Interesting 540 dyno test

We're running a 540 BBC on the dyno this week and it isn't going very well. The engine just won't rev past 6000 rpm. It is a hyd roller cam so that is the obvious suspect but it doesn't make any valvetrain noise at 6000 rpm and it has the correct springs in it and plenty of oil pressure. We actually think the problem is due to something weird in the EFI system and/or the intake manifold itself. We're going to switch over to a carb next week to see what happens. This engine has been on the dyno before and last time it acted weird. It has a lot of really good parts but something isn't correct somewhere. Hopefully we can figure it out. Here is a short video showing two dyno pulls back to back: https://youtu.be/4q-tV1mNl-g

Engine is making 730 hp on these pulls so it isn't a slouch, but it should be making more and it should be pulling higher so something is wrong somewhere. Plugs all look good, EGTs are normal, AFR is normal, etc. so no obvious clues.

For it to hit a wall like that I have wonder about spark? Rev limiter?

I am guessing though that if it was spark related, you might see a drop in egt, or the afr would go berserk?

What kind of EFI system, can you post a log?

When ever we hit a wall like that, its been the valve springs. But curious as to what you find.

Holley EFI system. It is a complete Holley kit. I'm not a fan of the 90 degree connectors that Holley used and they used a weird internal regulator that doesn't look to me like it will work properly. I think it is a fuel issue but I don't know for sure. Rev limit is set at 7000 rpm in the software. The data log shows a little ripple on the RPM signal after 6000 rpm which is what the trace looks like when it hits a rev limiter but we don't have one set at that RPM. We'll switch to a carb and MSD distributor just to see what happens. That is an easy test to run when it is on the dyno.

What does the BSFC do at the top of the rpm range?

Looks normal but you can't always trust the data since the fuel flow on an EFI engine is what the ECU is commanding, not what actually flows. Usually the same thing unless something weird is happening.

Just did a guy's engine on my dyno, stroked 340 Mopar and it acted just like yours. Ran good down low but fell off quick after 6,200 rpm. I told him to check the valve springs. They went home and pulled the heads, the valve pockets in the piston were deep enough but not big enough in diameter, the intake valves were just touching the edges under high load.

Chinese casting heads? Asking because I have seen this happen with various brands and makes of engines.

Yeah I've seen that several times including BB Chevy engines. The really cheap no name Chinese stuff works okay for a cruiser but won't make power at WOT. But that shouldn't be the case with this engine since the customer bought really nice parts including a Dart block and AFR 335 cnc heads. It isn't a high compression engine since it is heading into a street car, but my 470 Mopar with TF270 heads made more power on pump gas than this 540 is making. AFR 335 BB Chevy heads should flow a ton more air than Trick Flow Mopar 270 heads and 540 is 70 inches bigger than my 470 so something isn't clicking.

We'll get some runs on it this week with a 1050 Dominator and a MSD billet distributor and see what happens.

Good to know. Interested to see what it is!

It will be interesting to see what happens with a carb. That should eliminate the uncertainty with EFI.

Are you running out of injector pulse width, is there a limiter for it in the injection?

I checked that and injector duty cycle was only about 70% when the engine hit the wall.

We switched over to a 1050 Dominator and made some pulls. The engine is still really rough down low but smooths out at WOT with the Dominator and sounds pretty healthy. It pulls to 6200 RPM with the Dominator before the lifters start to complain. Power is roughly the same as with EFI but the curves are a little bit smoother.

At this point I think it is probably the intake manifold design and something wrong with the EFI fuel rails. It actually makes good power and the customer should be happy with it for a street engine. It makes enough power to completely destroy tires as well as transmissions and rear ends so it should be good to go. I guess he'll put it in the car and see how it performs. It might work just great once he gets it bolted up to a good converter. I have some ideas on how to fix the fuel rail layout so I'll suggest those. Changing the intake is a big deal in an EFI engine so I doubt he'll want to experiment with that.

Unless you’re duplicating a known good valve train combo....... big block weight parts, high rocker ratios, Hyd lifters and higher rpm’s can be a challenge to get sorted out.

Can you change the injection phase angle in the software? It could be fuel stand off in the intake where the fuel gets blown backwards up the intake and it acts like a rev limiter as the engine stutters because the mixture goes all to hell. When I was welding up custom intakes for rotaries, the more overlap I put into the motor, the farther away the injectors had to be away from the rotor, or in your case, cylinder. On some intakes, i could fix it with phase angle changes.

I agree. We proved to ourselves that the upper rev limit is the lifters. The lower RPM roughness appears to be manifold related. EGT values are all over the map at 2000 rpm but they smooth out at higher revs. The weird pulsing issue was due to the poor fuel rail design and the undersize fuel pressure regulator.

The injector phase table that I have in there is known good table for this type of engine. I didn't mess with it since it should work but there is always a chance that this motor wants something weird.

Did you try more valve spring? Or lighter springs/retainers. (smaller OD, titanium)

I've yet to see a loss of valve control come down to the lifter itself. JMO

I haven't read any questions to how stable fuel pressure is during a run.
Did I miss something?

Customer isn't interested in spending more money to pick up a few hundred RPM. The engine makes 740 hp at 6000 RPM which is more then he needs on the street anyway. If he decided to go racing he can switch to a solid roller.

Fair enough but certainly no need to switch to solid roller to run past 6k (or 7k).

I mean... that thing looks like an ancient holley pro-jection system? What old warehouse did you guys unearth it from? :P. Also if it's a true EFI manifold running a carb on it is going to cause fuel distribution issues as they're not designed for it. Would explain your low RPM roughness

It is the Holley MPFI kit for BB Chevy engines. It was recently discontinued so not on their website anymore. The intake manifold was an EFI version of their Strip Dominator. I'm not a fan of this kit but it is what the customer bought and brought to us to use. In the end it made decent power and worked fairly well at WOT but always ran rough at fast idle. We'll see how it works in the car. Not much we can do to fix it since I think the problem is inherent in the intake manifold and/or the fuel rail design. Could be why Holley discontinued the product.

Ah so it runs rough with the EFI on as well? Probably worth a look in the cal to see what the injector timing is and also spark advance...