The Mighty 3.0 MFI Motor Has Finally Had It

[Jeff Higgins]

Started smoking out of the right exhaust pipe during the first session at a track day on Wednesday. Called it a day and drove it home, about 60 miles, with it smoking intermittently.

Removing the top plugs revealed oil on #5. Unsurprisingly, a compression test revealed it was a bit low. Only 70 psi, where the other five were at about 150 (this was done cold the next morning).

*Sigh*. Only 125,000 miles on this build, completed 18 years ago. Only about 80 track days as well. I can't believe such a pampered little cream puff has failed already...

The motor is out and on the stand. Exploratory surgery starts tomorrow. I'm hoping it just broke a ring, that's kinda how it was acting. Both drain plug magnets were absolutely clean, no debris on either one. Pouring the oil through a coffee filter revealed nothing, no debris caught there either. Fingers crossed...

[icarp]

Jeff, Press on REGUARDLESS !!!!!!!
Well done

[stownsen914]

You thinkin top end rebuild only?

[Jeff Higgins]

I'll pop a rod loose and take a look at the rod bearing. I'm sure it will look just fine. So, yes, the going in plan is a top end refresh.

[pmax]

Good gas, but certainly not great gas.

[Ian Comerford]

Treat every failure as an opportunity…….

[al lkosmal]

Jeff,
Did you do a leak-down test? Might tell you the source of the compression loss....intake/exhaust/rings........

regards,
al

[Jeff Higgins]

Nah, skipped right past that. Heads are getting rebuilt and it's getting re -ringed regardless. It's time anyway.

[al lkosmal]

Yep

[Locker537]

Only 80 track days in 15 years? Slacker. ;-)

(Joking of course)

[Bill Douglas]

That clean and shiny. Can't be too much wrong with it

[Jeff Higgins]

Exploratory surgery complete. Part of the top ring land on the #5 piston has gone MIA. Looks like high RPM detonation.



So, I've discussed overheating problems I have experienced on the track. I've been exploring all possibilities. One cause can be too lazy ignition timing, and I've been running 24 degrees total. My motor is twin plugged, has 11:1 compression, and is run on pump gas (hence the lazy timing). In an effort to eliminate this as the cause, I have been sneaking up on more advance one degree at a time, listening intently for any "pinging". The timing was at 28 degrees total when this happened. That does not seem excessive, but could that have been it?

Another factor I'm considering is my recent eight state, darn near 4,600 mile road trip to our R Gruppe Treffen. We drove through some very, very, "off the beaten path" locales. Could I have picked up some bad gas (I actually did, from some of the food, but we're talking petrol here...)? Could it have started then (I was still running 24 degrees for the trip).

Or was it "just time"? I run this thing hard. Pretty damn hard, all joking aside. Small price to pay, really, at the end of the day. Having now torn it down and cleaned it up really reinforced the notion that it was just time to do it. Kinda fun, really. "Opportunity"...

[Jonny042]

Originally Posted by Jeff Higgins

Exploratory surgery complete. Part of the top ring land on the #5 piston has gone MIA. Looks like high RPM detonation.

In an effort to eliminate this as the cause, I have been sneaking up on more advance one degree at a time, listening intently for any "pinging". The timing was at 28 degrees total when this happened. That does not seem excessive, but could that have been it?

Seems too coincidental for it not to be the cause... what's the total timing on factory twin plug engines like a 964 or a 3.0RSR?

So one opportunity that might present itself is to bore out those MFI throttles and stacks a bit?

[Tom F2]

I've really enjoyed your saga of the 3.0 MFI. How does the #5 rod bearing look?

[gled49]

Jeff, in my 3.4 twin plug at 11:1 @ 26*, which was my race motor returned to the street, I stick to 98 octane non ethanol or 50-50 mix of 110 race gas and clear premium or when I was in AZ, I could get 101 ethanol at the pump. I personally feel 10.5:1 is the limit of compression, for twin plug, on street gas, for our old motors regardless of timing. You probably got a marginal load of gas that kicked it over the edge. Gordon

[Steam Driver]

My vote leans heavily on the “off the beaten path” fuel. Been there, done that one in Arkansas. Bought fuel in a little hamlet. Car (not Porsche) ran OK the rest of the day, but refused to start the next morning when cold. After going down a lot of paths finally drained the tank. Not sure what came out, but it only vaguely smelled like gasoline. Take away was avoid stations like that!

[john walker's workshop]

Yup, comp a bit too high. Kind of like cranking up the boost knob on a 930 and keeping your fingers crossed. You're buying new pistons anyway.

[Jeff Higgins]

Yeah, I agree - just too much compression. I have a new set of JE's on the way, this set with 9.5:1. Gas isn't getting any better, and I drive this thing all over hell and gone. It will be worth giving up a little punch for the peace of mind. I wonder if I will even notice it...

[pmax]

MFI, 11:1 and "modern" street gas, what could possibly go wrong ?

[Jeff Higgins]

Originally Posted by pmax

MFI, 11:1 and "modern" street gas, what could possibly go wrong ?

Right?

Honestly, though, 18 years, 125,000 miles, over 80 track days. She had a good run. Nothing to complain about. And, well, "that which does not kill us makes us stronger".

3.0 version 3.0 (there was actually a short lived iteration of this motor 20 years ago) will be better than ever. The wheels are already in motion - the pistons are on their way, I already have all of the gaskets, o-rings, and such, and I'm running the heads up to my good friend John Walker this morning for a rebuild. Life is good.