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How much HP can a T5 take?

24K views 15 replies 14 participants last post by  Burning Rubber12 
#1 ·
New to the forum here and forgive me if this question has probably been asked many times, but how much HP can a T5 stand for drag racing. Building my car now and the car currently has a stock (as far as I know) T5 in it. I'm thinking about possible different transmission combinations but for now I will probably just stick with this one to get my feet wet. Current engine combination is 306 roller with F303 cam, 1.6 roller rockers, Victor Junior intake, BG 750 carb, Trick Flow aluminum heads, flat top pistons. I do not know the HP. I am guessing probably in the 350 range? I do have a 351Windsor that will go in later. That one is making 550 HP at about 6400.
 
#4 · (Edited)
Torque, and especially the shock when the clutch is released fast, kill a transmission. If you have a high revving small engine and soft clutch grab, it can last a long time at 500 HP. If you have a monster clutch that grabs hard and big tires that grab, a stock motor will kill it pretty fast.

I put a good disk and plate in my 302, and supercharged it. It took about ten passes and it shaved all the teeth off a gear on the cluster.


The gears, within reason, don't care about the horsepower. The thing that breaks them is the torque and the huge surge of torque from a stiff clutch. A 351 with 550 HP will kill it pretty fast with a clutch that grabs hard and big tires.
 
#5 ·
The weight of your car will affect trans life, too.
 
#6 ·
I put 330hp/330ftlbs at the tire thru a stock T-5 for 3 seasons and about 150passes. Dump the clutch off the two step at 5000rpm 3150lbs. Prior to that I put about 200 passes thru it in the high 12s with about 230hp at the tires 3360lbs. I did bend a couple ninput shafts but I Never broke it. I did take good care of it. Rebuild it with fresh bearings and syncros every season to keep everything tight. Good shifter and proper clutch adjustment. Hope that helps.
 
#7 ·
There are a lot of factors on that question. The weight of the car, flywheel weight, clutch style and rear gearing. Then the other things are the hp and tq. the engine makes, then exactly which gear set you have, meaning which gear ratio set you have, then what style they are, then who made the gears. THEN ONE OF THE MOST IMPORTANT THINGS AND MOST OVERLOOKED THINGS IS HOW THE TRANSMISSION WAS BUILT AND IT"S CONDITION.

A lighter car, with a light flywheel such as a aluminum flywheel or stock 5.0 iron flywheel, should have less energy and less potential to damage a transmission, when launching the car at high rpm. The clutch design, base spring pressure, clutch disc design and material. A diaphragm pressure plate will have the highest base spring pressure and will shock the drivetrain the hardest. A long style clutch like a Ram 9000 series or McCleode Soft Loc will have lower base spring pressure and will allow slippage when the clutch is initially released, so the drivetrain is not shocked as hard. Then clutch disc design and friction material is important. You do not want to use a solid hub disc, you need to use a sprung hub. Then a friction material that is not overly aggressive. Kevlar discs are usually a bad idea for drag racing with any combo, the pucks will melt.
Then the transmission it's self. There are many different factory gear sets, with different torque ratings. The later factory 3.35 first gear sets are some of the better factory gear sets. The Cobra style pocket bearing gear sets are supposed to be good for more hp, some people disagree, but I have used the pocket bearing T5 gear sets to go very fast. Then there are the 2.95 and 3.35 1st gear ratio gear sets, with either the common torrinton bearing design and the cobra style pocket bearings. The Borge Warner gear sets seem to be the strongest from my experience, fallowed by the Tremec. Then there are aftermarket replacements for the factory gears, some of those are much weaker than either the Borge Warner or Tremec.

Then you have the G Force and Astro gear sets, those are very different from the factory gear sets. They have wider gears, with thicker teeth, less helix or straight cut gears. They also sell stronger output shafts. These parts are much stronger than the factory Borge Warner designed parts.

The biggest reason T5s break, is most are too loose, too much end play, either a result of years of wear and tear or being built improperly. I built a T5 that I used in three cars, the first one was a 12 second 85 GT, that I ran at the track regularly. That is actually the car I used to figure out what the problem was with the transmissions. I built a T5 that did not loosen up, it never loosened up after years of trips to the tracks on slicks. I then pulled that transmission and installed it in another car I built. That was a GT hatch that went high 11s, that car got totaled. So I built the car I have now. I put the same T5 in that car, most of the time the T5 was in that car, it ran mid to lower 11s. The last 306 engine combo I built that I used that T5 behind, made 418 whp, ran 11.02 at 125 mph. The car ran a best of a 1.49 60', with that transmission. I first built that transmission in '97, I ran that transmission till '06. I never broke a single part. I originally built the transmission with a pocket bearing style 2.95 1st gear set. That is the gear set I ran the longest in that transmission. I figured out the car could run quicker with a 3.35 1st gear set, so I swapped the gear set out, sold the old 2.95 gear set to a guy on this forum. I ran the 3.35 gear set for about three years, before I built the engine that is in the car now and switched to a C4 which was a huge mistake, I hate autos, they seem to hate me also. The only problems I ever had with the T5 was at one point I was not able to get Kevlar blocker rings. So I had to buy carbon fiber blocker rings from a local transmission supply shop. Those blockers would only last three passes, then I had to pull the transmission and replace the blocker rings. The Kevlar blockers would last me years without problems. It turns out the blockers I was buying were cheap junk, but at the time, they were all I could find. I finally got tired of replacing blockers and had the transmission Pro Shifted. I never had any problems at all after that, it would shift so fast people thought I had some special race 4 spd auto trans.
The Tremec TKOs and TKO 600 transmissions are definitely stronger, but they are very notchy, when they work correctly. The older TKOs usually did not have shifting problems. The new TKO 500s and TKO 600s have multiple problems that make them hard to shift at higher rpms. There are kits you can buy from Liberty gears that will fix the problems, but for what Tremec charges for their supposively superior transmissions, they should shift as good or better than a T5. They don't, when they shift the best possible, they are notchy.

So there are trade offs, either a good shifting transmission that if not built correctly, can break or a transmission that most likely won't break, but likely will need some parts replacements, to get it to shift at WOT.
 
#8 ·
Lots of good replies here.

The clutch is the trick to T-5 life. It sounds like you want to try the stock transmission until it blows (could be right off...) and then build it back strong.

There are several running the Astro A-5 gears at the strip and love them.

Tremec discontinued the original 1-2 style rings made of a composite material in mid-2011 replacing them with Carbon-Fiber rings. Tremec does not offer a Kevlar ring, but there may be an aftermarket Kevlar ring. I've just never heard of it... The new Carbon-Fiber rings are great and hold up well...
 
#9 ·
+1 my stock t5 took street and heavy track abuse for almost 2 seasons from a supercharged 347. It finally blew 3rd on the street not the track funny enough. But I've seen people break them with a lot less power and abuse. Kind of luck of the draw.

I rebuilt it with an astro a-5 gearset and it was sick, absolutely bulletproof, and better gear ratios, specifically first. If money is an issue, I'd say just run it until it breaks and rebuild it with good parts like astro. OR for insurance do it now and save the headache later. Like the guys said, it WILL break, just a matter of when.


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#10 ·
I rebuilt it with an astro a-5 gearset and it was sick, absolutely bulletproof, and better gear ratios, specifically first.
I have a brand new Astro A5 sitting around waiting for my mine to go. Finished another 9 week season in the low 12's and it's still going but my car only has about 350rwhp and 425tq when spraying.
 
#13 ·
Been several 7.30 - 7.50's in the 1/8 mile with a high mileage T5 that was never even gone into. Used a Steeda shifter and a Super King Cobra clutch from LMR. This thing saw lots of abuse on the street; plus my daughter actually learned to drive a stick-shift in this same car/transmission. Never had any issues with any of it and it shifted like butter.
I sold the transmission out of fear of breakage ( from some buddies and lots of horror stories on the internet) and went to a TR3550 and a Center Force DF clutch for a '96 Cobra. Worst mistake I've made with the car. I've missed more gears with the 3550 than I ever did with the T5. Huge disappointment. Going back to a T5; even with the reliability factor seeming bleak, I'll take my chances and enjoy being able to drive a stick again.
 
#14 · (Edited)
{Quote##:
The biggest reason T5s break, is most are too loose, too much end play, either a result of years of wear and tear or being built improperly. I built a T5 that I used in three cars, the first one was a 12 second 85 GT, that I ran at the track regularly. That is actually the car I used to figure out what the problem was with the transmissions. I built a T5 that did not loosen up, it never loosened up after years of trips to the tracks on slicks. I then pulled that transmission and installed it in another car I built. That was a GT hatch that went high 11s, that car got totaled. So I built the car I have now. I put the same T5 in that car, most of the time the T5 was in that car, it ran mid to lower 11s. The last 306 engine combo I built that I used that T5 behind, made 418 whp, ran 11.02 at 125 mph. The car ran a best of a 1.49 60', with that transmission. I first built that transmission in '97, I ran that transmission till '06. I never broke a single part. I originally built the transmission with a pocket bearing style 2.95 1st gear set. That is the gear set I ran the longest in that transmission. I figured out the car could run quicker with a 3.35 1st gear set, so I swapped the gear set out, sold the old 2.95 gear set to a guy on this forum. I ran the 3.35 gear set for about three years, before I built the engine that is in the car now and switched to a C4 which was a huge mistake, I hate autos, they seem to hate me also. The only problems I ever had with the T5 was at one point I was not able to get Kevlar blocker rings. So I had to buy carbon fiber blocker rings from a local transmission supply shop. Those blockers would only last three passes, then I had to pull the transmission and replace the blocker rings. The Kevlar blockers would last me years without problems. It turns out the blockers I was buying were cheap junk, but at the time, they were all I could find. I finally got tired of replacing blockers and had the transmission Pro Shifted. I never had any problems at all after that, it would shift so fast people thought I had some special race 4 spd auto trans.
The Tremec TKOs and TKO 600 transmissions are definitely stronger, but they are very notchy, when they work correctly. The older TKOs usually did not have shifting problems. The new TKO 500s and TKO 600s have multiple problems that make them hard to shift at higher rpms. There are kits you can buy from Liberty gears that will fix the problems, but for what Tremec charges for their supposively superior transmissions, they should shift as good or better than a T5. They don't, when they shift the best possible, they are notchy.

RBELL- what clutch were you using during this time?
 
#15 ·
Lot's of good info here. Thanks so much for all the replies. I bought this project car with the T5 in it. I think I am just going to go ahead and put the C4 in it, even though I would really enjoy the aspect of actually shifting it. I'm going to be a newbie drag racer at 58 years old, so I'm just going to keep it simple. :)
 
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