Drivetrain/Brake Issue?

[MOPARJ]

My buddy has a 72 Dart with a very similar motor as mine (318, xe268 cam, edelbrock 600 cfm carb, headers, 2.5" exhaust, flowmasters, MP dizzy, 3.21 gear [open], 2500 stall). It runs near to the same times that I do in my duster, which would be mid to high 14s usually.

When trying to do a burnout, he will stand on the brakes and bring the revs up. Once it reaches 2500 rpm, it will not rev higher, or spin the tires. When letting go of the brakes slightly, it still will not let the tires spin.

There should still be around 320-330 ft lbs of torque with this motor and it makes great power, even if the cam is a bit aggressive, so something should still be happening. Timing is set at 16 degrees initial and the motor runs flawlessly and efficiently.

Could the drums brakes in the rear be too tight, or is the open diff more of the issue?

 

[MOPARJ]

I should also mention that I think he said that it had 235/70/15 tires in the rear.

 

[rumblefish360]

Tires a bit tall. The engine sounds tired.

 

[MOPARJ]

Motor is fresh, only 15K. All vitals are great. Pulls hard.

The tc is a Hughes 2500, with 1000 miles.

 

[1968FormulaS340]

Im not sure i see a problem here. Zero wheel spin = all the power is going to the ground like is should be.

Also 235-70-15s are tall at 28" (much taller than stock).

Have him go to a 215-65-15 that will be closer to stock height. His car will probably be faster and be able to do a burn out when wanted.

 

[moper]

IMO, it should turn tire easilly. A similar 318 in a customer's car with a sure grip 3.23 rear and larger tires will spin all the way thru first. It wont carry far into 2nd but its a 318...lol. I believe his car went low 14s too. IMO, it's probably a combination of brakes and running/tune up. There are a million different opinions on "it runs good". I have several friends who accept "good" that I wouldn't...lol.

 

[rumblefish360]

Also 235-70-15s are tall at 28" (much taller than stock).

Have him go to a 215-65-15 that will be closer to stock height. His car will probably be faster and be able to do a burn out when wanted.

I agree here. Is that cam installed correctly. AKA, degreeded in?
Advance the timing could very well help. Limit the total to 52* and vacuum to 34 - + or - 2*

 

[MOPARJ]

Its a good runner. It lopes a bit more compared to mine with the same cam, except I am running a Holley, so I wonder if it is too rich. I have driven it and it feels just as strong as the same setup in my Duster, so I am a bit perplexed.

The cam is set up just like mine, staight up.

 

[moper]

Two "identical" engines can be worlds apart in quality and output with identical parts. Never mind the tuning as you mention. If he's happy. It doesnt matter. If he's not, there is room to improve IMO.

 

[MOPARJ]

Two "identical" engines can be worlds apart in quality and output with identical parts. Never mind the tuning as you mention. If he's happy. It doesnt matter. If he's not, there is room to improve IMO.

Im going to do some tuning on it for him, like check and adjust timing, but I think most of it is coming from the large tires.


I will say that upon driving the car myself, it performs extremely well. It makes every bit the power of a stock 340, probably 270-280 hp, 320-330 torque. Its a little soft until 2800, but pulls HARD up to 5500.