Thinking about goin carb
 

I am thinking about goin carb on my 13b 6-port.. i have a RB header strait through exhaust, S5 rotors in my S4 motor, removed emmissions, ps, and ac, and removed 5/6 port sleeves... i was wondering what would be needed for me to run a carb.. like what do i need ect.. also what size carb? vac or mech. advance? DP or single feed? any aditional info and results of this and pointers in the right direction would be really apprieciated. Thanks
Dave

First off, I don't know a whole heckuva lot about carbs. That said, there's a few things I do know -

You can't just get a carb from Summit or something and put it on - rotaries are really odd as far as carb settings are concerned, and it's best to start with a carb that's already set up or at least close.

You're gonna spend some serious money to go carb, too. Check out Racing Beat's site - I think they have a 6-port 13b carb setup. I'd also ask around in the 1st gen section - they're typically more handy with carb knowledge.

Dale

You would want to get a Weber or Dellorto already modified for a rotary and preferably one with the proper jets. Racing Beat makes an upper manifold that lets you bolt to the stock lower manifold. My carb is a Weber 48DCOE off an older Formula Mazda car. It runs so well we are afraid to rebuild it. We have tried to duplicate the carb(same jets, choke, emulsion tube, etc...) but have never got one to run as good as this one. Try www.thepartstrader.com if you can't find anything for sale on the forum. Just remember It might be cheaper to get a used haltech than a good working carb setup.

How do you like it? How noticeable the HP/TQ is? I know they make a LOT of difference, I've seen it, but haven't ride on one :(

You will need to disconnect your current in tank fuel pump and get a lower 6-7 psi 60-80gph fuel pump (inline fuel pump). Then you are going to need a distributor (out of a first gen most probably out of a junk yard or buy a rebuilt unit at a local car parts store). Two coils (for example two MSD blaster coils). A fuel pressure regulator, and fuel hose to route the new lines. I will be going with the Webber carbs, but if you do not know how to tune them you can buy a book on how to tune Webber and side draft carbs, I believe the book is made by SA publications. You can buy it at any muscle car performance parts store like Vic Hubbars, Summit Racing… Have fun.

Re: Thinking about goin carb
 

Yup, RB has the upper manifold that bolts to the stock lower manifold (you might get the 5&6 ports to work). Atkins also have a kit, and I know there is another palce but I just can't remember the URL :(

why go to a first gen distributor? The spark side of the engine shouldn't be affected by the fuel side. Or am I wrong?

An aftermarket fuel pressure regulator is all I would recommend for the fuel system mods. I've converted a couple EFI vehicles to carbs and found that the electric in tank pumps worked better than trying to add another piece of junk in the lines. The fact that the EFI pump will be cycling more fuel ensures that you probably won't vapor lock either.

I've heard about this, people running a carb with the stock ecu running the fire side...........

Anybody?!?

Jimmy is right. What I did was get a brass T fitting for the fuel line coming into the engine compartment. Route one side to the return line and the other to the carb. Put the fuel pressure regulator and an inline filter before the carb. I've seen this setup work on a car without the regulator but I wouldn't suggest it.

This is on my FP car so I don't know how long the pump will last if driven daily. Probably the same as a FI car but I'm not sure.

KNONFS - This carb was on the SCCA Alabama Region top CSP(1st gen RX-7) car about 7 years ago. It won the points battle two years in a row. I got to ride in the car and was extremely impressed with the power. They had put a stock S4 6-port engine in it to replace the 12A. It really pulled hard. I think the biggest improvement over the factory FI is eliminating the AFM. A properly tuned Haltech(or whatever EMS) will deliver the same performance if not better. The reason I'm starting with the carb is a friend loaned it to me till I can get all my FI parts together.

I agree with you, but the stan alone itself is close to $1100 at least plus the tunning. Atkins has a webber setup for $700. Not that I'll be going the Webber route, but who knows what might happen in the future ;)

HOLLEY 650 CFM.. RACING BEAT OR JAY-TECH 6 PORT INTAKE...JAY-TECHS ARE RARE THO.. AND U WONT BE ABLE TO FIT AN AIR FILTER ON TOP CUZ OF CLEARANCE(BUTWHOCARES,HALFOFTHECARB'D7'S DONT USE FILTERS) FUEL REGULATOR.. U COULD USE THE 1ST GEN DISTRIBUTOR.. THO MY COUSIN USES HIS STOCK S5 IGNITION...IM WAITING FOR MY REBUILD TO GO CARB MOST LIKELY... MY COUSIN RUNS HIGH 13'S LOW 14'S WITH THE STREET PORT 13B HOLLEY SETUP.. AND HE HAS A 90 AND I HAVE A 91 BOTH NA'S OF COURSE AND HE SMOKES ME BAAAAAAAAAAAAD.... I THINK ALL THAT HP COMES FROM NOT HAVIN THE AFM TO RESTRICT ANY AIR FLOW.... ALTHOUGH SOME PEOPLE DONT LIKE CARBS BECAUSE I ADMIT.. ITS OLD TECHNOLOGY.. AND WE HAVE EFI NOW.. NOTHING PULLS LIKE A CARB SETUP ON A NA ROTARY...

oops sorry for the caps....

FI is by far the better of the two methods of fuel management, but it's also far more complicated and expensive to fully realize an engines potential with it.

For the cost of the fuel injectors alone, I can buy a carb set up for my engine and make the same power of a dialed in haltech. (or whatever)

The carbs won't get the gas mileage because they don't know when the engine is under load or not, just that its pulling "X" amount of air at the moment. But, I can buy a lot of gas for the added expense of all the additional stuff needed to make an aftermarket engine management system work on my engine.

You can use the factory intake. Just strip the emissions crap of it. You already have the fuel injectors, fuel rail, throttle body, etc...... Pull the AFM off it and put whatever round air filter will fit on the intake tube thing. Tuning it properly is no different than properly tuning a carb. You go pay for some quality dyno time. I think tuning the stand alone EMS is probably easier. If you want the change the jets in the carb you have to shut the engine of and maybe let it cool down some. Then remove the jet or whatever to make your change or at the minimum twist a screw while the engine is still running. With a stand alone EMS you can sit in or beside your car, goto a certain screen and change some numbers to fatten or lean the fuel at certain rpm's. To me its just easier than getting under the hood again.

Sadly it all comes down to a money thing for me and probably many others so you have to get what you can afford.

Holley carb kit - $800
Can you use the carb kit and retain the EGI computer for spark? I'd imagine it would be unhappy but I've never tried it... so let's assume yes.

Malpassi regulator (allows use of stock EFI fuel pump) $130
-OR- Holley pump and regulator ($90) (this requires removing the EFI fuel pump and fudging the pickup with some tube, is your time worth saving $40?)

Guaranteed to fail emissions - variable cost (swap back to EFI every two years?)

No matter how you slice it you're almost at $1000. Fairly sure you can get a new E6K for a little more. Heck you can probably get a used one for a bit LESS than the cost of the Holley setup now that the new Haltech system is coming out and people will upgrade.

Should be able to find maps for a 6-port online.

Atkins sells the Weber kit for $750, or you could pay an additional $245 and get their MT8 EMS. However, the carb kit is much better if you are the type of person who likes changing out jets and spending several hours retuning the car every time the weather changes. :D
http://www.atkinsrotary.com/fuelinj.htm

480cc injectors won't make the 260hp my engine is capable of... I don't think you'll even try to argue this one.

So at a minimum I need a stand alone ECU ($1100) and 4 injectors ($500-900) and larger fuel pump ($150)which puts the cost of retaining FI a mere $1750-2200.

So how is it that the $750 carb setup is more?

http://www.rceng.com/technical.htm#WORKSHEET
480's look about right to me.
(Stock fuel line pressure is 34-40psi, and BSFC is about 0.5 stock but can get down to 0.45 when tuned well with an EFI)

However, if you really want a carb, then go right ahead and get one. It's your car.

260hp? going bridge ported then?

480? Stock NA injectors are 460cc/min, and can make ~260hp @ 85% duty, but that's definitely their limit unless you increase fuel pressure. A pair of Turbo 550cc/min injectors in the secondary positions up this to ~290hp, which is strictly PP territory anyway.
If you're making 260hp, I presume your engine's bridgeported? What fuel system are you using? You can get ECU's for less than that (I've seen E6K's for ~$1000 and Microtechs are even less), and if you pay $500-900 for a set of 13BT injectors you're an idiot. :rolleyes:
Whether you go carb or EFI, tuning costs will be similar (personally I think EFI would be cheaper because it can be tuned quicker), and aftermarket EFI will always outperform a carb (and I don't mean just peak hp!). If you're spending all that money, why not spend a couple of hundred more to get a vastly superior system?

My car is an 85 gsl, and i have a carb. Just a warning, they are a pain in the ass.... I would kill for EFI.

I just love a carb vs. FI debate.

If 4 injectors cost $500-900 just buy a wrecked TII and sell some parts of it to recoup some money, keep the injectors and send them to RC Engineering for cleaning and so forth. Thats what I did. Bought the unwrecked but not running 87 TII for $800(bad wiring problem) I sold some parts for $500 +/- and keep what I thought I would eventually use. I could have easily broke even but I gave the engine/transmission to a friend for his project. www.rotarymiata.com

Carb's not a pain in the ass, it just usually costs a hell of a lot less. Once it's tuned, you're golden. (The same can be said for EFI) If you're starting with a carb'ed car then it's much cheaper to stay carb than it is to convert to EFI.

HOWEVER, when you're starting with an EFI car, it only makes sense to go standalone EFI vs. convert to carb. Carbs are great and will get you 90-95% there, but if the cost is so close as it is in this case, why NOT go standalone?

Modified Bridge port actually. Rather than cutting the bridge open I'm swiss cheesing the area the hole would be in with a drill. Should be more stable for vibration and much easier on the corner seals. Should be a fun 10Krpm motor.

So why are all the turbo guys running 1000cc injectors to make 260hp? If I could get away with 100 bucks in used injectors and a SAFC and still make my power goal I'll keep the FI.

uh...

you're better off making the one big eyebrow than cutting a buncha little holes.

i don't see any turbo guys running 1000cc injectors to make 260hp! unless they're running only TWO injectors, or they're complete dumbasses...

I've got one for sale. PM if interest or email.
https://www.rx7club.com/forum/showth...hreadid=105994
-Mark