Originally Posted by Clayton A
I recently acquired a 1971 Chevelle
from my dad!!!! The engine sounds real good but I think the combination of parts are hurting the engine more than they are helping. I built the engine when I was 18 (12 yrs ago) and didn't have the first clue as to what I was doing. Dad knew how to put an engine together so that is exactly what we did. Now at I look back at some parts I used and I think we made a few mistakes. The engine block is a 1980 - 1985 350sbc Casting number 14010207 bored .40 over. The heads are Vortec Heads (bought new from Summit) Casting number 12558062 (milled for a higher c/r) I am thinking about changing the valve springs and rockers....any suggestions?, The intake is a Edelbrock Performer 2116. The carb is a Edelbrock Performer 1406. The cam is a Crane Cam with a 516 lift (I think the lift is way to high for these heads, can't remember the duration). Stock 350 crank that I had checked by a machine shop. I don't remember the brand of pistons but I do remember they were flat top style and a compression ratio of like 10:1 (Not engine c/r but the pistons). Not sure what the actual C/R of the engine is. I plan to go back through this engine and try and get all the right parts that I need to produce the best HP.
Any suggestions on what to do to produce the best HP from this engine? I plan to re-use the heads and crank but would consider swapping out the rest. I believe my dad has a Performer RPM intake that I plan to use.
Read through all of this; for kid that didn't know what he was doing this is a damn great first effort. Now while you don't know the true compression, just that these flat top pistons rate 10:1, I'm assuming against a 64 cc chambered head, at this point the unknowns that could modify that up or down would be the head gasket thickness, deck clearance, effects of any head milling being different from the piston manufacturer's calculations. The Vortec heads would need modifications to the valve guides to accommodate this cam's lift even with a 1.5 rocker.
The parts used in this build would produce an engine that runs between 380 and 400 horses on a crankshaft dyno. I guess the real question is what do you want power wise and how do you really plan to use it. From where this is at getting more power as a 350 will take better heads and camshaft to support running the engine up over 6000 RPM, this might also need some bottom end improvements. I'd really start at the oil pan as well; this engine is standing on the edge of what is safe and reasonable with a stock pan. If it isn't done already, the bottom end needs a trap door 7-8 quart pan, a crank scraper, and a good windage tray because when the revs start seeing 6000 plus getting oil off the crank and back into the pan starts to be an edgy problem with the OEM set up to where if one thing goes slightly wrong and you own a pile of junk in less than a New York minute.
The other way to go is bigger by putting in a 383 kit. This really fattens the torque and horsepower curves without having to resort to all sorts of exotica that is necessary to get a smaller engine to this kind of power as the smaller engine must be spun faster to get the power. Spinning faster requires living with power that is weaker in the lower RPM range which drives you to lower gearing to get the revs up to where the power is. Internal to the engine it pushes into much better quality parts and balancing as the forces go up to the square of the RPMs so that which is tolerable at 5800 revs is not at 7000. The old adage that “speed costs money, how fast can you afford to go?” is more attached to making an exotic engine build power than it is to making a larger engine, which is why Detroit tended to reach for the boring bar rather than multiple Webbers and solid roller cams back in the muscle car days. In this case a 383 at 5800 RPM will be happy with a good quality cast crank for example maybe even GM powder metal rods with parts balanced to a gram or 2, a 350 turning 7000 for the same power is going to be looking at a 4340 forging for the crank and rods with the balancing done at .1 gram or better. It’s this level of better that gets expensive very fast.