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Crotchety Old Bastard
 
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Because you have just purchased this car and do not know much about how it was (or was not) built it would be wise to turn your boost controller off.

Explore your modifications and get some A/F ratio data and then start bumping up the boost as your system allows.

You can melt a piston fast if your engine is not set up to handle the additional boost.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 03-08-2007, 09:45 AM
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Craig 930 RS's Avatar
 
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Makes you wonder what kind of treatment the car received prior to this purchase.
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Old 03-08-2007, 09:49 AM
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You are in serious danger of destroying your engine if you have messed with the boost already. You should not turn the knob ANY further than what it was set at, and even then you don't know if the prior owner was a nutcase or if he cranked the boost to sell the car, or what.

You need to actually have a read out of the Air to Fuel ratio your CIS is running to know if you can safely run ANY level of boost. You can adjust all this, of course, to a degree, but basically when on boost your AFR should never get above 12.3 at the most lean spot in your rev range, and it should stay around 12.0 if possible.

Unless you are ready to do this all yourself, turn the knob down and go to a mechanic.

Do not go out on the highway in 4th gear and start driving around randomly tuning it.

Don't do anything but check the AFR and tune it correctly for a given boost level, and don't try it yourself if you are not experienced in this matter.

You need a Porsche specialist mechanic that you can trust to drive your car and tune it with a real AFR meter and maybe a dyno.

My boost knob will turn up to 2.2 bars. That would burn up my engine in minutes. You have no idea how quickly you are going to ruin your engine if you just start turning that knob.

They call it the knob of death for a reason. And most mechanics will stick it under the seat or somewhere else so a guy won't mess with it.

Last edited by DDDD; 03-08-2007 at 08:36 PM..
Old 03-08-2007, 10:05 AM
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Definitely.

Adjustable boost appeals to the "I can adjust my car and do upgrades" side of the brain - aside from that, and the fact that it can make initial & final adjustments to incremental boost increases easier - it is an idiotic device.

Think about it: WHY would you want one?
Something else: Your CIS system goes full rich at a relatively low boost pressure.
When there is enough air volume to lift the CIS metering plate fully upwards, you *have then achieved maximum fueling*

That is it baby.....there ain't no more.
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Old 03-08-2007, 10:38 AM
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Get above .8 bar without verification of all functioning CIS components, and you are in unknown territory.

Check, verify, and keep the boost at one level.
I guess I don't understand the obsession with "adjustable boost" - on a stock CIS 930, it is damn foolish.
H2O, the ability to adjust boost upwards for more power is enticing, however there are severe detriments in doing so as Craig is suggesting above. Unless a person is technically literate with the specific upgrades done to their car (and presuming that these are the correct upgrades necessary to make the engine live) boost should not be increased. The 930 engine was designed for .8 bar boost and there is very little latitude to increase the boost before going beyond the threshold of stock CIS and pump gas.

The nuts n bolts of the problems are: air/fuel ratio correction to avoid a lean mixture as seen with stock CIS above .8 bar boost, ensuring ignition timing is correct, fuel octane adequate to avoid detonation.

The boost regulator indicates that your car has been run at elevated boost so perhaps it has sufficient upgrades, or not.

My opinion is you should spend a little time to investigate your upgrades prior to going foot to the floor. Heck, bone stock 930s should have timing and AFRs inspected. You never know what has taken place with previous owners, my own 930 being a perfect example.

Good to hear you are pleased with your car. As Craig said, try to include some pictures of the car itself. We never see enough!

Jim
79 930
Old 03-08-2007, 10:46 AM
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Geeze, a guy types up a reply and comes back sounding like an echo!
Old 03-08-2007, 10:50 AM
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If I had my car for one month I wouldn't think I am an expert already. You damn sure can go out on a highway and in 4th gear peg it to see what your boost is. I've had a 911 Turbo for 22 years, I think I know what you can and can't do.

Last edited by R Wilco; 03-08-2007 at 12:36 PM..
Old 03-08-2007, 10:55 AM
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Right on Jim and 4D - and, lacking a description of the possible modifications, a picutre or five may help us help you, H2.

These are very, very expensive to fix when they go KABLAMMO in the course of but 5 seconds...
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Movie: 930 on the dyno
Old 03-08-2007, 10:56 AM
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Okay i will tke pics this weekend and set it to 12 psi . Man getting my _ss kicked on this 1. I thought stock motors could handle 1 bar? I,ll bump the pics i psoted awhile back.
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Old 03-08-2007, 12:16 PM
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Quote:
Originally posted by h20cooled7
Okay i will tke pics this weekend and set it to 12 psi . Man getting my _ss kicked on this 1. I thought stock motors could handle 1 bar? I,ll bump the pics i psoted awhile back.
A qualified mechanic will tell you what you can set it to by reading your AFR. You could be set up to run 1.2 bar, on the other hand you could be set up to run .8 bar. Who knows, until you check?

There are ways for a mechanic to increase your boost with more fuel through the CIS and also additional fuel enrichment, and so on, and your car might even have that, but you need to find out.
Old 03-08-2007, 05:50 PM
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how can i tell if i have the larger fuel head?
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Old 03-08-2007, 06:17 PM
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Crotchety Old Bastard
 
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A bone stock 930 can handle 1.0bar IF the intercooler has been changed out to an oversized unit AND the octane of the fuel is sufficient. You also need a reliable boost gauge. The stock unit is not that accurate.

The deal is that you say that you don't know what you have so it is prudent to leave it at stock boost until you do know what you have. That's all.

You don't need a modified or Euro fuel head to run 1.0bar of boost on a stock or slightly modified engine with a stock C/R. You need proper A/F ratios. (A euro head is black while a US head is silver in color). The stock fuel head will support 400HP so you have some room there.
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Old 03-08-2007, 06:36 PM
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Even at 1.0 bar with a big IC and appropriate octane - bad things can and do happen.
To get that proper AFR at 1.0 bar usually requires more fueling in some areas ie more accurate and approriate fueling - and, as Brian says, it's all a guess unil you measure your AFR -- AND definitely do make a 100% system check- consisting of timing, distributor function, and the aforementioned appropriate fueling.

Yes, many times you will not need a different fuel head.
The adj. WUR......man...I'm telling ya, it really makes a difference.
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Movie: 930 on the dyno

Last edited by Craig 930 RS; 03-09-2007 at 08:01 AM..
Old 03-09-2007, 07:59 AM
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adjusted boost control but makes no difference.
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Old 03-09-2007, 04:59 PM
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yes it does make a difference , if i cut it off it will limit it to one bar. im just gonna leave off, the car is a handfull to drive with it cranked.
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Old 03-10-2007, 03:09 PM
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Quote:
Originally posted by h20cooled7
how can i tell if i have the larger fuel head?
IIRC the modded heads have something removed from them. Something to do with emmissions ? Hopefully someone who knows will comment.
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Old 03-11-2007, 01:46 AM
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I doubt that you do have the IA fuel head - the mods on your car look to be older, and the fuel head hasn't been around that long.

IA head has something to do with the metering slit opening width -
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"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 03-11-2007, 07:55 AM
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Quote:
Originally posted by h20cooled7
yes it does make a difference , if i cut it off it will limit it to one bar. im just gonna leave off, the car is a handfull to drive with it cranked.


You probably experienced more wheelspin, and maybe your car also squatted on acceleration even more than usual, as well as dramatic forward weight changes when you came off the boost by backing off the throttle. Just a guess.

You can always tune some of that boost back in, but you need to set the boost at one level and tune the AFR with an AFR meter around that specific level of boost, and after that don't touch the dial of death.

If your car is handling different under more boost and you don't like it, you then have to consider bigger rear torsion bars, and revalving your rear shocks to match, or upgrading them. Unless you don't mind all the back and forth weight transfer. It sure increases the sensation of acceleration!
Old 03-11-2007, 11:38 AM
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the car is set up pretty tight. is there a procedure for centering the drivetrain when you install the engine?
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Old 03-11-2007, 04:59 PM
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