Why does an 8psi turbo on stock motor blow a new headgasket, twice?

[Vermont320i]

2592BED2-14B8-4DC9-8E4E-2CBB00574C53.jpeg38FF328A-1225-442C-B05E-33673863C60E.jpeg
Plug 4. 3. 2. 1. Plug #4

#1 center electrode is broken and tilted, only held in by side electrode.

Block and cylinders don’t look bad, though I am no expert. #3 piston seems to be off center??? See below.

4C34B7A8-364B-4464-9CE1-4098B38F033B.jpeg

Will post pics of head in a bit, once they upload. #2 and #3 look like some detonation was going on. On #4, the one with no compression, the cut ring had come apart and was stuck in the exhaust valve. Damn.36549BB2-0F4C-47CD-A6E2-18875CFF4EF8.jpeg

Gasket was nearly breached on #3.

[Vermont320i]

5F8642B3-BF80-4483-A71B-7D547C00D3A8.jpeg Before cleaning, you can see cut ring wire under #4 exhaust valve.

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After some cleaning. Note detonation damage on #2 and #3, and scrapes on #4 where wire let go from cut ring.

While i might get the energy to keep going now, with an unheated garage I’m pretty sure this project is shut down for the winter. I see at least a head deck resurfacing, installation of a volvo turbo WUR, and putting everything. Back together. Or more likely, a new head, and maybe have to dig into the bottom end.

[PowerKraut]

Looks not so bad to me. Is the valve and its seat okay? I would do a valve lap and call it a day. New head gasket + ARP Studs. The rest is in the tune

[Vermont320i]

Looks not so bad to me. Is the valve and its seat okay? I would do a valve lap and call it a day. New head gasket + ARP Studs. The rest is in the tune

Agreed, and thank you!

[Vermont320i]

Valve and seat look okay, I have a new gasket on order and have ARP studs.

I am going to put it back together with a volvo 240 turbo WUR, make sure the wastegate is set as low as possible, and tune it to make sure never over 14.7 A/F ratio. Once it gets warmer, assuming that works, I will probably head toward better fueling system.

[PowerKraut]

14,7 is stoich by the book, but i would not run it there, except idle and on coast down. too rich (to a certain point) will not ruin your engine, too lean will cause failure very soon. So try to head for the richer side.

[autox320]

Agree with PK. As I've also said aim for 12.5 AFR at wide open throttle under load high rpms. Idle can shoot for low 14's but may never be that depending on other factors. WOT is main concern. Then work on drivability if have the ability to tune doing so. Otherwise there will be compromise on AFR's you'll see but midrange low rpm etc may like 13's. Tuning is all load dependent. For the M3 example it's so fast on the road to dial in via rolling road that strategic amount of holding left foot on the brake to simulate load is needed. Not a lot cause can put excess load it will never see in real driving and you'll tune too rich. This is why if no dyno finding a grade uphill to tune with making passes is real nice.

Shoot for 12.5 @wot above 4k rpms and kinda tweak for best running idle. May have to live with the rest of the powerband afr's just to keep in a good running window in the important areas. Tuning my carb is this way. There is compromise when lack of cell by cell tuning via efi controller.

Sand out those head chambers by hand or tool where it has pits. Those are hot spots if not sanded out.

[OLD MAN]

BoostedE21 - Attila very long ago member not active now.

Was the longest running E21 forum member with a turboed M10 E21. His father actually built the car first and then passed it on to Attila.

He fought with with AFR for ever, I want to say he and his father added a sound electrically trigged start up injector for WOT. They played with that car for ever!!!!!

https://www.bimmerforums.com/forum/s...id=7272579&pp=

[Vermont320i]

Sanding and keeping it richer than I thought. Hopefully the volvo turbo WUR will help with a good amount of this. Thanks!

[PowerKraut]

Since proper EFI systems became so affordable, its just not worth the struggle anymore. I drive a weber carb mk2 golf as a daily, all year long. i retune the carb twice a year at least and it still runs not so great sometimes depending on the wheater conditions.

I understand that you try to get the best out of the K-jet by now, but it the long run you want to turn up the boost safely anyways and then you would have to start fiddling over again. Still always excited to see progress here

[Vermont320i]

I will look into EFI upgrades later this year. Right now I just want to get it roadworthy for Feb 27th winter rally here in VT. For that, it needs engine running safely —-even without boost—— and a limited slip diff. I do have the guts from an e36 small case LSD to swap in.

[Sio2crew]

I wonder if the o.p. ever figured it out?

100% it was too lean for any type of boost or load on the engine. 11.0 to 12.5 seems to make the best safe power on most turbo na-t bmws I see.

Almost sounded like the o.p. had no reference vac line from the intake manifold to the fuel regulator?