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Give the person doing the machining the block and ask them to find out if the block will need to be bored out then get your pistons based on that. Not every brand of piston/ring combo is made for the same tolerances, too big and you get blow by and lots of piston slap issues too small and the pistons may not even move when its up to temp.

Give the person doing the machining the block and ask them to find out if the block will need to be bored out then get your pistons based on that. Not every brand of piston/ring combo is made for the same tolerances, too big and you get blow by and lots of piston slap issues too small and the pistons may not even move when its up to temp.

Whats why you bore the block to suit the pistons...

So basically, the engine builder might say "the block needs boring out 20thou (0.5mm)" so then I'd go buy some 20thou oversize pistons and the pistons would come with a spec sheet detailing the required bore clearances, which the mechanic would use to bore the block to the correct size?

  • 3 weeks later...
yeah, we dont want to re-invent the wheel here.... if only they would make a piston with a small dome.. :P problem solved

Dave, there are dome top pistons for the twin cam 30. Arias make them 9.2:1 CR, they also make another slightly higher CR piston also but cant remember what it was.

Edit. Found the info.

p/n= AP332104

10.6cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.2-9.4

p/n= AP332105

13cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.5-9.8

Edited by TiTAN

hey im just after a quick hand..

i have found some dirt cheap forged arias pistons with 8.5-1 comp ratio with the single cam head..

what would the comp ratio be with my rb25de head??

thinking around 7.8-1??

is their any down sides to decking the block to get higher comp ratio??

id like comp ratio of around 8.6-1..

cheers tom

  • 9 months later...
  • 1 year later...

Using either the RB25 or RB26 head on the RB30 block you need to use RB30E pistons the RB30ET pistons will result in a far too low compression ratio to be much use as a street car.

Hey guys sorry to revive an old thread. Im also building a 25/30, R33 S1 turbo head and RB30 turbo block and as TITAN said it will give me way to low compression ratio (to my liking anyway). I was looking more between 8.5-9.3 compression ratio. I dont want to spend a fortune on forged pistons (Im only looking no more than 350hp atw), so i was thinking more towards getting stock pistons. Do you guys recommend getting a RB30 NA pistons or should I go more towards RB25 NA/Turbo pistons?

Sorry for the n00b questionsclosedeyes.gif any help would be greatly appreciated

Thanks in advance.

http://cgi.ebay.com/...8#ht_1055wt_907 ermm.gif

HEHEHEHErofl.gif

  • 2 years later...

Sorry to dig up such an old thread but I searched long and hard and I can't seem to find the answer. With stock rb30e pistons and a r33 s1 rb25det head (obviously rb30 block) does anyone know how much I can deck the block before valve piston clearance etc becomes an issue? The block is stock as a rock no previous decking as far as I know

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