boreing a ls to 82mm?

[erebunicrx]

is it safe to bore to 82mm on stock ls sleves? im reving to about 8500 and will see about 200 whp.

 

[phunky.buddha]

I would go to 81.5mm max. You won't really gain that much displacement going out another .5mm.

 

[99SiRidinLow]

You should be good... I'll be boring my b16 to that here soon... Only because thats the smallest size the piston i want comes in

 

[hcivic.com]

why bore that big just go as big as you need to clean up the walls the extra .5 mm don't do a hell of a lot

 

[erebunicrx]

b/c for the same money for the machine work and pistons i will be gaining hp. i will be ok if i post it right?

 

[StyleTEG]

Originally posted by hcivic.com@Dec 22 2004, 05:25 AM
why bore that big just go as big as you need to clean up the walls the extra .5 mm don't do a hell of a lot

[post=435763]Quoted post[/post]​

A little bit of displacement goes a long way.

Keep in mind the difference in torque between a B18B and a B18C1/5

Thats a difference of 37cc's

Going from 81.5mm to 82mm is almost as big a change.

I don't know if I would rev past 8000rpm on stock sleeves opened up that much, but I wouldn't say boring half a mm doesn't do much.

 

[brian11to1]

Boring the LS to 82mm makes it a 1.88L engine

Also if you use 82mm LS pistons it raised compression. Im not sure if they make PR4's that big though... I know 81.5's are made.

 

[erebunicrx]

im going with somthing like wiseco or je's. i want arond 12:1 comp B). need some kinda compression for the 404's

 

[StyleTEG]

Originally posted by erebunicrx@Dec 22 2004, 08:12 PM
im going with somthing like wiseco or je's. i want arond 12:1 comp B). need some kinda compression for the 404's

[post=436118]Quoted post[/post]​

Thats going to undercam the motor like crazy. 11.6:1 CR is the sweet spot for 404's.

 

[erebunicrx]

where and how did you find that out? i've been trying to find out what the best comp was for awhile but was not sure

 

[StyleTEG]

Originally posted by erebunicrx@Dec 22 2004, 08:45 PM
where and how did you find that out? i've been trying to find out what the best comp was for awhile but was not sure

[post=436133]Quoted post[/post]​

When you change your cams or your compression you change cranking pressure.

Since the intake cam keeps the intalve valve open slightly passed bottom dead center, some compression is bled off during the compression stroke. The result is less compression than your static compression (this is refered to as dynamic compression).

Because of this you need higher compression with more aggressive cams, more compression is bled off.

The sweet spot in general is between 20% - 25% INCREASE in cranking pressure over stock. Losing cranking pressure is a bad thing. Anything above 25% and the resistance is going to slow down the pistons as it reaches TDC, and it will blunt your top end gains.

I also have 404s, so I basicly did some calculations with a dynamic compression calculator to find out what would be a 25% increase in cranking pressure over stock.

Turns out 11.6 - 11.7:1 is

 

[erebunicrx]

awesome thanks for the info. do have any ideas for the right pistons?

 

[brian11to1]

Anything that's like 11.5:1 - 11.6:1...

 

[erebunicrx]

ummm.. how about a brand.

 

[brian11to1]

Ooops, check IB Spec

 

[erebunicrx]

they dont list any for ls

 

[brian11to1]

As long as they are for B series you can use em. And as long as it fits your bore, you can use them.

 

[brian11to1]

http://importbuilders.com/pistons.html

 

[erebunicrx]

what about them fitting on the rods?

 

[brian11to1]

Check out IB's rod selection for the LS