MFi and Altitude

[nigel911]

Finally have my car in Colorado, the car has come from Florida. I am aware that at altitude there is less air so the car will run slightly richer / hotter - should I adjust the mixture and what's the best way of going about this? My house is just over 5000 feet.

[jstobo]

If you have MFI a barometric cell on the fuel injection will adjust the mixture for you. If you have CIS the CIS automatically compensates because the air is less dense and will push the throttle plate up less so it too will automatically adjust for you. If you have carbs-you will need to re jet to lean the mixture. You did not state the year of your T so any of these fuel systems are possible. I hope this helps.

[bkreigsr]

I can attest to the barometric cell doing the adjusting work. I drove my 73 coast to coast across the Colorado divide with no problems.

Bill K

[nigel911]

Showing my vast knowledge again.

Thanks guys, the wonders of MFi never cease.

[Grady Clay]

Nigel,

Your MFI does a pretty good job of altitude compensating with the aneroid on top of the MFI pump. You will find it slightly on the rich side as you increase altitude. As you have some significant driving here, you can ease it slightly leaner.

CIS is actually is less responsive to altitude correction. Ask Bill Lamb.

Generally speaking carburetors, MFI and CIS are designed to move rich as altitude increases. That works as you have to go over a pass.

When you live at high altitude, you want your MFI to run properly and appropriate mixture. That requires adjusting the mixture leaner. If you only adjust the main mixture to suit the situation, you must slightly re-adjust when going to sea-level.

There are some ‘tricks’ with the aneroid that can allow a given engine/MFI to better track the differing air density. The shops here know how to do that. It isn’t easy and requires a lot of finesse and testing. This is only useful when you regularly drive your MFI between altitude and sea-level.

When correctly adjusted, MFI works great at altitude. Better than carburetors or CIS.

If CIS is adjusted correctly at altitude, it absolutely needs to be re-adjusted before any performance use at sea-level. The altitude correction is not as good as MFI.


Everyone with MFI should become skilled analyzing, diagnosing and adjusting their system. If you, as an owner can’t, I suspect there are increasingly fewer ‘professionals’ who can, the Forum can help fill that need. The goal is to get every owner educated. With educated owners and the Forum, these great Porsche engines can last forever.

Even if Porsche AG chooses to not support MFI, I suspect the market will provide support for this very important part of Porsche history.

Best,
Grady

[fly4val]

Awesome Grady, my '88 is on its way to GJT on Sunday, this issue was in the back of my mind. GJT is same as Denver at mile high and it is going to be there for upwards of a year.

Do you have any recommendations on the front range?

val

[Type911]

Nigel,

Glad you & the car made it to Colorado !
Hope you can join us at the TDC in Durango July 20-22.

I'm sure Grady will chime in again, but I have heard good things
about Storz Garage. They should be able to dial-in your MFI for
altitude.

Storz Garage
Mike Walz & Bob Brown, Owners
1475 Vine St.
Denver, CO 80206-2015
303-333-1911

Val,
In GJT you should look up this shop !

Allen Johnsen Racing Services
Allen Johnsen, Owner
719 Winters Ave.
Grand Junction, CO 81501-3850
970-245-8685
ajrs55@cs.com[/email]

[zotman72]

Grady brought back some painful and expensive memories in his note above. My '74 2.7S CIS racecar was tuned for high alititude and toasted itself at Texas World Speedway in less than 20 minutes a few years back.
Back to MFI and Front Range. There is only one shop to go to for MFI and that is Eisenbuds. John Eisenbud is the master. The lads at Storz are great but they will defer to Eisenbud. My 2.4S MFI is slated to see John next week in hopes of making the Durango rendezvous this year.

[fly4val]

Many thanks Type911 and Zot.....I hadnt inquired about the western slope because of doubt.....seeing that there is someone right in town relieves my feeble mind a bunch...

[Type911]

Originally posted by zotman72
There is only one shop to go to for MFI and that is Eisenbuds. John Eisenbud is the master. The lads at Storz are great but they will defer to Eisenbud. My 2.4S MFI is slated to see John next week in hopes of making the Durango rendezvous this year.

Hope you can make it to the TDC !

Nigel,
Here is the contact info I found on another thread for Eisenbuds

Eisenbud’s, Inc.
John Eisenbud, Owner.
796 Valejo St.
Denver, CO 80204-4228
303-825-0322
eisenbud@privatei.com

[nigel911]

Many thanks to all, this board and its collective knowledge are invaluable and greatly appreciated.

The car seems to be running fine, if a little down on power. I am going back to Florida on Monday so it will have to wait until I return later in the month, I was planning on running it for a week or so and checking the plugs frequently. If it looks out of whack then it will be off to Eisenbuds for a tune.

The only slightly strange thing since finally getting the car to Colorado (other than the completely sheared rear brake lines where the transporter driver strapped the car down, quality work) is that it has developed a lower valve cover leak which it didn't have before.

[Danny_Ocean]

Sorry for the hijack, but...what is considered "high" altitutde? I'm moving some of my cars from FLA to the SW where my altitude will increase from 0' to 4000+'.

???

[Grady Clay]

John Eisenbud was my (GECo -> Rennenhaus’) first employee. I sent him to the Bosch MFI school at the time (~’70). In turn, he trained all the rest of a long line of great Rennenhaus mechanics. Many (including John) are now the Denver shop owners. Good guys all.


In addition to the above two shops (Eisenbud & Storz), I would add:

Greg Johnson
Eurosport, Ltd.
1855 W. Union Ave.
Englewood, CO 80110
303-789-2545

and

Pat Moyle
Motor Sport, Inc
1921 W Yale Ave.
Englewood, CO 80110
303-922-3560

There are even more.

A great bunch of guys all and we all learned a lot from each other. Some are 10+ years my senior and still working. In hindsight, I should have GIVEN Rennenhaus to them when I retired (’87) so they could have maintained the economy of scale. c’est la vie


Nigel; whoever you decide on, I’ll encourage you to have the specific tech start from scratch with a through CMA and not just a simple mixture adjust. All of these guys are very skilled (perhaps some of the best in the world) and probably will uncover some hidden problem(s) to your benefit.

I know you have been paying attention on this Pelican Forum. MFI and its subsystems are only part of the entire engine system including all of its subsystems. For successful performance, everything must be correct.

First, I recommend you put some miles on your 911. The best MFI analysis, evaluation and tuning (CMA) is done just after a drive to Pueblo (~100 mi), the day on track ($75) and drive home. I would do this with fresh oil and high octane fuel (pumps in Englewood) and new sparkplugs (NGK BP8ES). This allows a proper analysis of the current condition and settings of the engine.

All of these guys are very skilled Checking, Measuring and Adjusting (CMA) Porsche MFI. If they or you want, I’ll consult for free.

Best,
Grady

[fly4val]

Thanks again Grady for the enhancement(s); I know I'll be visiting the ref in GJT as soon as I get settled in the next couple of weeks.

V

[nigel911]

Grady, thanks once again for your knowledge and time. I am now back in Florida sorting out the final stage of my move, hope to get back to Colorado in time for the TDC, what will be will be.

You may well see this thread revived in a few weeks, thanks for your kind offer of help.

[304065]

And whatever you do, don't ever lift the pump by the barometric cell: it will destroy it.

[glenncal1]

Nigel-don't know if you have done it yet, but to register the car in the Denver area you need to get an emmissions test. Your car may fail for being too rich (my '71E did after coming from CA). I second (or third) the recomendation for Eisenbud for MFI work. He adjusted my MFI and then I passed emmissions with ease.

[nigel911]

Hey Glenn,

Not registered the car as yet, waiting until we have all vehicles in Colorado to do it in one go, apparently the Sheriff has to come out to check the paperwork and VINS before we can register the cars in CO.

Eisenbuds it is.

Thanks

[wprater]

There are some ‘tricks’ with the aneroid that can allow a given engine/MFI to better track the differing air density. The shops here know how to do that. It isn’t easy and requires a lot of finesse and testing. This is only useful when you regularly drive your MFI between altitude and sea-level.

Referencing this quote from Grady above, Im curious what these "tricks" are? I normally drive near sea-level, but half the time my car is driven hard from 6000-9000 ft during rallies and other events. The car runs overly rich there and I tend to lean the main reack a click or two. However, it would be nice to adjust the baro cell to compensate better.

Any insights or ideas are welcomed.

[tobluforu]

There are a few threads regarding the use of the shims under the cell. Do a search and maybe you can get enough info on the thickness you can use that might help.