To carb or not to carb

[fikren]

I was wondering if you could explain (if there are any) the benifits of running a carb setup over an fuel injection setup. Say you have a FC for example that is fuel injection and for whatever reason (system is dead) you are looking at other options.

Are there benifits from running a carb. I know they can be alittle bit more picky especially when outside sources (weather, temp) are involved but is there any gains with a carb over EFI.

Maybe also explain what some disadvantages are (daily/weekly tuning?) of running a carb over EFI.

Thanks,
Jonathan

[Sterling]

Primarily it's cost.
The cost of a decent carb setup is going to be far less than an EFI setup that yields the same power and range. The best of the best carb, built perfectly to spec for that engine, is going to be outdone by a tiny margin by a FI system costing 5 times as much.
Secondly, only arguably, is that few people actually will take the time to read up on how carbs work in an effort to understand how to tune it. Tuning carbs takes experience, which means lots of time for trial & error & frustration. No doubt about it.
And then there is a kind of mythology surrounding carbs; They're "old", "outdated", "finicky", "behave erratically with any environmental changes", ..."need weekly retunes" ;) ...
And, my personal pet peeve; this huge pool of misinformation regarding carburetor size, and what's appropriate for a particular engine. People fail to do the simple math necessary to demonstrate that some choices of carburetors are downright ridiculous, no matter what performance gain has been claimed.
Hand in hand with this, full circle back to the beginning, is that people just don't know how carbs work. With just a basic understanding of how carbs function, other myths get "busted", and carbs start to not look like the terrible alternative to EFI afterall.

I aim to do just that here in this section. But there's no denying that if you have the money to spend, a really good EFI system will be king on the street.
The track is a different story, as the window of used RPM is narrowed, and a properly sized carb can certainly be tuned to deliver the optimum mixture throughout that range. An expensive EFI system is not a guaranteed win over a properly done carb on the track. However, a big percentage of the time that a carb beats an EFI in a race, drivers being equal, you have to often chock it up to the EFI being "not the best" combined with the carb "having a really good day". Then there are those who just really know their stuff. Guys like Paul Yaw.

[SPOautos]

There have actually been some good indepth though maybe biast tests done that show a properly tuned carb can create more power than a fuel injection set up. Carbs atomize the air much better and also substantially cool the mixture. They also add in fuel based on the amount of air passing through them. This leaves a well tuned carb funtioning much like a mass air flow efi system. Most rx7's and highly modified cars run a speed density system which if you ask me isnt all that great in terms of it being finely tuned for all conditions. I think carbs would beat out a speed density setup.

The problem with carbs in the mainstream is that they require someone who actual knows what they are doing to tune them. This is not unlike the problem that tens of thousands of efi people face when they go to a standalone and realize they need someone to tune them or learn themselves. It just isnt something that is easy enough to understand for it to be benificial for the mainstream public. That is why there is such a benifit with efi from a mass market standpoint. Peoples cars don't go out of tune, its all controlled by a computer, and the manufacturer doesnt have to rely on a mechanic to know what he is doing to keep a car in proper tune. Its all done with a stock ecu.

Stephen

[tom93r1]

To expand on what was already said, I love the Weber 48mm DCO carb on my REPU. You could have the identical setup for easily under $1000, used for $500 or $600.

If you want something with similar performance characteristics to that weber you can buy a fuel injected throttle body for about the same price, but then you still need to buy an ECU and injectors and probably a few sensors so figure an extra $1500 or more. Ultimately for daily driving the injected setup will be more consistent and not need as much maintenance tuning, but on the track that generally isnt as much of a concern.

[warwickben]

carbs are cheaper and better for people who cant buy every part for there car at once.
because correct me if iam wrong you can do alot more upgrades to the motor before you have to get a new carb to keep doing upgrades.yeah maybe a rejet and a tune.

with efi certain upgrades make you have to get a custom tune. so if you in stall x part one week you need a new tune. then a month later you in stall x part and need another tune.


this is what a buddy told me that went to uti. is this true.

[85rx-7gsl-se]

carbs are cheaper and better for people who cant buy every part for there car at once.
because correct me if iam wrong you can do alot more upgrades to the motor before you have to get a new carb to keep doing upgrades.yeah maybe a rejet and a tune.

with efi certain upgrades make you have to get a custom tune. so if you in stall x part one week you need a new tune. then a month later you in stall x part and need another tune.


this is what a buddy told me that went to uti. is this true.

Sorta...Alot it has to be with how the ecu determines the amount of air entering the engine. In older AFM and MAF setups, the engine determines the amount of air in the engine by the amount of air that passes through a sensor in you intake. This system was used on FCs and allowed for a number of modifications on the stock tune. Modifying things such as intake and exhaust will increases the flow, but the sensor figures this out. Basically, you need an ECU mod when you are forced to upgrade injectors since the map is different depending on injector size. FDs and most aftermarket ECUs utilize a MAP based system which simply determines the air based on the pressure within the intake manifold. These systems reduce the restictions in the intake tracts presented by AFM and MAF systems, but unfortunantely, they are less forgiving on modifications and require remapping for any serious mods. Some cars such as the Subaru WRXs require a reflash for pretty much any upgrade or they with throw codes and run incorrectly risking your engine's life :(

[cewrx7r1]

I grew up on carbs. Both my Alfa Romeos had twin Weber 40DCOEs.
They ran great and made beautiful sounds. That was two 40DCOEs for 1299 cc of displacement with 28mm chokes.
Later used 32mm for my autocross prepared car/engine.

When I modified my 83 FB: rally port, headers, complete exhaust system, changed distributor advance curve, etc; I used a single Weber 45DCOE, with 42mm chokes. It ended up taking much of my time and modding of the emulsion tubes to run almost perfect. Why, the 12A really needs two 45DCOEs. Has to due to low internal fuel capacity for transistion from idle to main jets.

With what I know today and available WBs, FI would be so much easier to tune and more precise with more power.
Thus I would use the WEBER as only a TB and conveted to FI.

FI can compensate for air temp changes but the Webers don't. I never seen a carb with an air temp sensor.

[repu510]

most of the guys here have said it already. just to add my 2 cents:
carb pros:
1. a carb for the most part is simpler than fi
2. since the carb is a mechanical device, it can be easier to tune out of your garage with not much more than a screwdriver (but in either case, a dyno will help immensely)
3. that old school coolness!

carb cons:
1. requires a ton of patience (and experience)
2. susceptible to the environment, especially in temp and altitude extremes
3. rebuild and repair parts can be hard to find depending on the carb

fi pros:
1. higher potential for hp, reliability, consistency, and fine tuning

fi cons:
1. cost to buy
2. cost to tune/setup
3. cost to repair

so, each have their strengths and weaknesses. my opinion: stick with the same "type" of system that came with the car. you keep the character of the era in which it was built. i'm of the mindset to always upgrade, improve, and move forward if it makes sense.

[Latin270]

I always used carbs and still do on my 91 s5.

[FC Zach]

I havent had any problems with my set up other than spark plug fouling but fixed that with two 6AL's and three Jacobs Ultra Coils. Runs great and very strong throughout the RPMs. Many people are quick to judge carb users by saying they went the cheap and easy way out but I see it differently. I wanted simplicity and to just be different. Either you like it or you dont.

[85rx-7gsl-se]

If you are running N/A or Supercharged, carbs will work great. For turbos, I prefer EFI. Carb turbo setups are often great under full throttle, but iffy elsewhere :(

[jtbshaw]

If you are running N/A or Supercharged, carbs will work great. For turbos, I prefer EFI. Carb turbo setups are often great under full throttle, but iffy elsewhere :(

I think alot of this is due to what Sterling brought up earlier...people don't take the time to find out what is apporpriate for the engine. A blow-through style carb has proven itself to work just as well as a EFI setup. Where most people go wrong is have a standard carb, put a bonnet on it, load it with boost, floats act crazy and well.....boom! The most simple way to continue using a standard carb with boost is locate the pressure zone after the carb, and not try to push through the carb. Just my 2 cents, from a carb guy.

...edit...after re-reading my post, I felt that it sounded as though I was hammering you for not reading up on carbs....not the case. I wasn't trying to start anything. Just making a general phrase. You clearly stated that you prefer EFI for turbo apps.

[85rx-7gsl-se]

No prob man. Alot of the guys I saw in Florida were running draw throughs at the strip, not really the greatest setup :( . As far as blow-through setups, are they difficult to tune? Also, I kinda based my oppinion on alot of the factory turbo carb setups of the early 80s which were ehhh :)

[Sterling]

Lots of variables to consider.
Blow through carb set-ups typically delete the emulsion system in favor of a modified fuel bowl vent system in order to avoid siphoning at high flow. The emulsion system is there to bleed off main fuel draw signal at high velocity (thus preventing siphoning) and as a great side benefit, provides aeration of fuel prior to mixing in the carb. This helps with very fine tuning and fuel efficiency.
Lack of pre-aerating is not such a problem at extremely high velocity, but low to mid range can theoretically suffer, but how would you know?
Carbs utilizing annular boosters and other goodies can better disperse the fuel, coming close to mimicking aeration that an NA carb does.
Negating the emulsion system is a compromise, but blow through setups handle the charge much better than draw though, and they also have the even greater advantage of being able to cool the intake charge using an intercooler.
Even though the carb's emulsion system can be retained on a draw through system to produce an aerated, fine mist, it's basically taking a lace-delicate charge and throwing it in a Cuisinart. Drawing through the carb also doesn't allow for an intercooler, either. BUT, it's a lot easier to set up all around, and the "kick-ass" factor over NA far outweighs the increase from stepping up to a blow through setup using identical components and an intercooler. In other words, going from draw though to blow through setup using the same parts and an intercooler is definitely going to be better, but it's not going to "wow" you anything like when you went from NA to draw through. (Edit: -"On the street" is how I mean to end this. Well known in drag applications, using an intercooler and dry ice, the performance increase is all the difference in the world. However, it's obviously a different application, and not practical for the street applications in the context of this discussion.)

[jtbshaw]

.....Drawing through the carb also doesn't allow for an intercooler, either. ....

I beg to differ. It all depends upon how you locate the charged/compressed air. I personally know of two guys that are running turbo'd 4-port 13Bs with RB Holley 4777s with FMIC. We built a custom "plenum" and placed the compressed air underneath the carb. It didn't make a whole bunch of sense in the beginning, but after plenty of study on turbo setups, it made total sense. I will try and find the source that explained everything so clearly. I know I bought the book at Books-a-mil......some building turbo systems, or something of that nature.

[Sterling]

"Rx-7s don't allow for flight." is another statement which I'll stand by.
Can you fly one?
Why sure you can; if you drive it off a municipal parking building roof.
Can you figure out how to make an intercooler work with a draw through setup? Yes, of course you can. You can ALWAYS figure out how to make something work, but usually the cost in time and or money makes it prohibitive.
If it were an easy task, it would be the "norm". I'll go out on a limb here and suggest, without even having seen it yet, that the trouble gone through to get it to work in the examples you cite was far beyond the work to have gone the route of a traditional intercooled blow through system. I'll even go as far as to say that the performance gained from getting the draw through to work with an intercooler over using the same components in an intercooled blow through setup, if any at all, probably didn't justify the extra effort in time and expense.
I myself am not partial to either, and I plan on getting a large Camden for a streetported 12a, running my carb, and water injection at high boost. I very much celebrate ingenuity and the work and efforts people make to try new things or improve on things. But for the purposes of illustrative comparison, "no", draw through systems GENERALLY don't allow for an intercooler.

[85rx-7gsl-se]

I beg to differ. It all depends upon how you locate the charged/compressed air. I personally know of two guys that are running turbo'd 4-port 13Bs with RB Holley 4777s with FMIC. We built a custom "plenum" and placed the compressed air underneath the carb. It didn't make a whole bunch of sense in the beginning, but after plenty of study on turbo setups, it made total sense. I will try and find the source that explained everything so clearly. I know I bought the book at Books-a-mil......some building turbo systems, or something of that nature.

From everything I read on turbo systems...Intercoolers after the carb should be avoided as the intercooler is exposed to air/fuel rather than just air like most setups and the fuel from the mixture can become trapped or puddled in the intercooler.

[jtbshaw]

You can get oil from a blown seal in the I/C, but not fuel. The "cold" side of the turbo is nothing more than a compressor. There is no fuel/air mix running through a "conventional" setup.

Sterling, it was actually a simple setup. It looked akward, but it was very functional and didn't cost much (some aluminum sheet and 2 Holley 1/2" base flanges...metal of course).

On the Camden, I loved the ones I have owned. The only thing that most overlook, especially in the South where I am, is the cooling issue. Most don't address this until after the Camden has been installed and see the extra heat generated by the blower. The turbo setups that i have mentioned remained somewhat close to stock cooling due to the I/C cooling the charged air.

Look, guys, I'm not trying to say any of us are wrong or picking fights. There are just a select few people I know that like to have something different. The rotary is the 1st thing (there's not that many around here), and then anything else adds to that. I hope I haven't offended anyone, as that was not my purpose. Just as Sterling mentioned, these are rare cases of ingenuity and against the grain methods of making their system work. I was priviledged to have a small part in it.

[85rx-7gsl-se]

Oh, so you are just running the pressure under the carb? Most of the setups I saw mounted the carb before the turbo inlet, drawing gas through the turbo...these setups would result in fuel in the intercooler.

[jtbshaw]

There you go, I guess I finally explained it so that it could be understood. The system that you mention is very inefficient and I think that's what Sterling was bringing up that the gains were not worth the work involved or cost.

Yes, a custom plenum/chamber underneath the draw through carb allowed the system to fully function with the I/C. I even have a Camden manifold here that I planned to build the same setup for a IDA, but couldn't locate phenolic floats anymore for the IDA. The boost would crush the stock IDA floats, therefore needing a different material. I could be backwards since it has been almost 2 years since I was inside the IDA. It either has brass floats - stock, and needs phenolic for boost, or the other way around. Regardless, no one seems to make the floats needed for boost for the IDAs. Or at least to hold more than 7-8 psi. I was looking for something to hold up to 20-24 psi.

[85rx-7gsl-se]

Sounds cool. I re-read your post and it actually pretty clear, but the idea was kinda out there so..... My bad :( :D

[jtbshaw]

No problem. This ain't the first time I've had someone say that something that I've done is kind of out there. A lot of what we do is one off custom stuff. I just got back from a new client's home. Fuggin' 17,000 sq. ft. home with a built in movie theatre and 2 bay car wash. We get to build his custom stainless steel drop boxes for the in-home pressure washer system that we sell also. 2 weeks ago, we got the order to build 2 custom winch boxes for Dale Jr.'s new car trailer and his team mate Casey (sp? - I'm not a NASCAR fan) Mears' trailer, out of 1/4" aluminum plate. Now we are making Evo parts. Next week we will probably do a production run on our patented stuff......I love what I do.

Anyway, sorry to get off topic. Didn't mean to trash your thread Fikren. I love carbs. Glad we have someone like Sterling to work on/mod the Nikkis. IDAs have been my preference for many years.

[jgrewe]

I go EFI if given the choice. The biggest issues we run into is rules between carb and EFI. We can run a 48IDA or even a 50DCOE w/42mm chokes on any manifold or we have to run the entire stock intake system with any stand alone. The RPM's we run cause trouble with the stock intake runner lengths and the IDA set up is better above 8000 rpm. I'd rather be looking at number values on a laptop than a box of jets and e-tubes etc.
If you like to tinker with electrical stuff instead of carb stuff a Megasquirt can be set up very cheaply with almost all stock parts. The stock injectors on an FC will feed 250hp no problem. If you are running on the street the stock manifold is pretty good for driveability, how much time do you spend above 8K on the street anyway? Maybe half the time at most:driving: