FNFAL308

iTrader: (1)

I sure can't find it searching!

What is the max that a cylinder can be oversize for a piston? What is the gap specs between the piston and the cylinder wall? 350 ci chevy

Thanks!

sofakingdom

iTrader: (1)

There's not really "a" "spec".

Too many variables.

The type of the piston (forged, cast, hyper), the use it will be subjected to (street, racing, nitrous, fuel), the lifetime required (20 passes? 15 30-lap heats? 250,000 miles?), the user (grandma? 16-yr-old kid with no muffler? pro drag racer? phone company?), the importance of noise vs lifetime vs power output vs oil consumption... the list goes on.

Chilton's and such, and factory manuals, give "a" "spec" for tearing down a typical street motor with factory-stock pistons in it. Once ANY of those basic assumptions are changed, the "spec" is invalid.

What would you REALLY like to know?

FNFAL308

iTrader: (1)

What I'd REALLY like to know (very observant of you) is could I get away with rings and thro it back in.

I found my Chiltons and even tho it was not the exact 350, the .0007 to .0017 spec told me HELL NO.

So, to the machinest it will go. It does need a honing for surface rust and this will put it out of that range for sure. I'll try to get away with .020 over but may go .030 based on the machine shop recommendation.

Building it back stock for a work car - 18 miles per day. It may occaisionally see 4-5000 rpm but will not be a race car by any means.

89 TPI 350.

F-BIRD'88

FNF what are you trying to do there? re-ring a motor? The chilton specs are for a stock motor. if you don't have a lot of cash and don't mind a little noise at idle you can run a looser piston to wall clearance and a larger piston ring end gap than the stock spec calls for. The engine will not huff or smoke. The piston may make a little noise at idle. If you tend to beat on your car, a little extra clearance is actually a good thing. The more you beat on it the more things heat up and expand. If the motor is set up "stock" tight you run the risk of locking up a piston ring (ring butt).

Hone the cylinders and measure them and the pistons and go from there. You can run a lot looser than you think.

On one race motor, I remember running .009" piston to wall clearance. That is like running a .030" piston in a .040" hole" That motor dynoed at over 700hp N/A and made in excess of 1300hp on nitrous.

Usually with a stock type 350SBC cast piston you have a .005" "acceptable" "service limit" on cylinder wall barrel and oversize. You can hone it and re ring it and it will run just fine for a long, long time. We don't live in a perfect world.
If this motor has to pass a strict emissions test then you might want to build a more exact motor.

FNFAL308

iTrader: (1)

That's some info I needed. Back when (late 70s, early 80s) I just went ahead and got it bored and never thought about budget building. My paycheck went to my love - always a Camaro. So, I never thought about checking what I was starting with - just poured money in. Of course I wasn't married with 2 kids back then and a $1400 house note. 25 years older and deeper in debt.

I didn't even think about the emissions. It does have to pass emmisions in the Houston area and it will have all emmisions stuff on the engine in working order. The 305 TBI in there now has 200k+ miles on it and I got it to pass with a new cat and tune up. And it is blowing past the rings nicely... So this one should do that well even if loose.

I'll hone the worst cyl and check it. The 350 has a ridge that isn't big enough to catch a finger nail on and it was on the bottom edge - none on top. Hell if the bird was pre-82 I'd put a carb and I'd push the limit on the hp, keeping in mind the budget. If I could trade the 91 Bird (Work car) for an early model Camaro I'd go ahead and do a budget performance engine - God I miss those days. Solid cam, 850 holley, angle plug heads, etc. Aahhhhh.

I have to change the cam anyway and would like to do a solid roller instead of a hydraulic.

I have a complete donor car, 1989 IROC, from the front suspension to the rearend. It ran good but sat up for about a year on wet ground and pitted the cyls and cam. Exhaust, radiator, puter, keys, everything but air intake for the Bird. I just bought the air stuff from someone on here. It has a Goodwrench replacement 700r4 in it (not using for now) and a disc brake 3.23 posi that I am using.

Supervisor42

If it has negligble ridge, I wouldn't bore it. Don't forget the pistons wear also. If this is going to be a daily driver at stock power levels, have you thought about new stock cast pistons (shudder) and just honing the cylinders? Most people bore engines so they don't have to measure anything but ring gap and it's cheap. (they also like being able to call it a "355" instead of 350) Blocks should be bored when they are worn excessively or have scored cylinders. This also removes one rebuild life from the block.
p.s. don't tell anyone, but I didn't bore the engine I built for my '88 TA...
EDIT: Btw, why a solid roller instead of hydraulic for a stock level engine?

FNFAL308

iTrader: (1)

A solid roller would only be if I had a pre-smog car to drop the engine in. Then I would do a few performance mods to it and forget about the tpi and computer. Due to emissions, I am leaving it stock.