This makes good sense but wanted others opinions. I had my car put on the dyno and came out with the following numbers:

400RWHP at 6500RPM

379RWTQ at 3500 RPM (Dyno Graph shows TQ slides down ward after peak, not flat)

So, I had a 2800 stall at the time I put my car on the dyno. I was cutting 1.75ish 60’ times on that 2800 converter. I decided I wanted to improve my 60’s since I was running a 12.1 ¼’s. I was hoping going larger would get me into the 11’s. I went with a 3800 (closer to 4000 with my HP) Fuddle converter with a 2.3str.

After installing the 3800 converter I took it to the track and the 60’ times did not change. I started talking with some people and here is the thought.

If my peak TQ is at 3500 RPM and I am now launching at about 4000rpm. I have actually launched the car on the downward slide side of my dyno graph TQ wise. At 4000 RPM may car is showing about 360RWTQ on the dyno graph. If that is the case I am missing out on 20RWTQ by launching at about 4000RPM instead of 3500 RPM.

In theory would it not make the most sense to try to match your converter to your max TQ RPM? That would mean my converter should be a 3500ish converter?

Thanks,

Bill

 

That's what you are suppose to do. You get a stall that is just below, or at your max torque rpm, so you have the most torque when you launch. A higher STR rating will also help out. If you put a higher stall on where the torque falls off, you have less torque when you launch.

 

NA street/strip combos seem to do best with a converter stalling a few hundred rpm below peak torque. But YMMV. Is it spinning or hooking? Did your trap speeds change at all? What are your trap speeds? What does it actually stall at, is it really any different? If you are brake stalling, it may not be any different at all.

Rich

 

What is YMMV?

Car hooks pretty well, no spinning that I know of. I am trapping about the same as with the 2800 converter, 111.65ish. I will check my old time slips to make sure and repost tonight.

I can foot brake this converter to 3400 RPM the old one would only go about 2400.

I do footbrake the car on launch with this conveter since I have the stock 10 bolt and like to preload it to help cut the risk of exploding the rear. So, do you get better 60's flashing the converter off the line of footbraking? I would think footbraking since it is similar to using a line lock which people say helps their 1/4 times.

Thanks for your help!

 

YMMV: You Mileage May Vary

That is one loose converter if you can footbrake it to 3,400rpm! Again, is it spinning or hooking? If it's spinning when you launch, that's why your 60' didn't improve. If it's hooking, they should have (improved). If your traps are about the same, it is also as efficient as the old one, which is good considering how much looser it is.

Rich

 

It is hooking, not spinning. I will post current slips and old slip number in a couple hrs.

Thanks,

Bill

 

Yep,

MPH is about dead on:

2800 converter = 111.35

3800 converter = 111.60

60' about the same to both 1.7 - 1.75

Hmmmmm, I am getting a new strange 12 bolt with 3.90 gears, that should help.

Thanks,

Bill

 

well, here's somethin, what was the weather, heat humidity.. and track temp, prep... on both days you may have had a good day with the 2800, and a crap day with the 3800.

weather plays a major role, usually a couple tenths, so... you sway both ways a bit and you have the few tenths difference in stalls

and for your torque loss, well you may be losing out on torque, but your horsepower should be there after peak torque to carry you through, so you should still be faster launching higher, unless the tranny is slipping er somethin

 

I think your 3,800 converter is the wrong converter for your combo, at least from the data you posted.

Rich

 

toooo big...

 

Just like what was mentioned the track and weather could play a big role in this. I would have thought with that type of change that you would have seen some type of change.

Now from my experience is that in the day's of my stock head LT4 Hot Cam setup, I had a Yank ST3500 converter, pretty much one of the best setup's that I think that you can have. I since then went to a much larger hydraulic cam setup better heads and to a 355.

I started off with a 4800, I had to move the 4800 down to a 4200 due to the ET being about the same to the 4200 but the MPH was lower then the 4200. I switched back to the 3500 and my ET was slower but the MPH was faster then the 4800. The restalled 4800 to 4200 got me a better 60' and was just about as fast MPH wise to the 3500. The 3500 was more effecient on the big end then the 4200. Sounds confusing huh.

What I'm trying to say here is that you might have to make some adjustments to the converter to try to find it's sweet spot.