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Supermodel Dynoed! Long Update.

 
Old 04-18-2005, 02:51 PM
  #31  
Gretch
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Originally Posted by Jim R.
Good luck with it Seth.

Regarding the pinging, the GT chips do have more aggressive timing than S4 or GTS. I have to say that I have yet to get my car to ping under any circumstances since installing my SC kit. Be carefull with the ping--we are pushing 16 year old head gaskets past their design limits and ping will lead to early failure. As far as "throwing more fuel at it", I use a RRFPR and my boost, fuel pressure and RPM's all build linearly instead of higher boost down low. So in my application, the ratio of rise to boost for the fuel pressure works well without going rich under light throttle. As far as I know, Gretch's GT behaves the same way. Since I spend most of the time driving with light throttle vs WOT, this is key to driveability. Get it sorted, it will be much more fun.

Jim R.
Confirmed, just as Jim has described it. I get no pinging anywhere in the throttle range.....even on very hot days. And this too, is offered in the spirit of contribution. , and as proof that Jim and I are interested enough in what you are doing to actually read the threads.......
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Old 04-18-2005, 04:15 PM
  #32  
Seth W
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Very interesting. So what is the effect of putting an S4 chip in a GT?

1) Retards Timing--what else would happen?
2) Is there any downside? What about the cams and idle? would they get "weird"

I guess we would not know until we test it. Sounds more elegant than putting more fuel in the system.

Can someone explain what "more timing" is in less technical speak and the relationship between the cams and timing and idle. I'm not sure how the variables interact or (in the case of idle) whether they interact at all.
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Old 04-18-2005, 04:32 PM
  #33  
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SO a GT with an aftermarket tuner chip would be VERY bad for a S/C setup? Way too much ignition advance for the blower? Seems fine for stock cars?

I'll be at sharks in the park early waiting for a ride from one of these S/C beasts!
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Old 04-18-2005, 04:35 PM
  #34  
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I don't yet accept that ignition advance is the issue. I think it's lean on part throttle. I'd hate to give up advance on full throttle where there does not seem to be any problem at all. The charts clearly showed it going way lean when pinging.
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Old 04-18-2005, 04:44 PM
  #35  
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cams/valve timing is when the valves open or close for intake/exhaust. If you hold the intake valve open a little longer, you might be able to cram more air into the cyl. Theres alot of timing details to opening and closing the valves that i'm sure books have been written on. Won't even try to explain it because i'm not very knowledgeable in this area.

ignition timing is when the spark happens in relation to top-dead-center.

As the piston approaches TDC on the compression stroke, the spark actually fires before the piston hits TDC. This is because the time it takes for spark and combustion to happen (which can probably be measured in milliseconds), is actually slower than the piston moves. IF you were to fire the spark right at top-dead-center, the piston would already be on its way down the cylinder on power stroke before the mixture could fully combust. I think the idea is to time it so that full combustion happens just as the piston reaches TDC... this way, you get the full effects of the combustion pushing the cylinder all the way down the stroke. This is all to get an engine that runs normally... The timing of the spark is measured in degrees of crank rotation. I think spark timing values are something like "30 degrees of advance before top-dead-center". This means that the spark plug fires 30 degrees of crank rotation before the piston hits TDC (BTDC).

Theres a ton of variables that affect/are affected by ignition timing. It is possible to increase the advance so that the spark fires a little earlier, thus making the combustion more optimal/powerful. Retarding the spark is just the opposite.

Now, one important thing is that people generally refer to advancing and retarding the ignition RELATIVE to the stock timing. When you have "retarded" timing, that doesn't mean that you're firing the spark after the piston hits TDC, it generally just means that you've lessened the amount of factory advance.

I think most people agree on what i've written above. After that point, theres lots of theories and beliefs.

In your situation, the factory advanced the ignition to try to squeeze that last bit of power out of the GT. Unfortunately, when you have a supercharger that's forcing air into the cylinders and adding some heat to the air, the air/fuel mixture becomes slightly less stable. If you attempt to spark it, it may not combust properly (knocking/pinging). Higher octane fuels are more "stable" and can handle more of this added heat/pressure. More octane also means that the fuel burns slower so you can advance the ignition more to get more power of it.

That's all i'm going to say... theres a ton of info on the net.
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Old 04-18-2005, 04:46 PM
  #36  
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Originally Posted by IcemanG17
SO a GT with an aftermarket tuner chip would be VERY bad for a S/C setup? Way too much ignition advance for the blower? Seems fine for stock cars?

I'll be at sharks in the park early waiting for a ride from one of these S/C beasts!
You generally should not run a "performance chip" in an SCd car. You will get far more power from the SC than the chip could ever give you. And yes, too much ignition advance to run with a blower.
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Old 04-18-2005, 04:53 PM
  #37  
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Originally Posted by Bill Ball
I don't yet accept that ignition advance is the issue. I think it's lean on part throttle. I'd hate to give up advance on full throttle where there does not seem to be any problem at all. The charts clearly showed it going way lean when pinging.
Well, you can supress pinging with more fuel up to a certain point. When you say lean, what AFR was it running?

On my car, I ran it as lean as 18/19:1 @ idle, 14:1 on part throttle cruising, and 12.5:1 on WOT full boost. The 85/86 cars have the lowest ignition timing because they didn't have knock sensors. I think I heard my car knock a couple times when it was really hot and I was advancing my ignition w/ the SMT6 just out of curiosity... otherwise, I just can't make it happen.
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Old 04-18-2005, 04:54 PM
  #38  
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Mike:

That's more than I can absorb. I'm obviously focusing on the fact that at full boost, when you are cramming the most air, Seth's car is not pinging (AFR was 12 or 13 to 1) and when it did ping on partial throttle it was WAY lean (16-17 to 1). Why pay any attention to ignition advance until you have the mixture in the right range?
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Old 04-18-2005, 05:01 PM
  #39  
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To be honest, I really don't think ANYONE knows the answers to most of these questions.

When you hit WOT, the LH pumps the injectors harder. So, if the problem is fuel, then going WOT fixes it. If the problem is ignition, then more fuel might fix it too. So which is it? Well, since you say the AFR was 16-17, it could be fuel... but I assume you got that # from Tom's dyno. Tom's dyno is AWESOME, but we did prove with my car that measuring AFRs from the tailpipe after the cats is inaccurate (dynapak measured higher AFRs @ the tailpipe than my pre-cat wideband setup. It was also by varying amounts... not a straight 1-2 AFR increase across the board). Seth's car DOES have cats - right?
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Old 04-18-2005, 05:16 PM
  #40  
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sorry for being a pain-in-the-***...

I just believe that things work a certain way and I like to argue both sides of the coin and rattle some cages beacuse I don't think anyone knows for sure.
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Old 04-18-2005, 05:25 PM
  #41  
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Mike:

No problem. I'm very simple minded. I see what looks like lean fuel mixture and think it should be richer. Should part throttle 16:1 be OK? Is that why you are looking at advance? I was figuring the mixture should be no more than 14.X:1. I did notice it started off far leaner than that and even that alarmed me, but on WOT it stayed below 14:1 after 3K RPM.

Yes, Seth's car has cats.
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Old 04-18-2005, 05:31 PM
  #42  
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Meow.
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Old 04-18-2005, 05:52 PM
  #43  
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What prompted the comparison between GT and S4 EZK advance curves had nothing to do with total advance: The total crank degrees may/may not be identical, I do not know.
It is the slope of the advance curve ( crank deg. vs. rpm) that motivated the comment. The GT curve is more aggressive than the S4 in that the allowable total advance is fed in earlier at a greater rate than for the S4. I suspect their end points are very close.
As the pre-ignition was commented on as a part throttle, mid range RPM issue, the 'logic' was that a milder curve may be beneficial. Agreed that armchair quarter backing is a poor substitute to being there for the fun and real data .
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Old 04-18-2005, 05:56 PM
  #44  
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Ill throw this inot the pot of stuff to stir around.
I just did this this AM. The temp 2 inches from the inlet lobes of the SC was 117.f and in my fender 99.F
60 mph... slow roll on to 80ish..4th gear...slightly up grade.. I never went to WOT, so this is all partial load. each time i tried to put my foot down a little bit quicker.

I guarentee if i drop my fuel pressure a bit more i can get it to spike and for a longer duration. Not the two spike on the last two. A littel bit more aggressive on the throttle but not close to WOT. Still enough to generate partial boost. AS yo can see, my FP respond immediately.
I can run anything you want to see, let me know.
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Old 04-18-2005, 06:08 PM
  #45  
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I can run anything you want to see, let me know.
If you can run 30# injectors, and 85-86 fuel pressure reg referenced to the boost side of the mainfold without the Bell reguator? Without this configuration no amount of data will help. In fact, it will only cause confusion.
HTH,
Andy K
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