Okay...... after sleeping on it, I think I can better explain how you can have an inertia chassis dyno sheet where the power curve is not at all representative of what the engines power curve would look like, including have a big spike much farther up than where the engine tq peak is.
This is basically all pertaining to running a high stall converter on an inertia dyno.
One of problems is how the graph is displayed.
Without any time element to the graph, it doesn’t paint an accurate picture of how the run progresses from start to finish.

First we have to understand that the torque converter is the coupler that connects the engine to the load....... and that the stall speed determines at what point(rpm) full load will be applied.

Secondly, on an inertia dyno, the power is determined by the rate of acceleration of the drum.
Nothing is “measuring” the power output.
Accelerate the drum at a higher rate, power displayed goes up.

If you did a test with these parameters, you would get a dyno sheet that showed very low engine output at the lower rpms of the graph(and have no bearing on what the engine power would be at those points).

Assume the engine in the car has already been on an engine dyno and makes peak tq between 3000-3200 rpm(not that this matters, I’m just using it as an example to point out that even with a peak tq of a known lower rpm point, a loose converter will show peaks at a higher point than where they actually happen).
The car it’s installed in has a converter with an actual flash stall speed of 5000rpm.
The test will be conducted from 1200-5500 rpm.
The car will be in high gear, throttle held steady at 1200, drum speed stabilized, you push the button to start recording just before you push the throttle down....... the motor accelerates to 5500rpm, you push the stop button.
The data recorded will be from 1200-5500rpm.
On the tq/rpm graph, the point where the full load is applied to the motor(5000rpm) will be most of the way to the right side of the graph.
And there will be a big spike in output right at about that point....... because that’s where the converter started to couple, and the big change in acceleration to the drums occurred.

You could pick points along the graph at the lower rpms where the numbers were much much lower.
That’s because with the converter slipping so much, there isn’t much change in acceleration rate at the drum. The converter is still flashing up to stall speed and is not very effectively coupling the motor to the load.
The graph would have a lazy slope from 1200 to the point near where the converters stall speed is........then as you approach the stall speed, converter couples, drum rate surges, and you get a spike on the graph nowhere near where the engines actual tq peak is(in this example).

Here’s why this is not an accurate picture of how the run really happened, and why looking at a graph of the run with a time element attached helps tell the story.
When the start button got pushed and the throttle went to the floor, the motor immediately went right to the 5000rpm stall speed.
If the motors tune was sharp, that would happen in less than one second(1200-5000)....... yet it takes up 3/4 of the space on the tq/rpm graph.
If you plotted rpm on the y axis and time on the x axis, the line would go almost straight up from 1200-5000(and would all happen way at the left side of the graph), then at whatever rate the power being produced from 5000-5500 could accelerate the drums.
If the motor was making pretty good power, this whole run from start to finish would be maybe 2-2.5seconds...... because the load would have only been applied from 5000-5500rpm.

It’s not a long steady pull like the tq/rpm graph depicts, and the numbers below stall speed aren’t representative of engine output whatsoever.

The OP’s motor should have an engine output torque curve similar to the one I posted the sheet for.
That one had peak tq at 4000 rpm. At 5000 it’s already down 93ft/lbs from peak.
If you chassis dynoed that motor in a car with a 5000 stall speed converter, that’s where the highest torque will be displayed, since the torque curve is already well past peak, and that’s the lowest rpm where full load can be applied.

The other thing the rpm/time graph does is give you a nice picture of what the flash stall is.

What I’d like to know from the OP is, what’s the flash stall speed of his converter.
If you haven’t tested it yet, try this......
Disconnect the kick down linkage, put the car in drive...... let it up shift into 3rd...... hold the throttle at about 12-1500rpm and let the speed stabilize...... then floor it, and observe how high the tach needle “flashes” to.
For all practical purposes, that’s your flash stall speed....... i.e. the lowest rpm that full power can be applied to the wheels.

Alright, I think I'm following here. The torque converter isn't coupling until well past the torque peak of my motor, and when it finally does at 5200 RPM is the reason we see the spike.

This is the same converter I was using behind the old small block. It wasn't advertised as stalling that high, but the additional torque of the new motor pushed it that high?

So this is exactly what Gary meant when he said it was driving through the converter?

I can call Jake's on Monday and see if I can get those graphs.

Some additional information: tires are 285 Nitto NT555, kick-down cable was disconnected from the throttle body, overdrive was turned off and the pulls were made in third gear.

On an engine dyno, the throttle goes to wide open and the motor is allowed to stabilize against the load before the “pull” is started.
Most pulls are done from low to high rpm.
As long as the pull starts at an rpm lower than where the motor makes peak torque, you’ll get a good picture of the shape of the power curve, and where the peak occurs.

With a chassis dyno that has these same capabilities........being able to hold the load against the absorber to get things stabilized....... then starting the pull from that point....... the beginning of the pull would always be whatever the converter stall speed was.
That would always be the lowest rpm where output was recorded(if the test was conducted in that manner).
So if you had a 5000 stall converter, there wouldn’t be any data below that point.

Again, if the engines peak tq was well below that rpm...... that would still be the point on the sheet where the highest tq was observed...... and would in no way reflect where or what the engines peak tq output really was.

That’s how it appears to me.
By the looks of the graph, I’d say it starts to couple effectively at about 5000, and at around 5200 or so when it’s more fully locked up, it’s well past peak tq and you’re well into the downhill side of the tq curve of the motor, which is why it’s dropping off quickly right after it shows the peak.
It’s not until the converter is basically locked up that the power curve will mimic the engine power curve........and in this case that seems to be happening well beyond the engines tq peak rpm.

You should do the flash stall test to see if it agrees with what appears to be happening on that sheet.
I can’t believe there is any way a converter that was “right” for a small block would be correct behind a lower/mid rpm high torque 511.

I’m not sure exactly what kind of driving experience you’re looking for, but the OD trans and 230@.050 cam, unported std port heads, dual plane manifold....... kinda looks like a 3000-ish flash stall combo to me.
Which would likely be a pretty tight(very tight?) 11” unit.

As an illustration of how tq affects stall speed, the 8” converter I ran behind my 340 and then the 383.
4800 behind the 340, 5400 behind the 383.

Depending on what your what your SB combo was, I can easily see where the 511 could be 200ft/lbs better, especially down near where the converter would have stalled behind the SB.
And a difference in tq like that will have a huge impact on how the converter behaves.

Frankly, I’d think it should be pretty high on the list of things that should be changed.

i was thinking the same thing when i asked zippy what stall converter he has, if you look at his graph, it's about 5000rpm where the curve starts to look like what you see from an engine dyno.

in my opinion, the 4.10 gears have just as negative effect as the converter. mushy converter plus low axle gears reduces the drum rpm and acceleration rate. I don't think that engine needs either of these two factors. a lot of cubes and small cam should be a torque monster. I have a simplistic philosophy about some of this; you can let the engine do the work or you can work the engine. I think in this case the lower gears and looser converter are working the engine instead of letting it work. this engine probably makes gobs of low and mid-range torque and probably could be tuned to work with a stock 11 3/4" converter. add a 3.23 or 3.55 gear and I bet results will be different.

Exactly.
If you notice, there is a little upturn in the curve right about where he says the stall speed is.
It isn’t necessarily that there is a spike in engine power output at that point, but rather a spike in the acceleration rate of the drum, because of the spike in converter efficiency.

It would be interesting to see a rpm/time graph of one of those runs.
If the button were pushed right before going to wot, that area from about 3200-4800 probably happens in less than one second.

Lew, I agree.
With a stock/tight 12” converter and 3.23’s behind the OP’s combo........ the curve wouldn’t look anything like what he posted.

I’d love to see a torque/hp vs time, and torque/hp vs speed graph of that same pull at the beginning of the thread.

I think the rpm vs time graph gives the best picture of how the converter behaves.

3.23 gear, 1900 rpm stall. Pull done in second gear.


Mustang, not DynoJet

Russ, what are the dips on the upward slope...... tire slip?

it's my understanding that mustang dyno's are a little stingy compared to dynojets.

when I went thru the chassis dyno thing some years back I was looking for information to try and figure out which direction to go in. good information costs money and time. treat the exercise as part of the learning curve and make the meaningful changes for best results.

I can't get away with using a factory big block converter - my 518 is a 23 spline lockup variety. If I attempt to go back to a factory converter for this trans it would be one that was built with small blocks in mind. Is this a problem?

Sounds like you need to talk to some converter shops.

I would say, telling them the motor should produce around 600ft/lbs at 3200-4000rpm is a pretty safe bet when discussing your combo and figuring out the converter requirements.
I’m guessing it will be one of those “as tight as we can make it” situations.

Yeah, you're right. I'm looking over what is available for 23 spline 727/518 at Turbo Action and there is only one in three different configuration: regular, medium and tight. I already have the tight one, so now I'm thinking there is something wrong with it.

I got a couple calls to make tomorrow. I'll get back to this thread with what I find.

How does it drive on the street? If it drives okay at part throttle that might be a clue. If it is so loose that it feels like you're driving a rubber band then that would be another clue.

I don’t know why you wouldn’t just go out and try the stall test.
It’s free, easy, only takes a few minutes, and would give you valuable info.........for having a phone conversation with a converter shop, or just for knowledge about the overall combo.

Not to mention, if the converter flashes way less than 5000, then that dyno sheet becomes even more puzzling.

Edit: I went to the TA site...... looks like their 518 converters are 10”.

I would expect a motor combo like yours to flash a tight TA 10” to around 4000-4200 doing the high gear test.

Sorry if I missed this in another post, but aren't the rollers on the dyno jets like 5000lbs? It might be a case of the converter being ok on the road but gets pushed through with the load of the dyno drums.

I had a compton converter 2800 lock up in my A518, I now have a 4000 lock up that was built for my combo,it works awesome, PATC brand. 512 lowdeck