quote:

Originally posted by Lenny5160:
Using the 'K value' formula for torque converters, a difference of about 65 lb/ft will change the stall 300 RPM.

Yep that's it, assuming the cooler and lines flow, input shaft stator tube configuration is the same.

Plus or minus 100 rpm for differences.

Any idea what rear gear you have? What rear tires are on it? If it is slow to the 60’ this could be part of the problem

I did not see, but gas or alcohol? Are you running an in-line fuel filter? If you are running an in-line fuel filter just toss it

The real question is why is this thing down almost 100 hp?
That’s why it won’t run what you think it should. Depending on where you’re running, if your at any altitude at all, not at acto, it’s running pretty close to what I would expect a 875 hp car to run at 1950 lbs. Especially if the car has big tires or a wing on it.

Just throwing this pit there as we had a similar issue in our dragster. We had a red 7Al-3 box in the car. We had a timing retard chip that was pulling 22 degrees of timing once the brake was released. Was actually a 2 degree chip in it as we did not have a zero and juts forgot it was in there. So if you checked the timing even at a higher RPM it would read 33 degrees. Hit the brake and check it again and it was at 11 degrees. Car ran fine was just slow. Running 7.60's here in Vegas. Replaced it with a new 2 degree chip and car went 7.39 next pass. Just something to check. I was scratching my head trying to find the issue for a couple races, was just a fluke I put a timing light on it when he was warming it up on the stands and checked it after he had put it in reverse

can you post a picture of the plugs?


Joe

You've stated the wires are on correctly for a 5-7 swap. Have you verified the cam is a 5-7 swap cam?

I had the sportman 540 from shaffiroff on gas max 38 timing ran best 7.90. Changed to alcohol and added vacumn pump ran 7.75 34 degrees timing. I freshened it and bored it .100 to make it 565 same everything from shaffiroff runs 7.62 . I agree with checking the stall on convertor picked up 200 rpm after making it a 565.

FWIW I had a very similar issue when we built my hardtail didn't run anywhere near what most knowledgeable people thought it should. Went through all the stuff suggested here and continued pulling my hair out. Finally pulled the rear-end and took it to a very respected guy...turns out to be set up wrong! Had it set up correctly and car picked up 3 tenths in the eighth and was very consistent.

What intake is on this setup? And how big are the exhaust tubes? Had a 496 that was a turd until we changed the header size and intake. Still made the same HP, but accelerated drastically different after changes.

Am I the only one here that doesn't think 875HP equates to 7.70's at 170? I would expect 7.80's maybe but it would take at least 1000HP to go 7.50's at that weight of 1950. JMO.

quote:

Originally posted by bbtommyd:
Am I the only one here that doesn't think 875HP equates to 7.70's at 170? I would expect 7.80's maybe but it would take at least 1000HP to go 7.50's at that weight of 1950. JMO.

My car is about 80# lighter but it went 7.80s-90s with my 505 in it which was a little shy of 800 hp.

I'd expect the car in this thread to be going 70s-80s, and that's using my Midwest brain where actual altitude is around 1000' so it's on the slow side.