410 LA small block will not rev past 6000

[PRH]

Here’s a 416 bracket race combo with mild ported RPMs(270-ish).
Longer duration old school Chevy lifter SFT cam(easy on parts), and higher CR.
Notice how the power just tapers off at the top end.
That’s what running out of air looks like…….. as the VE numbers are falling pretty quickly.

 

[pittsburghracer]

Here’s a 416 bracket race combo with mild ported RPMs(270-ish).
Longer duration old school Chevy lifter SFT cam(easy on parts), and higher CR.
Notice how the power just tapers off at the top end.
That’s what running out of air looks like…….. as the VE numbers are falling pretty quickly.

View attachment 1716266353

Gradual up, plateau, gradual down. Can’t beat that.

 

[rumblefish360]

Don’t shim the valve springs. Your set up. Rocker to pushrod angle and valve tip placement and travel are next.

I was thinking lifters next if it’s a hydraulic.

Then the actual port flow of the head because i mimic what is said above. Very possible the head is undersized.

I think the intake is fine for the application. Ported or a single plane should deliver a few more rpm. The dyno graph crash is weird.

 

[273]

I have a 1972 Demon 4 speed, 3.91 gears,

* Edit 5252 rpm don't happen at 88 mph cause hp and tq are scaled different on this graph so this is all wrong.


90 mph obviously pretty much equals 5252 rpms, 90 x 336 x 3.91 / 5252 = 22.5" now I don't know why it comes out to a 22.5" inch tire, low air pressure, I did it wrong ?

But at a 113 with a 22.5" tire I'm getting 6598 rpms = 113 x 336 x 3.91 / 22.5"

View attachment 1716266187

 

[rumblefish360]

Ok, my dumb *** did not catch that this is a hydraulic cam. I don’t go over 240 at .050 with hydraulic lifters.

It may be the valve train going out of control.

Going back to post 2 where @rumblefish360 asked about rocker geometry. What do you have for rocker arms and what ratio?

Exactly, also the pushrod length which I forgot to type in before.

I can see where the engine is rpm and power limited by a 6K “Crash” is a little concerning.

 

[fishmens67]

I'd bet if a solid lifter cam is installed the problem will be resolved, providing the springs are up to snuff.
In the late 70's before I went solid had a few engines that would stand still above 6.
That's when I found a solid lifter could be used on a hydraulic shaft.

 

[273]

* Edit 5252 rpm don't happen at 88 mph cause hp and tq are scaled different on this graph so this is all wrong.



In 3rd gear with 3.91 I get a 29.5" tire @ 88 mph (zoomed in about 88 = 5252 rpm)

113 x 5.24 x 336 / 29.5" = 6744 rpm

Unless I'm totally wrong about something that dyno graph is showing your pulling past 6000 rpms.



*Edit, even if I take gears and tires out of the equation, (113 mph / 88 mph) 5252 = 6744 rpms.

 

[PRH]

By the looks of the graph, I would expect it’s pretty easy to determine when the power really drops off while driving the vehicle.

When it reaches the unhappy zone…….look at the tac.

If its a valvetrain problem, by the time it’s really nosed over hard………you’re usually about 3-400rpm past where the issue started.

Edit-I guess this was never really established………

At what point on the graph was the throttle closed, and what rpm was that?

Personally, I hate trying to diagnose potential engine problems from chassis dyno results, especially when there is a high stall converter in the car.

 

[Ceedawg]

Might be apples to oranges but my 383 with hy 509 cam would go over 7000 rpm, with zero lash and anti pump up lifters. Then I installed same cam, lifters and springs in a 440, dies at 5000. Haven’t figured that out yet.

 

[273]

Well if you look at 112 mph the dyno graph is showing about 400 hp and 360 tq if I'm reading it right.

400 hp x 5252 / 360 tq = 5836 rpms and a couple of mph above that it drops off. So 6000 rpms does seem to be the end of the road.


I now get why 5252 don't happen at 88 mph, cause the torque and hp are scaled different so even though they cross at 88 mph there not the same hp/tq amounts there.

 

[273]

Well if around 114 mph is 6000 rpm peak hp should be around 5252 rpm (100 mph) and peak tq should be around 3950 rpms (75 mph). Should this engine really be pulling hard a 1000 rpms above peak ? Is it breaking up at 6000 rpms or did they just let off the throttle ?

Edit* There actually looks to be a peak hp spike around 94 mph about 5000 rpms.

 

[PRH]

If the car has a high stall converter in it, the chassis dyno curve often looks nothing like the engine dyno curve.

For example, if the engine makes peak TQ at 3800, but the converter stall is 4800, the highest TQ number will be at the bottom of the chassis dyno curve……which will start at the stall speed, which is 4800 in this example.

I’ve seen dyno sheets from inertia chassis dynos where the shape of the curve doesn’t even remotely look like engines power curve.

 

[273]

If the car has a high stall converter in it, the chassis dyno curve often looks nothing like the engine dyno curve.

For example, if the engine makes peak TQ at 3800, but the converter stall is 4800, the highest TQ number will be at the bottom of the chassis dyno curve……which will start at the stall speed, which is 4800 in this example.

Agreed, But He said was a 4 gear car.

 

[PRH]

I didn’t catch the 4 speed info.

I re-read the OP.

I built this motor about 7 years ago and it has never wanted to rev past 6000rpm……….

falls on its face at 6000 rpm.
Attached is the Dyno Chart, you can see it droppes off hard like it's hitting a rev limiter.

It would seem as though since it’s been together for 7 years……he’d have a pretty good handle on the engines behavior.

I don’t know what it is, but I’m quite confident it’s not anything to do with the head flow on his build.

 

[273]

The dyno graph list peak hp as 416 hp @ 93.75 mph and best I can see tq is 455 @ that mph and peak tq is 475 tq @ 77.78 mph and hp looks to be about 360.

416 hp x 5252 / 455 = 4800 rpm
360 hp x 5252 / 475 = 3980 rpm

So 416 hp @ 4800 rpm and 475 tq @ 3980 rpm.

4800 hp peak is pretty low but it seem like it's a short peaky spike there for whatever reason, around the 100 mph point seems like a second hp peak broader more sustained at around 5200 rpms still way short of 6000 rpms.

 

[fishmens67]

but I’m quite confident it’s not anything to do with the head flow on his build.

So am I. There is enough cam to overcome a head flow issue at 6000 rpm.

 

[PRH]

The description of the problem sounds like every Hyd cammed engine I’ve tested that experienced lifter woes before the rest of the combo gave up.

Like this one(that really wasn’t happy trying for 6k):

 

[Newbomb Turk]

I didn’t catch the 4 speed info.

I re-read the OP.





It would seem as though since it’s been together for 7 years……he’d have a pretty good handle on the engines behavior.

I don’t know what it is, but I’m quite confident it’s not anything to do with the head flow on his build.

Yeah, I originally said head limits but that was before I figured out it's a hydraulic lifter.

I haven't messed with any hydraulic stuff since the early 2000's but back then, to get any RPM out of them we went to 20w50 oil and bigger pushrods and that was good for some RPM.

At this point I think they started going the other way...lighter oils. I don't pay much attention to hydraulic anything any more.

 

[PRH]

20+ years ago we chased our tales looking for more rpm out of my friends Stocker.
Adding spring pressure did nothing…….. in fact it seemed like when things went in the crapper, it happened more abruptly.

We were trying different cams from different suppliers, different ramp rates, etc……. Without success.
It was good till about 6k, but we really needed another 500rpm to get the car thru the finish line clean.

At that point, I was pretty sure the lobe designs and springs weren’t the issue.
So, we tested Hyd lifters vs solid lifters on the dyno.
Poof……with the solids, the engine would run to 7k no problem.

 

[273]

Yeah, I originally said head limits but that was before I figured out it's a hydraulic lifter.

I haven't messed with any hydraulic stuff since the early 2000's but back then, to get any RPM out of them we went to 20w50 oil and bigger pushrods and that was good for some RPM.

At this point I think they started going the other way...lighter oils. I don't pay much attention to hydraulic anything any more.

Maybe At the end there above 112 mph (around 6000 rpms),

But the engine hp is peaking at 94 mph (around 4800 rpms and 2nd peak around 101 mph (5200 ish) and pretty flat to 110-112 mph. Isn't that an issue that this engine hp peaks so low, and would it be an hydraulic issue at those low rpms?

To me it looks like their just letting off the gas around 112 mph maybe there's a slight issue just before they do.

 

[PRH]

I have no doubt, that on an engine dyno………with solid lifters in the engine, the OP’s engine wouldn’t produce a dyno sheet that had the curve nose diving at 6k.
Would the curves trajectory be heading downward? Possibly……..but not straight down.
And more importantly……….you’d never feel it lay over at 6k(if…….the lifters are in fact the culprit) in the seat of your pants.

That might even be possible with the “best of the best” HR lifters.

 

[273]

I have no doubt, that on an engine dyno………with solid lifters in the engine, the OP’s engine wouldn’t produce a dyno sheet that had the curve nose diving at 6k.

That might even be possible with the “best of the best” HR lifters.

But is it a nose dive ? @ 112 mph the engine is pulling strong, about 20 mph passed engines peak hp (94 mph), at 116 mph it's definitely off the gas.

So by 112 is still pulling, between 112-114 there's a slight drop could be valve float etc.. At 114 it drops a 150 lbs-ft instantly (valve float ? letting off throttle ?) then by 116 there definitely off the throttle.

 

[PRH]

I’m giving the owner the benefit of the doubt that after driving the car for 7 years…….he knows how the engine feels/behaves.

My 383 made peak power at around 62-6300, and was down a solid 20+Hp by 7k.

From the drivers seat that thing would rip right up to 7k like nothing.

 

[273]

Not saying there ain't any valve float quite possible but if it is it's at the end of this engines power curve anyways, and maybe he saying it won't rev instead of saying it done by 6000 rpm. Maybe it's both.
Where this engine peaks it's obviously far from a revver anyways.

 

[273]

I’m giving the owner the benefit of the doubt that after driving the car for 7 years…….he knows how the engine feels/behaves.

My 383 made peak power at around 62-6300, and was down a solid 20+Hp by 7k.

From the drivers seat that thing would rip right up to 7k like nothing.

But according to the dyno graph he provided it's hp peaking around 4800 rpm 2nd peak around 5200 so if it pulled to 6000 rpm that's similar to the 383 pulled vs peak hp rpms.