chevy engine advise

Hey everyone i gotta chevy 350 that i want to give it some more power

ok this is a low miles stock gm preformance parts 350 truck engine.  i want more power out of it.  my plans so far is a good intake, vortec heads, get a stroker kit and bore it out .30 over. 4bolt main kit. mildon 6qt. offroad oil pan.  the exaust system is factory 2 1/4" duals with glasspack mufflers.  i plan on trying to fabricate in an xpipe or at least a h pipe.  right now i have some $100 headers but i plan on getting some doug thourley tri-y's soon.  when i get the tri-y's i will probably just fabricate a new exaust with the xpipe built in.  what should i get for the fuel supply.  i will probably get a new carb or should i get one of those holley 4bbl tbi kits?  for the cam i waz thinking on the comp cams xtreme 4x4 ones.  what would be a good one for low end torque. i dont want anything extreme because this will be my daily driver and i want at least 8 mpg.  this truck is stock in all other ways.  i may get a 2 1/2" lift kit and go with 33's and 3.73's but for now i will go with 31x10.5r15's.  future upgrades will be rebuilding the th350 with a b&m kit and maybe 1 ton axles

now i think i covered everything so shoot away with advise for me

You are going about this wrong if you want max MPG too. First kep engine mods mild to moderate (no more than 215 degrees duration at .050) Second, you want to get CR ratio up to about 9 to 1 or so. Next, you want to loose the 3.73's and run a set of 4.10's for a couple of reasons. One being that with a mild lift and bigger tires it takes more power to move truck down road and your current mods reduce lower RPM efficency (especailly dual exhaust, honestly if you want best performance here, a large single exhuast with something like a flow master and a 3 inch tail pipe will breath well and improve lower RPM torque) so you need to keep RPM up a bit. Also deeper gear improve traction as well and you will see more seat of the pants improvement off road with 4.10's (4.56 if you are serious) vs 3.73 than with some more engine mods. As a footnote, I drove a 72 GMC 3/4 ton 4x4 with 4.10 gears for 10 years from mid 70's to mid 80's.  It had a SM465 with 16 inch split rims with 750 x 16 10 ply traction grip (nasty ones 32 inches tall) that were bias ply too. I got about 13 to 14 on highway with it depending on how hard I pushed it and around 11 or 12 in town. Engine was stock except for a competition cams H260 and a large single exhaust. Drove it almost 150 K mile before I sold it. The truck ran very well and was quicker than its modern counterparts. If you cam ip and stock current engine to try to pull 33's better with 3.73, you will murder MPG. If you are seriuos about keeping 3.73's with 33 and gettin good performance, scrape the 350 and swap in a 454 as it will deliver want you want and deliver reasonable MPG too while at it. Also unlike SB's, BB's respond well to dual exhausts.

Wow, I hate to disagree with Snoman, but I'd defintely go with a good set of headers and a dual 3" exhaust.  The X or H pipe will help too.

I wouldn't worry too much about building the engine internally if it's a low miles GMPP engine like you say.  A GM Performance Parts engine should be getting at least 330HP at the crank right out of the box.

The Holly TBI kit is nice and so are the Vortec heads, but you are talking about some serious $$.  I'd get a 750 (or larger) CFM carb with a good flowing intake, maybe a Ram Air setup and get a machine shop to massage the existing heads, add the headers and exhaust and 400HP is really a reasonable goal. 

You need to do some reading and match the size of the carb to the improvements to the heads and exhaust.  Too much carb with not enough exhaust or poor flowing heads is worse then doing nothing at all.  Be sure to check out the local shops and find someone who is an expert at high performance head work, not just a repair shop that also does heads.  With 400HP a 3.73 gear with 31" tires and that engine setup will give you decent MPG.  Setup like this I'd expect much better than 8MPG, I'd also expect it to go like stink.

I'm building my truck for 325 to 375HP with 3.73's and 32" tires.  The trick is to build for torque more than HP, that's what you feel when you're driving it, that's what you need  for larger tires without going too low on the gear ratio.  Torque is easily built with proper flowing heads, of course that means good flowing intake and exhaust to match.

Your logic is wrong because to get 400HP out of a 350 you have to wind it pretty tight and it will lack low engine torque even more and torque is what get you moving with taller gears not a high RPM power peak. ALso header and 3 inch exhaust you reduce lower RPM torque and efficency big time and not be MPG freindly. There are those that think bigger is better but this is not the case here. A big block will do quick well with 2.5 inch or so dual but not a small block with that size or bigger at lower RPM's. ALso headers add a lot of heat to engine compartment too which is not wise in a 4x4 all the time and if you go the headr route through away clutch fan and install a flex fan to move more air through engine compartment all the time to keep temps down under hood as they will really climb  at times without one. ALso if you must go header route, use some tri Y header as they have better low RPM torque and 2.5 inch pipes tops with 2.25 even better and install a cross over. A single 3 inch exhaust will flow well and make just as much HP on street and have more low end torque too and better MPG. I have been messing with 4x4's for over 30 years and things are not always as they seem on paper.

One more thing, bigger is not always better with TBI unit either as 600CFM will give you all the flow you ever need and a 750 will have lower mixture velocities through the bores and have reduced throttle reponce and efficency at lower RPM's. How you build a eng to run in a light weight strip car and a heavy 4x4 are to different matters.
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  The SnoMan
www.thesnoman.com

http://www.crateenginedepot.com/store/Circle-Track-Crate-Engine-350400-88958604-P26C53.aspx

385hp @ 550RPM, 400FtLb right out of the box.

http://www.edelbrock.com/automotive/crate951.html

410HP @ 4500RPM 408FtLb right out of the box.  Torque delivered smoothly from 1500 to 6500RPM.

http://www.edelbrock.com/automotive/crate_rpm_graph.html

Obviously these are not the engines our friend is using, but 400HP out of a small block is no big deal.  Headers get hot but so do cast iron manifolds, a ceramic coating will make the header hold the heat inside better then cast iron.

Physics is Physics.  Better airflow means more horsepower and more torque.  Torque delivered in the low RPM range is what works best with a 4x4.  You won't get there by restricting the exhaust.

I've seen your comments on air flow before, and I don't want to disagree with you in public.  Maybe we could have a frosty beverage some time and argue until we get tired.

Yes Physics is physic but thermodynamics and IC engine priciple are a different matter. (I study them in college in the late 70's and the theories have not changed. Maybe you drive WOT all the time, I do not and how a engine responds can very for a lot of reasons. There is not free lunch with a gas motor and to get good power at 5000 RPM you have to give up some at the bottom (unless you use forced induction then there are different rules. You can take your 400 HP SB and put it is a 4x4 if you want and a 300 HP big block will kick its butt off road big time. Been there done that long ago.

yeah i agree with going too big with duals and a sb 2 1/4 are enough

i dont want to go over 650 cfm carb because a 750 is more for something on a bb  what do you think about the vortec's and stroker kit.  i talked to my uncle again and he said he could find me a crank for a 400 for cheap and get it milled down cheep too as he is good friends with the guys at carquest.  what are your suggestions with the cam?  what cam would you pick.  also do you think im going in the right direction with the stroker, vortec's, comp cam, edelbrock streetmaster?  ive looked on the net about the streetmaster everyone says its a dual plane intake but the one i have looks like a single plane.  should i just get an edelbrock preformer intake?  what would be your suggestion on a carb too

The carb depends a lot on the cam you plan to use. I would "suggest" a Cpmpetion Cams H260 as it pulls well from about 1500 to 5000 RPM. Also if you stroke it remember to use 400 rods too with 350 pistons and double check your clearnaces and you will need a 400 SB harmonic dampner and a 400 SB flex plate to balance engine (or a 400 SB flywheel for a clutch) because the stoked engine is balanced externally. On carb, I would go with about 600 CFM for best throttle responce and overall power and a performer is a good choice too. Engine timing is something to tweak to and you want abot 38 degrees or total advance by 3800 RPM or so and 6 to 8 degrees at idle. Depending on CR ratio, it may not like 87 and will need at least 89 to do its best. Another hot ticket is a 400 block with a 350 crank (it is balance interanlly this way) with 350 rods and stock 400 pistons. It works out to about a 372 and it winds up better and has better top end power than a stroked 350. I worked with racing a few of these any years ago and they held up better than built 400 SB's and ran as fast or faster over all too because you could wind them a bit more safely.

I don't disagree that a bi block produces more torque, bigger bore=bigger torque.  But this fellow has a 350 now, I was trying to help him find the power he wants in the engine he has without buying a $2500 TBI kit or expensive heads.

I guess I'm a cheapskate, but buying and building a big block is going to cost $5k +/-... ouch!

BTW, just so you know.  When you were studying engine theory in the late 70’s I was rebuilding transmissions field and building race cars.  I did my study 10 years before that, so when you say you’ve been doing this for a long time, you ain’t talkin’ to no spring chicken here.

http://www.villagegeek.com/willys/Gallerys/DrivetrainSetup/images/DTSetup%20(15).jpg

Just so you know I started rebuilding and racing them in 60's and "studied" their theories when pursuing a engineering degree as elective courses for credit after miltary time that included supporting Vietnam effort. I got a A on my term paper for one of the courses on the topic of operational theories and how to improve a IC engines thremodynamic efficency. (It was 20 pages long too) I can build them and understand their design and threories and stress in them and can even calculate at what point what parts will yeild/fail from stress based on material used be it axles or engine parts.

A 350 is not a bad engine, I own to and raced many of them but as you boost the power from them, MPG will suffer. The 350 started life as a 265 (I even "played" with one of them in a 56 chevy) and grew with time but because of block/head design limitations power gains were harder to come by. The "Rat" was born as a HI Pr motor from day one with huge intakes and exhaust ports and valves and a "porcupine" head (staggered valves) to improve flow which gives it its destintive valve covers. Dollar for dollar any power you can yet out of a SB, you can beat with a big block and make same HP at a lower RPM where it is more useable off road. A 396 (or 402 which was a factory 396 bored 60 over last few years it was made) was and still is a beast and will take a terrible beating and survive. I remember some guys running 396's in chevelles and nova's on the street and REALLY beating them and they survived a lot better than the SB's trying to compete with them. If you want to talk about a really nasty engine and likely the most powerfull production engine ever put in a car, talk about the Pontiac 421 Tri Power. They were flat out nasty and a force to be reconned with before you even built them further. Fasest street car I ever rode in (that was not supercharged) was a GTO with that engine. With track slicks it would run 12's all day long and with street legal "slicks" you could not even hook it up solid until 3 gear as WTO in 1st was a joke and 2nd was not much better on a muncie rock crusher 4 speed. I also knew a guy that had a rare 1970 chevelle that he bought new with a factory 454/465 HP with 4.10 gears and a close ratio 4sp and he used to hunt SB's for lunch with it.  I would have liked to have seen that GTO and Chevelle run together but they were in different parts of the country. I could go on but what would be the point.

The Pontiacs only had one block a small block.  Thier 326, 350, 389, 421, and 428 were all the same small block.  The most powerful production engine ever made was the Buick 455, 1970 I think,  517ftlb of torque.  http://www.carcraft.com/techarticles/72278/

My only point was this fellow has a 350 already.  I was talking about getting the most out of it for the fewest dollars. 

I'm not real sure how it came to be that you think I am promoting a SB as a better engine for a 4x4 then a big block.