471 Big Block high rpm problems

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Miszny

Miszny

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Hi

I have been fighting with a problem that my car has since I got it.
The car is 1971 Plymouth Duster with 471 big block + 727 TF with manual valve body.
For ignition I have MSD 6AL with 7000rpm pill + MSD distributor.
Engine is simple combo with hydraulic cam (540/544 lift due to 1.6:1 roller rockers).
Timing is 18 initial and 36 total. I have one light silver and one light blue springs in the distributor. Full advance is at around 2300rpm.
Around 11:1 compression, I run it on premium fuel with additive.

Here is what happens:
When car is in park or neutral I can rev it all the way up to 6500 no problems.
It responds to gas pedal very quickly and starts great cold and warm.

Problems start when I drive. It seems that car is loosing power and starts sputtering/misfiring around 4500-5000 rpm on every gear. Up until this rpm range it really is quick and responsive.

Here is what I already did:
1. I swapped 911-16 Comp springs with 935DR Isky springs (I was sure mine are failing, new are a bit harder also)
2. New spark plugs (NGK with 6 heat value)
3. New spark plug wires
4. Shielded MSD wire between the ignition box and distributor
5. Checked carb tuning with AFR sensor
6. Checked carb and intake for air leaks

All these things changed nothing.
Yesterday I started backing out the distributor and checking for difference in behaviour. Turned out that when I backed it to 8 degrees initial and 26 total my problems were gone, but I could only rev it to under 6000, also felt like I lost quite some power.

H E L P, I am so frustrated by this!
Any ideas?
 
Fuel supply issue I would bet. Install an external gauge and see what happens to your pressure under load. If the pressure is good you are lean on jetting. Tell us about your carb.
 
The other possibility is rotor indexing in the cap is marginal and stops jumping spark with the retarded timing. Maybe even a bad or marginal ignition coil.
 
Yes I tried without the pill, zero change.
I also tried 3 different coils (2 MSD + one Bosch) with zero change.
 
thesiren74 said:
Msd box.
Click to expand...
How can it start good and drive up to certain rpm without problem and be faulty?
If box is bad why it revs high when i retard it? Damn if only I had anybody local that has a good box for a test...
 
Miszny said:
Yes I tried without the pill, zero change.
I also tried 3 different coils (2 MSD + one Bosch) with zero change.
Click to expand...
I bet you are going lean for one reason or another, either jetting or pump.... Maybe even sucking metering rods down or power valve closed with that much CID.
 
mguner said:
Fuel supply issue I would bet. Install an external gauge and see what happens to your pressure under load. If the pressure is good you are lean on jetting. Tell us about your carb.
Click to expand...
I have brand new Holley 125 fuel pump, I put harder spring in it, I have fuel pressure regulator and its set to 7psi.
 
Also I was checking AFR with some in exhaust sensor and and car was not lean at all. It was a bit on the reach side.
 
thesiren74 said:
Are you getting full throttle?
Click to expand...
Yes, when I drive it normally it works fine, plenty of power way low, smokes the tires under 2000 rpm. Not easy to drive legally with rpm at 5000 and more ;-)
When I am driving at like 60mph and I nail it in 2nd or 3rd I can test it.
 
What air cleaner and filter and how much hood clearance? My sixpack tried to suck the hood down till I scooped it.....
 
Was the balancer index when engine was put together??
 
Air cleaner / filter restriction will cause AFR to go rich and engine to crap out......
 
If all that check out we are back to rotor indexing in the cap. Quick check would be to swap distributors.....
 
I have K&N set with cleaner that takes air from top and sides.

Balancer was indexed by engine builder. It is forged crank with stock Mopar balancer.

Aslo I noticed one thing: When I take the air cleaner off and I rev it in park the engine sometimes dies or runs bad at high rpm.
 
mguner said:
If all that check out we are back to rotor indexing in the cap. Quick check would be to swap distributors.....
Click to expand...
Would be great to swap stuff but I am in Poland where car like mine is more exotic than Lamborghini... ;-)
I also have stock Mopar dist + chrome box + balast resistor.
Will try this setup probably next weekend if there is no progress.
 
mguner said:
If all that check out we are back to rotor indexing in the cap. Quick check would be to swap distributors.....
Click to expand...

Can I do like 0 timing advance and then turn the engine to #1 cylinder and check like that?
 
Can this problem be related to wrong camshaft instalation?
What if the cam was put there just using marks on sprockets?

My problem is zero experience, I try to learn as I go, also no people to get advice from locally.
 
0 DEGREES TDC mark on the distributor where #1 terminal is and #6. Remove the cap and see how the rotor corresponds to which ever mark it is pointing to. If it is not dead on or just a hair after you may have an issue. If it is closer to the next terminal in the firing order you may be able to get away with rewiring the cap.....
 
Some more info... Perhaps this helps?
The car was running ok when I got it, all was good but:
Someone that built this motor did not torque down the camshaft sprocket, it got loose and I was pretty lucky cause all fell apart on engine startup. All exhaust valves were damaged after. Intake valves were undamaged.

After this happened I took the heads off, then it also turned out that cam was bad (2 lobes wiped) so I got new identical cam + lifters, installed new exhaust valves. Heads were done by professional shop after it happened, and were ported and put together by the Koffels place in USA, I have full documentation with flowchart for them.
I also put new timing set and new bit harder valve springs and installed 1.6:1 Crane roller rockers... The engine was running on stock stamped valvetrain on camshaft brake in. It started right up, no problems with brake in. I put Crane rockers after. I set the valve lash to zero lash + 1/2 turn.
 
mguner said:
0 DEGREES TDC mark on the distributor where #1 terminal is and #6. Remove the cap and see how the rotor corresponds to which ever mark it is pointing to. If it is not dead on or just a hair after you may have an issue. If it is closer to the next terminal in the firing order you may be able to get away with rewiring the cap.....
Click to expand...
Will check it today and post some info.
 
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