Factory 402cid Dyno Sheet

[davepl]

Figured this might be of interest to some. This is the dyno sheet from my rebuilt 402 (engine dyno, not chassis). The original 310hp cam doesn't seem to be available anymore, so we used one that had almost the exact same specs. Other than that it's totally stock down to the ugly low-rise manifold. That's one ugly manifold, why they'd use a low-rise manifold like that on a truck with a foot of hood clearance is beyond me, but its the original so I kept it like everything else.

No port-matching, nothing fancy, just a .030 overbore. Original carb. I did upgrade the distributor to Pertronix3 internals, but that shouldn't add any power. AFR is on a different sheet but is pegged at about 12.2:1 all the way through.

This is gross hp, the way the factory did it pre-72, with headers and no accessories. It's only 330hp, but there are over 400 ft/lbs from about 2500rpm, so it's not too bad.

Not trying to make it fast of course, it's a Longhorn truck. But with 4:56s and a locker and a 200-4R deep first gear it should go 0-10 real nice if I can hook it up :-)

[Coley]

Very interesting stuff....
What compression ratio was the engine rebuilt to? (8.5:1 or?)
Were/are the heads the stock originals?
Nothing special inside in terms of pistons or?
Factory Quadrajet or?
Again, some great info there....thanks for posting.
Coley

[davepl]

Originally Posted by Coley

Very interesting stuff....
What compression ratio was the engine rebuilt to? (8.5:1 or?)
Were/are the heads the stock originals?
Nothing special inside in terms of pistons or?
Factory Quadrajet or?
Again, some great info there....thanks for posting.
Coley

Should be original compression ratio, though the .030 overbore might increase it a tad. We used the same piston height and crown/dish, etc. Then again I might have actually dropped the compression ratio because we used a composition gasket rather than shim steel, but the block deck had been cleaned up, so maybe it all offset. Quench was 0.60 which I think is too much, but it's not a race engine that I need to run the timing on the ragged edge or anything, so I'm not too worried. Would have preferred that a little tighter.

Interestingly, you cannot buy the correct 0.030 pistons for a 402, but you can buy 0.060 pistons for a 396. That's close, but its off by 0.001 if you do the math.

Heads are completely original. New valves and seats but no porting or gasket matching... I wanted it to be as good or bad as factory.

Original Q-Jet, though we did have to tune it (fuel is different than it was 40 years ago) to get the AFR right. Finding Q-Jet tuneup kits with rods and hangers and jets is weirdly hard to do.

Otherwise, everything on the engine other than the distributor internals is original to the vehicle (and date-coded to confirm it).

What's cool (to me, anyway) is that the guy I had do this engine is a retired NASCAR engine builder for a famous team. After retiring he moved from North Carolina up to my area, but still does engines and dyno tuning. Normally I build my own engines, but with that kind of Wizard available, who could resist?

For the curious, all parts and labor and machining and tuning included it was $6K. You could buy a decent crate engine for that, but since this is the original engine, wasn't an option for me.

[davepl]

Here's another page of info. I think the only other thing I have is the pyrometer readings, but that's pretty boring.

[bbcmudtruck]

Very cool! Thanks for shedding some light on what those old motors really did! It basically carries the torque through the entire curve.

[Prematuregrey]

Good info there. I really appreciate that. Makes me want to run mine on the dyno more and more. My BB definitely doesn't feel 330/400 by the seat of the pants though. I'm sure it has a lot to do with the 3.73's and 33" tires. As far as I know there are only a couple chassis dynos in my area so I wouldn't be able to get good engine numbers like yours. I want to tear mine down first and see what all the PO's have done also. Its got a factory HEI upgrade with a Eldelbrock 2.0 intake and Holley Performer on the outside but the internals are unknown. I know its got a big cam in it, unknown specs on it though and I'm not sure if there has been any other work done. The valve covers are over sized Holleys as well but that doesn't mean anything for sure, could be a roller setup under them. In the end I'm happy with its performance at the moment but know it could be doing better. I'd be dam happy to have the numbers you put up though.

0-10 is all that matters isn't it?