Forced induction and carbs?

[love ke70]

he is correct, you can tune the carb to a certain rpm, and it will make more power
but give worse economy, and less all round performance and it will depend on temp. all of which is looked after by a lovely ecu and some efi

[ViPeR_NiPPleX]

logic tells me that the venturi effect which creates an intake restriction shouldnt make any more power than the air flowing equivelent efi variant.

do we have any proof to show this is true? im just cannot help being skeptical

[mrshin]

...of course it depends on your intake setup. If you replace a really crap intake manifold etc. with webers, you might gain a bit of power. But then if you turfed the webers and put throttles on in place of them, you'd hardly be losing out!

[Hurricane]

there is nothin wrong wit ha carby turbo sset up dude, take a look at my TA22. link below

[oldcorollas]

he is correct, you can tune the carb to a certain rpm, and it will make more power

please provide examples.

why does the carb make MORE power than EFI? (for the same setup, ie ITB)

[joecoolmk2]

it'd take a lot of testing to get a carb to outflow a simple efi setup. if you saved your time and money and put it into the efi setup it'd be a lot better than any carb could be.

[love ke70]

Warren Johnson: Properly tuned, carburetors make more peak power than EFI in a Pro Stock engine. A carb’s pressure differential atomizes the gas a lot better than spraying fuel through an orifice. But EFI has a broader powerband and superior cylinder-to-cylinder fuel distribution. The 1,100- to 1,300-cfm dual carbs are good only over a narrow range, about 1,500 rpm at most. EFI performs well over 2,000 rpm or more. On average, if optimized, both systems perform about the same as far as how fast you get down the track. However, the EFI system is much easier to tune than a carburetor.

Carburetion Vs. Injection

One of the most oft asked questions is why do carburetors make more power then EFI and why do the car manufacturers use EFI if carburetors make more power?

A few years ago we used some contacts at General Motors to verify some simple facts from some dyno data we had received from a head to head comparison.

An engine was being constructed for Comp Eliminator style racing and the program was going to be electronically fuel injected. Well the system was giving the engine shop some questionable numbers. The shop removed the EFI system and installed some of our Pro Stock carburetors on the EFI manifold top so they could quickly compare systems.

The engine responded immediately with much faster acceleration rates and a 5 percent improvement in power.

The EFI designer was brought out to the site and try as he might he could not out perform those carburetors. When the session wrapped up carburetors were king by 24 horsepower.

I've heard similar stories and similar claims when comparing systems.

So when we analyze this information it really comes down to a simple fact. Carburetors and Electronic Fuel injection are two completely different systems. They share no concepts and each has a different theory.

EFI's claim is this: I will supply sprayed droplets of fuel at the proper air to fuel ratio all the time.

Carburetors claim: I will supply a pre-emulsed froth of fuel and air into the engine at a preset ratio.

The results proved the analysis of the concepts to be correct. In this case, the carburetor was supplying the engine in question with the proper air to fuel ratio, so the EFI's advantage was gone. Remember, EFI has a computer to tune the engine. You have you. If you know how to tune you'll have the advantage. Carburetors (at the risk of sounding chauvinistic) are a man's game. Guessing rarely works. You have to know how to actually tune an engine.

Remember a carburetor is an atomization/emulsion machine. An injection system is a proper air to fuel delivery ratio machine. Two different concepts. If a carburetor can be designed to supply the perfect air to fuel ratio all the time it should consistently outperform EFI. Its design lends itself to have an unfair advantage in atomization.

Obviously adiabatic expansion is the next question on the list. So if we take a good look at the carburetor we see its not only a perfect machine for atomizing fuel, it also has another advantage. The joule-thompson effect.

Tests performed using quartz plates and infra red sensors located in the plenum area beneath an NHRA Pro-Stock engine revealed an intake manifold temperature drop on a 85 degree day of almost 20 degrees as a result of the the carburetor creating this effect.

So when your neighbor with EFI is ingesting 85 degree air, your power-plant could be ingesting 65 degree air.

That's a nice advantage.

But let's not skip over the atomization advantage. In a high end designed carburetor the fuel is emulsed to lift it. Its a controlled froth. I won't kid you, it's very difficult to control. Its much easier to build a carburetor that operates on a vacuum to ratio concept. But the fogging advantage is gone. So when a customer asks, why is this carburetor more expensive than that builders carburetor as they look basically the same. Most of it is all in the emulsion package and the time spent flowing it and tweaking it to do its job. Remember in a high emulsion design .001 of an inch is a big deal. They're difficult to balance and require sophisticated equipment that many shops have never seen. Also, don't go poking things into the metering block passages to inspect them or look around. You might just lose 10 lbs of torque.

The disadvantage of carburetors used to be restriction. I remember back 20 years ago before booster technology really took off you had to size carburetors to operate on 1-2 inches of vacuum in the plenum at the starting line. The restriction alone was probably costing these engines a 2-3 percent power loss.

Tests we performed at Sonny's racing 5 years ago showed us numbers of about .6 in the plenum and spikes of about 1.1 to 1.3 in the runner at the finish-line. That's a pretty huge decrease and just for dynos sake when we built carburetors large enough to reduce this number by on average 40 percent we saw an increase of only about 3-5 horsepower on an IHRA Pro-Stocker. SO that advantage for EFI is now also gone.

Now that these same engines can operate on as little as .5 hg of vacuum at the starting line and only 1-1.2 at the finish-line, the restriction is nil. Really it all comes down to getting the air to fuel ratio correct. If a carburetor can do that, it should win the race every time. After all, by design, it's a superior emulsion machine.

Thanks for reading.


http://www.pro-system.com/scoop92102.html

sorry its so long

[oldcorollas]

pro stock...

almost single rpm useage... drag race....
i was going to suggest you don't use bracket drag racing for an example since many classes PROHIBIT the use of EFI

superior cylinder to cylinder distribution with EFI

[love ke70]

like i said

you can tune the carb to a certain rpm, and it will make more power

never said theyre better, just said you can make more power when theyre tuned to a certain rpm...

[ViPeR_NiPPleX]

i think ill just go buy an electric turbocharger, they seem to have good sales pitches.

[crowncustom]

I can recall in very early edition of fast fours and rotaries(I'd say quite a few on here were probably still in nappies or a bun in the oven )there was a setup done with two stock 4age engines where they had one running factory efi and another one running twin 40mm webbers and the one on carbs out performed the efi and this was done on a bench dyno.So don't under estimate the old carbie.
Cheers Brett.

[oldcorollas]

I can recall in very early edition of fast fours and rotaries(I'd say quite a few on here were probably still in nappies or a bun in the oven )there was a setup done with two stock 4age engines where they had one running factory efi and another one running twin 40mm webbers and the one on carbs out performed the efi and this was done on a bench dyno.So don't under estimate the old carbie.
Cheers Brett.

hmmm..... lets see.. a single throttle crappy EFI manifold..... vs ITB's

put quad throttles with EFI on the 4A and THEN you have an even comparison..

how about we put a single downdraught carby on a 4AG and see how it compares to the stock EFI manifold? (no fair i hear you cry )

[oldcorollas]

like i said
never said theyre better, just said you can make more power when theyre tuned to a certain rpm...

i think it's possible to make similar power, since a carby or EFI system is just a fuel delivery method.
but to say that a carby can make MORE power than EFI is incorrect.

[river]

Hi,

i think it's possible to make similar power, since a carby or EFI system is just a fuel delivery method.
but to say that a carby can make MORE power than EFI is incorrect.

Logic units concur.

A properly tuned carburettor system will deliver the same power as EFI and vice-versa.

seeyuzz
river

[love ke70]

unless of course one unit can mix the air/fuel mixture better to create a better burn
carby people claim theyre emulsification method does this more effectively and thus, more power.

but i agree that the difference is likely very small, and efi is better/cheaper all round