KV NA stroker build

[simon20vq]

Hello all
So I am building a stroker as some maybe aware.
However I need some help from you gents.
I bought some pistons off a user that would suit the build only to find they were 82.5mm and not suitable for the 81mm bores in my KV block (there mistake!!).
So I can either use those in a 7a block with some machining to reduce the compression height of the piston or ideally I would like 81mm pistons to suit the KV block, KV/7A rods and the diesel 95.5mm crank.
The standard KV pistons are to tall and I don't think there is enough material to machine down the crown and replicate the compression bowel.
So do you know of an audi/vw compatible piston that might suit?
Thanks in advance.
Simon

[Error404]

Can you not bore the KV out to 82.5?

[Rusty]

Why not over bore the current block and get more capacity? Plenty of strokers done like that.

[simon20vq]

I wanted to keep with the 81mm bores and have a complete stock looker. I have a 7a block so its and option to rebuild that as the 'stroker' and slip the 82.5mm pistons in but I really want to run with the KV block if possible and if the cost is reasonable.

[Error404]

Mine is 82mm and still looks the same from the outside

[K Simmonds]

Guess it would be approaching the maximum oversize but I can't see why a KV block wouldn't bore out to 82.5 mm, you'd get even more capacity as Andy says. Plus it would look exactly the same and and all ancillary components would be a straight fit.

[simon20vq]

Now your just confusing me!!

[K Simmonds]

I'm not super clued up when it comes to strockers, their rod lengths and piston crown height's ect, but a lot of the guys on here are and I don't want to give you advice based on guess work.

It would probably help if you gave us the exact details of the pistons you have, as well as the crank/rod details, I'm sure someone will be able to guide you in the right direction.

As it an NA engine you'll want significantly more compression than a turbo build.

[Rusty]

I don't understand what you mean by keeping it stock looking? As error says, no matter the bore or stroke, if you are keeping the OE block then it'll look the same...

Switching to a 7A block is very unlikely to work, unless you have all the ancillaries and are swapping to a 20V head, as it's likely to have many changes both large and small.

To clear things up, are you changing the crank from the original KV item? And are you fitting a diesel 95.5mm crank, a 92.8mm or other?

Might be worth outlining exactly what you are doing, to help people give you relevant advice

[simon20vq]

I have a set of pistons from a SA bus I believe there similar to KV ones in appearance. Standard rods and diesel crank. The plan was to 'machine' the pistons alittle as there a tad to tall for the application.

[simon20vq]

Replied to Kit while you were obviously typing Andy.
Yeah maybe I have to get the KV block machined then. I was hoping to just machine the pistons and rebuild. A friend could do that for me and there would be no cost involved.
Thanks for the replies/advise thus far.

[simon20vq]

Can anyone recommend a machine shop in Bath/Bristol area and a cost to re-bore?

[twoqu]

Not being critical but you will need to measure accurately rather than use the eyeball!
For an increase in stroke either the rod length or compression height of the piston needs to be changed.
If the compression height of the piston is changed then standard rods can be used. If not the rod needs to be changed.
So if these pistons are the same compression height as the KV then they will stick out the top of the block by 50% of the stroke increase. As the 10V uses bowl in piston then thats not going to work.
So you need to know the compression height of the piston, the rod center to center length and journal size and the difference in stroke of both stock and intended stroker. There are other variables to take into account as well.
Without knowing exactly what you have its difficult to add useful information.

[Rusty]

I had my engine built by Aelred, who uses places over Swindon way.

A friend used Ashley Engines many years ago. Might be worth speaking to them and see if they sound any good?

[simon20vq]

Thanks twoqu. The gudgeon pin location is moved on these to KV pistons but they also have a bowl in the piston. They are nearly right for application just a small bit of machining needed to the bowl and top to fit.
I'm not explaining myself well but I am aware of a lot of the variables that alter when stroke is changed.
I was hoping that someone had already done this and could say 'you need a piston off of........ and machine X to suit' Eh not happening yet!