8 cylinder front engine iconic vehicle
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By Crumpler
#140276
I’m sorry to bother you guys again.
I feel like I’ve been installing this SC for years now.

So running well, boost plateau at 2.5 pounds.

Should be ample boost after that with current blower and pulley set up.
I see a nice initial swing about 121 kPa by 3500 rpm but then falls off to 115 kPa by 4000 rpm.
Very reproducible.
After several tensioner revisions I feel that belt slip is not the issue.
There is no soft parts that could collapse pre blower.
Smoke test on intake good.
I’m going to drive without BOV tonight to try and eliminate that dysfunction from the list.
Question: boost leak test: how?
Can you turn crank to close all valves and pressure entire system? and if so what position? Throttle plate open I assume.
I remember 20 atdc?
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By Crumpler
#140331
BOV checked out.
Boost leak test gave me an active leak. Passenger rear engine area.
Throttle line to control valve to whatever purge valve this is going to canister was toast…..
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By worf
#140334
Hey, I got ‘nothin other than what you are doing: going through the plumbing.

D.R. spent a lot of time (and I spent some as he used me and a couple of others as sounding boards) figuring out where and how the various plumbing would be connected.

Obviously some stuff should never see pressure above 0. Some stuff may not care. Some stuff may be broken.

You might need to move stuff so that it’s not seeing boost.

Tank vent, primary vacuum, brake vacuum, accessory vacuum, plus whatever else is on an S3 that isn’t on an S4+.

You may need to add or change valves.

With my Twin Screw there are plenty of spots where you can get vacuum but no boost. No so much with yours.
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By Crumpler
#140414
Appreciate it Dave.

I found a detailed explanation of that S3 valve on RL.
Thermoregulated to open warm engine only and pull vapor out of canister to control valve, which in turn (my physics are fuzzy here) will selectively deliver vapors will vacuum control to TB to burn in certain transitional or WOT events?
So emissions concern only?

Sooooo. Here’s my (hypothetical) question.
If you cap vacuum. Delete control valve and purge valve. You are venting tank vapors through canister to atmosphere under the fender?
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By hans14914
#140438
If it helps, I replaced all the tank vent stuff with a BMW sourced valve, part number 13901433603.

It has a timer connector on it, is normally closed, and the quick-connect fitting actually slides right into the original hose very snuggly. It really simplifies the system with aftermarket controls.


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By worf
#140498
Crumpler wrote: Fri Mar 18, 2022 11:18 am Thermoregulated ... So emissions concern only?
Yes.
Crumpler wrote: Fri Mar 18, 2022 11:18 am Sooooo. Here’s my (hypothetical) question.
If you cap vacuum. Delete control valve and purge valve. You are venting tank vapors through canister to atmosphere under the fender?
I'm not going to say yes or no because I don't have the S3 motor and plumbing in my head and don't want to assume that it's like S4+.

The *engine* doesn't need the line to the tank vent system.

You DO need to make sure that the tank can breath. The volume of fuel used by the engine must be replaced by air.

After that, for a track car that will never need a thorough visual inspection of the emissions system again, all the rest can go bye bye.
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By Crumpler
#140599
Thanks Dave. I appreciate the fair insight into a rather unfair question to ask.

That wasn’t it, same god damn problem afterwards.
I don’t know man. I’ve got everything capped off except essentials.
I boost tested again to try and check intake gaskets. The side plenum blows off before I can find a leak.

Started a warm compression test. First two numbers were consistent but underwhelming 150.
Then I had to vomit, which I will detail in next thread.
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By worf
#140622
Crumpler wrote: Sat Mar 19, 2022 7:02 pm Then I had to vomit, which I will detail in next thread.
Yeah. I saw that.
:barf:
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By Crumpler
#140706
I was able to save my ass this morning.

Compression test results:

4. 165 8. 160
3. 170 7. 150
2. 155 6. 150
1. 165. 5. 160

I’m saying this rules out boost loss from bad rings.
But, what’s the 928 criteria to feel good about rings.
There’s a 12% difference between highest and lowest number.
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By worf
#140717
Crumpler wrote: Sun Mar 20, 2022 1:58 pm But, what’s the 928 criteria to feel good about rings.
There’s a 12% difference between highest and lowest number.
If the motor was shop cold then I would not be worried about the difference.

I always do compression test with warm motor and re-warm after four holes.
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By Crumpler
#140745
Hmmmmm.
This was a “warm” test. Meaning started and idled up to warm. About 160 degrees F on IR gun in the valley and about 125 on cam covers. Water temp was about 170F.
I did all eight, and not super fast, maybe 20 minutes total work time after shut down.
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By Crumpler
#140773
Found another weak area at an elbow and a pin hole defect actually in the intercooler casting.
Better boost leak test afterwards.

As tight as I can get the S3 top end at this point.
Took it out and got 129 pKA which I’m converting to 4 pounds boost. At between 3500-3800 rpm in fourth.
I guess I need to be more realistic about boost curve, what looks like plateau is probably my BOV closing with initially steep curve then flattening with very gradual increase in boost level from there.
I just expected different, all the “linear” output you hear about with the SC stuff.
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By worf
#141031
Crumpler wrote: Sun Mar 20, 2022 5:29 pm Hmmmmm.
This was a “warm” test. Meaning started and idled up to warm. About 160 degrees F on IR gun in the valley and about 125 on cam covers. Water temp was about 170F.
I did all eight, and not super fast, maybe 20 minutes total work time after shut down.
According to my spec book your S3 motor is 10:1 compression like the S4 motors. I would expect to see ~170-180 PSI on *my* gauge with a warm motor.

Have you had your heads 'done'? If not then I'd go 50/50 on ring sealing versus bent valves.

I have yet to find a head without at least one slightly bent valve. Also, carbon buildup between the seat and valve can cause low compression. But, lots of carbon buildup usually manifests as slightly "too much" compression on holes that aren't leaking.

However, I don't think the slightly deficient compression is the source of your boost limitation.

I really don't want to think about what is necessary to seal that 3-d jigsaw puzzle S3 intake for big boost. There are so many bits of rubber and clamps on that thing for its billionty pieces.
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By Crumpler
#141083
You know it’s funny, I just told someone, that in hindsight, I’m not sure an S3 is a reasonable candidate for boost for that same reason.

Big boost will blow the side plenums off, etc.

I’m sure this engine is tired. If I add oil to compression test and numbers and no difference, then valves not rings?

No heads have never been done.
But, probably I will do everything, question is when.
I have a spare engine here. if I was smart I would rebuild it while I’m driving this one. That one is a long story, it was a cam chain tensioner failure that I bought off Landseer.
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By worf
#141093
Crumpler wrote: Tue Mar 22, 2022 3:02 pm If I add oil to compression test and numbers and no difference, then valves not rings?
Won't hurt to do that. But, it isn't clear to me how diagnostic it would be. I can think of logical reasons for all the permutations that still leave doubt.

If the engine's never been apart (and I assume were talking about 80k+ miles on it now) then I'd assume that it has a 'little bit of everything' leading to those compression numbers.

If it's a low mileage short block then my bet would be valves and carbon.
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By Crumpler
#143054
Horrific or brilliant, I haven’t decided.
I can say that my cam seals haven’t leaked since I did this to my spare oil filler cap. And this (clean) picture is after several WOT runs.
Yes, track use only.
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By Crumpler
#144527
T clamps, silicone sleeves, a little rtv.
It’s getting ugly in there but it will now pressurize to 10 psi. Going to button it up and see it any improvement today on the road.
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By Crumpler
#145551
Saga continues.
No real change on road.

I have a smaller pulley 2.85, and pulled the 3.0 off.
Did see evidence of belt slip, so maybe that’s been happening the whole time. The logs don’t really look like what I had found researching belt slip but who knows.

The smaller pulley produced boost sooner in engine loads but same plateau around 3700 rpm.

At this point I’m going to revise the tensioner system, again.
Ordered a manual tensioner, a LS idler with 6pk, some tidbits.
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By Crumpler
#146227
Ok, must have been belt tension issue after all.
The new manual tensioner (fabricated) and on car.

Results show an actual linear increase, 4.5 pounds and climbing by 3300 rpm when I let off.
I can live with that and will finally move on.
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By worf
#146249
:clap: :clap: :clap: :clap:
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#146622
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