813KR$

My theory on the issue is: If the Holley is naturally wanting to give power at lower rpm's(since they are made for v8's). Shouldnt one of the main modifications be to decrease the size of the airbleeds to richen the high rpm's, for our rev happy rotories? Then get it to idle good and fix the turning bog (that every one seems to think is the biggest prob)?

Or does our high rpm small displacement, suck as much cfm at a high rpm as does the big displacements do at a low rpm? With my situation I think I would like a richer top end?

If anyone has any ideas, I would like to get one good thread on tuning Holleys for our engines! I would like to scare RB and move rotary performance forward!

Jeff20B

iTrader: (13)

Well, according to peejay, out-of-box Holleys like to sit on open plenums, like typical V8 manifolds. What RB does is to make the Holley work on a seperate runner manifold. peejay's solution was to plop an open plenum (like a 1" carb spacer) between the carb and a stock 12A manifold. It worked. Or you could machine a 1" thick piece of aluminum so both primaries can comunicate with each other. It's not about flow here, it's about the vacuum signal. Both secondaries - same thing.

peejay

You have a lot of misconceptions about how carbs and engines work.

Carbs don't care about engine size. They don't care about when the car makes power. They meter fuel for a given amount of airflow going through it.

The problem with the Holleys is that they run super rich at high RPM on a Racing Beat intake manifold. You need MUCH LARGER air bleeds. As Jeff20B said, the problem is the Holley is designed for a plenum intake manifold which has pretty much constant, linear airflow through it, while RB intake manifolds are "independent runner" and the airflow is pulsing, not constant.

BTW - just to clarify things here - "vacuum signal" has nothing at all to do with manifold vacuum, and has everything to do with the air flowing through the venturis.

Hamza734

You'd be well advised to check out Jim Downing's book

http://www.amazon.com/exec/obidos/tg...glance&s=books

It's super rare but it's probably the only book with the goods on carb'd engines. The Racing Beat tech manual/catalog also has a bit on carb tuning.

813KR$

I have heard before, that the holleys run rich up high, but I have also heard black smoke coming from the exhaust is a sign of being too rich. I have not experienced black smoke in my high rpms but have seen it while idleing? I would assume it is running rich down low but leans out in the higher rpm's?

So basically Peejay, you are saying I should get an open plenum spacer and lean out my air bleeds? I have tried the open plenum with a stock carb and it didnt run well, someone told me the stock carbs need to be tuned for the open plenum and that was the reason why mine didnt work well for me. Are you saying the Holley's are tuned for an open plenum? The open plenum, theoretically should keep the vacuum consistant and should run stronger since the vac signal does not pulse? Am I on the right track?

Hamza734

You should REALLY get the Racing Beat manual. They go into the pro's and con's of various carb setups (i.e. Weber vs. Holley) and talk about how to modify any given carburreator for use on a rotary.

It also has a lot of nice tips on engine tuning, suspension, lubrication, cooling etc.. All of it SPECIFICALLY related to Mazda rotaries.

813KR$

Well, the 1" open spacer, is NOT the way for me to go. I had the same results as I did years ago with the stock carb. Ran like ****, total ****!

I have a RB catalog and it doesnt say jack about tuning Holley's. Only fuel pressure, which is 6psi, for Holley's.

813KR$

I have my prims at 59 and secs at 62 seems to be running better than it has before.Since I have opened my intake up to match my engine ports, my fuel pressure wants to drop below 6psi. My holley fuel pump should be in soon and that will fix that problem! I will be taking it to the track soon and see if it IS running better, than Iam bumping up my prims to 60 and see wassup.

Brandt

I have a 12A bridge ported what whould be the best carb for me to run I bought a carter AFB for $50 at a swapmeet. But i found out that one of the shafts is worn out and gas leaks out the side. So now I half to decide wich carb I should use on it. Ive asked a couple of locals and they tell me 650 holley. What are your thoughts about it. Oh by they way 813kr i wired up the direct ignition but havent tried it yet i got the engine pulled to replace the flywheel

813KR$

That is a hard question! It all depends on the knowledge of carbs you have. If you know alot about Holley's/Carter's, bam, there is your answer. If you have plenty of money, then Weber's can be easily tuned to the "T". Weber's have everything adjustable so you can fine tune them exactly how you want them. Do you already have an intake for the Holley bolt pettern? If so, you need to also take that into consideration, Intakes are expensive. If you get a Holley make sure you get a Double Pumper!

Brandt

Ya my intake is for a Holley. So i think ill go with a 650 I found one in the papper today for $125 so im gonna go check it out. For some reason i cant get on my e-mail account is there some other way i can hook up with u. You should have went to the races last night. there was a dune buggy with a stock 12A running 7s.

813KR$

Damn, I planned on going, but thought it got rained out? Thats what I get for thinking! I had PM you with my cell. I dont know much about carbs, but what I have heard about carters, sounds like they are a little easier to tune that the Holley's? Might want to consider that before buying one? How much do you know about Holley's/Carter's?

813KR$

"I have my prims at 59 and secs at 62 seems to be running better than it has before.Since I have opened my intake up to match my engine ports, my fuel pressure wants to drop below 6psi. My holley fuel pump should be in soon and that will fix that problem! I will be taking it to the track soon and see if it IS running better, than Iam bumping up my prims to 60 and see wassup."

Update: prims are at 60 secs still 62 got the fuel pump on and ran a 9.5 in the 1/8, not much better than my previous 9.6. Iam thinking about going to 62's in the prims and 60's in the secs see if there is a difference? Wont be doing that for a while though, I have many other things to concentrate on before that!

813KR$

Calling, Peejay, Sterling, Rx-7Carl and any other carb fella's:

New theory.

Ok, that theory was blown out of the water. How about this one. The rotary engine is inefficient compared to the piston. So do the Holley's not atomize the fuel as good as what our engines need? For example with the Webers, you can adjust the emulsion tubes, which I think is one part of the process of atomizing the fuel with the air. Which in turn should give you more bang for the A/F mix. The reason I have started thinking along these lines, is When I run my car at the track I run headers only. The sound is quit choppy and rough, like spitting. When I had my old engine which had a Nikki, Though loud as ****, it was very smooth and creamy like, with your average rough street port idle. Any thoughts?

Rx7carl

2 different manifolds. Totally different runner lengths and plenum styles. Could account for the difference. Also, I think youd do better to run someting after the headers. Long dual pipes collected into a 2.5" pipe as far back as possible. Run them under the axle if possible.

813KR$

Dual pipes, too much money, too much work. My headers collect to one. This IS a daily (broke)driver!


Shouldnt the runner lengths be in my favor, since the RB intake has longer runners. Should, theoretically mix the A/F better, no? My Holley set up sounds like **** compared to the smooth Nikki.

rmriggin

might as well add my 2 cents to this discussion...
I am running a RB Holley intake manifold that has been bored out about an inch down to make it open plenum. On top of that I have a 1" open spacer. I am running a 600CFM Holley with vacuum secondary. I am using a white spring for the secondaries I believe. My jetting is 57 on primary and the metering plate for secondary (equivilant to 70 jets or something). I have an RB header with 2" straight piped back to a Magnaflow muffler. I am running 2nd gen direct fire ignition using the transistor trick and 2nd gen bur7eq leading and 1st gen br8eq-14 in the trailing. I pre-mix and so far have had great driveability with my setup. One pump and it starts right up (even when it has been sitting outside and it is 20 some odd degrees F (oh yeah, and choke is always wired open). Doesn't smoke on heavy acceleration or on decel (might spit some flames?!). I have not been able to confirm my gas mileage with it yet (gas guage is inaccurate). I am actually surprised with how well it has been doing for the past several months I have been running it. I have been using the stock fuel pump the entire time (really should get a better pump because I am sure I would have even better driveability). So far only adjustment I have had to make on occassion is the idle adjustment screw (need a new spring).
I actually have been curious about putting on a 500CFM Edelbrock AVS carb (more on that when it happens).