Which overbore?

[BlackTalonSi]

Yeah guys, in the very near future I'm going to be rebuilding my engine(92 6-bolt)....As far as the block goes, I'm curious as to what if anything I should take into consideration, when deciding on whether to go with a .20, .40, or .60 overbore. This is the first rebuild of the engine(that I know of) and I know they recommend a bore on the first rebuild. Won't boring out my block increase displacement??? And does an increase in displacement(or bore) constitute or necessitate(make necessary) an increase in boost. What are the advantages, or disadvantages....Does it make for better low end or top end power??? Does it help for a stronger, more reliable engine, does it effect gas mileage, etc. etc. etc...Also can someone explain why going with .20 or .40 over pistons would mean going with .20 or .40 over bearings???, I'm puzzled.....Help me out guys I need to order a rebuild kit soon....Any other tips you could give for a strong rebuild on a limited budget($1-$1,500) would be GREATLY APPRECIATED.....Peaaace

 

[gritsak]

yes it will increase displacement...and you dont have to increase boost when you do an overbore..not sure where you got that idea..theoretically you will gain low end tq. with a bigger bore.

unless you block is messed up i would just leave it alone and he-hone it, or at most to a .20 over...any power you are gonna make over the stock bore can be easily made up in boost...plus when you get more then .20 its hard to find pistons. most companies sell off the shelf pistons in .20 and you can even get a set of 2g pistons in .20 over.

 

[BlackTalonSi]

yeah, I've found 2 places that sell .20 over kits, slowboy and machV, so I was leaning towards .20 over...the only .40 over I've seen are from JE and unfortunately I don't have that kinda cash....Another thing, none of the rebuild kits I've found include connecting rods, is there anything I can do to my stock rods while they're out, pressure wash or shotblast???? Will they have cracks or any other signs of stress???....I've heard the term 1g BIG rods?? is that what's in my engine??(92 6-bolt, 4g63t w/manual tranny)....

 

[NOSNUSE]

Your motor has the big rods, you should have them magnafluxed to find minute stress cracks in them(this can be done by a machinist), I would go only .020 over bore due the fact that the larger bore will thin out the cylinder walls and also cause more internal heat. While the rods are out you can remove the hot spots in them by sanding down the factory casting imperfection and shotpeening them as well.

 

[1gTURD]

you will gain displacement from boring the block but not significant at all. It will barely raise any power... more or less its resurfacing the cyl walls and is done soley for that reason. 60 over is coming close and there really is no reason to go overboard boring an engine. As far as bearings... no you can keep the same bearings (size) but i would replacethem, they are cheap. Clevite 77's is what ive used in my motors. as far as the rods.... you can flux them but i disagree with polishing and shotpeening as i have come to learn that they are actually weaker when polished and shot peening. (at least for crowers and eagle rods) stock rods will have more casting imperfections than that of crower or eagle so it may not be true for stock rods. But it depends on how much power you want out of the motor before you decide on rods or rod modifications. personally i would sleep better at night going with crowers or eagle for anything over 300 hp.

 

[SoSprayMe]

Originally posted by 1gTURD
you will gain displacement from boring the block but not significant at all. It will barely raise any power... more or less its resurfacing the cyl walls and is done soley for that reason. 60 over is coming close and there really is no reason to go overboard boring an engine.

Word.. boring it that much will really weaken the cyl walls which is never a good thing. And you would be weaking the engine, that you are trying to strengthen. That right there is an oxymoron. To top it off the performance gained from the boring is so minimal you won't notice it, not even on a dyno. Lose-lose situation.

G'day,