Please help - Headers & MFi

[nigel911]

Posted last week about using headers rather than heat exchangers on a 72 MFI. Apparently there is a way of using headers and rigging the thermostat on the MFi to compensate for enriching the mixture on startup and whilst running, but I cannot find a practical guide - I am not too technically minded.

Can anyone describe or guide me to a step-by-step solution?

Surely someone must have done this as there are many aftermarket suppliers of regular headers for MFi year cars. I don't need the heat and don't want to run $1000 on heat exchangers alone when I can buy headers and a new SS muffler for $800ish.

Many thanks

[Paul Thomas]

Go to www.supertecperformance.com they have some neat options for this.

Paul

[nigel911]

Thanks for your help Paul. I visited their site but couldn't find details on the issue - I have emailed them, fingers crossed.

[Paul Thomas]

Did you look under the Bosch heading?

[nigel911]

Doh!

[BK911]

I've seen several MFI'd track cars with headers. They use a block off plate for the thermostat. This is on my to do list, but waaaay down the list. I was going to block off the thermostat and adjust the MFI after the car was completely warmed up. It may run rough when she first starts, but should run fine once warmed up.

Good luck!
BK

[nigel911]

P-Thomas, Supertec performance do have a solution - it is a hand operated thermostat adjuster. Unfortunately it is $375 + shipping, kind of defeats the object of trying to save a few bucks -the cost of the headers and the thermostat adjuster work out about the same as the SSI's.

BK, when you mention blocking off the thermostat, would you physically remove it and block it off or just block off the vent entrance?

Thanks for your help guys, thought there would be an easy solution to this one but evidently not.

[Grady Clay]

This is an easy solution.

Take some steel (1/8-3/16) and cut/grind it to the profile of the thermostat mount surface. Weld, braze, or silver solder a M5 nut to the center. Take a M5 hex bolt and round the end. Add a lock nut and presto you have a cold start adjuster.
You can screw it down (by finger) until it bottoms and then back it off so there is 0.5 mm or so clearance (1/3 turn). Tighten the lock nut and you are ready to drive,
For cold starting, simply back it off a few turns (colder more turns), start and immediately put it back to the “off” running position.

My recolection is that there are several (2-3) turns before it starts effecting the cold start mixture.

10c solution.

Best,
Grady

[Flying Toaster]

Originally posted by Grady Clay
This is an easy solution.

Take some steel (1/8-3/16) and cut/grind it to the profile of the thermostat mount surface. Weld, braze, or silver solder a M5 nut to the center. Take a M5 hex bolt and round the end. Add a lock nut and presto you have a cold start adjuster.
You can screw it down (by finger) until it bottoms and then back it off so there is 0.5 mm or so clearance (1/3 turn). Tighten the lock nut and you are ready to drive,
For cold starting, simply back it off a few turns (colder more turns), start and immediately put it back to the “off” running position.

My recolection is that there are several (2-3) turns before it starts effecting the cold start mixture.

10c solution.

Best,
Grady

Hi Grady. I would love to see pictures of how this was done. I am not quite picturing the mechanism. Thanks, -John

[Lukesportsman]

I'm debating on headers in the future for my RS spec engine. I'm hoping they might open it up some on the top and sound more buff. I would also love to see/hear more details on this modification.

[Grady Clay]

Guys,

On the front cover of Wayne’s 911 Engines book, at lower right,
is a photo of the exact thing I made for my MFI 25+ years ago. DIY cost is next to nothing.

Un-do the lock nut.
Back the adjusting screw out 2-3 turns (warm less, cold more).
Start the car.
Screw it back in asap to less than finger tight, i.e. some clearance.
Tighten the lock nut.
Away you go.
In warm weather and/or just driven, you don't need to use it at all.


Image (C) Wayne Dempsey, 2003

Best,
Grady

[derek murray]

i think grady is referring to something like this... please correct me if i'm wrong, so i can revise the drawing.... oh, ya... the drawing is not to scale...

[Flying Toaster]

Thank you Derek & Grady. After seeing Derek's drawing, now I understand what was spoken of earlier. Your right, very easy to construct. So once the car is started, smoothed out, tighten the bolt until it bottoms the plunger out, then back off a 1/4 turn? Sounds too easy....

[Grady Clay]

Yup,

Good diagram. I meant to do that a few weeks ago but docs intervened and I forgot.

With the thermostat off you can see the piece that it must contact. I prefer to grind and polish a slight radius on the end of the adjusting bolt.

I use a regular nut and just tighten the two nuts together with two wrenches. I don’t use a Nyloc.

I have always been concerned to have tight metal-to-metal contact. The thermostat has spring give to it. From screwed in to contact (light finger tight) there is at least a turn out before it effects the mixture. I tighten to light finger contact and then back it out a little (1/16 turn). When you tighten the lock nut it tends to increase the clearance.

A more elegant solution might be to use an old thermostat housing and the thermostat spring rate.

Best,
Grady

[Matt Smith]

Nice, Grady.
Does anyone have a schematic for a cabin adjustable one? I guess it would work off the hand throttle.
I've never liked that concentric washer thermostat. I don't trust it!!

[Grady Clay]

Matt,

Don’t be afraid of the MFI thermostat, it works great. Once it is warm it is off and it has no effect on the mixture. I put a hot air tube in my 914-6 right heat exchanger for the MFI thermostat. Works great (2.8S MFI).

For cold start there are two other options. First is the cold start solenoid on top of the fuel filter console. You can wire a remote switch if you want. The other is the early MFI pumps have a cold start enrichment solenoid. Again, you can wire a remote switch if you want. Those are a lot easier than a remotely operated “thermostat.”

You want to drive your MFI so it warms up as soon as possible. A little lean crummy running during warm up is acceptable compared to oil dilution.

Best,
Grady

[nigel911]

Know what I'll be doing this weekend. Looks like I'll be going for plain headers after all, saves a bunch cash.

Many thanks for the help, this board is a great resource.

[Matt Smith]

thanks. I agree it's nothing to be frightened of, but I still don't like it much. I use to use my '72 for the daily commute (not now though) and i got sick and tired of waiting for that thermostat to cut out.
It doesn't really get cold enough to justify it here IMO, so maybe I'll try the plate & bolt idea. It's not exactly a hard mod is it?

[Ho Hum 74]

This is a great and simple mod.

I wonder if I could present youi guys with an issue that I'm dealing with...

My motor (2.7 RS style MFI) is fine until warm and idles perfectly. When warm it insists on idling at 2k rpm. Sometimes (after cleaning out the plates in the thermostat) it will only come down to 900 rpm idle after the car reaches a stop. WHY is that?? I have a squirter system (cold start vlalve??) and I'm wondering if this is malfunctioning and enrichening the mixture. Any ideas??

Thanks
Tristan

[nigel911]

My car did manifest the symptoms you describe, I lubed all MFI joints and fitted a new return spring on the MFI throttle linkage (above the fan, across the stacks), seemed to solve the problem.

I had a bad cold start valve - car would start perfectly from cold however once warmed up and the engine turned off it was almost impossible to restart. Cold start valve basically flooded the engine, didn't realize the engine was actually warm. I live in FL so didn't really need it anyway, just disconnected it.

One other idea, accelerator crank bell housing bushes gone? They are plastic and deteriorate, then the linkage does all sorts of strange things to the throttle. Replace with bronze bushes from our host.