notthd

Hello All, Its been a while since I have been on line and had a strange question. I have a racing 915 transmission in the shop with a taller 1st and 2nd and all new syncros and was contipating putting it in my 85 euro 930. I wanted to install a light weight flywheel and was looking at this transmission thinking it would be a monster on the street. I unserstand my 4spd is and has been a blast on the track but my car sees more stop lights than finish lines. Has anyone out there put a lightweight flywheel on a mid to late model 930 or have any experience with 4-5spd conversions? My 4spd has always been cluncky going into 3rd even though the car only has 35K miles on it. Thoughts?

Thanks you in advance. Mike

srf506

I'm not sure the LW flywheel is the way to go. I think the engine might have trouble at idle (unless of course you let it idle at 1200 RPM or so). I think it needs the mass, especially in a street application. If it was a pure competition car I might have a different opinion. As to the 915 it'd probably hold up under "normal" street use, just not as long as the 930. But, I'd be real concerned about running anything over about 350 HP through it in any kind of track usage unless you're willing to pull it and rebuild a couple times a season. I just don't think its sturdy enough to handle the torque for the long-term.

I'm also not a great believer in the "conversions." Like everything I'm sure its a function of who designed the kit and who's installing it. I might look for a '89 or later model 5-speed and use that box instead.

spuggy

1st is great for pottering about in town. You don't need a taller 1st, because you have to get out of it as quickly as possible - and you really don't want to get into boost in 1st - you'll understand in about 1/5 of a second when you drive it, but a taller 2nd and 5th is good in a 915.

You will need to change your driving style - 2nd is the weakest gear. It's not HP that the 915 can't take, it's torque - especially at low RPMs. If you launch gently, roll the throttle on in 2nd and then go for it from 3000 RPM, it'll feel like you picked up 100 BHP (apparently - I've never driven a stock 930). But it'll be really buzzy on the freeway without a taller 5th.

Use the latest 915 you can (they get stronger as they get later), and I would suggest don't bother if it doesn't have a spray bar kit, a stiff side cover and a WEVO bearing retainer. If I was doing it again, I'd have used the WEVO exchange diff and intermediate cases for extra insurance.

Don't use an early 915. The mag cased one in my car was in a pretty bad way after 25,000 miles living with mild 930 power (blued 5th gearset, spun bearings). Mind, it'd done 250,000 miles total (including a number of miles in front of a blown 3.0 motor) - and been gone through once or twice before...

A 915 Sachs power clutch will hold a mild (310 crank HP) 930 just fine. More than that you'll need more pressure plate. See if you can guess how I know this....

notthd

Thanks for the replys- Ross motorsports built this transmission orginaly and beefed it up for track or heavy street use. It was in a 265hp 911 with a lightweight flywheel and I remember that car launching like a rocket. It reved quickly and spooled up quickly. I was trying to combine the strong points of both cars.

My 930 is running stock boost with SSI headers and SS exhuast and takes a few seconds to spool. I thought if I lightened the rotating mass it will rev quicker and spool faster combining the great launch with a boost push at the top of the gears. I do know they installed stronger gears and syncros for a 3K total. I just do not remember exactly what is in the trans or have the assembly knowledge to identify upgrades it may have. I do know it is not a mag case. I also wonder if the lightened flywheel will help ease the torque shock between 1st and 2nd because the mass will decellerate quickly also...? Thoughts

Are there any fit up issues or differences that will prevent a direct bolt in?

spuggy

Sounds to me like you'll love it. The 915 gearing - especially in a lighter tub - reduces turbo lag (apparently) and makes a stock or mild 930 feel insanely fast.

I wouldn't worry about the lightened flywheel bringing benefits; the 930 is a torque monster. Heat capacity would be a bigger concern.

You'll be (or should be, if you want the box to live) slower 0-60ft, but from everywhere else you'll have a silly grin on your face.

PO tracked my car, the 5th gearset bluing we think was from oil starvation from slosh under prolonged boost... You should be fine for the street. Or fit an internal spray bar setup like the factory did for racing. An LSD with a high lockup on decel is very nice for keeping the tail feeling planted...

You may want to check you have the correct stub axles in the 915 to mate with your existing axles/CVs ahead of time... The flywheel and clutch just bolt up, my understanding.

I used to have horrific tranny flex when lifting off if driving hard in the lower gears; fitted WEVO semi-solids on the tranny (and Sport engine mounts), which hugely improved that at the cost of slightly more transmission noise in the cabin.

I think the 930 mounts a hair further back in the tub with the 930 or G50 boxes? I don't know if that translates to anything you need to do there.

In a 911 with a 915, the 930 just mounts where the 911 motor would, obviously...

notthd

Thanks for all the knowledge- I'll keep you posted on the final fit up if we swap them out. I am planning getting a Gtech base line on the original peformance for compairison. I will post the results.

Thanks again- Mike