Putting together a budget street car combo, and cam grinder suggested a at minimum at 2500+ stall converter (230/236 at .050 duration). I've found a local guy selling a very nice used dynamic 9.5" converter that stalled at 3800rpm behind his 340 with a 509 purple cam, 10.5:1 compression, and 4.56 gears in a street duster. My combo is a 3700lb volare wagon with an aluminum headed 8.5:1 360 running a 3.06 rear axle ratio (may go to 3.23 at some point). I have read that the lower numerical gear ratio will make the converter flash higher, but I wonder if the weight, lower compression and power will drop the converter stall speed to something more usable like a 3000-3200rpm flash point.

Looking for some input on this one since the combo will need a converter as I currently only have the stock 1800-1900 stall converter for it. Wondering if even a factory high stall (if I can find one) would be a better option, but I am trying to keep this on a budget (I know, the problem for everyone these days).

Thanks!

I used this to calculate mine

More HP/torque will increase stall speed
Heavier the vehicle, the higher it will push the stall
Lower gears, such as a 2.73 or 3.08 gear, will increases stall

The mathematical constant that defines a converter's stall speed (in rpm) is called the "K" factor
K is the observed stall speed of the converter divided by the square root of the applied torque
The relationship is expressed mathematically: K = RPM/torque^0.5
Once the K factor for a converter is determined, the stall can be predicted for different torque values

The lower torque you are making than the other guy will help lower the stall.

BUT

You are considerably heavier than the other guy with a considerably higher gear. This will raise the stall, likely more than your lack of torque will offset.

Pass on that used convertor.

Something like a TurboAction 17805M would probably be a better bet.

Don't know if this is any help but changing from a 4.10 to a 3.73 rear gear increased stall by 1000rpm on our combo.

Helpful info guys, thank you! I will pass on this one then. And just for future, at least I now know that the more weight and lower numerical gear ratio will INCREASE stall speed.

But that is somewhat artificial. The definition of flash is the highest rpm seen before the car moves. The car moves sooner/easier with the 4:10 than with the 3.73. That earlier movement might be more beneficial that then increase in flash rpm. Did the car improve in the 60’? Always trying to understand more about the converter

fluid can tighten or loosen the converter, Straight tractor fluid to straight dexron or a mix of them can move the stall a few hundred rpm.
IF this is a "street" race or no prep type deal, looser is usually better....just saying

Depends, I flash to 3500 rpm because that is all my 6” tire can hold. The rest of the combo wants 5000+ flash. Some in the FAST use a programmable box to pull timing. Not there yet. My SLR is pretty low with 4:10 and a low 1st gear 904. Lets me tolerate a small bit of wheel speed before I need to pedal.

A 230@.050 cam is a lot of duration for a heavy car with a 8.5-1 360 and a
3.08 axle. Been there, you will not like it. Not a happy combo on the street
Doug

No, 60ft dropped a 10th. Slower by 2 10ths, Mph dropped 4 - 6 mph while rpm remained roughly the same through the traps. Slip increased from 10 to 17 %. I have since fitted another converter but no track time as yet.

Its just a street car that I am trying to NOT turn into a full blown race car lol. It may get nitrous or a blower in the future though...

I can't remember, but what I recall the tractor fluid, like hygard, tightens by a couple hundred rpm, right?

Honestly, I thought that too, but this is what was recommended by the cam grinder, even giving all of the information on the combo. They also recommended an even larger grind, but I chose the smaller of the 2.

That said, something like this, would you say would like more or less converter? I am back and forth between this converter I mentioned in my original post, or a factory high stall 340 converter. Other then what I have already noted, the car MAY get a set of 3.55 gears in the future, but I know it will hurt the driveability on the highway, so that is slightly up in the air.

I'm wondering the same.
I just picked up a 360/380hp crate engine. 3400 pound car, 3.23 gears, 27" tall tires and a 904 based lockup. 230 ish duration at .050 I think
1 3/4" Super Comps, 650 AVS2, and an irresponsible driver.

I drive mostly highway, I like to drive at a brisk pace, but should I change the converter? It's a lockup trans and probably not a lot of options...? Factory 318 4 barrel engine in it now. 155hp?
I could swap cams in the 360/380 if necessary but I would rather not!!!

Sounds like the converter definitely not happy. I know people who have tried increasing slip % at the top to try and increase torque multiplication down track, but no real results yet. 10% seems a bit high. I’m at 4-5 % at the stripe. Which car?

ATI makes 20w and 30w type f transmission fluid. Going from the 20w to the 30w affected mine about 200 rpm

Runing a low gear like the 3.08 doesnt allow the rpm to get high enough to couple. We ran Dizusters turbo car with a 2.76 gear. It ran 10.50's but the slip was as I recall was over 25%. Why? The car wasn't done accelerating. My street car ran a 5300 with a 3.55. Slipped like mad. Felt like it had a V V T trans. Same converter with a 4.30 it drives great on the street. Cam, converter, gear all have to be in sync to drive nice.
Doug

8" ATi converter, it was originally specified for a 750 ish HP 528motor. It worked ok with the 572/580 motor and and 4:10 rear, showed over 900hp on a good day at the track going off the numbers and the weight (4023lb). Stall was originally 5200 (4:10) and it would go to 6000+ with the 3.73 gear. Data showed around 9 - 10% slip (4:10) which I was OK with as the car worked ok. I guess the change in rear ratio pushed the converter too far
We have fitted an ATi converter (9 1/2") that was built for our 655ci motor with 1000+ hp and a 4:10 rear, hopefully that will improve things.

i agree.it will really hurt torque. A cam like a Comp 268h would be ideal,,,,,

Stalled higher or lower with the switch?

So in this case, would the 2500 stall or the 4000 stall be ideal? Cam company said 2500+ stall for converter giving them all the combo details. Maybe the lower stall would work better as to couple sooner?