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Do 8 Stack EFI or Weber Carbs Run Good On The Street?



Do 8 Stack EFI or Weber Carbs Run Good On The Street?


The answer isn't so simple, but 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.

As far as “looks” go, the Webers and/or 8 stack EFI systems are really cool, but as far as drivability, 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% o time. Even when older Le Mans cars came into the pits, (R Model Shelby’s, FIA Cobra’s, GT-40’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” cams they used with long durations. Big cams and open port induction systems do NOT mix at low RPMs AT ALL unless you have a LOT of cubic inches to keep enough volume 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 on the lower RPM side.

weber 8 stack carbs

Contrary to popular belief, 8 stack 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 carbs, by like 5 - 7 times in many cases! Many of them are 2,000 to upwards of 6,000 CFM! The 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 air velocity = no fuel delivery. Low air velocity = poor fuel atomization and sluggish acceleration. At least with the EFI systems the fuel is atomized due to 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.

weber 8 stack carbs

On any engine, at low RPM, if you stab the throttle with 8 stacks, 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), 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 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.

weber carburetors

Another bad point is; when you have “healthy” cams with lumpy idles, (like most hot rodders like), 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. 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 worked on some RACE CARS does NOT mean it will work worth a CRAP on your car on the street! 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.

weber 8 stack carbs

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 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.

There are lots of engines I turn down building for people because what the customer wants, and what will run good, are often two different things. I will not build an inferior engine that isn’t up to my quality or strength standards, nor something that will run like crap! MY name and reputation are on it, so it HAS to be built TOUGH and run like a striped-ass ape. I didn’t get my unsurpassed reputation for building “Bad Ass” cars and engines because they run like crap, or run weak, or fall apart. LOTS of other engine builders would be MORE than happy to tell you everything you want to hear, and take your money, but I won’t. 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.

weber 8 stack carbs

Now the question becomes; “CAN you build an engine that runs good with IDA or IDF Webers, or an 8 stack EFI system?” Sure you can, as I often do, but ONLY if the rest of the engine is set-up for it, as well as the car, AND how it will be driven. Most of the time these requirements are not parallel with what the customer THINKS he wants. I DO build quite a few 8 stack carbbed and EFI engines for both street AND race use that run fantastic, BUT they have to be set-up with everything else to go along with it to make it run right, which isn’t always what the customer wants, or was expecting to have to do, especially if he was hoping to have a lumpy cam and good low to mid range torque.

So in a nutshell, yes, the 8 stack carb or EFI systems DO look awesome, and they CAN be made to run nice, BUT, 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.

weber 8 stack carbs

If you want to learn more about this kind of stuff, in much greater detail, be sure to check out our Auto Shop Videos series by clicking HERE. We have one titled "Performance Carburetors" that covers all of this kind of stuff, and MUCH more that you'd probably like. These make great Christmas, Father's Day and Birthday gifts!

8 stack carbs

 

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