Is this cyl/head still good, what caused? 930
 

Just took the heads and cyl's off my 82 930 engine and the #1 piston was pretty chewed up. Few pics below... Everything stock in pics along with head studs.

1. Is this a result of detonation?
2. Is the cyl still good? Can it be fixed by machining surface down a little and adding gaskets at base of cyl? Note there is a rub mark inside cyl which can be seen in pic.
3. Are those black radial lines on the head/cyl interface the result of head lifting and gas escaping? Saw on one or two other cyls in exact same place.
4. Is the head still good? If not can it be fixed?

...gotta love those digital camera's. Can see more detail than you can see with naked eye.

Thanks!!

http://forums.pelicanparts.com/uploa...1131935024.jpg http://forums.pelicanparts.com/uploa...1131935045.jpg http://forums.pelicanparts.com/uploa...1131935056.jpg http://forums.pelicanparts.com/uploa...1131935068.jpg http://forums.pelicanparts.com/uploa...1131935082.jpg

Looks like localized overheating to me...

...can be caused by detonation, sometimes carbon build up causing local hot-spots causes pre-ignition or uneven burns.

IMO neither of those are usable. I certainly wouldn't

That, dear Sir is major-league detonation.

IMHO, you need a new piston & cylinder. A competant, experienced machinist can fix that head when the valve job is done.

When you dismantled the engine, were the rings still intact?

Sorry - I should have looked at the pics a little better....

Ok, thanks, as I suspected...

Few other questions:
1. What does detonation sound like? I didn't hear anything unusual.
2. Is the #1 cyl the most prone to this on CIS cars? When I was taking intake system off the fuel line that goes to the #1 injector really has a pretty sharp 90 bend to it right as it goes into the injector and the others loop around and give a much straighter shot.
3. Started monitoring A/F with innovate system last season. At what A/F should I be concerned at in on track driving? I've read to shoot for 12.2 on turbos, but really wasn't sure at what number I should be concerned at as it starts to lean out a little at higher rpm.

Joe:

1) Its VERY difficult to hear detonation in these cars and I'd advise anyone that if they are going to rely on their ears as the defacto "knock sensors", they better have deep pockets. Detonation issues MUST be dealt with proactively by using good gas, fuel enrichment, twin-ignition, and conservative boost levels.

2) Cylinder-to-cylinder temperatures vary and the #1 is hot.

3) You need to maintain AFR's in the 11.2-11.5 range with an air-cooled turbo engine. With a single point AFR setup, you cannot tell which holes are too lean or not.

You guys can correct me if I am not correct.

Joe can fight his detonation with:

Less boost (do not think he is crazy on boost now. Maybe 1.4bar, Joe?),
More fuel (to a point),
Twin plugging,
cooler intake charge (bigger intercooler)

Love to see these in order of importance.
Keep in mind this is a race only car. Joe still has cis with a 7th injector (Joe?)

Thanks

Ed

Here a start.

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/251323-79-930-turbo-heads-good-shape.html

John

Dude (to quote Ed),
Here's the rest at bargain basement prices.

http://forums.pelicanparts.com/showthread.php?s=&threadid=228125&highlight=930+an d+pistons

John

If only #1 is bad, check the injector. I had three bad cylinders and after a flow check on the injectors found, you guessed it, three bad injectors.

Also, a 3.3 cannot live with 1.4 bars unless other things are changed. Intercooler, fuel enrichment, twin plug, or/and race fuel.

Here's an A/F ratio that'll scare ya....


http://forums.pelicanparts.com/uploa...1132161908.jpg

IMO, 1.4 bar is insane.

Anything above 1.0 for roundy-round track use should have twin plug and race gas.......and should have EFI.

To answer ed's questions:

1. 1.4 boost LOL!!! Ed you're killing me! Max i've run is 1bar and usually less. however, before this turbo, i did have ebc set to overshoot, probably to 1.2bar because the thing wouldn't maintain boost to red line, but that 1.2 was tapered off before 5k. new turbo is no problem
2. possible
3. maybe! now that I just got those heads.
4. new turbo blows much cooler air. i can tell by ebc because it backs off gain when it's cool out so i don't overboost. the intercooler is much colder now also.

...and yes I run the andial 7th injector, but tell it when to come on. ;)

Thanks for advise in checking injectors, I'll have that done. OK, well, where can I have that done?

Based on where I'm running now, I don't think there is a reason for this to happen. 1bar or less, straight 110, monitoring with a/f with innovate... However the a/f monitor and straight 110 is new this year, so I'm thinking this is old problem. but what the heck, I need to fix now.

Here is another opinion, based on experience I've had with my 930 and a C2T on the other side of town.

A properly tuned CIS car, in 3.3L, can provide excellent AFR control without a separate fuel enrichment fixture. I dialed mine in to provide 12.0:1 AFR from 3500 - 6000 rpm, and it provided this at 4lbs of boost (accel enrichment). I think Steve is correct regarding his suggested AFR's on a CIS car, but mine liked 12.0:1 much better (per the dyno numbers) - about 18 or so more HP on top. We could get a little better HP with 12.5 - 12.8, but head temps really started to climb. When I tore the motor down, there was no sign of detonation.

Although good insurance, a 3.3L motor does not absolutely require twin plug like a 3.6L and up (with high boost) to avoid detonation. If you really want to play at 1.0 bar and above, invest your money in a crankfire ignition that you can map at higher RPM and boost levels. Timing is critical and often overlooked, even on CIS cars.

I bought matched injectors at Marren Fuel Injectors (www.injectors.com). In addition, I extrude honed the CIS intake to ensure equal flow through each runner. With an infrared meter, I measured the temps (at idle, about 1 1/2 inches from the exhaust port, on the primary pipe) to within 75 degrees, down from 275 degrees prior to matching and flowing.

Thanks Don. ...I am actually looking into the electromotive XDI. What did you end up setting your timing at in your crankfire setup?

What type of mods did you do to get A/F? Did you do the IA fuel head mod, play with WUR, etc...

btw -- where did A/F go above 6k?

Joe,
FWIW - I'm ditching my CIS for EFI, but with the CIS setup, I am able to maintain 12.0:1AFR all the way to redline. I have the Euro CIS system with almost new injectors, and I also have the Andial FEU. It gets to a point where I would try to lean out the car as I'm running a bit too rich according to the LM-1.

hobbieboy -- what power are you making? ...want to sell your injectors? I may want to buy.

I haven't dyno-ed my car since new turbo/headers/cam. I'm guessing 375rwhp. My only comparison is @ Tremblant, a GT3 cannot pull away when we both come out of the corners at the same speed.

I'm selling the entier intake/fuel head/BOV assembly if you are interested.

Don, just to confirm-you got your average ex temps down from 275 to 75deg? do you belive that this was soley due to the matching and flowing of the intake?