How much hp/torque can a 928 drivetrain withstand?
#16
Rennlist Member
I think the main components that need to be beafed up probably are in the first stages of the gear box. at the CV joints, there is already up to 4000ft-lbs of torque right, so only in first gear will you see those forces. at the drive shaft and 5th gear, you only see engine toruqe (say 400ft-lbs). anderson was breaking 3rd and i think he may have broken 5th as i did, but my failure was due to having a nasty vibration on the dyno due to having the e-brake partially engaged. ( we lost 100hp on that run before it broke 5th gear input)
as soon as you get to 2nd or 3rd gear, the parts out to the CV joints are probably plenty strong. i think the only way to break a CV joint is drag racing on drag slicks and getting a good "bite" .
mk
as soon as you get to 2nd or 3rd gear, the parts out to the CV joints are probably plenty strong. i think the only way to break a CV joint is drag racing on drag slicks and getting a good "bite" .
mk
Originally Posted by Evil Patrick
Well, The Bastard puts 400 ft lbs to the ground and that's through an 85/86
BW 5-speed with early posi retro-fitted [thanks, Mark Anderson / 928 Int'l!].
400 to the ground means there's about 460 going in (if you use the 15% rule).
Only problem I have? Wheel spin. Lot's of it!
Aside from just focusing on the tranny, the rest of the drive train needs to be up
to the task as well. From the flywheel to the lug nuts. Since I'm not stock until the
intermediate shaft and forward clamping collar, I can't speak to the 928 flywheel,
pilot bearing, clutch disk/s, pressure plate or throwout bearing, but the torque
tube assy and back is all Porsche 928 "stock", with the exception or the retro-
fitted posi.
BW 5-speed with early posi retro-fitted [thanks, Mark Anderson / 928 Int'l!].
400 to the ground means there's about 460 going in (if you use the 15% rule).
Only problem I have? Wheel spin. Lot's of it!
Aside from just focusing on the tranny, the rest of the drive train needs to be up
to the task as well. From the flywheel to the lug nuts. Since I'm not stock until the
intermediate shaft and forward clamping collar, I can't speak to the 928 flywheel,
pilot bearing, clutch disk/s, pressure plate or throwout bearing, but the torque
tube assy and back is all Porsche 928 "stock", with the exception or the retro-
fitted posi.
#17
Drifting
The 10psi 89' auto I play with has 1.5 years under this level of boost, is around 500rwhp and has had no transmission modifications other than Redline synthetic D4 fluid and an additional cooler. It has yet to slip or act up in any way, it also had 70k miles on it when we started.
We did have a rebuilt axle give up and went back to a new one with no problems since. The rebuilt ones are not hardened when redone and they do not last even 1 year on that kind of horsepower.
We did have a rebuilt axle give up and went back to a new one with no problems since. The rebuilt ones are not hardened when redone and they do not last even 1 year on that kind of horsepower.
#18
Burning Brakes
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There are many of us running 5 speeds that will tell you this is not an issue if you have control of your right foot
Originally Posted by Hughett
One of our brethern from Alaska swears by the auto trans (on his twin screw)..claimed that it was far better to deal with as a 5-speed would make for more difficult traction. Then again, I don't think he makes too many jack-rabbit starts either. However on the twisty track, winding out, his car was awesome! And torque probably more even.
Harvey
Harvey
#19
Rennlist Member
exactly!
does this mean if you are doing 30-80mph, its like doing it 18,432 times?
i think the main thing we dont think about, and sometimes speed tv references this in their TV reporting of races, is that in our races, we shift 15 times per lap, so x 20 laps of a race at Infinion (a 2.3mile track) 200-300 times a session. thats 600 to 1000 shifts a weekend. i got about 75 race days on the Holbert car now, so thats near 75,000 shifts, all at WOT, all with 5000rpm engine blips for downshifts. no mecy shifting!!! in the wear of the holbert car, i wouldnt even consider my spririted street driving a factor. maybe a rounding error at best! Ive put 25,000miles on the holbert car now to date.
I think if you are using the 928 for street, there are no worries for using 500 to 600ft-lbs of engine torque, especially if you are not using 1st gear and drag slicks.
mk
does this mean if you are doing 30-80mph, its like doing it 18,432 times?
i think the main thing we dont think about, and sometimes speed tv references this in their TV reporting of races, is that in our races, we shift 15 times per lap, so x 20 laps of a race at Infinion (a 2.3mile track) 200-300 times a session. thats 600 to 1000 shifts a weekend. i got about 75 race days on the Holbert car now, so thats near 75,000 shifts, all at WOT, all with 5000rpm engine blips for downshifts. no mecy shifting!!! in the wear of the holbert car, i wouldnt even consider my spririted street driving a factor. maybe a rounding error at best! Ive put 25,000miles on the holbert car now to date.
I think if you are using the 928 for street, there are no worries for using 500 to 600ft-lbs of engine torque, especially if you are not using 1st gear and drag slicks.
mk
Originally Posted by mark anderson
Maybe the real question is at "how long will it last and a certain torque level." If you look at a track like Road America you are at WOT for 80% of the time. A typical weekend has about 2 hours of track time so you get about 96 minutes WOT with little or no wheel spin to lessen the load. I can't imagine how long it would take to get that amount of WOT on the street. That's like doing 0-100 9,216 times.
#20
Guys, you are talking in terms of torque here...it is torque that limits the capacity of the parts from a stress standpoint. F=ma and T=Fd. The HP is simply the product of torque and speed. You could have 500 HP at 6000 RPM and a different engine with 500 HP at 3000 RPM. The 3000 RPM engine would be making 2X the torque of the 6000 RPM engine...same HP. In this case the 3000 RPM engine would require more robust driveline. 400 ft-lbs running a race is a lot different than a weekend warrior 30 seconds of manifold pressure wet dream boost run. The way you use it does matter and plays a huge role in the life of the parts... The higher torque for extended periods of time will fatigue parts faster...add heat and you can be looking as scrap metal in short order.
With that said I have placed over 475 ft-lbs through a stock 1981 driveline in "weekend mode" (minus dream time thank you) without any issues.
Now, who wants to talk about high temperature strength of a cast piston?
With that said I have placed over 475 ft-lbs through a stock 1981 driveline in "weekend mode" (minus dream time thank you) without any issues.
Now, who wants to talk about high temperature strength of a cast piston?
#21
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Originally Posted by mark kibort
exactly!
...i got about 75 race days on the Holbert car now, so thats near 75,000 shifts, all at WOT, all with 5000rpm engine blips for downshifts. no mecy shifting!!! in the wear of the holbert car, i wouldnt even consider my spririted street driving a factor. maybe a rounding error at best! Ive put 25,000miles on the holbert car now to date.... mk
...i got about 75 race days on the Holbert car now, so thats near 75,000 shifts, all at WOT, all with 5000rpm engine blips for downshifts. no mecy shifting!!! in the wear of the holbert car, i wouldnt even consider my spririted street driving a factor. maybe a rounding error at best! Ive put 25,000miles on the holbert car now to date.... mk
Harvey
#22
Banned
Originally Posted by mark anderson
Maybe the real question is at "how long will it last and a certain torque level." If you look at a track like Road America you are at WOT for 80% of the time. A typical weekend has about 2 hours of track time so you get about 96 minutes WOT with little or no wheel spin to lessen the load. I can't imagine how long it would take to get that amount of WOT on the street. That's like doing 0-100 9,216 times.
#23
The Parts Whisperer
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Originally Posted by animal8526
but doesnt overcoming inertia actually cause more strain on DT parts than sustaining speed? I mean, I imagine those types of sustained speed are really tough on the engine itself, but not so much on the DT.
#25
I deliberately sidestepped the issue of piston/con-rod integrity as those are solveable with $$.
Certainly it is torque that breaks things and I only mention horsepower as that is what most tend to speak in terms of.
Obviously, the drivetrain could withstand 5,000 horsepower - as long as you never use it and the question of a street car, not race car - meaning more weight, lower gears action and, in a world,
drag racing - ie hammering it.
I'd rather have a 400 hp car that I can do nearly anything I want - and immediately - rather than a 500 horsepower car (or more torque car), for which I have to ginger the accelerator and slide the clutch so not to bust it.
What I am reading seems to confirm my inclination that the 928 motor has far more horsepower potential even in stock long block form than the drivetrain can withstand if that power is fully used. But this also raises issues, then, I never faced in other car I had. For those, the issue was making horsepower. For this 928 project, the question is deciding how not to make too much horsepower (meaning torque).
Long ago I learned that a street car that is short endurance or overbuilt to the point of breaking itself is not the route to go.
There are also concerning comments that support limiting horsepower. For example, "as long as you do not have drag slicks on it" and of being careful with the accelerator. The response is "damn, I was hoping to take it down to the run-what-you-brung 1/8th mile track just for the fun of it in the only non-USA V8."
Oh well...
Mark O
Certainly it is torque that breaks things and I only mention horsepower as that is what most tend to speak in terms of.
Obviously, the drivetrain could withstand 5,000 horsepower - as long as you never use it and the question of a street car, not race car - meaning more weight, lower gears action and, in a world,
drag racing - ie hammering it.
I'd rather have a 400 hp car that I can do nearly anything I want - and immediately - rather than a 500 horsepower car (or more torque car), for which I have to ginger the accelerator and slide the clutch so not to bust it.
What I am reading seems to confirm my inclination that the 928 motor has far more horsepower potential even in stock long block form than the drivetrain can withstand if that power is fully used. But this also raises issues, then, I never faced in other car I had. For those, the issue was making horsepower. For this 928 project, the question is deciding how not to make too much horsepower (meaning torque).
Long ago I learned that a street car that is short endurance or overbuilt to the point of breaking itself is not the route to go.
There are also concerning comments that support limiting horsepower. For example, "as long as you do not have drag slicks on it" and of being careful with the accelerator. The response is "damn, I was hoping to take it down to the run-what-you-brung 1/8th mile track just for the fun of it in the only non-USA V8."
Oh well...
Mark O
#26
On the otherhand, transmissions and torque tubes aren't THAT expensive on the used market, so I suppose there is only one real way to tell how much the drivetrain can take on launching... $300 to $1200 experiments. I better start rounding up more spares...
Mark O
Mark O
#28
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Originally Posted by DFWX
On the otherhand, transmissions and torque tubes aren't THAT expensive on the used market, so I suppose there is only one real way to tell how much the drivetrain can take on launching... $300 to $1200 experiments. I better start rounding up more spares...
Mark O
Mark O
#29
I broke my TT... and Im running the original 320hp
On the other hand.. Im not sure yet why it broke.. It seemed like someone had been there before trying to weld it together.. but im not sure. It was kind of hard to tell just by looking at the broken ends of the TT.
On the other hand.. Im not sure yet why it broke.. It seemed like someone had been there before trying to weld it together.. but im not sure. It was kind of hard to tell just by looking at the broken ends of the TT.