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Walt Fricke's Avatar
 
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EFI Questions

I'm changing over my 2.8 race motor from 46mm Webers to 46mm TWM throttle bodies and Electromotive TEC3 EFI. I've had to make choices and run into issues on which I'd like some advice.

1) I have set up the fuel at the engine in a loop, with the high pressure line from the fuel pump splitting with a Tee, branching off to each fuel rail, and then comming together off the backsides of the fuel rails at the rear of the car, where the pressure reducer, plumbed as a Tee, will shunt off excess pressure into the return line.



Any issues with doing it like this?

2) This fuel pressure regulator is not manifold pressure modulated. For a race motor, would I get better performance with a regulator which kept the pressure differential between the fuel and the intake into which it squirts constant? Or will using the fuel map do just as well?

3) I thought the carburetor linkage would just hook up. Wrong. I can't really get the drop links short enough, and even if I do I can't get full range of motion.

First, the butterfly shaft on Webers is about 30mm up above the manifold flange. But the TWM's shaft is 57mm, which means it is 27mm closer to the end of the end of the cross shaft linkage arm.

Then the ball joint on the Weber is about 33mm out from its pivot on the butterfly shaft. The TWM's ball is 42mm out - a longer lever arm.





My first thought on dealing with this is to remount the ball 9mm inward. That should at least make the butterflies close and open fully, should it not?

I don't know what to do about the drop links, as I think I will have to do without the lock nuts for the adjustments.

4) I plan to use the fuel pump for a '77 through '80 911: Bosch 0 580 254 984. I think it should be able to provide 40psi regulated and support the maybe 300 flywheel hp I'd love to make. I have my trusty Holley Reds sending fuel to an external surge tank from two pickups in the fuel cell, and the Bosch will pick up its fuel from the bottom of the surge tank, which is located right above the Bosch.

Will this pump do the job (assuming it works - it was in my parts collection and handy)?

I see mention of folks using a Bosch pump with a "944" in it somewhere. I note that the 3.2 motors had a pump with a "944" number. Maybe the 944 motors had pumps with a 944 in the designation? Is this a better pump for my purposes?

5) This motor previously ran, under different ownership, with 40mm TWM induction and the TEC3. Max torque was at 5200, and HP at 6500. I don't have figures for running this motor with the Webers I put on it.

All I am doing here is upgrading to 46mm throttle bodies and intake manifolds, still ending up at the 40mm intake ports. The TEC3 box still has the maps in it for the 40mm intakes.

Any suggestions on making a change to the fuel map? It is running a GE980 cam (no change there). I would hope I might need to richen up the top end some because of better breathing, and the torque and HP peaks might move up a couple of hundred RPM.

Add 5% enrichment as a WAG first and see? Run as is and keep close eye on the EGTs (probes in #2 and 5 exhausts)?

I have the Innovate LM2 air/fuel recording system, though with my carbs and leaky headers I never got any useful air/fuel data at all. I now have the Buckley headers, and all the connections and joints are tight, so I am hopeful that the AF recordings will be useful.

Walt
Old 09-13-2010, 10:41 AM
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Walt, just to get this moving I'll offer a couple thoughts and then relinquish the podium.

Typically you see the high pressure feed go first to one rail, then the other, then to the regulator, and then the return goes back to the tank. This is how a lot of factory setups are plumbed. I assume you split the feed and then had each rail feed the regulator for more consistent pressure between the two? Having the regulator fed only by the second rail would result in a pressure difference between the two due to frictional losses and the bends in the hoses. But I would also be concerned that liquids take the path of least resistance and wonder whether the regulator might open from a pressure signal from the higher bank, stagnating flow in the opposite bank.

Can you source an in-tank pump? That's what I did. Eliminates the issue of surge and pickup-- ATL makes a "black box" surge tank with a holder for the pump, you simply put it under the foam. You can even mount the pressure regulator on the tank itself so it dumps directly back into the tank, with a peanut gauge up front.



I yield the balance of my time to the Gentleman from Portland who will (hopefully) make any further advice from me irrelevant. . .
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Old 09-13-2010, 11:49 AM
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Fuel pressure regulator

Walt

John C's comments above are certainly true of many production based "open loop" systems - but I would be inclined to go with your "closed loop" setup in the interests of balance (overkill perhaps). I use open and closed loop here not in the control threory sense of the the words, but more in the plumbing sense...

However - I suggest you use a fuel pressure regulator that references manifold pressure.

Flow through the injectors is a function of differential pressure between fuel rail and manifold pressure and the injector on time. You want to keep the differential constant so that the fuel map can control the delivery via the on time.

I guess it depends on how much part throttle driving you intend the motor to do...

John

Last edited by jcge; 09-13-2010 at 05:03 PM..
Old 09-13-2010, 04:49 PM
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John,

I understand why you would want a pressure compensated fuel pressure regulator in a forced induction context. Presumably you would want the pressure in the fuel rail to be a fixed pressure above the pressure in the intake tract-- and if you went to 1 bar in the intake tract, you would end up with less fuel, assuming that flow through the injector is a function of the size of the orifice, how long it's open and the relative pressures on either side.

According to the latest METARS Denver Airport is about 30 inches of mercury right now.

AirNav: KDEN - Denver International Airport

That is close enough to 29.92" Hg to mean we don't have to worry about different numbers for the elevation for this scenario.

Suppose that Walt's at the track and the pressure is 29.92 or 1013 millibars. At idle, the overlap of the cam allows him 25 inches manifold pressure. A pressure compensated regulator would reduce the fuel pressure by the amount of vacuum vs. it's baseline setting (within the limits of governing), so he's basically going to 12.3psi or 846 mb. For an NA engine the pressure only goes one way, down.

Now, doesn't the EFI system have a MAP sensor to compensate for reduced atmospheric pressure? I guess it would be good to have only a single variable to control. In the turbo context you MUST augment the fuel pressure or flow will stop, but I wouldn't want the system to be confused.

I have a Wilton regulator, got it from a hot rod shop, the thing is WAY overkill for my purposes but you could basically throw it down the stairs and it would work. It's basically a diaphragm with a spring, it has a gauge port but no pressure port. The spring doesn't know or care what the pressure is in the intake tract, it just holds back the diaphragm and associated valve to permit the fuel to pass or not. Seems like that would be independent of MAP and therefore would control a single variable.
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Old 09-13-2010, 06:17 PM
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John C

Some clarification....and I agree with your pressure calcs above.

Manifold pressure referenced regulator ensures that the ECU can accurately meter fuel through the injector based on injector "on time" as the sole fuel delivery control. This is the basic premis of mapped EFI.

Without manifold pressure reference for the regulator, the mixture at any other than WOT will be increasingly rich at greater manifold vacuum, and conversely increasingly lean at boost, for a given injector on time.

By how much ?? At 5 bar set point, a variance of (5+1)/5 = 20% richer at full vacuum. At 4 bar set point (4+1)/4 = 25% richer at full vacuum. In trying to tune an aftermarket EFI system , I'd want to eliminate this as a variable, assuming you want to retain good control at part throttle.

MAT, MAP, TPS and O2 are used to determine engine load (air flow), and hence injector on time from the data map, depending on the control strategy that is being implemented.

I don't believe that MAP calcs are used by the ECU to compensate for the change in differential fuel rail pressure, which is I think what you are getting at ??? Please correct me if I've misinterpreted.

So the question is really, how much part load vs WOT control is required in this application.
Old 09-13-2010, 07:44 PM
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I will add my $0.02.

1. the plumbing will be fine. The injectors will see the same pressure on each side. Unless there is a blockage there should be plenty of flow.

2. The regulator does not need to be pressure compensated. Rising rate FPRs can be difficult to tune. These are commonly used in boosted systems to allow one single size of injector to have decent idle (low flow) Through full boost (high flow). It can be difficult, especially with high impedance, to control this large dynamic range.

3. My TWM setup has the same arms. I raised the height of the cross bar by shortening the lower bell crank rod. this helps but provides a quick off-throttle (idle) transition. yes, it is not optimal.

4. the CIS or Carrera pump should be fine as long as you regulate the output. The flow should be within the capabilities of the pump. I see no reason to change it.

5. You have now reached the point of no return and must tune the engine. Does the Tec3 have a datalogging capability? you will need this. Drive carefully while logging to make sure your AFRs are in check. Make changes to the map as needed.

The 46mm ITBs will flow more air all the way around. If the 40IDAs were not air flow limited you would not need to make many changes. Otherwise, you would need to add more fuel to compensate for the extra air. I would think that you would need to pay attention to the acceleration parameters to account for increased swept area of the butterfly valve on throttle transitions. This will be like increasing the accelerator pump delivery. Too little and the AFR will spike lean giving poor throttle response. too much and the car will bog.

All the general knowledge of tuning carbs applies to EFI. YOu just use keystrokes to make changes.
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Old 09-13-2010, 07:59 PM
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Thank you, all.

There is a MAP sensor in this system. In the picture you can just make out a rather large "accumulator" chamber made from plastic pipe. Hoses connect it to two fittings, one on each manifold (I think each of these actually "reads" two of the throats). Another hose goes from this cannister to the sensor itself.

I am assuming that when the MAP senses a vacuum (idle, for instance), the ECU is programmed to subtract some fuel because the diffferential pressure between the fuel rail and the intake will be higher. etc.

I do see that Electromotive suggests running a regulator with a vacuum port. However, the previous owner used something I think TWM sells which does not have this feature. He said the engine ran just fine once he got it tuned, He's an aerospace engineer, and I tend to believe what he says.

The history of this engine is: 1) Raced with 40mm TWMs and TEC 3 EFI
2) Sold to me with about everything except the fuel pump and surge tank.
3) I put on my 46mm Webers, with appropriate tall PMO manifolds.
4) Now I am putting 46mm TWMs on these manifolds, planning to use the same maps (still stored in the ECU, and on a laptop, and a CD, etc) it had when it was run with the smaller throttle bodies. To start out, anyway.

So it is teething issues in the transition I am thinking about.

Walt
Old 09-14-2010, 12:02 AM
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Here is what I hope is a simple question:

The former owner of this motor/EFI gave me his data. I see that he set the rev limiter at 7,600, and I am sure I can figure out how to boost that to 8,000, which is where I want it for my track.

He also has the 16x16 tables for VE and advance. They stop at 7,600. If I just rename the final column to be 8,000, and let it smooth out the small differences, will I get in big trouble? That would be quicker as a start than redoing 14 or so of the columns. I won't be shifting above 7,600, but my memory tach tells me that where I shift is not the peak RPM.

Walt
Old 09-14-2010, 11:16 AM
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Quote:
Originally Posted by Walt Fricke View Post
I'm changing over my 2.8 race motor from 46mm Webers to 46mm TWM throttle bodies and Electromotive TEC3 EFI. I've had to make choices and run into issues on which I'd like some advice.

1) I have set up the fuel at the engine in a loop, with the high pressure line from the fuel pump splitting with a Tee, branching off to each fuel rail, and then comming together off the backsides of the fuel rails at the rear of the car, where the pressure reducer, plumbed as a Tee, will shunt off excess pressure into the return line.
Any issues with doing it like this?
We have our EFI'd 356 running from the tank through a pump (Walbro 190 (i think)) through the filter, through a "Y", with a line into each fuel rail, and each return side goes straight into the Aeromotive fuel pressure regulator, then returns to the tank. Your setup seems pretty solid, but I wouldn't want the pressure regulator or "T" just hanging from the hose. I can't tell if thats a bracket there or not. When using "T"s instead of Ys and sharp corners instead of radiused ones, you may end up with some fuel pressure loss at higher fuel demands.


Quote:
2) This fuel pressure regulator is not manifold pressure modulated. For a race motor, would I get better performance with a regulator which kept the pressure differential between the fuel and the intake into which it squirts constant? Or will using the fuel map do just as well?
When you're normally aspirated, the diaphram in the FPR won't care. .. or at least thats what I was told. Our vacuum/manifold pressure port goes to nothing, and we just use the ECU to tune.


Quote:

3) I thought the carburetor linkage would just hook up. Wrong. I can't really get the drop links short enough, and even if I do I can't get full range of motion.

First, the butterfly shaft on Webers is about 30mm up above the manifold flange. But the TWM's shaft is 57mm, which means it is 27mm closer to the end of the end of the cross shaft linkage arm.

Then the ball joint on the Weber is about 33mm out from its pivot on the butterfly shaft. The TWM's ball is 42mm out - a longer lever arm.

My first thought on dealing with this is to remount the ball 9mm inward. That should at least make the butterflies close and open fully, should it not?

I don't know what to do about the drop links, as I think I will have to do without the lock nuts for the adjustments.
Welcome to hot rodding. ours were too long as well, so I made some shorter ones. get a piece of steel rod, a right hand and left hand die and have at it. As I recall our TWM levers were longer than the Solex's as well.


Quote:

4) I plan to use the fuel pump for a '77 through '80 911: Bosch 0 580 254 984. I think it should be able to provide 40psi regulated and support the maybe 300 flywheel hp I'd love to make. I have my trusty Holley Reds sending fuel to an external surge tank from two pickups in the fuel cell, and the Bosch will pick up its fuel from the bottom of the surge tank, which is located right above the Bosch.

Will this pump do the job (assuming it works - it was in my parts collection and handy)?

I see mention of folks using a Bosch pump with a "944" in it somewhere. I note that the 3.2 motors had a pump with a "944" number. Maybe the 944 motors had pumps with a 944 in the designation? Is this a better pump for my purposes?
Its good that you're using a surge tank. I wish we had one, or at least a surge bucket inside the main tank. Have your return line from the motor dump into the surge tank, not the main one. Our fuel pump is a Walbro and works like a champ. They make them in several different sizes for different power requirements.

Quote:
5) This motor previously ran, under different ownership, with 40mm TWM induction and the TEC3. Max torque was at 5200, and HP at 6500. I don't have figures for running this motor with the Webers I put on it.

All I am doing here is upgrading to 46mm throttle bodies and intake manifolds, still ending up at the 40mm intake ports. The TEC3 box still has the maps in it for the 40mm intakes.

Any suggestions on making a change to the fuel map? It is running a GE980 cam (no change there). I would hope I might need to richen up the top end some because of better breathing, and the torque and HP peaks might move up a couple of hundred RPM.

Add 5% enrichment as a WAG first and see? Run as is and keep close eye on the EGTs (probes in #2 and 5 exhausts)?

I have the Innovate LM2 air/fuel recording system, though with my carbs and leaky headers I never got any useful air/fuel data at all. I now have the Buckley headers, and all the connections and joints are tight, so I am hopeful that the AF recordings will be useful.

Walt
Its good that you have the base maps from the 40mm throttle bodies, but consider them as JUST base maps. The LM2 will be an invaluable tuning tool. I love mine. But if you ever consider running in closed loop, or using the TEC3 for data logging, you may want to get an LC1 or other permanently installed WBO2 sensor. Back to the base map question, if you are using different injectors, different pump, different fuel pressure, or different plumbing, the fueling will be off. If you didnt change the cam or the intake track length, I dont think your peak torque would have moved much. As for the 5% all around increase, its probably a safe starting point. And I thought I read somewhere in here that you also wanted to bump up the max RPM. Id advise against that because as you increase revs, the internal stresses on the motor increase geometrically, but if you can afford it, go for it.

Good Luck.
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Old 09-14-2010, 12:57 PM
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I would still use vacuum reference to the FPR as this will make the tuning a lot easier (flatter VE table) and compensates for the atmospheric pressure differences both on ECU and FPR.

If MAP signal is unstable at idle/low loads, just use Alpha-N blending until say 1500-1700 rpm, speed density after that.

The "944" pump is actually 044 pump, but it is a clear overkill. CIS pumps are around 10-15 % less capacity at the same base pressure (say 3.0 bar) and they will do just fine.

Tuning should be ALWAYS open-loop, closed loop tuning will give you a lot of headache.
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Old 09-14-2010, 10:48 PM
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