How long did it take you to dial in a 2.8 MFI?

[BigD9146gt]

Hello all,
I'm at a crossroads with my engine, and what to do about the injection. The motor is a '72 with Mahle 2.8 RSR pistons and barrels, twin plugged E heads ported to 36 int & exh, MFI pump rebuilt by Gus to 2.7RS (that's what he wrote on the top), E stacks bored to 36mm, DC-60 cams, 1 5/8 headers, Dansk sport exhaust. (I think we figured it at 10.1:1).

Now I'm temped to sell the MFI, buy TMW's, an EFI, and spend an hour or two at the dyno to call it good. Has anyone here tried to dial in an MFI with similar or other combo's? Realistically, how long does it take (assuming the guy dialing in the injection is good)? I understand MFI isn't as flexible as EFI, but would I be close with current parts?

Thanks in advance.

[Flieger]

I do not have experience setting up the pump but since it has been worked on and tuned up by the master, I think you are almost there. It should not be hard to get it tuned, provided your throttles are in spec (butterflies and shafts not worn or your slides nice and smooth). Just need an air/fuel meter that can log data to a laptop while driving and then turn the adjustment screws a few times and that should be it. Just follow the Check, Measure, Adjust procedure.

A vintage, hotted-up, high-compression 2.8 RSR engine screams for MFI. There is nothing like it for throttle response and mechanical feel. Keep going on your original vision.

[356RS]

The 2.7RS pump is tailored for the S cams and 8.5:1 comp ratio. Your 2.8 engine with 10.1:1 comp will require an adjustment of the main rack to richen it up and then a correction on the idle adjustment to lean it back. The DC-60 cams should be fine with the RS spec pump but the headers may be too big for good low end torque. I think you will get some very good results on the Dyno and the RS spec pump should dial in with fair results as long as you don't touch the black & white governor screws that Gus has set.

[Jeff Alton]

Don't be fooled into thinking 2 hrs on the dyno with an efi setup will suffice Unless this is a race only motor and drivability in of no concern, but even at that........

ITB's with a properly tuned EFI system has all the throttle response (maybe better) than MFI, and can be made to run nice and clean from idle to redline with enough patience.......

Cheers

[BURN-BROS]

Originally Posted by Jeff Alton

Don't be fooled into thinking 2 hrs on the dyno with an efi setup will suffice Unless this is a race only motor and drivability in of no concern, but even at that........Cheers

+1

Originally Posted by Jeff Alton

ITB's with a properly tuned EFI system has all the throttle response (maybe better) than MFI, and can be made to run nice and clean from idle to redline with enough patience.......

Throttle response is about the same provided each system is functioning within it's parameters.

Idle quality is usually better on the MFI system when running aggressive cams

EFI will be, without a doubt more efficient across the whole rpm band. The closest I got to stoic tuning an MFI'ed car was a 2.4E and that was 13.2/1 @ idle and 12.5 @upper rpm. The vast majority of them ran the best with mid twelves at idle and low 12's at rpm.


Tuning an MFI in the car can take as little as an hour and can go for days. It will totally depend on what you are willing to live with if there is a hiccup in the rpm band.
My vote is MFI, but if you go EFI, get something with data logging as it is a great tool to have.

[Raceboy]

Originally Posted by BURN-BROS

+1

Idle quality is usually better on the MFI system when running aggressive cams

Don't know what EFI systems such opinion is based on, but I've never seen better idle quality than properly tuned EFI, compared to MFI. Not to to mention carbs.

If you're trying to set up idle on an engine with aggressive cams and ITB's and doing that on speed density, I'll understand (vacuum signal is non-existant and very noisy) but with Alpha-N? I've always got excellent idle and even on street cars that have 300+degree duration cams and have to pass local annual inspection and smog tests. Not as strict as CA, but nevertheless (max 4.5% CO)

Care to go into details?

[stownsen914]

Don,

I have a 914/6 track car powered by a 2.7L MFI engine. My engine is ported, GE80 cams, 10:1 compression. My MFI pump was prepared by H&R Injection as a race pump. It ran reasonably well out of the box, but it took me a couple seasons of tinkering to get the setup to the point where I was really happy with it. My car is used on the track only.

My pump has three enrichment adjustments: idle circuit and main circuit (both as stock) plus a gross enrichment adjustment that is a race pump option that goes in place of the warmup enrichment circuit. I was able to get the engine close to right with just these three adjustments (the gross enrichment adjustment helps a lot, as it allows a much wider range of enrichment than the standard main circuit enrichment adjustment). But to get it really "right" I had to adjust the fly weights inside the end cover of the pump. This solved a mid-range leanness issue that I was not able to get rid of with the three enrichment adjustments alone. I did the fly weight adjustment on the advice of Hans from H&R.

If you like your MFI, don't give up! EFI isn't exactly simple either ...

Scott

[356RS]

Scott,
Your engine set-up sounds great. I'm all for the MFI set up on all engines from 2.0 up to 3.0L. Above the 3.0 I think EFI / ITB's run better. Glad to hear your GE-80 cams are working well with the MFI. Is your "gross enrichment adjuster" the same as the one in this photo? I use it just to get the engine started.
Don, I hope you stay with MFI.

[BURN-BROS]

Originally Posted by Raceboy

Don't know what EFI systems such opinion is based on.

Yes you do, you answered answered it in your own post.




What's really neat is that MFI really is Alpha-N....just without lamnda correction.

[BigD9146gt]

Thank you all for your input! i'm not so scared of putting the MFI in anymore, however the ignition is my next problem... who's got the cheapest twin plug distributor setup? Cheers, Don.

[stownsen914]

Originally Posted by 356RS

Is your "gross enrichment adjuster" the same as the one in this photo? I use it just to get the engine started.

My adjuster is on the same part of the pump, but set up a little differently. Yours seems to be a manual warmup/cold start setup that must be connected to a lever in the cockpit. Mine is modified with a set screw, so can be used as an enrichment setting that has a wider range than the regular main circuit enrichment adjuster that sits inside the allen bolt at the end of the pump.

[colescrogham]

There is a basic adjustment I always performed on the dyno to see how the injection pump was going to work. Turn the man rack enrichment to the right in 5 click increments until the engine has a lean misfire in the stacks when you make a pull, then turn it back about 5 clicks. You can adjust the idle enrichment until it idles (no black exhaust) by turning that adjuster left to lean it out and it minimally affects the main rack adjustment.
Usually when things don't run well with MFI it is some other issue than tuning the main rack, like fuel starvation from the filter or tank, improper dwell, etc. I'd follow the CMA manual and leave tuning the injection pump alone for now. If you want to ditch the MFI let me know! It is without a doubt the best system ever used on a Porsche 911 engine unless you want to go full electronic.
As for the distributor, Richard Clewett makes the best system which is crank fire based. You could go a cheap route and convert a 964 distributor for twin plug app. too.

[stownsen914]

Sounds like good advice from cscrogham ...

In troubleshooting a tuning issue of my own MFI, I just called Hans at H&R Injection. A couple reminders from him:
1. Idle circuit is good for up to 2000-3000 RPM.
2. Anything above that is main circuit.
3. If you have the "extra" gross adjustment like I mentioned in my earlier post, it affects the whole RPM range, unlike the other two enrichment adjustments.

As cscrogham notes in his post, remember that the two circuits are adjusted in opposite directions! Idle circuit goes richer by turning clockwise, whereas main circuit goes richer by turning counter-clockwise like a faucet.

One other thing that messed me up once and is worth mentioning. MFI is sensitive to fuel pressure. It needs 15 psi or close to it, or it just won't run right especially under power. The stock fuel filter housing has a pressure regulator/limiter valve in the fitting for the fuel return (to the tank) line. That is supposed to keep pressure up, but over time the spring can wear out, resulting in pressure loss. I had this happen once, and it took me a while to discover that fuel pressure was the issue. The engine was breaking up badly in the mid and upper RPM ranges. To fix it I bought a fuel pressure regulator like the ones you find in Summit Racing catalog or similar, and now use that as a limiting valve in my fuel return line (I left the stock limiting valve in place since it now opens at only 10 psi).

Scott

[356RS]

Scott, You stated that the idle circuit was good for up to 2000 - 3000 rpm? Actually the idle circuit "#1 screw in the governor screw capsule" is good till about 1500 rpm then the #2 screw starts to take the spring load till about 3500 rpm then it's all on the #3 screw. Interesting note on fuel pressure. 15 psi or 1 bar at idle is great but more importantly the electric fuel pump must be able to flow over 1800cc per min through the MFI pump at high rpm's. I have seen fuel pressures as low as .1 bar at 7000 rpm's with no problem. IMHO The MFI pump needs the flow of fuel more than a set pressure of fuel.

[stownsen914]

Originally Posted by 356RS

Scott, You stated that the idle circuit was good for up to 2000 - 3000 rpm? Actually the idle circuit "#1 screw in the governor screw capsule" is good till about 1500 rpm then the #2 screw starts to take the spring load till about 3500 rpm then it's all on the #3 screw.

Interesting -- are there 3 different idle adjustment screws on the MFI pump? Internal or external? I am only aware of the one spring loaded idle adjustment on the end of the pump.

Originally Posted by 356RS

Interesting note on fuel pressure. 15 psi or 1 bar at idle is great but more importantly the electric fuel pump must be able to flow over 1800cc per min through the MFI pump at high rpm's. I have seen fuel pressures as low as .1 bar at 7000 rpm's with no problem. IMHO The MFI pump needs the flow of fuel more than a set pressure of fuel.

When I had some rough running issues, H&R mentioned fuel pressure to me and its importance. Sure enough, when I put the regulator in to keep pressure at 15 psi, the issue went away immediately. Since I made no other changes, I assumed that inadequate fuel pressure was the issue. Seems like my experience has been very different from yours ...

[356RS]

Scott, Not 3 idle springs, just 1. Behind the cover plate that has the idle adjustment sticking out is the spring governor capsule. When you adjust your idle mixture by pressing in on the screw it is connecting it to the governor capsule screws. Photos below:

[356RS]

Sorry to get off track on your thread Don.

[BigD9146gt]

Originally Posted by 356RS

Sorry to get off track on your thread Don.

Are you kidding me mate!?!? This is great stuff! If you didn't post it, I'd probably be back on a few months asking anyway...

Cheers mate,
Don.

[stownsen914]

The pics that 356RS posted above show the adjuster screws for the "fly weights" as some call them. They allow more adjustment of the pump's enrichment if the external adjustments aren't getting you where you need to be. I had to mess with them once when I had a mid-range rich condition that I couldn't get rid of on my 2.7L MFI race engine.

Scott

[356RS]

OK, lets fix this screw myth about "enrichment"on the spring governor capsule . The #2 black & #3 white screws are not for enrichment. I left out the #1 Idle. Although with some pump space cams, like the 2.4 T , they will cause enrichment in some areas, (Jeff's MFI Open Heart) but that's not what they are for. They are for setting up the predetermined spring tension on the flyweights ( different tension for different space cams) so at a given throttle & rpm the tip or sensor that rides on the top of the space cam is in the correct location of the contour or mapping of that particular space cam. These springs are checked and or adjusted by taking measurements off the main rack movement at certain throttle settings and pump rpm's. Below is a Bosch pump test sheet. "A" shows the correct setting of the springs required to put this particular pumps sensor in the correct location/contour on the space cam at different rpm's @ max throttle. "B" shows the 3 springs. This is the first check or adjustment that is done on the test bench when a pump is ready for testing.



If the pump was set up right "the 3 springs adjusted to the correct measurement" then when performing the flow tests you should see the correct amount of fuel "C" in the photo below. Notice the 2000 rpm @ max throttle in "A" and the same 2000 rpm @ max in the photo below: 7.00 mm on main rack full throttle delivers 47 - 48.5 ml of fuel in 1000 strokes of the pump. As long as the springs are set correct the sensor will follow the mapping contours on the space cam, the main rack will control the amount of plunger opening and you end up with the proper amount of fuel delivery from the MFI pump. I hope this explains the function of the 3 springs.