steve8586iroc

I am building up a vortec headed 350 with a LT4 hot cam and rpm air gap intake, I want to run around a 9.5/1 cr with about a 0.040" quence clearance. I was looking for a d-cupped dished piston but have not found one suitable for this cr, if I use a flat top piston then my cr will be more like 10.4 and thats too high to run with iron heads and no egr. I am doing everything I can to keep this engine out of detination like using a ceramic coating on the pistons( when i find the right ones) and combustion chambers, using an air gap intake to isolate the incomming air and using as tight as quinch as possible. Anyone have any ideas on a good piston to use. I might be able to get away with a 10.0/1cr but no more.

Thanks, Steve

poncho9789

Try a speed pro or federal mogul (they are the same pistons)forged piston number 844-l2441f30 it has a compression of 8.35:1 on a 64cc head and that is baised on a head gasket of normal thickiness ie .035-.040.

steve8586iroc

Hey Poncho, I lived in Longview from 82 thru 86 and still have some family( ant and cousins) living there. Anyway I think that a 12cc dished piston would get me in the ballpark somewhere around 9.3/1 so I'll keep looking.

Thanks Steve

Matt87GTA

The TRW/SpeedPro/Federal Mogul p/n L2256 is a flat top piston with a 9.6:1 CR with 64cc heads and .039 Head Gasket. They are forged. But if you order them, make sure to get about three sets....... it will take that many to put ONE decent set together.......

Laterzzzzzzzzzz

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Matt

1987 GTA L98 MD8 GW6

"Stop Lights timed for 35Mph are also timed for 70Mph"

steve8586iroc

Thanks Matt.

Steve

SUPER-SPORT-CHEVY

Well no 10.4 is not too high to run with iron heads and no egr. If you were to get a good set of head gaskets and a multi step retard system you would be fine. But not every one wants to go through that trouble "it's understanable". What is the combustion chamber size exactly? i'll just go with Matt and say 64cc. Speed Pro makes coated pistons that run you 9.69-10.N/A compression depending on heads 24.99$ a pop. summit has all the specs you just need to look and decide exaclty what you need for your setup.
Good Luck.
SSC

Box of Rocks

Steve,

I'll jump in here because it may help. A few things to ponder:

1)With zero deck height you will have either .039 or .041 quench area automatically, depending on which brand head gasket you use. Fel Pro has a .051" thick gasket that adds about 2cc to head volume, thus reducing compression about 1/4 point.

2)The highest VE ratios are found using hemispherical combustion chambers with dished pistons (where compression can be maintained) but those are not found on the Vortec heads you have, so the best piston for YOUR application is a flat top with 2 valve reliefs.

3)Your cam is rated at 218/228 duration, and this is sufficient to bleed off low RPM compression. Big cams have their own built-in EGR systems, and this is caused by overlap. You will have a moderate EGR effect with that cam.

4)Want to run 10.4 compression with your combo ? I would. Dropping to 9.5 to one gives away about 6-7% total HP, which on a 350 HP motor is about 21-25 ponies. Torque drops a like amount.

TRY THIS:

Lightly grind and polish the entire combustion chamber on those Vortecs until they shine like a mirror. De-burr / Grind or round-off any sharp edges in the chambers and also on the piston tops. This eliminates hot spots that cause detonation.

With the motor back together, tune it using timing and fuel octane as your variables. Less initial advance and better gas fight detonation. You can use cheap gas, but you will need to use less advance with it.

Keep the engine operating temp under 195* F, and direct the coldest air possible to the engine. Each 11 degree drop in inlet temp = 1% rise in HP.

On a 350 HP car, dropping the inlet temp 33 degrees = 11 HP.

You CAN run 10.4 on the street. I'd rather see you run the Comp Cams XE268 grind (224/230 duration) because it has closer lobe centers (110*) and better valve acceleration. Those closer lobe centers also fight detonation better than 112*, and improve bottom-end and mid-range torque, but the HOT cam will do.

Hope this helps.

BOR

3)

RW91B4C

I hate to tell you this but I wanted to get my new Trickflow 210R heads (chambers)coated, until I read something. Aluminum discipates heat, it doesnt hold it like iron, that is why you can run higher CR with aluminum. This means if you get the chambers coated they will hold in more heat (like iron) and be more prone to detonation. This is just what I've read, and it makes sence to me. Just letting you know. Feel free to correct me if I'm wrong.

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91 B4C 305 TPI - SOON TO BE 383
TREMEC 5-SP, STOCK 1-BOLT REAREAND w/342 GEARS
K&N, AIRFOIL
EDELBROCK HEADERS, DUAL CAT TO HOMEMADE Y-PIPE & 3.5" SINGLE PIPE W/ FLOWMASTER
CRANK PULLEY, MSD, FUEL PRESS REG
COWL HOOD, WELD WHEELS
14.1@ 98MPH
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OTHER RIDE
67 CAMARO - STREET CAR
BIG BLOCK, PUMP GAS
350TH w/ATI 10"
12-BOLT w/373 GEARS
10.90s ON MOTOR - ET-STREETs w/MUFFLERS

ws6transam

You are wrong. The ceramic keeps the heat in the exhaust gases where it belongs, not the head. The hot spots refers to glowing metal that has retained heat because the surrounding metal cannot pull it away fast enough. The ceramic coating rejects the heat, keeping it out of the metal in the first place. Therefore, it will reduce detonation by slowing down the transfer of heat into the base metal, allowing the head to efficiently transfer away the heat that does manage to make it through the ceramic barrier.

Essentially, the head stays cooler, the exhaust stays hotter, and the combustion process becomes more efficient.

steve8586iroc

Thanks everyone. I just wish I has a set of 6.2" rods to go with my set up then I know I wouldn't have a problem with the evil dude called detonation. I'll run whatever octane gas it takes so I have only to tune the ignition and fuel curve to acheive my goal. Did I forget to mention I will be running a 670cfm tbi in a 91RS?

Steve