combustion chamber volume and alky

January 22, 2019, 05:19 PM

358T

Chamber shape, squish, quench and other things that myself and most others don't understand enough to talk intelligently about is where its at no matter the size. Imo, big inch alky burning engines with fancy raised port shallow valve angle heads (or even fancy small block heads) can behave more like a high end nitrous engines when it comes to this area of the build. You really need to talk to a cylinder head guy and/or engine builder who understands this (which there doesn't seem to be many or at least many that care to know...) to get the full picture of what is going on.

Here is an example of one thing that can make alky look bad in these situations... lets say that the wet flow of the chamber already puts a good bit of fuel close to the plug when on gas. Now double the volume of liquid. This puts the spark plug at a much higher chance of getting wet and therefore misfiring. This is the type of stuff that becomes more and more important as people push the envelope on these big engines with these fancy heads

Scott

January 22, 2019, 05:19 PM

mavman

On SBF, once you get much over about 14:1, the tuning "window" gets smaller, but ET/MPH do not increase all that much. Haven't dealt with SBC much other than sprints which are usually 16:1 give or take. Also it seems with the SBF stuff I've used, consistency seems to improve with higher compression ratios.

January 22, 2019, 06:19 PM

Mike Frizie

Just a random thought/question. I noticed the SR20 head comes from brodix with a really tight chamber . Didnt know if that contributes to its running better on gas.

January 23, 2019, 08:33 AM

TOP38

quote:
Originally posted by 358T:
Chamber shape, squish, quench and other things that myself and most others don't understand enough to talk intelligently about is where its at no matter the size. Imo, big inch alky burning engines with fancy raised port shallow valve angle heads (or even fancy small block heads) can behave more like a high end nitrous engines when it comes to this area of the build. You really need to talk to a cylinder head guy and/or engine builder who understands this (which there doesn't seem to be many or at least many that care to know...) to get the full picture of what is going on.

Here is an example of one thing that can make alky look bad in these situations... lets say that the wet flow of the chamber already puts a good bit of fuel close to the plug when on gas. Now double the volume of liquid. This puts the spark plug at a much higher chance of getting wet and therefore misfiring. This is the type of stuff that becomes more and more important as people push the envelope on these big engines with these fancy heads

Scott

Scott,
your on the right track but one thing about fuel, if it goes in as a liquid it comes out as one. You can't burn a liquid, it has to be atomized. Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space. If I were ever to build an alky motor with an HP/CID over 1.8 it would with injection. I feel high pressure fuel injection has a much better chance delivering both the quantity and quality of air and fuel needed to have the engine run as it should.

January 23, 2019, 08:36 AM

TOP38

quote:
Originally posted by DRB Motorsports:
Just a random thought/question. I noticed the SR20 head comes from brodix with a really tight chamber . Didnt know if that contributes to its running better on gas.

The size of these chambers is directly related to the valve angle, lower ones equal smaller chambers. The power comes from the air flow capacity these heads provide.

January 23, 2019, 10:54 AM

Lenny5160

quote:
Originally posted by TOP38:
Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space.

I'm not sure how you can state that cubic inches aren't the issue. A 1000 hp 632 is going to use the same amount of fuel and air as as 1000 hp 555, and in the same size combustion chamber.

HP/CID can be constant and cubic inches are the variable, or cubic inches can be constant with HP/CID as the variable. Increasing either variable will lead to the same fuel/air issues when dealing with alky.

January 23, 2019, 11:53 AM

TOP38

quote:
Originally posted by Lenny5160:
quote:
Originally posted by TOP38:
Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space.

I'm not sure how you can state that cubic inches aren't the issue. A 1000 hp 632 is going to use the same amount of fuel and air as as 1000 hp 555, and in the same size combustion chamber.

HP/CID can be constant and cubic inches are the variable, or cubic inches can be constant with HP/CID as the variable. Increasing either variable will lead to the same fuel/air issues when dealing with alky.

This may help you understand better. If I assume Alky at 5 to 1 and gas at 12 to 1 AFR's and lets just say I need 50 portions of gas to make 1000 HP then I'd need 50(12/5)= 120 portions of alky to do the same along with the corresponding amount of air. Now increase the HP to 1500 HP, then I'd need 1.5 times those amounts since the power is coming from the fuel! But it all has to fit into the same space so there is more fuel and air being jammed into the motor (increased volumetric efficiency = higher HP/CID) to occupy the same space! Managing over twice the amount of fuel for alky over gas is the challenge that increases as you increase HP/CID. Large inch BBC's got tagged with this issue due to the popularity of this motor along with the development of spread port heads which increased the HP/CID due to their added air flow capabilities.
BTW James Monroe ran a 588 CID (if I remember correctly) with 12 degree heads and alky injection in TD a bunch of years ago with no issues just to prove a point and help his customers.

January 23, 2019, 12:17 PM

Lenny5160

quote:
Originally posted by TOP38:
quote:
Originally posted by Lenny5160:
quote:
Originally posted by TOP38:
Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space.

I'm not sure how you can state that cubic inches aren't the issue. A 1000 hp 632 is going to use the same amount of fuel and air as as 1000 hp 555, and in the same size combustion chamber.

HP/CID can be constant and cubic inches are the variable, or cubic inches can be constant with HP/CID as the variable. Increasing either variable will lead to the same fuel/air issues when dealing with alky.

This may help you understand better. If I assume Alky at 5 to 1 and gas at 12 to 1 AFR's and lets just say I need 50 portions of gas to make 1000 HP then I'd need 50(12/5)= 120 portions of alky to do the same along with the corresponding amount of air. Now increase the HP to 1500 HP, then I'd need 1.5 times those amounts since the power is coming from the fuel! But it all has to fit into the same space so there is more fuel and air being jammed into the motor (increased volumetric efficiency = higher HP/CID) to occupy the same space! Managing over twice the amount of fuel for alky over gas is the challenge that increases as you increase HP/CID. Large inch BBC's got tagged with this issue due to the popularity of this motor along with the development of spread port heads which increased the HP/CID due to their added air flow capabilities.
BTW James Monroe ran a 588 CID (if I remember correctly) with 12 degree heads and alky injection in TD a bunch of years ago with no issues just to prove a point and help his customers.

I completely understand that. What I am asking is, why is it different for these two scenarios?

1. The HP/CID goes up 50% with the same CID

2. The CID goes up 50% with the same HP/CID

In either case, the fuel/air demand goes up 50% within the same combustion space.

This is directed to your point that cubic inches aren't the issue, but rather the HP/CID is the issue. I'm saying that it is more or less the same issue. At a certain power level, whether you get there through efficiency or just raw cubic inches, it becomes difficult to move enough alky and air through the engine properly.

January 23, 2019, 12:21 PM

Lenny5160

I can see why it becomes a problem with a small engine and high HP/CID, because velocity is very important and the volume of alky required hurts the cause.

I just also see a point where it becomes an issue at large cubic inches, even without a high HP/CID.

January 23, 2019, 01:03 PM

358T

quote:
Originally posted by TOP38:
quote:
Originally posted by 358T:
Chamber shape, squish, quench and other things that myself and most others don't understand enough to talk intelligently about is where its at no matter the size. Imo, big inch alky burning engines with fancy raised port shallow valve angle heads (or even fancy small block heads) can behave more like a high end nitrous engines when it comes to this area of the build. You really need to talk to a cylinder head guy and/or engine builder who understands this (which there doesn't seem to be many or at least many that care to know...) to get the full picture of what is going on.

Here is an example of one thing that can make alky look bad in these situations... lets say that the wet flow of the chamber already puts a good bit of fuel close to the plug when on gas. Now double the volume of liquid. This puts the spark plug at a much higher chance of getting wet and therefore misfiring. This is the type of stuff that becomes more and more important as people push the envelope on these big engines with these fancy heads

Scott

Scott,
your on the right track but one thing about fuel, if it goes in as a liquid it comes out as one. You can't burn a liquid, it has to be atomized. Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space. If I were ever to build an alky motor with an HP/CID over 1.8 it would with injection. I feel high pressure fuel injection has a much better chance delivering both the quantity and quality of air and fuel needed to have the engine run as it should.

I know I'm on the right track.

Honestly, I know enough about it to be "very dangerous" but don't claim to know it all or have skills to make the changes needed. And I don't disagree with you on the fuel injection.

Yes James did a 12* profiler engine and it ran very well. Keep in mind though that SSRE and their engine builders had some influence in it also.

Scott

January 23, 2019, 01:25 PM

TOP38

quote:
Originally posted by 358T:
quote:
Originally posted by TOP38:
quote:
Originally posted by 358T:
Chamber shape, squish, quench and other things that myself and most others don't understand enough to talk intelligently about is where its at no matter the size. Imo, big inch alky burning engines with fancy raised port shallow valve angle heads (or even fancy small block heads) can behave more like a high end nitrous engines when it comes to this area of the build. You really need to talk to a cylinder head guy and/or engine builder who understands this (which there doesn't seem to be many or at least many that care to know...) to get the full picture of what is going on.

Here is an example of one thing that can make alky look bad in these situations... lets say that the wet flow of the chamber already puts a good bit of fuel close to the plug when on gas. Now double the volume of liquid. This puts the spark plug at a much higher chance of getting wet and therefore misfiring. This is the type of stuff that becomes more and more important as people push the envelope on these big engines with these fancy heads

Scott

Scott,
your on the right track but one thing about fuel, if it goes in as a liquid it comes out as one. You can't burn a liquid, it has to be atomized. Cubic inches is really not the issue, it's HP/CID and as that number goes up the more air and fuel occupy the same space and as you stated that more/twice the fuel for alky vs gas in that space. If I were ever to build an alky motor with an HP/CID over 1.8 it would with injection. I feel high pressure fuel injection has a much better chance delivering both the quantity and quality of air and fuel needed to have the engine run as it should.

I know I'm on the right track. Honestly, I know enough about it to be "very dangerous" but don't claim to know it all or have skills to make the changes needed. And I don't disagree with you on the fuel injection.

Yes James did a 12* profiler engine and it ran very well. Keep in mind though that SSRE and their engine builders had some influence in it also.

Scott

But James setup the injection system, which was not the norm that most use with regards to pressure on the Ron's systems! So it was a combo of both builder and injection specialist! LOL

And BTW, the motors are all smarter than the wizards out there, they do a very good job of hiding their secrets otherwise there would be no more performance improvements to be had by anyone!

January 23, 2019, 02:37 PM

Goob

Smokey said that you get very little HP advantage from Alky until you get over 15:1 static ratios, then it was good for up to a 5% HP increase, which doesn't sound like much until you figure a 900+ HP baseline....it's probably mostly from the cooler intake charge? Obviously a "low" compression engine is going to love Alky for low end torque, because you are putting in liquid compression.
Of course, that's too much generalization with the variety of small chamber flat top and big chamber dome combinations available today.

15:1 with domes, I run gasoline, for a variety of reasons. My car doesn't move ET any more than the alky burners at any particular event. I can see no reason for the expense and upkeep of an Alky system for what I do.

January 23, 2019, 03:25 PM

Dave Koehler

That was probably said in the 60s or 70s. Perhaps even earlier. Smokey is a messiah to many of us but he was wrong.
That reads like something I would hear from a gas carb guy that had never run alky.
Firesuit is on.

FWIW I think a maximum of 14:1 on alky works the best all around.
Above that the window gets real narrow with very little gain if any other than dyno bragging rights.
I assume most realize that those dyno numbers seldom happen outside of the cell.

Honestly, with the big cubes these days most make more HP by mistake than by design.
It would seem chasing diesel compression ratios makes little sense.

Which brings up a what if question.
Would someone "soften" the chambers versus a smaller dome and create a better alky happy scenario??

January 23, 2019, 10:28 PM

Strange Magic

quote:
what chamber volume is considered too small when running alky? bbc 582 with 15:1.

Some of the fastest stuff I've seen is up around 123 to 125 cc's.

quote:
Yes James did a 12* profiler engine and it ran very well. Keep in mind though that SSRE and their engine builders had some influence in it also.

Throw nitro into anything and it will run pretty darn good.

quote:
Smokey is a messiah to many of us but he was wrong.

Thank you. Glad someone said it.