top end swap ?'s

[6r8ph1X]

mine blows a fart but it's farting even worse than before lol

did some tinkering last night but to my demise, it's running worse than before lol. My baby is either pissed at me or is trying to tell me something.

[3X00-Modified]

Update your thread?

I'm thinking some of it has to be from the PCV system missing.

[Money pit Beretta]

My 90GT took off the line like a V8. Thats what makes me think the FDR was better(that and the engine was set up for low end power). Also I had a 83 Z28 and when the lock up happened the RPM would only drop 200rpms after it went into 4th gear. At WOT it would not lock up untill you backed off the gas. At WOT and 90mph the 90GT would go into 4th and it was more than just a 200rpm drop. My 95 only gets off the line half as good or less. 3X00 are you sure your not thinking of the THM125C?

[IsaacHayes]

Jon is right the 3spd has lockup just like 4 speed does.

When I'm in mine on the hwy, you give it gas you feel it unlock (RPMs go up a bit),
more gas, goes to 3rd,
WOT it goes to 2nd.

The FDR may be similar on the two trans, but the 3 speed had higher ratio gears and closer together. The 4 speed has long tall gears that are far apart.

But by changing the FDR on the 4spd, you will essentially make it like it's geared lower. The gears will still be far apart however, but by bringing the RPMs up that will help with low end grunt. Also a higher stall from a W body or whatever will give you more jump off the line as it's like dumping the clutch at a higher RPM... the engine will bog less....


With a higher stall converter, when it locks up you will see the RPMs drop much more.

[Cliff8928]

3t40 is a 3 speed with converter lock up... the 4t60e is a 4-speed with converter lockup.

Also beretta 3t40's vs 4t60e's FDR was like a 2.96 vs 2.92 3t40 being the 2.96... That's not enough to even blow a fart at.

Some of the 3T40 models had a 3.18 ratio as well. Usually in the GTs.

[3X00-Modified]

The THM125C and 3t40 are the same transmission... they only have 3 gears... NO overdrive like the 4t60e.

Also the individual gearing of 1st 2nd and 3rd are different than the 4t60 gears which could have given you the feeling of the older car taking off quicker, but the FDR diff wise is typically the same.

4t60e gears
1: 2.921
2: 1.568
3: 1.000
4: 0.705

3t40 gears
1: 2.84
2: 1.60
3: 1.00

http://www.domesticcrew.com/tony/transpage/125C.htm

Check the specs link

[1988GTU]

I have 3 gears and a TCC lock up. Not OD, not 4 gears, but it is suppose to act like an OD.

Tire size can change gearing too.

[3X00-Modified]

I have 3 gears and a TCC lock up. Not OD, not 4 gears, but it is suppose to act like an OD.

Tire size can change gearing too.

"Technically" it can't be an OD since OD referrs to a higher than 1:1 gear ratio, and really all a TCC lockup does is stops your converter from slipping


Just busting your stones... lol

haha, but yeah it does a similar thing and helps gas mileage since converter slip is limited.

[1988GTU]

I have 3 gears and a TCC lock up. Not OD, not 4 gears, but it is suppose to act like an OD.

Tire size can change gearing too.

"Technically" it can't be an OD since OD referrs to a higher than 1:1 gear ratio, and really all a TCC lockup does is stops your converter from slipping


Just busting your stones... lol

haha, but yeah it does a similar thing and helps gas mileage since converter slip is limited.

lol I forgot about all that. I still hate TCC lockup. Feels terrible and if you use a cheap brand you'll be back in there within a year or two.

[Money pit Beretta]

Check this out, we are way off toipc anyway.http://www.gmtuners.com/gmtransinfo.htm
lots of great info there and if you click on the ID charts you can get alot more info.

[3X00-Modified]

Check this out, we are way off toipc anyway.http://www.gmtuners.com/gmtransinfo.htm
lots of great info there and if you click on the ID charts you can get alot more info.

Yeah sinister perf is an old chart... he doesn't include the 3t40, he only has one trans that's in the Beretta the 4t60e, and I already have a book on that with all the ID's and what cars they were in and what gear ratios they were and what torque converters came with them and so on...

[Money pit Beretta]

I thought you might, but others may not. Well this toipc is done. It will now be locked.

Oops, looks like I can't lock it. Guess you'll have to do it 3X00.

[3X00-Modified]

Can now be locked? You want it locked? I can do that for you.

[Money pit Beretta]

Yea I do, we went off topic and if anybody wants that off topic info they will never think to look here. Is the lock going to be a Mod only thing here?

[3X00-Modified]

Yes topic locking is a mod only function... You think regular users would have that ability... man topics would be out of control.. LOL