Dyno results are IN! Too much torque for 901?
11-12-2004, 01:34 AM
#16
RL Technical Advisor
Originally Posted by L8 Apex
I don't launch the car from stoplights, but, it sure is fun to put down some power in first or second after rolling. Is this too harsh? Or does it require dropping the clutch from a standing start to do the damage...
The reason it needs rebuilt at all is because second gear is essentially nonexistant. All of the other gears seem solid, including first. I've read that second gear is part of the mainshaft so the entire component has to be replaced, but some of the receipts I have indicate that the 2nd gear dog teeth were replaced about 10k miles ago. Are the dog teeth the same as the gear itself? The receipts also show 5 synchro rings, 2 op sleeves, and a speedo gear drive. This was done at 102,398 on the odo. At 103,875, the first gear op sleeve was replaced. The car is now at 113,500 and second is out again.
If the 911 tranny is no good for this application (assuming I'm not very disciplined / gentle), and the '74 915 w/ mag case is no good with the stock ratios... then I'm thinking my only / best option is to buy a 915 and have it totally regeared? It does have the 7:31 final drive... how much do gear sets run for the 915?
BTW, I'm running 205/55's.
Steve - tried to call you around 4:00 Pacific but no answer. I'll try back tomorrow.
Thanks,
Jason
The reason it needs rebuilt at all is because second gear is essentially nonexistant. All of the other gears seem solid, including first. I've read that second gear is part of the mainshaft so the entire component has to be replaced, but some of the receipts I have indicate that the 2nd gear dog teeth were replaced about 10k miles ago. Are the dog teeth the same as the gear itself? The receipts also show 5 synchro rings, 2 op sleeves, and a speedo gear drive. This was done at 102,398 on the odo. At 103,875, the first gear op sleeve was replaced. The car is now at 113,500 and second is out again.
If the 911 tranny is no good for this application (assuming I'm not very disciplined / gentle), and the '74 915 w/ mag case is no good with the stock ratios... then I'm thinking my only / best option is to buy a 915 and have it totally regeared? It does have the 7:31 final drive... how much do gear sets run for the 915?
BTW, I'm running 205/55's.
Steve - tried to call you around 4:00 Pacific but no answer. I'll try back tomorrow.
Thanks,
Jason
One should abstain from stomping on the throttle in 1st gear with a 901,.......2nd gear is OK,....
The 915 is far more tolerant of that sort of thing.Never,.......ever, drop the clutch on these cars unless your bank account is well stocked and you won't miss it.
Indeed, 2nd gear is part of the mainshaft (unless you have a 904 mainshaft) and is replaced when you break that gear. The dog teeth are the engagement teeth on the gear that grab the operating sleeves. With bad dog teeth, you'll not be able to shift the tranny without really yanking on the shifter (not a good idea).
The '74 915 is a good tranny for your application and you'd need to regear ANY tranny for best performance in any case.
My apologies for missing your phone call. If you got the voice mail, I was on another line as my phone traffic is somewhat heavy.
If you leave me a message, I ALWAYS call people back,...
11-12-2004, 01:49 AM
#17
L8 - if you ask Steve the above questions over the phone, can you post his reply here?
It also may be that your question just can't be answered as specifics differ from case to case.
I kept my 915 - if I break the 911 trans. it will be a bad thing, but I can still convert back to the original 915... with some degree of $$ expenditure and hassle.
It also may be that your question just can't be answered as specifics differ from case to case.
I kept my 915 - if I break the 911 trans. it will be a bad thing, but I can still convert back to the original 915... with some degree of $$ expenditure and hassle.
11-16-2004, 01:15 AM
#18
RL Technical Advisor
Originally Posted by randywebb
L8 - if you ask Steve the above questions over the phone, can you post his reply here?
It also may be that your question just can't be answered as specifics differ from case to case.
It also may be that your question just can't be answered as specifics differ from case to case.
Jason and I spoke of the well known shortcomings of 901's and the cost to make it as rugged as possible. We factored that against the durability of the 915 in these applications.
Given that a rebuild is necessary and that a re-gear is desired, we talked about gearing on his car with the 15" tires in use. Jason mentioned the use of 16" wheels/tires and I pointed out how that adversely affects ride height on narrow-bodied cars due to fender clearance with those 26" diameter tires.
My suggestion was to aquire a 915 with the 8:31 R&P for its ruggedness and favorable gearing potential with Jason's 205/55-15 tires. This makes 1st gear much more useful (compared to a 7:31) and changing 2nd through 5th was going to happen in any case.
Factoring the engine's RPM range and Jason's rear tires diameters, I'll come up with an appropriate gearstack that will really make his car "sing" without ruining its roadability. An LSD will be a plus, too.
Gears make such a HUGE differerence.
11-18-2004, 10:03 PM
#20
Advanced
Thread Starter
Guys,
Randy, sorry I didn't reply to inform you of the phone conv, been out of town and spending free time shopping for trannies. Thanks to Steve for the update post.
I found a '75 tranny that has the 8:31 final drive and the mechanical speedo drive. Steve, if I go with this tranny but don't change the gearing, will that be a problem? I had no idea that gearsets were ~$500 a pop, and I don't want to spend $2k on gears right now. I was thinking they were around $150 a set. You mentioned above that the 8:31 will help w/ first gear, and since all the other gears were being changed then it wouldn't matter. I'm assuming the rest of the gearing will be as on a stock '75 if I keep my lower pro tires, will I be happy with the gearing? How does it compare to the stock 911??
Here are the '70 ratios:
11:34 A
18:32 GA
23:28 O
27:25 V
29:22 ZA
This is with the 7:31 final drive.
One last thing - third gear in this car is WONDERFUL, I'd like to keep it close to where it is. Does anyone have the ratios of the '75 915?
Randy, sorry I didn't reply to inform you of the phone conv, been out of town and spending free time shopping for trannies. Thanks to Steve for the update post.
I found a '75 tranny that has the 8:31 final drive and the mechanical speedo drive. Steve, if I go with this tranny but don't change the gearing, will that be a problem? I had no idea that gearsets were ~$500 a pop, and I don't want to spend $2k on gears right now. I was thinking they were around $150 a set. You mentioned above that the 8:31 will help w/ first gear, and since all the other gears were being changed then it wouldn't matter. I'm assuming the rest of the gearing will be as on a stock '75 if I keep my lower pro tires, will I be happy with the gearing? How does it compare to the stock 911??
Here are the '70 ratios:
11:34 A
18:32 GA
23:28 O
27:25 V
29:22 ZA
This is with the 7:31 final drive.
One last thing - third gear in this car is WONDERFUL, I'd like to keep it close to where it is. Does anyone have the ratios of the '75 915?
11-18-2004, 11:38 PM
#21
RL Technical Advisor
Originally Posted by L8 Apex
Guys,
Randy, sorry I didn't reply to inform you of the phone conv, been out of town and spending free time shopping for trannies. Thanks to Steve for the update post.
I found a '75 tranny that has the 8:31 final drive and the mechanical speedo drive. Steve, if I go with this tranny but don't change the gearing, will that be a problem? I had no idea that gearsets were ~$500 a pop, and I don't want to spend $2k on gears right now. I was thinking they were around $150 a set. You mentioned above that the 8:31 will help w/ first gear, and since all the other gears were being changed then it wouldn't matter. I'm assuming the rest of the gearing will be as on a stock '75 if I keep my lower pro tires, will I be happy with the gearing? How does it compare to the stock 911??
Here are the '70 ratios:
11:34 A
18:32 GA
23:28 O
27:25 V
29:22 ZA
This is with the 7:31 final drive.
One last thing - third gear in this car is WONDERFUL, I'd like to keep it close to where it is. Does anyone have the ratios of the '75 915?
Randy, sorry I didn't reply to inform you of the phone conv, been out of town and spending free time shopping for trannies. Thanks to Steve for the update post.
I found a '75 tranny that has the 8:31 final drive and the mechanical speedo drive. Steve, if I go with this tranny but don't change the gearing, will that be a problem? I had no idea that gearsets were ~$500 a pop, and I don't want to spend $2k on gears right now. I was thinking they were around $150 a set. You mentioned above that the 8:31 will help w/ first gear, and since all the other gears were being changed then it wouldn't matter. I'm assuming the rest of the gearing will be as on a stock '75 if I keep my lower pro tires, will I be happy with the gearing? How does it compare to the stock 911??
Here are the '70 ratios:
11:34 A
18:32 GA
23:28 O
27:25 V
29:22 ZA
This is with the 7:31 final drive.
One last thing - third gear in this car is WONDERFUL, I'd like to keep it close to where it is. Does anyone have the ratios of the '75 915?
First, I would tell you that you cannot even buy non-standard (racing) ratios for the 901 for $ 150 so any regearing exercises do require a realistic budget,...
Still, close-ratio gears are the biggest improvement you can make to acceleration and FAR better than the vast majority of engine modifications.Listed below are the ratios in the '75 915. You should do the math factoring your rear tire diameters and bear in mind the 3.875 final drive here instead of the 4.43:1 that your 901 has.
1st 11:35
2nd 18:33
3rd 23:29
4th 26:26
5th 28:23
If you want an 8:31 equipped 915 to perform properly, you'll need to lower 2nd through 5th gears. The result will give you a REAL neat gearstack that will make a very big difference,...
11-19-2004, 08:06 AM
#22
"For all you gearheads"
Dude - let me enlighten you. Anyone who owns a 1970 Porsche 911 wth fuel injection that spits fuel out the manifolds when you drop the pedal and has a transmsson that people try to start out in second gear - is a gearhead.
YOU are a gearhead. Not that there is anything wrong with that.
Dude - let me enlighten you. Anyone who owns a 1970 Porsche 911 wth fuel injection that spits fuel out the manifolds when you drop the pedal and has a transmsson that people try to start out in second gear - is a gearhead.
YOU are a gearhead. Not that there is anything wrong with that.
11-19-2004, 10:39 AM
#23
Advanced
Thread Starter
Sorry!! Didn't mean to offend anyone, should have said "FELLOW GEARHEADS!!" I would never think of excluding myself from such unique and diverse group. I consider the term "gearhead" to be a COMPLIMENT, not an insult!!! 
