dom1102

Hi, does anyone know the correct piston ring specification for Alusil bores? I have just had a 951 engine rebuilt using JE pistons and rings. The engine has done 2k miles and already has significant bore damage. The parts were specced and rebore carried out by an Alusil block specialist (Goznays UK), who assures me the correct process was used and the correct JE parts used. The guys who put the engine together (Promax UK), tell me the JE rings were the incorrect spec for an Alusil bore. Side note; the engine was carefully run in for 1k (of the 2k miles) on mineral oil. The oil was then changed for royal purple synthetic oil and the car driven normally. As soon as I started using it normally (full power), it was evident that there was excessive breathing from the engine. I am willing to accept that there might be another issue if the rings are not to blame. There is so much misinformation re Alusil so I am looking for a response from someone with qualified experience to help me try and figure out what has gone wrong here.

SoloRacer

Cool engine. Will you have it out this summer?

gruhsy

Just installing the 5 inch exhaust, then intake, fuel rail, new -8AN fuel lines, gauges then tune. Hopefully by Friday.

Jason

Tom M'Guinn

So sorry to hear that! JE pistons are not generally made to go into Alusil bores, so I'm not sure there is any "correct" ring spec. A local machine shop here used to make racing engines with JE pistons for their own shop cars, but even they admitted that some of those engine would gaul-up. If you take that motor apart, you might find scuff marks on the piston skirts to match those in the bores. While it might be the rings, I think it's equally likely the skirts are sticking to the walls. If you want to run JE pistons, you would want to look into sleeving the motor or having the bores Nikasil coated. Otherwise, you are better getting the Mahle pistons (or maybe the new Wossner pistons that claim to be truly alusil compatible).

Duke

Tom, you can update my listing with dyno numbers.

Chris White

Long f’in week at the dyno….more little PIA things than you can imagine. Seems like I was fabbing up parts every night for little fitment tweaks – final tuning on Monday!
The Dyno owner says his engine dyno is conservative - but the first power pulls seem to offer a glimpse at the possibilities!

On the base map with very conservative timing, no cam timing changes and limited to 15-16 psi =
582.2 hp @ 6800 and 516.6 ft lbs @5400
Good torque curve – over 450 ft lbs from 3800 to 6800

I left the camera sitting in the dyno room – so no videos until Monday!!

Chris White

Specs for the list – 3.1liter (106mm bore) MID sleeved 16v (968 head with variocam removed and individual adjustable cam gears) Dry sump, GT35R turbo, SFR stage 2 headers, SFR intake and custom throttle body. TecGT full sequential w/80lb Deka4 injectors in a custom fuel rail

dand86951

Chris, you have to be happy and excited to see those results.

mudbuddha

Good stuff Chris...Can't wait for some vids. Btw, my 3L MID block still holding up well...

RolexNJ

Chris, thanks for the updates. That sounds very promising and with conservative settings all around. Hopefully you may have a chart too so we can see the results, and the curves as well.

Thom

What kind of tranny can hold that much power without a rebuild at every street corner?
My butt dyno suggests I'm only around 350bhp yet the tranny is already taking a serious beating

Chris White

A couple of choices –
968 6 speed
924 turbo ‘snail shell’
951 with lots of cooling and a gentle foot.

Duke

Great results Chris. Welcome to the club
What injector dc at max power? you must be very close at maxing out the 80 lbs.

Chris White

Nope, lots of head room left! In theory (a theory I don’t want to test!) it should hit 100% duty cycle at just short of 1.8 bar of boost at 7000 rpm. I don’t plan to run 26 psi!

Full sequential is the key. I really like the new high impendence Siemens injectors – very controllable at short openings too!

Duke

That sounds extremely optimistic Chris, considering 1.8 bar should net over 800 crank hp with an efficient turbo.

By the way, what fuel is being used? Pump fuel or race fuel?