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Old 09-08-2004, 09:41 PM   #101
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Willwren : You stay out of this! haha...I wanna see what others think
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Old 09-08-2004, 10:02 PM   #102
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Quote:
Originally Posted by DrJay
It seems you have the right thoughts but you're not taking a good enough look at the whole picture. This isn't just "detonation = bad" but an entire look at how detonation happens, how bad it really is, and how the computer can compensate.
.
I'm speaking in the context of the L67 that detonation is a must to avoid because the pistons are weak...dealing with detonation after the fact is dangerous for these engines.

That said I can tell you that the many small and big block Chevy engines I've had all took a lot of abuse the the stock cast aluminum pistons and never failed.

I've seen way too piston L67 pistons failures to believe that any detonation is acceptable.

Cheers,
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Old 09-08-2004, 10:05 PM   #103
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Quote:
Originally Posted by Foghorn
I've seen way too piston L67 pistons failures to believe that any detonation is acceptable.
Yeah I think thats one of the reasons they put knock sensors in it...but what do you think about the little "game" from my last post?
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Old 09-08-2004, 10:50 PM   #104
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I have 25 years of experience building, tuning and racing nearly every Pontiac and corporate engine that ever came in a Pontiac. My company has built and tuned more 3800 Series II performance engines than any other company. And we've programmed several hundred PCMs for these cars as well.

Someone on this board emailed me privately with some questions related to this topic. I'm going to copy and paste those questions along with my answers, in hopes that it helps us all. You're not all going to agree with what I have to say, and that'* OK. That said, here goes:

<<1) Will low octane (87) hurt the motor>>

Some will argue yes, but I disagree. No harm will be done directly due to the octane, with two caveats. First, the KR system has to be functioning perfectly or you'll get broken pistons. This wouldn't have been true in the old days, when ring lands were the weak link, but today'* hypereautectic pistons are extremely brittle. They can survive 700 horsepower, but they cannot survive detonation. Second, cheapass fuel is usually lower quality as well. This means that fewer additives may be used. If your 87 octane has all the same detergents and other additives as a premium fuel, disregard that statement. But please understand that this is not normally the case.

<<2) Will high KR hurt the motor even though the PCM is pulling timing to compensate>>

Some will argue yes, but I disagree. The engine runs hotter (not colder as some will say) in the combustion chambers with excessively low timing. This increases the risk of cracked cylinder heads between the valves. And the risk of engine damage when a knock spike gets filtered out inadvertently is much greater with low octane fuel.

<<3) Is high octane Race Gas useful for adding power other than allowing the pcm to add timing>>

In L67 engines, definitely yes, mainly due to the extra power from higher oxygenation levels.

<<4) Does oxygenated race gas provide more power per combustion stroke than normal gas>>

Absolutely. Anyone who doubts this should be forced to run back to back dyno tests.

<<5) What is the KR cap of the INTENSE PCM (15 like the DHP?)>>

Yes. We can change it, but there'* no reason to do so in my opinion. If you have a need for more than 15 degrees of KR, you've got issues so big that the PCM can't save you.

<<and what is the stock PCM cap for timing retard>>

Same. We leave this unchanged in our PCMs.

<<Will oxygenated race gas do anything for the car other than provide knock reduction?>>

It will also make gobs more power.

<<7) If the answer to 6 is no then would the car make the most power on the least octane gas allowing max timing and no kr.>>

Well, sort of. With everything else being equal (specific gravity, oxygenation, etc.), running too high of an octane fuel will actually REDUCE power because there'* not enough time for the complete mixture to burn and higher octane fuels burn slower. In our engines however, we are ALWAYS octane limited. This is because true unleaded fuel can't be commonly found above 100 octane. There'* 110 out there, labeled unleaded, but it contains other heavy metals. I've seen many cases where that fuel will annihilate an oxygen sensor just as quick as leaded fuel. If 120 octane unleaded fuel were available for our cars though, it'd slow us down.

Hope this helps.

Scott
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Old 09-08-2004, 11:09 PM   #105
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Quote:
Originally Posted by DrJay
Quote:
Originally Posted by Foghorn
I've seen way too piston L67 pistons failures to believe that any detonation is acceptable.
Yeah I think thats one of the reasons they put knock sensors in it...but what do you think about the little "game" from my last post?
I honestly don't know for sure, but I do know that it'* too costly for my blood with an L67. I mean it'* not a question of instant destruction when you have detonation, but if it persists it'* only a question of when...not if.

Cheers,
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Old 09-09-2004, 12:06 AM   #106
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Quote:
Originally Posted by DrJay
This can hold true for almost anything else on your engine. I know I'm being facetious but wouldn't this be the same as "You shouldn't use a MAF sensor because if it fails you'll run lean and burn a piston or valve" Or, "Fuel injectors are more prone to clogging which will make it run lean and burn a piston, you shouldn't use them." Or even "Superchargers are dumb, if even one sensor goes out with all that added heat and pressure you'll be sorry." I'm sure you get my point. I think its great that you take advantage of the extra power to be had by using premium fuel and I'm not going to try to convince you (or anyone else) to use a lesser grade. The point here is more for knowledge on the matter. You and others (and me!) know more now about fuel than when we started this. Now if you use lower octane because of it is your own choice.
You will find the manufactures go out of their way to always default the sensors and systems to keep from killing the motor. If for no other reason to save them warranty work from a maf failure for example.

OBDII actually gave the pcm the ability to "reason". Once all of the system monitors are set and the pcm see'* a problem it will look to other systems to confirm the problem. If the other systems don't back up what it sees it will actually substitute a known good value for the sensor. If the maf gives a reading that the pcm expects will lead to knock for example and the engine doesn't start knocking them the pcm will decide its a false reading. That is one of the reasons the smog program in Calif. will fail you if enough of the system monitors (or system ready) aren't set.
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Old 09-09-2004, 12:14 AM   #107
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Uh ohhh someone brought out the big guns

While I don't want to question your intelligence as you have TONS more hands on experience than me, I do have questions reguarding your statements. Maybe you can help me understand. I'll go in order.

1. The amount of detergents in the gasoline of ANY grade is mandated by the EPA. They all carry the same amount. Here'* a quote:

"EPA requires the use of additives to control the formation of engine and fuel supply system deposits in all U.*. gasoline. An interim program has been in place since 1995 which requires the use of detergents to control intake valve deposits (IVD) and port fuel injector deposits (PFID) in gasoline engines..." and "As of July 1, 1997, detergent manufacturers have been required to sell only properly certified detergents to their detergent blending customers. In addition, detergent blenders must blend certified detergents at the prescribed concentration into all gasoline they distribute. Furthermore, distributors must sell or transfer only gasoline and post-refinery components (PRC) properly additized with certified detergents. As of August 1, 1997, gasoline retailers have been required to ensure that all gasoline sold or transferred to the ultimate consumer is properly additized with certified detergents. Implementation of the detergent certification program will realize the full expected environmental benefits of controlling IVD and PFID, namely, reductions in emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), and improvement of fuel economy. "

http://www.epa.gov/otaq/regs/fuels/a...e/fact7gda.htm



3 and 4 (and I think 6?). Oxygenated fuel can not provide energy, and is actually LESS powerful (because space is taken up) than non oxygenated fuel. They actually use oxygenated fuel in the winters, incase that was news. Here'* a few quotes, two of which were used earlier:

"It should be noted that because oxygenates contain oxygen that can
not provide energy, they will have significantly lower energy contents.
They are added to provide octane, not energy. For an engine that can be
optimised for oxygenates, more fuel is required to obtain the same power,
but they can burn slightly more efficiently, thus the power ratio is not
identical to the energy content ratio. They also require more energy to
vaporise."

http://www.uvi.edu/Physics/SCI3xxWeb...solineFAQ.html

"Oxygenates are just preused hydrocarbons . They contain oxygen, which can not provide energy, but their structure provides a reasonable antiknock value, thus they are good substitutes for aromatics, and they may also reduce the smog-forming tendencies of the exhaust gases [15]. Most oxygenates used in gasolines are either alcohols ( Cx-O-H ) or ethers (Cx-O-Cy), and contain 1 to 6 carbons. Alcohols have been used in gasolines since the 1930s, and MTBE was first used in commercial gasolines in Italy in 1973, and was first used in the US by ARCO in 1979. The relative advantages of aromatics and oxygenates as environmentally-friendly and low toxicity octane-enhancers are still being researched"

http://www.repairfaq.org/filipg/AUTO...l#GASOLINE_015

"Reformulated gasolines usually contain oxygenates, which have less energy per gallon than the hydrocarbons they displace. The most mileage loss that may be attributed to oxygenates is about three percent. Each gallon of oxygenated gasoline will yield slightly less driving distance than a gallon of conventional gasoline. This fuel economy loss is less than three percent, and is often not detected because so many other variables can account for fuel economy loss."

http://www.countonshell.com/products...oline_faq.html

Note that the last one is from Shell themself.

I guess thats all I have at the moment.
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Old 09-09-2004, 12:31 AM   #108
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Quote:
Originally Posted by Buzz38
Quote:
Originally Posted by DrJay
This can hold true for almost anything else on your engine. I know I'm being facetious but wouldn't this be the same as "You shouldn't use a MAF sensor because if it fails you'll run lean and burn a piston or valve" Or, "Fuel injectors are more prone to clogging which will make it run lean and burn a piston, you shouldn't use them." Or even "Superchargers are dumb, if even one sensor goes out with all that added heat and pressure you'll be sorry." I'm sure you get my point. I think its great that you take advantage of the extra power to be had by using premium fuel and I'm not going to try to convince you (or anyone else) to use a lesser grade. The point here is more for knowledge on the matter. You and others (and me!) know more now about fuel than when we started this. Now if you use lower octane because of it is your own choice.
You will find the manufactures go out of their way to always default the sensors and systems to keep from killing the motor. If for no other reason to save them warranty work from a maf failure for example.

OBDII actually gave the pcm the ability to "reason". Once all of the system monitors are set and the pcm see'* a problem it will look to other systems to confirm the problem. If the other systems don't back up what it sees it will actually substitute a known good value for the sensor. If the maf gives a reading that the pcm expects will lead to knock for example and the engine doesn't start knocking them the pcm will decide its a false reading. That is one of the reasons the smog program in Calif. will fail you if enough of the system monitors (or system ready) aren't set.
Hmm thats interesting...maybe you can help me answer some questions on it.

If you were to hook one of those a/f calibrators that piggyback on the MAF sensor and set it to run lean would the PCM override this? How about rich? If so, how do they work then?

I'm guessing this wasn't built in too well for the OBDI computers as TelePlayer had this to say: "Until I cleaned out my MAF I heard plenty of knocking, whatever the PCM was doing did not help."
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Old 09-09-2004, 12:40 AM   #109
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Quote:
Originally Posted by GreenMachine
I see alot of mods to improve performance, not gas mileage, so I'm trying little things here and there. I have some other interesting findings, but I'm saving them for another thread.
Dead wrong. I now get 29 mpg highway, with the cruise set at 75. When I first bought the car (stock, after the first tuneup) I got 25-26 on a GOOD day. Virtually every mod I've done has increased mileage.
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Old 09-09-2004, 12:51 AM   #110
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Quote:
Originally Posted by willwren
Quote:
Originally Posted by GreenMachine
I see alot of mods to improve performance, not gas mileage, so I'm trying little things here and there. I have some other interesting findings, but I'm saving them for another thread.
Dead wrong. I now get 29 mpg highway, with the cruise set at 75. When I first bought the car (stock, after the first tuneup) I got 25-26 on a GOOD day. Virtually every mod I've done has increased mileage.
Other than the intake of course
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