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Old 09-24-2011, 01:48 AM   #1
Brad54
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Default Injection versus carbs: how much more HP?

All else being equal, how much more power will mechanical injection, like a Hilborn unit, make on an engine over carbs?

I realize there are variables here, so I'm just looking for generalities.

Talking about it with a buddy of mine, and he said when the big Porsche race engines in the '70s went from Webers to mechanical injection, they only picked up 10hp, so he's applying that to everything.
I don't believe drag racers in the '60s and '70s would have spent that much on mechanical fuel injection for a measly 10hp.

Incidentally, I'm thinking about it for a Corvair engine (164ci). Factory rating with carbs was 140hp, but throw that number out... I'd be adding a bunch of compression, a bunch of cam, roller rockers, etc.

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Old 09-24-2011, 02:04 AM   #2
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Default Re: Injection versus carbs: how much more HP?

On what fuel?

From what i understand, all things being equal (manifold style, etc) carbs make more HP over even electronic fuel injection, -if it's tuned to the gnat's ass. The air bleeds do a VERY good job of emulsifying air into the gas before it even enters the venturi.

The charge cooling seen from a wet manifold is an extra bonus that efi doesn't enjoy.

For mech injection on alcohol, i'd think that it made more power than carbs simply because it would be harder for the carb to pull enough booze to satisfy the richer air/fuel mixture needed.

As for mfi on gas, maybe it's the nozzles being highly effective at atomizing the gas?

That's what i've picked up and welcome anyone with more info/practical experience to learn me up some. - been wrong before, i'll be wrong again.

-rick
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Old 09-24-2011, 03:34 AM   #3
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Default Re: Injection versus carbs: how much more HP?

Speaking from my own experiancwith a set of Enderle SBC port injectors VS early factory 2x4 set ups for drag racing, id go with the Endele any day , just for the simplicity . We ran gas, but most the Jr. fuelers of the time ran Enderle's also. I'm sure many also had good luck with Hilborns. It's an apple/orange thing. I am an old fart and really hated electronics when they first came on the scene, old dogs can learn new tricks. What is apparent is the longevity and dependability of newer engines. One thing is the lack of raw fuel on cold starts that washed the walls causing scuffing and resultant wear. It is an interesting thread !
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Old 09-24-2011, 05:43 AM   #4
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Default Re: Injection versus carbs: how much more HP?

I have run both and your question does not have an easy answer. Engines are like people and each wants just a little bit something different. To optimize the best torque or power from a certain "combination" means matching the fuel and spark curve to exactly what the air draw through the engine will be. That being said, some engine packages/combinations may or may not like the air flow from the intake manifold whether it is a carb or stack set up. The engine doesn't care how the fuel gets there as long as it is the right amount at the right time. I am speaking normally aspirated obviously. Boosted is another story. Does that make sense?

Some guys may switch from carb to injection and pick up while other may slow down and vice versa. It all depends on your engine.

I am sure you will get a ton of opinion on your question but if you really step back and look at it and based off my personal experience, this is the story. If someone sees a huge gain one way or the other when swapping, I would say they were way off on the combo with one of them.

Low speed throttle response is usually better with a correctly set up mechanical injection system but peak torque and power should be about the same "all things being equal". However, that is really tough to do.
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Old 09-24-2011, 05:45 AM   #5
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Default Re: Injection versus carbs: how much more HP?

Quote:
Originally Posted by 69fury View Post
On what fuel?

From what i understand, all things being equal (manifold style, etc) carbs make more HP over even electronic fuel injection, -if it's tuned to the gnat's ass. The air bleeds do a VERY good job of emulsifying air into the gas before it even enters the venturi.

The charge cooling seen from a wet manifold is an extra bonus that efi doesn't enjoy.

For mech injection on alcohol, i'd think that it made more power than carbs simply because it would be harder for the carb to pull enough booze to satisfy the richer air/fuel mixture needed.

As for mfi on gas, maybe it's the nozzles being highly effective at atomizing the gas?

That's what i've picked up and welcome anyone with more info/practical experience to learn me up some. - been wrong before, i'll be wrong again.

-rick
I would agree, injection makes the car more tuneable in some cases and more driveable but offers very little actual increase in horse power. (if any)
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Old 09-24-2011, 06:55 AM   #6
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Default Re: Injection versus carbs: how much more HP?

I have run the same engine with EFI and carbs. It was a 318 in a pickup. The four barrel AFB setup had lots more power, and gained 5 MPG over the throttle body injection. This is a stock, smog-optimized injection unit, not a hot rod unit.
Years ago I helped a friend set up a Hilborn injector for street use. It was a real pain! Every time the barometer changed an inch or so, the thing went rich or lean. Modern electronics would make a lot of difference, but when that thing worked, all hell broke loose! Hard to beat eight individual straight-through intakes at wide open throttle and high RPM.
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Old 09-24-2011, 07:27 AM   #7
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Default Re: Injection versus carbs: how much more HP?

The key is in the wording. Hilborns made a bunch more horse power than the carbs that were available AT THE TIME. The old Hilborn mechanical ain't changed much in 50 years (I'm not including the new electronic version) while carbs have made huge advances since 1955.
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Old 09-24-2011, 07:36 AM   #8
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Default Re: Injection versus carbs: how much more HP?

When i was running my Hilborn injected Caddy on alky it had loads more hp and low end torque than it has know on tri-power and gas.
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Old 09-24-2011, 07:52 AM   #9
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Default Re: Injection versus carbs: how much more HP?

For me, the advantage of injection over a well-tuned carb is the increased reliability to handle today's corrosive fuels. Also holds it's settings better, and if electronic, adapts to conditions continually.
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Old 09-24-2011, 07:53 AM   #10
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Default Re: Injection versus carbs: how much more HP?

I remember an article in one of the mags. about roadracing an early corvette, they used the early GM mechanical fuel injection over the dual quads. Simple reasoning as the wcfb's would flood in turns. No real gain in HP, just a happy engine. The same goes for offroading, a guy would have a tough time keeping a carb from flooding while rock crawling.
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Old 09-24-2011, 07:58 AM   #11
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Default Re: Injection versus carbs: how much more HP?

I've been an EFI 'tuner' since 2000, and I can tell you that there are a TON of variables involved, almost too many to consider.

In my experience, mainly with port carburetion (sidedrafts on inline motors), I could tune for amazing low end torque and decent top end, or wicked top end with a soft low range. With an EFI setup with a lot of thought put into it (plenum size, runner length, etc), it was possible to have perfect low and high end outputs. The end result was usually the same whether on carbs or MPI, it was the behaviour of the engine that changed. Same went for mpg. I wasn't stuck tuning for tq, power, or mileage, I could have it all.

Gotta tell ya though, I have been tuning/hacking for local shops since 2000, and when I started learning about carbs I learned more about the way engines work than in a decade of EFI tuning. You can make a car run great on EFI without putting any thought into the mechanical portion, but to make something run perfectly on carbs...you've GOT to know the whole package.
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Old 09-24-2011, 08:14 AM   #12
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Default Re: Injection versus carbs: how much more HP?

I'd hazzard a guess that for normal street driving and under equal conditions a basic injected motor would run better and probably get a little bit better mileage. With newer EFI systems and a computer you might be able to have it all, as a lot of the engine's other settings are also automatically adjusted. Gary
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Old 09-24-2011, 09:25 AM   #13
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Default Re: Injection versus carbs: how much more HP?

Too many varibles. Maniflod design being the big one. Individual runner manifolds are tricky to tune. I think that you'd see a lot more mechanical fuel injection in unlimited class racing if that was what made the most power.

But for just plain bad-ass looks, it's way cooler that a 4500 on a Victor.
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Old 09-24-2011, 10:09 AM   #14
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Default Re: Injection versus carbs: how much more HP?

Quote:
Originally Posted by Brad54 View Post
All else being equal, how much more power will mechanical injection, like a Hilborn unit, make on an engine over carbs?

-Brad
Well, if EVERYTHING else is equal (timing, airflow, fuel mixture, etc) then there would be NO difference. The engine doesn't care how the fuel gets there.

That being said, in practice, you would most likely see a difference one way or the other. Which way would depend on how well you tune each set up.
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Old 09-24-2011, 12:08 PM   #15
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Default Re: Injection versus carbs: how much more HP?

As with many other issues, it would be in selection and tuning.

We have never lost a customer (at least permanently) to fuel injection, either mechanical or electronic.

My GUESS would be that if a fuel injection specialist were hired to select and tune a system AND a carburetion specialist were hired to select and tune a system; either system could be installed and the owner would never know the difference.

The big advantage from a hobbyist's standpoint today of efi is to readily adapt to a multitude of different fuels. If the pump says E-10 it could be anything from E-0 to E-20 or so. A properly setup efi with the necessary sensors could adapt much better to this than any carburetor.

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Old 09-24-2011, 01:11 PM   #16
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Default Re: Injection versus carbs: how much more HP?

I worked with injected inlines and multi-port heads. I used both Hilborn and Algon side draft systems. Both gave excellent results. Then later I was introduced to Weber carburetors and decided to spring with some big bucks to buy three #40's. In my opinion if I had three more I would probably not see much difference (1/4 mile ET) than I experienced with the injectors. I don't know what the Custom Throttle bodies would do for me.
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Old 09-24-2011, 01:46 PM   #17
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Default Re: Injection versus carbs: how much more HP?

I wanna see how you plan to drive the pump on a corvair engine...this should be interesting

and here's an injected corvair that was on Drag Week....not quite what you had in mind, but the car scoots
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Old 09-24-2011, 07:58 PM   #18
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Default Re: Injection versus carbs: how much more HP?

Years ago I built a ballsy Corvair motor that ran 140 heads with Crown intake manifolds. They may still be available from Clark's Corvairs. The manifolds accepted Weber 40IDA3C carbs that came stock on 911 Porsches back in the day. Awesome, simply awesome.

40IDA3C Webers are close to unobtainium these days with prices to match.

I only mention this because the Crown manifolds could be adapted to electronic fuel injection rather easily.

To mount the Crown manifolds the original cast in head 140 intake was milled off. Then the low spots were filled with weld and the surface was milled again. Each port was fitted with an "O" ring. The intake was held in place by the top row of head bolts.

This same technique could be used to fit a purpose built manifold with stacks, etc.

I don't think fuel injection will give you much over the Webers. I would not mess with mechanical injection for a one off. Electronic is the way I would go.

Pictures from the net.
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Old 09-24-2011, 08:04 PM   #19
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Default Re: Injection versus carbs: how much more HP?

I dont know if you noticed, but mech. fuel injection pretty much disappeared from N/A gas class and comp elim. motors around 1975, replaced by tunnel rams and carbs, and its been that way ever since.
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Old 09-24-2011, 09:43 PM   #20
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Default Re: Injection versus carbs: how much more HP?

There are a lot of sportsmen racers using mechanical injection these days, I think mainly for alcohol though.
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Old 09-25-2011, 12:20 AM   #21
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Default Re: Injection versus carbs: how much more HP?

A mechanical injection motor on methanol with the nozzles further from the valves has a heavier intake charge that has more inertia. On some motors this can create slight positive pressure in the intake port. Theoretically you can get over 100% volumetric efficiency with the right combination. That's a theory I've heard at least.
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Old 09-25-2011, 12:33 AM   #22
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Default Re: Injection versus carbs: how much more HP?

I saw an interview with prostock drag racer, Warren Johnson. He said the main advantage of fuel injection over carburetion is consistency.
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Old 09-25-2011, 12:53 PM   #23
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Default Re: Injection versus carbs: how much more HP?

Quote:
Originally Posted by squirrel View Post
There are a lot of sportsmen racers using mechanical injection these days, I think mainly for alcohol though.
yes, still used alot for alcohol. Because of the problems for getting sufficient fuel volume through a carb designed for gas.
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Old 09-25-2011, 04:31 PM   #24
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Default Re: Injection versus carbs: how much more HP?

Thanks for all the input guys.
The reason I was asking is because I was talking to a Bonneville racer that has a Corvair, and it got me to thinking. (unfortunately for us, the "F" engine class records were obliterated last month by someone who's been racing there for 20 years).

It'd be a wide-open-throttle condition, not driving around on the street.

The class allows for carbs or mechanical injection, no EFI.

The stock Corvair 140 intake is a horrible design, with lots of bends, so stock carbs weren't an option. I like the Crown manifolds for the webers, topped with a 6-port "tunnel ram" type intake with a single carb, or mechanical injectors.

Squirrel: driving the pump would have been with a cogged belt off the crank.

Still thinking about this, because there are a couple classes a Corvair would fit, with the right combo I think I could get in the record book... but then what? A Bonneville Corvair is pretty much a one-trick pony, and it's limited to one or two classes, because you can't do an engine swap.

Thinking "Stude" now...

-Brad
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Old 09-25-2011, 06:10 PM   #25
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Default Re: Injection versus carbs: how much more HP?

After electronic injection took over in Indy car racing everyone bolted on the mechanical injection for qualifying because they got more HP than the electronic at wide open throttle and that what Indianapolis became- a WOT track. For final tuning (i.e. carburetion day...what a misnomer!!!) and the race the electronic injection was reinstalled because of the consistency needed for the varied conditions a race throws at the team.
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Old 09-25-2011, 08:29 PM   #26
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Default Re: Injection versus carbs: how much more HP?

None.
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Old 09-26-2011, 07:36 AM   #27
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Default Re: Injection versus carbs: how much more HP?

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Originally Posted by rjaustin421 View Post
After electronic injection took over in Indy car racing everyone bolted on the mechanical injection for qualifying because they got more HP than the electronic at wide open throttle and that what Indianapolis became- a WOT track. For final tuning (i.e. carburetion day...what a misnomer!!!) and the race the electronic injection was reinstalled because of the consistency needed for the varied conditions a race throws at the team.
Some sportscaster with no sense of history suggested a few years ago that "Carburetion Day" should be renamed fuel injection day; but wiser heads prevailed.

Carburetion Day is a reference to the early history of the track; as two of the four original investors (Mr. Wheeler and Mr. Schebler) were carburetor manufacturers.

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