Iván

Hi,

I live in Bogota, Colombia. Does any one of you know what should be the maximum boost of a 1986 951 in an altitud around 7,000 feet above the sea level?

thanks,

NerfRacing

well,that makes a post from every continent that ive seen except for africa and antarctica

guardsred951S

Wow! I've never even been that high, let alone live there. Unfortunately, altitude is a serious performance killer.

Is your 951 stock?? What does the stock boost gauge read when at wide open throttle?

The air is a lot thinner at high altitude so the turbo will have to work allot harder to produce the same boost level as it would at sea level. I'm thinking if it will even be able to produce the the same boost level, it won't be for very long.

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Iván

Keith,

yes my car is stock, how ever, you should see how much power non-turbo cars lose !!! Aprox. 10% every 3,000 feet.

Maximum boost I´ve seen: 1.2 bar. A Porsche mechanic told me that over 1.3 would be harmful for the engine.

Thanks,

Ivan

M758

Hmm, Here in Arizona I have taken by Turbo to 8500 ft. Don't remember anything different about the car. I did some pretty hard running to.

Really depends on how the wastegate is controlled. Is it controlled by absolute pressure or pressure above ambient. If it is the latter then there will be less aboslutre pressrue, but the same added pressure. If it is absolute pressure then it will be a slightly greater pressure differential.

Rob

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by igs951:
<strong>Maximum boost I´ve seen: 1.2 bar. A Porsche mechanic told me that over 1.3 would be harmful for the engine.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">If you are only seeing 1.2 on the factory gage, this is means you are only getting about .4 bar of boost (atmosheric pressure at your altitude should be ~.8 bar). The factory spec for your car is .7 bar of boost at sealevel (1.7 on factory gage) at 3k RPM's third gear under full load. You might have a boost leak or the DME is going into it's safe mode and limiting boost to the 1.2 bar absolute that you are seeing.

Rob

Iván

Very interesting information Rob. How can I know if I have a boost leak?

I am new to turbo charged engines.

Iván

guardsred951S

0.4 BAR boost = 5.9 PSI boost = not much

Factory is 10.7 PSI on the '86 I believe so there's probably something wrong. Do you have a dyno in your area? If you could get some time the car should produce 180-190 rwhp or so. A little less is OK, especially at your altitude. A stock 951 will be hard pressed to produce more, even at sea level.

Boost leaks are a common HP killer. You'd have to pressure test all the lines associate with the turbo, wastegate, recirculating valve and intake. Also, a high mile wastegate can vent early, and sometimes shims are a good idea.

The DME will resort to its low boost setting if it sense a lean A/F mixture. The resricts power but there is an adjustment on the DME somewhere - I've seen it talked about.

Check out these threads:

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=18;t=003922" target="_blank">Can performance chips help solve my horrible fuel mileage?</a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=18;t=003921" target="_blank">predict the cause of power loss contest...</a>

The first one has some stuff about DME adjustment and the second has some stock boost and HP numbers for a 951.

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jchaley

I live in denver 5000+ ft. it takes 3psi on a mechanical boost gauge for the factory gauge to sit at the 0 boost position. The factory gauge is a absolute gauge, mechanical gauges are differential. That being said at 7000 ft the mecanical gauge will read what the factory spec for boost is (about 11psi i think)but it will take around 4psi of boost for the stock gauge to read any boost.

john

Iván

Thanks everyone,

I bought my car 4 months ago, it is a 1986 951 with 24,000 miles. The car is in excellent form, in and out. I better check it with the mechanic. Problem here is that there are not many 944, therefore, it is very difficult to compare one car with another. I think that even the mechanics are not very familiar with water cooled cars. There are lots of 911´s though.
Iván

GaryK

I live in Colorado too, bought my '89 locally, and usually drive at between 5000-8000ft. Jchaley is right; it takes about 3psi of boost to reach the 1.0 bar absolute on the stock gauge. So at higher altitude, a turbo has to work harder/spin faster to reach a particular absolute boost level, see pressure ratio. Plus the thinner air really hurts spool-up. So turbo sizing for a street car becomes even more critical than at sea level. You need a larger compressor to run efficiently at higher boost levels, but still need to minimize lag.

Then there's the problem of insufficient water and oil cooling in high altitude, hot, dry climates, particularly on the track.

Still,like you say, it beats the 20% power loss of NA cars at this altitude.

Btw, can anyone tell me how the altitude compensation module on the ECU works?