ScaryFast

Is there any problem running a 4+3 tranny (L98 C4) on a RR track? Do you ever need to use the OD gears on long straights, or is 4th gear tall enough to handle it?

I'm running a ZF6 but just looked at an older 4+3 car.

JaxVette

I ran my '84 with the 4+3 for 5 years or more on nothing but roadrace tracks. It was putting out 350HP and the tranny stood up well. Finally lost 3rd gear after a 100K miles. Replaced with another 4 speed tranny and kept going.

For all the tracks I ran on with the exception of Pocono Raceway, having to utilize the overdrive was never a necessity. But, the few times I tried it at the end of the back straight at VIR, the car would kind of lug, rather than pull when going from 4th to the overdrive. It was better to just leave it in 4th and run to the brake zone.

But, for just going out running hard and having fun, it was good. Certainly not as nice as the tranny in my Z06, but more than adequate for the tracks on the east coast.

WNDOPDLR

My 88 track car had the 4+3. I had lots of other things to sort out, but the 4+3 never gave me any problems. Gearing on top end was OK after I got rid of the stock manifold and went with the miniram. I eventually switched to a ZF, but still have the 4+3 as a back up. I would not hesitate to use it again. You will probably want to put a lock out switch on the OD.

AUTO_X_AL

Our 4+3 has worked pretty well. We're in the process of hooking up a toggle switch for the OD. We've never used the OD on a RR course yet but with a 3.54 the straight at Grattan requires a little more top end. It's been a champ at all the Michigan courses and has held up well. You just need to make sure and take care of them. Paul @ Liberty Gears hooked us up with some stronger shift cams and a few other parts to freshen it up. Based on what he told us we were better running the 4+3 rather than converting to a ZF6 based on expense and availability of parts.

AUTO_X_AL

With a 3.07 I don't think the OD would be needed at Grattan. With a 3.07 you can run Gingerman almost the whole way in 3rd.

c4cruiser

There was some discussion a few years ago regarding the 4+3 for HPDE/track days. The consensus was it will be fine as long as you don't engage the OD unit.

As I recall, the OD unit doesn't really like constant shifting in and out whre there is lots of power being applied. If the OD is used, it should be used in conjunction with the clutch pedal just like you would be shifting the 4-speed portion.

Change the OD fluid before each event and use a new filter even if you don't intend to use the OD. Heat will be an enemy of the OD unit if it's used so it might be worth thinking about a small tranny cooler for the ATF. The stock "cooler" is just a line running thru the right side radiator tank, just like an auto tranny.

My 87 can hit 128 or so without the OD unit engaged. That's about 5300 rpm in 4th with 275/40-17 tires. That's more of a limit on the ability of the engine to breathe with the stock intake. Takes awhile to get to that speed even with an older ZZ3 cam and port-matching in the runners and plenum but a stock exhaust system.

mrc24x

128mph w/ 3.07's in 4th topped out. In 2006 I had 250rwhp so it wasn't that big of a problem but if you have much more than that you will be riding redline for a ways down the long straights.

Kanmer

The 4 speed side of the tranny is almost bullet proof. Its +3 side that is very frail. Stay out of OD and the thing will be ok.

Bob

ScaryFast

Thanks, guys. So a ZF6 swap would be nice in the future, but it's servicable as is for now...

69autoXr

Fourth gear in both trannies is 1:1, so it will be no different than the ZF.

Bill Dearborn

Depends on where you are going to drive it. I had an 86 w 4+3 that I used to run at Watkins Glen. There was another fellow with a 90 ZF that used to attend the same events I went to. I could hang on his bumper through most of the course but he would just pull away when he hit 5th coming out the esses onto the back straight. I know the engine will rev to 5600 rpm before the limiter cuts in but if you are running a stock intake the power level falls off so quickly after 4500 rpm you need to get into a higher gear so you can get back into the engine's power band.

Bill

AUTO_X_AL

That's why you can rig the OD to use as a 5th gear. A Z51 OD was .67. Good for a few extra mph.

0Randy@DRM

We had a joke for the overdrives but when we ran them in the 24 hour. They would last for exactally 23.5 hours. There was a lot of heat problems also going on.

Randy