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Old 07-02-2019, 12:47 PM   #29
Dixie ZL1
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Originally Posted by 95 imp View Post
Or, run down to Home Depot and buy some Xylene to dump in the tank for more octane. elevation will also have an affect on the octane requirements though. 91 might be just fine on a stock motor. It all comes down to what the knock sensors are hearing.
Inexpensive way to overcome 91 octane fuel if you don’t want to go flex. Honestly though E50 is a really inexpensive way to the get the best performance gain per $$ spent if you’re willing to do a tune

https://www.summitracing.com/parts/m...0aAtcMEALw_wcB
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Old 07-02-2019, 01:32 PM   #30
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So spraying the fuel directly on the crown of the piston doesn’t help run leaner and higher timing?
You adjust your A/F leaner under WOT because it's dumped on the crown instead of over the valve first? Cruising, ya. idle, maybe. WOT? No.

12.x/1 whether it is a carb, EFI, SFI, or DI feeding the cylinders. (If you want to split hairs, maybe a wee bit more on a carb setup due to variances in wet flow characteristics. Some cylinders will always end up rich and some lean).

The computer DOES give you a LOT more control (and immediate self adjustment) of engine requirements for the load it sees vs. carb jets and points timing. I'll give you that. You can take the timing to the ragged edge because you have the KS circuit to pull you back. It still doesn't change the physical principles occurring in the cylinder.

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Originally Posted by 6spdhyperblue View Post
Designing the air envelope to insulate the flame front has no impact?
So, now, because of that technology, you can run 87 octane? Or, are you still at 11.5:1, recommended to run 93 octane, and still need to prevent detonation/auto ignition in the cylinder?

There isn't any flame front during compression. That means zero effect on pre-ignition. It *might* have an effect on detonation. I'd have to read up on it to see what they are trying to accomplish. On the surface, designing an "air envelope to insulate the flame front" is counterproductive.

When controlled ignition is started, you want the flame front to progress as rapidly and smoothly as possible to exert the most force on the piston.

Insulating it suggests it is intentionally being slowed down. My guess is it has more to do with flame impingement than anything else.

Thinking about it, that makes more sense. The fuel is in the "middle of the chamber and "doesn't have time to reach the chamber edges". Therefore, there is an "air envelope around the metal" which minimizes emissions and wear, but maximizes fuel efficiency and power. It also might be why oil is sprayed on the bottom of the pistons. They are absorbing more heat since they are not insulated (back to fuel dumped on the crown) and take more concentrated heat than the head/cylinder walls used to.



But, I will do some homework on it.
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Old 07-02-2019, 01:55 PM   #31
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Originally Posted by Dixie ZL1 View Post
Inexpensive way to overcome 91 octane fuel if you don’t want to go flex. Honestly though E50 is a really inexpensive way to the get the best performance gain per $$ spent if you’re willing to do a tune
I'm not here to say it doesn't work. Clearly, it does. And I agree E-fuels work pretty good.

What I am saying is that there is more than one way to skin a cat. We are talking theory here and all trying to learn and clear up misinformation.

For me, I'm scouring the boards looking at other people's hard earned knowledge and learning about the specifics of the G5LT1/F-body and how I can fit it into my plans/goal when I pull the trigger and get one.

Right now, I'm just trying to give back by sharing what I know.
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Old 07-02-2019, 02:09 PM   #32
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I'm not here to say it doesn't work. Clearly, it does. And I agree E-fuels work pretty good.

What I am saying is that there is more than one way to skin a cat. We are talking theory here and all trying to learn and clear up misinformation.

For me, I'm scouring the boards looking at other people's hard earned knowledge and learning about the specifics of the G5LT1/F-body and how I can fit it into my plans/goal when I pull the trigger and get one.

Right now, I'm just trying to give back by sharing what I know.
My last comment was only with regard to 91 octane as stated. If you have 93 available there are many ways to skin the cat. Not as many is you only have 91 octane fuel available. One option would be tuning for 91, but the car does that to some degree with KR anyway.
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Old 07-02-2019, 02:50 PM   #33
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Originally Posted by 95 imp View Post
You adjust your A/F leaner under WOT because it's dumped on the crown instead of over the valve first? Cruising, ya. idle, maybe. WOT? No.

12.x/1 whether it is a carb, EFI, SFI, or DI feeding the cylinders. (If you want to split hairs, maybe a wee bit more on a carb setup due to variances in wet flow characteristics. Some cylinders will always end up rich and some lean).

The computer DOES give you a LOT more control (and immediate self adjustment) of engine requirements for the load it sees vs. carb jets and points timing. I'll give you that. You can take the timing to the ragged edge because you have the KS circuit to pull you back. It still doesn't change the physical principles occurring in the cylinder.



So, now, because of that technology, you can run 87 octane? Or, are you still at 11.5:1, recommended to run 93 octane, and still need to prevent detonation/auto ignition in the cylinder?

There isn't any flame front during compression. That means zero effect on pre-ignition. It *might* have an effect on detonation. I'd have to read up on it to see what they are trying to accomplish. On the surface, designing an "air envelope to insulate the flame front" is counterproductive.

When controlled ignition is started, you want the flame front to progress as rapidly and smoothly as possible to exert the most force on the piston.

Insulating it suggests it is intentionally being slowed down. My guess is it has more to do with flame impingement than anything else.

Thinking about it, that makes more sense. The fuel is in the "middle of the chamber and "doesn't have time to reach the chamber edges". Therefore, there is an "air envelope around the metal" which minimizes emissions and wear, but maximizes fuel efficiency and power. It also might be why oil is sprayed on the bottom of the pistons. They are absorbing more heat since they are not insulated (back to fuel dumped on the crown) and take more concentrated heat than the head/cylinder walls used to.



But, I will do some homework on it.
In my experience I can run way way leaner than any pfi or carb.

A lot less heat on the crown and edges in the chamber from the last combustion event helps prevent preignition during the compression stroke leading up to the next

You can see they’ve blatantly increased compression when moving to di

Sorry for the shit posts, I’m on the run today

Last edited by 6spdhyperblue; 07-02-2019 at 06:27 PM.
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Old 07-03-2019, 12:58 AM   #34
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Originally Posted by 6spdhyperblue View Post
In my experience I can run way way leaner than any pfi or carb.
What kind of numbers and at what load?

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Originally Posted by 6spdhyperblue View Post
A lot less heat on the crown and edges in the chamber from the last combustion event helps prevent preignition during the compression stroke leading up to the next
Actually, the crown is the hottest part and the edges are the coolest.
The coldest are where the water jackets are located. The hottest (edge) is the piston crown. Traditionally, heat has to travel from the crown, thru the rings, to the wall, and then the jackets. Or, thru the wrist pin, rod. Or oil splashed on it from the rotating assy. Now, we have direct oil spray. (As a side note, oil spray is also used in the Duramax engines).


"Flame impingement" occurs on the edges (3D wise) in the combustion chamber. Why? it's cold there. This is where HC and CO on your smog test come from. Incomplete combustion.


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Originally Posted by 6spdhyperblue View Post
You can see they’ve blatantly increased compression when moving to di
Here's the thing... We had factory produced 11-12.5:1 CR engines in the Sixties. Some how they ran just fine without DI.


What happened? The Smog Nazis, gas shortages, and the unleaded, low octane transition in 1971.

Compression (and HP) took a dump. Big cube motors were gone. What we got were, exhaust choking cats, egr valves, smog pumps, etc, in an effort to meet Big Brother's requirements.

Mid 80's seen EFI and a resurgence in power.

90's we had the G2LT1/4 with 10.5:1 and 3 way cats.

Now we have DI giving us even better fuel economy and less emissions.

So, to say that DI is the reason we have factory produced high compression motors is false. DI is the reason we have them back with all the rules and regulations skewing the playing field.


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Sorry for the shit posts, I’m on the run today
No offense taken...

Last edited by 95 imp; 07-03-2019 at 03:06 AM.
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Old 07-03-2019, 06:09 AM   #35
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I am comparing ls3 compression to LT1

Fueling .89-.88 lambda full load

In my experience, these engines are predisposed to knocking more when rich than lean compared to older engines.

Car is making power with the benchmark cars here for what it is


Edges I was referring to in that last post were edges in the chamber not necessarily the piston. But the area between the rings, ring lands, edge of the piston does seem critical in terms of preignition with DI from all the lspi things we seen.
Most seem to think it’s only related to boost but I’m sure it does play some part in NA too
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Old 07-03-2019, 10:04 AM   #36
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I am comparing ls3 compression to LT1
Ok... Ok.. I see your point. What I am saying is the ONLY reason it got the CR bump was due to being able to control emissions. I'm going to guess NOx specifically because that goes up as compression goes up. I do not know if the second cat help clean it up as well. I do know that the D-max had to start using DEF to combat NOx emissions as diesels were targeted by the smog freaks.


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Originally Posted by 6spdhyperblue View Post
Fueling .89-.88 lambda full load

In my experience, these engines are predisposed to knocking more when rich than lean compared to older engines.
I would think that it is due to combustion chamber efficiency as well as the injector in the cylinder better atomizing the fuel allows you can go leaner? Usually you go heavy to help cool the air charge at the expense of unburnt HC's.. It really doesn't matter, if the motor is making more power, reliably, give it what it wants!


[QUOTE=6spdhyperblue;10561674]
Edges I was referring to in that last post were edges in the chamber not necessarily the piston. Usually the water jacket areas are the coldest and the flame front dies off around them because they suck the heat and extinguish the flame.


Quote:
Originally Posted by 6spdhyperblue View Post
But the area between the rings, ring lands, edge of the piston does seem critical in terms of preignition with DI from all the lspi things we seen.
I think this is true in any ICE. The heat as no where to go. It's bottled up trying to flow thru a floating ring (in the groove) without solid contact to transfer. Carbon builds up on the rings due to incomplete combustion because they are in solid contact with the heat sucking walls. Get enough build up and you can create a hot spot.

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Originally Posted by 6spdhyperblue View Post
Most seem to think it’s only related to boost but I’m sure it does play some part in NA too
No doubt it is in both. It is more frequent and pronounced in boost motors because you are artificially increasing the CR. More squeeze raises the charge temp.
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Old 09-07-2019, 10:30 PM   #37
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The position taken by the tuners in Florida is an understandable position. It all boils down to what they may or may not know about particular types of engines. Ethanol is corrosive. Running E85 requires valves and valve seats hardened to resist the corrosive nature of ethanol. If the tuners don’t have a way of confirming that the valves and seats in an engine are hardened to support E85, they are smart to walk away from it.

Now, specifically for Camaro, I am pretty sure...90+ %-ish sure, that the valves and seats in LT1 are hardened to support E85. And from what I can tell, the E85 kits that are sold replace a part of the fuel line that might also be impacted by corrosive ethanol, so getting the sensor and tuning for E85 is really all LT1 needs.

My background for saying this is that when I was in Powertrain Portfolio Planning at GM, I had an engineer assigned to working with Product Engineering and the people in the company who managed GM’s fuel economy reporting to determine which vehicles using which engines would be planned to use E85. GM’s position was to maximize the credits that could be generated from using E85 capable engines. 3.5L and 3.9L OHV engines were targeted, as were 3.6L FWD (but not RWD) engines. A lot of small block V8s were also targeted, as a lot of the GM truck portfolio was to be outfitted with E85 capability. This is where Camaro and Corvette benefit. With so much truck volume being E85 capable, it made sense for the engine plants producing those engines to use the hardened valves and seats for everything, whether they were E85 intended or not. Fewer part numbers to track and inventory and separate.

There was typically additional E85 content that needed to be added at the vehicle assembly plants. Not totally certain what that would be for Camaro, since it was not intended to come from factory E85-capable. I think fuel pump may have been one of them, but I wouldn’t swear to that.
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Old 09-07-2019, 10:42 PM   #38
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the heads on all LT1s are the same between the trucks with E85 and cars. part #12678972 . dont know about the components in the fuel pump but all vehicles made since the 90s have had to have PTFE rubber for everything in the fuel system.
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Old 09-08-2019, 04:19 AM   #39
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To add my 2 cents, cam guides can corrode in my coyote application, chevy is ahead of the game in my opinion concerning e85. Skinning cats is fun R&D. I enjoy the research.
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Old 09-08-2019, 08:51 AM   #40
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the only honest downsides i can see are making a lot more $80-$100 oil changes and if the car isn’t driven much, the moisture collection. beyond that, properly use ethanol and let your high comp marvel of engine technology eat, figuratively and literally speaking.
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Old 09-08-2019, 05:25 PM   #41
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the only honest downsides i can see are making a lot more $80-$100 oil changes and if the car isn’t driven much, the moisture collection. beyond that, properly use ethanol and let your high comp marvel of engine technology eat, figuratively and literally speaking.

The 'extra' oil change thing is a myth.
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Old 09-08-2019, 08:26 PM   #42
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The 'extra' oil change thing is a myth.
i plan to do analysis but that wont be till the end of next year
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