Re: LOST 10mph AND ABOUT 6 TENTHS
 

I agree, grounds are most likely weak.
Run a redundant ground wire from the side of the engine block back to the battery ground. Or, if your ignition box is inside, as most are, to the ground that is common with the ignition box and battery.
Use a good size wire and a star washer under the connector at the block.
Also, if you don't have a good size ground wire from the box to the battery negative post put one in.
Grounding to the chassis is always a crap shoot in a race car and the root cause for the majority of electrical problems.
Good Luck
Chuck Gallagher

I should have said this about engine block grounding. The most important task your battery does in your race car is provide a steady, high level of amps (current) to your ignition system. Racers in all forms of motor sports have been able to make more power over the decades by putting more fuel and oxygen inside the combustion chambers and completely igniting that mixture with higher power spark across the plug gap from the coil. The power (amps) of those sparks will never be greater than the resistance of the current path from the threads (ground side of the plugs) of the spark plug back to the negative post of the battery.
A weak engine to battery ground path does not always produce engine miss, usually just incomplete combustion resulting in less power.

Re: LOST 10mph AND ABOUT 6 TENTHS
 

When I weld on my car I ALWAYS disconnect my MSD and all grounds to the engine block. Jerry Doughty from Louisiana was the racer that had to DE MAGNETIZE his stocker. Perhaps him or his brothers could jump in here on this thread. I remember it involved a compass and a cell phone ...his stocker had the same symptoms as your car....

Re: LOST 10mph AND ABOUT 6 TENTHS
 

[[/QUOTE
Jeff This car use to be fuel injected and it still has the high pressure pump in it with regulator to knock down the pressure. regulator is set at 7.5 lbs also we dyno'd the engine and it still has the same power from when it was built[/QUOTE]

If the engine ran good on the dyno , then what parts are different between the car and the dyno ? Usually the dyno has it's own ignition box and it's own fuel system . Maybe check these two systems out to start with .

Re: LOST 10mph AND ABOUT 6 TENTHS
 

Does the car have a timing retard box. I hade one go bad. I had the box checked, MSD said it was good. Hooked up box and car was slow, removed box and the car was fixed.

Re: LOST 10mph AND ABOUT 6 TENTHS
 

If the engine ran good on the dyno , then what parts are different between the car and the dyno ? Usually the dyno has it's own ignition box and it's own fuel system . Maybe check these two systems out to start with .[/QUOTE]

We took the coil and ignition box out of the car and ran it on the Dyno made good power

Re: LOST 10mph AND ABOUT 6 TENTHS
 

Thanks so much! Think we will be taking this car apart almost completely to check it all out!!

Re: LOST 10mph AND ABOUT 6 TENTHS
 

I don’t think anything was in the car when we welded but still a good thought - thank you! Nothing is a bad idea at this point!

Re: LOST 10mph AND ABOUT 6 TENTHS
 

Is this a Quadrajet motor or Holley? If it’s a q-jet I would bet money it’s in the fuel system.
It’s critical to have enough fuel volume and a q-jet on a 454 SS motor would really stress your fuel system. A good pump like a Magnafuel, a #10 line from the cell to the regulator, appropriate return line, and a # 8 line from the regulator to the carb would ne required. Even if it’s a Holley I would do the same thing.

Re: LOST 10mph AND ABOUT 6 TENTHS
 

Is the chassis still lose? Are all the wheels free, brakes bearings? What about the rear end? Could it be getting tight and slowing the car? Just something else to think about.

Lee.

Re: LOST 10mph AND ABOUT 6 TENTHS
 

To slow down that much, and not have a miss, or a bog and not blow up quickly, has me thinking the timing is backing up on it. Somehow.....We had a bad transmission last year after the filter gasket became unseated and lost .13, but our MPH never budged, and your loosing both. That's a hundred horsepower your dropping. Do your headers look like they are getting hotter than normal? Like its baking the coatings ect?