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Re: Converter stall Speed

Posted: Sat Oct 21, 2017 1:16 pm
by lefty o
with less torque, and less weight it will have less "stall" or slippage if you will.

Re: Converter stall Speed

Posted: Sat Oct 21, 2017 4:29 pm
by Brian P
1972ho wrote:
Sat Oct 21, 2017 11:02 am
See how you guys are talking converters I have a question about a converter I plan to run on a different engine combo.I I’m running a C-4 behind a engine that the converter is already maximized on,But I want to run this set up behind a ford v-6 that makes hp and torque around the same rpm as the v-8 that it will replace.Now the amount of hp is about the same but v-8 makes around 100 more ft/# than the v-6.So do you all think that this converter will stall and function the same behind the v-6 as would behind the v-8,providing nothing else is changed except the weight the car will weight about 140 less with the v-6.Thanks
The stall speed is in proportion to the square root of the torque being put through it. And that torque is, at least to first approximation (assuming naturally-aspirated gasoline-fueled spark-ignition 4-stroke engine with relatively "normal" cam timing), in proportion to the displacement. You haven't told us what the torque of both engines is, or in the absence of knowing that, what the displacement of both engines is, and you haven't told us what the stall RPM is in the current application.

If we make an ASSumption that the current engine is a Ford 302 / 5.0 litre V8, and the engine that you are proposing to replace it with is a Ford 3.8 litre V6, the new stall speed will be sqrt(3.8/5.0) = 0.87 times whatever it was before. If the ASSumptions are wrong, then that number will be wrong, but I've given enough information for you to figure out what that number is.

It's probably close enough that the car will drive OK with it unless you are insistent upon splitting hairs.

Re: Converter stall Speed

Posted: Sat Oct 21, 2017 11:41 pm
by F-BIRD'88
You do not give enough info to create a "K factor" formula for your Ford conveter.
But I will take a rough stab at the new stall sped behind the V6. The V6 makea bout 100 ft/lbs LESS than the V8 according to you. Roughly it will max stall about 400rpm Lower at launch behind the V6.
This is a rough estimate.

The weight does not effect this.

STALL speed and "slip" ARE NOT THE SAME THING. These are 2 VERY different things.
This is part of the reason people do not have a good handle on how it all works.

Re: Converter stall Speed

Posted: Sun Oct 22, 2017 12:24 am
by lefty o
you certainly dont!

Re: Converter stall Speed

Posted: Sun Oct 22, 2017 4:01 am
by Gotzy
Thanks everyone for all the comments, there's been some very interesting and useful posts.

it's just a cheap RWYB car for fun twice a year so after being offered a cheap 3,000 stall converter we've decided to bring the stall down to the cam to see if we can move our shift point further down the track and run out of rpm closer to the finish line.

It is a miss match of a combo but we decided yesterday, in the name of safety, to not attempt to make faster, just hopefully a little quicker so it'll be a 10.9x car. Weather permitting we'll be at the last meeting of the year next weekend, I'll post up the results just foe interest sakes.

We agree on the rear axle gearing but as it's a Volvo rear axle we are limited to choices so sort of stuck with it.

Re: Converter stall Speed

Posted: Sun Oct 22, 2017 1:07 pm
by F-BIRD'88
Working with what you got if you retard that thumper cam
a good bit it will shift the engine power curve up in rpm.

It is a 107 lsa cam that is "advanced". About 5 deg on a 102 deg in c/l 102/112 centers.

Retard it 5 to 7 degrees so it is "straight up" or a hair (2 degrees) retarded.

107/107 or 109in/105ex centers.. This will shift the power band up. Not a complete cure but a step in the desired direction. Peak hp will increase a bit and the upper rpm will be more powerfull. (above 5000 rpm) where you need it.

It will perform better with that 5000 stall converter.

The real fix is a cam swap to a high reving capable solid cam
But this current cam adjustment will help you.

Re: Converter stall Speed

Posted: Sun Oct 22, 2017 1:53 pm
by F-BIRD'88
Further working with what you giot:

If the tunnel ram is the offy turbo thrust and the plenum under the carbs is fully divided then removing that divider in the plenum will increase top end power especially if the carbs are small (450x2 carbs). This really limits top end with a tunnelram. Tunnel?Rams like to breath deep to make power.

Really you need 2 650++ carbs,,, but this will help.

This removing the plenum divider and retarding the cam
will really help that motir be more friendly to the 5000 stall converter. The little carbs may even want more plenum volume+height... Add 1 or 2 carb spacers under each carb for effect..

Re: Converter stall Speed

Posted: Tue Nov 07, 2017 6:42 pm
by Gotzy
Thanks for the extra comments F-bird, more to think about

You mentioned early the car needs 4.56 gears, would these just make me run out of revs earlier?

Re: Converter stall Speed

Posted: Wed Nov 08, 2017 9:31 pm
by Brian P
You haven't told us at what RPM your engine makes peak torque, nor at what RPM your engine makes peak power, nor what the redline RPM is. Tell us that!

Re: Converter stall Speed

Posted: Thu Nov 09, 2017 7:05 am
by Gotzy
Hey Brian

Cam is rated to 6,400 and when on the rolling road the converter wasn't locking up until 5,700 ish so we couldn't see the power curve as it was pretty much already over, for the torque anyways. Shifting at 6,500 gave the quickest times and then running the last 100 yards at 6,000 which appears to be its mechanical limit

Re: Converter stall Speed

Posted: Sat Dec 02, 2017 3:01 pm
by Ron E
We ran the same engine/trans/converter in several in several configurations.
At 3100 lbs 2.45, 1.45, 1.00. 4.56 gears. starting line flashed to 5200 RPM
""""""""""""""" 1.45, 1.00, 4.56 gears starting line flashed to 5200 RPM
at 2400 lbs 1.45, 1.00 4.56 gears starting line flashed to 5200 RPM
""""""""""""""" 2.45, 1.45 3.33 gears starting line flashed to 5200 RPM.
Autometer play back tach
In our case, the above gearing and weights didn't effect the stall RPM. From best to worst weather we would see a little less than 100 drop. Makes sense as the engine made less power in the heat.
Can't/won't argue the theory involved. But, those were the numbers.