Do 8 Stack EFI or Weber Carb Systems Run Good On The Street?
The answer to this question isn't so simple and it depends on whether you're talking about 8 stack carburetor system or 8 stack EFI systems because there is a huge difference between the two. Not just in the way they function, but in the way they run as well.
In a nutshell, if you're talking about 8 stack carburetor systems, then the overall the answer is no, not as well as you think, or as they advertise them to be. The engine MUST be set-up so it will work for the applications, and/or how it is intended to be used & driven, with a lot of emphasis on the word "driven".
As far as “looks” go, the Weber and/or 8 stack EFI systems are really cool, but as far as drivability on the street goes, especially at lower to mid RPMs around town, idling, etc, they are not very cool. This is especially true for the carbs.
Think about what they were designed for and ONLY came-on… ROAD RACE cars. Cars that are AT upper mid, to high RPMs, 99% of the time. Even when older Le Mans cars came into the pits, (R Model Shelby’s, FIA Cobra’s, GT-40’s, and even Ferraris, Lolas, McLaren's, etc.), they didn’t idle low like any street car does. In fact, the idles were set way up to about 2,000 - 3,000 RPM so they wouldn’t have idling or stalling issues, and to keep the air velocity (momentum) up so they wouldn’t pop and sputter though the “stacks” due to the “big” road race cams they used with long durations for continuous high RPM racing.
Big cams and open port induction systems (carburetors) do NOT mix at low RPMs AT ALL unless you have a LOT of cubic inches to keep enough volume of air and velocity going through them. You have to “ease-into” the throttle to GET to the higher RPMs needed for where systems like these run good at. Anything below that, it can (and often IS) a complete turd, or at very best, “quirky” and doggy off the line and on the lower RPM side.
Contrary to popular belief or what the advertisements tell you, 8 stack carburetor systems like Webers do NOT make good low to mid range torque, especially on the street. In fact, quite the opposite. The CFM of a typical system is MANY times more than a pair of large 4 barrel carburetors, by like 5 - 7 times in many cases! Many of them are 2,000 to upwards of 6,000 CFM!
8 stack EFI systems DO work a bit better than the IDA or IDF Weber carbs though simply because fuel is delivered via high PRESSURE spray rather than being reliant on “air velocity” to “pull fuel" through the main jets via the boosters. No, or low air velocity = no fuel delivery. Low air velocity = poor fuel atomization and sluggish acceleration. At least with the EFI systems the fuel is atomized and delivered by the high fuel pressure, but again, the air volume and lack of velocity (air speed), as well as the lack of a plenum (like intake manifolds have) doesn't help in the low to mid range RPM area. Engines don't run on air, nor do they accelerate from low RPM with no velocity or fuel atomization... especially carburetors.
On any engine with an 8 stack carb system, at low RPM, if you stab the throttle, the air velocity drops to virtually zero, which means the engine falls on its face because it only gets a quick squirt of fuel from the accelerator pumps and then sees not nearly enough air velocity to pull fuel from the boosters to meet all of that volume of air, so it is REAL sluggish off the line. Low air velocity and no fuel = a complete turd of an engine. Again, EFI systems don’t have this problem (as much), BUT, they do still have low-end to mid range response and power issues (as compared to say, a single 4 barrel carb or a typical EFI system), simply because of the fuel being delivered under pressure (not reliant on velocity or the “Venturi Effect” to pull fuel through the boosters).
Also, they are quirky off idle because when you crack it open, the engine takes a HUGE gulp of air through 8 large throttle plates. The surface area is immense and in most cases, the throttle plate is much larger than the intake valve itself! Cracking-open 8 large butterflies is the same CFM equivalent as opening a very large 4 barrel to about 1/2 or more throttle! If you were at an idle and you mashed the gas of a 4 barrel carb that is WAY too big for your engine, what's going to happen? It's going to fall on its face! It would be very “quirky” at off-idle and low RPM acceleration, especially in traffic. Compound this with tall street gears and you REALLY have a slug off the line!
Now imagine TWO large 4 barrels on your engine. Now it's REALLY going to be sluggish off the line and in acceleration through the lower RPM band, and what did I say earlier about 8 stack systems? They are usually 5 - 7 times larger than most 4 barrel carbs! How would your engine run with 5 - 7 four barrel carbs on it? How would your low-end acceleration be? Yeah... not so great. In fact, it would be a complete turd! The 8 stack carb systems are quirky for this same reason. They are really designed to be run at 1/2 to wide open throttle at higher RPMs where the air velocity going through them and pulling off the boosters is high, which makes them respond really well. How often on the street are you at 1/2 to wide open throttle? Keeping in mind that 1/2 throttle on a 2,000 - 6,000 cfm 8 stack system is like ¾ to full throttle on two VERY large 4 barrel carbs! It makes it quirky, jumpy, and yet doggy at at low RPMs. This is even compounded on smaller cubic inch engines (350 or less cubes) or with cars that have tall rear-end gearing.
Another bad point is; when you have “healthy” cams with lumpy idles, (like most hot rods have), it makes “reversion” caused by the overlap in the valve timing. This reversion can cause 8 stack systems to pop and sputter at low RPMs, not to mention the compounding fact that “big lumpy cams” already kill bottom-end torque as it is because they have low air speed and low idle vacuum signals. This is why you don’t see race cars (drag racers, road racers, circle track, etc) take-off from an idle or just above an idle. They all take-off from higher RPMs, and for good reason… because the engine NEEDS to be at higher RPMs to be in its power band to GET launched. If race cars didn’t take off at high RPMs, or have low gears, high stall converters, trans brakes, etc, they would literally fall on their face off the line. They launch like they launch for good reason… because they HAVE TO. Do you want to HAVE to drive your street car like race cars HAVE to be driven? I doubt it. Just because something “looks” cool and works well on some RACE CARS does NOT mean it will work worth a crap on your street car! The only race cars you see running 8 stack systems are road race cars, nostalgic dragsters, and Sprint cars, all of which run at continuous high RPMs and who really don't care about low speed idling or low to mid range response.
None of this even touches upon the horrible geometry of the bell crank linkage system these 8 stack systems have. They make the gas pedal REAL hard to push, and without enough return spring pressure, they can (and sometimes will) stick at wide open throttle, or not return to a full idle position when you let off the gas easily. This doesn't make street driving much fun. Sometimes they need to "slam shut" to assure all 8 throttle plates close to their full idle positions. Of course none of this matters, nor is even an issue when they are in the element that they were originally designed for, which is ROAD RACING and running between 1/2 and wide open throttle like they did in LeMans, Daytona, etc. This is the kind of stuff the average "Joe" is clueless of and is stuff the manufacturers don't tell you about because they want to sell you their cool looking products.
There are lots of engines I turned down building for people over the years because what the customer wants, and what will run good, are often two different things. I wouldn't build an inferior engine that wasn’t up to my quality or strength standards, nor something that would run like crap because it was MY name and reputation on it so it HAD to be built TOUGH and run like a striped-ass ape. I didn’t get my reputation for building “Bad Ass” cars and engines because they ran like crap, or weak, or fell apart. LOTS of other engine builders would be MORE than happy to tell you everything you want to hear, and take your money, but that wasn't me. I ONLY tell you what the absolute TRUTH is, and I pride my reputation on it. It may not be what you want to hear, but you can bet yer ass it's the TRUTH.
Now the question becomes; “CAN you build an engine that runs good with IDA or IDF Webers, or an 8 stack EFI system on it?” Sure you can, as I often did, but ONLY if the rest of the engine is set-up for it, as well as the car, AND how you plan on driving it. Most of the time these requirements are not parallel with what someone THINKS he wants. In my day when I had my shop, I built quite a few 8 stack carbed and EFI engines for both street AND race use that ran fantastic, BUT they had to be set-up with everything else to go along with them to make them run right, which isn’t always what the customer wanted, or was expecting to have to do, especially if he was hoping to have a big lumpy cam and good low to mid range torque. Those two simply do nt go together, even without an 8 stack system.
So in a nutshell, yes, 8 stack carb systems and EFI systems DO look awesome, and they CAN be made to run nice, BUT, most of the time they WILL be quirky at low RPMs and you MUST build the engine and the car around it or it won’t run very well and you’ll be hating it. You can’t “just” bolt one of those systems on and expect it to run right without taking a LOT into consideration first, and sometimes those considerations weren’t exactly what you might have wanted to hear, do, or run.
This set-up is on a 545 cubic inch big block Ford I built for this absolutely stunning 33 Ford roadster for a client in Texas.
Some might ask: "Well if they don't work that well on the street, then why did you put them on a street rod?" The answer to that is firstly; that is a 545 cubic inch engine, not a 289 Ford in a Mustang with 48mm IDA Webers on it. Secondly, I built the engine specifically for those 48mm Webers, and they're IDF types, not IDAs. IDAs are more suited for race applications, where the IDFs are a bit more suited for the street because their internal circuitry and fuel delivery is a little better suited for the street. This engine is actually the engine in the very first picture at the top of this tech tip with the chromed carbs and the red distributor cap.
Hey, if you liked this tech tip then please be sure to share it with your fellow gear head friends and on your favorite car forums by copying the URL at the top of the page and sharing it with them. Thanks!
