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Cam advice

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shimniok

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I'm trying to find some cam advice and figured if anyone could help the Chevy folks could. :) I'll come clean and admit I don't really have a Chevy but let's pretend I do and hope you can forgive me :D

Given: 5000# vehicle, 400cid Chevy, GM TBI, performer intake, 33" tires, 3.73:1 gears, low stall, 3spd tranny, runs 2600-3000 hwy rpms; 2600 @ 65mph. Goal: haul gear, people up I-70 passes in 3rd with power to spare for a 4000# trailer someday.

What kind of cam and compression ratio would you pick? I still have to pass stringent CO dyno emissions. I have Desktop Dyno (DOS) so full cam specs would be really helpful. Also do you have factory cam specs for 400cid motors in heavy trucks?

thx!
Michael
 
TBI is your limiting factor.

9:1 and the biggest computer friendly grind you can find, which is 212 @ .050" or so.
 
TBI and 400 is not a good mix IMOHO.
The TBI is a noose around it's neck.
If a TBI plant is your goal I would stay in the 350 range.
Most cam grinds out there are based on a 350.
That would be sorta like dropping in a 454 and putting a 2 barrel manifold and carb to get good mileage.
 
Ok, forget I said TBI. :) Let's forget the induction system. That isn't what I'm after. I'm trying to build up a motor, I'll bolt on whatever I need to. :)

I want to try and figure out what kind of grind best fits given the tall gears, low rpm's, big vehicle weight, and 3spd constraints...

I could put a race cam in there if I wanted to and have all the hp I want, but in a very heavy vehicle with auto trans it's going to be a nightmare to drive in the city and torque in my cruise rpm of 2000-3000 will be abyssmal...right? I could put in an econo grind, but will the motor will have nothing above 3500rpm?

many thanx
Michael
 
Why build a 400 for a 350 CI parameters?
TBI is the limiting factor is it not?
All of the advantages of more cubes which will take a bigger cam and running a bigger cam allows the use of higher compresion.
are lost on TBI.
Clearer translation now?
 
I agree with you that TBI is not ideally suited to deal with a 350, but on the other hand, while you may not have optimal 4000+ RPM performance, I bet it'd still have quite a bit more low end torque than any 350 and with a few mods, I'm sure it'd run just fine.

If it was a race car, I'd say no, too much power lost in the buildup. Seeing as how it's a truck, I don't think making that last 20 ft/lbs matters anywhere nears as much as the fact that it will still run when it's halfway on its side or has a heavy trailer behind it and is lugging down. :D
 
Alrighty then we have some parameters to work with.
The first part of ant build is determining what it will be used for.
Extermly heavy? what's that?
If this a paper project dump the SBC and get to business with a BBC.
If ya actualy had something to work with it would make suggestions easier.
From the do it right the first time scenario... build a BBC
 
Goal: haul gear, people up I-70 passes in 3rd with power to spare for a 4000# trailer someday.
Click to expand...
That would be pretty tough to pull a 4K trailer up a hill in 3rd gear if the passes on I-70 are like some of the hills I have heard are in Colorado. It would take one radical 400 to do that. Even a built BBC would have a little bit of trouble maintaining around 50mph(3rd gear) with a trailer weighing 4K in the Co mountains.

i would carb the motor, cheaper and capable of providing the apropriate power building fuel, especially in the higher RPM range that you could need for pulling in 2nd gear. I have a comp cams 268H cam. 454" lift in and out and 218 duration. There are better cams out there but I like it and works well in my 400.
 
Ok, thanks for the input. I'm trying to understand what's realistic. I can live with slower speeds with the trailer attached. No prob.

So if I'm going to struggle with the trailer, I at least I want to run 75mph with ease in 3rd with JUST the truck, 4 people, and camping gear (call it 5500#) with 3.73's, 33"s, and 3spd auto.

Is it even possible to build a 400cid thumper motor that builds 400+ lbs-ft of torque below 4000rpm to solve this problem?

Or is a better answer to build max horsepower from 4000-5500rpm and rely on 2nd gear in the hills?

Michael
 
Good heads, exhaust, and intake can give you a 500 ft lb and 450 hp....400 SBC....

I would opt for better gears too....

A BBC or CTD would be easier to live with, and prolly last longer....

As for smog legal, well I can't help you there. Cheapest of the three options would be to build a BBC, and keep an eye out for a T 400 trans. w/a big cooler.... :waytogo:
 
shimniok said:
Ok, thanks for the input. I'm trying to understand what's realistic. I can live with slower speeds with the trailer attached. No prob.

So if I'm going to struggle with the trailer, I at least I want to run 75mph with ease in 3rd with JUST the truck, 4 people, and camping gear (call it 5500#) with 3.73's, 33"s, and 3spd auto.

Is it even possible to build a 400cid thumper motor that builds 400+ lbs-ft of torque below 4000rpm to solve this problem?

Or is a better answer to build max horsepower from 4000-5500rpm and rely on 2nd gear in the hills?

Michael
Click to expand...
Once again I think your hopes are a little high. 75mph is a lot even without a trailer. You will probably be heavier than 5,500 pounds with a few people and a bunch of gear. You would need one hot 406 to be able to do that...big enough to where it sucks premium fuel along with octane booster and in a much faster manner than you would like. It just would take too wild of a cam and compression to make that kind of power that would actually usefull pulling hills.

My mild 406 makes about 400ft lbs at the crank and starts in around 3K+. It makes good torque but I bet it would have a hard time managing 65mph in those nasty CO hills empty.

I would build a mild 406 and be happy with 55mph up a hill at say 6K or I would swap to a bombed cummins. A cummins is about the only engine besides a nasty fuel drinking blown stroker big block that will pull hills without dropping below 65mph with or without the trailer.
 
Thanks for the info. I really appreciate everyone's help. Earlier when I said I didn't have a Chevy I meant I had another non-Chevy vehicle. :)

Sounds like the Chevy motors can be built to put out sick power just like I've always read. Of course if I had a Chevy truck I'd run a 454. :)

Since I have a J*** (a four letter word around here I guess) Grand Wagoneer the current 360 is a dog, especially from idle to 2500. A buddy has similar rig with taller gears and dusts me up hills I can barely pull 60 on. His AMC401 has high CR and stock cam. I wanted to emulate this.

But I was debating whether to do an econo grind that puts 450 lbs-ft at 2000 and drops off like a rock from 3500 up or an Edelbrock Performer or similar that runs over 430 lbs-ft 2000-3500 and 320 hp @ 4000.

I figured I could learn based on what grinds Chevy trucks with 400's ran. Sounds like a good strategy in that case is to build for a 3000-5500rpm power band and use 2nd for the hills where needed.

Michael
 
I think you are on the right track. I would build it to make good mid range power.
 
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