1982 70hp bore questions

[Hoopty]

So I have a 70hp that needs piston rings and maybe a new piston in the top cylinder. I also may need to bore it out due to condition of the sleeve and I have a few questions about boring. If I were to bore out the motor would I need oversized pistons for it or will 0.015" or 0.030" over rings trick on the stock piston. Second question, if I were to bore it out 0.015 over or 0.030 over which size would be smarter and how much power would be estimated to gain? I would be boring all cylinders in this case not just the top. Thanks guys

 

[flyingscott]

You will need to replace the pistons if you bore it. The machine shop who does the boring will tell you how far it needs to be bored. There will be no power increase from boring the motor you will still have a 70 hp motor.

 

[Faztbullet]

You cannot put oversize rings on stock pistons

 

[Hoopty]

You will need to replace the pistons if you bore it. The machine shop who does the boring will tell you how far it needs to be bored. There will be no power increase from boring the motor you will still have a 70 hp motor.

So it wouldn't increase the power output in any way? Could I get away with only boring the top cylinder? The other cylinders and pistons are in good condition.

 

[Chinewalker]

Yes, you can do a single cylinder. Pistons are weighted to take that into account - IF you stick with the same style pistons. If you try mixing aftermarket (Wiseco,etc.) with OEM then you are likely to run into problems. If you go this route, hone the other cylinders to a fresh surface and put new rings in.

Yes, you will get a power increase - back to 70 hp. It's likely that your last few times out you were somewhat less than that...

 

[Silvertip]

Without looking of the bore of your engine lets use a Ford 302 V8 as an example. The standard bore and stroke for that engine is 4 x 3 inches. If you bored the engine .030" you would increase the displacement from 302 cubic inches to 306.13 cubic inches. You likely could not measure the HP increase. On your engine the displacement increase would be insignificant.

 

[Faztbullet]

Reason the HP doesn't increase is your only increasing CC's not CI's....maybe 1 -2 hp if you do all three. I get tickled when at ramp and somebodys crowing about their bored out rebuild...I always ask em did they go up pitch in prop?....always silence.