the big end of the 1/4 mile.
Keeping it in 3rd and letting 'er wind out will improve the MPH considerably.
But watch those revs though!
I always used to shift into OD right after the line. USED to. I did just as I always did but I guess was still at WOT, shifted into OD and bam...snapped input shaft.
Don't do that anymore.
BTW, I've been 121mph and still in 3rd. I think that was 5200 or so. But the converter was locked. That's the only way for me.
Now if I could just get back to 121mph. Might have a good ET
Don't do that anymore.
BTW, I've been 121mph and still in 3rd. I think that was 5200 or so. But the converter was locked. That's the only way for me.
Now if I could just get back to 121mph. Might have a good ET
I guess before I get to caried away with this I need to check some thing. I'm going by the factory tach and shifting into all gears manually around 5200. Maybe this stock tach is way off. I think I did check the factory tach to my scanmaster rpm readings once and they where the same. I cant remember for sure so maybe I should look into it again. If I am at 5200 in drive and only at 110 mph or so then I do have a problem right?
Jason
Jason
trading t/a
I'm Angry!!!!!
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- Aug 6, 2001
- Messages
- 1,120
Looking at my math:
110 mph with a 3.25 gear left in third should net you 4620 rpms give or take.
110X336=36960X3.25=120,120/26=4620 rpms
110mph with a 3.55 gear left in third should net you 5046 rpms give or take.
110X336=36960X3.55=131,208/26=5046 rpms
Now if you are on a smaller tire(some street radials actually measure close to 25.1")
110X336=36960X3.55=131,208/25.1=5227 rpms
I have seen stock tacjs off as much as 200-300 rpms, but that's the max I've seen. With you stated setup your tach would have to be off 600 rpms, not impossible considering what we are dealing with. Is there any chance that the gears you thought were 3.25 were actually 3.55? If the VSS is off it could throw off the tach and scanmaster alike. I believe the VSS for our cars are 17 for the driven and 43 for the drive gears. Grey and Red seem to stand out in my head. I had worked quite a while on these when I swapped from an auto to a T-5 in my last Firebird. If you are sure that the gears are correct I'd look into the vss indicating a bad tach reading which in turn would theoretically make you shift early possibly losing some good mph and consequently ET's.
HTH
Pete
110 mph with a 3.25 gear left in third should net you 4620 rpms give or take.
110X336=36960X3.25=120,120/26=4620 rpms
110mph with a 3.55 gear left in third should net you 5046 rpms give or take.
110X336=36960X3.55=131,208/26=5046 rpms
Now if you are on a smaller tire(some street radials actually measure close to 25.1")
110X336=36960X3.55=131,208/25.1=5227 rpms
I have seen stock tacjs off as much as 200-300 rpms, but that's the max I've seen. With you stated setup your tach would have to be off 600 rpms, not impossible considering what we are dealing with. Is there any chance that the gears you thought were 3.25 were actually 3.55? If the VSS is off it could throw off the tach and scanmaster alike. I believe the VSS for our cars are 17 for the driven and 43 for the drive gears. Grey and Red seem to stand out in my head. I had worked quite a while on these when I swapped from an auto to a T-5 in my last Firebird. If you are sure that the gears are correct I'd look into the vss indicating a bad tach reading which in turn would theoretically make you shift early possibly losing some good mph and consequently ET's.
HTH
Pete
What is being forgotten here is converter slippage,which I belive may be your problem.If your using a 26" tall tire and 3.25 gears but only hitting 110mph in 3rd gear then your converter is slipping around 12%(624rpm at 5200rpm)
Same reason why I trap 122-124 at 5500rpm in 3rd with 3.08's even though mathmatically I should be at 138mph.
Also the reason I'm going to a lockup converter for next season
HTH,
Steve
trading t/a
I'm Angry!!!!!
- Joined
- Aug 6, 2001
- Messages
- 1,120
That's a possibility, never included converter slippage! Don't know where, but I usually figured most people lock their converters. Wonder if a three disc converter or five would help the slipping or should he lower the stall(while maintaining the same launch boost) thus increasing top end efficiency!
Checked my tach to my scanmaster and they are right with each other.
The convertor is a 9" art carr non lock up so locking it isnt even an option. Its supposed to be like 3200 rpm stall. My tires I run at the track are 27.1" tall.
On the stock rear end I made a 119mph pass that I was in OD for a few hundred feet. That was with 29.5" tall tires! I think I have major conv slipage. My RPMs dont really drop that much after each shift ( thinking maybe 500) Ill have to check this out real soon on the street. Right now the car is down d/t a pre-turbo exhaust leak.
Jason
The convertor is a 9" art carr non lock up so locking it isnt even an option. Its supposed to be like 3200 rpm stall. My tires I run at the track are 27.1" tall.
On the stock rear end I made a 119mph pass that I was in OD for a few hundred feet. That was with 29.5" tall tires! I think I have major conv slipage. My RPMs dont really drop that much after each shift ( thinking maybe 500) Ill have to check this out real soon on the street. Right now the car is down d/t a pre-turbo exhaust leak.
Jason
turbov6joe
Signal 1 J-12
- Joined
- May 22, 2002
- Messages
- 2,220
Loose that converter and get a multi-disc LU and see what kind of numbers you have then. IMO these motors should be spun as low as possible unless you have a girdle, or at the least billet caps and studs on the mains. If you look at a dyno graph, the power really drops off in the higher rpm range unless you have a BIG cam to keep it up. There is really no need to spin in higher than 5600-5800 rpm.
I think If I do any thing that expensive it will be to go to a turbo 400 and a switch pitch. I can get the whole set up for $1500. I should be able to get decent money out of my set up so the actual cost out of my pocket wouldn't be to bad.
Jason
Razor.........
Have you ever messed around and made a few runs not locking the convertor? If so where you itno OD and stuff? How much et and mph do you get when you lock it? Do you think I'm losing very much running a loose non lock up convertor?
TIA: Jason
It seams to me that guys locking thier convertors are getting alot of bang for the buck out of there set ups
Have you ever messed around and made a few runs not locking the convertor? If so where you itno OD and stuff? How much et and mph do you get when you lock it? Do you think I'm losing very much running a loose non lock up convertor?
TIA: Jason
It seams to me that guys locking thier convertors are getting alot of bang for the buck out of there set ups
Jason,
there are two trade-offs in this stuff. One is the smaller converter will get you a better 60 foot and drop your et's due to less mass, higher stall, etc.. problem is at the same time it gives you those benefits, it takes away from the top. Ive run with converter unlocked and the car will have to go into OD to cross the line. Same time, the 12 inch converter cars are slower to the 330 mark.
I guess why they make that 9x11 converter trying to capture the best of both worlds.
So yes the ideal coverter would be light weight, really high stall, and can handle high torque lock-up.
Yes if you get the mph up, the et will fall. but its tough to fight against that wall. The tradeoff is huge. And the $$$ as well.
Actually Rob TTA1387 he typically locks his at 90 MPH. I've looked at his direct scan runs and it looks like another gear. I lock mine at the line since I dont like how it locks at 90 mph..kinda a flare. But hey I have an el-cheapo 12 inch.
Yup to the itty bitty $$$$ lockup converter..theyre great when they work
and you can afford them 
there are two trade-offs in this stuff. One is the smaller converter will get you a better 60 foot and drop your et's due to less mass, higher stall, etc.. problem is at the same time it gives you those benefits, it takes away from the top. Ive run with converter unlocked and the car will have to go into OD to cross the line. Same time, the 12 inch converter cars are slower to the 330 mark.
I guess why they make that 9x11 converter trying to capture the best of both worlds.
So yes the ideal coverter would be light weight, really high stall, and can handle high torque lock-up.
Yes if you get the mph up, the et will fall. but its tough to fight against that wall. The tradeoff is huge. And the $$$ as well.
Actually Rob TTA1387 he typically locks his at 90 MPH. I've looked at his direct scan runs and it looks like another gear. I lock mine at the line since I dont like how it locks at 90 mph..kinda a flare. But hey I have an el-cheapo 12 inch.
Yup to the itty bitty $$$$ lockup converter..theyre great when they work
and you can afford them 
