Overboring - benefits and worth it?
Aug 7, 2011 | 12:28 AM
#1
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Overboring - benefits and worth it?
I've been deciding on how should I build my car and while looking at pistons, I see std bore, 85.5mm and 86mm. What are the benefits of going bigger pistons and is it worth the effort to have bigger pistons (tuning and power wise)? Also, will I need to bore my block to put in these bigger pistons?
Aug 7, 2011 | 08:39 AM
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Yes you'll need a bore/hone for bigger pistons.
More displacement means more power, however going too big comes at the price of reliability.
The thinner the sleeve becomes the more likely it is to break.
Wider bores help unshroud valves. 4g64 blocks have better luck at bigger bores, as they have bigger bores from the factory. 4g63 blocks that still run coolant have been known to crack a cylinder at about 700 whp on a mustang dyno
More displacement means more power, however going too big comes at the price of reliability.
The thinner the sleeve becomes the more likely it is to break.
Wider bores help unshroud valves. 4g64 blocks have better luck at bigger bores, as they have bigger bores from the factory. 4g63 blocks that still run coolant have been known to crack a cylinder at about 700 whp on a mustang dyno
Aug 7, 2011 | 04:04 PM
#4
Boring should be viewed as needed only if your current bore is no longer straight and/or it is scored. The overbore allows you to start fresh with a clean hone on a straight cylinder. Performance gains from "boring" is negligible, you cannot bore the 4G's out enough to make a considerable difference in power just from an overbore..
Aug 7, 2011 | 04:26 PM
#5
^^ completely correct. The difference in volume is very small so the gains will be the same. I have seen a built .30 over pontiac 2.5l on the dyno run almost identical to the brand new identically built standard bore. Both had identical setups for the same race car.
My advice for the OP would be to do alot of reading in anything you can about performance and terms used and understand what they mean. Maybe get a book or something on basic engine building. Not a slam on you because everyone has to start from somewhere.
My advice for the OP would be to do alot of reading in anything you can about performance and terms used and understand what they mean. Maybe get a book or something on basic engine building. Not a slam on you because everyone has to start from somewhere.
Aug 7, 2011 | 04:36 PM
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^^ completely correct. The difference in volume is very small so the gains will be the same. I have seen a built .30 over pontiac 2.5l on the dyno run almost identical to the brand new identically built standard bore. Both had identical setups for the same race car.
My advice for the OP would be to do alot of reading in anything you can about performance and terms used and understand what they mean. Maybe get a book or something on basic engine building. Not a slam on you because everyone has to start from somewhere.
My advice for the OP would be to do alot of reading in anything you can about performance and terms used and understand what they mean. Maybe get a book or something on basic engine building. Not a slam on you because everyone has to start from somewhere.
I have the book "How to build a 4G63T" and have been reading the bottom end chapter and "More Displacement" section. It tells me stroking it will yield bigger results than boring it but I just wanted to know if it's even worth trying to bore while the motor is apart.But yes, I will stay with std bore unless it needs to be bored out. Thanks guys.
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