engine build help

[travisr1988]

My 79 Chevy 3/4ton with a turbo 400 and 4.10 gears needs it's 350 rebuilt. I'm on a rather tight budget, which is why I'm using either the milled 882s that were on it or the 305 tbi heads I have. Also why I'm using a quadrajet. Anyways...cam choice is the hardest for me as I am new to engine building and am being told different things. I want my truck to develop some healthy power, I was thinking a comp cams 12-234-2 would be my best bet to keep it peppy but still decent in gas mileage (I know I know 3/4 ton and gas mileage don't exactly mingle well) the best I got before was 13mpg with the correct tires and tuned just right...didn't last long before it dropped to 11mpg. Previous cam specs are unknown, had a nice lumpy idle, not so much low end though. Pistons that were in it were 30 over flat tops with 4 valve reliefs. I think 40 over with same piston design would be best. How's it all look to you guys? I ask you guys because you have trucks like mine that you have tinkered with and aren't like my dad and obsessed with stock everything (his truck is no where near stock ironically). Thank you guys in advance for the input.

[bd]

This...
http://forum.73-87chevytrucks.com/smforum/index.php?topic=26161.msg217491#msg217491
...and other discussions by the same poster.

[travisr1988]

now see, we're back to generics...not for a specific build...just a one size fits all. So far the most helpful person I've seen was on that thread and it was Mr. Weyand. I was not only asking about cam, but whether what I have is sufficient for what I want. I understand a lot of people ask the same questions over and over, and generic advice doesn't help much, anyone would be happy to learn what the numbers mean, and get a cam that best suits their setup specifically rather than a generic setup and end up unsatisfied. I come to you guys because my father (great mechanic, but doesn't share much knowledge) stonewalls me and says stock is what you want before I can say what I want out of this truck. Saying a certain cam works good with these trucks given a 3.08 rear gear and stock heads does not help anyone match the right cam when variable have changed and they don't understand how that affects the equation.

[rich weyand]

The cam IS the engine.  All else exists to serve the cam.  And advice about what cam to use in a flat-tappet 350 with stock-ish heads installed in a 5000 pound vehicle is already pretty specific.

Note that "had a nice lumpy idle, not so much low end though" are the same thing: a lumpy idle means the cam is designed for higher rpms (and thus has not much low end), whereas a cam designed for low end will run smooth at idle (because that's near the low end).

I sought out professional advice and was told to use the Comp 12-235-2 as the best 350 cam in these trucks if you are sticking with the flat-tappet setup.  I second-guessed that advice and went to a 12-300-4, which is even beefier on the bottom while giving up breathing at the top compared to the 12-235-2, which is not the best choice for everybody.  It works for me because I drive it almost exclusively in town and and country roads.  Basically no highway mileage at all.  And sometimes I'll drag a fallen tree out of the woods.

[travisr1988]

I'll be stuck between 45mph and 60mph everyday, so if I'm understanding correctly the 12-235-2 or 12-234-2 would be bets suited for my truck with the 4.10s. Thank you for the help and not running me off.

[454Man]

What rpm does the engine cruise at during those speeds?

What's under the hood??? If you have to ask maybe we shouldn't race...

[Captkaos]

Selecting the components for a motor alone outside of the drivetrain isn't a good choice.  Sure you could get a 350 that makes 400hp but if it only makes the power above 6000rpm and has no bottom end requiring you to run a huge stall what is the point.
You already limited yourself with cost, so that will be the limiting factor.  And before you start deciding on boring one out, have it checked, it may be to far gone for .040 or it might not need it at all.
You need to decide how you want it to perform, and lay out what all on the truck you don't plan to change and then spec the motor to optimally match what you are after.
Are you willing to run a stall, change gear ratios, change tire size etc etc.  Where will the motor be operating at the most, what kind of driving do you do?  All this needs to be sorted out before..

[travisr1988]

motor will be operating at 2300-3500 rpm most of the time. Gears are staying at 4.10. tires are staying at 31". no stall.

[Irish_Alley]

imo you dont want the rpms to be that high, if you want mpgs keep it low. would love to see my truck stay under 2k while cruising. i have a sm465 38s and 4.10 rears. and if i have the opportunity i will step down to 3.73 just for better mpgs

[travisr1988]

Ok guys, sorry for making this difficult, but I picked up a 77 step side short bed 1/2 ton with a straight 6 and th350 that does not run. It has either 3.42s or 3.73s in the 12 bolt rear according to sources (250 L6 with 3 on the tree(original trans) had only those 2 options for rear gear). This is now what I'll be building the motor for. I may use the th400 but am currently undecided.

[rich weyand]

I would just use the TH350 that's in there.  Why make extra work for yourself?  If it's got over 150,000 miles on the trans, I might put in the TH400 if it had lower mileage while I had the whole thing apart, but otherwise, why bother?

[travisr1988]

Supposedly the th350 has less than 2k on it...but there is a cable that was never hooked up and since I can seem to get the straight 6 running long enough to put it in gear and see how it acts I'll just have to open up the trans and see how it is...I'll put a shift kit in while I'm at it.

[rich weyand]

You really like to do extra work, don't you?  I would flush it and put synthetic ATF in it, and that's about it.

I don't think you even need to change the governor for that swap.  Parts book looks like its a GM #370367 for a 1977 C10 with 250/292 and same for the 350.

[travisr1988]

Hey Rich, would you use resurfaced 882 heads (unsure of how much was taken off during resurfacing) or stock 305 heads from a 91 olds?

[rich weyand]

I'm not a heads guy, but I wouldn't use the 305 heads.  I would probably run with the resurfaced ones (after doing a displacement measurement to see how much they took off, and then calculating the resulting compression ratio) or get a set of used stock 76cc heads for next to nothing.

Someone who knows more about heads should chime in here.