dand86951

George for me it was two cylinders as one coil drives two, and what I experienced was just what you are describing. Easing into the throttle I could take it all the way to 6000 no misfire, partial throttle, low boost was ok also. Full throttle 15psi or approaching 15psi, it would just surge buck miss and not make any more power. If I backed off the throttle a bit it would smooth out and run fine. This was on a track day when it happened to me, so I wasn't a happy camper. I tried leaning out the fuel map bit by bit and still had no luck. Out of exasperation I took the plugs out, checked them and then just arbitrarily set them down around .020. I say around because I couldn't find a gap gauge so it was just tap tap tap the electrode until it looked a lot smaller. Put them back in and presto the car ran great.

Days later the car started doing the same thing so I just got a new coil and swapped the two out until it went away and then put the plugs back to .025. If I had to describe it it was just like running into a rev limiter with fuel cut.

In my mind and I could be way off I just think your system should be able to fire a very rich mixture and with the MAP based system it is hard for me to think it could be so rich it would miss fire, although I do know too rich and it will miss fire. If it is just mixture then it may indicate you were set for a very safe mixture to begin with.

George D

That's exactly what was happening, but only in the early AM and at high altitude. The outside temps were around 45 to 55 degrees. Looks like I'll regap the plugs and check things out next trip up there. It hasn't happened since that morning.

Thanks for the information.

George

dand86951

The temps are another data point. Since it was happening in the cool of the morning the actual Density altitude was lower as cool air we all know is denser therefore more oxygen per volume. So if anything the car wouldn't have been running richer but slightly leaner due to cooler temps. If later in the day after it heated up it was doing the same thing then it would have been richer due to the higher Density Altitude.

Also changing the gap on the plugs gives you another reason to drive back up to that beautiful place in the mountains.

TurboTim

The air density between cool and warm air at high altitude will not be the same as sea level.Just because this car has EMS on it does not mean you can get away with running extremely rich mixtures and not having it "choke" itself with fuel.Yes the ignition system is better then a stock system but if there is too much fuel,you cant fire it correctly even with individual coils per cylinder.I could take Georges car right now at sea level and make it so it wont rev past 2k by adding in a crapload of fuel.I could also get it so it wont even fire at all.There is alot of adjustability with the TEC but it doesnt mean that you will not be affected by the same things that can plague a factory set-up with MAF.Too much fuel means....... no go fast for you. It is not a big deal as this has only happened at elevation and the fix is simple......if George can figure out how to open up the software on his laptop. LOL

nize

15psi of 50degree air at sea level
15psi of 50degree air at 8000feet

are they different density?

George D

It is not a big deal as this has only happened at elevation and the fix is simple......if George can figure out how to open up the software on his laptop. LOL

Thanks Tim. I'm still trying to open the software on my laptop. I will call you tomorrow afternoon to get it open. I haven't even looked at what is at my disposal. I'm just a technology user, and not very good at that either.

Thank god I have other talents and folks that know more than me willing to help.

Tim, I never got your fax. I'll call you after my morning appointments.

George

jmayzurk

Thank you!

And when the turbo is not compensating for the difference in atmospheric pressure at altitude (i.e., under vacuum), the MAF sensor is still measuring correctly.

So I don't understand why altitude makes a difference...

George D

Well, there is much less oxygen available at 8000' vs sea level. Ask me when I'm running up there as compared to here. I run out of breath much faster at altitude.

Our motors burn fuel with air and many components that make up "air". Now, I'm thinking that if I increase boost pressure to compensate for running too rich at altitude, I don't have to lean out my TEC system. I don't think I'm wrong, but I'm willing to learn if I am.

This is what I know:

Inches of Mercury = (in. Hg.)
Atmospheres = (atm)
Kilopascal = (kpa)
Millibars = (mb)

Pressure equivalents to: 1.0 atm = 29.9 in. Hg. = 760 mm Hg. = 101.3 kPa = 1013.25 mb

Atmospheric Pressure = 14.7 psi & 13 cubic feet of air = 1 pound

Power Loss due to Altitude
Air Density decreases at a rate of 2.9% - 3.0% for each 1000 ft. of elevation above Sea Level.

Naturally Aspirated: Atmospheric Pressure 14.5 psi (It's hard to ride at sea level 14.7 psi)
Atmospheric Pressure @ 9000 feet = 10.5 psi
Pressure Loss = (14.5 - 10.5) = 4.0 (4.0/14.5) = 27.58 % @ 9,000 feet


Does a Turbo lose power with altitude? Yes!
Atmospheric Pressure = 14.5 psi, Boost = 10 psi, Total Pressure = 24.5
Atmospheric Pressure @ 9000 feet = 10.5 psi + Boost of 10 psi = Total 20.5 psi

Approximate Pressure Loss = (24.5 - 20.5) = 4.0 (4.0/24.5) = 16.32 % @ 9,000 feet
The power loss due to altitude is much less with the Turbo. The critical difference is that you can flip the switch on the Turbo to 15 lbs boost and get your sea level HP!!

Turbo considerations: As altitude is increased the turbo fan must increase rpm to maintain a constant boost pressure. So, if I just turn up my boost to compensate, I shouldn't be running too rich........RIGHT? I've got enough turbo compressor to probably hit 35psi, so I can compensate for altitude.

I think it was something else. I've got some tuning to do. I'll regap the plugs for starters. Got to get my software up and running to do some datalogging. I got a bit carried away with the above post, but it caused me to think and share.

George

George D

Jeff, I don't have a MAF anymore. My TEC GT system reads from intake pressure. Air density does make a difference. We are no longer measuring voltage required to keep a constant temp, it's all about the intake pressure now. Pro's and cons of each system are part of the deal. I'm going to get it figured out and show you some tail soon.

George

ehall

Since we're on the turbo board, it might be worth doing some research on the engines of U.S. WWII fighter planes, especially the P-51 and the P-38, which actually had a turbo supercharger.

I don't mean that for you George, but for lots of others reading this thread. One of the great advantages of U.S. fighters was their ability to move fast at high altitudes. It took a long time for the Germans to catch up, or vice versa, depending on your take, but it was absolutely key to U.S. fighters operational envelopes. Our birds were built to boom and zoom, meaning start higher than your enemy and ive on them, then climb again.

The engine dynamics have many similar applications to George's problem.

George D

I'm up way too late, but don't have a good book right now. Wife is asleep, so I'm typing, doing some research and learning. Ehall has created some OT, but fun none the less.

The P51 Allison engines had 6-1 compression. Bendix-Stromberg SD-400D3 speed/density injection (carburators) and anti detonation 50:50 water-methanol injection anti-detonation injection (ADI). These 12 cylinder engines had alum water jacket heads, steel lined cylinders, forged aluminum alloy pistons , two stage engine driven superchargers, 10.25" engine impeller, 12.1875" auxiliary impeller. They had max hp rating 2,250 hp war emergency rating (WER) at 3,200 RPM. Imagine a gas motor with 2250hp at 3200rpm! These motors stopped production in 1948!!! If they had Nicom coating the steel sleeves would not be necessary and the motors would not have weighed 1595 lbs.

I could go on, but the apark plug gap was: Sparkplug gap = 0.012-0.015"

Ehall, I'm going to regap my plugs. They had something here. I'm always amazed at how the little things make a difference.

George

ehall

Go back to your homework George. The P-51B had the Allison. The P-51D, the model that brought all of the fame to the airplane, had a Rolls Royce Merlin engine.
The P-38 was actually designed by Kelly Johnson, and the Turbo supercharger combo is what made the bird so fast for it's time. It was clearly out-performed by '44, by a good handful of fighters, but was WAY ahead of it's time.
Just some interesting thoughts based on altitude and performance. Afterall, these were the last of the piston fighters.

dand86951

George, Ehall, you guys sure know how to burn the early morning oil, I can barely burn the midnight oil. George I think all of your statements about pressures and altitude are correct. Just for a bit of clarification, the metric system uses Bar as a standard pressure rating and it is equal to 100kpa = 14.5 psi. This is not 1 atmosphere which as you stated is considered to be 14.7psi at sea level on a standard day temp of 15 degrees celsius (59F). So even at sea level when the temps go up the density altitude goes up.

As you said above the air at altitude holds less oxygen per cubic foot and so even though you pack it into the cylinder at the same gauge pressure it has less oxygen therefore slightly richer mixture as the MAP system is firing injectors based on the manifold pressure without knowing what the actual Density Altitude is. The TEC has compensation tables for air temperature to allow for an increase or decrease in fuel based on inlet air temp.

dand86951

Another point is that most factory MAF systems as Tim pointed out have a barometric pressure sensor which feeds compensating information to the ECU to modify the fuel curve. The 951 has that in the stock system and I would guess Jeff's 993tt would have it.

jmayzurk

Actually, cars with MAF sensors from the factory don't need pressure/altitude sensors, because the MAF compensates for this already. MAF sensors measure air mass, not volume.

The stock 951 has a flapper door measuring air volume, so it needs a barometric pressure sensor to compensate for changes in air density. So would a car with a MAP sensor.

I was under the impression that George is running a MAF sensor, which is why I'm confused at the existence of this problem. George, are you running MAF or MAP with TEC3?