Eco modded - hi comp low boost 998
Turbo Mini Forums

I know the topic has been discussed before but can't find the thread anymore.

There was a guy (one of the Pauls IIRC) who was on a high comp low boost small bore project.

This is appealing to me since my setup will not be an all out HP monsta
(standart pistons, standart cam, 12G295 head, IC, 8 to 10 Psi) aiming at 90 to 100 bananas.

So, I wanted to discuss the topic.

1) I think I will go for a 3.1 diff while fitting the X pin diff
One used one is for sale for 45 € and is told to be in good running order.
What do you think ?
What shall I look at / measure ?
Will I be better with a 2.9 ?


2) I have not been able to find the CR vs boost chart (but I red about once !)
Here is what I have in mind :
PSI - CR - target HP
10 - 8.5 - 100
9 - 9.3 - 80
( 8 - 9 - 90 )
( 7 - 9.4 - 80 )
6 - 10.3 - 70


Please, correct me !


3) Head :
I have been well taught not to skim an unskimmed 12G295 (and I have one)
I can try and find a skimmed one (I found one that was 73 mm thick so obviously massively skimmed)
or
I can work on a standart 12G202 or 998 head

Alpa has worked on the 998 head only to find it doesn't flow enough and doing something in the region of 55 HP at the wheels on 5 Psi.
Honnestly, that is a bit low for the pain and associated risk to fit a turbo (in France modified cars are forbidden)

Alternatively, I can buy a 1098 cranck and pistons to artifficially up the CR out of the unskimmed head
=> not easy and probably more expensive than find a skimmed 295 or an opened 940

Related head question :
Will smaller valves help low speed tractability off boost ?

Thanks in advance

Edited by Advantage on 3rd Jun, 2009.

Rusty by nature

I run a 998 with a 12G295, at 9psi with a CR of 9.3:1. Not sure of bhp, but over 80. It gets to 60mph in 8.5 seconds and does over 40mpg.

Does any of this help?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

It sure does.

9.3 out of a 12G295 means it is skimmed, right ?

Rusty by nature

No. Standard 28cc chambers on flat tops.

I can't remember what cc is in the head gasket, so it's 9.3:1 max, it may be lower slightly. I also never take into account ringland volumes, airs on the side of safety.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

So your head was not modified as per Vizard (must had some cc's) ?

As air is blown rather than drawn, easing air in doubles the benefits, ain't it (vs N/A) ?


Also, what do you think about the diff : 3.1 or 2.9 ?

Rusty by nature