Converter Questions

[fourtenposi]

I had a SBC 406 with an 8 inch converter stalled at 5300 rpms, shifting at 6200 rpms falling back to 5800 rpms on the shift with a 3 speed. Cars best et was 6.81@99 mph in the 1/8 in the best air I have seen at the track. Estimated hp is around 520-530.

Build my new motor Estimate hp is around 600 hp. Backed it with a power glide. Converter stalls exactly the same and falls back to about the same as before, be yet the car runs 6.55@105 in worse air then before and the sixty is the same 1.48. Started shifting at 6600 and it would fall back to 5800 on shift. Bump it up to 7200 rpms and it fell back to about 5900 on shift. It may want more, I will find out on the dyno next week.

All rpm numbers are recorded with my data logger.

Is there an explanation as to why the stall didn't change? The motor is making a bunch more hp, is this suggesting that the more is making the same amount of torque as before. I beleive the converter is about 400-600 rpms to tight with the glide.

Thanks in advance

Bill

[jmarkaudio]

Bill it depends on the torque you made at the stall point, both may make about the same torque around 5300, the new iron may go up higher after that where the old one falls off. It may want about 500 RPM more stall, requires cutting. And more...

[fourtenposi]

What are you referring to when you say it requires cutting and more?

[jmarkaudio]

Sorry, more stall requires cutting the converter open and money. Unless you had one of Marty's bolt together.

[Marty Chance]

fourtenposi - sorry it has taken so long for me to reply. (jmark is correct) your old motor and new motor stall the converter the same because they make close to the same power at the stall point . Stall speed is dictated by power but we are NOT talking about your motors peak power , stall is dictated by the power the motor makes from and idle up to launch rpm. The new motor is faster because it is making more power.

[fourtenposi]

No problem,

The way I understand it, it is that torque that dictates where a converter will stall. would you say both motors are making peak torque in the same place or just the same torque at that rpm?

Say you have motor A it makes peak torque of 500 footpounds at 5300 rpms. Then you have motor B makes 500 footpounds at 5300 rpms but peaks at 5600 rpms at 550 footpounds. Would these motors stall the converter in the same place? Is this what is happening with my motor?

With a 60-80 hp gain in power, I was expecting the converter to stall higher. Would I be correct in saying that if the motor were making more torque at 5300 rpms it would stall higher?

Thanks in advance.

[jmarkaudio]

Torque does dictate stall, but within the range that the converter is designed to stall. Diameter, stator design and fin angles all play into range of the converter. Since most likely both engines produced the the same torque within your converters range, there was no change. Now cut the stator to gain stall and put it in the range your new engine makes peak torque, it would stall more with your new combo than with the old one. Get your new engine to make more peak torque at 5300 RPM and it will stall higher. Once you get the dyno info on your new engine you will find out where the stall should be. One of the comp motor engine builders on ST gave me what I consider to be a good way to figure it out, he said if you find the best average HP over a 1200 RPM range, the low RPM number (usually a few hundred RPM over peak torque) is your stall point to shoot for, the top RPM number (usually a few hundred over peak HP) is your shift point. My feeling is that this would work for most circumstances, obviously extremes like a very small engine might want a bit more and a very large engine a bit less. Normally aspirated of course, power adders change the requirements. I can tell you I had 3 8" converters behind my SB2, my old 5500 stall ran about a tenth slower than the 7100 stall, the 6500 stall was .02 to .03 quicker than the 7100. Peak torque was about 6300, so you can see where missing a little high (OK a lot) was better than going the other way. Now if were only that simple.... add to this two different converters that stall the same but one will ET better than the other... I have my 8" that stall 6500, I'm told a 9" could be built to stall that much, and I wonder too how a 7" might perform if it could be made to stall that low, which would work best? This seems to be where the trying multiple converters come into play. Maybe Marty will jump in on this one again...

[Marty Chance]

Again jmark has given correct information and i would agree with all he said and would like to add , this is where the "magic" can make some differences and the magic usually comes in stator designs . If you were going to try a 9" the converter could be designed with a high stall pump impeller and a high torque multiplying stator , or the 7" could be designed to lock up very aggressively (for a 7") and have less torque multiplication but take advantage of the decreased rotating mass , which is faster ??? that can only be answered by trying both and each car combo may have a different result and if that is not confusing enough i would also add that you can build the same stall speed converter many different ways (example 8" 5600 stall) and get a different et and mph out of each even though they stall the same. A converter like a clutch can be fine tuned to the application and you will make subtitle gains but many people feel the gain is not worth the investment of time and/or money , while others love to tinker with things and have a blast being able to play around with there converter and make a gain. Thanks Marty

[fourtenposi]

Thanks for the info,

I am just trying to better understand the converter.

[jmarkaudio]

Bill, you will have a better idea once it goes on Larry's dyno as to what area you want it to stall. The fun part is getting the best converter in that stall range for your combo. That can try your patience and wallet a bit....

[fourtenposi]

Hey Mark,

I am leaving my current converter as is because it is so consistant. I found a deal on an 8 inch bte converter and I am going to get that one set pending the dyno numbers. I am not looking for it to be perfect, I am a bracket racer so consistancy is key. I just want to see what the car with do with the correct converter and gears. I don't think the et reflects what the motor is actually making. But I think I will be sacrificing some consistancy. I figure it has to be 400-500 rpms to tight if the motor is really making power to 7k.

[jmarkaudio]

You will lose consistency if you lose traction, a good converter with the right stall won't be inconsistent. I think you will find some ET with about 500 RPM more stall, as long as you still hook.

[fourtenposi]

I agree Mark, I am on a small tire, So traction may come into play. Although it may like the extra hit on the tire and make it even more consistant. We shall see what happens. So what would you think 500 rpms to tight was worth. Most cars I see running my et are in the low 1.40s high 1.3xs. My sixties now are 1.48. I think it is off a 10th in the sixty.

[jmarkaudio]

A tenth is probably close, my dad played around with a lot of converters in his old Malibu (406, roller cam, Pontiac raised port 867 heads) and the best is one my brother is still running, a Continental that stalls around 5800.

[fourtenposi]

Should the stall speed on the t-brake be the same as where it falls on the shift?