Help with CR
Turbo Mini Forums

Hi everyone, im building my first turbo mini and i am looking to be running between 7-12psi of boost. I have so far:

hif44 turbo carb
plenum
metro turbo inlet manifold
t2 turbo with downpipe and exhaust manifold
1275 NA block with standard NA head
metro turbo oil pump
standard metro turbo crank
standard metro turbo cam
upgraded fuel pump and fuel lines
bulkhead box
bleed valve
boost gauge

i know i definatly need better pistons and better exuast valves on the head, but i dont want to go doing things because i dont know much about compression ratios and the last thing i want to happen is it to go BANG, i was hoping i could buy some dished pistins and that would lower the CR, i want to stay at 1275 and not overbore, and i dont realy want to do much work on machining the head other than what may be nessisary for the new valves etc. i had a search for relivent info and was slightly confused. Can someone recommend the right pistons i should use, and any other parts or work i have to do

If you are willing to go to the trouble of buying new pistons then you must buy overbore pistons. You will seriously be compromising the life of the engine if you put new pistons in sloppy bores. You are best putting all the info into a CR calculator and finding out what dish or chamber size you need.

9:1 wiould be good for 12psi with a good IC.

Will you be using mappable ignition?

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

ahhh i see, i didnt take that into consideration. im on a budget and thaught a re-bore would be expensive. i wont be using mappable ignition, maybe as an upgrade once ive sorted lots of other isues out

The cost of a rebore is probably only about £40 so it's nothing in when compared to how important it is

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

ohh right, im glad to know that now, thaught it would of been costly, hmmm the window of power opens up abit more now aswel, what would you recommend going out to? im hoping for between 110bhp-130bhp

The cheapest option would be to have the chambers enlarged to drop the compression, much cheaper than a rebore & new pistons.
The NA pistons will take some boost, or if it's the standard Turbo pistons you have these are a good item and will take 15+psi.

Edited by Turbo Phil on 30th Mar, 2010.

WWW.TURBO-MINI.COM

blimey gary your rebores are a lot cheaper than here lol

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

How much do you pay Robert ? £40 is all I paid the machine shop last time to. Now I have my own machine, it's free !

WWW.TURBO-MINI.COM

do you guys know anyone in the north wales area that can do this for me, im torn between getting a re-bore and just enlarging the chambers. Another thing i thaught was if i re-bore then the cc will be increased and might cost me more on insurance.