410 LA small block will not rev past 6000

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FastMatt

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Hello all,

I have a 1972 Demon 4 speed, 3.91 gears, with a LA 410 CID stroker, it's 12.3-1 Comp, Ported Eddy heads with 2.055" intake valves, Hughes 242/246 @0.050 cam with 0.587/0.592 lift with Hughes 1.6 shaft rockers, Hughes PN 1129 springs installed with 145# closed pressure and 360# open pressure. Eddy Performer RPM intake port-matched, TTI Step headers with dual 3" exhaust with X pipe and a Gen 1 FAST EZ EFI, FBO Limiter plate in the Dizzy running 20 deg initial advance with 30 deg total. I built this motor about 7 years ago and it has never wanted to rev past 6000rpm I always thought it was a problem with the old Mallary High Fire 6 that was on it (rev limiter set to 7000 in both the High fire and in the EZ EFI). The car Dynoed 416 RWHP and 475 RWTQ so it has always been allot of fun to drive. But I finally got a wild hair and removed the High-fire 6 and installed a NEW FBO box and new coil, and the car idles better on the FBO and seems to have better throttle response but still 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. Anybody have experience with a set-up like this with a problem reving? Could be valve float? Performer RPM just cant flow enough? Not Enough cam? I have thought about going to a solid roller the lighter solid lifters may kill 2 birds with one stone...

I know the A/F is kind of all over the place but the old EZ EFI only allows 3 Target A/F , Idle, WOT, and Cruise. No provisions for A/F based on RPM it just tries to reach the target A/F at WOT does not seems to do the best job of it... WOT set to 12.8-1 A/F...

Any help will be appreciated

Demondyno.jpeg
 
Two things come to mind for this issue. While there could be others, y questions are;

Are the valves springs installed at the correct height with enough pressure?

Are you sure the valve train is right on the geometry?
 
rumblefish360 said:
Two things come to mind for this issue. While there could be others, y questions are;

Are the valves springs installed at the correct height with enough pressure?

Are you sure the valve train is right on the geometry?
Click to expand...

The Springs were shimmed to get the pressures Hughes called for 145# closed and 350# open (at 0.550 lift) they were very close to those numbers. I could always throw some more shim under them to get some more pressure that would not be too hard to do, the cam only has 592 max lift on the Exhaust side so coil bind should not be a problem Coil bind not till .750".

The lifter preload was measured and set to what Hughes recommended.
 
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Ok, first off, what happened to the Mallory ignition?

Aside from that, you have 410 inches, your heads are undersized and your cam is way too small. I’m surprised it will run to 6k. It’s out of air.

Do you have graphs of torque and HP? If so, can you post them up??

I’ll run some cam numbers off of it if you do. That should be fun. And interesting.

Ok, I see the graph. It doesn’t have RPM on it. We need that RPM.
 
Most likely the lifters giving up. Just a guess, it's going to give up around that RPM anyways.

IIRC, Hughes puts a bunch of preload on the hyd lifters. I never set stuff that will see that RPM at more than 1/4 turn, most of the time, 1/8 turn
 
I vote lifters too.

Dave likes a bunch of spring pressure for his cams and if you set them up like he recommends, along with the fast rate cam, todays lifters usually cannot keep up.

Tossing in some solid lifters and see if that makes a difference.
 
Newbomb Turk said:
Ok, first off, what happened to the Mallory ignition?

Aside from that, you have 410 inches, your heads are undersized and your cam is way too small. I’m surprised it will run to 6k. It’s out of air.

Do you have graphs of torque and HP? If so, can you post them up??

I’ll run some cam numbers off of it if you do. That should be fun. And interesting.

Ok, I see the graph. It doesn’t have RPM on it. We need that RPM.
Click to expand...

I was afraid the cam was too small. But it does make me feel better thinking it may just be out of cam and not something "wrong". The car is a blast to drive, makes allot of lo end.

We did the best we could with those Eddy heads porting them and the larger intake valves, at the time was not many choices that I could find. I see Trick flow has heads now, I have always had very good luck with trick flow on other applications. Are the trick flows currently the best option for small block Mopar?

Ya the Dyno print out is in MPH, I could always dyne it again. I could also calculate the RPM off of Tiresize/Gear but it would not be exact because of tire growth, and when strapped to a dyne they get squashed down anyway.
 
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Using your numbers you’ve posted here’s what I get for cam numbers. This is assuming you want peak power at 6000 and peak torque at 4000.

This is just what you need to make power to 6k.

266
281
107
104

I’ll run the numbers for what you’d need for cam timing if you want to make power to 7k.
 
crackedback said:
Most likely the lifters giving up. Just a guess, it's going to give up around that RPM anyways.

IIRC, Hughes puts a bunch of preload on the hyd lifters. I never set stuff that will see that RPM at more than 1/4 turn, most of the time, 1/8 turn
Click to expand...

Ya I thought 0.080-0.095 seemed like allot. That would be easy to back off some and test, good idea. Thanks
 
Newbomb Turk said:
Using your numbers you’ve posted here’s what I get for cam numbers. This is assuming you want peak power at 6000 and peak torque at 4000.

This is just what you need to make power to 6k.

266
281
107
104

I’ll run the numbers for what you’d need for cam timing if you want to make power to 7k.
Click to expand...
wow that's a big cam! Not sure that will work with the EZ EFI, thy don't like to work well with very little vacuum.
 
FastMatt said:
wow that's a big cam! Not sure that will work with the EZ EFI, thy don't like to work well with very little vacuum.
Click to expand...


Damn. I forgot about that and my math doesn’t account for that. I don’t know if one that does.

For S&G’s I ran your engine again but this time to 7k. This is what my math says.

269
284

109
107

And to get lobes like that somewhat reliable you’d need to be in the high .6xx to low .7xx lift range.

I agree it would piss off your EFI.
 
crackedback said:
Most likely the lifters giving up. Just a guess, it's going to give up around that RPM anyways.

IIRC, Hughes puts a bunch of preload on the hyd lifters. I never set stuff that will see that RPM at more than 1/4 turn, most of the time, 1/8 turn
Click to expand...
Yep the valvetrain is starting to get pissed off starting at 5800. Fast rate cams and hydraulic lifters are an evil match.
A lazy lobe is better for revving with a hydraulic.
 
Isn't he gonna need a lot more cylinder head ?

410 x 7000 rpm / 1,100,000 = 2.61" ish minimum csa

410 x 7000 rpm x 0.0009785 / 8 = 351 cfm

472tq x 7000 rpm / 5252 = 630 hp
509tq x 7000 rpm / 5252 = 679 hp

Guesstimated tq at peak hp (7000 rpm)
(410 x 1.28 tq:cid x 90% = 472 tq @ 7000 rpm)
(410 x 1.38 tq:cid x 90% = 509 tq @ 7000 rpm)
 
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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?
 
on our stockers , we run zero lash with hyd lifters, also run anti pump up style, our engines will run to 7500 rpm, cam is 262 .265 duration at .050. lobes are very aggressive . just food for thought, btw , springs are 140 seat and 360 open
 
The dramatic drop off at 6k suggests valvetrain [ control ] or ign. Ign is 'external', so a lot easier to check out. Is the ign box getting the reqd voltage?
If you have another dist, I would try that. Are you running a rev limiter? If so, I would disconnect it; & I would try another ECU & coil, third time lucky.....

Valve train. I do not think you need another cam. 1.6 rockers require more spring than 1.5 rockers. You could try some solid lifters, lashed at 0.006-8" hot [ & make them permanent ] . Your current hyd lifters may be bleeding down [ oil aeration ] or pumping up. Unfortunately troubleshooting the valvetrain may entail spending some $$$ unless you are lucky enough to have parts laying around....
 
Won’t rev past 6000? Dang I guess you’re just gonna have to send that thing to me and start over…
Don’t worry, I’ll cover the shipping on it.
 
Most Mopar and aftermarket ECU's start to breakup at 5500/6000 RPM just FYI

ecu chart 2.png


ecu III.png


ecuII.jpg
 
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With those heads and 4 inch crank I don't think they can flow enough air to make power over 6,000 rpm. My two cents.
 
I’m going with it being a lifter issue.

When the power curve falls off a cliff and the engine runs into the wall………it’s never the flow capability of the heads.

Here’s a 410” pump gas street engine.
10:1, rpm heads with minor bowl and pinch work(flow 265-ish).
Held the power well past its 5900 peak, and finally dropped off when the rev limiter kicked in.

Without the rev limiter intervening, with the lobes that were used on that cam, the curve wouldn’t likely have nosed over until the springs allowed the valvetrain to get out of control, which should have been close to 7k.

Sure, the power would be tapering off before 7k, but that’s not the same as what I’m seeing with the OP’s graph.



IMG_1543.jpeg
 
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I second the “if the head work was done well” the heads are not the reason. If the cam will do it (I have no idea) my guess is the lifters giving up or ignition
 
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