Opinion on torque converter replacement

[Steve W.]

Rebuilding my '75 L48 with increased HP to 325. The stock THD350 is also in the shop for rebuild / overhaul. Both previously untouched.

It has been suggested that I replace the stock torque converter with a 'looser' (their words), smaller diameter, one... in order to make better use (driveability) of the added power.

Does that make sense? What does make sense in this case?

[William C.]

Re: Opinion on torque converter replacement

Hard to say, but if you installed a "big" camshaft on the way to the extra hp, a "looser" converter might be the only way to get it off the line. 180 hp to 300+ is a big step, but it can be done many ways, so really hard to say what way to go without complete specs on the engine revisions.

[Steve W.]

Re: Opinion on torque converter replacement

Increased HP comes from flat head pistons for 9:1 C/R, more aggressive cam, 3 angle valve job etc. OK, probably closer to 275-300 HP. Also, exhaust system is now '74-style true dual, vice the 2-into-1-into-2. Hope this helps.
I have also been told that the HP quotes of that era were inaccurate and meant to appease government and insurance interests. Begs the question of whether the 165 or 180 rating was accurate or not. I am not sure.

[Dennis C.]

Opinion on torque converter replacement

I would be curious whether you find you have increased or decreased the driveable horsepower figure.

[Patrick H.]

Re: Opinion on torque converter replacement

I would be curious whether you find you have increased or decreased the driveable horsepower figure.

OK Duke.

I was hoping for a list of the modifications.

Patrick

[William C.]

Re: Opinion on torque converter replacement

Fundamentally, you have altered the camshaft and improved the exhaust. The question is what are the actual specs of the cam you installed? I might note that the L-98 TPI engine is rated at only 240-245hp depending on year. The '75 HP figures were net as were the earlier (post '71 engines). The '75 was the first year for the cat Converter, and the early models were like sticking a cork into the exhaust. I presume you can get by without smog equipment in your area?

[Duke W.]

Re: Opinion on torque converter replacement

I would be curious whether you find you have increased or decreased the driveable horsepower figure.

Dennis - you've become so erudite.

Off the top of my head I can think of at least a half-dozen ways to measure "horsepower", notwithstanding that with a three speed transmission there are three vehicle speeds that maximum HP is actually delivered, and maximum horsepower revs are the opposite end of the spectrum from converter stall speed.

Engines are not one dimensional, and peak horsepower is not actually a very good indication of how an engine will perform in normal road use. What really counts in converter selection (and real world road performance) is torque bandwidth.

to paraphrase an old adage - people buy horsepower, but they drive torque - just ask Dennis!

We can probably give you some guidance if you give us some basic cam specs such as what are published on the "cam card" that accompanies most new camshafts. Were the heads massaged beyond the multiangle valve seat work and flow tested? Also, what is the rear axle ratio?

Duke

[Clem Z.]

Re: Opinion on torque converter replacement

we use 6 cylinder transmission converters to "pep up" the bottom end when GM deballed the V-8 corvette engines. these "looser" converters really made a difference in the pickup from a dead stop with the taller rear end gears. they were much cheaper than the after market which were selling the same converter just painted a different color.