I have a problem with a relatively fresh engine that is driving me nuts. I hope someone can help with things I haven’t thought of checking.

The problem is a high RPM breakup. It acts just like you are hitting a rev limiter. I have seen valve float on other engines act a lot like this as well. In first gear it pulls very hard until about 5500 to 6000 RPM when it very suddenly starts sputtering and just won’t gain any more RPM. The moment you shift to second it is pulling hard again until about the same RPM.

The engine is a 451. (400 block with a 440 crank.) The engine was in a ‘Cuda I bought a few years ago. It was supposedly fresh at that time and should have had less than 1000 miles on it. I never noticed this problem while the engine was in the ‘Cuda, but it may have been there since I didn’t drive it much before removing it.

When I pulled the heads and a couple of bearing caps the engine did appear to be fairly fresh and looked very good internally. I found damage to the underside of one of the rocker arms that looked like a pushrod had bent and popped off the rocker stud and jammed under the rocker arm. However the pushrods that were in the engine showed no sign of damage. The pushrods were about 1/8 inch too short. I also found damage to one of the hydraulic roller lifters. It appeared that the bottom keeper was broken. Probably from the former pushrod failure.

I replaced all the lifters and pushrods, getting the correct length pushrods this time. I had the Edelbrock Performer RPM heads cleaned up with a valve job and a .005 plaining. I also had the machine shop check the spring pressures both open and closed as well as coil bind. The cam is a Crane 68953 hydraulic roller with 230 and 236 duration with .563 and .574 lift. The spring pressures were right on the money for what the cam card called for. My lift numbers are based on 1.6 ratio rocker arms and the machine shop said I had anywhere from .050 to .060 remaining before coil bind. I am not sure if the rockers arms are 1.5 or 1.6, but wanted to be safe.

Comp Cams said they think I could be binding the valve springs. They said they thought that I should have at least .100 left over after max valve lift. Actually I may be close to that if the rockers are 1.5 ratio. Also I don’t know if the cam is advanced or not. Comp said a 4* cam advance could cause the same problem.

I am using a stock Mopar electronic distributor that I recurved to be all in by 2000 RPM. Total advance with no vacuum advance is set at 35*. I have replaced every component in the ignition system including the distributor’s electronic pickup. I am using a chrome Mopar Performance coil, MSD wires, a chrome 8000 RPM ECU and a .8 ohm resistor. The plugs have been changed and looked very good. They appear to be the right heat range and the only problem I noticed was a little wetness on 5 out of the 8 of them. Probably from thrashing it shortly before the plug change.

I am carburated with a Holley 850 double pumper. The floats are right on the money and the fuel pressure at idle is 7 pounds. The pressure when it breaks up is 5 pounds. The pressure when pulling all of second gear is 4.5 pounds.

The heads are Edelbrock 60929’s with 2.14 and 1.81 valves. Compression ratio is 10.08 to 1. The intake is an Edelbrock Performer RPM. The headers are Hooker Competition. Power output should be approaching 600 HP and feels like it under 5500 RPM.

Got any ideas?

I have an old cap I can put a hole in and check rotor phasing with. Since all mechanical advance is in by 2000 RPM, that should be easy to look at. I have never tried free revving it to 6K and really don’t want to.

Why do you suggest different timings? As the engine went back together I did check that the 0* mark was actually at TDC. The balancer is a good fluid aftermarket one. For a while I did have the advance set at a total of about 40* and there was no difference as far as the problem goes. In fact it may have had more power when I had it set like that. I was running 93 octane pump gas and am now running 110 octane fuel.

Chris, i would suspect fuel, if its dropping below 5 lbs. that could cause a problem, on a stock engine you prob. wouldn't notice anything, but a race engine @ high RPMs will not like this, i had my pressure set @ 7 lbs. on my 451, from beggining to the end of the 1/4 mile it stayed "rock" steady at 7 lbs., you need to fix this problem, i'll bet it runs great after that.

OK, I ran a test using an old distributor cap with a hole drilled in it and a timing light. With the vacuum advance disconnected the rotor phasing was absolutely perfect. Connecting the vacuum advance put it off by about the width of the rotor contact tip, but of course that goes away under wide open throttle.

I found that the distributor is installed 180* off. #1 is at the bottom not the top. I don’t see this as a problem as long as the rotor lines up, the timing is correct and the plug wires are landed appropriately.

I tried free revving the engine in neutral and found that a slight miss starts at about 4300 RPM and gets worse the higher you go. I didn’t rev past 5000 RPM though. I realize that free revving is a poor test of anything and the miss I felt may just be because there is no load on the engine. Under a load it does not miss at all and pulls very hard then I hit that non existent rev limiter and it flat stops gaining RPM. I would think that fuel pressure would not be an issue when free revving since there is no engine load and no real fuel demand.

I am pulling my hair out. Does anyone have any other ideas?

Are you running any kind of rev limiter on the car? I just figured out, after many hours of pulling my hair out and sending my entire ignition system off to Don Gould, that my AutoMeter Sport Comp II tach is off by 600rpms...Only in the upper range...Autometer comfirmed that the tachs are calibrated at several points throughout the travel and is entirely possible to have the top end out of wack and the bottom (idle) reading correctly.
My car felt the same way...I was actually hitting the rev limiter, but the tack had me fooled into thinking the car wouldn't rev up enought to hit my predetermined rev limiter on the MSD unit. The tack was BRAND NEW.

No Rev limiter. The ignition is all Mopar Performance replacement stuff. I just wired in another tach to verify the one in the dash, but at least through 5000 RPM or so they read the same. It is raining here and I can’t get on the street to test the tach under a load, but I don’t see why it would be different.

Comp Cams thinks valve issues. Either the cam is advanced too far or the springs are binding. I can’t easily verify cam advance and didn’t check it when the engine was apart. I also can’t easily verify coil bind beyond what the machine shop told me.

Other friends think it has to be ignition. However I have replaced everything and even disconnected the tach just in case it was loading the negative side of the coil.

Another source says fuel supply. I have run a carburetor out of gas before and it doesn’t recover instantly when you shift to second gear like this does. Also I have a 700+ HP street Hemi in another car and I run the regulator at 5.5 PSI to a pair of Edelbrocks with no issues to 7500 RPM.

Please keep the suggestions coming. I will try anything at this point.

Had the same exact problem with a Road runner I built a few years back.It started missing about 55oo shift to 2nd and would start pulling hard again.I tore the whole car apart trying to find the problem,sent off the ignition system to MSD came back good.Did all the fuel system checks,tried diferent carbs,same results.Pulled my hair for half a season then finally went ahead and changed valve springs,even though they were new and to my suprise it cured the problem.

reluctor gap (.005") EDIT long shot, might cut another hole in the junk cap in the side & check the clearance between the rotor blade tip & the terminal on the underside of the cap. Might sub in another set of plugs

Don't know what you are running for compression, but you might try closing the plug gap to .025 - .030 just to see if that helps. If it does, you don't have enough secondary voltage to light the plugs at higher cylinder pressures. Might wanna make sure you are running the correct voltage to the ignition primary side also. Assume you ohm checked the wires ( should be under 2000 ohms ) and they are good?

Did you check the distributor of play in the top bushing??? What jets and power valves in that 850.
I hope it does not have those little in line fuel filters at the carb??

do you have adjustable rockers??

What type of oil system do you have? How many qts? Big pump?

Wow, what a nice set of responses. Here are the answers to all the questions.

I haven’t done anything with the valve springs beyond the machine shop checking the pressures when the heads were off. I was holding off on that until the easier items are looked at.

The reluctor gap is set to .008 like the book shows. I did try a new set of plugs. I changed from Autolite to Champion as well. I have had several different brands of cap and rotor on it and all acted the same.

Compression ratio is 10.08 to 1. The plug wires are MSD and when I checked resistance the longest one was about 200 ohms. These wires are supposed to have 45 ohms per foot and all came out very close to that. I did check the supply voltage to the coil resistor while driving by running a wire into the car and it stayed solid at a little over 14 volts.

The distributor does not seem to have any excessive play. I have not had the carburetor apart yet so I don’t know how it is jetted and what power valve is in it. It does not have the composite fuel filters at the inlets. I have one Earls filter in line and have also tried bypassing it with no effect.

Yes, I have adjustable rockers. Lash is set at 0 plus ¼ turn. Also the valve train is quiet and I have decent vacuum.

The oil pump is a regular high performance one running about 50 to 60 lbs. The pan is a Mopar 6 quart and I also have a windage tray sandwiched between the pan and the block.

The next thing I think I am going to try is to bypass the coil resistor completely. This should bump up the spark energy substantially. I know I can’t run it that way for long, but it should prove to be a valuable test of weather or not I have sufficient spark voltage. The miss I saw just starting when free revving it to 4500 RPM is beginning to make me suspect the valve train.

Chris, make sure the ECU is grounded "good", i would run a spare ground wire just for it, it still sounds like an ignition problem, but my next guess would be the valve springs, seeing it still breaks up standing still, i'll say its not the fuel now, unless its falling to 0.

The reason I had asked about the oil pan size and pump volume was I had a simular problem with mine. As it turned out, I had to change from a 402 pan 4 qt to a 6pk/hemi 6 qt. It solved my popping problem. Not enough oil supply to the lifters. with a hv pump and 4 qt stock pan. Engine goes 6200 rpms again with no issues now

You sure your getting the pre load right?? seen many push down till they fell resistance but that can be .100 down if the lifters did not load completely or pumps down a bit as you turn it over.
The visually method making sure the plunger is coming up to the wire stop is the best way!
Here is what I would try. back all the adjusters off 1 turn if they are still quiet go 1/2 turn at a time after that till it ticks then go back 1/2 turn.
NEXT
This is time consuming but after you may want to do one at a time. (or pull the intake! LOL)))
It sure sounds to me like pump up valve float???
Hard to hear good from hear though!!!

The gas filters I'm talking about are in the carb behind the big nuts on some holleys and they are notorious for clogging up
these baby's most people now pull them and toss them??
http://www.summitracing.com/parts/HLY-162-500/

More great ideas. I will try them all.

joedust451, I believe the ECU is well grounded. At least I know the bolts are tight and it is chrome plated, not painted, so it should be. I’ll check for voltage between it’s housing and the battery’s negative post while the engine is running just to be sure the ground is making it all the way there. I’ll also check resistance between the same two points with the engine off.

Alyerpal2, I could throw another quart of oil in it, but I have watched the oil pressure gauge and it sits rock solid at 60 lbs or so regardless of RPM.

Dodgem, You have given me an idea. Maybe when I test this weekend I will record what it sounds like and post it here. Valves are where I am heading next. I just spoke with the machine shop that did the heads and they suggested I set the lifters at 0 lash hot. They believe this would eliminate any possible pump up issues. As far as method, I think I will back them all off until they are loose and then wait an hour or so for them to bleed up, if they will? I normally roll the pushrod between my fingers while tightening the adjuster until I feel resistance. That should be 0 lash. These were set by putting #1 at TDC and then adjusting the #2 intake and #8 exhaust, etc. When I adjust them this time I think I will use the #1 intake at full lift then adjust the #6 intake method.

Dodgem, I do not use the composite brass fuel filters you are referring to.