Carb to EFI hp gain?

[hifi875]

carb should make more power, especially on the top end. What I hear is that a carb atomizes fuel better than efi. efi should have more bottom end and be more responsive, but other than that shouldn't make more than a carb

[supremeefi]

As mentioned a carb should actually make a few more hp at peak than an EFI. But the trip there will normally be better with a well setup EFI system.

[PTAddict]

Originally Posted by hifi875

... What I hear is that a carb atomizes fuel better than efi ...

Not quite true. EFI injects fuel at a much higher pressure differential than a carb, and thus achieves much finer atomization. What is true, though, is that the longer path from fuel introduction to intake valve on a carb setup provides slightly greater time for evaporative cooling, and thus possibly slightly higher charge density. But the overall point remains - with identically configured intake systems, carb and EFI will produce almost identical peak power within the margin of error.

Of course, one of the great advantages of EFI is that port injection allows much more flexibility in intake configuration, which can and does yield benefits in mid range performance in particular.

[chr2002ca]

Depends on the manifold. If you're just swapping out the carb for one of those EFI throttle bodies that has the injectors in it, you won't see too much difference other than cold starts, MPG improvement, and easier tuning. Switch to an MPFI setup with separate injectors for each intake runner in the manifold and you're going to see further improvement in throttle response also and MPG. It's not until you change the manifold to a tunnel style unit with the throttle body mounted on the front(like an Edekbrock Pro-Flo XT) will you see any noticeable increase in horsepower. So I agree with others. A straight carb-to-EFI swap using the same manifold will not make much difference in horsepower, with the slight edge on peak HP going to the carb. Several magazines have proved that already also. I just recently spent some $K's to swap from carb to an MPFI setup and I could care less about extra HP because this EFI stuff is the bomb. Well worth it once you get all the sh_t plumbed and wired.

[supremeefi]

Originally Posted by chr2002ca

Depends on the manifold. If you're just swapping out the carb for one of those EFI throttle bodies that has the injectors in it, you won't see too much difference other than cold starts, MPG improvement, and easier tuning. Switch to an MPFI setup with separate injectors for each intake runner in the manifold and you're going to see further improvement in throttle response also and MPG. It's not until you change the manifold to a tunnel style unit with the throttle body mounted on the front(like an Edekbrock Pro-Flo XT) will you see any noticeable increase in horsepower. So I agree with others. A straight carb-to-EFI swap using the same manifold will not make much difference in horsepower, with the slight edge on peak HP going to the carb. Several magazines have proved that already also. I just recently spent some $K's to swap from carb to an MPFI setup and I could care less about extra HP because this EFI stuff is the bomb. Well worth it once you get all the sh_t plumbed and wired.

Otherwise your info is correct but that statement isn't.
Pro Flo XT's etc aren't for every application. If the rest of your combo isn't well mated to the power band that intake will provide you may actually lose hp/tq.
I've seen measurable gains on mild builds by doing multiport EFI on dual planes, have one on my car. I started out with an EFI'd single plane intake, went to a dual plane modified for EFI and the difference was night and day, from idle to wot. The added runner length and/or smaller plenum area proved beneficial, the exact opposite of the Pro Flo/Mini Ram type stuff.

[GregWeld]

I don't think people are doing EFI for hp/tq gains --- I think people are choosing it for drivability.

[mnm99]

I'm doing EFI soon too. Just better all around. Temp changes, Cold starts, Off throttle response, gas mileage ect...

[chr2002ca]

Originally Posted by supremeefi

Otherwise your info is correct but that statement isn't.
Pro Flo XT's etc aren't for every application. If the rest of your combo isn't well mated to the power band that intake will provide you may actually lose hp/tq.
I've seen measurable gains on mild builds by doing multiport EFI on dual planes, have one on my car. I started out with an EFI'd single plane intake, went to a dual plane modified for EFI and the difference was night and day, from idle to wot. The added runner length and/or smaller plenum area proved beneficial, the exact opposite of the Pro Flo/Mini Ram type stuff.

Opinions and results vary. All depends on your setup, as you mentioned. I should've mentioned that.

[Revved]

WOT total HP on an identical engine with a perfectly tuned carb will be essentially the same as it would be on EFI. You have to remember that tuning for WOT or your "BIG NUMBER" is the easiest thing to tune for. How many cars have you seen that run great at WOT but are horrible to drive around town? Greg mentioned half the story- that EFI is going to give you better all around drivability but taking that point further is that EFI is going to give you better fuel control throughout the range most likely broadening your USABLE horsepower and torque. By properly controlling fuel flow throughout the entire range you are also gaining fuel economy, managing proper engine temperature,cutting down on unnecessary engine wear due to over or under fueling, and saving you money.

Stating it simply carburation has three main modes. Idle, part throttle, wide open. Everything in between is a fudge of those three. When we tune carbureted vehicles we use a FAST dual wide band 02 meter and can dial them in pretty damn well and get huge drivability gains over a vehicle "tuned by ear." Typically it takes us about 8 hours on a blown big block carb application of driving, tear down, drilling, jetting, driving, tear down, adjusting timing curves, etc.. again and again until what we are seeing coming out of the engine is "dialed in." When done.. the drivability is huge, torque curve is huge... I'm convinced that if you have to run a carb using a dual 02 meter is the best way to accurately tune it. (yes- EGTs as well but how many street cars are driving around with a bung in each of their primaries!)

I can do the same thing with a sequential EFI blown big block in about 2-4 hours tapping away on a laptop. Is there more time getting to that point...yes. I'm OCD... I tailor my wiring harnesses to fit the vehicle... even if they come prefab..I cut them apart and tailor them. Typically I put about 25 hours into wiring an EFI system...I build electronics panels to mount all of the fuses and relays, I put connectors anywhere the harness touches another harness. But when I'm done it looks like it was born there.

I would disagree on carb atomizing fuel better... With a port injection setup you have 8 high pressure pin point applications of fuel instead of 4 big holes sucking low pressure fuel through four straws. EFI gives accuracy and efficiency again and is less succeptable to ambient temp changes (ie. fuel dribbling down the intake walls from your carb)

my .02

[Ron Sutton]

Originally Posted by Revved

WOT total HP on an identical engine with a perfectly tuned carb will be essentially the same as it would be on EFI. You have to remember that tuning for WOT or your "BIG NUMBER" is the easiest thing to tune for. How many cars have you seen that run great at WOT but are horrible to drive around town? Greg mentioned half the story- that EFI is going to give you better all around drivability but taking that point further is that EFI is going to give you better fuel control throughout the range most likely broadening your USABLE horsepower and torque. By properly controlling fuel flow throughout the entire range you are also gaining fuel economy, managing proper engine temperature,cutting down on unnecessary engine wear due to over or under fueling, and saving you money.

Stating it simply carburation has three main modes. Idle, part throttle, wide open. Everything in between is a fudge of those three. When we tune carbureted vehicles we use a FAST dual wide band 02 meter and can dial them in pretty damn well and get huge drivability gains over a vehicle "tuned by ear." Typically it takes us about 8 hours on a blown big block carb application of driving, tear down, drilling, jetting, driving, tear down, adjusting timing curves, etc.. again and again until what we are seeing coming out of the engine is "dialed in." When done.. the drivability is huge, torque curve is huge... I'm convinced that if you have to run a carb using a dual 02 meter is the best way to accurately tune it. (yes- EGTs as well but how many street cars are driving around with a bung in each of their primaries!)

I can do the same thing with a sequential EFI blown big block in about 2-4 hours tapping away on a laptop. Is there more time getting to that point...yes. I'm OCD... I tailor my wiring harnesses to fit the vehicle... even if they come prefab..I cut them apart and tailor them. Typically I put about 25 hours into wiring an EFI system...I build electronics panels to mount all of the fuses and relays, I put connectors anywhere the harness touches another harness. But when I'm done it looks like it was born there.

I would disagree on carb atomizing fuel better... With a port injection setup you have 8 high pressure pin point applications of fuel instead of 4 big holes sucking low pressure fuel through four straws. EFI gives accuracy and efficiency again and is less succeptable to ambient temp changes (ie. fuel dribbling down the intake walls from your carb)

my .02

Agreed x2