yuchao4363

Hey fellas,
I used to surf this board religiously before it got its new look but havn't posted in awhile. Had a quick question for you tech guys. I'm building my 383 (flat top Hypereutectic pistons and Eagle cast steel stroker crank) and I have a set of GM 441 heads with 2.02/1.60 in. valves, pocket ported, and I was wondering if running a Comp Cams 292° Magnum hydraulic, with 292/292° of duration, 244/244° of duration @ 0.050 in. lift would be too much? I'm looking for around 400hp and ft/lbs for torque. It's gonna be a street/strip car *mostly street. Will be running it with a 700r4 (performance built of course with the corvette servo, transgo shift kit, etc) and probably 3.73 in the rear. Would 244 duration @.050 be too much? Should I go with some around 230 instead? I appreciate all the help. (also will be running 1.5 rockers, victor jr. intake, and a edelbrock 600 cfm carb).
Yuchen

sofakingdom

iTrader: (1)

With typical off-the-shelf pistons (compression height 1.54") and an un-decked stock block, you're going to have about .045" of deck clearance (pistons .045" "in the hole" @ TDC). Hypereutectic flat-tops usually have about 6cc valve reliefs. A typical head gasket (1010 for example) is .039".

Run those numbers, and you'll find your compression is right about 9:1; somewhere between 8.9 and 9.2, depending on a few of the details.

That's too low for that cam.

In fact, it's borderline too low for a 230° cam. You'll have one of those motors that makes OK HP at higher RPMs, nothing real special, but OK; and a real soggy bottom end and a soft leave, and poor gas mileage.

"There's no such thing as too much cam, only not enough motor". That's not enough motor for that cam.

Those are OK heads, as stock heads go; nothing special though. You might want to look at selling them and getting something with some smaller chambers.

Doing nothing except getting 64cc heads, raises your CR by a full point, to 10 even. That's plenty for the 230°, and almost in the same area code (if not the ballpark) for the 244° one.

I'd recommend changing the heads rather than going to domed pistons, if this is a street motor especially.

Other things you can do to get the compression up out of the toilet might include getting pistons with a 1.56" deck height (usually they cost alot more, because they're not "rebuilder" type products); and zero-decking the block to the rotating assembly. If you took that route, your CR will come up closer to 9.7:1, with the 76cc heads. Again, in the range for the XE274, but not really enough for the 292.

yuchao4363

Thanks for the reply. To clarify a bit more I bought a 383 short block from theenginestore.com and they said with the 76cc 441 heads I would have a CR ratio of 9.6:1. I'm not sure exactly what the specific specs of the motor are, they're suppose to email me a detailed list of all the parts. Even so with what you mentioned in your post I'm a bit hesistant with running the cam with a duration of 244. I really invested too much time and money on the heads so I was wondering if anyone had any other suggestions. I'll sacrifice max hp but I don't want to end up with a engine with ok HP at higher RPMs, but liked you said "a real soggy bottom end and a soft leave, and poor gas mileage." Thanks for all the help in advance.
Yuchen

sofakingdom

iTrader: (1)

The thing you really need to know, is the deck clearance. There's more to that than just a parts list. You need to know EXACTLY what machine work was done, which can often be VERY difficult to evaluate from what a vendor will usually be willing to tell you; if not impossible.

Rather than try to piece the info together from some list and then "guess" at what machine work was done, or figure out what they mean by "Stage 2 block prep" or other commonly encountered verbage, just measure the deck clearance yourself. It's pretty easy. All you need is a way to find TDC (piston stop or dial indicator), a straightedge, and a feeler gauge.

Set the motor to exactly TDC, lay the straightedge across the cylinders, and see what feeler fits between the highest part of the piston and the straightedge. That's your deck clearance. Measure all 4 corner cylinders and take the average, if they're not too terribly far different.

Until you know that, it's all guesses; no matter what you "calculate", you have no guarantee whatsoever, that any of it is anywhere even remotely near reality. Once you know the deck clearance, you can actually calculate something and come up with an answer that has a relation to the real world. Just bypass all the useless stuff and proceed directly to the actual fact in question.

F-BIRD'88

You can build a 400hp 383 with the parts you've got using that 292 cam but you need to take care of the details to make it come together for ya.
You need to maximize the compression ratio to as close to 10:1 as possible.
You can shave your heads to reduce the chamber size. you can also select thin head gaskets to adjust the cr. but as stated above you have to determine the piston deck clearance yourself to accuratly calculate the cr.
If your piston clearance is .025" shave the heads to 72cc and use the .015" shim gasket. if the piston are .045" down at TDC, shave the heads to 70cc and use the same .015" gasket. Use Champion RV8C or AC R42T plugs.

441's are typically 76cc's but can vary. (cc your heads) You can flat mill them to about 69cc's if nessessary. The heads probabily need more porting too. but can flow enough air once done right. Don;t be a wimp,,You can do this at home. Search my posts on porting 305 heads. The job is the same.
You will want at least 3.73's (4.10's better) and want a high stall torque converter. 3500 stall is best. A modded 12" converter is not going to cut it. I'd change to a th350 trans/and 10" 3500stall for this one. The distributor will need recurving using LOTS of initial advance at idle (20 to 26deg@idle) for the big cam to idle nice. I would advance this cam in the motor a bit more to a 103 intake C/L for best performance. 106 intake C/L is normal. move it 3 degrees. Get a 750cfm carb. The Edelbrock is fine, but a 600 is not big enough for this motor. Use long tube headers with a minimum inside diameter of 1-5/8" and big exhaust. 2.5" dual or 3.5"-4" single with race muffler.
If you take care of these details the 292cam will not be "too big". It will be "just right".

sofakingdom

iTrader: (1)

Cams are cheap.

Block work and head work are expensive. Especially when you bought and paid for an assembled short block, and you'll have to disassemble it and eat what you destroy (the confidence that someone with more knowledge than you assembled it) by doing that.

I would not build a motor around a cam, and MOST ESPECIALLY not a street motor; rather, I would look at the motor I actually have, and pick a cam that matches it properly. Doing thousands of dollars of machine work to bend a motor to the needs of a $100 cam, is backwards thinking.

Likewise, if putting money into THOSE PARTICULAR HEADS was a wise thing to do in the first place, then you'll have no trouble selling them and recouping most or all of your expenditure, if you determine that they're not the right thing to meet your particular goal. If spending that money was NOT a good thing to do, then spending MORE money to pepetuate the mistake, is also not a good thing to do. Don't get all hung up on "just because I have them, I have to run them". Bad decisions get started and continued past their useful life that way.

In short, if I was building a street motor and found myself with your colection of parts, I'd be looking at cams in the mid 220s of intake duration, and low 230s of exhaust duration. A low compression motor like that will go faster with less cam, than with more.

yuchao4363

sofakingdom, F-BIRD'88, thanks for all your input, it's helped me immensely. I've decided to go with different heads, it's just the smarter choice and I don't want to get caught in the mentality of "just because I have them, I have to run them." Since I'm still on a budget I'm looking at trickflow 23 degree heads probably the 64cc ones.