To high compression !!!help needed
Turbo Mini Forums

hi
i have a compression of about 10:1 and i am gojng to put a mirage motorsports turbo kit on it and i need to get my compression down to 8:1 how could i do this without changing the pistons? could i open up the ports on the head?

my engine spec is
1293 not skimmed
mg metro head
cooper s pistons high compression
276 kent cam


Will

chambers in the head.. but i dont think you're going to get down to the right sort of CR just with head mods.. if you can afford a mirrage kit, then go the extra mile and get decent pistons too - it'll be well worth the extra outlay. and it means you wont have to rebuild the engine after melting a stock piston

yer but i cant really afford new pistons as well coz i will have to completely strip the engine again and then get the pistons removed and then buy new ones then pay to get new ones fitted could i run a t2 on 9:1 compression?>

i dont know.
We're going for 8.5:1, and that's only running low boost (10psi ish).. if i were you i'd rather run a standard T3 and get good pistons.

im going to run a t2 for deffo do u recon 9:1 would be ok?

you'll get bored of 7psi take your time save money and do it right otherwise like me you'll want to start again!

Get a modified head, and use that car. This way, you'll eliminate lots of teething trouble before you up the boost. 9:1 is Ok of an intercooler is present and high boost is not used.
I'd just get a decent head and get going...

i am going to fit a intercooler to fit behind the front grill and i recon it will fill most of the gap behind the grill so would it be ok to run 9:1 compression? i would get the chambers resized so it would drop to 9:1 but what psi could i run it at? and would it melt the pistons?

hi wkd
IMHO
if you remove the beak out of the cylinder head this should give you around 28cc of chamber volume on a stock 1275 turbo the C/R will be around 8.5:1 so.....................

together with a "good" intercooler plumbed in i personally so no reason to run the motor at 12 psi boost providing the engine is not clapped out say bearings etc and its not a smoker

The problem with removing the beak, is less squish effect. This further increases the likelyhood for detonation. I'm not saying it can be done, but I'd rather leave the beak in. I think the beak is 1,5cc in total...
I'm a big fan, of elaving CR up, but increase squish. This means boost levels could be kept high, but with better off boost figures and better ignition..

This is all theory, I've never seen any proof on the A-series, but I have on other makes.

would it be ok to remove the beak to drop it to 8:1? or would this just create more problems? and is 12 psi boost 2 much? would you guys do it this way?

this is all well and good guys

but.................. i think! wkd is wanting to get a usable motor with out going into mapped ignition and the like which could confuse him?

may be this will come later ?

i would like his comments!

having said that one of my motors is running the head
de- beaked

8.4:1 cr distrib, standard stock pistons and 14 psi of boost standard cam hi lift rockers
and there is enough DRIVABLE power to have some seriouse fun!

in my book! the phase 2 is just a touch too radical for good road manners

big numbers are not always the best!

thanks benros you are completely right so i think i will get the mirage kit and fit a t2 with my engine how it is at the moment but do some head work to lower the compression does that sound a gd idea? or not coz i dont want to build it and it blows up lol

Edited by wkd_6592 on 20th Jun, 2005.

the T2 and the mirage are a great combination
opt for a kent 266 cam or the mg metro N/A CAM
and a good intercooler

oh! and while your at it change the standard diff if this is still in there

as its the weak link

opt for the minispares one 4 pin diff HIGHLEY recomended by everone on here

you should end up with a nice FAST usable motor
as long as you dont go too greedy with the boost

as soon as its built you NEED to go on a rolling road session ASAP to set the fueling and ignition advance properly if you let a turbo engine run lean you will melt the pistons

this is my genral advice to you
others have their own oppinions
go for it ! make it happen

thanks for ya help everyone i am goin toi do the t2 on the mirage kit and i am goin to fit a intercooler and a dump valve can anyone suggest a gd intercooler for a t2? and tell me where when u fit the dump valve i know you take it off either the plenum chamber or the intercooler plumping where is it best to fit it and where does the pipework go off the dumpvalve?

it's best to plumb the dump valve into the plenum chamber, and plum the boost / vacuem hose into your inlet manifold

Team Racing

klkl cheers what about an intercooler have u got one to recomend i can get off another car?
and also what about an exhaust? i have an rc40 back box is that to small? what exhaust do u guys use?

Edited by wkd_6592 on 20th Jun, 2005.

do a serch for intercoolers
i think jimster placed a link someware with loads of pics of coolers
turbo dave has also wrote some Very Good topics on this issue

Regarding the exaust the rc 40 is a good one power levels are unaffected up till around 125BHPish......if just the back box is used

as you dont need to silence a turbo engine so much as a n/a engine as one well known guy stated that a turbo is a kind of rotary muffler!

i think with the mirage kit you will get the down pipe with this ?

maniflow exaust company will do the rest for the bits and bobs you need ?

if your buying the mirage kit ask them to supply the pipes to the rc 40 see what comes with it.

iain supplys the hoses bends for the intercooler PM him and does all the carb rebuild kits as well etc

wkd one other thing my friend

your cylinder head go fit some race valves obtainable from minispares

and do the genrall porting mods as well but dont alter the ports inlet and exit too much as this affects port velocity and will make your turbo a little less responsive to pick up

the exaust guid bosses tont take too much off there also as they are needed to conduct heat away

Cheers Benross for the advice. I know where Minispares is, as I live in Potters Bar lol