Hi guys. This is technically an EFI topic, but I want to be sure the non EFI geniuses on the forum get a chance to weigh in here.

The question here is this:

If the timinng is too late, and the fuel too rich, does some of the combustion take place in the exhaust, after the exhaust valve opens? If so, can this happen even if you are getting pre ignition, or right on the edge of preignition, if the mixture is too rich?

When I sent my calibration file to Eli at Accel for advice, he wrote back and said the timing under boost was too retarded, and the fuel too rich to possibly cause damage to the turbo impeller. The thing is, I have been pulling out timing and adding fuel to get rid of detonation. Right now I have the timing at around 13-14 under boost.

When Total Performance put the engine on their dyno, thus not getting the benefit of the intercooler, they pulled out so much timing and added so much fuel to kill detonation they literally killed the power. It was way too rich, and down to 4 dgrees advance under boost. On the street, with the intercooler working, I had to lean out the fuelmap to get it to run under boost at all.

Should I maybe be thinking about water injection to control detonation, or perhaps a bigger intecooler. I know part of the problem is that perhaps Eli does not understand the nature of the smallbore, long stroke slant. Give me your opinions you slant racer guys, and expecially those with turbos.

Thanksfor your thoughts, and opinions here.
Sam

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Late spark will start combustion later and can result in combustion carrying into the exhaust cycle. This can lead to continued combustion into the exhaust manifolds and in extreme cases, into the turbine section of your turbo depending on it's location.
Start with basics: you tune any application by FIRST setting up your A/F and once you have this where you want it, then you tune your spark. Many questions... what is your intake air temperature? What manifold pressure (boost) are you running? What is your compression ratio? Are you using a modified head?

One of the disadvantages of the slant engine is there is no quench to promote mixture turbulence. Without turbulence, the engine will tend to be more prone to detonation and this will limit how much boost you can put into the engine.

Mitch

Thank you Mitch.

Compression ratio-8.5

Boost, 8-9 lbs

Head ported, but nothing more.

I can check intake charge temp. It may be awhile before I can get it on the road, and do a data log that includes intake temp. There are a few minor technical details I have to get worked out.

I can lock the timing at a safe spec, and tune the fuel map with no timing change. Is this what you are recommending? I would certainly not want to take it into boost under those conditions.

Thanks again for the interest.
Sam

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You need to first verify your A/F. Typically, you would want to do preliminary WOT runs with a safe spark curve. Dial in your A/F, then tune your spark. There is no other way to do this. If this were my car, I would use 15-17 degrees spark and tune for a flat 11.75 - 12:1 A/F. Once you get your A/F correct, tune for spark. The best way to find a safe spark curve is to use a load bearing dyno or WOT the car and let it pull against it's own weight in fourth gear. Intake air temp is a very large factor in how much spark you will be able to run. You will need to pull spark once your IATs climb over 120 degrees or so. Do you have an accurate wideband?

Mitch

Thanks Mitch. I do not entirely trust my wide band. It seems to make sense some of the time, and not others. I am not sure how to calibrate, or verify it. Most of the times it seems to agree with what the narrow band is indicating, but once in awhile it gets a wild hair and gets goofy. I am looking into getting a pyrometer so I can check the exhaust temp also. . I am going to reconfigure the intercooler first. I am not entirely happy with the setup, and think it is part of the problem here. I will follow your avice as soon as the harware work is done. Thanks
Sam

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EGT gauges are evry slow to reespond to real world happenings. Buy the time you see high EGT's its to late. Learn to turn other ways its better.

And agian, Plug Readings,Plugs reading & then some more Plug Readings.

Jess

At 13-14 deg and those boost/CR levels, I don't see how you should be getting detonation unless it's lean. IIRC, Cameron Tilley said his timing pulled out with boost and was minimum of about 14deg at 17psi boost (and 550HP at the time).

Maybe it is not pulling timing out as much as you think? I assume you've calibrated the computer advance with a timing light? Any chance the injectors are maxing out? Should be able to datalog duty cycle and O2 and WBO2 and look at the data. Can you datalog the knock sensor too?

Just throwing out a few ideas...

Lou

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Home of Slant6-powered fun machines since 1988

Check out higher sensitivity knock sensors. I have had wide ranging results with GM knock sensors. My personal choice for high tolerance sensors had been used 3/4 or 1 ton crewcab sensors from manual trans trucks. One of these made a huge difference in a car application with endless problems with code throwing.

Knock sensors are almost useless on solid lifter engines. The lifter "noise" makes them pull timing.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks for all the ideas! I don;t have the knock sensor wiried into the ECM yet. I am still trying to get it to run without this. I wasn't yet concerned about boost timing, and Fuel, but Eli's comments just raised the question in my mind, and I thought I would pass it on. I intend to do intake temp data logging as soon as it is running again. I rewired the harness, regrouping the functions in bundles that are not taped up. I can see them all if I need to trouble shoot. I put a new TPS switch and pigtail in, and hope she behaves now. If not, then the ECM goes back once more. The TPS harness did look beat down from pressure from the TB intake tube. That is why I am reconfiguring it.

Lou, thanks for the feedback about Cameron's engine. Do you know what kind of cam he is running?

On the positive side, this ECM has a powerfull design, and should be great if I can get it all working.Sam

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Cameron was running a mild cam when I rode with him, something like the MP 0.436" cam or slightly more. It idled and sounded like a stocker when not under boost.

BTW, I went by the shop with the 68 Dart and the paint doesn't look as bad as I remembered. They are respraying a couple of spots where the metal bunched up and they had a drip. I think it will look good!

Lou

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Home of Slant6-powered fun machines since 1988

Lou, What can you tell us about Cameron's turbo, intercooler, and tuning maps that are relvant to this issue? Do you think he controled detonation with superior head design, cam intercooler, or timing and fuel? How did he manage high horsepower and stay away from detonation? Does he have water injection or some other octane booster? Does he run race gas, or does this beast run on pump gas? Do you know the displacement of his motor? Is it stroked? HOw much is it bored? Wht kind of compression is he running? Lotsa' questions.
Sam

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Fuel and spark were the main components - cam, head, comp all similar to yours. He also did NOT run a knock sensor, which I would guess makes things easier psychologically. I would bet that thing scares you way more than it should.

He did chassis dyno tuning so the intercooler was not operating very efficiently. I don't see how that affects tuning much unless you are doing long pulls (more than 1/8 mile or in quick succession) under boost, which I haven't seen you do.

I would worry about the knock sensor trustworthiness first. 13 deg timing and sufficient fuel should keep you well away from detonation.

Lou

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Home of Slant6-powered fun machines since 1988

The compression of the turbo instantly raises the air intake temp. On the road, this is compensated for by the air rushing over the intercooler fins thus lowering the temp of the air charge. If the air is not moving over the intercooler(sitting still in fron of the dyno), then the air charge is warmer than on the road, and the tuner dials in fuel for hot air, instead of cooler air. Thus, too much fuel, not enough advance. Mind you, this is only a theory to try and explain why the tuner put in so much fuel, and took timing out. I think someone suggested this to me, but I cannot remember who. Now it sounds logical to me, and am sticking with this until someone can prove me wrong.

Of course this theory could be all wrong, and this wierd fuel and timing map could be the results of incompetence, and believe me, I dont; rule that out. I even have slightly paranoid thoughts of maliscious intent on the part of the tuner, as he was fired by the shop shortly after doing my work. It's not likely, and I like to think the best of people, but it is possible. EVentually here, I will be able to see more of the tuning tables, and will know more. Until then, it has suddenly gotten too cold to work on cars, so I won't know for awhile yet. I really envy you guys who live down South or out in the Southwest. In the meantime, I keep my car mojo alive by hanging out ont he forum, and reading the posts.

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I will say again, you must tune your A/F with a safe spark curve FIRST and once you get this correct, then you tune your spark. At the OEM level, a mean best torque spark map is made by running an engine typically at 14.64:1 A/F on an engine dyno. A borderline knock spark map is also generated under the same controlled conditions which includes standard temperature and barometric pressure, 205 degrees coolant temp, 14:64:1 AF, various grades of fuel octane. Modifiers in the tune include adding spark for richer A/F, higher ECT and IATs, EGR, lugging and so on. You do not have the benifit of starting with an OEM spark map, so you will have to generate your own. Get your A/F stabilized at around 12:1. Then work at generating a safe spark curve. The best way to do this is by letting the car pull WOT against it's own weight in fourth gear while using a listening device to detect detonation. Snap-on has a device you can use in-car. If you look at hundreds of tuning calibrations, you will find that spark will always follow your torque curve which, in turn, always follows your volumetric efficiency curve. If your application develops boost early, you will most likely have to pull some timing at peak torque. Just remember that once you start to detonate, it will not stop until you lift off the throttle - no matter how much spark you pull or fuel you add. You must stay out of detonation. Period. Also, IATs have a very pronounced affect on how much spark you will be able to run. In a FI application, your knock sensitivity with regards to IAT becomes compressed. You must be able to meausure your IATs and your tune must pull spark as your IAT increase.

Mitch

Thanks Mitch. That is the best, most direct, helpfull, specific, and concise description of tuning EFI I have ever read. It is packed with usefull information. I will print this out and put it into my manual.
I will certainly start data logging IAT in the future.
(AS soon as the weather gets decent again). Till then, I am doing plumbing again. The boost on this turbo does come on early.
Sam

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