New Converter, Different Shift Points?

[1320racer]

Originally Posted by S/ST 3040

My car is a back-halved 67 Barracuda. It weighs 2620 lbs. with me in it. The engine is +.060" 340 w/9.24:1 compression, OEM 596 castings w/1.88" IN valve, roller cam, Victor 340 manifold and Holley 950 carburetor. I run an aluminum drum, 904 transmission w/2.45 1st gear and trans-brake. Dana 60 w/5.57 gear. Either 31.2" or 32.6" tire.


I have been using an 8" ATI converter that hits about 6250 RPM on the brake and it has worked pretty well for the last few years.

Fast forward to this year, I decided to swap to a tighter 8" converter and it hits about 5800 RPM on the brake.

Anyway, here's my question: Is it typical to have to alter your shift points after swapping to a "better" converter?

What's your criteria that has you believing it's "a better converter"?

The one critical bit of information you omitted and frankly the first and foremost bit of information necessary when discussing converters, in the absence of dyno results is... your cam's duration @ .050?

Without it, there is no meaningful discussion or advice.

Lastly, you have an engine combo that maybe makes 500+HP and 400+ ft/lbs. torque at probably around 5000 RPM. A converter that flashes to 5800 is too loose no mind one that flashes to 6250 IF the goal is to "shave some ET." The fall back RPM is what is most important.

[ss3011]

There is a lot more to a torque converter than just stall speed . There is the torque multiplication, coupling point, and efficiency curve . Maximum torque multiplication happens when there is no output rpm, and decreases to 1 to one at the coupling point . Efficiency is zero at zero output rpm and approaches 100 % when output rpm approaches input rpm (engine rpm) . Since the converter works based on input torque, as you change things like the tire size, or the gear ratios ( both in the trans, or rear end ratio) this effects where on these curves your running . This is why you can see improvements in one part of the run , but lose in other points . As for modifying a particular converter , if you want a higher stall speed, a typical modification is to bend the pump fins towards the negative direction . This will raise the stall speed , but will also increase the multiplication, and the down side will reduce the efficiency . So you may see a better 60 foot time, but may lose mph . There are so many things that can be changed to dial in the "perfect" converter, but as we all know, change the weather, and you may need a different converter combination .

[1320racer]

Bottomline is based on the limited info the OP supplied, both converters are too loose and neither converter is near optimum for the combo. There's no magic required in the year 2016 to get the right converter for a ~ 500HP n/a small block, 1/8th mile bracket car

[S/ST 3040]

Originally Posted by 1320racer

What's your criteria that has you believing it's "a better converter"?

The one critical bit of information you omitted and frankly the first and foremost bit of information necessary when discussing converters, in the absence of dyno results is... your cam's duration @ .050?

Without it, there is no meaningful discussion or advice.

Lastly, you have an engine combo that maybe makes 500+HP and 400+ ft/lbs. torque at probably around 5000 RPM. A converter that flashes to 5800 is too loose no mind one that flashes to 6250 IF the goal is to "shave some ET." The fall back RPM is what is most important.

Maybe I should have not used "better" and I understand there is more to converters than stall speed. I just figured, I'd tried a couple of different converters with two tire sizes. (basically, a gear change) and hoped it was enough data to give the guy at ATI some direction to go.
It looks like, everybody agrees it could pick up with the "right" converter?

[1320racer]

again, what is your cam's duration at .050?

[S/ST 3040]

Originally Posted by 1320racer

again, what is your cam's duration at .050?

IN Closes 63º ABDC @ .050"

[1320racer]

run the other way from whoever told you that cam was what you needed!!

You are wasting your time with converters with that cam that's at least 40 degrees too big for your 9:1 bracket engine!

FTI, the cam in my 15.5:1 598 has similar duration @ .050.

[S/ST 3040]

Originally Posted by 1320racer

run the other way from whoever told you that cam was what you needed!!

You are wasting your time with converters with that cam that's at least 40 degrees too big for your 9:1 bracket engine!

FTI, the cam in my 15.5:1 598 has similar duration @ .050.

It is a turd!

1.2664 60'
3.85 330'
6.058 660'
9.66 @ 135.4 MPH1320'

[1320racer]

a 9.66 best at 2600 lbs. IS a turd!

[Mike Pearson]

Originally Posted by S/ST 3040

It is a turd!

1.2664 60'
3.85 330'
6.058 660'
9.66 @ 135.4 MPH1320'

Those numbers are not real shabby for something that you built yourself. Non of us started out setting the world on fire. Just keep asking questions and talk to the educated guys about your combo, Talk to the cam companies about a good cam for your combo. Also stick with the better converter companies for a converter that will optimize what you have. Best of luck with your ride and the most important thing is you have fun with it.