Porvair

Hi all - I'm relatively new to the forum and 951s, having acquired a 1988 Turbo S in Oct 2014. Bought the car as a street and track toy and have had it out twice on the track and am very impressed, but working out some minor (and not so minor) issues. V+Car was generally well miantained and has been a DE car since the early 90s.

Car has 136k and is pretty much stock with a Lindsey Boost enhancer set at 9.5 psi and a recent Lindsey chipset.

At my first event in July, I had an issue with a significant loss of power under full boost in 4th gear, which turned out to be deferred maintenence that was cured by new plugs, wires and cap/rotor. Embarassing as this is basic stuff, but I did not notice that on the street as its hard to get to a prolonged 4th gear full boost run without jeopardising my license, and it degraded over the day. Doubly embarrasing as my lap times were bested by a Chevette - a very fast turbo Chevette, but still a Chevette..

2nd track day was last week at NJMP, post tune up and post installing the Lindsey chipset. I also installed a Autometer boost gauge but did not install a wideband AFR, which I now realize was a mistake. In any event, the car ran very strong early in the day and I saw 120+ on the straight with up to 17-18lb boost in 4th. As the day progressed I saw slightly lower speeds but was not sure if that was meaningful, but the car felt fairly strong. It is a new car for me so we are not yet completely connected. Got in 100+ track miles, but it seemed a bit sluggish and a bit loud putting it onto the trailer.

Pulled the car out last weekend for a drive about town and it was very sluggish with the turbo spooling late (3,400) and lower than usual power both on and off boost, and a very rough idle at 1,000 or so. I played around with the basics and found that I could pull plug wire #4 with no effect on idle. Pulled the plugs (whihc had 200 miles on them, 50% track) and 1-3 were light and slightly toasty and # 4 was dark and slightly moist. Swapped #3/#4 to see if I had a fouled plug, but no difference at idle.

Next step was a compression test on #4 which was negative, as in none (well mayby 8 or 10 lb).

So - I am guessing based upon researching the forum that I may have toasted a valve or worse. Does not sound like a head gasket as neither the oil nor coolant was fouled, although I used a pint of coolant and and similar amount of oil at the track (with the oil usage sounding to be normal for a long track day).

Since I began the process of pulling the head to see what really happened, but I figured that I would get this put there as I can see that this is a very knowlegable community and others have dealt with similar issues.

Hope to have the head off next weekend which imagine will confirm the issue. I also need to determine the cause, but that is tough to do without confirming the problem. Wondering if the chipset contributed to this but I do not know if I had a lean condition as I did not have a wideband. That might have been a costly error on my part, but also wondering what one is supposd to do when you see lean AFR - other than not running the car in that condition. I did send the injectors out today for cleaning and testing in case that was a contributing factor.

If it is a valve issue, I'm wondering whether it is generally better to have the machine work done locally (there are some decent machine shops in Long Island) or pick up a head via Lindsey or another 944 vendor.

Thanks and apologies for the long intro email.

jerome951

When I burnt my valve (also #4 using factory chips) I could hear it loudly in the engine bay with the car running. Granted, mine was a major blowout (I could almost stick my pinky finger through the hole). If there's no abnormal sound I'm leaning toward a head gasket.

Yes, your oil usage sounds normal for track use, but you shouldn't be using/losing coolant. When doing the compression test did you happen to have the coolant reservoir cap off? If so, did you experience coolant overflowing?

In the long run doesn't really matter: the head needs to come off anyway.

BTW, the oil cooler seals are much easier to replace w/ the head off.

Porvair

Thanks Jerome. It did seem a bit louder under the hood but not it was not that loud. The muffler was a bit loose and I tightened that up but once I did the compression test I realized that the head was coming off anyway so I did not focus on that. I did not have the coolant cap off when I did the compression test, but I did pump up the cooling system to 10 psi with a hand pump and it held but I only left it on for 5 min or so.

I will add oil cooler seals to teh list of things to do while I'm in there. Any other PITA maintenance that is simpler without the top of the engine in the way?

Porvair

Also Jerome - did you determine what caused your burnt valve? Bad injector or some other lean condition?

jerome951

My injectors seemed to be OK (I had them checked afterward and they weren't bad). Valve blew through while doing 130+ around Nascar turn 3 at Daytona the first day of practice. I ran the previous race and let the fuel tank get kinda low (it was a 90 min enduro that I tried running w/o refilling; had ~1 gal in the tank at the end), but engine never seemed to stumble (I wasn't running an AFR gauge at the time). I'm guessing the long WOT pulls at Daytona didn't help.

Here are a couple other items that are easier to access w/ the head off:
Cleaning engine grounds
Replacing or checking heater control valve
Coolant and vacuum hoses
Checking/replacing wastegate control valve

Porvair

#4 exhaust

So I can confirm that I did burn the #4 exhaust valve. Any thoughts from the community as to likely causes? I sent the injectors out for cleaning and testing and pre-cleaning the flow was OK on all 4 but the spray pattern was only "fair: on 1 and 4. So I am guessing that the Lindsey 951 Max chip may have contributed with pushing the boost up too high for the 93 octane that I was running, leading to excessive exhaust gas temps and the burned valve.

That said, I'm new to the 951 scene and would appreciate any thoughts from the more experienced folks out there.

Thanks
Sean

Tom M'Guinn

It looks like your head is o-ringed, which is not stock and would suggest your motor has been run hard in the past, and that the heads been off and probably rebuilt. Might take extra caution to confirm those are all factory valves and not cheapy replacements. Other than that, your thoughts on its failure are good. You are flying blind without more data, and those chips/set-up is probably not helping. Get yourself a zeitronix wideband, a Vitesse V-knock, and the Laust EGT kit, and you'll get engine-saving data next time out. Oh, and ditch the boost enhancer in favor of an actual boost controller, and upgrade the chips/software

Porvair

Thanks Tom - I appreciate the advice and the Zeitronix kit looks quite nice (the AFM and a real boost controller were on the list but I will add EGT and knock sensor).

What are the options on the replacement valves? I see "AE" brand valves at a few vendors ranging from $25 to $45 per; are those quality, or is genuine Por$che the best (or only) way to go here?

Tom M'Guinn

I don't have any experience with the AE valves, but see this thread:

https://rennlist.com/forums/944-turb...um-or-not.html

Oddjob

17-18 psi boost on 93 octane for track use is pushing it. Keep an eye on fuel pressure (mixture), run on the rich side. And best to use race gas.

I see over 1700F EGTs on long straights at only 15 psi, and run 105-110 octane mixes (depending on ambient temp), and its pretty reliable. Have burned plugs when deviating from that recipe.