DiscoQuinn

I've searched high and low, browsed through 30 pages of results on multiple forums. There seems to be a strong lack in a thorough guide on Carbing a 13B. Does anyone have a good link to every step of the process. There's bits and pieces in each little thread, people debating about it and very few conclusions.

If you've completed this task, can you provide a good explanation of the process?

Thank you.

rx7fcfc

iTrader: (1)

dont do it man youll make more power in the long run with injection system and your mpgs wont go to hell

john ward

iTrader: (7)

Buy a carb and manifold from racing beat. Get a different fuel pump and regulater. Use a distributer and ignitors from a first gen. Buy two coils and your done.

tuscanidream

iTrader: (6)

Why's that? I know I'm comparing peas to pods, but my carbed ninja makes the same power as the fuel injected at way better fuel milage. And carbs are tit. No computers and wiring and crap. Tuning fi is expensive and a pain.

So I guess I need to be schooled in roto carbing as well.?

Hazard15301

iTrader: (5)

Go hang out in the 1st gen boards for a while. They'll learn ya something.

SirCygnus

iTrader: (1)

yah no ****. everything there is carbed.

SuperMattyP

iTrader: (1)

I'm in the process of switching my 88 13b over to a blow-thru carb turbo. It' actually pretty straight forward.

I'm using a holley 6504bbl and a stock T2 manifold and turbo. I'm leaving the stock ECU and ignition system in place and only removing the fuel injection. If the ignition system gives me too many problems I'll switch to a different set-up but I think I'll be just fine for now.

I'll let you know (op) how it turns out. I've got a build thread going right now in the "resotration" section.

SirCygnus

iTrader: (1)

i would not do that. the timing will be too advanced and you'll most likely blow that **** to kingdom come.

ericgrau

iTrader: (1)

Carbs aren't too popular here and I can see why. Carbs basically tune it for one or a handful of points, while fuel injection tunes it across the entire spectrum. Fuel injection does consume a little power letting carbs show off at those certain points but overall the powerband and mpg band is lacking. As in even if your peak horsepower is better your acceleration and overall horsepower may be worse, and even if freeway mpg is higher at a certain speed city mpg or even a different freeway speed might not be so hot.

SuperMattyP

iTrader: (1)

Can you go into a little deeper detail? I'm assuming the difference is that the timing coming from the ECU on an NA engine would be higher than a TII ecu?

Wouldn't a simple MSD boost retard controller solve this issue?

Aaron Cake

iTrader: (1)

If you want to downgrade to a carb, it is pretty easy.

Pick up an appropriate RB lower intake for the carb you wish to run. Mazdatrix as well as some of the other vendors sell them.

Either get a fuel pressure regulator designed to drop the pressure from the EFI pump, or get a fuel pump designed for a carburetor. You'll need to wire the pump to run continuously with the key on, so jump the ignition switch to the main fuel pump relay (unsafe). Put an inertia/flipover switch in series with that line to make it safe.

Get an electronic distributor from the 1st gen years 82-85. Remove the CAS and stock coils. Install dizzy and wires. Use two 1st gen coils or equivalent aftermarket. See the 1st gen FSM for how to wire it up.

And you're done. You have now downgraded your car and can enjoy poorer fuel economy and less power overall.

But wait, you're going turbo....So, you need to boost prep the carb. You'll also need more fuel pressure, so get the appropriate rising rate regulator.

You can't advance timing under boost, so you'll need to lock the dizzy at 15 degrees or so by removing the vacuum can, removing the flyweights and tack welding the plate. Note that you can't use a MSD retard box because the car has two ignition systems; leading and trailing. You'd need two of everything (big waste of money). Now you have a 15 degrees of timing at all load points, so enjoy the poor fuel economy, poor idle, glowing exhaust manifold and anemic performance in the midrange. But hell, it will be really fast at wide open throttle, and that's all that counts, right?

Meanwhile the guys that spend $1000 on an "expensive" and "complicated" standalone are making 500HP, getting 30 MPG on the highway and have a car that starts hot or cold...

SirCygnus

iTrader: (1)

what you can also do is run zero split.

Evil Aviator

You will need to specify the reason for your conversion if you want specific help. For example, are you planning to race in a certain class that does not allow EFI?

Also, I am a bit concerned that maybe you are going to be in over your head on this. Tuning a carb requires a great deal more experience and skill than tuning EFI, and if you don't even have a basic idea of the required components then it is unlikely that you would be able to tune it.

+1

Carbs are analog and therefore generally tuned by curves and lines rather than points. Depending on the carb and the tuner, they can be pretty accurate for a given condition. The main performance problem is that they do not compensate well for changes in weather, fuel, or operating conditions.

With everything else being equal, a carb will have slightly LESS power than a comparable EFI setup due to the venturi effect. For some strange reason the uneducated drag racers swear up and down that the venturi helps performance, but apparently it never crossed their mind that it would be easy to add venturis to an EFI setup if that were actually true, lol.

The proper method is to use a fuel pressure regulator and fuel pump designed for a carb. An EFI fuel pump will heat up the fuel, reducing engine performance.

DiscoQuinn

Finally a decent answer.

I am swapping a free 13B into an '82 corolla wagon. It's a keg, but missing most of the parts. I've found a carb intake locally for peanuts and avoiding changing the entire fuel system and rewiring much of the car. I'm really not to concerned with a power decrease from removing the EFI, as the motor is lighter and will still put out more power than my exploded 60hp 4ac engine.

I am not going turbo, this thread is a bit of a mash up. In any case, I do acknowledge the efficiency of EFI over carburetters, however, the simplicity and diagnosis, and repair of EFI problems on the fly at the track will be much easier on my self, my limited amount of tools and nearly no budget when/if things go wrong.

For the sake of simplicity I'm going carb. I have done this complete swap before, a 13b S4 EFI into a carb'd corolla, and found the process quite exhausting.

It's really irritating coming to a forum and a majority of the replies having nothing to do with the topic. If I was concerned about fuel economy I wouldn't be putting a rotary in my car.

Evil Aviator

You could have avoided a lot of the irritation had you explained your unique situation up front.

See the Racing Beat Tech Tips on setting up a carb:
http://www.racingbeat.com/mazda/perf...lications.html

DiscoQuinn

My apologies. Thank you for the great link.

thejallenator

iTrader: (14)

1000 bucks seems pretty low for a full standalone. itll be another 100-400 bucks for a tune. then if you add to the car you have to get it tuned again, and all this time you are putting the motor into someone elses hands. hoping they dont f it up.

now with a carb just abhout anyone with car knowlegede can tune a carb, and it wont cost you 1500+ more like ~100 bucks for jets and an afternoon of your time. but no matter what someone is going to say im wrong. watch

SirCygnus

iTrader: (1)

its true, but ultimatly, you are wrong. i say that just to spite you.

different strokes for different folks.

gerald m

I know what you mean DISCO about negative input but be patient these guys do know there stuff they just need a good explanation of what you are doing... Anyone having problems with poor power bands on a holly can do a few things to help overall performance .. For racing on and oval track we use to have problems with ( dead spots ) at different rpm .. I found that if the power valve is totally removed and the hole plugged ... Then you jet the thing up about 6 sizes to start with then just experiment up or down until you have the right combo ... When the power valve is blocked off the carb no longer relies on different pressures in different parts of the carb to preform but delivers in ratio the same amount of fuel to air right through from idle to wide open .. This operation should not be attempted buy inexperienced hands but it does work with very good results and will preform as good or better than that dam fuel injection without problems half way through race day .. Holly has a huge selection of jets compared to most.. With big engines we cut the back of two 500 cfm hollies mounted them back to back to keep them closer together same as they did for the 440 six packs nothing worked better.

Aaron Cake

iTrader: (1)

Ah, it helps to know the context. Otherwise we all just assume you are converting a 2nd gen to a carburetor. Just one nitpick though, you don't need to rewire the entire car to run EFI. A standalone system is just that, standalone. It needs only a few connections to the car such as 12V, ground, and IGN. Now obviously, you'd have to swap fuel pumps and add a return if needed.

Going with a standalone system is far easier than adapting the stock ECU. However, once the stock ECU harness is simplified down to the bare minimum, then it's about as many wires as a typical standalone.

It's all about context. Without knowing this was a swap, going to a carburetor seems silly. And there's nothing to say that a rotary has to be poor on fuel. My 500HP 2nd gen, on a well tuned standalone, does about 25-27MPG on the highway. And that's with a bridgeport.

An entry level Haltech is right around $1000. And if the car is stock, the rest of the fuel system can be left alone so you can use the existing injectors, pump, etc.

-Holley manifold for 84-92 6 port: $268 ( http://www.mazdatrix.com/getprice.asp?partnum=16476 )
-Holley 600CFM carb w/rotary mods: $960 ( http://www.mazdatrix.com/getprice.asp?partnum=18045 )
-Add a new low pressure fuel pump: $100, parts store
-New set of plug wires: $59 ( http://www.mazdatrix.com/getprice.asp?partnum=W4502 )
-Used coils (or new aftermarket), used dizzy: $??? (free to $100)

Oh yeah, and a box of jets: $100

The Haltech Spring RE is just around $1000.

And no, not anyone with car knowledge can tune a carb. It is just as easy to poorly tune a carburetor as it is to poorly tune an EFI system. Except that poorly tuning a carburetor is generally faster than poorly tuning an EFI system.

thejallenator

iTrader: (14)

still going with this haltech set up that wont fix his issue, a standalone does a man no good if he cant tune it. but whatever, you know all there is to know about these cars so nobody can beat you in a fight.

as for the tuning a carb, i guess what i shoulda said is that its a lot easier to get the carb tuned than the ecu. i know a lot more people that can tune a carb than tune an ecu, in fact ive never met a person that can tune an ecu.

and your prices for going carb are a little biased, the man doesnt need to buy everything brand new from mazdatrix, most parts can be picked up here for nearly half of what you said.


now after that, i would like for you to explain how going stand alone can simplify this. and before you say a word remember that the guy isnt going to keep the car the exact same way so the car may need to be tuned more than once. and to me paying a man to adjuct the ecu everytime i change my car doesnt sound fun, id rather learn how to jet a carb, or find a buddy that works for beer and pizza

Aaron Cake

iTrader: (1)

I agree, in the OP's case, sticking with a carb setup is probably the way to go simply for ease of installation. He has already mentioned that he has done the EFI version before and is familiar with it. However, what I have an issue with are those people who automatically say that installing a carb instead of EFI on a 2nd gen is "cheap" and "easy" and can be tuned "fine".

It may be "easier" to tune a carb because there is very little tuning that can be applied. Apart from changing jet sizes, changing venturi sizes and a few other tweaks to set the characteristic of the fuel curve over only a few points (idle, primaries, secondaries, WOT) there isn't much that that can be done. The result is a "tune"that is faster to achieve than an EFI setup, but at the same time, the tune is far more crude. And then when the weather, atmospheric pressure or VE of the engine changes, the tune doesn't and the car doesn't run as well as when the carb was first set up.

Then compare that to EFI where even the most basic ECUs have a 12x12 table which allow you to set th fuel curve at exactly where it needs to be. And the fuel curve in infinite, because the ECU applies corrections to that curve based on temperature, atmospheric pressure, AFR ratio, throttle position, etc. etc. to keep the fuel curve ideally. Yes, it takes far more time to set up, but the result is an exact tune, not an approximate tune you get with a carb.

And honestly, tuning an ECU is not exactly hard. Grab a laptop, plug it into the car and start tweaking. The principles of tuning are the same whether it be a carb or an EFI system. Pick up a book on basic tuning ("Performance Fuel Injection Systems" from HPBooks), read it, and then learn a new skill instead of refusing to even consider it because it is "hard" and "complicated".

I wasn't aware that used parts were allowed, so that changes things a little. Just like carb parts, standalones are available used as well. A friend a few years ago bought a Haltech E6 for $200 complete with harness. I have two spare Megasquirts sitting in my shop right now that are set up for the 13B and cost nothing.

Yes, in his case, the carb is probably the best choice. But ditching an EFI system and converting to carb is silly, and mainly done due to misunderstandings. Be careful about paying in beer and pizza though, because the result is often a job worth a few beers and a pizza.