Discussion
My son and I built an Ultima GTR with a dry-sump'ed 539 (dyno'ed) 383 followed by a Getrag 6-speed transaxle.
As I read some of the recent posts regarding the greater-horsepower (600-700 HP)engines, it seems logical to ask the question as to the weakest-link in the system. In this case it may be the transaxle.
If this question has been asked before I apologize, but on the other hand, if you are talking about horespower you should also be talking about the concepts of longevity and durability of the entire drive-train. Some high-performance rececars are designed for balls-out performance for only one or two races. Obviously, at greater than $10,000 a pop it doesn't seem realistic to destroy your transaxle too often for a street vehicle. Will the transaxles suport this much power and provide longevity at the same time?
I'm just interested in some opinions regarding the weakest link in the system.
Thanks for your feedback!
David
David,
this is a popular topic, and you'll find plenty of posts with varying amounts of informative matter spread thru them...
Torque is the problem, not the HP, the SBC is a relativly low reving engine designed for heavy cars/light trucks, and as such it produces a lot of bottom end torque.
Compare that to most flat six Porsche engines, which are basically buzz boxes, and like to rev, but don't have much torque, compared to the SBC at least.
Hence the G50 series, including the G50/6 speed I have in mine were only designed to take about 1/2 the torque that the average 383 SBC puts out...
Out right failure of the transaxle is unlikely, as the Ultima is light, and therefore it is difficult to get all the power to the ground, with sticky tyres on a seasoned 1/4 mile track... well, everything has a fatigue limit, most likely your gearbox, which probably has some degree of wear already, will just wear out faster.
You can of course, modify the transaxle, mount oil coolers, pressure lube sprays on the main ring gear, hardened gears etc etc etc.
Ultimately it comes down to duty cycle, i.e. how often you press the loud pedal all the way down...
However, and as something I am considering in the nearish future, is that you can use a 996 GT2 Turbo gearbox. These already have an oil cooler, and the Turbo flat 6 motor develops about 450hp/~500lb, and you can get one state side, from PHII. I have spoken to some UK suppliers for this transaxle, and they have seen Porsches with ~650 bhp, and the boxes are fine.
IMHO, you're better off following GMans example, and getting your engine to rev higher, if you want to preserve your transaxle...
Cheers,
Peter
this is a popular topic, and you'll find plenty of posts with varying amounts of informative matter spread thru them...
Torque is the problem, not the HP, the SBC is a relativly low reving engine designed for heavy cars/light trucks, and as such it produces a lot of bottom end torque.
Compare that to most flat six Porsche engines, which are basically buzz boxes, and like to rev, but don't have much torque, compared to the SBC at least.
Hence the G50 series, including the G50/6 speed I have in mine were only designed to take about 1/2 the torque that the average 383 SBC puts out...
Out right failure of the transaxle is unlikely, as the Ultima is light, and therefore it is difficult to get all the power to the ground, with sticky tyres on a seasoned 1/4 mile track... well, everything has a fatigue limit, most likely your gearbox, which probably has some degree of wear already, will just wear out faster.
You can of course, modify the transaxle, mount oil coolers, pressure lube sprays on the main ring gear, hardened gears etc etc etc.
Ultimately it comes down to duty cycle, i.e. how often you press the loud pedal all the way down...
However, and as something I am considering in the nearish future, is that you can use a 996 GT2 Turbo gearbox. These already have an oil cooler, and the Turbo flat 6 motor develops about 450hp/~500lb, and you can get one state side, from PHII. I have spoken to some UK suppliers for this transaxle, and they have seen Porsches with ~650 bhp, and the boxes are fine.
IMHO, you're better off following GMans example, and getting your engine to rev higher, if you want to preserve your transaxle...
Cheers,
Peter
I've only broken a stub shaft in the rear upright.
No transaxle trouble in around 22,000 miles and 50-60 drag strip passes.
Of course I'm using the G50/52 by PH2.
Jeff S
www.schwartzperformance.com
No transaxle trouble in around 22,000 miles and 50-60 drag strip passes.
Of course I'm using the G50/52 by PH2.
Jeff S
www.schwartzperformance.com
www.mendeolatransaxles.com trans is comming out with a V8 Specific trans soon. It is the solution IMHO. Also here is link for talk about the issue.
www.ffcobra.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/35/t/000202.html?
>> Edited by stig on Thursday 29th September 13:13
www.ffcobra.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/35/t/000202.html?
>> Edited by stig on Thursday 29th September 13:13
Hey Karlo,
now I'm not knocking the engineering reasons for that underbody aero kit, but I do think it makes the GTM look like it backed into a low wall - all IMHO of course!
As for the G50, the only time I've heard of any failures, is from a Porsche racer back home who chews thru at least one gearset a season - then again with a 750bhp Turbo flat 6, that's not all he'll be chewing thru.
IMHO, with the typical use an Ultima see's, the G50's are ideal (cost vs performance) for 'most' peoples needs.
now I'm not knocking the engineering reasons for that underbody aero kit, but I do think it makes the GTM look like it backed into a low wall - all IMHO of course!
As for the G50, the only time I've heard of any failures, is from a Porsche racer back home who chews thru at least one gearset a season - then again with a 750bhp Turbo flat 6, that's not all he'll be chewing thru.
IMHO, with the typical use an Ultima see's, the G50's are ideal (cost vs performance) for 'most' peoples needs.
No, Just helping get the word out. I made the switch From GTR to the GTM when I saw the GTM 2 years ago. In less than two years I think there will be more GTMs than GTRs. Provided everyone finishes.
55 kits have been ordered by people.
>> Edited by stig on Thursday 29th September 13:13
55 kits have been ordered by people.
>> Edited by stig on Thursday 29th September 13:13
Additionally: Karlo could you refrain from posting pics at the bottom of each of your replies. Put some in your profile by all means (that's what it's there for 
) but Pistonheads isn't really an advocate of the huge-picture-signature thing. The gassing station is slow enough as it is (popularity has its price)
Cheers
) but Pistonheads isn't really an advocate of the huge-picture-signature thing. The gassing station is slow enough as it is (popularity has its price) Cheers
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