On a chassis dyno with an auto trans, you can only get WOT readings as low as the whatever the converter stalls.

For example, If you had a converter that stalled 3500...... that’s as low of a rpm that you could apply full power to.

This can be one of the reasons a power curve on a chassis dyno might not look anything like the same motors power curve fron an engine dyno.

If you have 4500 stall, but the motor actually makes peak tq at 3800....... on the chassis dyno the peak tq would be at the beginning of the pull, at 4500.

My cheap B&M ‘2400’ stall converter is the first performance converter I’ve ever had unless you include a factory high stall unit I ran behind a warm 225 in my ‘73 swinger. I’m still getting used to it but it seems to move the truck from a stop around the rated stall if I’m leaving normally in traffic, it will spin to 2000 to keep mph steady at a 40-50mph cruise, and flashes to 3000 if I nail it.

So dyno data will probably be 3k up

I agree!!!! Shift it at 5500-5800 and you could shift this thing anywhere from 5 to 6k and it won’t change your et much if any. I don’t think you’ll hurt anything shifting it higher but there won’t be any point. I had a 511 with 11.5 and mild ported heads with a 274@050 solid and even it was done @6k. The cylinder heads were just out of breath no matter the cam size.
There’s very little point in stroking with a standard head. Other than it doesn’t cost much more. I did it because I plan to upgrade the heads and these were what I had for now.
I moved these heads to a 440 stock stroke in a truck and with a 232@050 roller they are still done at 5500. Made 490hp@5200 and 554tq at 4000. It’s a nice flat curve and pulls hard.

I think you’re making decent power for bolt on source heads. That would be enough for really low 11s in a. A-body.

Have you done the mph/tire dia/gear ratio math to determine rpm?

The reason the power is climbing at the claimed 5500 rpm is because I don't think 75 mph = 5500 rpm. I get something more like 4600 rpm.

Interesting observation Russ...... I never did the math for 2nd gear.

I don’t know what the rear tire diameter is, but for 3.21’s, a 28” tire and 75mph I get 2889rpm in high gear with no converter slip.
Multiply by the 2nd gear ratio of 1.45 and I get 4189rpm....... plus you’d add in some converter slip(which should be minimal with a “2400” converter).

I kinda took it that he was letting off the throttle at 5500, and that was the end of the pull...... but we don’t see the big drop off after the throttle is closed on the sheet...... so, maybe it’s not where the pull ended but where the data acquisition stopped.

I wanna say....... it’s a rare thing for me to be able to look at a chassis dyno sheet and think to myself....”yup...... that all looks right”.

If I hadn’t heard him bounce off my limiters I would be asking the same question. The first time I was majorly freaked out because it sounded hreat then broke up a little and he let off.

After making this post I had the same thought- looking at the sheet again. I had figured that the difference in 5000 and 5500 would be how wide 500 rpm was on the X axis. But no- that’s not time it’s mph so things happen faster on the right side of the paper. So all the dyno sheet tells me is that my torque curve was vastly increased by tuning the spark map. I also pulled up an internet gear, ratio axle ratio, & rpm to mph. Even if my 27.25ish tall tires grew to 28” the numbers don’t make sense unless the B&M converter is just mush and only spins the trans 75% of engine speed? Like I said it’s my first hotrod with two pedals.

Here is my conclusion, one or more of your data are simply wrong, and your power curve is not what you think it is when you think it is.

If you tuned for improvement, fine. But you're on here asking about making sense of bad data.

Your buddy needs to fix his stuff, or you need to go to a different dyno that is working properly.

I will bet your peak power is below 5500, and best et shift rpm 6000 or less.

I don't like Mustang dyno's. They seem to be very tight dyno's giving small numbers IMO. My 511 has 11.3:1 compression, 270@50 SFT/.650" on 110* cam and Edel max wedge heads. I often find myself shifting at 6000rpm now days. The engine just sounds and feels like its ready to shift there. This is street driving and if the tires spin I let it rev to 6800 before its ready.

There’s probably a shop with a dyno-jet 248 inertia dyno not too far from you.
They’re the most popular chassis dyno from what I can see.

If you get more curious about how your build stacks up at some point in the future..... bring it to a shop that has one of those........ make sure the rpm pick-up is working properly....... do your pull in high gear....... make a few pulls.

There’s enough data out there taken with that type of dyno so you’d have plenty to compare to.

I've only been on a chassis dyno a couple of times with an automatic trans and both times the results were very odd. I might try it again with my Duster but this time I'll have the EFI system recording engine RPM as well as driveshaft RPM. And I'll have a manual valve body trans. I think with those tools I'll have a fighting chance of getting useful data.

I have limited experience comparing "all the numbers", ie engine dyno to chassis dyno to track performance. But where I have direct data along with other observations my conclusion is that a not-happy engine dyno compares well with a Mustang dyno, and both correlate well to track data.

But for this discussion it is immaterial, whether it's on a Dyno-jet or Mustang, IMO. The OP does not seem compelled to brag about HP numbers, but certainly needs accurate power curve to rpm data to make meaningful conclusions.

I've found out not all motors and the rest of the parts in the car will want to be shifted at or near peak HP or peak torque to go as fast as the car can
My first pump gas stroker motor was a 400 block stroked to 4.25 originally with a set of mildly ported 906 iron heads with 2.14 intakes and 1.81 exhaust valves and solid roller cam with 260@.050 on the intake lobes and 266@.050 on the exhaust ground on a 108 LSA installed 1 to 2 degrees advanced on the intake lobes. I put a Eddy low deck OEM style six pack intake and set of 440 vacuum carbs that I had C&J engineering modify for better street performance, that motor ended up having right at 9.25 to 1 compression ratio on all eight cylinders.
I had that motor dyno tested and tuned the first time on a DTS engine dyno at the Carb shop facility in Ontario, CA, it made peak torque at 4500 RPM (644 Ft. Lbs.) and peak HP 612 at 5500 RPM.
I ended swapping the heads later to a set of Eddy RPM that where CNC ported by MCH and I increase the stroke later to 4.300 to help up the compression to 10.29 to 1 .
I had it dyno tested up here in Oregon on a Studka engine dyno that was not calibrated correctly at that time but it still made peak torque at 4500 to 4600 RPM and peak torque at 5500 an d5600 RPM depending on the tuning.
I started racing the car by shifting at 5000 RPM and then 5500 and ended up learning that the car would run the quickest ET and MPH by shifting at or above 7000 RPM
On your deal shift it where it wants to be shifted, it will talk to you

I agree. with more detail than I was going to post.

Example of pretty much a picture perfect chassis dyno run.

Looks like probably a std trans, and the tq and hp scaling are the same, so the lines actually cross on the graph like you’d expect at 5252.

When the tq and hp are on different scales, but on the same graph, the lines won’t actually “cross” at 5252, but the values do.

Yeah I have great looking graphs from the chassis dyno sessions with my Coronet. That is a manual transmission so we just get it up to speed in 5th gear and then floor it. The curves come out looking just like engine dyno curves. However, I've been at the chassis dyno (same dyno) with automatic cars and the graphs are a mess. The combination of a torque converter and the kick down function turns the graphs to mush. I'll probably try it again with the Duster just for grins.

This is a pretty good chassis dyno thread from a year ago:

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2527400/1.html

Seems like the take away here is mission accomplished on the street tune and with no rpm data, doing pulls in 2nd gear, and thru a torque converter means the numbers are basically meaningless. On the dyno with the sniper/hyperspark there was no gain messing with AFRs and great gains pasting in a slightly tweaked table from the v4 software to replace the simple timing map. I’m happy with that, especially since WOT is just a tire smoke switch on the street anyway, even before the tuning session.


I will continue to assume I probably have hp in the high 400s at the crank and much higher torque not that it matters. I have to find someplace to weigh the truck and see if it’ll lay down a consistent mph at the strip to get an accurate hp estimate. I doubt it’ll dead hook so ETs might be all over the place and I probably won’t put in the work to get the best 60’ possible- more like learn how to feather the launch. The sniper does have some interesting launch control timing retard and 2 step functions that might provide some entertainment if I ever explore them.

I love to learn about this stuff but in the end I’m all about about the smiles per gallon 👍

If you can get reasonably good and repeatable launches, and the ET/mph repeats pretty well....... and know what it weighs......... you’ll have a good idea what it makes for power.

Of course....... that assumes everything works as it “should”.

I remember following Mark M’s post when he put it up. I was very interested because my build is really close but with a different converter, and a flat tappet. His cam has less duration but higher lift so it’s probably a wash there- really similar.

I didn’t have his problem of driving through the converter though- mine only flashes to 3000 at WOT.

All the talk about inertia chassis dynos vs a load cell having an accurate torque measurement from moment to moment made me wonder though- we did datalog the runs and review the logs along with dyno graphs as we tuned the motor. So I do know that the good pull ends at 5500 rpm. So if I had what looks like 445 tq at 5500 that computes to 466 hp. With 15% driveline loss that would be 548hp and 617tq at the crank which sounds like the optimistic side of reasonable.

Man it’s easy to twist some math around to make stuff sound good based on some rubbish! It will be fun to go back and ressurect this thread after I get real data from a scale and a dragstrip.

The purpose of this thread originally was to see if I was foolish to set my rev limiter to 5500. I will probably put it up to 5800 to keep things safe and try shifting a little higher. I suspect if it is faster shifting higher it would be because the next gear gets to start out in a better spot rather than the motor really wanting to rip at higher rpm in the lower gear.

Truer words have never been spoken!!!

I’d start out with a 5500rpm shift point, and after you have some decent consistency...... try upping it a couple hundred and see what happens.
I’d be pretty surprised if your combo responded favorably to 6000rpm shifts....... but that’s why you test.

What’s the basic engine combo again?
Header size, carb, etc as well.