Hello,
I am new here and really need some help. The truck has a 1971 440 with flat top forged pistons,forged crank,LY rods, lunati 509 lift cam,516 heads ported with 2.14/1.74 valves, edelbrock performer intake and a holley 800 mechanical secondaries carb.


So far I have changed plugs,wires,distributor,cap,rotor, fuel pump,carb, still starts popping at 4500 rpm no matter what I try. I have also disconnected the gas tank and ran the fuel pump from a clean container hoping it was a tank issue to no avail.
The timing is at 10 degrees advance at idle and pulling to about 35 degrees total at 3200 rpm.
Thanks in advance,
Sam

Welcome Sam. Rotor Phasing. Drill a 3/8" hole in the top flat of the dist cap 2/3 of the way between the center terminal and the #1 cap terminal and shine your timing light above the cap straight down which'll in effect freeze the rotor like a strobe light on a dance floor at idle. If the rotor tip is too far away from the underside of the cap terminal it will miss as the spark cannot jump that distance. If using vacuum advance you want to duplicate the same amt of vacuum you have when it missed as vacuum advance will shift phasing clockwise (on a big block) and at 4500 is that at WOT or highway cruise (high vacuum). under load the ign system will tolerate less distance between rotor and cap terminal before missing but checking the distance at idle will get you started. If you have a Mityvac you can pump up the vac can at idle & note where the rotor moves. If there's a problem with the fuel pump pushrod worn down it could cause a delivery issue (will it miss at 4500 in your driveway or just at speed?). Best/easiest would be to tape a round vacuum gauge (most have a psi side) to your windshield & run neoprene line to the carb INLET & see how much pressure you have at the offending speed (& LOAD). Need at least ~3-4 psi under load. Could possibly have a vacuum leak & causing a lean miss at 4500. Not sure how to check for that without a LM1 meter or similar but I myself might try installing a junk power valve that's been gutted to enrich the mixture or possibly removing it just for a quick test. Holler with any news

Thanks for the reply. Sitting in the driveway it will rev with no issues. it is only at the track that it does this. I have changed out the mechanical pump and went with a holley blue pump and regulator. I just changed the distirbutor cap and rotor today would you still think this may be a problem with them not ligning up.
I originally had an edelbrock 750 on it and then went to the bigger holley and so far everything I have changed has has no effect. I am at my whits end with it. Oh almost forgot to mention the vacuum advance is not connected at this time.
Thanks Sam

Either rotor phasing or fuel delivery. Caps and rotors are carbon copies and will not change rotor phasing. Having no vac adv makes it easier to sort out. Generally running the car up thru the gears if it is ign it will miss in all 3 gears at the same LOAD and RPM. If it's good at 4500 in 1st and 2nd then acts up in 3rd that points to fuel delivery as it takes time for the need to outstrip the delivery unless the fuel delivery system is EXTREMELY inadequate which I do not think is the case here. Whereas an ign miss will happen at the same load/rpm no matter what gear you are in. I'm thinking fuel but if need be drill the hole in the cap & check rotor phasing at idle. Ign sub issues; MAY need a rotor with a .060" longer blade NAPA Echlin MO3000 which helps some with phasing issues(& we can fix phasing directly) and check ECU ground and pickup gap but first let's pin it down to ign or fuel

I realy think it is ignition. It does it in every gear. I have never checked rotor phasing before. What exactly am I looking for. I have the cap I just took off today so I can use it so as not to damage the new one. Should I drill the existing hole larger to see or drill a new one?
Thanks Sam

Yours must have a vent hole. Not sure where it is located. You want a seperate drilled hole in the roof flat 2/3 of the way between the center terminal and the #1 plug wire terminal so you can look down & see if the rotor metal blade is pointed too far in front of or behind being dead even with the metal cap terminal around the circumference while running using the timing light

You didn't say which ignition system you are using. If it's the Mopar style with an ignition box (OEM/Orange/Chrome), try another "known" good one. I've seen a couple of the Chrysler style boxes act like rev limiters.

Not sure if other brand boxes can malfunction in a similar manner.

Do you recall if it started after you changed anything?
Always run 35* timing? Different brand fuel? Change plugs? (Oops, nevermind on the plugs!)

When I got the truck the ignition box went out the next day so I grabbed another one I knew to be good. The truck fired right up after that. I do not know if the problem was there then or not as I did not take it to the track for about a month to see what it would do.
I did just drill the cap and it looks to be firing about dead center of 1 and 8. Hopefully this helps out on figuring what I need to do next.
Oh yeah I have tried adjusting the timing up and down and it still acts the same.
Thanks Sam

The rotor tip is to the right almost perfectly between number 1 terminal and number 8 terminal.

To the right (clockwise) of #1 would be the #2 terminal & we're still missing something as it would not run if it was that far off & if the drilled hole is between the center & #1 you would not be able to see the rotor blade that far off & tell that it's in the middle unless I'm missing something.

going counter clockwise to the right when standing on the passenger side of the truck you have number one then number eight. It is pointing almost between them just slightly more to the number one side. It does not make much since to me either. Thanks for hanging in to try to help though.
Sam

Thanks, I will try that tomorrow weather permitting.

i had an engine popping/misfiring through exhaust,turns out it was a sticky exhaust valve, i added a liter of trans oil to gas tank,drove it hard and the problem was gone by 1/2 tank


just a thought

New springs with that cam?

Rotor phasing problems have plagued big blocks for decades. At one time I believe it was AndyF who machined reluctors with a number of grooves to allow lining things up right. I don't think he has any left. I haven't been aware of anyone else doing this.

R.

Yes new springs. We pulled the engine out of a drag truck that is was running great in. it only had a couple of passess on it at the time. It had an msd set up on it but I was unable to get it with the engine. Do you think I would be better off ordering an msd distributor or maybe a mopar performance one rather than messing with this distributor?
The other question I have is about the compression. I know it has flat top pistons and 516 closed chamber heads. Anyone have an educated figure on the compression? I am not sure how close to the deck the pistons come up to unfortunately.
Thanks Sam

Without knowing how far the pistons are down in the cylinder at TDC and the ccs of the heads there is no way to tell compression ratio.

That was I was afraid of. I know they are closed chamber heads with allott of porting work and bigger valves. I guess in a few months when I get ready to upgrade the cam to a roller I will find out then. I was told it was 10.7 but when I started researching the heads I found an article that I can't find now that said the combo should put me over 12.1 . I am hoping that is not right.
Sam