2mm over bore?

[Guishnu]

Hey there folks,I have found a guy here in the UK who can make me forged pistons for the engine. However, i have the option to run a larger piston.

Is it worth it? How much bigger do you think i should go?

Sorry for another questioning thread...

Chris

[Q45tech]

Since the bore is squared in [ pi/4 x Bore^2 x Stroke] a 2% boost in bore yields a 4% increase in displacement which might increase power by 4-5% depending on a hundred other things.

Pretty expensive way to increase power.

[Guishnu]

Right.You are just a super automotive, internet, answering machine sir!

My situation is, the engine is being completely rebuilt and there is no difference in price between a 92mm piston and a 94mm piston other than the cost of the re-bore, which isn't massive. However, is it worth doing? In your fairly expert opinion, would it be worth doing? For a high HP and higher revving turbo charged application, would cutting 2mm out of each bore weaken the block?

(just done some rough figures, and a 2mm oversize in each bore, should increase displacement to almost exactly 4.6ltrs) IF my figures were right. However maths was never my strong point.
Modified by Guishnu at 12:56 PM 5/29/2007

[nismofly]

a lot of times people will overbore 1mm to refresh the cylinder walls, not necessarily to increase power

if he could do 93mm thatd be your best bet, a lot of times 2mm is where people start to consider the limit

[Mettler]

According to an engine builder down under here, you can safely overbore the engine to the limits of the headgasket's bore diameter which, if I remember rightly, is around 94mm... but then that's for NA application, so I can't advise how the bores will hold up to boost application.

[sijoko]

The Cast-in-place iron cylinder liners are 2 mm thick so I would say that 94mm pistons should not be a problem. Remember that the stock bore is 93mm, so you don't have to remove that much material to get to your new 94mm bore.

[defrag010]

also, remember that a 2mm overbore is only 1mm off of the actual sleeve thickness.

[PopPop]

Where are U guys getting these cylinder thickness quotes from. I know it has been years since I have done any measuring but, if I remember correctly the VH45DE Sleeve/liner insert measures out at around 101.6mm. In this case will leave plenty of room to go to 98mm if U want to have the pistons made! John Dixon even has 95mm or larger pistons with stock sleeves so what does that tell you?

[sinfiniti]

Where are U guys getting these cylinder thickness quotes from. I know it has been years since I have done any measuring but, if I remember correctly the VH45DE Sleeve/liner insert measures out at around 101.6mm. In this case will leave plenty of room to go to 98mm if U want to have the pistons made! John Dixon even has 95mm or larger pistons with stock sleeves so what does that tell you?

sorry not by my calculations.

zerothread/244488also

Yes, its bored to 98mm with new liners fitted.

[sinfiniti]

did a serach and found this:

zerothread/180455

Pistons and rods were custom made for me. Crank is stock, bigger capacity is from 98mm overbore.

Overbore must loose some strength but the engine builder is happy it'll be fine. Some in NZ are apparently 4". The liners are some sort of really strong steel, they were expensive anyway!! Can find out what material / spec if you're interested.

Thanks for the comments.

[sijoko]

Where are U guys getting these cylinder thickness quotes from. I know it has been years since I have done any measuring but, if I remember correctly the VH45DE Sleeve/liner insert measures out at around 101.6mm. In this case will leave plenty of room to go to 98mm if U want to have the pistons made! John Dixon even has 95mm or larger pistons with stock sleeves so what does that tell you?

The 2mm thickness liner info was in the SAE paper submitted by Nissan on the VH45DE.

John Dixon is using aftermarket sleeves with his VH. Maybe, he remembers how thick the original liners were. Nissan cast the liners below the head surface so it is hard to tell by looking at the block. If you can see the liners on a VH, then you are looking at aftermarket sleeves.

[defrag010]

well, depending on how thick the actual aluminum casting is around the sleeve, you can press in any size steel sleeve you want inside the alum casting if you stay dry sleeved. Are the 4" bore motors wet sleeved?

[sinfiniti]

The 2mm thickness liner info was in the SAE paper submitted by Nissan on the VH45DE.

John Dixon is using aftermarket sleeves with his VH. Maybe, he remembers how thick the original liners were. Nissan cast the liners below the head surface so it is hard to tell by looking at the block. If you can see the liners on a VH, then you are looking at aftermarket sleeves.

Yeah, that is in line with what i have said.I was trying to convey that the STD liners are not 5mm, so there is no way that the bore wiil support the amount of over-boring Mr Dixon has used on his build, HENCE the remark about where are u getting your bore figures from.Doesnt really matter though.