What is the benefit of using 83mm bore pistons as compared to using 81mm bore pistons?

I’ve ordered Darton Pro Sleeves, and have read that people use 83mm bore pistons. The sleeves are bored for 81mm pistons from Darton, but are capable of 84mm bore.

What does a wider diameter piston do differently than a slightly smaller diameter piston?

 

it wont basically do anything when ur running boost! 81 mm is spec for 1.8l and 84 mm is spec for a 2.0l. that extra displacement isnt worth the hastle of paying more for a custom piston and head gasket, b/c you aint going to feel the diff. Also you will lose some of the motors reving capacity.

 

more displacement.

 

That's not entirely true. 81mm doesn't always neccessay mean 1.8L. 81mm is just the measurement of the bore(diameter). And 84mm doesn't automatically mean its a 2.0L. It all depends on the block.

You will notice the difference b/t a block with 81mm pistons and a block with 84mm pistons. You know feel the extra torque. Is 84mm worth it? YES!

The only reason why I wouldn't suggest going 84mm on a street car is because you will have less wall to play with if anything bad were to happen to the block, esp. with force induction.

FYI- Custom pistons doesn't neccessary mean more money!

edit- Im assuming it's a sleeved block.


[Modified by ekb18c, 9:08 PM 12/18/2002]

 

the increased bore is felt on the street.

i'm running 84.5mm in my ls block.

when the car is in vacuum and not boosting, you can feel the difference quite noticeably.

 

Go with an 83 or 83.5. This will give you most of the displacement and plenty of cylinder wall left to go bigger later if anything happens. The bigger bore is definately worth it! Whoever say's it's not is just plain wrong It makes more power, torque, and spools up a turbo quicker.

Also, bigger bore doesn't necessarily mean you lose the ability to rev. The only down side is a heavier piston, which won't make too much of a difference. Now changing stroke is a whole nother story that will affect your redline.

 

wait, am i confused? how can you use an 83mm piston in an 81mm block? am im confused?

 

tony,

On a GE 81.5 mm b series block w/ oring, does the o ring groove prevent you from boring it out to 83mm?

 

No, you can go up to 84.5 with the oring. The ring is placed in a particular spot relative to the headgasket grooves, not realtive to the bore. It's in the same spot for an 81mm as it is on an 84mm. Bore away my friend....

 

You sure Tony? Reason I say this is because wouldnt say a b20 and a b18 stock gaskets have different head gasket grooves in relation to the fact that one is bigger bore? We had to replace the O-rings once because they were placed to far out on the sleeve.

 

Hmmm, i've never used a b20 headgasket. I always use a b18 gasket bored out. Being that the b20 gasket is 84mm stock they would put the grooves further out. When you use a b18 gasket and bore it out the grooves are in the same spot. All of the motors i build have the rings in the same spot and use bored b18 gaskets with no failures. I can see it being different with the b20 gasket though. It's not a matter of piston size, more which headgasket you use.

 

i don't know where you got this from but not one thing is true!!!

 

thanks, i've been wondering about that question for a long time.

 

werd, bro. i also don't think we need to worry about people taking his advice, when Tony (a.k.a. THE MAN) is in here indirectly refuting it. Tony and others who are members of winning race teams =

People who don't know and try to mask it with bad spelling and grammar =

Benny, like Tony says........do the 83-83.5mm and you'll have a nice happy medium betwixt added tq. with more displacement, and room to grow later on. On a side note benny, check your pm's.

 

83mm pistons are just as easy to get as 84mm. If you can't find them then you're looking in the wrong place. I have them in stock and arias keeps them in stock at all times.

 

Here is my shameless plug and opinion.

http://cgi.ebay.com/ws/eBayISAPI.dll...item=749122187

 

Man, it must've been hard to find those 83mm pistons...

 

tony1...

how much for a set of four arias 9.5:1 83mm pistons?

 

No 86mm are hard to find, trust me. I have a B16 that's been sitting in my garsge for almost a year now because I have to get custom pistons and I don't want to.