I ran the first Sniper and it never got as good of gas mileage my quadrajet did. Had to use a low profile single plane intake to make it work


Put it on my big block and it was just drowning it, literally. 8 miles to the gallon was it's best. I didn't want to switch to a single plane so I sold it and put on a tripower....thats 3 carbs and it gets 11 mpg now

The only thing you will gain over a carburetor is starting it without pumping it the first time in the morning. After that the carb will start without pumping when it is warm. What's the big deal of stepping on the gas pedal. Any other issues is the owners fault not keeping up with maintenance or tuning. If you have a hot start issue use an electric fuel pump

 

Quick update...at 70 mph up to a show and back, my 525hp 427 is getting 13.8 mpg today after a fillup, the stock 396 I had the sniper on only got 8 mpg while my 430 hp 327 got 16 with the Quadrajet and 12 to 14 at its best with the Sniper using the variable timing adjust feature....you arent going to get a vastly different mpg with these bolt on carb looking EFI units.

 

Some users of EFI just have bad experiences. Usually those bad experiences boil down to EFI quality control issues from the manufacturer, and the end users personal and technical preferences. In the end, you have to go with what works best for you.
Some of the last few posts bring up some interesting points:

1. I never really experienced the carburetor being more sensitive to various engine issues and I had several over about 25 years. Not that it isn't true. I've just not seen it like I have with EFI. I've not seen a carburetor detect misfires, react to exhaust leaks, react to bad valve train geometry, coolant temperature issues, etc. That's what I really meant. The carb has no feedback mechanism it is responding to. You can also "tune out" vacuum leaks (sometimes unknowingly) with a carb, but the EFI will respond to those. Generally speaking a carburetor is reacting to a given set of physics properties (mechanical / airflow) but nothing else.
2. Intake manifolds: Both single plane and dual plane will work fine with a throttle body EFI unit. Single planes don't suffer the lower end torque losses with EFI, so you'll gain some benefits there while mitigating the negatives. Dual planes work fine too, but the single plane manifolds work slightly better with the higher RPM benefits. Try and find an EFI car built in the last 30 years (trucks and low end torque vehicles included) that have a dual plane manifold. There are none.
3. As far as the EFI units not getting at least the same gas mileage or better than a carburetor, in my experience, something is wrong with the EFI unit or some other parameter or tune. From a chemical energy point of view, if both engines required X amount of fuel flow to maintain a 14.5 AFR at the O2 sensor, at a given load, then that fuel flow requirement doesn't change regardless of what is putting air and fuel into the engine. The advantage of EFI is that you can control every aspect of every point of engine load and tell it exactly how much fuel you require and it will adjust to atmospheric conditions, engine coolant temperature, inlet air temperatures, the list goes on. If you want to build a tune that runs leaner in certain conditions (for better gas mileage), you can, without even busting out a wrench.
4. Lastly, I think when people state that the only thing someone considering EFI can gain by going to throttle body EFI is starting it without pumping the pedal, is a gross over simplification that simply isn't true. I realize that there are some folks that the EFI thing just didn't work out for them for various reasons, but I have personally experienced the opposite of that assessment as well as other people I know. A well tuned and functioning EFI unit offers so much more than just cold start efficiency. I'm not bashing carburetors, I had several over 25 years before switching to EFI. I tweaked and tuned those as well. I switched to EFI for ALL of the capabilities I gained moving beyond a carburetor - and it was so much more than quick cold starts.

I hope the OP goes into the Carburetor / EFI question with eyes wide open. The experience here on the forum is awesome, with lots of good opinions and inputs.

** If you're going to treat a new EFI unit like a carburetor - save your money and stick with the carburetor. **

 

We bought our Holley Stealth Sniper several years ago and I found it to be fairly easy to install as long as you followed the instructions and have a good trusty salesperson to guide along the way. I bought mine from EFISYSTEMPRO.COM down in Florida. The reason is simple, they offer 2 years of post sale support when you buy a system from them. There is a Really nice guy there who is very qualified to help design and de-bug a newly installed system. He gets in touch and introduced himself right after the sale, then he gave me his contact information for customers so I have a direct line to him virtually anytime I need any advice.

My wife and I planned on spending $2500 for the swap and would go higher to get the help you might need installing it or getting it debugged. I was planning on a new F.I. Fuel tank but since my tank is in excellent shape so I used a Holley OEM style in-tank fuel pump and built in pressure regulator and new fuel level sending unit . Then I got the master install kit and they sold me everything for ~$1700 which meant I was still below budgeted amount. It was in my hands in 2 days and the kit was and is amazing. My nasty little 427 running high compression sounds pretty healthy even cruising along in the neighborhood with the Stealth Sniper hiding under the L88 Hood parts. It looks very similar to a modern Holley carburetor so most people assume it is a Carbureted BB.

I was worried about which to buy after hearing the pro's and con's of the various systems. If I did it again I would use a new intake manifold system that has the fuel rails and injectors and new throttle body like the newer cars did. I currently have a standard BB built as a clone of the L88 with a Edelbrock RPM AIR GAP dual plane intake on my 427. I am now working on adding the timing controls incorporating my existing MSD Ignition system which allows the computer to make timing changes based on the timing is in fact locked at 15*. One the ECM and the engine's are both set to 15* the system can then do all timing controls as it just tells the MSD when to fire the ignition. Then the coil and MSD box are still "firing" the spark plugs the but Sniper will control when and how far to advance the engine to get maximum power without getting near the dreaded "KNOCK ZONE".

If you want the easier way then the throttle bodies like used on my Chevrolet Truck for almost 300.000 miles without any sort of problem. I like the performance but have not been able to get a highway mileage number. The systems with the individual injectors for a fuel rail like the Edelbrock Pro FLOW 4 EFI system look nice. I would have to look at the software package they give the buyer because I want to see what it can really do. The Sniper has been a good basic controls using the handheld, The data logging is kind of a PIA but the software they give you from Holley is outstanding as far as I am concerned. You can go in an adjust system where it might need some help, it is wonderful and very powerful.

 

The aces timing control works exactly the same way.vI chose the non cdi control version though.

 

Edelbrock pro-flo 4 gives you a look at what you can do on your tablet or phone.

 

I thought the carbs in my cars were awful. I test drove a C3 today. Oof. Good luck to whoever buys that car (to be fair, it needed everything, but I stalled several times just driving normally).

Sure, the TBI offerings have gotten better. But so what? Step into the late 90s with an LS swap instead!

I'll probably get called a liar, again, for saying this, but if you think you want a Sniper EFI setup, price out a junkyard LS swap while you're at it. You can complete a swap for the price of the Sniper. You get EFI, a new to you engine, a roller cam, and 40 years of engine improvements.

Yes, you'll need to do something about the exhaust (but you wanted to do that anyway, right?)
Yes, you'll have to reprogram the stock ECU, or add a Holley Terminator X, or whatever.
Yes, you'll need a new clutch. But I bet your car already needs a new clutch.

Here's an example (not a junkyard swap, but should give you some ideas). 27.6 MPG!*
https://www.corvetteforum.com/forums...completed.html

(33.1 mpg is claimed in the thread, but that's Imperial Canadian gallons. It's closer to 27.6 miles per Freedom gallon).

 

With my old carb and a Edelbrock Performer level 350 with my TH700R4, the best highway mileage I got was 21-22. Which actually was pretty good IMO back in the early 90s.

Fast forward to today...

~430 hp 383, same transmission, but with a Gear Vendors behind it. Ancient 1990 era TPI ECM with highway mode fueling kicked in...

25-26 mpg in 4th gear with converter locked.

28-29 with the GV activated doing ~2000 rpm at 80 mpg... lol.

The port fuel injection just thrives at low throttle cruising at low rpm with no lugging the engine. In fact I can actually accelerate in that double OD. It's not neck snapping by any means, but it's definitely not lugging the engine. I couldn't do that with a carb.

 

Yeah we get it... C5s are better... and c 8's even better. its all where we want to draw the line in the sand..

 

Augie's right. It really does come down to where each of us wants to draw the line as per modifications.
I run a simple form of throttle body EFI. That I really put some time into as per tuning mind you.
When I open my hood, as I do often. My car appears to the average individual to be a period correct somewhat hotted up original car.
And that's what I want.
It doesn't look like a transplanted engine from a newer car. Because it isn't.
I had her out today. Cars and Coffee in the morning and then this afternoon a spirited drive through the Hinterland near my home.
Keeping in mind that I do also have a modern sports car. And I am a professional mechanic. My standards and expectations are extremely high.
My throttle body injected old Gen 1 engine actually really, really runs nice. Super nice!
One of the main reasons I switched over in the first place was fuel economy. As we pay well over 2 bucks a litre for petrol over here. So every little bit makes a difference.
And no, I didn't need a new clutch, I had replaced my clutch with a RAM unit just before my EFI Conversion.
No, I didn't want or need new pipes. I like my chambered exhaust.
Yes I really did want to update my fuel system at the time. But pull my engine????
No.
And yes I really did put in some time getting this tune spot on. To the point of it running like a modern car, no compromise. So, yes they auto tune the base map only! And only to what YOU tell it to learn to!
So, if someone is getting worse fuel economy from EFI, regardless of the type. There is a issue somewhere or they haven't tuned it properly. Expecting it to magicly learn fuel economy without setting up parameters for it to run in that way just isn't going to work. And if parameters are set up and results still are not being achieved means something is wrong!

 

Anyone who is experiencing a dramatic loss in fuel economy going from a carburetor to an EFI system should start asking some serious questions. Something isn't right, because what you are effectively saying is that your engine now needs 30% to 40% more energy to do the same amount of work? Assuming the chemical energy in your gas hasn't changed, nor the air density, then your AFR would be extremely rich - or while running on a carburetor it is extremely lean. Otherwise, where is the excess fuel in the EFI unit now going? It's not being "burnt" because your engine wouldn't require it to do the same amount of work. Just physics in action. If unneeded fuel is being delivered then the O2 sensor should be getting buried with unused fuel. OR the tune is bad and it is commanding excess fuel OR the O2 sensor is bad OR there is a bad exhaust leak / unwanted air getting in upstream of the O2 sensor... Something isn't right.

Here's some real numbers from my C3 (supercharged 385 CID). In my theoretical situation I'm cruising down the highway in the maximum gear at 1750 RPM doing 60 MPH. According to my Sniper fuel flow, I am burning 22 lbs/hr of fuel at that engine load. Premium gasoline is about 6.35 lbs / gal which burns about 3.46 gallons / hour. I can get about 24 gallons to a tank which would get me about 6.8 hours of driving (assuming a constant speed over that distance). My speed at that RPM is 60 MPH which would net me 411 miles in 24 gallons. That equates to about 17 miles per gallon of fuel. So, on an average drive to and from work for me I get 17 miles per gallon if I could cruise the whole way. My average AFR target for that same drive was 14.4. Keep in mind this is a supercharged 385 GEN 1 SBC and I'm getting an average of 17 miles per gallon (cruising miles). I could probably do even better if I leaned out my cruising target AFR numbers a bit more and I drove more conservatively. Now that is an ideal number, and taking that same drive and looking at the numbers in another way: it's a 24 mile drive using an average of 21 lbs/hr therefore on a stop and go trip (without getting "spirited" during the drive), I burnt 1.65 gallons in 24 miles. That equates to 14.5 miles / gallon. So, for the couple of examples I used I ranged from 17 miles / gallon to 14.5 miles / gallon. Perhaps I'll try this again and try to purposefully get better gas mileage.

Anyway, that's just some real numbers to play with. I guess the point of this discussion with respect to the "EFI vs Carb" question is EFI fuel economy. We've seen some examples where it doesn't seem advantageous, in fact down right hideous. We've heard some experiences that counter that experience. From a physics point of view, a carburetor or EFI unit doesn't dictate the amount of fuel an engine requires at any given load, the engine does. A properly tuned EFI system should be delivering a target AFR as specified by the user. Stoichiometric AFR of 14.7 (probably actually 14.3 for modern fuels) will achieve the most efficient burn, but EFI can literally be set to chase that exact number if that was desired. Therein lies the EFI advantage - more precise AFR control at all engine loads.

 

Augie,

I would really like to know more about the ACES EFI system. I'm especially curious about the software side / tuning capabilities. Perhaps as you get it installed you can share some of your experiences.

 

I have a feeling from the research ive done so far that if the system is lacking anywhere, The software is where it will be. Hardware wise for what ive got for $900 is pretty impressive.

One drawback I found is my drop air cleaner doesnt fit and will need modification.

 

When you put this on I’ll need to know some pro tips from you. I already ordered the kill shot with the external pump (since this car already has one)

 

I agree with you, EFI is a great advancement and works well if set-up correctly from the start. My main point is that these C3s with dual plane intakes will not be easy to tune and make peak power using a TBI EFI system. The fuel air distribution is all over the place and will require a thick spacer to correct and we don't have the hood clearance for that. All the closed loop control you talked about is true if the A/F distribution is even, otherwise you are adjusting the average and risk damage if some cylinders are too lean. If I were to do it again I would get an intake made for Direct port injectors and an air only Throtle body running the Terminator X ECU or similar.

 

I have an ebay special single plane in my ebay shopping cart if this turns out to be true but the air gap has the divider cutup and I can also make that bigger. I have to remove the 1" spacer im running now to be able to utilize the cowl cai im running now due to the aces TB not clearing a drop base cleaner base.

 

Exactly. At the end of the day whether it’s SFI, batch fire, throttle body injected, or a carb all these fuel delivery methods deliver an atomized fuel air mixture before the intake valve. Direct injection is a different animal.

The infinite adjustability of a GOOD EFI system with timing control gives EFI a leg up but you can get a carb pretty darn close.

 

Direct port injectors and an air-only throttle body? That sounds familiar!

If it were important for someone to retain an original Gen 1 SBC, how would you do this? Other than @Fly skids up!'s excellent build thread, is there another example to follow?
https://www.corvetteforum.com/forums...ld-thread.html

 

I did see a number of these systems for a SBC when looking at different setups myself... like this? https://acesefi.com/products/the-joker-sequential-efi-cdi-master-kits

Ive had both mpi and tbi cars and trucks now and didnt really see a difference in how well one ran over the other honestly but im sure the mpi would have the performance edge. It just was never an issue in my crossfire vette.. My 85 TPI camaro had all sorts of idling issues though which they supposedly worked out after the first year. My old dodge ran well enough with the mpi though. Even after I bored out the throttlebody and swapped in different injectors. While I totally see how MPI has advantages over everything else I dont really see how a TBI setup could possibly actually be inferior to a carb setup though. Side by side one simply has more tunability with better performance from idle up to maybe WOT where a carb may have an advantage depending on how its setup. From my understanding TBI is a hybrid between the mpi and carb setups.

 

If you wanted to keep the Gen 1 SBC, but move to a tuned port injection system - without moving toward a tunnel ram system, here is the blueprint to do it. The parts are still available (I did the research several years ago) for the most part. It would essentially be a single plane manifold with injectors and fuel rails at the ports, with a air only throttle body. You'd have to use an engine management system like the Holley Terminator, but this setup works great - and it can retain some of the look of a Gen 1 SBC - and have all of the advantages of tuned port injection.



Here is most of the parts list, although not every little thing...

300-260
HOLLEY EFI SBC EFI INTAKE MANIFLD AND FUEL RAIL KIT, SINGLE
PLANE 4150 MEDIUM PLENUM SIMILAR TO VR JR
Use 522-368S Short Injectors.

112-588
Throttle Body, Universal, Multi-Port, EFI, 4150 Square Bore, 1,000 cfm,
Cast Aluminum, Polished, Each

522-368S
Holley Fuel Injectors, Sniper EFI Fuel Injectors, 36 lbs/hr., 12 V, Saturated
Circuit, Set of 8

550-936
TERMINATOR X MPFI UNIVERSAL, bb/sbc

538-13
MAP Sensor, Bosch-Style, 2-Bar

558-201
Injector harness designed for EV6-style fuel injectors. For use with
Holley HP and Dominator and Terminator X EFI systems.

558-443
USB/CAN HARNESS, USED WITH CAN PLUG ON SNIPER, TERMINATOR,
HP, TERMINATOR X AND DOMINATOR ECU'S

534-10
Coolant Temperature Sensor for Holley EFI and commander 950 systems

558-465
Wiring Harness, WIRING HARNESS, CAN SPLITTER

565-200
HOLLEY EFI DISTRIBUTOR, DUAL SYNC, SBC/BBC

8222
Coil, Blaster, High Vibration, Black, Blaster 2

EDL-FRC Edelbrock Fuel Rail cross over line and fittings Includes:
4x -6x-6 ORB for each rail
2x -6x45 Deg hose ends
1x -6 Race Hose 1ft