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To Sleeve or to Forge??

T

The_Geoffrey

New member
Joined
Aug 30, 2019
That?s is the big question?!

I?ve just got off the phone to the guys who will be doing all the machining work to my B230FT and he had told me that with 185,000 miles on the engine it will likely need oversized pistons.

I?ll be honest it?s not something I?ve budgeted for so it?s a bit of a set back. My question is can anyone recommend some oversize pistons that are reasonably priced. Failing that is it possible to rebore and sleeve the block back to 96mm and reuse the old pistons with new rings?

Power goal is 300-400WHP if that helps anyone.
 
To sleeve the block and re-bore it would run more than buying a set of pistons and you would be left running used, worn pistons. Wait until he actually measures the bores and pistons before making any decisions one way or another.
 
You need pistons before he bores the block, just like 2manyturbos says.
When i machined my block i take pistons to machine shop and he recommended little bigger piston to wall clearance because this is a powerful turbo motor...
 
The additional problem with forged (for DD use) in my experience is that the motor often ends up consuming oil - until the pistons properly heat & expand the looser gapping required can allow for oil consumption that you won't see with tighter cast piston (ring) specs. Of course there are other factors that can contribute to that.
 
Grab some OS b230ft pistons from FCP or IPD. A full set is ~$380 with rings.
If you’re engine has “normal” bore wear, it’s probably .004-0.008” piston to wall clearance on a stock bore.
It’ll be very easy for your machine shop to either bore and hone, or just hone to the next larger size.
Make sure they pay attention to the piston to wall clearance for stock pistons. Even with a turbo motor they are set up very tight. Too loose and you’ll have piston slap when cold.

To have all new sleeves installed, new rings, and old pistons, you’re looking at maybe saving some money..... maybe. The used piston skirts are probably scuffed pretty bad though.
 
I just had the same decision. 360tkm block and had to go oversize. New OS Mahles were 400€ from Skandix, not too bad IMO. And the should be ok for your power goal. Cleaning, measuring, block overbore and crankshaft polishing was 300€ total.
 
lookforjoe said:
The additional problem with forged (for DD use) in my experience is that the motor often ends up consuming oil - until the pistons properly heat & expand the looser gapping required can allow for oil consumption that you won't see with tighter cast piston (ring) specs. Of course there are other factors that can contribute to that.
Click to expand...
You are mixing up 2 different things.
Forged pistons grow more with heat (compared to cast), so they need more clearance at the top and at the skirt. We only care about the skirt when finishing the bore to match the piston.

Ring gaps are generally the same for cast and forged pistons, but the gap varies depending on how much heat the rings will see.

Some decent reading
http://blog.wiseco.com/everything-you-need-to-know-about-ring-gap
 
mikep said:
You are mixing up 2 different things.
Forged pistons grow more with heat (compared to cast), so they need more clearance at the top and at the skirt. We only care about the skirt when finishing the bore to match the piston.

Ring gaps are generally the same for cast and forged pistons, but the gap varies depending on how much heat the rings will see.

Some decent reading
http://blog.wiseco.com/everything-you-need-to-know-about-ring-gap
Click to expand...

yeah, I was going to say, I never noticed any excessive consumption on the 2.5L setup, at least not til it split the bore.. but that was a different cause and effect.

as far as op's horsepower goals, they're well within the range of oem pistons, but I would replace the stock rods while it's all apart. good advice has been provided, get the bores measured and then see if any of the normal OS pistons will work. Also, consider tracking down an NA block for use as they tend to be less worn in the bores (esp if you can find a lower mileage unit). Addressing oil feed/return is simple.
 
linuxman51 said:
Also, consider tracking down an NA block for use as they tend to be less worn in the bores (esp if you can find a lower mileage unit). Addressing oil feed/return is simple.
Click to expand...

This is what I did when I went with custom CPs on the 16v rally engine. I was able to hone the block and get a nice piston to wall clearance on a 96mm piston.
 
When I rebuilt my spare block last summer, Cylinders 1 and 4 were too worn for oversize pistons and had to be sleeved. Cylinders 2 and 3 were within spec for +1 pistons.

Your machine shop should be able to tell you once they measure it. OEM pistons are only $60 - 80 each depending on size with rings. Cheaper to go oversize pistons than sleeve. I think I paid $150 for a sleeve and $50 for a bore?

This was a turbo block with squirters. It was theorized by someone smarter than me that they squirter blocks wear bores faster.
 
Thanks for all the great replies.

So it seems sleeping isn?t cost effective against new pistons however I don?t have to go forged.

I can get the Mahle pistons in the UK for around ?400 which is quite reasonable considering. Not something I had planned or budgeted for but it?s added piece of mind for the future. The engine will also be getting forged rods so shouldn?t have any issues with handling 400whp. I was going to upgrade to 12.9 head studs and an ARP main bearing cap stud kit, but I have read that it?s not really necessary for my power goals so the money saved there can pay for the pistons.

I also have a 2.3L carb engine which is currently in the car that the new engine is going in. It?s a 1987 744 GL with 245,000 miles on the clock. When this comes out I?ll probably strip it down to see if it?s usable as a +T engine.
 
yeah, maybe get head studs if you're feeling really froggy, but in the 400hp range I would just run new oem head bolts and call it a day. I haven't run anything but factory hardware in the mains on any of my engines, and I've got one currently with oem pistons approaching 700whp
 
Aren't we running into questionable wall thickness (or lackthereof) when oversizing to 96.5 or 97mm though? For a 300 whp sure who cares but any more sounds like asking for trouble...
 
The common OEM oversizes are 96.3 and 96.6mm iirc.
If going over 97 and a poor tune, sonic test the bores.
 
mikep said:
You are mixing up 2 different things.
Forged pistons grow more with heat (compared to cast), so they need more clearance at the top and at the skirt. We only care about the skirt when finishing the bore to match the piston.

Ring gaps are generally the same for cast and forged pistons, but the gap varies depending on how much heat the rings will see.

Some decent reading
http://blog.wiseco.com/everything-you-need-to-know-about-ring-gap
Click to expand...

never mind. I was conflating the ring gap with the piston clearance :D
 
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