[Bobtempest]

On Direct Scan does the duty cycle % and the Inj. PW real accurate? I have been reading 19.70 INJ.PW and 102.6 on a set of 83lb injectors on a 10.25 at 134.44 with a bad sixty(1.59). Fuel pressure was running with the boost. No knock and 02s 812-820. Clean run but have maxed the injector?

 

[Steve Wood]

It's a good question and I don't know the answer.

I assume you are running an egt to set the fuel with? O2s are probably not much use the way you run.

Perhaps, if one has a very loose converter, one uses a lot more fuel on the run but I am sure you have plenty of pump.

I think there is a growing belief that one needs injector than we usually compute, but I would think you would still have a bit left in the low tens unless it was really pretty rich. I think Jeff H is running 83s and has been around 9.8 but I think Jeff uses a relativly tight converter and does not wind it up too much on the line.



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[Steve Wood]

That indicates 19.2 would be 100%. What is the limitation in the ecm?



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[Steve Wood]

What was your rpm?



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[Bobtempest]

Steve,
I use a Ford heated O2, the #s really match up well with EGT. The stock did not. The max EGT on this run was 1548, which was a little rich but with 0 knock. My setup likes fuel. At 1600 the knock starts. I shift at 6000 and cross the line at 6200.

------------------
Bob Hinson
Stage 2 offcenter tuning under way
so far a [email protected] with a easy 1.59 sixty- stock ECM, Double XP pumps with stock lines, 0 knock, more than full weight

ROLL TIDE

 

[Quick Toy]

From what I understand the % pulse width is what the ECM is commanding divided by the maximum possible time the injector can fire from the time the intake valve opens till the next time the same valve opens again (2 crank revolutions)

The time, in milliseconds, from intake valve opening to intake valve opening is
60,000 x 2/rpm.

60,000 x 2 = 120,000
120,000 /RPM

If we take your 6000 RPM shift point and plug it into the equation we get:
120,000/ 6000 = 20ms or 100% duty cycle

Your DS reading of 19.70/20 = 98% duty cycle

Looks like you are almost maxed out. I imagine you could run slightly over 100% duty cycle if you really want to squeeze a bit more out of them… then again it’s your car!


Paul

------------------
1972 Toyota Celica with a 87 TR drive train.

 

[Steve Wood]

Thanks, Paul

First, I think a number of these cars may run better richer than the normal belief.

Secondly, if you were shifting at 5400, you would have 89%.

Shifting at 6200 gets you right at the 102% number.

I wonder if the standard fuel line is beginning to be a limiting factor-again more so it you use a high stall converter so that the engine is pulling more than 4000 when you launch. I did not notice if you mentioned the launch rpm...

Does your DS log show much difference in o2s from the beginning of 3rd to the end....I wish I had faith in them

I wish we could log egts...



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[Bobtempest]

Thanks Steve and Paul,
The 02s in 3rd stay from 816 and 824. It was a little fat off the line at 851 and came down when it went into second. I too have found the need for a little more fuel than some have said. I have never blew a fire ring on any of my engines either.

------------------
Bob Hinson
Stage 2 offcenter tuning under way
so far a [email protected] with a easy 1.59 sixty- stock ECM, Double XP pumps with stock lines, 0 knock, more than full weight

ROLL TIDE

 

[teking]

Well let's do some estimating here. Our cars ran ~ similar, but I had 72's at 90% duty at about 6000 rpm, with the FAST wb system set for 11.6:1 a/f ratio. Maybe you are just making very rich passes. I think in general a gasoline engine will start to rich misfire in the 9's:1 a/f ratio range. If we assume you are near 90% duty at 6000 too, then we can try tweaking the 11:6:1 a/f ratio by a factor of 83/72 = 1.15x. I get 10.1:1 a/f ratio, so I'd say the above is a possible answer at least

TurboTR

 

[Bobtempest]

Todd,
I think you are right, I may have been a little rich, particularly a fat 1st gear. There is much room to turn up the boost without getting lean knock. I can get back to the track in Jan. and try some things. I believe I will end up with some 96lb injectors later. Thanks

------------------
Bob Hinson
Stage 2 tuning under way
so far a [email protected] with a easy 1.59 sixty- stock ECM, Double XP pumps with stock lines, 0 knock, more than full weight

ROLL TIDE

[This message has been edited by Bobtempest (edited December 15, 2001).]