Change to 8:39 R&P, change gears, or wait for G50?
08-13-2005, 01:04 PM
#1
Burning Brakes
Thread Starter
Change to 8:39 R&P, change gears, or wait for G50?
I'm nearing the completion of a major project of rebuilding my 79 930's engine and converting to EFI. I should have about 550 fwhp. My original plan for the tranny was to put in a 8:39 R&P.
After doing some searching here I still can't decide. I've seen mention of the 8:39 being too weak and of 1st gear being too short for high hp cars. Any thoughts on this? I also see that some folks think the gear spacing is too wide, doesn't the high torque of these motors make that not really a problem? If I choose this option I'd have to have someone install the R&P. Cost about $3,000 for parts and labor.
Another option would be to change 2nd thru 4th gears. This would close up the ratios, but I'd like 2nd gear to rev to 75-80mph for the occational autocross. This would make 1st to 2nd closer but 2nd to 3rd and 3rd to 4th spacing would stay the same if I want a reasonable tall 4th gear. If I choose this option, I think I can change the gears myself. Cost about $3,000 parts.
My last option would be to leave the tranny alone and wait a year or so until I can spring for a G50/50 upgrade. If I choose this option, I can do the work myself. Cost would be about $8,000 parts.
After doing some searching here I still can't decide. I've seen mention of the 8:39 being too weak and of 1st gear being too short for high hp cars. Any thoughts on this? I also see that some folks think the gear spacing is too wide, doesn't the high torque of these motors make that not really a problem? If I choose this option I'd have to have someone install the R&P. Cost about $3,000 for parts and labor.
Another option would be to change 2nd thru 4th gears. This would close up the ratios, but I'd like 2nd gear to rev to 75-80mph for the occational autocross. This would make 1st to 2nd closer but 2nd to 3rd and 3rd to 4th spacing would stay the same if I want a reasonable tall 4th gear. If I choose this option, I think I can change the gears myself. Cost about $3,000 parts.
My last option would be to leave the tranny alone and wait a year or so until I can spring for a G50/50 upgrade. If I choose this option, I can do the work myself. Cost would be about $8,000 parts.
Last edited by 125shifter; 08-13-2005 at 02:00 PM.
08-13-2005, 04:47 PM
#2
125Shifter,
Welcome here.
Many will tell you to wait and do the G50/50 upgrade and chage the 2-4th gearing to shorter ratios.
Or
You could shorten the gearing on the 930 4speed box and put in a good LSD. The 930 box is a very strong box and is what they used in the 934. I would contact Paul at Guards Transmission on the parts, he's pretty good and many would agree with me on it.
For me I prefer the 4 speed box as long as your in the power band, you save time changing gears on the straights and I built my car for straight line acceleration. However if I were to track the car more often, I'd go with the G50/50.
Whichever one of the two g/boxes you go with, your good. However I still would contact Paul at Guards Transmission.
Lastly tell us more on your car, what exactly have you done to it? Any photos?
Welcome here.
Many will tell you to wait and do the G50/50 upgrade and chage the 2-4th gearing to shorter ratios.
Or
You could shorten the gearing on the 930 4speed box and put in a good LSD. The 930 box is a very strong box and is what they used in the 934. I would contact Paul at Guards Transmission on the parts, he's pretty good and many would agree with me on it.
For me I prefer the 4 speed box as long as your in the power band, you save time changing gears on the straights and I built my car for straight line acceleration. However if I were to track the car more often, I'd go with the G50/50.
Whichever one of the two g/boxes you go with, your good. However I still would contact Paul at Guards Transmission.
Lastly tell us more on your car, what exactly have you done to it? Any photos?
08-14-2005, 12:58 PM
#3
Burning Brakes
Thread Starter
Here's what I'll have when complete:
98mm JE pistons, 7.7:1 comp. (measured)
Pauter rods
Stock crank
Heads opened to match Carrera intake
stock Carrera throttle body
Exhaust port cleaned up
Performance valve job by EBS
New stock valves
C2 cams
Twin plug
Full bay intercooler (probably 24x10x3.5)
K27HFS
Patrick flywheel
B&B header
Zork tube after turbo
On the gearing, I'm leaning toward changing all four gears. Changing gears will give slightly better gear ratios than a R&P change and I should be able to change them myself.
98mm JE pistons, 7.7:1 comp. (measured)
Pauter rods
Stock crank
Heads opened to match Carrera intake
stock Carrera throttle body
Exhaust port cleaned up
Performance valve job by EBS
New stock valves
C2 cams
Twin plug
Full bay intercooler (probably 24x10x3.5)
K27HFS
Patrick flywheel
B&B header
Zork tube after turbo
On the gearing, I'm leaning toward changing all four gears. Changing gears will give slightly better gear ratios than a R&P change and I should be able to change them myself.
08-14-2005, 07:21 PM
#6
Burning Brakes
Thread Starter
I plan to run 1 bar boost but I'd like to control it with the ECU and maybe run less boost in 1st gear.
I have the engine together and the rear suspension (Elephant Racing bushings and 31mm T bars) and brakes overhauled. The next step is preparing the transmission and trial fitting the engine and tranny so I can design the intercooler. After that I'll put the EFI and ignition system together.
I'm planning to use the Autronic SMC and 500R CDI with wasted spark ignition.
I have the engine together and the rear suspension (Elephant Racing bushings and 31mm T bars) and brakes overhauled. The next step is preparing the transmission and trial fitting the engine and tranny so I can design the intercooler. After that I'll put the EFI and ignition system together.
I'm planning to use the Autronic SMC and 500R CDI with wasted spark ignition.
