SEW QUIK

My modified 1978 930 engine is out, rebuilt, and is getting an EFI conversion at Jerry Woods. While it was out (always dangerous thinking...), I thought about regearing the lower gears in my 930 4 speed box. Cost is about $1000/gear, and is way cheaper than a G50 conversion. I only drive the car on the street, about 40 miles each day roundtrip to work. Any positive or negative input from forum members who have done this, or thought about it, would be greatly appreciated...

shockm

I love my stock gearbox in my '86. I have the 3.4 EFI setup with about 700hp and the gearing seems perfect. I would wait and see how you like it with the added power. Obviously, you'll need a stronger clutch.

DDD

Re-gearing in which direction?

I have a lowered overall ratio. First gear gets to 45, 2nd gets to 75-80ish, 3rd gets to 115-120ish and fourth gets to 150-155ish.

If I had any more power than I do, I would go with a stock 1st gear and 2nd, at least, possibly keep the lowered third and fourth just for the break neck acceleration on the highway.

My first runs out REALLY fast, like straight into the redline and the rev limiter cuts in, and then I have time to shift.

If you are going to have under four hundred horses, it is fine, but over four hundred I would not go lower in 1st and 2nd. 3rd and 4th, you can play with, IMO, however you want.

My acceleration in third and fourth is awesome. And I don't have the roads around here to do over 150 anyway.

JBrown

I have a similiar set up to DDD. I have 400rwhp and I love the shorter gears. I too dont go over 150. The shorter gears really makes the car go. On the highway all I have to do is drop to third and the car is gone. I love it

YYC930

My driver for a while was a 400 + HP 930 with stock gearbox ratios.

The last thing I had time to think about when accelerating thru 1st and 2nd was how to make it go faster !! Try the car first......I think you'll be surprised that you don't need it.

SEW QUIK

Thanks for the feedback. The motor had been built previously by Imagine Auto to 441 hp with CIS. I drove it about a year with that motor and the stock 4 speed, and it seemed to pull strong once it reached 3000 rpm. How much of this was due to the stock taller gears, and how much was due to the relatively old design K27 11/11 turbo, I can't say.

Now it will be EFI tuned and programmed on Jerry Wood's engine dyno, and the plan is to make about 450- 500 reliable flywheel hp. The turbo is changed out for a Garrett ball bearing 30R. The other mods are usual: full B&B, port to 36 mm, SC 330 cams, 3.4 L P&C's, etc.

I was thinking that shorter gears 1-3 would help with street acceleration, but I would like to hear what others have to say. I cannot safely exceed 120-130 mph on our Bay Area roads, and I have been told to keep 4th gear stock for highway cruising and mileage....

911rudy

The trouble with lower first is, as mentioned above, that it winds up so fast that its hard to keep it under the red line. I think we all wish for better low end acceleration but it is sort of tricky to pull it off without ending up with a twitchy beast. I built an AC Cobra replica a few years ago and learned the relationship between the tranny and the rear end. You might be better off going with a higher ratio rearend than a gear change. Try to find someone with a combo that you can test drive or ask this forum what gear or rear end ratios they have and how it performs. I ended up with a close ratio tranny and a lower ratio rear end in the Cobra. It worked great but the highway rpm at 70 mph was a little high. 1st gear went to 60 at red line so it was a perfect street car. The original Cobras had both close ratio trannies and high ratio rear ends for a mind blowing acceleration but no highway manners. Keep us informed because it is of interest to all of us.
Rudy

RarlyL8

The proper combination of tuning, cams, headers and turbo can eleminate lag. Once that is done and you see huge torque by 2000 rpm your gearing should become more in line with your expectations.

Gino

I've shorten 2nd, 3rd and 4th with 383 RWHP and 374 TQ, and it's a real sweet ride now. Other 'better breathing mods' help like headers, K27-7200, free flow exhaust and such help too. I do not track the beast so I couldn't tell you what 'gear set setup' would be best for what track.

All I can tell you is that it won't do over 148 mph, besides where can you even do that on the street. Around town I can actual use 3rd gear, and on the highway in 4th passing/chasing is no sweat as I'm already in the turbo zone churning 3500 rpms at around 72-75 mph.

$1000/gearset seems high. I'll double check my receipts (and provide the actual tooth counts if you'd like), but I'd swear the gears where more in the order of $650/each.

DDD

I honestly think you have the wrong idea going with a shorter first gear with 500 hp. If I were in that position, I would want to do the opposite and make sure I could reach 60 in first gear. That will be your quickest 0-60 time; not having to shift at 44 mph after your first gear flashes through the redline in the blink of an eye and hits the rev limiter.

Shorter gears are going to give you wheelspin with that hp.

I don't think you will achieve a better 0-60 time with a shorter gear.

DDD

Let me dig my hole deeper and suggest that I also think you should consider limiting fourth gear to about 165-170 or so, to get wicked top end.

IMHO, you are thinking backwards about the whole gearing thing.

Keep a stock first and second, and maybe lower third a little, and fourth back to about 165, and you'll have a FAST car with 500 hp.

The difference in gas mileage is not going to be much, and the rpms will not be bad on the highway, they will put you right in the sweet spot of your turbo, which is what you are trying to achieve in the first place.

I have talked to people like Pat Williams, who limits all his builds to 170 mph in fourth, because it is fast enough for most people and it makes fourth gear a monster gear, instead of getting an extra mile per gallon.

Why have a short as heck 1, 2, and then 3, but have a long drop off to fourth gear on the highway just when you want to keep up with a Corvette or Cobra Mustang? Step on the gas and wait.......

Anyway, that is my two cents worth.

Aspemo

I have just got back with my car. It has a rebuild gearbox and the 3rd and 4th gears are lowerd 15%. So top speed with 305/30 x 18 is around 175 Mph.

And a new LSD from Kaaz. The CIS system is at it's maximum and has an extra 7th injector a 1000cc/min. Broadband lambda shows around 10,5-11,5 at 1.2 Bar pressure.
Exhaust temp around 900-950 C.

The car is tremendous in acceleration and feels more powerful in 3rd and 4th gears than before the regearing.

125shifter

I'm still in the process of tuning my engine after a rebuild and EFI conversion, but even with the improvement in lag, the gear spacing is too large. I'm planning to lower 2nd, 3rd, and 4th so it tops out around 180mph with 315/35-17 tires instead of the theoretical 200 mph with stock gearing.

PimPim

To DDD...

I must ask you what 0-60 time do you have on your car???And how much Hp did you have.

Thnx

//PimPim

www.garaget.org/pimpim

E-Man

Reviving an old thread to hopefully learn from others that have regeared a 930 4 speed gear box.

The objective is to achieve closer ratios while maintaining the same transmission but swapping gears. I will give up 4th gear, and therefore 3rd gear will be the final ratio. I would like to replace gears 1,2, and 4. these three new gears will all be lower than the original 3rd gear, but also closer and therefore I can spend more time in boost. So top speed will suffer but I will have four gears that are closer to each other than the OEM box now. Has anyone done this and if so what new gear ratios did you use?