nitrusmr2

I just pulled the worn out POS motor from my 78 Corvette. Its not the original motor. The pistons are flat tops and .030 overbore but the piston to deck clearance seems huge. There is nearly 1/16th to 3/32th of an inch between the block deck and the tops of the pistons. Is this normal? Did smogged up car run shorter pistons to reduce compression ratio?

Thanks,

Aaron

EDDIEJ82

Most stock small block chevys run a .250 piston to deck clearance

mandm1200

I thought the stock clearance was .025".

MotorHead

Put a straight edge across a hole and use a feeler to see how much is there, stock is around 0.020" to 0.025" could be a little more or less but not 1/8 of in. If it is 1/8th of an inch Bubba has been hard at work

nitrusmr2

.025 huh? Mine is WAY more than that...probably close to 3 times that. This probably explains why I had only 120psi compression.

Next week I'll take it to the machine shop and see if it can be honed (probably not) or bored. How bad is .060 over for a ~300hp application? It's an 010 high nickel content block so I think I should be OK.

See ya,

Aaron

Matt Gruber

they are "rebuilder" pistons designed to reduce compression.

EDDIEJ82

My bad :o My fingers like to get ahead of my brain sometimes

Matt Gruber

u can check for taper yourself.
put a ring near the top, and slide it to the bottom. check end gaps in both positions. divide by 3.14, the difference is taper.
it might not need a trip to the shop if the bores are decent.

nitrusmr2

You guys missed this one. I did too. The machine shop caught it in about 15 seconds.

327 crank in a 350 motor. The stoke difference is 1/4 inch so the pistons would be sitting 1/8th too low at TDC.

Anyone want to buy a 327 crank? Its been turned .020 on the mains and .010 on the rods, it needs to be turned again, but .010 more will fix it.

Aaron

djcwardog

OK! Perfect excuse to go the other way - 400 crank and stroke it to 383...

nitrusmr2

Damn, I should have done that. The machine shop had a good 350 crank in stock though. Here is the run-down of the build:

041 casting heads, oem on 1969 300hp 350
1.94 intake 1.5 exhaust valves
Crane Blue-Racer cam 214 intake 224 exhaust @.050
lift was about .442 intake .465 exhaust
Roller tip 1.5 rockers
flat top piston with valve reliefs
.040 over 10:1 compression
Holley Street Dominator intake manifold
Holley carb - I haven't decided betwen the dual feed (probably) 750cfm unit I have or dropping down to a 600cfm single feed.

Hoping for ~300 flywheel hp and ~240rwhp.

Thanks,

Aaron