sweetege

Who's done this with a K&N intake a header and straight pipe or straight thru mufler or (specify) and with a holley carb (500 to 600 cfm or what ever you use). Anotherwords what would be the best setup?
Thanks,
Michael

SilverRocket

150hp is more like it!

MosesX605

Yeah. 150 hp is probably the best you can get from a NA stockport 12A. Which isn't bad, considering that you started from 100. That's a 50% increase from bolt ons!

For exhaust, there is really only one option, IMHO: Racing Beat. www.racingbeat.com sells the best exhaust system for the RX-7, and they also sell the Holley kit for the 12A, premodified. If I were you though, I'd check out Sterling on this board, for less than the Holley Carb, you can send your carb to him for modifications that will increase flow significantly.

sweetege

I found a 600 to 700 holley around here rebuilt for about $170 (around there). Is that good?? The reason i did'nt want the stock carb was because of all the emissions crap, I thought if i take all that stuf of then it would leave holes. and is that too big of a carb?
Thanks,
Michael

enigma32

It's not a problem to remove the emissions stuff and still use the stock carb.

I believe pratch has a tutoral for doing just that.

rotary emotions

Best carbs to use are Weber, Dellorto or Mikuni. Holley is an option in the states since it's easier to get, but it ain't the best solution. And 200hp is way over it. Expect about 150 with complete RB system and a good intake/carb. The mikuni/rb combo I have is estimated on 156hp, though I haven't got proof of that. It's just what was said when they were sold new.

Wankelguy

That Holley is too big, and you will not see anywhere near 200hp without porting work. In fact, 150hp may be a little bit optimistic with just carb and exhaust work. It really depends on how good you are at tuning.

jr69187

damn i wish i had mine on a dyno before i blew the water seal cause it was finnally runninf right. i would say i had alittle over 145 hp maybe better. i know wiht the blown seal i was running quarters in 15.46. which was good considering it was running compression through the radiator.

jr

mar3

iTrader: (8)

He didn't say stock port. A little hard for a big streetport, but should be easy for a bridge-port. Piece of freakin' cake.

Sterling

Here's a quote from Holleys 1976 book, "Holley Carburetors & Manifolds"; page 6 under the paragraph, "Air Flow Requirements";

"Because the air an engine consumes has to come in through the carburetor, knowing how much air the engine CAN consume will help you select the correct carburetor."...

-Engine Displacement - expressed in cubic inches displacement (CID)

-Type of Engine - two-cycle or four-cycle. Two-cycle engines have an intakestroke per cylinder every revolution. Four-stroke engines have an intake stroke per cylinder every other revolution.

-Maximum RPM - the peak RPM which the engine will "see". ..."

...It then gives the following formula for a 2 cycle engine - which is the one that applies to rotaries;

(CID x RPM x Volumetric Efficiency) divided by 1728 = CFM.

The formula for a 4 cycle;

(CID divided by 2) x (RPM divided by 1728) = CFM [this effectively cuts the displacement in half for the formula]

There is another whole page on determining VE (volumetric efficiency), but without a dyno of some sort, you can't get it on your own. You can use 100%, but the outcome would be a high CFM #. It could be argued that you should use 100% VE in an effort to always attempt to achieve it, but experience tells us that it's not possible.
I use Paul Yaws determined 88% VE from his publicly released dyno testing with what I believe to that date was one of the most optimum carbs you could put on a 12a (his carb). He may have set the calibrations to the best possible temperature and air density to fluff any resulting # he could for marketing purposes, but I don't really know.
So let's use 88%, which BTW, is around the same (a few % higher) than your average bigger piston engine with auto driveline.
We'll use the two-cycle formula because the rotary fires both chambers once every revolution. (three sides, but the internal gear means the eccentric shaft spins three times for every rotor reveloution.)

(CID x RPM x Volumetric Efficiency) divided by 1728 = CFM
(70 x 8400 x .88) divided by 1728 = CFM
517440 divided by 1728 = CFM
299.4 = CFM !

All that means is that if we put a 300 CFM carb on the engine, it had better be a damn good carb that flows FLAWLESSLY at its maximum flow.
No carburetor on earth does that. Typically, there is a perfect flow band in a carburetor that will precisely deliver excellent air / fuel mixture throughout. As it reaches its max flow capability, it's gonna start acting funny; not flowing smoothly, that sorta crap. So we want a carb that is over 300 CFM so we are'nt maxing it out and getting into the "gotta work fer it" part of the high end RPM band.

Yaw says the stock Nikki flows 365, but Carl just alerted me to the fact that he quotes a few different flow figures on his site for the stock carb. Go figure. Carl will be testing flow rates very shortly. But what I think this clearly illustrates is that there is not so much a need for a bigger carb as much as for a very TUNABLE carb. You know now that the engine will max out at around 300 CFM without any cold air ram box, or other fancy tricks, and you want to select a carb that can flow a bit more, #1 to be sure you got more than just the minimum, and #2 to be sure you're not making your carb work too hard at the highest flow point.
Makes sense that a 425 or so carb that flows really well would do it. The biggest thing that people don't realize is that the carburetor needs flow VELOCITY to work really well. The flow is determined by your engine. So put a 600 carb on there, and the engine wants 300 CFM, that's a slow flow rate for that big carb. Put a 425 on, and that's a fast rate for that carb. The VOLUME is the same, but the VELOCITY is very different. The smaller carb will have more vacuum action to "suck" the fuel out of the main circuits...WAY too rich, if it wants to. But that's good, becuse you can install fuel jets that determine maximum amount of fuel it can flow, and you can install different air bleeds to "bleed off" that hi vacuum signal, thus curtailing your air fuel mixture to what you want.
On the bigger carb, there's probably plenty of vacuum signal...once the carb gets the flow velocity up. But that velocity might not happen till you're in the 4K RPM range. Idle circuit, which does'nt rely on vacuum (as there is none when the throttle's closed) and the transition circuit become EXTREMELY important in these carbs in order to eliminate bog associated with mashing the pedal.
In the smaller carb, the velocity is there down lower in the RPMs, and it will be more responsive.

Now having said all that, there is a trade off...Most of the driving done in performance rotary cars is going to be relatively high in the RPM band. Just by its very nature, the rotary needs to be driven at least above 4K RPM to take advantage of any performance the engine can give. So here's where the carburetor size theorey can get lost for most. Driving style plays an enormous role in proper carb selection.
Once you're up in the RPMs, you might not notice so much the difference between the two carbs rated CFMs.

When we rework Nikkis, we open the primary venturis and remove a few bits that are obvious impedences in air flow. We rejet it, and install threaded stock emulsion tubes to which Holley style airbleeds can be installed. This, along with my accelerator pump modification, will give all the best you can expect from a Holley 425 CFM carburetor...and it's still a stock part on your car. An equivilant Holley carb, however, will not offer the tunability of the Nikki carb...EVEN STOCK!!!

Anyway, hope this helps you to understand that bigger is not necessarily better.

Rx7carl

Agreed, a 700 Holley (assuming a vacuum secondary) will probably never open the secs.

Im still tweaking the #'s, but Im getting about 300 CFM for the stock Nikki uncorrected for baro, humidity and temp. And that isint big enough for even a stockport engine for max performance. Your guestimates are spot on I bet Sterling. 465CFM is the smallest 4150 Holley I know of (but then Im no Holley expert). And thats what RB matches to a stock port motor, wonder why.....

And velocity is VERY important, I bet thats why big 2bbls dont work as well down low, hell thats why they came up with 4bbls isint it?

GUZZLR

does anyone know how many cfm a 48mm IDA Weber will flow?

From my experience they are a very efficient carby!

sweetege

so sterling pm me back and tell me how much it would be for you to rework mine, and after that what size would it be. And again is 170 good for a rebuilt 700?
Thanks,
Michael

Rx7carl

Do NOT use CFM numbers to compare 2bbl and 4bbl carbs. They are baselined at different pressures. Like comparing apples and oranges.

The_7

hey rx7carl, can u explain in more depth why u cant use cfm ratings to compare the 2 and 4 bbl carbs?

Barwick

www.sdjmotorsports.com does an ITA buildup for 12A's that I believe puts out 162 at the flywheel with his whole setup (intake, engine, and exhaust). No porting or anything.

Rx7carl

Like I said, they are flowed at different pressures.
The standard for a 2bbl carb is CFM@3"hg and for a 4bbl its CFM@1.5"hg. This may have changed but AFAIK thats how it is rated.

WHat happened was when 4bbl carbs came out (circa 1950's), they tried to test to the standard that was 3"hg. Their flowbenches wouldnt pull that much vacuum on a big 4bbl so they derated the test to 1.5"hg and thats been the standard for 4bbls ever since. They really should apply that standard to ALL carbs so they can be accurately compared. Again AFAIK the SAE has never done that. If anyone has anymore info on that please post it.

steve's dog

if this gives you any idea....my fb on a stock port dyno'd a 117 (rotorhead) with a K&N filter, dellorto carb running rich, and pacesetter headers, gutted cats, and a pacesetter muffler. so with full racing beat exhaust and a well tuned carb, you know what you can expect.

rotarygod

iTrader: (1)

The Holley manifold is the single best flowing manifold for the rotary out there. It even outflows the Weber style manifolds. Notice I didn't say it neccesarilly makes more power. One way to increase the power of a Holley equipped system is to do a small amount of porting on the manifold. By grinding away some of the wall directly under the carb between the left and right runners of the corresponding ports (primaries to primaries, secondaries to secondaries) you can get more power. Don't get carried away and go too big though. The bigger you go, the higher your torque peak goes too. This gives you the benefit of pulse interaction between each side of the engine which it didn't have before. As with any gain there is a loss too. A trade off for more mid to high end is decreased low end. I have driven both setups (Holley and Weber) and I liked them both. I personally thought the Holley system felt better on the top end but then again each engine wasn't set up identical to the other one in regards to porting so it isn't a very accurate comparison.