'75 EFI tuning

[IT Manta]

I had my ITB manta on the dyno saturday with some interesting results. This is the first time i have actually had an OPEL with L-Jet on a dyno. The bottom line is that the air flow sensor maxes out and runs out of resistor path before the engine hits redline. the engine actually starts to lean out at 4500 and by 6000 is in the danger zone. seeing as I cannot substitute meters, I have come up with some solutions. I would like to run it by those of you that know EFI. My plan is to tighten the spring until the meter does not max out. To compensate for the then leaner mixture I will increase the fuel pressure. Then in order to fine tune the fuel curve I will adjust the wiper position to obtain the best comprimise in torque to maximize the curve in the 4500-6000 range where the engine will operate the most. The engine produced 88hp and 103lb/ft at 4300 before leaning out and the torque dropping off. Before leaning out the torque was still climbing nicely. I am sure that if I can make the needed adjustments it will do around 100hp and 115lb/ft at the wheels. We also dynoed two ITB Volvo's. A 142 that I built put down 119hp and 125ft/lb at the wheels and a friends 240 was at 103hp and 109 lb/ft. The 240 was a stock engine with 100k+ miles.

[gtjames]

I'm not sure if I completely understand. Are you talking about tightening the air flow meter spring? The spring that returns the door to the closed position? If so, that would only worsen the condition. The meter is sending a varing voltage signal to the control modual depending upon the position of the door (the door position varies in relation to the amount of air entering the intake). By tightening the spring, it would close the door further, sending a signal to the control modual that there is less air entering the intake. The modual would respond by sending less fuel into the engine (decreasing injector pulse time). I think I read a thread on here about aftermarket control moduals that are available. I think that would accomplish what your trying to do more effectively. I hope I'm following you, if not, I apologize.

James.

[RallyBob]

A rising rate pressure regulator is commonly used to 'tune' L-Jetronic. Tune it until 4500+/- or so with the air flap tension and idle air bypass. Install the rising rate regulator, and adjust until your fuel curve looks better. Cartech makes one that can be fine tuned quite nicely, but it's over $200.

IIRC, Pete Mills used this method in his old championship-winning ITB Manta and achieved somewhere around 118-120 hp. He had a Microdynamics FPR unit, which was $450 almost 15 years ago, but worked nicely.

[IT Manta]

James- yes tightening the spring will make the system leaner, but I cannot have the arflow meter "maxing out". I will compensate for the added leanness by increasing fuel pressure.

Bob- I hoped you could help. I am very familiar with The BEGI/Cartech regulators. I have used a couple of the styles in other projects. Now typically the rising rate regulators only adjust to positive manifold pressure to enrichen mixture (over and above the normal off idle enrichement). I do believe he has a newer model that can enrichen below positive pressure (I will check). Now how can I use the idle bypass air?

[gtjames]

very interesting!

[RallyBob]

Cartech part number CAR-2023 is for N/A engines, and can be adjusted to compensate for manifold pressure increases at higher rpms. Yes, even N/A engines have some positive pressure in the upper rpm range, especially with restricted breathing.

http://www.cartech.net/fmu2020.htm

[IT Manta]

I would probably go with the unit that also allows adjustability of the base pressure. Bob, you mentioned the idle air bypass as a tuning option? Is there some effect other that idle speed? I could see it as a way of getting aditional air.

[davegt27]

The Aux air valve could be adj to bypass more air but if you’re lean already you need more fuel so an ADJ FPR is a must.

I would mod the TPS to go to full enrichment at 4500 rpm

You could try it at the Dyno by installing a toggle switch so you could switch the TPS to go to WOT at your command

You could put a mega squirt inside the stock FI ecu housing but they might say something about a vacuum line running to the ECU

But you could mount the MAP sensor inside the AFM lock the AFM wide open and have just the electrical connection going to the Mega squirt ECU board ha ha

The big thing is to be able to adj the AFR your self and get it some what close before you go to the Dyno

The direction you want to head in is having the AFM locked open (to get the most air) also bypass even more air with the Aux Air valve

HTHs
Davegt27

[Sportwagon75]

I'm not sure if this is useful for your situation...but I was told that the brain box for some VW busses was good to use with certain performance upgrades. Based on this information, I went and snagged one from a 76 VW Bus and tried it in one of my 75 Mantas. The only significant change I noticed was a little rougher idle and you could smell the unburned fuel at idle. It seemed to be running much richer. Under load I couldn't discern much difference. I still have this brain box if you're interested in trying it. I've also been told that you have to have the right box that used the pre-resistors. Using the wrong one can bring disastrous results...or so I'm told. I only know the one I have works fine. You can search the other F/I threads for more detail as I know this has been previously discussed in depth. And I know there are others who know more about such things than I. I do know that Gary's new Sportwagon is running a VW Bus brain box since I spoke with the P.O. at Carlisle and he told me how he did his homework to set it up. Might be interesting to have Gary dyno his Sportwagon. As I said...just a thought.

[IT Manta]

Thanks Scott I will do some research.

[dallasmanta]

I have been running group b components on my 75 manta for years producing good torque and top end. The pieces I had switched out with the help of the bosch factory rep who was into racing in the early 80's was the brain box, the air box the clog free injectors and the thermo time switch. The Mods done to the engine came from C&R in Youngstown OH. The basic engine was a high compression (9.5:1) mild street cam, HD lifters, high grade racing valves, springs keepers etc. The package was rated to produce between 115 and 120Hp. Adding the group B injection package increased hp and torque and decreased MPG. it will run from just right to rich. I can not get it to run lean. The high end power is better and the engine does not feel like it is running out of lungs. This was an acceptable trade since I also run a factory AC unit with a 65 amp alt. and a host of electrical power sucking devices. This car now has 106K miles on it since the build back in the early 80's and will still chirp tires in three gears. A five speed would fix the MPG issue.

[RallyBob]

Originally Posted by dallasmanta I have been running group b components on my 75 manta for years producing good torque and top end.

Yes, this later system would help a lot, but unfortunately is not legal for ITB. The larger air flow meter from the 2.0 L-Jetronic is WAYYY bigger than the 1.9's. Wouldn't get through tech though!

[jordan]

I've actually started doing something on my efi project, basically just some polishing and grinding but still advancing a little (I got a new camera so I decided a picture was necessary)

[IT Manta]

Bob is right, I have to work within the allowable modifications to stay legal. I have installed a high quality fuel pressure regulator (SX) and will adjust fuel pressure and air flow meter adjustments to maximise power in the 4000-6500 range. I was just setting the car up on the dyno two months ago when a lifter broke holding #4 exhaust valve open and bending the valve. I will try again in a week or so when I get the head back.

[dallasmanta]

Did not know the rules but one of the things I looked into was running a turbo on the Low compression engine at the time of rebuild. I worked with a friend who used to race fiat X-19 in the same class as the Manta in Oklahoma (THis for for the SCCA group racing) and some of the mods he made was to reduce the spring tension on the air flap ( air box) for faster RPM gains higher fuel delivery rates with a fixed pressure regulator in the fuel rail circut. This made his car very fast on the circut.

On the turbo front the bosch tech guys told me to put a variable resistor in line with the thermo time swith under full acceleration to make the cold start injector enrich the fuel mixture on the top end so the engine was not running lean resulting in cracked head. Some thought if they fall with in the confines of the IT rules