89importeater

hello i have a 355 four bolt main, roller rockers with heads that have 76 cc chambers with 1.94/1.50 or 2.02/1.06 valves. got a couple of questions how can i tell which vavles i have and also what kind of cam can i run with this setup. i want a lumpy idle, even if ill have to run a vaccum canister. if you need more info just ask and i will help the best i can. also i plan on changing carb and intake to so that wont be a problem. i tried a search but couldnt turn up much. thanxs

five7kid

iTrader: (14)

The easiest way to tell which valves you have is to measure them.

Actually, I think that's the only way.

Sounds like you have 882 heads. It isn't hard to get a lumpy idle with them, but getting any sort of performance is a different matter. Most likely you'll have low compression with those large chambers (what pistons do you have in it?), so a lot of overlap (which is what causes the lumpy idle) combined with low compression will make for one sick dog.

The heads, compression, cam, intake, and carb need to be chosen as a package to produce a particular result. When you start off by limiting yourself in one of those areas (in this case, the heads), you constrain yourself on the others and the results.

89importeater

i have 10.5 to 1 compression with trw flat top pistons. i know its not the best pistons out their but i didnt put them in their.

sofakingdom

iTrader: (1)

Your numbers don't add up.

So how big is this motor anyway?

If it's a .030" over 350, with stock deck height on the block (9.025") and the usual extra .020" of deck clearance that most TRW pistons have, 5cc valve reliefs, and .039" head gaskets (FelPro 1010, 7733PT2, etc.), then I come up with approx 8.4:1 compression. If it's a .030" over 400, it's STILL below 9.4:1. If it happens that these heads have had money wasted on them by putting in bigger valves, then the chambers will be a couple of cc's larger than 76, and the CR will be even lower than that.

CID would make a big difference to cam selection.

Or likewise, knowing what your CR REALLY is, will also make a HUGE difference to picking the optimum cam.

89importeater

ok well basically you are speaking a foregin language with all you just said. thier a guy that goes to my church that builds gm motors. i think ill take it to him or have him come over here to help me out because im so lost its not even funny. i hate being confused.

sofakingdom

iTrader: (1)

Basically what I just said is, according to the parts you have listed, your compression is actually a full 2 points lower than what you think it is; unless your motor is a 450 or larger.

Which makes it impossible to properly spec a cam.

Your heads most likely are terrible, so going too wild on the cam would be a bad idea from that point of view as well.

TRW pistons might not be "the best", but they're better than ALOT of what they might be instead. That doesn't have anything to do with the issue at hand. I just have a pretty good clue as to what you've got; having built as many motors as I have over the last several decades, alot of them with TRW pistons, I'm fairly familiar with their product line in a general way.

If I'm right about your compression, your car will go SLOWER with a "lumpy" cam than it does now with whatever it has; maybe ALOT slower, if your current cam is a good match to the rest of the motor. That would be a mistake.

five7kid

iTrader: (14)

Is the engine assembled?

The "882" to which I referred is the last 3 digits of the head casting number. It is located under the valve cover MorTec, Inc., Chevy V-8 Engine Block and Head Casting Number
Locations . If those are your heads (which I and I believe sofa suspect), then ditto to everything he said.

89importeater

no actually the last number on the heads are 624 (462624)

five7kid

iTrader: (14)

882's twins.

89importeater

so what kind of cam would yall suggest i put in. this is tha cam that cam out http://www.compcams.com/Technical/Se...umber=12-206-2

Sonix

iTrader: (1)

yea, that's about what I would suggest to put back in. Something like a compxe 256, which is pretty similar to that one.

Lower duration will help you have some low end torque. The rest of the motor is "optimized" for that. Meaning that a big cam to get big power will not work in your setup.

89importeater

will this be any improvement over what i already have or would it be basically the same. in other words would it be noticably better or is it just a waste of money.

Sonix

iTrader: (1)

I don't think it'd be worth the investment.

89importeater

well im not sure about these cams because you guys through me out to left feild with your responses but at any rate what about these? i dont know what these will do thats why im asking you guys because yall seem to be very knowledable about this anyways.....a) duration .050 218/218 lift .457/.
457 b).050 235/240 .490/.490 c).050 227/233 .489/.504

sofakingdom

iTrader: (1)

You can't pick a cam intelligently from inside a knowledge vacuum. You REALLY need to figure out exactly what you've got, before trying to spec a cam. Otherwise it's a total crap shoot. Pretty cam specs on paper don't make a motor run good; matching the cam to the rest of the motor, does. Some mighty ugly cams will sometimes work surprisingly well, and some real fine cams will sometimes be complete snails. It all depends on the combo.

Personally I think (b) & (c) are TOO MUCH for what you seem likely to have, and (a) is on the ragged edge. Which is to say, you could still do better with something else. But that depends on what you've really got.

Sonix

iTrader: (1)

you need to find out what your exact static CR is before you can get a halfway decent cam for your setup.

I have cam c, it works great.... In my setup, 10:1 CR, manual trans, ported heads, good quench

B) is way too big for you.

a) is just about right, it's not a split pattern (212/218 is a split pattern, 218/218 is a symmetrical pattern, see?) split pattern cams tend to work better in most cylinder head designs, like stock ones.) This cam is pretty close to what you already have.

Seriously, you need better heads, and to match up your compression ratio to your cam, and your cam to what you want to do with the car, and ideal powerband. No matter what cam you throw in that motor, assuming it's a 350 with 624 heads, you'll have a tough time going over 300-325HP.

89importeater

how do i find out what my cr exactly is then. also what are some good heads that yall would recommend thats not to awefully exspensive. im not about the go buy all of this stuff right now it will be later down the road. as of now the main focus of this project is the body. oh by the way the engine is out of the car so if i need the engine to be out to figure out the cr thats fine because its on an engine stand now. thanxs again for all the help its kinda hard to afford alot of this stuff just working part time at a grocery store because im still a college student so this may take longer to complete than i thought.

Sonix

iTrader: (1)

alright, my personal opinion would be to start with better heads.

I'd recommend porting some 416/601 heads. Cheap, and you learn a lot in the process of porting, I think both of those are key. That'll raise your CR ratio as well, and they flow better than those 624 heads. The heads you can get for a song, the porting equipment gets pricey. Budget $50 for the heads, and $150 for equipment, i'm being realistic here, not flying high on dreams.

Otherwise, you can get Vortec heads, and a vortec intake manifold, for ~$800. I'd say closer to $900-1000 when the smoke clears.

Pull your heads off your motor, and measure you piston depth at TDC with a feeler gauge and steel straight edge (ruler).

Don't plan on using those heads, so you can forget about CR for now.

89importeater

well i can surely afford 50 for heads and 150 for equipment. i guessed it would be 500 or more. but also i guess after i get new valves and spring and all the misc. stuff it wouldnt come out to being that cheap. but yea still i would like to know how to find cr. and where can i find heads and the equipment to port?

Sonix

iTrader: (1)

do a search on head porting. Sitting bulls thread has just about everything you need to know. Doom86 and myself have a few threads on the finer points of porting. Anything F-bird88 wrote is golden.

search for cc'ing your heads.
find a compression ratio calculator online.
measure your piston depth.
then do the math and you're set.

yea, the parts on the heads you'll most likely need to buy, but that's the same if you buy new heads or port 416's, or use the heads you have now. You'll need more spring if you want to run a halfway respectable cam, and go fast.

89importeater

alright thanxs everyone for your help on this topic im done with this for know but im sure there will be more questions in the future about this whenever i
focus my attention more on the drivetrain, as for know about to have car towed to school so i can do something i know more about, bodywork