crazy looking dyno sheet

HI guys

I just dynoed a new motor and was hoping one of you experts could look at the dyno sheet and may be try to guess what the problem is
4.15 stroke 4.380 bore trickflow 240 heads six pack with all the promax stuff
hughes STL4246BS3-9 242 intake 246 exh 109 lsa 105 centerline 600 lift
The motor ran very nice smooth idle and ran it up to 5700 smooth as silk but the dyno sheet looks crazy

is the intake a eddy dual plane?
If so they have a inherent low peak HP RPM limit due to the manifold being designed for stock muscle cars back in 1968
I built a pump gas low deck stroker motor (505 C.I.) with a low deck Eddy intake and 1970 440 carbs, it made peak HP at 5500 RPM and peak torque at 4500 RPM the first time I dyno tested it.
I ended up swapping the heads and cranks shaft to improve the compression ratio and it made peak HP at 5600 RPM and peak torque at 4600 RPM
I've been racing and winning with Mopars since 1964, I started on a very low budget and ended up assembling all my motors, that stupid six pack motor would make the car run the quickest and fastest by shifting it at or above 7000 RPM
Drive it first and see what yours does by shifting it at 5000, then 5500, then at 6000 and above until you find out what your motor likes on the shift RPM
Dyno sheets are one thing that these stupid motors can't read
Good luck

Looks like a hiccup at 4300. When was the last time the dyno was calibrated?

Starts out good for the first few lines, then falls on its face.

It’s down 75-100 tq & hp(if running adequately sized headers)

Is it the dyno or the induction?
Or something else altogether?

It’s not using much fuel...... which kinda goes along with the low output.

Here’s a 505, Stage 1 RPM heads, 252/260-112 SFT caml, 2-2 1/8 headers...... also a 6bbl on an Ede manifold.

From 5000-up, the fuel flow was 240’s-250’s-260’s..... with it topping out at 266@6000.
It was in the 220’s by 4700(you’re barely over 220@5700).

Does that dyno service have a good reputation for accurate, and maybe even more importantly, repeatable numbers?

If you’re interested in getting to the bottom of it, “what I would do” is see if you can borrow a fairly decent single 4bbl manifold and a good working 850 or 950 carb and retest it.

Bring that 6bbl with you to the dyno, and if the power curve looks better, and the numbers are more in line with what the motor “should” be making for power...... you can reinstall it and start chasing the tune.

If the shape of the curve, and the numbers are similarly low with the single 4bbl on the motor....... there is something else going on.

Thank you so much for taking the time to look it over
It is a stock aluminum 6pk intake from jegs that has been port matched
I think I will try the 4bbl, I have a performer rpm and a holley 1000 cfm hp unit here
I will keep you informed

Thanks

Here is one we tested recently just for another comparison. 505”, TF240’s, stock iron 6barrel intake, comp Hyd Roller around .580”. 10.9:1.

Vac secondaries.... you verified the end carbs were operating correct right?

If i seen a drop like that 300 rpm after peak torque, i would suspect that you had a tiny bit of detonation. Some dyno's are super sensitive to detonation because of the water valve configuration.

I will say those BSFC numbers are weird as hell, usually the engine is most efficient at peak torque, your numbers don't make any sense. Did you have any afr numbers?

Joe

my guess would be for the mid-rpm dip is where the end carbs opened and created a flat spot. i would think there would be a fuel flow dip at that rpm. carbs may be flopping open and need some control or fuel flow may be marginal.

Well I just don't know what to think
I could not hear any detonation @ 35 degrees and 93 octane Maine gas
I watched the outboards open and they stopped at about 3/4 of the way for a second then went completely open but I could not see the rpm at the same time
The plugs were clean
The motor had a good idle even down low at 750
The motor ran very smooth thru the whole range
The only thing I noticed out of the norm was when the throttle was shut down I got a long puff out of the carbs

I think it's odd that up to 3600 fuel flow was increasing with RPM and torque as it should. Then starting at 3700 it dropped to a low at 4100 and then recovered such that at 4300 you had the same fuel flow as 3600. It then began increasing again. So, how can you have an increase in RPM, with lower fuel flow and torque? The only explanation I can come up with is that the dyno didn't load the motor up in that RPM range. Did you do more pulls? If so, how do they compare?

I think I am going to install in the vehicle and test and tune that way
I know everything is good mechanically so it is all about the tune at this point

Yes it looks like it has a problem past 5300rpm. One thing is a dyno is a tool, and horsepower and torque measurement is just two of the things it should be able to do. On your print out no A/F readings, no exhaust temps, etc. If it does not run quite right you need information to help solve the problem. I don't know if the number is accurate but right when you have the issue the BSFC looks like it goes lean. But if you go to the dyno, take the time to get some sensors on the engine. Bragging numbers are great, but info on what is happening inside the engine under load is what I use a dyno for. A look at a spark plug is also critical in reading if an engine is happy.

Personally, I’d much prefer trying to sort out a 6bbl/tuning issue on the dyno(where the results of a change are instantly quantifiable) than try to do it with all the other added variables that go along with what happens at the track.
But that’s just me.

Was it tested with headers on it?
Will it be run in the car with headers?

If it had headers on it, regardless of the shape of the curve........the power numbers seem really low.