Breaking up, falling flat, pop & sputter above 5,000 rpm, & overheating

[superbee_68]

Need some help with this fresh build, having some trouble getting it all dialed in. Here is a list of pertinent info to help diagnose:

1968 Coronet Wagon
1978 low mileage 440 from a motor home, average of 110 psi compression cold
Mopar purple 509 camshaft, 248 248 @.050", .509 .509 lift w/ 1.5 rocker, 108 lsa, 2,600 to 6,000 rpm operating range
New timing chain and high volume oil pump
Mopar performance single plane intake
QFT 750 cfm double pumper, 93 octane pump gas
Aeromotive 11203 fuel pump, Aeromotive return style pressure regulator, w/ return line, 10 gallon fuel cell, 6.5 psi fuel pressure
Full length headers, off-brand flow masters that dump before the axle
440 source billet distributor, running 16 degrees advance at idle, 36 degrees total timing
MSD 6-plus w/ MSD 12 volt blaster coil
Proform electric water pump, 35 gpm, thermostat with metering valve removed, basically a gutted thermostat
Jegs aluminum radiator and electric fans
All new wiring from Painless in the car
Dakota Digital gauges
727, manual valve body, 3,500 stall
4.88 gears w/ spool, Caltraks, drag radials

Quick history, bought the car as a nearly finished project, everything listed above was in the car, it just lacked wiring (not a single wire in the car when I got it). I spent the last two months wiring the car with a painless kit, getting it running, breaking in the camshaft, and getting it ready to go down the track. Although the build may sound a bit strange using a worn out old motor, the idea was/is to dial in the car on a low horsepower motor, while building a 500 in. monster to throw in it next year. There was plenty of money spent on good parts by the PO, so I guess I can see his logic, and will continue the plan.

The car fires right up, idles great, revs quick, and is generally impressive at lower rpm's for being a worn out old junkyard motor. But I have two major issues:

The engine stops pulling around 5,000 rpm or so, spits, sputters, pops, you name it. Once you grab the next gear, all is well again until you hit around 5,000 rpm again. Rev limiter is set at 6,000 rpm. I did a plug read, full throttle pull, killed the ignition while at full throttle, coasted to a stop, and pulled a plug. The entire ceramic looked like a nice tan color, except for a small darker/black spot near the strap. Seems like the AFR is pretty dang close, if not right on. I tried going both directions, smaller and larger, on the air bleeds for the high speed circuit, and nothing changed, car still has problems above 5,000 rpm. It pulls hard until it hits around 5,000 rpm. My only guess left is that my dakota digital tach is way way off and I am hitting the rev limiter. I am picking up the tach signal from the proper plug on the front of the ignition box. Any other thoughts? It's not exactly the same rpm every time, varies by 100-200 rpm. But this dakota digital tach is real bouncy so its hard to tell. The idea was to shift at 5,600 rpm and set the rev limiter at 6,000 rpm.

I cannot keep the thing cool. I get out of driveway, make one pull on a back country road, and I have to head home in a hurry before it over-heats. The fans definitely cannot keep up at idle, the temp creeps up and up slowly, with no end in sight. Looking up the fans on Jegs website, it looks like I have around 1,400 CFM total. The water pump is rated at 35 gpm. The aluminum radiator is huge, takes up the whole opening on the car, but it was a fairly inexpensive universal radiator form JEGS. My first thought was I don't have enough fan. Before I start spending money, any suggestions?

Like always, any and all advice is greatly appreciated.

 

[Mike67]

I cant speak to your problem directly but I do know you can go into the programming of you DD setup and adjust your tach signal response speed.
Easiest way to validate is to use an electronic timing light, it will give you your true rpm...

 

[RT K_line]

Just a shot in the dark but I don't see any mention of head work. Possibly valve float if springs were not changed.

 

[superbee_68]

I remember programming the dakota digital tach response speed at the fastest refresh setting after seeing how bouncy the tach is, but it didn't seem to help at all. I may call them and ask how to get a better tach signal.

RT K_line is correct, there was no head work done at all, stock valve springs. Are there any sure ways to diagnose high rpm valve float? I hadn't even considered it! Good idea!

 

[Mike67]

Whats that cams effective range?
I would think you could hear the valves floating, clattering.
Also look at the cam info and it should give you a recomended spring.

 

[jts]

Hsad a problem with a 408 popping between 4 and 5000 that about drove me crazy. No one else figured it out for me either. picked up a hotrod mag. one day and a little article told about breather cover sitting to close to the carb. Guess what! I had changed my breather 3 months ago and that was it. Just try one time with the breather off. Might not be your problem but don't cost nothing to try. Don't remember the theroy but it leans the carb out. jts

 

[PurpleBeeper]

The tach could be off for sure (un-hook rev limiter maybe?) BUT, I have to cast my vote for valve float. At least with the old purple shaft 292/509 cam it was right on the edge between strong single springs & double springs. There's no way that cam is OK with stock valve springs, so be careful & don't drop a valve trying to dial it in. At least with some stronger springs, keepers & locks you'd be safe (& you can put those on without disassembling the motor if you run each piston to TDC and hook up a compressor to you spark plug hole... as long as your rings are at least decent).

You probably don't want to hear this, but the more I think about it I'm thinking you might want to consider pulling the heads and just get a basic valve job with some new springs/keepers/locks until you build your stroker. 4.88 gears and a 3500rpm stall makes me think you're not just running to 7/11 in the car.

 

[superbee_68]

Mike67, I had the wrong cam and specs listed in the first post, which have been updated to:

Mopar purple 509 camshaft, 248 248 @.050", .509 .509 lift w/ 1.5 rocker, 108 lsa, 2,600 to 6,000 rpm operating range.

The cam card is long gone, but it looks like Mopar Performance P3690933 is suggested, but no longer available.

 

[Mike67]

Ya, Im no engine builder but I think those stock springs might be a little light w/ that cam...when new they probably would have floated at 4800 if it is all from the same rv...
Im with everyone else change the springs, call Hughes or Mancinni they should be able to get you what you need.
Good luck

 

[coloradodave]

Hsad a problem with a 408 popping between 4 and 5000 that about drove me crazy. No one else figured it out for me either. picked up a hotrod mag. one day and a little article told about breather cover sitting to close to the carb. Guess what! I had changed my breather 3 months ago and that was it. Just try one time with the breather off. Might not be your problem but don't cost nothing to try. Don't remember the theroy but it leans the carb out. jts

Are you talking about the 'air filter'? If so, Then it is something to check...

 

[superbee_68]

You probably don't want to hear this, but the more I think about it I'm thinking you might want to consider pulling the heads and just get a basic valve job with some new springs/keepers/locks until you build your stroker. 4.88 gears and a 3500rpm stall makes me think you're not just running to 7/11 in the car.

That made me laugh! Definitely not just running to 7/11, it is street legal with wipers horn and turn signals, but will spend most of its time on the track with the current drive-train. I would rather spend the time and money on the next motor, but this one has to live until the new motor is ready. I think I could justify changing valve springs, inexpensive and easy to do. I would rather not pull the heads, a lot of work, hidden costs, and more time and effort than I want to spend on the junkyard motor. I just want some sort of "verification" that the valves are floating and I don't have another gremlin causing the issue before I start changing parts.

Here's my plan, set the rev limiter down to 4,500. That way I should for sure know what the rev limiter feels and sounds like. If I am just hitting the rev limiter, I will work on getting a better tach signal and shift sooner. If its not the rev limiter I am hitting and it's valve float, I will dial the rev limiter up 100 rpm at a time until I "hear" valve float, then back it off a few hundred. This should keep it alive until I order and install some better springs. I guess either way, the consensus is new springs are worth doing if I want this motor to live. The car is way to fun to drive the way it is right now, to sentence it to an early death over a cheap part!

Anyone have any ideas on my over heating issue?

 

[jts]

Are you talking about the 'air filter'? If so, Then it is something to check...

I had used a dropped base and it had moved the top of the air filter housing or I call it the air cleaner top down closer to the carb. I wish I could find the article but have no idea where it is now. I believe they recommended like an inch above the air horn and bowl vents. jts

 

[PurpleBeeper]

That made me laugh! Definitely not just running to 7/11, it is street legal with wipers horn and turn signals, but will spend most of its time on the track with the current drive-train. I would rather spend the time and money on the next motor, but this one has to live until the new motor is ready. I think I could justify changing valve springs, inexpensive and easy to do. I would rather not pull the heads, a lot of work, hidden costs, and more time and effort than I want to spend on the junkyard motor. I just want some sort of "verification" that the valves are floating and I don't have another gremlin causing the issue before I start changing parts.

Here's my plan, set the rev limiter down to 4,500. That way I should for sure know what the rev limiter feels and sounds like. If I am just hitting the rev limiter, I will work on getting a better tach signal and shift sooner. If its not the rev limiter I am hitting and it's valve float, I will dial the rev limiter up 100 rpm at a time until I "hear" valve float, then back it off a few hundred. This should keep it alive until I order and install some better springs. I guess either way, the consensus is new springs are worth doing if I want this motor to live. The car is way to fun to drive the way it is right now, to sentence it to an early death over a cheap part!

Anyone have any ideas on my over heating issue?

That sounds like a pretty good idea in my opinion.... good approach.

 

[BeatersRus]

was thinking on your overheating,assuming you are running new everything
fan clutch water pump thermostat and making sure your hoses have the springs so they dont collapse too.

did they Flush the motor out thru the block Freeze plugs?
cause,lemme tell yas,theres a whole Bunch of dirt casting sand and crap up inside most of these motors.
ive flushed motors 2-3 times for tens mins at a time working all the angles and still not cleared completely.
best way to do them is to dig inside there while flushing to get most out.

 

[Zeppelin264]

What ignition are you running?

Edit: NVM, MSD6al. So much text to read!

 

[Cranky]

933 or equivalent at the very least for that cam and I suspect you're hitting 5k or better pretty quick with 4.88's. Do you have good flow while watching it warm up with the radiator cap off? What's your initial and total timing? Do you know where the cam is degreed in at? With 110 psi it will most likely like a LOT of total timing.....

 

[WileE]

I gotta go with the thinking of the valve springs. Has anyone checked each and every spring pressure, both seat & at lift ?

 

[Garys1969RR]

I really think you are getting valve float, causing the motor to pop at high RPM. I had a 509 cam in my 451 with some pretty stiff springs. It always ran great, but once when doing a burn out in the water, it over revved and started popping out of the carb. I suspected valve float then. Also, most 440s with stock heads are going to stop pulling around 5000 RPM or so. The heads simply can't flow enough air at that RPM to keep up with the motors demands. Get some after market alum heads, properly set up, and then it will rev alot better. My 440 6 pack with Eddy heads, roller cam and rockers, actually has a surge in power between 5000 and 6000 RPM. I have never felt that with stock heads. The stockers just gradually fall off as you approach 5000 RPM.

 

[superbee_68]

was thinking on your overheating,assuming you are running new everything
fan clutch water pump thermostat and making sure your hoses have the springs so they dont collapse too.

did they Flush the motor out thru the block Freeze plugs?
cause,lemme tell yas,theres a whole Bunch of dirt casting sand and crap up inside most of these motors.
ive flushed motors 2-3 times for tens mins at a time working all the angles and still not cleared completely.
best way to do them is to dig inside there while flushing to get most out.

New water pump (electric), no fan clutch as they are electric fans, thermostat was new but gutted to remove the valve, hoses are the plastic corrugated style that do not collapse. Motor was flushed, but I doubt the freeze plugs were removed. I bet there is still some build in the cylinders, but the motor was not overheating the motor home when driven home from buying it.

933 or equivalent at the very least for that cam and I suspect you're hitting 5k or better pretty quick with 4.88's. Do you have good flow while watching it warm up with the radiator cap off? What's your initial and total timing? Do you know where the cam is degreed in at? With 110 psi it will most likely like a LOT of total timing.....

The flow looks ok, not a raging river or anything, but I can see a decent amount of flow through all the tubes. I wonder if I should just remove the thermostat completely?

The initial timing is set at 16 degrees advanced, and the total timing is set at 36 degrees advanced. No vacuum advance, and the advance curve on the 440 source distributor ramps up quickly. The cam is degreed straight up, just a standard timing set was used, so no advance or retard could be put in.

With 110 psi compression, what would you suspect is a safe maximum for total timing? I've always heard and read 36-38, but I am no expert.

I gotta go with the thinking of the valve springs. Has anyone checked each and every spring pressure, both seat & at lift ?

Spring pressures were never checked, motor was pulled from motor home, cam & lifters swapped, b-body oil pan & pickup, new cover gaskets, new oil pump, then dropped in the wagon. The whole process does sound unconventional but I can understand the goal the PO had in mind. I think a smaller cam or swapping the springs should have been part of the plan.

 

[WileE]

All those parts, a 509 cam, on a low compression engine, and valve springs never checked on stock heads. I don't get it.