MFI Junkies

[Paul Thomas]

I am sending a MFI hard line to Classic Tube to get an estimate on making up some teflon braided lines for my car. Some of my hard lines seep a little around the injector and i just think it will look cool.

Obviously, the more that they make, the cheaper it will be. Does anyone else have any interest in getting a set? I am not suggesting anyone sen me any money, i will repost when i find out the estimate and any one wanting a set can call them.

Paul

[Rot 911]

Can those lines handle the MFI pump pressure which is in excess of 250psi?

[Zeke]

Why does Classic Tube have to be consulted? They are specialists in bending hard lines. If you're going to a steel braided line, can't Earl's or any other of the dozens of people who make up braided lines do this?

We have a guy here in Long Beach (Deering Ind.) that seems to have every fitting known to mankind, and can fabricate swedged or screw on, but he's way expensive. I go to another shop and they have had everything so for.

[Paul Thomas]

Kurt, I told Tom at Classic Tube the operating pressure and he said The teflon lined hose would be fine. The factory used this type of line on the RSR's. I would think that brake line operates at much higher pressure than this, and many of us use it.

I called Classic because they are on the east coast and they are doing all kinds of tube now. I am sending him a line because he wanted to see one to make sure they do it right.

Paul

[Fritz]

My brother used to hang around Russell's way back when so here is the little bit I remember.

Most of the hose types are good for pressure. It is the fittings on the end that determine how much pressure it can take which is why the brake lines have the STEEL fittings. Don't even think of using the aluminum fittings.

The quality all comes down to who assembles the fitting onto the hose. For something like brake lines and fuel lines get a pro to do the assembly. They have the nice blades to cut the hose properly and the tools to correctly attach the fittings.

I think the new carbon fiber (Kevlar?) wrapped lines are pretty slick and better than the stainless wrapped lines. They might make a neat looking set-up.

[jstobo]

Remember all fuel lines with MFI are equal length.

[Grady Clay]

Another issue is the rigidity of the pipe vs. hose. This is a separate issue from the working/burst pressures. MFI is a pulsed system where the pressure pulse is initiated in the pump, not at the injector. That nice squeak the injector gives is from the sudden pressure pulse and the abrupt opening and closing of the nozzle. It seems to me that any increase in “give” in that high pressure plumbing might be undesirable, more so at idle and just off idle than at full power.

If you have a fuel leak at a nozzle, fix it. Any fuel seep is a major fire danger.
You can have the SS/CF braided hose “look” by covering the steel lines with braid and heat shrink plastic. The best of both worlds.
I asume people have re-plated their pipes with cad, polished and chromed, other.

Best,
Grady

[Zeke]

Interesting point, Grady. I have used a lot of airless paint spray equipment an still own one. They work at about 1500 lbs. pressure. When you pull the trigger, the hose jumps. There is also some 'give' to the line, you can tell as the pressure builds. And, of course, the hose is flexible with stainless steel fittings, not brass. If it were solid steel, I don't think the paint system would be very smooth, oposite of what you want in fuel injection.

[Tim Walsh]

umm.. is this what you're going for?

http://www.supertecperformance.com/bosch.phtml

[Paul Thomas]

No, Tim, this is more of what i'm going for. Albeit not a very good pic. The ones Supertec offers are hard plastic that have to be heated slightly and formed to the shape you want. They were used on factory race cars like 917/908/910. A freind of mine has them on his 910 and says that they leak and have to be replaced often.

If you look in BA's handbook at pics of the 934/935 motors, these types of lines were the norm

Paul

[Tim Walsh]

Very interesting.. these are plain plastic flexible lines that might last a long time?

[JDilger911]

Paul,
I'm new to the forun, but a long time 911S owner, Early 911S Registry and R Gruppe member. I am very intersted in the fuel lines as you discribe. If they look like the ones in the photo, I'm a buyer whrn you can come up with the price. Please email with any information.

Thanks

[derek murray]

I am also interested.

[Tyson Schmidt]

Are they lighter?

(Well, you knew I was going to ask!)

[Grady Clay]

Yes that Supertec stuff looks great.

While driving around this morning I was thinking, trying to understand the mindset of the engineers when they applied the MFI to Porsche. They had two distinctly different requirements, first for race cars and then for using the same (similar) system in production 911s.

Disclaimer: I am going to preface this by saying these are just my recollections, not the product of proper research. If I inspire someone to do the research, great.

Remember this Bosch MFI system was used on many other cars, Mercedes the most notable (W196?). The first production MB to have MFI was the ’55 300SL and 300SLR Gullwing. Was MFI responsible for the ME-Bf109 being able to pull negative Gs while the GB and US (carbureted) fighters couldn’t?

The first MFI attempts for Porsche using MFI, that I can find, were the RSK in ’57. The first MFI six was probably the 901/21 in the 906 factory prototypes in ’66 and 906 customer cars in ’67. Then all the 910s were MFI and on to 907, 908, 917, 911RSR, and more. The early development was probably driven by ease of fabrication as I think they all used flexible plastic lines. Additionally, race cars need to be able to be serviced in a major rush (say in the hot pits at Le Mans) so steel lines would be a hindrance. The issue of good idle with C6/910 cams and good emissions at just-off idle weren’t even considered in these race engines. If it idled, ran, and didn’t fowl the plugs, that was OK. Race engines were not expected to last very long (in years) without the replacement of almost everything. If it could make the 24-hour, it was OK if it died on the cool-off lap. Along in the ’67 years, Ludvigsen reports, that Porsche changed it’s race car policy to only use brand new cars at important races and sell them to privateers immediately afterwards, or reduce them to test-mules.
Porsche also experimented with the Kuglefisher system and MFI direct injection (like a diesel.)

I think that when Porsche engineers were tasked to put the MFI on the high-end street engine, they stepped back and looked at the overall picture. The issues were (in part):
SAFETY – no fuel leaks, customers don’t like their new ’69 911S up in flames. These pressure pipes are all steel-on-steel robust compression fittings, no gaskets. I’m not a hydraulics engineer but I think they are 6000+ PSI level.
DURABILITY– they didn’t want to tell their customers that some hoses wouldn’t outlast the warranty period. Notice how Porsche carefully clamps the pipes together and with rubber dampening.
EMISSIONS – I think the idle and just-off idle issue was a major concern. It’s amazing they were able to certify MFI through ’73 – even in California.
FUEL ECONOMY – This only became a major issue after the ’74 oil embargo.
DRIVABILITY – The idle and just-off idle issue that everyone with MFI has to deal with is influenced by the injection nozzles. Each nozzle has a slightly different opening characteristic on increasing pressure (closing also.) I think Porsche (Bosch) tried to solve this by having the pressure increase very quickly. This means the first, little injection of fuel was at full pressure and atomized correctly. This necessitated the steel pipes. Envision that there is a soft rubber hose between the pump and nozzle. Nuff said.
COST – you notice you never saw MFI on a VW bug or Chevrolet, although Pontiac Bonneville had MFI in ’57-58. The Porsche racing program and us customers were willing to stand the expense.

All in all, we should count our blessings that Porsche was (is) willing to push the envelope.

Best,
Grady

[Tim Walsh]

Hmm. didn't the corvette have MFI in the late 50's? I know there's a corvette fuelie but don't know any specifics..

[Grady Clay]

Tim,
I could be wrong but I think the Vette was AFC sorta with a single throttle plate.
Of course everyone uses some sort of FI now. All manufacturers have taken different routes to the current situation. I'll bet every manufacturer in the world has tested the Bosch MFI at some point.

Best,
Grady

[Tim Walsh]

Grady,
just did a quickie web search and got the diagram to the 56 fuelie. It looks to be a CIS system, but different than the bosch CIS that we know. It was done up by rochester
http://www.motortrend.com/roadtests/classic/112_0304_test/index2.html

[Tim Walsh]

TO get this back on topic. If I was building a nonsleeper MFI engine I would definitly want to go for these depending on price. But I've decided to go with a single plugged hi compression solex cammed 2.4 (on MFI of course)

[Grady Clay]

OK, more on topic.

Who is a hydraulic engineer who can address the issue of the hose/pipe expansion? I suspect the instantaneous peak operating pressures are much above the 260 PSI reported.

An interesting and useful experiment might be to borrow someone’s suitable pressure transducer and actually measure the pressure pulses. The instantaneous data could be compared between steel pipes, factory plastic tubing, and proposed aftermarket tubing.

Tim,
What base engine are you building on?

Best,
Grady