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Groundhog

L26 Piston Choices

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I'm looking to buy some flat top pistons to achieve a higher compression ratio.

Based on other forum posts it appears that a compression ratio of around 10:1 is what I should be aiming for as a weekend driver with a mild cam.

 

One engine shop is stating that they have fitted L20 pistons to achieve this.

Given the L26 stock bore is 83 mm, and L20 bore is 85 mm, this is a 1 mm or 40 thou" oversize.

 

Has this been done by anyone else?

What compression ratio is achieved with the L20 pistons?

I am assuming that gudgeon pin size is compatable also.

 

If there are other piston options out there I'd be pleased to hear about them.

Thanks

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I have a full set of 6 flat tops with matching rings in standard size unused if you have a standard bore?

the c/r is all gunna depend on what head you put with them.im goin for about 9.5:1 on my build with triple webers and it should perform well.standard these engines were under 9:1 and still went great.get a get flowing head and your laughin.

actually i will have a reco n42 up for sale too soon....

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Hey,

 

I've got 30 sets of replacement pistons that I have been meaning to sell. They are old stock from my father business that has been sitting around.

 

They are +20" and +30" L24 and L26 flat top pistons with valve relief’s cut in. Rings and pins supplied.

 

Without knowing your cylinder chamber cc’s it’s a bit hard to tell you exactly what comp you will achieve. They are the same comp height as standard without the dish in the top of the piston so the comp with rise closer to your desired target.

 

These are an option if your are interested $75

post-101783-0-97976400-1459503484_thumb.jpg

Edited by dattocam

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Hry,

 

I've got 30 sets of replacement pistons that I have been meaning to sell.

I expected that to be a typo until I saw your pic.

Gotta love hoarding Datto parts. We are all guilty of it.

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I'm looking to buy some flat top pistons to achieve a higher compression ratio.


Based on other forum posts it appears that a compression ratio of around 10:1 is what I should be aiming for as a weekend driver with a mild cam.


 


Doing abit of calculations, the compression ratio of an L26 with an E88 and N42 head are roughly the same. All else remaining the same, a stock L26 should have 8.3:1 compression. If you get some flat-tops this will yield 9.3:1 compression. If you want to go higher, you can get 0.8mm and 1mm head gaskets which will up the compression to 9.5:1 and 9.6:1 compression respectively.


 


If you're budget conscious, go with the flat-tops and potentially a new head gasket and be done with it.


 


One engine shop is stating that they have fitted L20 pistons to achieve this.


Given the L26 stock bore is 83 mm, and L20 bore is 85 mm, this is a 1 mm or 40 thou" oversize.


 



Has this been done by anyone else?


What compression ratio is achieved with the L20 pistons?


I am assuming that gudgeon pin size is compatable also.



 


Anything can be done if the geometry is right. The L20 and L26 pin heights and diameters are the same so you're fine there. The bores are different and depending on the piston head design as well the piston dish volume will be different as well.


 


A bored out to 85mm L26 with L20 pistons will yield 8:1 compression. If you manage to get some L20 flat-tops you're looking at 9.6:1 compression.


 


If my calculations are correct, just go with the L26 flat-top pistons, your life will be so much easier. 

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I expected that to be a typo until I saw your pic.

Gotta love hoarding Datto parts. We are all guilty of it.

Yeah dad has a problem

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L20 pistons (assuming you mean L20B, ie 4 cylinder pistons) come in two types. Those fitted to 200B's and series 1 bluebirds have a fairly decent dish in the top. Those fitted to series 2 bluebirds have less of a dish in the piston top, the compression in these was up 0.5 compared to the earlier ones.

 

Point is, they are both still dished pistons so compression won't be much different to standard.

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Great feedback on the Forum and just the kind of feedback I needed to dispel the myth the engine shop is trying to sell me.

I've sent PM's re the pistons. |
Thanks Daretobedifferent with the calcs on compression ratios. I'll stick with stock bore and flat tops and then some head work and mild cam which will keep the costs down.

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The engine shop is partly correct - late bluebird pistons in an L26 will increase compression slightly due to both the extra capacity and less dish in the pistons, but it won't get you to 10:1.

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