Which is faster carb or Fuel injection?

[Adger Smith]

Joe,
The V-6 engines you and I run might be the type engine that really benefits from EFI. As you know they are subject to some real weird pulses in the manifold. As you stated fuel in the intake a real problem. EFI could be a help. I have played with 5 different intake configurations to get the best. The best still has some crutches in to help the carb with mixture distribution. I think EFI would help because of the dry flow.

[jmarkaudio]

Originally Posted by Lee Valentine

1985 Camero came with both carb-263 hp or tuned port F.I.-258 hp. These are the NHRA factored ratings. Engine specs are the same excecpt for the induction.

What carb? Airflow makes a difference.

[pbp1]

After stumbling upon this thread, I couldn't help but to jump in. Even though I work in the EFI industry, I do not consider myself a guru, but rather a student of the game. Here are some observations I have made and theories I believe.
1. As originally stated, EFI offers much better control of fueling, individual cyll tuning, etc which should equal a "fuller" torque curve. That being said, it is rare to find a racer who is willing to invest the time and money required to get the last few potential horsepower out of their combo.
2. I believe that we are just at the beginning of manifold / head / header design dedicated to EFI engine packages. These three areas have been science'd out over the last 50 - 60 years for carbs, EFI technology in these areas has a lot of catching up to do!
3. There is a balance between atomization, airflow, and mass of the mixture that is required for not only optimum power, but accelleration. We have all seen or heard of Dyno heroes that made killer numbers but when put in the car, wouldn't accelerate. I have been told that a dry throttle body and intake runner can flow more air because there is no fuel occupying that space but the other side of that coin is that a mixture of air and fuel has more mass and velocity to help it enter the port. I am sure there are engineers smarter than me who can explain this better than me but what I have seen tells me that both are important. Injector type and placement is critical. I have seen some very "out of the box" ideas that looked ridiculous produce very good results, particularly in some Engine Masters projects I have had the privilege of being involved with.
4. As far as the throttle bodies being a limiting factor, I can affirm what Dave Layer has shared with Ed. My preference is to tune in Load Indexed Speed Density mode. In that mode, the values you put into your main fuel table are estimated Volumetric Efficiency numbers. You know that these are correct when the engine runs at your target air fuel ratio with minimal correction. When you get to this point with your tuneup, you have effectively built an accurate airflow model of your engine with the Base Fuel or VE table. My point in bring this up is that in an LT1 based SS engine, the VE numbers will dive at about 7800 and sometimes, the MAP sensor will even show slight vacuum in the manifold even at WOT. The throttle body is definitely a restriction.
The reason I love what I do is that there is still so much to learn and develop in the world of EFI.
To answer the original question, I believe most of the fastest Stock and SS combinations are EFI but more importantly, going forward, I believe there is more potential to find an advantage with hard work and ingenuity in an EFI application than there is with a carb application.
David Page
Fuel Air Spark Technology (FAST)

[Signman]

Dave, It's great you jumping in here!

Agree the potential is there for EFI to out perform a carb BUT:

When we are talking about Stock we have what we have to work with. Super Stock is a different case with the only limitations nefore the intake port being the throttle body. If the stock throttle body originally rated at 600 CFM may fow up to 750 CFM, a carb originally rated at 750 CFM will outflow the throttle body.

Using sequential fueling and individual cylinder timing potentially can deliver flatter HP and TQ curves along with faster ETs. Reservations are with speed. The volume of commands the ECU must make at high RPMs processor speed along with sensor and injector speed / accuracy are limiting factors. Had a short conversation with a racer working with this and his comment was the injectors go static. Next step would be larger and/or faster injectors with more fuel pressure, probably double what we are using.

[pbp1]

Sorry, you are correct, my comments were focused on SS. As far as the speed at which commands are given from the ECU. I can only speak with authority about the system we make but we use dual 25mhz processors in our ECU so that gives us a potential of 50,000 commands per second. I seriously doubt any engine has a need for more than 50,000 different commands before you get past the 60' mark. LOL. Most modern ECUs have at least this much capacity. As for the injectors going static, that is a simple matter of running out of injector capacity. If your engine needs 288 pounds of fuel per hour and you are running eight 36 pound per hour injectors, the ECU cannot get any more fuel out of the injectors. Most injectors are not linear in their fuel delivery above 80% duty cycle. The ECU controls the injectors as to deliver the requested amount of fuel based on the injector flow rate you have defined in your tuneup. The ECU cannot know or account for inconsistencies in the injector flow characteristics (as you have above 80% duty cycle) so when you injectors are above 80%, the engine is not actually getting the fuel that you (or your ECU) thinks it is. He can turn the fuel pressure up effectively making his injectors "bigger" but there are limitations to that as well.

[art leong]

It's not about stock. But I remember the old Rat Roaster manifolds for the hemis. The instructions from Chrysler to epoxy popsicle sticks in the manifold to stop fuel puddling.
Fuel injection solves problems like those. I had never had an ecu that was tuneable till my Neon. So it took a while till I could tune it myself (due to fear of new things)
I have just scratched the surface as far as tuning goes. When I get the car out again I'm going to switch from a MAP/RPM axis to a Throttle position/ RPM axis. To keep the plugs cleaner driving around the pits. I also will go in and smooth the boxes (go from 500 rpm increments to 100 rpm increments).
Any changes I make are done at the track, and I can go back to exactly what I was running before I made the change.

[HTMtrSprt]

Originally Posted by art leong

It's not about stock. But I remember the old Rat Roaster manifolds for the hemis. The instructions from Chrysler to epoxy popsicle sticks in the manifold to stop fuel puddling.
Fuel injection solves problems like those.

Actually, big cam and cylinder head racing engines still have this problem, even with efi. ECR engines (sprint cup) went through a ton on development work when NASCAR switched to EFI - they lost a little power at first but with more work to cam/head/intake they eventually recovered the power. Of note though, they tested with a manifold incorporating a window in an intake runner and were amazed to see the fuel from the injector flowing BACKWARDS up the runner toward the plenum at certain speeds. The observation was backed up by readings from individual cylinder O2 sensors showing large amounts of fuel swapping from runner to runner necessitating a large amount of individual cylinder fuel corrections to make them run properly.

As for low speed tuning, I've tuned numerous racing engines with low vacuum and they CAN be tuned to run just fine (not loading up) in speed/density mode.