Question for LT1 gurus - Dyno data
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From: Marlboro country MA
Question for LT1 gurus - Dyno data
I took my '92 LT1 to the local dyno shop yesterday and did three runs. http://forums.corvetteforum.com/zerothread?id=278720. The engine is stock, except cut lid/K&N filter and muffler elims. Last fall I replaced the opti, plugs, and wires. At high RPM, it sometimes runs rough.
Here are all 3 runs superimposed. Notice that the HP and torque curves become somewhat noisy above 4400 RPM , and extremely erratic above 5000 RPM.
Looking at just run 1, when the engine was coolest, shows the problem the worst:
So here's my question: given that the opti, plugs, and wires are new, what should I do to fix this? Do I even need to fix it? I just ran a 13.97 at 100.87 with a 60' time of 2.18 on street tires. What would you do? Major mods are not part of the future for now.
Here are all 3 runs superimposed. Notice that the HP and torque curves become somewhat noisy above 4400 RPM , and extremely erratic above 5000 RPM.
Looking at just run 1, when the engine was coolest, shows the problem the worst:
So here's my question: given that the opti, plugs, and wires are new, what should I do to fix this? Do I even need to fix it? I just ran a 13.97 at 100.87 with a 60' time of 2.18 on street tires. What would you do? Major mods are not part of the future for now.
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Re: Question for LT1 gurus - Dyno data (ZylaRace)
Try a new coil ... check your fuel pressure ... make sure that your plugs are gapped properly.
I had missing above 4k with my stroker and I just gapped the plugs a little smaller ... all fixed. It's probably something simple.
BTW, that doesn't look like a problem with the opti... when my opti was going out, my dyno curve didn't go complete erratic, it just had certain areas that would drop a large amount for a small part of the rpm range. Of course if your opti was really on it's way out, then your dyno curve looks about right for it, but you say it's new ... soo......
[Modified by Glock'94, 12:37 PM 4/15/2002]
I had missing above 4k with my stroker and I just gapped the plugs a little smaller ... all fixed. It's probably something simple.
BTW, that doesn't look like a problem with the opti... when my opti was going out, my dyno curve didn't go complete erratic, it just had certain areas that would drop a large amount for a small part of the rpm range. Of course if your opti was really on it's way out, then your dyno curve looks about right for it, but you say it's new ... soo......
[Modified by Glock'94, 12:37 PM 4/15/2002]
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Re: Question for LT1 gurus - Dyno data (Glock'94)
What's you reve limited set to?
Mine was erratic up top till I had it reprogrammed.
as I recall he lean it out, the factory runs them rich.
Mine was erratic up top till I had it reprogrammed.
as I recall he lean it out, the factory runs them rich.
Thread Starter
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Re: Question for LT1 gurus - Dyno data (BrianCunningham)
check your fuel pressure ...
What's you reve limited set to?
I appreciate your help, guys.
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Re: Question for LT1 gurus - Dyno data (MTVette)
It's set on the chip
Don't go too high though or you'll join this guy ...
http://vette.ohioracing.com/majmods.html
Go ahead with the fuel filter first.
[Modified by BrianCunningham, 12:34 AM 4/16/2002]
Don't go too high though or you'll join this guy ...
A word of warning, 6200 RPM is the Limit for a stock LT1. I set my rev limiter to 6400 RPM against the advice of Justin Vandersall (Superman Vette Mechanic). The motor lasted for maybe 10 revs at that limit. The LT1 rod caps can not take high RPMs. The cap on the number six cylinder stretched. The piston began to slap against the head when down revving. As soon as the engine cooled the bearing spun.
Go ahead with the fuel filter first.
[Modified by BrianCunningham, 12:34 AM 4/16/2002]
Melting Slicks
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From: Ca.
Re: Question for LT1 gurus - Dyno data (MTVette)
Another thing that can cause your dyno graph to look like a sawtooth pattern is hitting the knock retard (due to too much timing/too lean/etc...)-it takes out timing and then feeds it back in over and over.
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Re: Question for LT1 gurus - Dyno data (drive it)
I'd have to agree with knock retard. This is EXACTLY what the dyno graph on my 95 Firebird LT1 looked like when I was experiencing false knock. By setting knock retard to 0 for the range I was having a problem with, I was able to get a perfectly smooth graph. Now, the problem is how to fix your problem. You could have a tuner burn a chip with the knock retard set to 0 for that range, but that's really the method of last resort. The first thing you need to do is find someone with Diacom (or other diagnostic software) that can monitor the knock sensor and knock retard to verify that this is the problem. Then you need to figure out what's causing the knock, is it really there or is the sensor just picking up "false knock". False knock is a common problem on many LT1s, especially if they've been modded. I know on 94+ models, you could change the knock sensor module out with the LT4 unit which is supposed to be more discerning. Does anyone know if this applies to 92-93 LT1s as well? I forgot to check you sig for mods, but do you have roller rockers, headers, or cat-back? Any of these mods seem to cause false knock. Hope this helps.
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Re: Question for LT1 gurus - Dyno data (EvanLT1)
I was getting a false knock when I installed my muffler eliminators
( after the tuning I mentioned previously )
I've got the LT4 module, now I'm AOK
( after the tuning I mentioned previously )
I've got the LT4 module, now I'm AOK
