c/r and boost
Turbo Mini Forums

hi everyone, not been on here for a while but just seen my dads turbo and thought hmm

so ive got a question, dont know if anyone could help but my minis current spec is rebuilt 998 with pockets for a 12g940 head and a morspeed ph3 camwith a c/r of 10.5-1. Ive got a metro turbo head, and my questions are
1. if i put this metro turbo head on, would it lower the c/r enough to allow some boost? dont know how much 'some' is but enough to run a bit more power than its got already. which is 71bhp

2. is the ph3 too 'wild' for a turbo? as i have no idea

thanks for looking


oh and i should have 2 t3's for sale soon

firstley whats the ccs in the pistons
the standard 940 head has 21.4 cc in there

Will-h on here has a 998 producing a BLISTERING 155bhp and 165ft pounds of torque and revs to 8000rpm
with one of my modded 12g 940 race heads.

yes the phase 3 cam junk that especially on a 998 best go for the N/A Mg cam or a .......... kent 266

wil-h is running the mg cam ... i think ?

what blower are you running ?etc........

Not sure we have that much torque Steve, more like 140. However, in answer to your questions.

Even with pockets with a standard 940 head you will need to do something to lower the compression a bit. Opening out the chamberes is easy enough.

Yep ph 3 is too wild, MG cam is what we run. I am sure a better cam could be developed, but it works well.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

ah right, thats a shame about the cam, i was hoping i would have to take the engine out, would the engine just not run if i kept it in? even though it runs fine at the minute, would the turbo just make it alot worse?

if i did open the chambers more how much boost would i be able to run?

my engines got flat top pistons, and dont really want to take them out to replace them.

im not sure which turbo to use either if i choose this route, would a t25 be ok?

Have you read this? http://www.turbo-mini.com/62147.html

If they are standard pistons then that will be the limiting factor.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

a T2 would be a good turbo for this engine, the phase 3 cam is a no no !

what ph3 cam are we talking about here?

you say that you dont want to take then engine out so i persume you already have one installed.....on an NA motor?

just to clear up are we talking about the Avonbar ph3 cam?

in your first post it sounds like we are but im just confused as to why you would have one installed on an NA motor?

It is a morspeed ph3 cam for NA motor (read the post again). Even an avonbar ph3 cam is too much for a 998, for that matter so is the avonbar ph2.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

sorry, im a foooooolllll!!! must learn to pay attention! GOON!

looks like ill be chaging the cam then, is the one you use the metro n/a cam or the turbo cam? or were they the same? thanks for the like ben, was interesting. with the turbo that was used does it not come with the actuator atached? and did the bracket bolt on where the bolt that holds the breather cover on? and why was the lambada sensor added? does it make it easier to set the carb up?

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

ahh right, well thanks for the help guys, much apprecieated

Obviously your compression ratio of boost will be vastly different from your compression ratio on boost from the reseach I have done you have three considerations

1 Static compression ratio

2 dynamic compression ratio

3 Altitude you are runing the engine at

Now having looked into this myself and limiting my engine build to a dynamic compression ratio of 14.7:1 which is somewhere around 260psi, with a specified maximum boost I can reverse engineer the engine build to a specific static compression ratio. Again if you know your static compression ratio you can work out how much boost you can run too give you a safe dynamic compression ratio.

To maintaine a dynamic compression ratio around this figure but run more boost would mean lowering the compression ratio which I am told would make the car very unresponsive of boost if it were lowered below 8.5:1. so knowing all this your window for performance gain could be very small, which is when the wallet takes a big hit.

Own the day