Chasing major gremlin, hope this fixes it!

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Went back to stock plug gap. ran poor. Replaced controller box and it ran a lot better! Low end is almost completely back. Decent 60' but still .1 off from normal. Loss of power up to about 5500rpm then it takes off with strong top end until next shift, then loss of power again until 5500rpm then takes off strong. Considering putting stock coils back on to see what happens. Was advised to jet up 3 numbers and see result.
 
My little 10 second bracket car slowed down about 5 months ago, and I've tried everything I can think of to identify the problem.
'70 Duster with 750hp GenIII Hemi, all motor, Pro Systems 1050 Dominator, MSD 6Hemi ignition control. Built in 2013.
Ran consistent numbers since 2014, then they started falling off drastically. Losing .1 to .2 on 60ft 1 second on ET 1/4 mile.
New valve springs. Will run smooth at 7500rpm. I usually don't run it past 7000.
Replaced/cleaned everything in the fuel system, no change.
Replaced coils/plugs/ignition controller/batteries in the electrical, no change.
Advanced/retarded timing, jetted up, jetted down, very little change.
Plugs read just about normal.
Any suggestions?? Compression check??
 
RockinRobin said:
My little 10 second bracket car slowed down about 5 months ago, and I've tried everything I can think of to identify the problem.
'70 Duster with 750hp GenIII Hemi, all motor, Pro Systems 1050 Dominator, MSD 6Hemi ignition control. Built in 2013.
Ran consistent numbers since 2014, then they started falling off drastically. Losing .1 to .2 on 60ft 1 second on ET 1/4 mile.
New valve springs. Will run smooth at 7500rpm. I usually don't run it past 7000.
Replaced/cleaned everything in the fuel system, no change.
Replaced coils/plugs/ignition controller/batteries in the electrical, no change.
Advanced/retarded timing, jetted up, jetted down, very little change.
Plugs read just about normal.
Any suggestions?? Compression check??
Click to expand...
tires and torque convertors used to do that for us . A 750 h.p. gen 2 hemi was hard to hook up back then .
 
famous bob said:
tires and torque convertors used to do that for us . A 750 h.p. gen 2 hemi was hard to hook up back then .
Click to expand...
Same brand/size tire this year as always.
PTC torque converter, could be a good suspect but they only loosen, don't they. I've never heard of one getting tighter. RPM's through the traps are lower than normal.
 
RockinRobin said:
Same brand/size tire this year as always.
PTC torque converter, could be a good suspect but they only loosen, don't they. I've never heard of one getting tighter. RPM's through the traps are lower than normal.
Click to expand...
didn`t catch that. Sounds like a leak test may be needed. bad air ???
 
Cam losing a lobe? Pull valve covers and line up tip of dial indicator in pushrod hole and check lobe lift.
 
skrews said:
Cam losing a lobe? Pull valve covers and line up tip of dial indicator in pushrod hole and check lobe lift.
Click to expand...
I would presume you would need to know what the lobe lift is supposed to be. B.E.S. racing engines Comp cam custom grind for them. No info. on cam.
 
If one int or exh lobe is different from the other respective int or exh lobes, there's a problem.
 
RockinRobin said:
Same brand/size tire this year as always.
PTC torque converter, could be a good suspect but they only loosen, don't they. I've never heard of one getting tighter. RPM's through the traps are lower than normal.
Click to expand...


I've seen many of them tighten up. They loose very little stall speed but the eat power like jack the bear.

I had a customer who killed his converter dicking around in his driveway. He lost over one second. ONE SECOND. Back on the dyno an my engine laid down the exit same numbers.

In the end, it was the converter.
 
RockinRobin said:
My little 10 second bracket car slowed down about 5 months ago, and I've tried everything I can think of to identify the problem.
'70 Duster with 750hp GenIII Hemi, all motor, Pro Systems 1050 Dominator, MSD 6Hemi ignition control. Built in 2013.
Ran consistent numbers since 2014, then they started falling off drastically. Losing .1 to .2 on 60ft 1 second on ET 1/4 mile.
New valve springs. Will run smooth at 7500rpm. I usually don't run it past 7000.
Replaced/cleaned everything in the fuel system, no change.
Replaced coils/plugs/ignition controller/batteries in the electrical, no change.
Advanced/retarded timing, jetted up, jetted down, very little change.
Plugs read just about normal.
Any suggestions?? Compression check??
Click to expand...

If its making 750 and in a Duster it should be WAY down in the 9’s. Not anywhere close to 10’s.
My old all steel 70 Duster with 300+ pound driver has been 9.60’s and made 708 horse. And that is on Mopar super stock springs. Probably would run 9.40’s if it made 750
 
UPDATE:
I noticed that the O2 sensor was on the header collector only about 12" from the end of the pipe, so I extended the exhaust it is now 24" past the O2 sensor. We'll see if that changes readings.
Pulled transmission pan. Only a little grit, no chunks.
Checked plugs. Most are normal to slightly lean. 1 on each bank is a little rich, but I have to idle back to the trailer, so this may not be accurate.
Oil filter had no chunks inside.
Compression test:
Lowest: 212 Highest 252. About a 20% difference. Average about 230.
#6 was 212, 230 with oil
#8 was 220, 230 with oil
most others didn't change much with oil, but it looks like rings are worn and it's time for a rebuild.
What do you say folks, do you agree?
 
Rings,bearings and valve job. Hone the block, gaskets where needed. That's a freshen up. It will be just like new. And should not take long. Not to much money. That's all good!
 
hangn0ut said:
Rings,bearings and valve job. Hone the block, gaskets where needed. That's a freshen up. It will be just like new. And should not take long. Not to much money. That's all good!
Click to expand...
Agreed, just hope the cam and lifters are still ok. Last time I honed a block was over 30 years ago with a drill. Do they still do these modern motors the same way?? Maybe should replace timing chain while I'm at it.
 
I would definitely get it honed by a professional. These things with thin rings and such, I would not want the hone too "gritty". Was really hoping it was something stupid simple!
 
408 swinger said:
I would definitely get it honed by a professional. These things with thin rings and such, I would not want the hone too "gritty". Was really hoping it was something stupid simple!
Click to expand...
Thanks! Turns out the motor is just a little worn out from 5 years of drag racing.
 
Lol, gives me something to look forward to. I have four years on my 426!
 
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