HELP: stall converter? RV cam? im confused!

[jveik]

i have a big dilema here. im restoring a 73 chevy truck and so i was looking into just using the stock converter and tranny and using a low to midrange cam from edelbrock that is good for idle to 5500. someone at my work insists that i get a bigger cam and upgrade to a higher stall speed converter, which doesnt seem very appealing to me since the turbo 400 i have only allows single digit mileage as it is with the 350 i had before i gutted the truck to the bare frame.

what do ya all think? low end power with a bit of fade at high rpm's in a torquey cam, or good higher end cam with cruddy low end that requires an aftermarket stall converter?

i bet the weight factor is a huge part of this decision, as the truck is rated at 5500ish pounds, or "freaking heavy." i like the idea of a low end cam mostly, but will i experience horrible top end power due to that option? help lol...

[curtis73]

I think you're on the right track. Stick with the milder cam; something that can retain the stock converter. The tighter converter will save you a MPG or two, as will the milder cam. When selecting a cam for mileage, a good indicator is the overlap. Keep overlap close to stock and you'll not affect mileage too much. More mileage and power can be had by a very careful ignition curve as well.

Don't worry too much about a wimpy top end. A mild cam will make power from 1000-5500. A wilder cam will make power from 2000-6500. You just adjust your gearing accordingly to make use of the powerband you have.

[rollin_on13s]

Curtis is definitely right here.

One more thing-You need Torque!!

Just a bigger cam won’t neccessarily give you any more power for that big vehicle.
Unless the rest of your motor (heads, intake, carb, compression, exhaust) is set up to also make higher RPM horsepower, all that a bigger cam will get you is lousy throttle response, a little bit of midrange, the ability to rev more on the top end while not really making any more power- oh and horrible gas mileage.
Combine a small-block motor like that in a heavy vehicle with a stock rear diff ratio, and you’ve got a sluggish, gas-guzzling noisemaker.
(even with a bigger converter).

A best bet would be to buy an entire valvetrain that will maximize the capabilities of the setup that you have. If you’re looking to invest a little more in your motor, a well engineered roller camshaft, followers, and higher lift roller rocker arms will give you more torque and HP- in the low and mid-range where you really need it.
Part of the reason that a modern 5.7L Z28 can hang with a 1960’s bigblock Chevelle (While redlining at only around 5700 rpm) is because of technology- and definitely not because of a bigger camshaft.

A 1000-5500 powerband is totally respectable.
Take a look at stock replacement camshafts sometime. A lot of older stock SB Chevy cams were only really good to about 4500 rpm. I’ve had plenty of stock chevy V8s that were completely useless to rev past 5000. Making solid power all the way to 5500 won’t give you bragging rights, but it will give you a lot of midrange torque, and enough lowend response to really move that beast.

[MagicRat]

Excellent advice.

Consider a different transmission, too.
The THM 400 is an excellent, extremely durable trans but its inefficient.
A lock up converter and a OD fourth gear help a lot for mileage.
My 3/4 ton Chevy (THM 700R4) van tows a 3000 lb boat. With cargo and passengers the rig is over 8000 lbs, yet comfortably cruises in overdrive with a locked converter. This combination is much more efficient than my THM 350-equipped van.

So consider a THM 700 trans. It has a slightly lower 1st and 2nd gear than a 400. Try for an 87 or later trans, they are a bit stronger, but avoid the computer- controlled 4LE80's.

[jveik]

thanks for all the imput guys... i was looking into the whole 700R4 thing and it looks like a great thing to have. I saw an ad in my local thrifty nickel for rebuilt turbo 400's for 250 bucks and 700R4's for about 500 bucks, so i might as well chip in the extra 250 bucks and it will pay for itself in mileage. that lockup converter looks pretty appealing as well... the best i could get with my 400 was about 12 mpg city which prolly aint bad but could be a lot better for how small the engine is. yeah the dude at my work seems to have mostly "book smarts" and doesnt have much to show for it other than a pile of crap ford aerostar van lol. i think ill go with the torquey cam. i wish you could have lopey idle at the same time, but i guess ill have to save that for maybe a different project down the road.

by the way, the cams can go higher than the speed listed, just with bad efficiency, right? i remember using the all stock motor to hit 60 in first gear once too try and blow the old motor and made it sound like an indy car and it didnt blow up or anything as far as i know lol...