Pro Stock What If - Carb/EFI

[andyf]

As for Pro Stock, the jelly bean guys killed it just like they killed NASCAR. I understand how it happens but when you make everything look the same nobody cares anymore. Pro Stock was cool back in the Pinto vs. Vega vs. Monza days. I understand how that cubic dollars and safety issues eventually led us down the path to everyone driving a jelly bean. Next someone will say that it is too dangerous for drivers and we should just race robot cars and then someone will say that cars are bad for the environment and we should just have simulated races on a laptop with the computer generating a random winner.

I think the answer is for people to just ignore Pro Stock if they don't like it. Eventually someone will invent a new class that is interesting and then it will be fun to watch for a few years before NHRA decides it needs to get the jelly bean treatment and then it will die too.

[hoffman900]

My opinion should be pretty clear by now, carb. And I'll give an example. A customer recently asked me to build a stretched carb for a high end build, the one that they had been running they were not happy with. This is a no expense spared BBF, 1500 HP range. They we unhappy enough with the original carb to put FI on it. It lost 50 HP.

An injection system is always metering the past, reading from sensors and then making changes.Even though it's slight it still makes a difference. It also delivers in pulses, so the air and fuel are not in an as homogenous mix. And last unless you are injecting above the butterflies you do not get the temperature drop from fuel vaporizing early in the intake tract.

Carburetors sense the airflow changes immediately. They meter fuel in a continuous stream to mix with incoming air. They atomize and vaporize fuel early in the intake to lower the charge temps. They are simple to work on, simple to fix and get parts for, and are cheaper.

Now if I thought that in any way there was an advantage to FI within a reasonable price range I would on it. I am an audio engineer for live TV sporting events, I have a background in basic electronics, I've done some 3D drawing for some of the carb components I use. I've built my own computer towers, install all my own software. I don't see an advantage for most N/A applications, and in some cases forced induction.

the key point here is "reasonable price range" most of the EFI system people retrofit to engines that were running a carb is using tech from the 70's and 80's but charge prices from today. for the price the carb cools the inlet air more than an average EFI setup and hence makes more WOT power but other than that and the cost/simplicity that's the only advantage and its not a carb vs efi thing its the lack of proper application or they arent using the full capability of the system.

if you were actually trying to develop a EFI setup there is no reason you cant address the inlet charge cooling and be better than a carb in every single way and more, and that's just on the fuel delivery side and ignores the other benefits of the black box.

if you build a bespoke manifold without the compromises inherent within a carb, multiple injector per cylinder, high fuel pressure, proper fuel phasing, individual cylinder trims and more and still cant make more power WOT than a carb you probably need to find something else to do. Even for a relatively simple setup outline above The technology has been around for almost 20 years but from a cost point of view its much big investment compared to a carb.

if you throw a single injector per port or throttle body injector on carb manifold running at a few bar pressure that runs at high DC you aren't close to optimised its amazing they get within a few %

I also respectfully take exception to Mark’s assertion that the carburetor sees the cylinder instantaneously. Looking at pressure graphs, it’s clear there is a delay before the carb would ever see the signal (and in the delay to get the low pressure fuel moving through the carburetor), add in a wet plenum and that lag is even further. The carb is always acting to what came before. Furthermore, the carb, due to its function, only works one way. This ultimately restricts what you can do downstream due to reverse flow through the carburetor.

Honda’s 2010 F1 engine development got into using wave speed (function of density) to look at fuel atomization and to tweak it until they had the densest column. Carburetors do not have that level of control. Heck, watching the Kaase video of the clear manifold, it’s incredible how much liquid fuel is just hanging around inside the manifold on a carbureted engine.

I think an O2 sensor in a very fast moving exhaust, and with processor speeds what they are and the fuel pressures being used, EFI is reacting much faster than a carburetor.

[digger]

My opinion should be pretty clear by now, carb. And I'll give an example. A customer recently asked me to build a stretched carb for a high end build, the one that they had been running they were not happy with. This is a no expense spared BBF, 1500 HP range. They we unhappy enough with the original carb to put FI on it. It lost 50 HP.

An injection system is always metering the past, reading from sensors and then making changes.Even though it's slight it still makes a difference. It also delivers in pulses, so the air and fuel are not in an as homogenous mix. And last unless you are injecting above the butterflies you do not get the temperature drop from fuel vaporizing early in the intake tract.

Carburetors sense the airflow changes immediately. They meter fuel in a continuous stream to mix with incoming air. They atomize and vaporize fuel early in the intake to lower the charge temps. They are simple to work on, simple to fix and get parts for, and are cheaper.

Now if I thought that in any way there was an advantage to FI within a reasonable price range I would on it. I am an audio engineer for live TV sporting events, I have a background in basic electronics, I've done some 3D drawing for some of the carb components I use. I've built my own computer towers, install all my own software. I don't see an advantage for most N/A applications, and in some cases forced induction.

the key point here is "reasonable price range" most of the EFI system people retrofit to engines that were running a carb is using tech from the 70's and 80's but charge prices from today. for the price the carb cools the inlet air more than an average EFI setup and hence makes more WOT power but other than that and the cost/simplicity that's the only advantage and its not a carb vs efi thing its the lack of proper application or they arent using the full capability of the system.

if you were actually trying to develop a EFI setup there is no reason you cant address the inlet charge cooling and be better than a carb in every single way and more, and that's just on the fuel delivery side and ignores the other benefits of the black box.

if you build a bespoke manifold without the compromises inherent within a carb, multiple injector per cylinder, high fuel pressure, proper fuel phasing, individual cylinder trims and more and still cant make more power WOT than a carb you probably need to find something else to do. Even for a relatively simple setup outline above The technology has been around for almost 20 years but from a cost point of view its much big investment compared to a carb.

if you throw a single injector per port or throttle body injector on carb manifold running at a few bar pressure that runs at high DC you aren't close to optimised its amazing they get within a few %

I also respectfully take exception to Mark’s assertion that the carburetor sees the cylinder instantaneously. Looking at pressure graphs, it’s clear there is a delay before the carb would ever see the signal (and in the delay to get the low pressure fuel moving through the carburetor), add in a wet plenum and that lag is even further. The carb is always acting to what came before. Furthermore, the carb, due to its function, only works one way. This ultimately restricts what you can do downstream due to reverse flow through the carburetor.

Honda’s 2010 F1 engine development got into using wave speed (function of density) to look at fuel atomization and to tweak it until they had the densest column. Carburetors do not have that level of control. Heck, watching the Kaase video of the clear manifold, it’s incredible how much liquid fuel is just hanging around inside the manifold on a carbureted engine.

I think an O2 sensor in a very fast moving exhaust, and with processor speeds what they are and the fuel pressures being used, EFI is reacting much faster than a carburetor.

you dont even need to use an O2 for feedback if eveything is tuned properly and compensations done correctly. many systems are run succesfully on open loop

[jmarkaudio]

While it is not sensing the individual runner demand, it is sensing the overall volume of air that flows thru the carb and meters fuel to suit as it changes immediately. I am an audio engineer for live TV Sports remotes, and I see the delays that can happen when processing thru digital circuitry in equipment that ranges from $100K to nearly a million. Sure F1 runs well, you wouldn't want to or could afford to buy the injection system they run, and then spend the money and time they do to tune them. Most here wouldn't have that much in their whole engine. And sure for a street driven car with a reasonably decent FI system it can eliminate a lot of things that are a little bit of work to do with a carb, although the right carb and engine combo can run really well.

[Mike Laws]

the key point here is "reasonable price range" most of the EFI system people retrofit to engines that were running a carb is using tech from the 70's and 80's but charge prices from today. for the price the carb cools the inlet air more than an average EFI setup and hence makes more WOT power but other than that and the cost/simplicity that's the only advantage and its not a carb vs efi thing its the lack of proper application or they arent using the full capability of the system.

if you were actually trying to develop a EFI setup there is no reason you cant address the inlet charge cooling and be better than a carb in every single way and more, and that's just on the fuel delivery side and ignores the other benefits of the black box.

if you build a bespoke manifold without the compromises inherent within a carb, multiple injector per cylinder, high fuel pressure, proper fuel phasing, individual cylinder trims and more and still cant make more power WOT than a carb you probably need to find something else to do. Even for a relatively simple setup outline above The technology has been around for almost 20 years but from a cost point of view its much big investment compared to a carb.

if you throw a single injector per port or throttle body injector on carb manifold running at a few bar pressure that runs at high DC you aren't close to optimised its amazing they get within a few %

fwiw: While at my former company, we hosted a couple of 'carb shootouts' that were fairly successful and watched by many. The carb vs efi debate was as popular then as now, so I proposed a shootout and invited leading companies from both venues. Like the carb shootouts, there would be 2 engines, provided by different builders with open rules regarding the induction systems. (any intake manifold, throttle body(s), carbs, pumps, etc.) The (open) structure was included with the invitations along with an agreement to disclose the price of the system provided by each company. At least 4 prominent carburetor builders committed immediately. Not one efi company committed or even responded. This was 5-6 years ago.

[jmarkaudio]

I'm still game...