What's purpose of the "venturi tube"?

[kalasend]

Hi, What's the use/purpose of the venturi tube(under the intake manifold)? And how the car would be affected if I install hose kits that eliminate the venturi tube?

[Mahler9th]

This thing affects the vac that the booster sees. It is not used in the final turbo cars. Since it relates to the booster's specs, I would not remove it, unless you are changing the booster. Of course while "under there" it is best to make sure all clamps are good and the fittings are tight,,, a lot of us replace the crimp-ons with good German hose clamps... who wants a vac or boost leak?

[ae1969]

No problems running the venturi delete on the early turbos.... You will not notice anything...

Just get the 2 updated hoses and get rid of the octopus.

Way too many locations for vacuum leaks......

[Lawrence Coppari]

ae1969, what do the updated hoses eliminate? Mine is stock and like you said, there are too many places for vacuum leaks. Plan on removing intake this winter for some maintenance work and would like to eliminate the octopus.

[Porsche-O-Phile]

If it's properly maintained and you use good hoses and clamps you won't have any leaks. If you're really paranoid, use a little sealant on the ends of the hoses where they plug into their various adapters and components, then clamp.

[nize]

lawrence;
the venturi delete has numerous writeups on rennlist;
http://forums.rennlist.com/rennforums/showthread.php?t=230466&highlight=venturi
http://forums.rennlist.com/rennforums/showthread.php?t=230466&highlight=venturi
http://edge.no-ip.com/index.php?d=rennlist%2Fventuridelete

i've done a lot of research on the cv-or-no-cv issue and i would NOT recommend eliminating the cycling valve unless you're going to be replacing it with an electronic boost controller. manual boost control just doesn't provide the safety check that the cv or ebc does.

[ae1969]

The problem with venturi is the plastic is brittle......well all the plastic on these cars are brittle. There is an o-ring in the venturi as well. Most people missed that one as a source of leaks.

The 2 hoses as explained in nize's threads is the best solution by far.

Less is more when running a turbo.

[nize]

i am still convinced that installing a manual boost controller on the 951 is not wise.

[Lawrence Coppari]

nize
Thanks for the references. Just finished downloading and will make the changes when I do the yearly in December.

[AaronM]

Originally posted by nize
i am still convinced that installing a manual boost controller on the 951 is not wise.

For the mechanically non-sensitive, no, it's not. Anyone with any ability to understand the mechanical interactions and properly maintain their vehicle will have zero issues with an MBC that is properly adjusted and installed. It requires more mechanical sensitivity and more attention, but it's perfectly safe when done properly.

[nize]

without the cv, and without electronic monitoring/adjustment, there is no failsafe.

let's say you get a tank of bad gas (it happens!) and the engine knocks. you'll still be running full boost with a manual controller and engine damage will result without you ever realizing it.

with the cv or electronic control, it will automatically prevent full boost.

going manual boost control effectively eliminates the purpose of the factory knock sensor.

[AaronM]

Originally posted by nize
without the cv, and without electronic monitoring/adjustment, there is no failsafe.

let's say you get a tank of bad gas (it happens!) and the engine knocks. you'll still be running full boost with a manual controller and engine damage will result without you ever realizing it.

with the cv or electronic control, it will automatically prevent full boost.

going manual boost control effectively eliminates the purpose of the factory knock sensor.

If you can't hear knock, you have _no business_ in a 951. Period. The factory knock sensor in the 944/951 is quite primitive compared to modern units and won't sense knock significantly before it is audible.

Again, if you can't tell when the engine is knocking, you've got no business having a car like this.

This is a personal thing of mine though. I have a severe dislike of ever relying on a "failsafe". It encourages operating outside of proper safety margins and discourages responsible tuning. It's the same reason that I don't like traction control, ABS, or stability control.

[ae1969]

Originally posted by AaronM
If you can't hear knock, you have _no business_ in a 951. Period. The factory knock sensor in the 944/951 is quite primitive compared to modern units and won't sense knock significantly before it is audible.

Again, if you can't tell when the engine is knocking, you've got no business having a car like this............

I agree with this....

......... by the time you have seriously knocked is too late.

The factory system works because in all intent and purposes its pretty conservative....

You have full boost that is basically bled as you build it......

The minute you start modifying. No fail safe will ever save you....

It just takes a second of serious detonation to end the fun....

[nize]

1) i would think that installing a boost enhancer and leaving the cv in place would provide enough failsafe to save you.
2) i would also think that installing an electronic boost control unit in place of the cv would also save you.
3) i would also think that going to megasquirt would also save you.

the main reason is because they actively monitor your a/f, boost, knock, spark, etc, etc, etc. and adjust things accordingly.

when things go wrong, the car computer will automatically;
1) retard spark timing
2) decrease boost

if it can't do one or the other (or both!), it further increases the possibility of damage.

granted you can tell when the engine is knocking, when the brakes are locking, when the tires are losing grip, etc. but there's just no way your reflexes can out-perform a computer that's making adjustments 20 times per second.

[Porsche-O-Phile]

The MBC/EBC discussion has been debated ad nauseum. Generally, yes an EBC is a "better" system, although there is NO problem with running an MBC so long as it's maintained and the car tuned.

I would also put forth the position that an MBC is superior to the stock CV setup as I have yet to see a CV (particulally on our aging 951s) that isn't horribly prone to failure by the plastic nipples cracking off where they meet the body of the CV itself. I don't suppose I need to tell you that if this happens to the nipple going to the WG line (easy to do if that line gets caught on something or tugged on inadvertantly), you'll easily overboost the car and end up with bad things happening. As such, the advantage of a good MBC is that (1) it's new, (2) it's (usually) metal, and (3) it enables you to route the line to the WG intelligently on TOP of the engine where you can actually see it - not buried behind the engine where you have no idea what kind of condition it's in or even if it's connected.

When I recently cracked my (third) CV, I said "eff this" and went to an Accuboost MBC. It's been completely incident-free and works quite well. I check the tuning on the car about once a month as part of good general maintenance and I think that's perfectly adequate.

I will eventually go with an EBC and dual-port wastegate for an even "safer" (and more tunable) setup, but I sleep quite comfortably with my MBC in place - certainly more so than after I discovered a hard, brittle, cracking WG line and CERTAINLY more so than after I discovered my third CV had cracked at the nipple the "SUPRISE!" way (when I got on it and wondered why the boost was trying to slam my head through the headrest into the rear seat). Fortunately I figured it out and eased off and didn't damage anything, but the stock setup my certainly CAN and WILL fail. At the very least, get a new CV. First person to make a metal-cased one or one that otherwise gets rid of the crappy plastic **** will get my $$$ for it.

[nize]

i wonder why a metal replacement cv doesn't exist yet...

[AaronM]

Originally posted by nize
1) i would think that installing a boost enhancer and leaving the cv in place would provide enough failsafe to save you.

granted you can tell when the engine is knocking, when the brakes are locking, when the tires are losing grip, etc. but there's just no way your reflexes can out-perform a computer that's making adjustments 20 times per second.

We've been over the idea of an MBC in line with the CV ad nauseum. If you don't understand by now that having an MBC in-line with the CV is functionally no different than having the CV removed completely I don't know how else I can explain that.

Tell that to all the people who bought cars with ABS and started sliding through snowy intersections because the ABS couldn't read traction for ****. If you're depending on electronics yo save you, you're doing something very, very, very wrong.

[nize]

then why does boost sciences (the makers of reliaboost) say otherwise?

from;
www.boostsciences.com/ReliaBoost%20Installation%20-%20944T.pdf

ReliaBoost Installation - PORSCHE 944 Turbo

The ReliaBoost Controller can be installed with or without the factory cycling valve in place. This is recommended, as the factory valve in conjunction with a fully tuned controller will virtually eliminate all manner of spiking.

[Mahler9th]

wow, I cannot believe these discussions are still going on after all of these years....

On my last 951, I installed a Tial WG and a manual boost controller. I had no problems. Of course this was a street/track car, with many modifications (e.g., turbo, suspension, etc). I ran as high as 1.1 bar on the track. It all worked great. Of course, this car was VERY highly maintained, and I built a semi-race engine foro it (chronicled in Excellence years ago).

I have a good friend with an ex-Rothmans car that was later raced in Firehawk by Milledge, et al. It also has an mbc.... and he runs as high as 17 psi, though rarely. This car has some really neat stuff on it...

The really cool stuff can be seen on the 924 GTPs and GTRs which I get to visit occasionally. These cars have some really neat things on them, and are very rare.

Anyway, for a street car, I see no reason to get rid of the cv and stock boost control setup. Worked fine and did not require any special maintenance.

-

[AaronM]

Originally posted by nize
then why does boost sciences (the makers of reliaboost) say otherwise?

from;
www.boostsciences.com/ReliaBoost%20Installation%20-%20944T.pdf

ReliaBoost Installation - PORSCHE 944 Turbo

The ReliaBoost Controller can be installed with or without the factory cycling valve in place. This is recommended, as the factory valve in conjunction with a fully tuned controller will virtually eliminate all manner of spiking.

They aren't saying what you're saying. They're saying that it functions identically whether the CV is there or not.

There isn't even the remotest hint in what you've quoted that they are claiming the failsafe remains in place. All they are saying by that is that boost will not spike past what the MBC is set for. That is true of any good MBC regardless of the presence of the CV.

And even if they did claim that, it wouldn't make it correct. It's simple, 9th-grade physics. No amount of advertising could change that.