Robwsup

I made up a "poor man's" boost gauge today. Basically, I ran a small 5/32" line into the area under my radio. I haven't ordered my regular vacuum/boost gauge so I just used an SMC 0-30psi air pressure gauge. I took the car out and ran it a little. The boost peaks at 15psi (exactly by brand new gauge) on the dot, then slowly rolls down to 10psi near redline. What has been done to my car?

I am the third owner of my 87 951. The second PO, that I bought the car from was NOT a PORSCHE enthusiast, he was more like a "I've got money because I have a Porsche" kinda guy. He told me that the first PO (original owner) had installed Weltmeister chips, and had "maybe done some other performance stuff". There is no MBC or LBE that I can find. I am thinking maybe aftermarket wastegate? or maybe stock gate with stiffer spring? The car runs great and fast as hell.

On a side note, since I am already running "safely" with boost up to 15psi, could I use a MBC later on to maintain boost at 12psi to redline instead of letting it roll down to 10psi?

Thanks for any help,

Ski

There is nothing wrong with the boost on your car. The cars are set to get .8 to 1 bar(11.7 to 14.7psi) and with the K26 you will be down on boost by the time you get in the upper rpms, just like your car is doing. The factory wastegate has some bleed off protection built into it. If you want to hold a bit of the boost longer, 15 to 13, maybe even down to 12, get a new wastegate and MBC. Speedforce Racing has some really nice Tials and Lindsey Racing does a conversion of the stock wastegate.

Silverbullet951

ROb, if you install a custom MBC, you can bypass the cycling valve and you will have 15 psi all the way to redline. That's what I did.

Gary

[quote]Originally posted by Silverbullet951:
<strong>ROb, if you install a custom MBC, you can bypass the cycling valve and you will have 15 psi all the way to redline. That's what I did.</strong><hr></blockquote>

If you have a Lindsey boost Enhancer, you don't need an MBC nor need to bypass the cycling valve (to the best of my knowledge) since it'll block anything under the preset boost (which BTW is adjustable) before the signal get's there. You should also be able to hold the boost until redline.

At least, that's what I understand from what I've read here - I welcome correction from the experts.

PS (O/T) - Finally decided on the Lindsey MAF and placed the order That's new version with the additional fuel control. Hopefully, I'll be able to cut some of the lag a little. And if I can find a K26/8 at the local breakers ... all the better!

adrial

Robwsup, 15psi is definetely not stock boost.

Someone probably shimmed the spring in the wastegate. If the car does indeed have weltmeister chips...then you're fine, no worries. 15psi is perfectly safe.

Danno

From his boost behavior, I suspect a banjo-bolt restrictor jet. Get an LBE and you'll be able hold boost longer to redline.

adrial

Ahh good call danno..I forgot about that.

Robwsup, To check for a jet in the banjo bolt..remove the banjo bolt. It's the bolt on the top of the left intercooler pipe I believe. If there's a jet in it, it'll be obvious.

si

My 951S has Euro products chips and a LBE, the car didnt seem to dvlp mor boost, so I shimmed the wastegate as I thought the spring may be weak, and at the same time adjusted the LBE to a cautious 13psi, Anyway, the car wont run properly with the LBE at 13psi, On full throttle loads, boost is cut (not as violent as overboost), if you back off the throttle a bit it will reach full boost and accelerates quicker. So I wound the LBE back to stock and the car now runs better, reaching a max of 2bar (on the stock gauge) before rolling off. Obviously I would like to run 1bar boost to peak rpm, any ideas what the prob is, do you guys think I need some more shims, maybe the wastegate cant handle it?? thanx

Si 91 951s, silver, blu lther, 17in cups, MINT

Silverbullet951

bypass the CV.

Danno

Si, sounds like you're getting a boost-spike when you nail the throttle quickly. Thus setting off the overboost protection fuel-cut. Or, it could be a loose intercooler pipe/hose clamp. Those usually show up as stumbling at quick & high boost levels, but usually holds if you roll it on gently.

aka 951

Boost cut varies with rpm on the stock chips. In other words, you may not hit boost cut at 15 psi and 3500 rpm while hitting it at 15 psi and 4500 rpm.

Loki

aka 951 is exactly right. With stock chips I can peak at up to 20psi(just a test, i don't run it this high), but at anything over 9psi at 5400rpm(3rd gear) i hit the fuel cut off. Bypassing the CV won't fix this problem, need new chips.

Chris

Silverbullet951

Didn't he say he has weltmiester chips? I have never had a problem with the fuel cut on my car and i have ape stage II chips. why would he have problems?

toddk911

I also have Weltmeister and as I was informed they can run a little more boost with a/f problems or cutt off.

3 Turbos

I'm confused. On my stock boost gauge, it starts out at 0.4 for the 1st hash mark. After 2 more hash marks it goes to show 1 bar, 4 more hash marks before 2 bar.

If 1 bar = 14.5lbs, than 2 bar = 29lbs of boost?

What is it when my car under load goes to the last hash mark right before the 2 bar.

I can't be running approximately 26.1 lbs of boost, can I??

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