std 998 turbocharged without intercooler: what's max safe boost ?
Turbo Mini Forums

Hi,
What's your experience about the max safe boost we can run before engine destruction ? Especially without intercooler ?

I'm currently running 150mbar.
I've read here someone telling 5psi are OK, 7psi -> melted valves.

Thanks

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

assuming a maximum of 9.5:1 CR then 7psi should be safe.

But increase it with care, any pinking and back it off. Also keep the ignittion in check, max 25 deg advance.

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

www.twin-turbo.co.uk

Thanks Wil
The CR is 9.3:1 std 998 head, the chambers were enlarged and smoothed, the head skimmed by 1.5mm (in the oil passage, then welded :) ).
Actually I've been unable to make it ping when it was N/A since I've installed MPI injection.
It was starting to ping around 40 deg @4000 with HS4 carb.

7psi without intercooler ?
25 deg at which RPM ?

At 150 mbar the air temp rises by 4 deg w/o intercooler, seems OK.

Edited by alpa on 1st May, 2008.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

25 degrees maximum ignition advance.

WWW.TURBO-MINI.COM

Ok, 25 deg this is what I have at high 5000. Could I set 25 from 3000 ?


Now the main pb is to install the old T3 low boost wastegate, to be able to control the boost. Currently it's mechanically limited with the diesel wastegate, but it's unprecise and sometimes it hits the 125kpa limit (which cuts 2 injectors)

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

Basically 25 deg max on boost.

At lower boost levels and on cruise you can up the advance as necessary.

I ran my 998 at 6.5 psi with no IC and worked fine. Got an IC now but still only run 7.5psi.

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

www.twin-turbo.co.uk