Top alcohol and Indy motors both have boost and both are smaller CI. Even the TA/FC guys are dropping cubes below 500 because of OD rules and smaller motor allow more rpm which just so happen to spin blower faster for more boost. So neither can really be used as comparison for OP.

Wonder if anyone has increased induction track when switching. Running heads that are bigger with bigger intake to allow for more air /fuel volume of alky motor? Again is carb really big enough to meet requirement.Like putting 600cfm holley on your 632" race motor. Most have stated injection is quicker in large majority of cases.

a large engine (600 cubic inches or bigger) with a compression ratio above 15:1 will make more horsepower and run faster on gas than alcohol. The break even point is on an engine around 582 inches that gas and alcohol run very close to the same, below 582 cubic inches an engine will run faster on alcohol

quote:

Originally posted by Lenny5160:

quote:

Originally posted by TOP38:
If this were true blown alky motors would be making even less!

With higher HP/CID numbers, usually over 1.8, alky needs some attention in order t make the kind of power it is capable of making.

Attention such as a blower?

No.

quote:

Originally posted by racerdude2054:
a large engine (600 cubic inches or bigger) with a compression ratio above 15:1 will make more horsepower and run faster on gas than alcohol. The break even point is on an engine around 582 inches that gas and alcohol run very close to the same, below 582 cubic inches an engine will run faster on alcohol

Don't agree with this either.

the more efficient the engine is the less difference you will see on switching from gas to alcohol. On real efficient engines you will actually lose power. On the larger displacement motors on alcohol the fuel saturation in the port the fuel starts separating out of the air stream. the air stream cannot support it (keep it atomized). Can't fight the laws of physics.

quote:

Originally posted by TOP38:

quote:

Originally posted by racerdude2054:
a large engine (600 cubic inches or bigger) with a compression ratio above 15:1 will make more horsepower and run faster on gas than alcohol. The break even point is on an engine around 582 inches that gas and alcohol run very close to the same, below 582 cubic inches an engine will run faster on alcohol

Don't agree with this either.

neither do I

Alky used to give a lot better performance but with the advent of a lot better flowing cylinder heads the gap has narrowed significantly. The small chamber heads (IE most big chief and even the 20 degree stuff) take a different cam for gas vs alky. John Kyle did a lot of work on that with the 18 dgree stuff. Carb builders are having to relearn a lot with the fuel delivery for these higher flowing heads and the demands of those motors. I do know that it seems when you get into the 600+ naturally aspirated motors your carb needs to really be totally custom built for the fuel curve due to the amount of fuel that is needed.
On the cam shaft side there is a huge need to have an alky specific cam as gas cams really want to get the heat out of the chamber where alky prefers to have some there. This is not an issue with the blown applications as the blowers are creating that heat and the alky is cooling the charge but there is still a massively high level of heat coming in; so comparing a blown application to a NA application is an apples to potato comparison.

All the above being said alky is a lot more consistant. If I look at my combination I can run low 4.70's at 500 ft and high 4.70's at 5500 feet. my combination is deadly any where I go. I rarely change the dial on my car once I make a pass down the track as my car repeats like time slips. I see most on gas loose an easy tenth and a half or more going from 500 to 5500ft in DA. i see gas guys who dial honest change 4-5 numbers in a race and their cars move that much, and these are guys that win championships and big money bracket races so they don't have junk.

X2
Thanks Boz!
Very well said!!
IHRA ACDELCO Canadian Nationals
Top/et Iron man Champion
Don Davis 57 Corvette Super Gas roadster
SDPC 582 Head hunter on Alky

Ron C
I pretty much agree what you have stated about HP on gas vs alky with regards to how efficient the gas combo vs how much you may pick up switching to alky. But that's not he subject here.

Boz
Number of good points also but again we aren't talking consistency here.

Not that this example is an exact match it is close, had a HH 565, ran a terminator on it, everyone said switch it to a gas carb and you will pick up,,, tried a good loaner gas carb one weekend, lost a tenth over the alky injection.

The bottom line here is that an alky feed larger cid motor built to make over 1.8 HP per CID needs to be built differently that a gas combo. The heads and chambers need/want different things. Also, I have not seen an alky carb or carbs that can do the job that alky injection, especially a high pressure setup, can do which regards to addressing both quantity and quality of the fuel delivery required for alky to develop the intended HP levels.

I will also add this, even if the alky motor makes the same HP as the gas motor, the alky combo will be quicker down track do to the added torque provide, ie more area under the HP/Torque curve for a give rpm range!

quote:

Originally posted by TOP38:


The bottom line here is that an alky feed larger cid motor built to make over 1.8 HP per CID needs to be built differently that a gas combo. The heads and chambers need/want different things. Also, I have not seen an alky carb or carbs that can do the job that alky injection, especially a high pressure setup, can do which regards to addressing both quantity and quality of the fuel delivery required for alky to develop the intended HP levels.

I will also add this, even if the alky motor makes the same HP as the gas motor, the alky combo will be quicker down track do to the added torque provide, ie more area under the HP/Torque curve for a give rpm range!

I agree the motor needs to be different to optimize alcohol and I agree that even at similar hp the alcohol motor is usually faster.

What I am not sure of is original poster was asking why big motors make more power on gas and we have some ideas but I do not think anyone has definitively answered that question. I even think if we know for sure why it is then we could tune so every motor would out perform gas motors.

quote:

Originally posted by TOP38:
Ron C
I pretty much agree what you have stated about HP on gas vs alky with regards to how efficient the gas combo vs how much you may pick up switching to alky. But that's not he subject here.

!

It's directly related to the question. The larger the engine the less efficient it is.

gas,alky heck just throw gallon of nitro in the jug and let eat.It eat anything you throw at it especially hip pocket.LOL

quote:

Originally posted by Curly1:

quote:

Originally posted by TOP38:


The bottom line here is that an alky feed larger cid motor built to make over 1.8 HP per CID needs to be built differently that a gas combo. The heads and chambers need/want different things. Also, I have not seen an alky carb or carbs that can do the job that alky injection, especially a high pressure setup, can do which regards to addressing both quantity and quality of the fuel delivery required for alky to develop the intended HP levels.

I will also add this, even if the alky motor makes the same HP as the gas motor, the alky combo will be quicker down track do to the added torque provide, ie more area under the HP/Torque curve for a give rpm range!

I agree the motor needs to be different to optimize alcohol and I agree that even at similar hp the alcohol motor is usually faster.

What I am not sure of is original poster was asking why big motors make more power on gas and we have some ideas but I do not think anyone has definitively answered that question. I even think if we know for sure why it is then we could tune so every motor would out perform gas motors.

Because they aren't built correctly and usually using a carb which can not supply both the quantity and quality of fuel needed but they can for gas

quote:

Originally posted by Ron C.:
the more efficient the engine is the less difference you will see on switching from gas to alcohol. On real efficient engines you will actually lose power. On the larger displacement motors on alcohol the fuel saturation in the port the fuel starts separating out of the air stream. the air stream cannot support it (keep it atomized). Can't fight the laws of physics.

Digest this and you will have your answer, especially the last sentence.

quote:

Originally posted by Ron C.:

quote:

Originally posted by Ron C.:
the more efficient the engine is the less difference you will see on switching from gas to alcohol. On real efficient engines you will actually lose power. On the larger displacement motors on alcohol the fuel saturation in the port the fuel starts separating out of the air stream. the air stream cannot support it (keep it atomized). Can't fight the laws of physics.

Digest this and you will have your answer, especially the last sentence.

Ron

In any given motor, you need x fuel ad y air so that ratio is a fixed given. So other than some of the factors I stated, why are you saying the alky comes out on larger motors and not on smaller ones when the AF is the same? Just wondering about your logic here? Ya, more hp means more fuel but more air also.... In either case if designed correctly, you'd have the same amount of fuel and air in a given port per unit of volume.

amazing that drag race engines are still built like they were in 1960, albeit better hardware everywhere, but the basics haven't changed.
Something as simple as a properly designed squish area as opposed to a 100yr old flat cyl head deck surface outside the chamber is one of the keys that is still missing most of the time.
The silly "chamber softening" that NOS builders refer to has been a part of 2-stroke tech since the 1960's.
Has a huge impact on detonation and speed of flame travel, much of the reason alcohol in engines as described "don't work", they aren't built correctly for a different fuel.

BTW a number of years back before James Monroe did up the blower motors with the Ron's deal he did a 12 BC motor using a Ron's setup but with a twist from the normal tune up, ie fuel pressure and this motor did not suffer from the usual BC cylinder head issues and develop the design power it should have and used less fuel than other combo's making less HP,,, may want to talk to James if you really want to build a larger higher HP motor on alky for more details. But one of the important keys here was both the quantity and the quality of the alky fuel being delivered by the injection system.

quote:

Originally posted by TOP38:
Carb's have come a long way and I would say they can supply enough fuel, even if two are needed but they still don't seam to deliver the quality of fuel needed due to the amount the motor requires to develop the high HP numbers.

If the A/F mixture flowing through an intake manifold is always the same, why would there be a quality issue with carbureted alky only on high HP motors?

quote:

Originally posted by Lenny5160:

quote:

Originally posted by TOP38:
Carb's have come a long way and I would say they can supply enough fuel, even if two are needed but they still don't seam to deliver the quality of fuel needed due to the amount the motor requires to develop the high HP numbers.

If the A/F mixture flowing through an intake manifold is always the same, why would there be a quality issue with carbureted alky only on high HP motors?

Carb can't atomize the fuel required to deliver anywhere near injection can. Why do you think my 565 lost a tenth on a gas carb over alky injection? This was not a 600 or larger CID motor, it made about 1040 with the injection setup.

quote:

Originally posted by TOP38:
Why do you think my 565 lost a tenth on a gas carb over alky injection?

Because alky is a more powerful fuel. It runs cooler and carries its own oxygen.

That's not uncommon at all.

I know you're a sharp guy, Al. I just can't understand why you're telling Ron C that he's wrong, when you're basically saying the same things.