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Discussion Starter · #1 ·
guys,

I posted this a couple of days ago at the other 350z forum... have a question regards to my high cr pistons... wondering to know if there is anyway to cut a set of pistons out in different shape to achieve the same compression ratio because the pistons that I have got, the crown section isn't as high as the ones offerred by Esprit.. but they are also desigh to do 11.5:1 CR (at least on the packaing box and the bore is 95.78mm).. Here is the link to that thread and photos...

http://www.my350z.com/forum/showthread.php?t=151751

Thanks for the input in advance!

cheers,

richie
 

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Richie
With the Std piston the unswept area ( piston crown & combustion chamber area @ top dead center ) is 62.7 cc to achieve the Std CR of 10.3 to 1.

To achieve a CR of 11.5 to 1 the unswept area will be 55.5cc .

So that new piston has to take up 7.2 cc more displacement than the stock piston to get your 11.5 CR

I know how to measure that area when assembling a motor, but how to do it with just the pistons ?

You could push the top face of both pistons into some modeling clay or plastersine, but both would have to be pushed in an identicle distance & then measure the capacity in cc's of the indentations in your mould.
If the new piston displaces 7.2cc more your right on 11.5 CR.

CR = swept area + unswept area divided by unswept area.
So our motors are 3498cc divided by 6 = 583cc per cylinder

583 + 62.7 = 645.7 divided by 62.7 = 10.3
 

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Discussion Starter · #3 ·
thanks peter! Appreciate for your help! Jarek suggested me the same thing too... and just by the "look" of those pistons, they seem to have 7.2cc larger... but I shall call up Nizpro to confirm that.

Thanks a lot for your help!

cheers,

richie
 

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Discussion Starter · #4 ·
Peter:

Wondering to know, what is actually the piston/wall clearance for the stock engine? According to the measurement written on the box, the bore is 95.78mm, that's 0.01" over bore and they suggest that 0.003" piston/wall clearance is needed... does it mean that I will need to bore the cylinder by at least 0.01"? :)

Or does anyone know about that? thanks

cheers,

richie
 

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Peter:

Wondering to know, what is actually the piston/wall clearance for the stock engine? According to the measurement written on the box, the bore is 95.78mm, that's 0.01" over bore and they suggest that 0.003" piston/wall clearance is needed... does it mean that I will need to bore the cylinder by at least 0.01"? :)

Or does anyone know about that? thanks

cheers,

richie
richie
The cylinder block has the bore grades stamped on it
Grade 1 is 95.500mm to 95.510mm, Grade 2 95.510 to .520, Grade 3 95.520 to .530
The grade 1,2 & 3 pistons are all .02mm smaller, so stock has a piston/wall clearance of .02mm

That 0.003" clearance is a inch measurement not metric. .003" is .076mm

Assuming that the piston does indeed measure 95.78mm & the manufacturer requires a .076mm (.003") clearance
Then if you have grade 3 bores, your new bore size will need to be 95.856. Thats about .012" to 013" inch
Simon will be able to work out if it can be honed or needs boreing.
Why did the piston maker make them that large or did Simon order that size ?
 

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Discussion Starter · #6 ·
Peter,

Simon gave those specs to SPS, then they made those based on those specs... I thought they would have made the pistons according to what they duplicated for you in the first batch... but it doesn't matter... The machine shop should be able to figure it out... and with this set of pistons, the engine capacity will be at 3519c.c. instead of 3498c.c now... don't think there will be much diff. with this tiny increase of capacity anyway :)

Wait to see what a set of 06 lower plenum can do to the car since I have cams and VTC pulleys... might be able to get some torque back... will keep you posted! Thanks pete!

cheers,

richie
 

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Discussion Starter · #7 ·
Peter:

I finally know why I have 95.78mm written on the box.... we are running 0.008" overbored pistons, and the manufacturer requires a 0.003" clearance.... so the bore size will end up 0.011" larger than 95.5mm bore and resulting in 95.78mm bore.... those numbers add up nicely :)

Thanks!

richard
 
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