Horsepower for a 72 with a 400

[pscmj84]

My friend has a 72 Cheyenne that says 400 on the front side. I am a little confused as to wether this is actually a 402 Big Block or 396 small block. It seems pretty quick, especially in the mid-range. Feels like 0-60 is in about 8-9 second area. I have searched previous posts about this. Do you think a stock 400 would be that quick? Seems like estimates are from 210-375HP and from 300 to 400 lbs/ft so I really I have no idea which one it is.

[Hooter]

most likely it is a 402 . Any big block is gonna have some power to it even 366 have a little torque. What i have learned 9being a 67-72 truck guy and a first generation monte guy0 is that a 402 was a 396 with flaws so chevy bored them out 30 over and voila a 42

[slam33]

It's a 402, and if it has the 396 badge, thats a BB also

[pscmj84]

I forgot to add that I was wondering what the horsepower estimates are for the truck also.

[minibike]

A stock 72 402 has 210 HP at 4000rpm and 320 foot pounds of torque at 2800 according to the Chilton's repair manaul. That sounds low to me, though.

[pscmj84]

Yeah after riding in that truck that seems low to me. Its a long bed model so I would guess it weighs well over 4000 pounds with everything in it.

[trukman1]

Just for the record...You have to remember that in prior to 1970 the government was starting to eyeball the muscle car situation and by 71 smog pumps appeared on some vehicles. The auto industry knew about that before most people (obviously) and started down-playing horsepower ratings.
Also, about the 402 being a bunch of rusted blocks that GM wanted to salvage, I'd heard that too ,however, after meeting with some GM personnel, some of which were engineers 20+ years (10 years ago), it was pointed out to me that GM wouldn't change to new emblems, marketing, etc. for a batch of bad engines. They would have simply scrapped anything not up to standard as was the customary business practice in those days. I was told 1) The 402 was simply a way to economically overcome the empending smog equipment add-ons, and 2) Since the 396 was the standard BB, labeling the new engine 400 seemed like someone just rounded up the number and it didn't attract much attention from the government. The average consumer, however, would realize this was just a larger engine. (Makes sense to me but they could have just been feeding me a line, who knows.)
Anyway, I've got a 402 that runs way better than any 210hp engine I've ever driven so maybe someone out there has put theirs on a dyno and can give us the scoop. Gary

[minibike]

The Chilton's manual called it "advertised" horsepower. Maybe it was intentionally rated lower.

[jflem3]

I've got a 71 c/20 that used to have a 402/400 (now sitting on stand right now and a FI 454 is going in its place). I'm Pretty sure the 71's were rated at 310 gross HP and 240 SAE net HP. SAE net is the way motors are rated today. My 71 was significantly quicker than my 90 454 burb with 230HP/385lbft.(bad emissiions JUJU) although there was a several hundred pound weight difference. the little 402 revved easier
A well broken in 402 (not tired) w/ a good dual exhaust would easily put out 250-275 net hp and over 300 if you do a mild cam and intake.

[pscmj84]

Its only got about 42k miles so it could be considered to be in the "well broken in" phase.

[fastbagged68]

dont the heads have small valves? Something like 2.06int. The big horse power vette motors i believe had 2.19 int valves. That would make a world of difference.

[pscmj84]

It could benefit greatly from some better breathing and a more some agressive cams. When you get on it it just sounds almost like it isn't even trying as hard as it could, like it could do more if it wanted to. Its got some great torque though, its the only automatic i've seen that squeaks the tires going into second gear!

[jflem3]

you've got to watch the costs of changing to larger valves in a set of heads, it usaully ends up being cheaper to buy a finished set of heads. and then it isn't much of a stretch to buy new aftermarket heads,( they usaually come comlplete with springs and all you need for one price. that way outflow the stock heads and won't lose low end velocity.

the small valves are still larger than the biggest small block valves and the 400sb's can make some ponies.