Fuel Injection in your C3

[Stallion]

I just saw an add in the paper for a '73 and the guy supposedly had a turbo in his Vette that shelled out 400 hp. I was just wondering how many of you went from carb -> injection for your C3. Is it a good idea?

How exactly does this injection work? I mean, why does it give more power?

Thanks!

TR

[WayneLBurnham]

Fuel injection does not typically give you more power over carburation. It usually gives you much greater control of your fuel use, mid-range power, mileage, emmissions and ability to adapt to changing atmospheric conditions without cracking the hood.

Several rags have done decent side by side comparisons of carburation vs. fuel injection (or "carb" vs. "EFI".) Hot Rod and Car Craft, the two leading generalist performance publications and I believe Corvette Fever all did one in the past year. All reached the same conclusions: EFI was great for tunability - laptop adjustments especially - and mid range drivability, especially with exotic setups like forced air (turbos and superchargers) and higher flow nitrous, but offered no top end power improvements over the proper set-up carb.

A good carb with a tuning kit is $250-450, such as a tricked-out Holley or one of the Demons or a Carter AFB or Edelbrock Performer (a Carter clone).

A good adjustable EFI system, such as GM's or Ford's or one of the good aftermarket ones from Edelbrock, Holley, Accel or others is anywhere from $1,250-5,000 - typically about $1,600.

That's a 5:1 cost difference for the same function. Not only that, but secondary costs and concerns with the EFI include this nest of information gathering sensors - and sensitive injectors.

EFI is neat. If you have a weird application a carb with its vacuum signal driven mechanical circuits is not reliable on, especially with abnormal pressures of air, it's a lot easier to use EFI instead, even with its up to 20 additional electronic inputs.

If I go forced air on my monster engine I will seriously consider it, if I can find a system readily adjustable to such a large displacement engine. For me though, for a more conventional set-up a good carb is just the cost effective way to go and I'm giving up no power to use one.

[Scott81]

Do a forum search for "patsnitrovette" and "vettedan" and talk to them about their conversions. Both have sweet Sharks!

[Mako]

As noted above, swapping a perfectly good carb setup to FI is expensive and of limited benefit from a power perspective.

You can get increased milage and lower emissions from a closed loop (O2 sensor) FI setup, but you pay through the nose for the priviledge.

Personally if I had a hankering for FI in a Shark, I'd swap in either an LTx or LSx engine and T56 tranny. You get a hell of a lot more engine that way, a double over drive tranny and a lot of other excellent things.

A lot of guys are doing precisely that too. The LTx is particularly easy, as the computer programming tools are all avialble and reasonably well understoood by the motorhead community. The LS1 will be just as easy in a couple more years.

A Z06 in a '69 sure would be a purty sight to see wouldn't it?

CYa!
Mako

[patsnitrovette]

Scott thanks,but also 70ls-1 too,Im so glad i switched to fuel injection,i went with tpi cause i did a favor for a guy and he gave it to me,so all in all i have about $800 into the complete swap with custom chip made.I was tired of getting 5 mpg with my previous setup,and the ease of starting it just reachin the window turn the key and fires right up even yesterday when it was 7 degrees out.
And mako yes that z06 motor would be sweet!Also ive seen plenty of injected motors running in the low 12,s and high 11,s.

[Stallion]

When you say mid-range power, you refer to the RPMs? And top end power would be with high RPMs like when you race? Or is that not what you mean by that?

patsnitrovette, you bring up very good arguments to change to injection. I understand that if you have a bad carb setup that it's good to go with injection, but with an efficient carb setup you might as well keep it.

Thanks!

TR

[DarkShark]

I'd rather mess with injectors and tune via volt meter. I hate the leaks and mess that old carbs are notorious for. EFI is simple tune and forget... that is unless something breaks or goes bad!!

[Stallion]

Is going from carb -> fuel injection a big modification, or does it require little to do?

[WayneLBurnham]

would probably be a more correct term in this case, sorry...

Basically, at Full Throttle, or Wide Open Throttle, carbs and FI perform indistinguishably. Both deliver power based upon the maximum amount of air that the "throat" can pull in past it - they will each measure out the appropriate amount of fuel to accomplish this.

This can occur at any given speed or engine speed. It's the steps in between (as idle is more a utility thing that works well in either also) where it's easier to get FI to accurately deliver the appropriate amount of fuel to the air your engine is calling for based on where the throttle cable opened the butterfly to.

In fact, carburetion really only "works" exactly in a fully-controlled fashion at as little as two places: at idle and at wide open throttle. Some add a mid point or two where the fuel is precisely measured also, but most carbs rely on the "fudge" of squirting some fuel in the otherwise carefully measured fuel to speed up the transition from idle to wide open throttle - or to go to somewhere in between and function powerfully and not too wastefully. Incidentally, multi-barrelled carbs often double these "fully controlled" points. That squirting is acomplished by using an "accelerator pump," which also might be multipled.

Fuel Injection can even go one better and gets the fuel in there before the engine vacuum sucks in the fuel that would normally be measured by the carburetor's fuel metering circuits.

This makes FI generally capable of faster, more appropriate responses to changes, other than the extremes of just flooring the pedal or dropping it off. It also makes it less dependant upon engine vacuum for accurate functioning, and thus much more immune to odd vacuum leaks than carburetion.

(This latter advantage is way, way offset by its disadvantage due to the potential of errors to sensor damage or electrical shorts, low system voltage and so forth, which does little to a carburetor.)

Oh, BTW, I agree with DarkShark78 - on one point. Old carbs SUCK!!! I would only get a new one out of the box!

But you can get a new Edelbrock Performer Carter AFB-clone or a
Demon improved-Holley, with all the common bolt-on improvements for $300-400 or an upgraded Holley for $500.

My carbs don't leak! Tune with a screwdriver, fuelie-boy!!!

Oh, one more thing, FI-freaks are always on about their cars starting after leaving them parked in a center of an iceburg since the last mastadon used the last carburetor without doing anything more than reaching in the window and twisting the key when it's 4 degrees above absolute zero. "Carbs can't do that."

Please.

Living in a civilized part of the country without ice all the time, :t I can't claim lots of experience with the more extreme tests of this.

Yesterday morning though, I got in the car at 5AM when it was 23-25 degrees, unusually cold for this brightest part of the best part of America. I got my substantial proportions in the driver seat, somewhat nimbly I may add, did not even touch the gas pedal and turned the key. I'm running 35 degrees total advance, 11 of it mechanical. New Edelbrock 750 Performer - manual choke with the choke wired full open. I need to install my new Holley mechanical fuel pump because the stock one fuel starves it on a full throttle launch from start after I hit about 5200 or so unless I let off on it for a second.

It started within a second after sitting there for ten hours.

Carburetion won't start in the cold. Pfft.

I do like FI - and will probably go that way eventually - on the ultimate engine. Carbs, however, work fine, especially the ones out in the last five years, and especially if you don't try to cobble a busted up one together or make an improperly chosen one do on your application.

[MaineShark]

Wayne got it: carbs deliver the correct fuel/air ratio and only a few spots, while EFI gives the correct fuel/air ratio at all points. This gives a much wider powerband. For a street-driven car, this can be a big plus.

But (there is always a but...), like Wayne says, anyone with a screwdriver and some know-how can tune a carb. EFI requires special equipment to tune.

EFI is also more expensive, but you can make some of that back with better gas mileage, if you drive a lot. Don't expect it to pay for itself, but it can help defray the cost a bit.

It is also a significant amount of work, but nothing that can't be done, with some thought and patience. Having the CAC has been a big help; I've done EFI systems from scratch before, but never on a 'Vette, so the specialized ("will this fit here?", etc.) knowledge available here has been a big help.

Oh, Wayne, 23 degrees isn't cold

Joe

[Stallion]

I see what you mean. If I ever decide to go totally custom on a C3 then I think I'll put in EFI. Just curious, the F means fuel and the I means injection but what does that E mean? Thanks!

[WayneLBurnham]

EFI: Electronic Fuel Injection

This is to differentiate it from earlier mechanical Fuel Injection, which I suppose you could call "MFI," although nobody has as far as I know. (These were also known by the inventor or maker or style: Hillborn Fuel Injection.)

(Some fossil carb guys maintain we only call it "EFI" to make fuelie-boys FEEL more important - the way only an extra letter can...)

you have different types of EFI too:

TBI: Throttle Body Injection

PFI: Port Fuel Injection

Throttle body setups, both typified by Chevy and Ford's offerings of the early '80's began as little more than a carburetor body bottom with the top end with all the metering circuits cut out and replaced with a couple or four injectors. These bolted onto standard intake manifolds like a carburetor.

The early ones SUCKED!!! They got a LOT better... Some of the newer ones are very good indeed.

Port systems are more aimed at performance from the beginning. While they also have some system to control the air coming in, it is certianly not a modified bottom of a common carburetor - it's something specially designed and is wholly a part of the intake manifold.

The real difference of a PFI or TPI (Tuned Port Injection) or some other variant though is that they actually inject the fuel straight into the cylinder, either right into the head (rare) right in front of the valve or somewhere along the individual intake runner on the intake manifold - lower portion (most common.)

If you go down the path to Mordor and get into EFI, you'll hear lots of discussion about several key parts of an EFI system: the air flow system, the air flow measuring method, injector capabilities and fuel pressure design.

That first one is addressed a lot by the size of the main air restriction, expressed in mm - you'll hear 40, 45, 50, 52mm, etc. : the air flow capacity increases with the square of the increase of the bore. The second one is often cheated to get more out of a factory system. Two big methods exist - one by the determining the mass of air directly (hence "MAF" for Mass Air Flow.) I am not familiar with the other, I believe earlier, air flow measurement method, but I believe it depends upon a computer calculating other data which is less direct and hence, less reliable.

Injector capacities vary basically with engine displacement and top engine speed. A bigger flowing injector is, obviously, for an engine that moves more air one way or the other. Fuel pressure design is controlled by: fuel pumps (at least two) selection, fuel line size and fuel return valve selection (as well as top injector capability.) A given injector will flow more fuel if you crank up the pressure, but it still takes slightly longer to get the plug of gas in there if the injector is smaller in capacity, and there are optimum pressure ranges to "spray" the fuel into the cylinder. Really large displacement engines will often use multiple injectors per cylinder as well.

If you can pry some fuelie-girl or boy away from their laptop, upgrading their gas pedal's operating system, worrying about their electrical system dropping below 11.69V for more than 0.0578 seconds or watching a pirated endless loop DVD's of "The Fast and the Furious" on the 11" LCD screen (with 5 kW Surround Sound with 8 15" subs) they just put in their CRX that used to be their main car, they could really give you a better overview than I, being both dinosaur and a caveman. After all, I'm still really not comfortable with "0" yet, let alone decimals or "binary."

:t

(Man, am I gunna hear it when I decide to go EFI on my PoS!!! I guess I just won't admit it - ever!!!)

[Stallion]

Thanks for the reply and I understand about the injections, WayneLBurnham. TBI doesn't sound like the way to go, either (). Say you were putting in PFI system in your previously-carburated Vette. Would that be big modification? Would you have enough, say, clearance with the hood? How would this all fit in the Vette?

Thanks again!

TR

TR

I'm in the middle of installing an LT-1 in my C3. I intend to use the 400 transmission that was stock because I just had it rebuilt before I decided to do this.

The central issues for me are cooling and brackets. I don't intend to do a lot of ECM modifications... more like stock, including 02 sensors, etc.

There are some excellent books on understanding GM fuel injection that you can get from Amazon...

I'm using a 96 LT-1 so that I get OBDII (better computer, more programable features). I don't know if I'm going to send the ECM off or if I'm going to try to find a hack so that I can set up the ECM with an adapter and a lapt top (this appeals to me... but I would rather drive the car than learn to program and hack the GM codes...).

I also have heard to stay with reputable wiring setups... some, for example, have poohpoohed painless wiring as being mickey mouse... but I have no perspective on this yet.

I am going to try Andy Grove for the brackets.

I don't care about a bunch of chrome, etc. This is going to be a driver, not a hood up show car.

I'm still learning but I can let you know what I find out as I go...

C#

[MaineShark]

TR, for just installing EFI, what you are basically looking at is replacing the intake manifold and carbeurator with the EFI manifold. The distributor is replaced, in most cases, and the computer and wiring from the EFI system is grafted into the car's wiring. You also end up installing a new fuel pump and fuel line, since EFI needs much higher fuel pressure than the carb. You also need to install an oxygen sensor in the exhaust. That's pretty much it, for generic stuff. Depending on the exact application, you may need to change other things (like replacing the mechanical fan, changing brackets, etc.).

Joe