[67Lemons]

Originally Posted by HWYSTR455

Modern Musclecar Technologies Inc appears to be using a RW dyno:

https://modern-muscle.com/products-services/tuning/

.

That’s not the same company, the one that dyno’d the car was in Texas and doesn’t seem to exist anymore. The previous owner said that his club rented the place for the day and they all brought their cars and the facility tested them but he doesn’t know the dyno used.

[67Lemons]

Really great conversation, I appreciate it if for nothing else to get a better idea of what some folks actually experienced with these cars back in the day.

I think the car runs good for what it is and appreciate the additional suggestions such as the clutch. While I don’t feel that the clutch is slipping, especially since I can’t get it to slip, anything is possible and I’ve already purchased a new clutch but haven’t had time to replace it yet.

Yes, still has the original 7K3 heads (numbers matching) and I am pretty certain that the used lifters that came with the car were from the car so I’m only assuming a cam was changed for whatever reason. It certainly doesn’t sound like a it has a camshaft more than stock IMO. I the link below is from the day I installed the new exhaust.

https://youtu.be/qRysRd31pJk?feature=shared

[Formulajones]

Originally Posted by steve25

Sounds normal .
Don’t forget that all birds carbs openings where intentionally limited to make the GM rule hold.

For example the 366 hp motor in the A body was only 345 in the F body.

It's the same engine. There is no carb limiting on mine LOL. I think people, at least anyone performance minded, caught onto that deal pretty early on back in the day.

[Tandyman]

FJ , the Net horsepower rating is flywheel HP. There are going to be significant HP loss through the the transmision and drivetrain. That means Rear Wheel HP has to be less than the Net HP . Thats what I expect to see.
Glenn

[Formulajones]

That's true in a perfect world but this stuff isnt exact. The factory ratings were fudged in a lot of cases. People with different types of dynos and depending on who's running it that day. You have correction factors based on location and weather that day. It just varys.

What I do see is a stockish 72 Pontiac 400 making 250 rwhp. That's nothing out of the ordinary from my experience tuning and dynoing this stuff.

[67Lemons]

A point brought up to me elsewhere is what size tires I’m running. With the at least 10 year old 235/60/15’s there was no issue smoking the tires, once I installed the new Cooper Cobra 255/60/15’s (27” diameter) that went away unless the clutch is dumped at 3k.

[steve25]

Well that then is flat out proof that with the Cam you have your gearing is right on the edge .

[chiphead]

With 98CC heads, I come up with 8:1 compression.

What is the base timing and total timing? 16* base and 34-36 by 2500 should add some pep. What octane do you use? Try 87, it burns faster so its like advancing the timing.

If this engine is pumping 150 PSI, it's gotta be a small cam. Can't be be larger than a 067 grind. Maybe advance the cam 2* or use a Summit 2800.

Long term, adding the TKX would be best performance improvement overall.

[Formulajones]

When these cars were new they came with a tiny tire most of the time barely measuring 26" tall. That helps tremendously getting away with a horrible effective gear ratio. People today, me included, install taller larger tires.
The problem with a stick shift is if you're already dealing with a lazy effective gear ratio like a 2.54 with 3.23's, it only gets worse with a taller tire.

Hence the suggestion to go 5 speed and even up the rear gear a smidge. With a 2.87 1st gear your low end problems go away and with a .68 overdrive you gain highway cruisability better than youve ever had before

[SD455DJ]

Quote: "I believe Cars magazine had a road test of a ’72 lemans GT with the L78 400, M-20 4-speed trans and a 3.55 Safety Track rear end and they got it down to 14.40’s at 99 mph in quarter mile tests. Now surely they could be exaggerated times, or a super-tuned example, who knows."

Here is the article from the SS&DI March 1972 issue...14.37 at 98.04 mph!

Dennis

[TXSTARFIRE]

Pretty impressive!

[Lee]

In the late 90's I worked on a '72 GTO. 400 with the 3-speed Dearborn manual trans. Totally stock, well maintained, original owner (he traded his rust-bucket '65 GTO in, to buy the '72).

He wanted a baseline, so we took it to the dragstrip. Best runs were in the 15.7's, on skinny whitewall tires.

I did a lot of work on it, but the car went straight to the body shop as soon as I finished. Body shop turned into a horror story, and it was years before the car ever got back on the road. I never got to take it back to the track.