Roland Kunz

Hello

A well adjustet MFI is very on the throttle. Even the slightest pressure gets direct relatet to power. It just fills fuel into the chamber when carbs and EFI still need time to calculate & react or generate a rich mixture. This is also very helpfull if you like to drift on the edge.

Problem is that most MFI´s are not adjustet proper and the skilled people retire in the next years plus most people never drove a perfect car and noone can remeber how a perfect MFI goes.

Will the similar story can be said about the Rochhester injection from the Duntov Vette´s.

Grüsse

Bob Spindel

I didn't realize this discussion was going on when Ron, with whom I've been communicating about his new '72 911 purchase asked me these questions in a private e-mail. (I'm new to this Discussion Board thing.) My response was:

"If there is any difference in power, which I doubt, I can guarantee you won't be able to detect it, unless maybe you're Mario Andretti. If you need any convincing about the supposed difference in power, keep in mind that the MFI system was developed for Porsche's race cars, and used in them through the 1970's. They didn't use Webers, although they were available. That ought to tell you something.

I think the debate arises because it is easier to change the characteristics of Webers, and if you make engine mods, like changing pistons, or installing larger valves, etc., it's much easier to match the required fuel/air demands of the altered engine using Webers (or any other carb). It's a lot harder with MFI.

Another reason people prefer Webers (or other carbs) is because they somehow feel it is difficult to tune the MFI system. It isn't. In fact, it can be a lot simpler. It's just that there aren't too many peoiple around who still know how to do it, including a lot of Porsche shops and dealers, even though it's a snap.

Stick with the MFI. It's a very solid, effective, responsive system."

And about his comment about the cost of rebuilding an MFI pump, I wrote:

"Why rebuild it? Those pumps are built like battleships. I'd bet dollars to donuts that yours is fine. I'm sure all it needs is a cleaning, and maybe some new gaskets. I've rebuilt four cars with MFI. They had between 160,000 and 205,000 miles on them. In each case I removed the face of the pump, and the covers on both sides and bottom, swished some cleaner around inside, made sure everything looked ok, and put the covers back on with new gaskets. They all worked fine. Because yours has been sitting so long, it's possible that the pump shaft seal is bad, but that too is not an impossible do-it-yourself job."

Bob Spindel

U.S.

I have carbs that run great. Used the stock filter (did some rerouting to make it work) and an additional filter at each carb to keep the dreaded dirt out. Looks fantastic too. Takes some getting to know you to get them into tune. And I vote for MFI. A well set up MFI is better all around.

JPIII

Seve Wrote:
>I'd suggest confirming the pump outputs >using the calibrated vial for that purpose >and make sure that the float levels are >perfect at 3.5 psi of fuel pressure.

Since we have you here.........:-)

My float gauge has 4 lines. At the bottom,
2 spaced about 1/8 inch apart, a gap of about
1/4 inch, and 2 more limes, 1/8 inch apart at the top.

After a fair amount of head scratching....the directions saying to set the levels between the upper lines...I set em' at the 3rd line from the bottom. It wuz clear as mud at the time :-)

My fuel pressure is at 4.5 lbs. I could use a
recommendation for a good pressure regulator, if you think a reduction will help. I just LOVE cutting into them SS braided lines (sigh).

Haven't checked the volume of the acc pumps, but they sure look to be squirting a bunch of juice.

I have an MSD unit and coil that's going in....soon. You convinced me, there.
An RS dizzy, also.

Could use a plug recommendation....I prefer NGKs.....plug gaps? The engine has 9.6:1 compression and Solex cams. I've been using BP5ES but think they may be a tad hot. Want to do some track driving this spring.
NGK numbers get larger as the plug gets colder, right?

OkieRon

Thanks for the replies guys!
And thank you Bob Spindel. Bob, even though you are new to the message board, you deserve big stars under your name.
Bob has rebuilt at least four cars, (at least 2 911's and a 240Z- see http://members.rennlist.com/spindel/ )and he did the engine rebuilds himself. He has been an invaluable help to me- the new kid on the block. After reading Bob's emails and tech articles on pelican, I could build a bridge to the Moon with just a Haynes Manual and a set of metric wrenches.
After reviewing the discussion I plan on rebuilding the MFI myself and will keep all posted.

Thanks
Ron Horton
72 911T Targa

Steve Weiner-Rennsport Systems

JP: (who's Seve?,...... )

In order,.......here we go!

Your float guage is calibrated for Weber's and Zenith's. The top pair of lines is used for Weber's and lower pair of the lines are for Zenith 3-bbl carbs. Make certain that the liquid's meniscus is not below the bottom of those two lines, otherwise you'll have a flat spot,.

I use a Holley low-pressure (1-4 psi) fuel pressure regulator and set this at 3.5 psi BEFORE I set float levels. If you follow these procedures, you'll not likely need to do this again. I also use a Racor # 110 Fuel Filter unit. This has a replaceable cartridge and is also a water separator. You will be a very miserable fellow if you ever get water into Weber carbs as every passage must be totally blown out. This is quite tedious & time consuming.

Guessing on accelerator pump outputs does not cut the mustard, get the vial and measure it precisely. This is VERY important.

You'll love the MSD & coil. They perform "almost miracles" on carbureted and MFI'ed engines.

Indeed, NGK's get colder with bigger numbered heat ranges; this is the opposite of the Bosch ones. They are fine plugs and I use 'em too. A BP5 is rather warm for an air-cooled engine and I would use a "7" for your combo. Projected nose plugs are a good choice.

Hope this helps,........

ps:
ROFL,....BTW, I saw one of your posts on Pelican the other day about our pricing,..... I would simply offer that we are not really expensive; You simply get what you pay for and our level of knowledge, expertise, and integrity hopefully saves people money in the long run by getting goods & services that are properly selected and executed without compromise. This way, you never have to do something over again because it was not done correctly in the first place,...

Weber setup is not a bad case-in-point.

JPIII

Seve (or Steve, if you prefer :-), wrote:
>Weber setup is not a bad case-in-point.

Touche':-)
No slight was intended. I have seen the quality of the work you fellas do and it is most impressive. I'll never meniscus it again......

I admit to being a CSOB, however, there is a method to my madness.....I hope. I am one of those unfortunates who learns by doing. Now, thanks to you, I my list of "do's" has grown a bit.
Thanks for answering my dumb questions, again.

Now if I could just figure out how to
stick them graemlins in here.....

Steve Weiner-Rennsport Systems

Hi JP:

Call me anything but not late for dinner,....LOL.

I understand,...no harm, no foul,.... I just wanted to make a point about these cars and the specialized skills and knowledge to do certain things RIGHT. Beyond a certain point, we should not practice medicine upon ourselves because we all understand our personal skills and limitations. This is what's referred to in the "Peter Principle" and there are some cases with automobiles that the same principle applies.

There is no question that human's designed and built these things, and human's will maintain and repair them, as needed. Its just that the final costs of aquiring that level of education can be very expensive and its cost-effective to have a specialist do some things for you. LOL,....Caveat Emptor.

Happy to answer any questions,....the only dumb questions are the ones that are not asked.

Hope to see you at our next Tech Session; Jan 26th. A very Merry Christmas to you, Sir.

JPIII

Steve:
You wrote:
>Beyond a certain point, we should not >practice medicine upon ourselves because we >all understand our personal skills and >limitations.

Hah.....that's what my dotctor said when I wanted to perform my last bowel resection.


As I recall, I inquired about putting my freshly rebuilt engine on your dyno.

Now that the engine is in the car and all contaminates are safely confined therein
:-), do you have a chassis dyno? Come spring, when I have it running to the best of my limited skills, I'd be interested in some time on one (if I can look over your shoulder while you "tweak").

What is the topic for the 26th?

And a Merry Christmas to you, sir.

Steve Weiner-Rennsport Systems

Hi JP:

We do have 2 chassis dyno's very close by that we use for different purposes.

One is a Dynojet 248C for RW power measurement and fuel/air mapping, the other is a Mustang load-type dyno for chip mapping and tuning. Both can operate in the inertial mode but only the Mustang can produce power measurements while under load.

Different tools for different purposes and either one would work fine for fine tuning your fuel mixture and timing.

Regarding the PCA Tech Session on the 26th; I've been asked to do a presentation on Street driving and DE Preparation. Should be fun,........

Hope you and your all have a very Merry Christmas and enjoy good health for '02.

John Luetjen

I've got MFI in my '69 E and I wouldn't consider changing it for webers. Compared to an EFI car (such as my previous 944) the throttle response is awsome!!! Even more so compared to CIS cars. I don't have any back to back experience with a weber equiped cars, so I can't comment. I doubt that a weber's response could keep up with the pre-programmed response of the MFI. It essentially has an "Analog computer" machined into the cams in the fuel pump which unfortunately makes it difficult to "reprogram" for non-standard engine combinations.
Good choice doing the work yourself, I adjusted mine using some common sense and it made a big improvement. Here are some references.

1) The factory shop manual has excellent information and theory of operation, but glosses over the internal details.
2) Check out the following site. They have a lot of great information. http://staging.huntinter.com/johncar/TipMFI.htm
They have a Bosch MFI manual that you can download which covers all of the internal details. There is also a "Porsche MFI Manual" that is smaller that covers the adjustment and tuning of the MFI. It has some drawings for adjustment tools that you can make yourself. You can also buy the tools from many of the larger Porsche Parts companies.
3) Keep the tools in your glove compartment along with a note pad to record the number of "clicks" in or out that you adjusted the settings. Then just tweak the adjustments based on your daily driving. Doing that I was able to learn that the my car's previous owner had the MFI tuned way to rich. After resetting the mixture adjustment, the car now runs great with wonderful throttle response.

BTW, I get about 20 MPG in my 69E. Try to do that with webers!

PS: I also found that an MSD ignition helped clean up the idle and <3000 RPM running.