Looking to see what C4 experts would recommend for a torque convertor stall speed/rear gear ratio set up for totally stock TPI, car is an 89. Just looking to make the car a little more fun to drive, may do headers down the road, but that's about it.

 

Gears will do the most especially if it has a 2.59 base gear. G92 3.07 D36 are available used and normally reasonable. If you have a G92 3.07 already. True duals and long tubes would be a better place to start.

 

No need to change your stall speed if the only thing you are changing is the gears and adding headers. The need for higher stall speed in the torque converter is need when the torque curve of the engine is changed to start producing torque at higher rpms. Your TPI engine makes torque starting at very low rpms so the stock torque converter will be just fine. Changing to gearing in the 3:73 range will certainly provide a much stronger feeling car but you are still limited by the TPI’s inability to breathe at higher rpms. Also consider how high the engine will be turning at highway speeds when making the change in gear ratio.

 

3.07 gears will work well. The stock converter in your car is a 1600 stall. The stock converter stall speed in 1985 and 1986 vettes was 2000 to 2200. Pick up one of those converters and it will add some excitement.

 

L98 needs at least 2000rpm stall, pick up something 2000-2200rpm.

3.07 gears is all an A4 L98 needs, the 6-speed already has enough gear in 89.

 

Lingenfelter sold me a converter years ago. OEM GM 2200rpm. Right out of a Chevy S10. Yes, thats what they were putting in their L98 Vettes... OEM...
As far as gears, 3.0 is fine. If you plan on modding later on, staying with TPI, I would get a D44 with oem 3.45 and nothing higher.. TPI is RPM limited, unless you have different intake..

 

I think you will notice a nice "bang" from a 2,000RPM TC; add a TransGo shift kit for even more "fun".

 

2200-2400 with a 3.45.
F-Body cars with a 305 and the G92 package got 3.42s, I am runnign a 3.45 9-Bolt in my IROC. It is as deep as you can go without the TPI running out of breath to soon due to lack of RPM.

 

If you drove my Brothers 88... you would agree on a converter change. Need and Want are different... you would want to enjoy that TC change, but no you don't need to.

 

I had the Australian 9 bolt in my 87 IROC with a 350 TPI. It only had 3.27 gears.
It was actually a fun car to drive. It had allot of room for growth in engine, tires, brakes, suspension etc etc.

 

Generally, a nice stall is the first thing i do to an A4 when modding.... It is the best "bang for the buck" mod you can do. Yank SS 3600 is my weapon of choice in my 4th gen fbods, and my LS2 AWD TBSS....

Not sure about the C4 platform...

 

A L98 has a power range that pretty much dies at 5000 rpm on a cold day.
3.07 gears and a 2000 to 2200 rpm stall is perfect.
3.45 ro 3.73 is too much.
It will be fun, but for short distance stuff.
Its not allot of torque, but nose dives quick.

 

GM literally put 3.42's behind 305TPIs if you ordered the right package. It had performance numbers (with a 5-speed and a hard top) better than the 350/3.23 cars. Yes it had some weight advantage, but the gearing advantage was the main reason and it obviously didn't run out of breath. Couple that with the wider rear tires of the C4 and why would you go through the effort of a gear change and not get the most out of it you can.

Crazy

 

You win.. Better opinion..

 

It's not just opinion and I don't want to say a fact because each car can be a bit different, but it is an opinion formed around data.
So an 89 Vette weighs about 3450lbs with a 200lbs-ish driver.
It has a 245 net hp engine. These numbers would estimate roughly a 14.05 @96MPH in the 1/4. And data/estimates I found by searching Corvett forum through Google has many members that would agree this is a fairly accurate estimate and expectation of a stock C4 TPI. Say we are going to a lower gear, so we will be a bit faster, and just use 100mph as our estimated trap speed. 89 had 275/40/17 Tires or 315/35/17... both 25.7" in Diameter

At 100mph, 25.7" Tire, and a 3.07 gear you are at about 4000 RPM 18% Torque Increase from a 2.59
At 100mph, 25.7" Tire and a 3.45 gear you are at about 4500 RPM 33% Torque Increase from 2.59
At 100mph, 25.7" Tire and a 3.73 gear you are at about 4875 RPM 44% Torque Increase from 2.59

TPI runs out of breath at 4600 and start to fall off, but doesn't stop running. You are good to 5000-5200 RPM. So you have some room for growth. If you are staying otherwise close to stock, it is a great gear. Now, this is if you are racing 1/4 miles only, when mostly we operate our cars generally between 25-85MPH. Why would you want to leave the feeling of adding 15% more torque at any RPM to your engine just because you may run out of breath in a 1/4 mile eventually?

As I mentioned, my L98 has a 3.45 gear and 700R4 behind it but also has a supercharger. It is no way feels out of breath as it approaches 5000 RPMS, but I know it is on the stock intake. The stock heads and cam have a bit more as test with other intakes have shown. I am now changing my runners rather than my gears to get some more RPM. There would also be the option of running a taller side wall or going to larger diameter rims later on if I need more MPH room. However, racing would be a minor use of the car compared to it feeling 15% stronger every time I drive it.

 

I was considering the same improvments when I got my new (to me) C4. The idea was to put as much power (torque) to the wheels as the stock design was capible of. Ultimately, after much parusal of the boards, i decided to go with a 3.55 rear end, and a TransGo Jr shift kit, with an added .470 TV booster valve, and a Durell deep trans pan. I'll aslo be getting a new chip from PCM of NC (which I might suggest to you as well). I think that will give me the C4 that Duntov would have intended.

I'd love to tell you how it all worked out--but its in the shop now getting all that done.

In my imagionation its all worked out great ;-)

Ronn

 

This argument has been settled for many, many years now. I you're talking stock or relatively stock TPI car, 3.07 is the optimal gear.....at least as far as quarter mile performance. If you take a 3.07 car and change to 3.54s or 3.73s it will be slower in the 1/4. The steeper geared car will 60' better, but will be slower on the back end. I have a 91 TPI A4 car that I used to race pretty extensively. I has had all of the common mods over the course of the 20 years I've owned and has had multiple rear ends and gearsets. It has had 2.59s, 3.07s and finally 3.33s. When I first went to the 3.33 I was attempting to find that perfect TPI rear.....steeper than 3.07s but not as steep as say, 3.54s. At the time another forum member, Vic'89 and I used to race together quite frequently in a Corvette Challenge series and we had almost identically mods on our A4 TPI C4s. The only major difference was Vic had 3.07s and I had the 3.33s. My car would consistently 60' better than his car and his car was consistently faster on the back half of the track. He would almost always turn better ETs than me. BTW, Vic was definitely one of the authorities around here on modding TPI cars to wring every last tenth out of them and I'm fairly certain he would agree 100% with me. He likely had 1000s of passes on TPI cars while collecting data on almost every mod imaginable. Obviously when you throw mods like a supercharger it changes the parameters.

 

Cool... as I said why give up the feeling of extra torque for something you hardly ever do?

See above... OP is near stock and said nothing about racing. I literally addressed that point. He said just more fun to drive... I was making the point that if you do take it to the track for some fun its not just going to fall on it's face.

I also remember when TPIS or maybe it was SLP showed the best ETs with a TPI was having it shift at something like 4600RPM. That may be true, but do you know what that feels like on the street when the 700R4 is adjusted to shift that way? We don't drive around race cars, and as I said above, we mostly operate our cars between 25-85mph. If I was building a car intended for the 1/4 as it's primary function, I would make other choices.

Notice, I am not challenging what you say is true about the 1/4, but do notice I said

 

Just wanted to thank everybody for the advice on what I should do as far as a gear swap goes. Seeing as how the car won't be for drag racing and seeing as how I don't want to spend thousands of dollars on outdated intake parts ( if I could even find them ) or computer tuning, I think I will still be going with the 3:07 gear ratio as the differentials are available ( on E Bay ) and decently priced. I think this with a 2400 stall convertor and later on some headers will get me where I want to.

 

Same question with a modded LT1 with 3.07 or 3.45 gears?