vortech35091RS

Hey guys, Im currently building my engine, and I have a few people telling me my compression ratio will be to high to run on 92 octane gas. Maybe you guys have a little more knowledge then them, and possibly you can give me a clue on to where my compression ratio will be? Well....Here's what I've got.

-350 small block chevy
-Flat Top Pistons (4 inch bore)
-305CC S/R World Torquer heads
-ZZ4 CAM
-Wiend Stealth Intake
-600 CFM Edelbrock-cARB

The Engine has been hot tanked and honed, and almost everything is new, (just needs to be built) the block although came off a 92 Z28 and only had about 80,000 miles on it.

Any more questions about the engine, just ask.
Would be nice if I got some input.

vortech35091RS

Also, how much HP would you guys determine? Thanks

Dialed_In

iTrader: (3)

Going to need to know your chamber cc's, deck height, valve relief volume and gasket thickness.

Put together and tuned properly you'll probably be around 300 crank hp

F-BIRD'88

What is the part # of the pistons? Has the block been decked? Thoses head are "nominaly" 58cc but rarely exactly 58cc.
based on a standard bore flat top piston, standard block height, felpro gasket 8.9cc and assuming the heads are actually 58cc yes your cr will be a little too high for 92 octane gas. 10.32:1.
Many rebuilder pistons are not standard pin height, thats why I need the part #. eg: 345np wil lower the cr.
You need to cc the heads. they range in actual size.
There are many ways to adjust the finished cr to get what you should have. 9.5 to 10:1.

Deshroud the combustion chambers by a few cc's , select a thicker head gasket are just two. First you need to accuratly determine where you stand now.
You need to know:
bore size , stroke length, rod length, piston to deck clearance @ TDC, valve relief volume, head gasket volume, cylinder head volume. Until all these are known for sure its really a guess.

vortech35091RS

Wow, I would have never thought that my compression would be that high, I figured It was be high to a point where I would have to run 92 and nothing lower, but high than 92 thats B/S. Yeah those heads are 58 cc's, as far as pistons go......The engine rebuild kit im buying can come with different kinds of pistons at no extra charge (dome pistons/flat tops) what would you recommend to lower my compression a little?
Chris.
p.s sorry for the long reply

Sonix

iTrader: (1)

if the pistons they told you about where the TRW/sealed power H345's, then you're about in the boat I am in.
A dished, cheap hyper piston isn't really available.

The SIL1470 has a 1.54 compression distance, and 13cc dish, which should work well for you, but it is a cast piston.


I'd recommend like f-bird mentioned, de-shroud the chamber, maybe open it up to your liking, and get a nice cheap flat top hyper piston.

F-BIRD'88

I recomend you clarify which piston . ( pin height)
a H345NP piston or any other flat top piston with a 1.54" pin height will be fine (9.8:1 cr w/58cc heads). It will sit an extra .020" down the bore at TDC. Many rebuild kits use this piston. (But not all) The stock SBC piston pin height spec is 1.56" It makes a difference.

Further if using a 1.56" pin height spec flat piston you could open up the heads combustion chambers (with a die grinder) by 4 cc's and lower the cr from 10.32 to a managable 9.8:1.

five7kid

iTrader: (14)

With polishing and nothing else, my World 305 S/R Torquers came out at 64cc.

What's wrong with H423NP pistons? Hyper, 10cc dish.

F-BIRD'88

NoDa thing would give you a 9.77:1 cr using 58cc heads on a stock 4" bore 350 Another good choice.

vortech35091RS

This is the rebuild kit im getting soon, if this helps with some specs. or if you guys know any questions I could ask the seller.

http://cgi.ebay.com/ebaymotors/Chevr...1828QQtcZphoto

F-BIRD'88

This is a Enginetech rebuild kit. Many ( but not all) of the pistons are built with "compression height compensation" . Fancy lingo for non stock 1.54" pin height. You can download their catalog online and check for yourself.
This particular kit comes with .010 mains and .020 rod bearings. is that what you want? Others are available.