Lonely P-owner needs help getting nuts off (just how big is this thing?)

[RarlyL8]

Need some help from you 930 guys -

Motor is a '78 930. There is an aluminum nut/bolt/plug thing in the very front center of the top intake manifold. I need to find a replacement for it but do not know what size it is. It has a hex head for removal. 18mm?
I plan to tap the replacement to accept a 1/8 NPT fitting for my boost gauge. Don't want to harm the original, might want to put it back it some day.

Thanks.

[Doug Zielke]

I just searched PET for the part you describe, but can't seem to find it shown on the 930 intakes. Any way you can post a picture?

[RarlyL8]

Thanks for looking Doug.
I tried to post a pic when I wrote this thread. Wouldn't work for some reason. I'll try again this evening.

[jkcrewsn]

Hey Rarly, I looked for that on my '79. Is it under the intake (air filter housing)? I couldn't see anything like you are describing.

[RarlyL8]

The "intake" that I am referring to is the top one that houses the two turbo pipes (inlet and outlet). Sits on top of the regular intake that houses the throttle body.
The "plug" is located right in the middle of this intake, facing you as you look at the motor from the front (the intercooler will cover this area). It is right above and to the left of the throttle body.

Boy I wish I could post a pic right now, very confusing. The 930 manual does not call this piece an intake. They have a couple of different descriptive terms for it that I can't recall right now.

The "plug" is aluminum, approx 18mm (round) with a female allen head for removal. It is only about 1/2 inch long.

[zuffenhausen]

The large casting above the throttle body is actually the pop-off valve. It bleeds excess charge pressure to the intake side of the turbo. I'm don't remember the plug you're referring to when I did the top-end rebuild on a '78 930, but I don't doubt that it's there. My question is: Why do you want to tap into that for your boost gauge when the factory already provides a boost gauge and a tap for it? Also, there are several hoses that I recall going to this casting and you could easily Y into one of those.

-zuff

[RarlyL8]

I'm gonna do my best to post a picture of this tonight. I need to go through all of them and see if I have a good one.

The reason for using this plug is because my mechanic buddy suggested it. He does lots of 930 race car stuff. Says that's what they do, so that's what I should do. I listen to him because I'm damned green to this and he's been doing it for 25+ years.
I've made a bunch of mistakes with this motor that he has bailed me out of. The motor is going into an SC so there is no factory boost gauge. He plugged the original site on the motor and set me up with several feet of steel braided line and 1/8 NPT fittings. I still have to find adapters for the boost gauge that will go
where the clock is now. Other aftermarket gauges use the brake booster to tap in. He says that's cheesy and may read false.

I remember the manual refering to this casting as a pop off valve, but it doesn't look like any pop off valve I've ever seen. Finding good info on the actual mechanics behind this junk pile has been very elusive. I've got a couple of books ordered, we'll see if they can help out.

[RarlyL8]

This pic isn't the best, but it's all I have right now.
You can see the "plug" just above the coil. It is the round aluminum button facing you on the black pop off valve casting.

[Doug Zielke]

Rarly, I looked (hard) at PET again and cannot find that part.
The illustrations in PET are not very detailed, so I looked at the parts list to see if it was described there. Not anything even close.
I think this is starting to bug me more than it is you!

[emcon5]

It ain't a plug, but is this it?



# 14 shows up as:


#15 is a sealing ring, 900 123 009 30, which subs over to N 013 816 1

Hope this helps,

Tom

[zuffenhausen]

Ah, thanks to the pic from emcon, it's all so clear now. That plug is the one your mechanic put in to block the stock tap for the boost gauge! It's no wonder we couldn't help identify it--it's not a stock 930 part. Anyway, I would just go ahead and drill the plug you have. If you want to put something back there later, put in a stock boost transducer.

-zuff

[RarlyL8]

Thank you, thank you, thank you all.

My mechanic didn't put this aluminum plug in there - that is where my confusion came from. Must have misunderstood him. I think it was there when I bought the motor. Sorry for the confusion, I wasn't looking for part #14 in my manual 'cause I didn't know it even existed!

You guys are great. I'm a hotrodder with a past consisting of big cube V8s, carbs, and blowers. This is my first foreign engine rebuild, first foray into the dark abyss that is CIS, and my first experience with turbos. Boy have I had an awakening!

What is #14? What is its function in the stock configuration?

[emcon5]

Originally posted by RarlyL8
What is #14? What is its function in the stock configuration?

Boost pressure sender, see the second pic above for the number and the sub.

Tom

[RarlyL8]

I read the part number and description Tom. Seems stupid to me. Why do you need a pressure sender? Isn't that what the pressure does all by itself?
So what does a pressure sender do that an open port to a boosted plenum cannot?

[zuffenhausen]

Originally posted by RarlyL8
I read the part number and description Tom. Seems stupid to me. Why do you need a pressure sender? Isn't that what the pressure does all by itself?
So what does a pressure sender do that an open port to a boosted plenum cannot?

The stock boost gauge on the 930 is electronic, not mechanical. A wire goes from the sender to the gauge, as opposed to a hose going to a mechanical gauge.

-zuff

[RarlyL8]

Yep it is.

This has been bugging me so last night after work (yes I work too much) I opened up the 930 shop manual and looked for this diagram.

There it was. An elecric boost sensor. No wonder the stock 930 boost gauge is junk.

Sorry I bothered all of you with this question. I had the answer right in front of me but never thought to look there for it.

Thanks just the same.

[zuffenhausen]

Originally posted by RarlyL8
No wonder the stock 930 boost gauge is junk.

I think "junk" might be a bit harsh. The stock boost gauge in my 930 always worked and seemed to be fairly accurate. I'll admit the gauge is small and mostly useless, but so is any boost gauge without a telltale simply because if you're on boost in a 930 and you're watching the gauge instead of the road, you're heading for trouble. Anyway, my point is that there's no fundamental reason why an electronic gauge can't be every bit as good, if not better, than a mechanical one. They're certainly much simpler to implement. You'll know that first hand as you go snaking that hose through your tunnel and dash!

As an aside, out of curiosity I once used the stock gauge to see how much boost it took to maintain an indicated 150MPH on a flat stretch of vacant interstate. The answer was 0.5 bar, interestingly enough. That's good evidence of the nonlinearity of wind resistance, as I'm sure twice as much boost (the car had a 1 bar spring) would only get you to 175 or 180.

-zuff

[RarlyL8]

Interesting observation concerning boost at a steady speed.

My reference to the stock boost gauge as junk does not come from my own experiences. I've never owned a 930. This is what Ive been hearing from folks who do own them. Maybe my info pool is biased. For some reason my mechanic has a real distaste for the stock unit. He has me spending a lot of $$ to put in this mechanical telltale gauge. The line alone was $100, and you're right, I'm not looking forward to running it.

As an interesting side note, my 930 manual details the method for checking a bad electronic boost sender - they use a mechanical gauge. It says to "excellerate sharply in 1st or 2nd gear while having a passenger observe the boost gauge". HA! Things must be happening pretty fast!

[beepbeep]

Well why not letting OEM pressure-transducer sit where it is and just use T-pipe on pressure-line going to the wastegate? It's much easier...

[zuffenhausen]

Originally posted by RarlyL8
Interesting observation concerning boost at a steady speed.

Yes, it surprised me that it only took 0.5 bar to hold it there, but it made sense to me later. The car was very stable at 150, and the engine didn't seem to be working too hard.

For some reason my mechanic has a real distaste for the stock unit. He has me spending a lot of $$ to put in this mechanical telltale gauge.

I can understand why he doesn't like it. The gauge works fine, it just doesn't give you much useful information. It's small, only reads to 1 bar, and keeps no history of your maximum boost, which is probably the most important thing a boost gauge can tell you. The telltale gauge is a much more useful instrument. And yes, it costs some $$$. Another plus is that it replaces the clock, which in most 911s I've seen is another useless (read: broken) instrument.

HA! Things must be happening pretty fast!

Yes they are!!! I remember the first time I test drove the 930 before I bought it. After driving around timidly for a couple of miles to get familiar with the car and get it warmed up, I was really wondering what all the hype was about. The car didn't seem very strong at all. So I developed a not-so-brilliant plan to watch the boost gauge as I really got into it for the first time. I found an open stretch of road, started out at moderate speed in second gear and then planted it. Nothing happened at first as I stared at the idle boost gauge, and then as suddenly as the needle started to move, I was slammed back in the seat and was holding on for dear life! Needless to say, my eyes jumped from the boost gauge to the road real quick. What a rocketship! The word "boost" is akin to the word "magic" in my book.

I actually have a real love/hate relationship with the 930. It's an amazing car, yet ultimately not a very satisfying one to drive on public roads what with the masses of inattentive SUV and minivan drivers clogging things up, not to mention the police! I mean, the end of second gear has you doing well over 90MPH, and there are two more gears to go! And I swear the car pulls as strong in third as it does in second. But the off-boost performance is so poor, and the on-boost performance so violent, that it's rare you find any occasion to have fun with the car on public roads. At least in my neck of the woods.

I'm curious, what is this project you're working on anyway? Are you dropping that turbo motor into your GT2-bodied car?

-zuff