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NZPhil 06-06-2018 04:49 PM

Injection Carb
Can anyone offer any experience or recommendations on injection carbs for a small block? Also a inlet manifold to match. Thanks

Big Dave 06-06-2018 05:23 PM

Are you referring to the latest fad in automotive fashion which is to sport a TBI EFI system? The Car mags have been pushing them as the greatest thing since sliced bread. But then the Car magazines are paid by the advertisers to push things hence the "fad" moniker. What is in fashion this week, but is gone the next.

I might point out that the factory moved from carburetors that were vacuum driven to electric actuated carbs that were computer controlled, to a TBI EFI system over time, because the emission requirements imposed by congress where tightening annually. The factory had to lean out the burn, add catalytic converters, and jump through a bunch of hoops (solenoids and adjustment lock outs), to get the car to run at all; because they where so hobbled bt the emission requirements.

During this time Holley carburetor, sales took off as people who lived in states with out annual emission checks ripped off their TBI units and replaced them with a carburetor and non-computer controlled distributor. If you didn't want to buy a Holley, a Rochester Quadrajet bolted up to the TBI manifold because all the factory did was to put a heater under the twin injector TBI. When you pulled the TBI and the heater off you had a low rise (Corvette) QuadraJet EGR equipped cast iron manifold staring you in the face.

It wasn't until we had TPI (Tuned Port Injection) that EFI started work as well as a carb; though today TPI has been superceded by direct injection with variable valve timing on top of ignition curve timing all controlled by a programmable computer. That system on a LS-x motor is hard to beat with a carb, though people try it just to look sort of old school.

A carburetor will out perform a TBI unit at a fraction of the cost, in every test except ease of start up. It will allow you to use a far more radical cam in your build (TBI is MAP based and as such is very sensitive to any variations in manifold vacuum). TPI is MAF based as are all of the factory EFI systems today.

And a carb isn't sensitive to changes in altitude. (if you tried the Pikes Peak Hill Climb race with a TBI fueled 454 it would blow up before it reached the top because it would be running far too lean). Chevrolet issued a warning to all service departments to owners of 454 powered light trucks to have the computer changed out before attempting to drive above 3,000 feet and to have it changed back when you returned home if you lived near sea level; such as I do in Florida (though I used to drag a camper trailer up and down the Rockies, Seria Nevada, Cascades and Olympic ranges on vacation).

A TBI is just a way over priced electronic carb that is very restricted in it's use, Luckily advertisers and marketing people can convince you to buy one if you have a polo player embroidered on your shirt (or an aligator) or any other brand name shirt or shoe or pants that are considered to be high fashion.

Big Dave

68WASAGOODYEAR 06-06-2018 08:46 PM

Thanks for this post Big Dave. You may have just saved me $1200 as the Holley was one of my upcoming mods.

NZPhil 06-07-2018 01:59 AM

Well said Big Dave, based on what I have read so far I also have my doubts. I think I have a lot to learn.
Can you offer any advice on what I should be looking for in selecting a carb and inlet manifold? My objective is a reliable engine with approximately 300-350hp once finished, however I am doing it in stages by replacing the substandard bolts on parts first. Thanks

Big Dave 06-07-2018 10:02 AM

Carbs are sized by cfm (cubic feet per minute). Every make (Holley, Carter, Rochester, Solex, Zenith, Weber, Edelbrock, all) will mix the exact same amount of fuel to air. Not one will make more power than the other.

The only thing that makes a Weber the most expensive and the Solex the cheapest is the ability to tune it. With a Weber every part including it's cfm rating (venturi) can be changed by changing the parts that make the carb work. There is nothing that can be changed on a Solex.

Just having the ability to change out the individual parts to tune it isn't the only thing that makers one brand more popular than the other. You can change everything on a Weber, but I wouldn't want to try it on the side of the road. With a Holley you can because it is completely modular, and will fall apart with just a screw driver. The Carter AFB that was sold to Edelbrock to rebrand it as their store brand carb requires the top to be removed (less messy than the Holley in that the gas stays in the carb body), but in doing so you can loose small hair pins and springs that are required to make it work. As such tuning is best done on a work bench, not the wild out doors that is often found in the pits of many race tracks.

This is the reason Holley and not a Weber or a Carter AFB/AVS appear on more American muscle car than any other brand. Despite the fact that if it was built by GM and had a four barrel it was equipped at the factory with a Rochester QuadraJet. The Rochester works just fine but it is a royal pain to tune that requires you to bend steel rods and replace springs to tune. But once tuned it will perform flawlessly for the life of the car. Even I won't attempt to tune one and I have been tuning race cars for over a half century (it is far easier to buy one all ready rebuilt and pre-tuned to your needs by an expert on a flow bench).

I have been rebuilding and tuning Holleys since 1963 when I got rid of my last engine with two fours or three duces as a carb set up instead using one big Holley four barrel that makes more power. People either swear by Holley or swear at them. I have made good money by repairing the damage done by other experts who helped out their friends by attempting to tune a carb that was in tune before they started to change things.

As I said a Holley is completely modular but it is sized and mixes air to fuel by using parts that are designed to work together. As such I have discovered metering plates from the wrong carb attached to the main body that sizes the carb, or an attempt to convert a vacuum secondary to a double pumper (or worse just sticking a screw in the linkage) by changing only some of the parts. Most of the time (about 98%) a carb out of the box works just fine as is. If it ain't broke don't fix it!

Big Dave

68WASAGOODYEAR 06-07-2018 11:00 AM

1 Attachment(s)
Dave, what is your opinion on something like the Edelbrock Pro-Flo EFI? Seems more like a true FI with the dedicated intake and rails. Or is this more snake oil? Easy starts and the "self learning" appeal to me since I'm not looking to race or even tinker with it - I just want it to work every time with minimal fuss. Thanks again.

Big Dave 06-07-2018 01:05 PM

Know someone on another board who programs EFI for a living (pro racing mostly). If I remember correctly they use a Chrysler CPU and Bosch injectors on a Victor Jr. manifold. That will work just fine.

Compare it price wise to this combination:

Proform 650 cfm DP carb $400.

Edelbrock Performer RPM Air Gap $265

This combination will work equally well without any fuss on your part. It also doesn't require a separate EFI fuel pump ($287) not included in the kit


The Pro-Flo 4 EFI system requires a high pressure fuel system providing 43-45 or 58-60 psi of fuel pressure with a flow rating of 57 GPH
(215 liter/hr). These fuel system requirements can support up to 600 HP. The following recommended options are available separately.
nor the computer controlled HEI distributor, nor an app to download software and updates, nor a new gas tank ($267 if you have a 1965-'66 Chevy Impala) with a separate return line nor a fuel pressure regulator which is also not in the kit. You get the carb and manifold for $665, a savings of roughly $1689 plus shipping on four items.

If you live in a cold area you have to learn to turn on the ignition first to allow the electric choke to heat up before you pump the gas twice then hit the ignition switch to start the car in the morning.

Big Dave

NZPhil 06-08-2018 01:59 AM

Thanks Big Dave I’m sold on going with a Carb, so much less mucking around and will more than meet what I need and so so much cheaper.

lovebohn 06-08-2018 10:34 AM

You might be correct on the price, but I have had zero problems with my Holley Terminator TBI setup. I now can go out flip the key and it starts, I don't need to mess with sitting in the car until it warms up or hope the electronic choke keeps it at idle. Sure there might be a learning curve but is it any different than a newbie trying to tune a carb? I have zero lag or hiccup at any speed or throttle position and can adjust my timing on the fly. I have bought the Dominator ECU which gave me transmission control so I'm now playing with gear changes and torque converter lockup points. This ECU has a million I/O options so I can tweak my electric fans to turn on or off at a certain speed or temp. To each their own, but saying TBI is a marketing push is a little much.

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