I have been driving my SCCA ITE RX-7. For almost 3 years. and during this years. one thing really bother me. Not too many people can answer me the Question of Peripheral port.. However. since I need to drive the car faster at first place . it doesnt really bother me a first.
BUt now a day. I begein to drive better so the same Q come back...
How come my 13B PP is not making power pass 8000RPM.

A little bit of my engine first. one of locoal GT3 Racer in SCA build it for me( Gary uematsu). He use the Pablo Mobius's Peripheral PORT design some thing similar to RB PP design. and I use brand new 1987 Turbo Housing and NEW 1991 NA Rotors. Blanance the motor and fly wheel. RX3 shaft with oil jet mod. Compertion oil pump(120PSI)
I also have WEBER 48 IDA. and Racing beat header and custom 2 inch EXauest that merge around rear diff area.
The best power I got from this combo is 212.5 at 7800RPM( see the pic below). I was kind da disapoint. but since I am still pretty new at Road racing. SO I figure to drive it faster first.

I drove this set up for little over a year. and I happend to talk to Pablo Mobius him self at locoal race track. he told me the problem of my set up is my Carb was too small. he told me to got Gene BERG 58 IDA with 48mm choke, 265 main jet and 120 air( he told this set up will go for 290 WHP. but releastic I will be happy if I got 250WHP+). also a locoal GT2 racer EVAN xxx( sorry evan forget your last name..) my intake maifold is also too long..

After few month of saving. I finally got the money to buy me self a Brand new 58IDA from geneberg.( all I can say they do a amazing job on this carb).

I went to Performance solution( a fab shop behind MAZDATRIX that do all the fab work for DAVE and BOB's EP RAce car) to get my custom 58 intake manifold. The owner MATT, also point out. my intak manifold was not level at first place. so need to get that done also.MATT manage to short 1 inch off from my old intake manifold

After all the work done. I went to Dynamic Racing Solutions. to use their Dyno JET(02/20-05). During the first dyno pull(4th gear WOT). due to my WAter temp problem. they just shut the car off,A big NO NO on race carb set up. so they flood my engine. and since I was on a group dyno day. so there are still people bhind me waiting. so that was the only dyno pull I got. A much better curve compare to my 48 IDA.

 

By looking at my Dyno Graph. I think I have few problm. Acoarding to the wide band they are using. I am running too lean at 5000 to 6000, A/F at this range was hight 13 and low 14. from 6500 RPM up the A/F got little rich but still too lean form my understanding? I think idealy you should have 11.5 for WOT?. So I might need to change my jet again. I might try small air jet and bigger main jet next time mabe 110 on air and 275 on main.

By compare to the DATA avaiable on the net. I think the power I am making is not too bad( mabe a 10 HP lower at same RPM RANGE), but the power will not extant behind 8K

My power still drop behind 8K but not as bad as my old intake setup(not level and too long). The guy build my engnie say the shift point of this engine is 8.5K, but every one told me PP will just start to make Power at this RPM. DAVE from MAZDATRIX even shift his Street port engine at 10K....

Mabe my port just not big enought?

the problem of exauest ?

Any advice is welcome,
REGARD
Thanks in advance
JAY

 

mazdatrix sells a pp that makes 310 hp, im really shocked at your numbers.

http://www.mazdatrix.com/r-20.htm

i have no experience with pp's, but plan to do it in the future -- electronic fuel injection.

 

I think the number they use (310-315) is base on 48 IDA 9K+RPM.


Good luck on your future PP project. Hope you have some GREAT muffler stand by. you wont understand a Tiny 1.3 13BPP will have noise level of Top Fuel DRAG CAR... Some time it will take mucher longer than you thought to MAP a 13BPP. because not too many people do this type of stuff. I was consider to do a EFI. ( I have every thing ready.HALTECH E6K,55mm IDA style throttle body. and 990cc injectors.but a last min change my mine, because Carb was easier to setup and more people have experience of it .

 

What about exhaust diameter?

-Fanis

 

what's your ignition timing at? Did they set that up for you? You definately should be making more than 235. Racingbeat is making 300 with a 51 IDA on a 13b PP. I would definately just play around with the jetting as well, maybe try to richen it up and see how the engine reacts. ask some fast PP guys whats they're ignition timing is set at. Basically just try to chase down what could be hindering your power.

 

300 rwhp or 300 flywheel HP?

235 rwhp = ~ 276-293 flywheel HP (15-20% losses).

I'm not a tuner but it seems to me you wouldn't want it as lean as 14:1 @ 5500 rpm nor as rich as 10:1 @4500 rpm. I'd think the 12.5-13.5:1 a/f ratios is where you'd want to be. 11.5:1 seems like turbo engine a/f ratios.

 

mm.. I set up my timing use what RB provide from their Catlog.( cant rember how much). I think 300HP. is engine HP, not on wheel. yes, once I finish my custom air box I will go out to do a dyno and play with jets!!
I want it 300 Hp Flywheel hp or 250WHP. About the suddent drop of A/F at 4500RPM. I think this is normal for WEBER IDA carb. IDA got one of those PUMPs. it will shot extra fuel to your intake if you WOT it. it will cause suddent drop of A/F
but for sure I will rich up the mixture at Top end

 

sounds good, (forgot they're bragging rights are like FWHP) let us know how it turns out.

Ron

 

would it be possible to muffle the exhaust sound of a pport engine enough to be "bearable" on the street? i dont mean quiet or anything, but not as loud as a drag car! lol. i know this would lose a lot of power but im just wondering how loud would it be with a really restrictive stock type exhaust?

 

yep it is possibe. I rember the First Rotary power CAR.(NSU 80). it got PP engine.

I dont know how quite you can get. it is possible, some people do drive PP on street, but not many.

NO TQ at low end. and too much over lap. you need special gear ratio to make it work right . you will see tone of blue smoke come from your muffler during idile.... etc etc.

how ever one day. I hope I can build a 20B PP street driving RX-7

 

The reason you don't have much power is because you don't have any hi rpm torque. Your torque is falling off way too soon.

What size venturies are in the carb? Should be 45 or 46 mm.

Is your air filter big enough?
Do you have a cold air box built around the air filter?
Is your exhaust free flowing?
What diameter is the throat of the collector where the 2 pipes merge together?
What is the pipe diameter after the collector?
Is the muffler a straight thru muffler?

My 13B PP motor likes to run rich, around 12.5 A/F ratio.
Set spark timing at 24 deb BTDC leading and 16 BTDC trailling, measured at 3500 rpm or above.
Use only NGK -115 spark plugs.
With those rotors, run 93 octane Amoco or Chevron gasoline with 100:1 oil premix.

 

That engine needs more fuel. Way too lean on bottom end. Try to get the air/fuel ratio to around 12.5 or 11.5. It should make more power at a higher rpm. I bet that motor wants 25-32*L total advance.

My 12a Jbridge put 205 to the ground @ 9200rpms and it liked 11.5 on dynojet WinPEP.

Evan Gardner made peak hp @ 8800rpms using smaller endurance size PP sleeves back in SU/ITE days.

 

Just a curious question. I noticed that he used 87 turbo rotorhousings with 91 N/A rotors. Now would power output be affected because of the timing difference with s4 and s5 rotorhousings? There is a slight variance in the leading spark plug hole placement between the two series.

 

Nah. That's pretty common to use turbo housings because you don't have to port out the wing that's in the n/a 13b exhaust port. There is a varience but minimal impact.

 

The collector for this setup really needs to be 2.5" ( bare minimum) to 3" and the muffler had better be a straight through design. No "turbo" mufflers as one very well known rotary person keeps recommending. Power will absolutely die compared to it's overall potential this way. The carb also obviously needs some retuning. I don't see it as an issue with the intake.

 

Good point.
During my dyno. I did not have any Air filter(I still need to build mine air box)

yes my exhaust is pretty free flowing... I have Racing beat road race header and 2 inch pipe all the way back.
the Collecotr size is about 2.5 inch wide. the throat should 2 4/3 inch
The muffler I am using now is MAZDAspeed LAVA Rock muffler with 4inch inlet and outlet. plan to add another Eddlerock RPM stainless muffler.

BTW when I mesaure the length of my exhaust. from Racing beat header back. it extend about 85inch so with header my exauest will be more than 100 inch long. mm.. I think I found another problem. the exauest I got is too long. RAcing beat recomand the exauest to be 89-94 inch long, how if I do that I will need to cut a big hole to place the muffler. I think this is what I will do I will design a 89-94 inch system and it will merge at middle of car. then I will run a megaphone collector to a bigger dia pipe. and collect with my LAVA rock...

on my plugs. I use 10.5 on leading and 11.5 on trailing. mabe next time I will use 11.5 on Leading.

I think during my next dyno Tune. I will try to rejet my CARB. mabe increase the fuel pressure( I was 6 psi of fuel, however during 48 IDA time I did run up to 10 pis at one point, and my car did not flood )

and will check about ign timing...
thanks for all the help

 

some more thoughts how far off are you from others dyno numbers with 13b PP at the wheels? What kind of Apex seals are you running? I don't think that 6" difference makes a huge difference, its all about tuning the car to your needs. RB preaches long primaries where as SDJ collects right where the RB header stops, who's right? I'm not sure. maybe the 235 RWHP isn't as far off as we're making it.

Ron

 

Something still does not look right on the DRS dyno sheet. The torque numbers just don't look right. On everyone else's dyno sheets, Torque and horsepower numbers always cross each other at 5250 rpm, but your's do not. Maybe I just am not reading your dyno sheet right.

The RB road race header was way ahead of anything else when it first came out, but it is not the best header now. The problem with the RB header is that the pipe turns too sharply, too close to the engine. There are 2 newer headers now, that flow better. The SDJ header is really good and makes big power on PP motors. Since it has a collector built in, then the rest of your exhaust system is simpler by running 3" pipe all the way back. The downside of the SDJ header is that it is very expensive, used to be $550. One of my competitors used one on his 12A PP SCCA GT-2 racecar, and it was a very powerful car.
The ISC header is almost a bolt in replacement for the RB header, but it flows much better. The pipes come straighter out of the motor before they turn, letting the exhaust get out of the motor easier.
Your exhaust system looks like it could use a better transition, a more gradual expansion, from the collector to your muffler.
I don't know the details on the spark plug placement on your rotor housings, so my spark timing numbers I gave earlier do not apply to your housings. Keep in mind also that the Mazda Factory Racing PP housings had different spark plug locations too, and that is why they made best power at 20 deg leading, 20 deg trailing spark timing. I am just telling you this to make sure you understand that these numbers will not apply to your housings.

A cold air box is very important. Breathing the hot air under the hood, even on a dyno run, will cost you 20 to 30 horsepower.

 

Speedturn: Just commenting because I noticed it, but the DRS dyno sheet does have HP and torque cross at 5250. It's just that they use different scales for HP and torque on there, so it doesn't *look* like they cross.

 

Thanks Kenku - I didn't compare the numbers and catch that.

 

i think your best bet is to go fuel injected. injection will always make more power over carbs.
for your PP 13b i recomend the electromotive TEC3R. it has a tps blend feature that helps stabilize radical camed/serious ported rotary engines. do some research i think ull like what they have to offer u.

 

While this engine isn't peripheral ported, Paul Yaw did find some interesting intake power on the dyno. Check out this link to see what he did. This is something to consider. The relevant info is about halfway down.

http://www.yawpower.com/dec2004.html

 

To BMS2004:

I am runing RE Cabon apexi seal.

To SpeedTURN

yes I understand what you talking about on IGN timing. The timing I got now it run pretty well. so I might not change it until I run off of thing to change . In the mean time I will build my airbox. and design a better exhaust first. BTW what is your on whp at 8000RPM? just want to do a compare

TOTEZTnTUNE
EFI is great. but Require a lot of time and money to make it work right. Even thought I am still runing CARB. The thing I got(58IDA, MSD 7AL) is pretty good already . so EFI will not be my option here.

 

No injection system has ever made more MAX POWER than a "properly set up" Weber, or Weber style IDA carburator. At WOT the EFI offers NO advantage.
If fact it is less effective, as most EFI's don't offer mapping above 9000 rpm in a fire / cycle configuration (once every rev. or every 360 degrees) 4 Cycle piston engines fire once every 2 revs. or 720 degrees.
Rotary engines, even though a 4 stroque Otto cycle internal cumbustion engine,
fires once every revolution like a 2 stroque.
A well tuned Rotary will pull well into the 9600 to 10k range.
Fuel economy is another issue, and the carb. does NOT compare at that, BUT MAX power ?
Thats what we're talking about & dealing witth here.
And lets CHECK UP HERE, we are talking about club racing ie: SCCA, NASA, NASPORT, ect. NOT IMSA or ALMS, were fuel economy becomes an all important issue.
Botton line, You have the correct pieces to make 290 RWHp. or 330++ @ the fly.
Something else is up here.
Could be one thing, or a combination of many factors. Though I have my own personal view on this, I'm NOT going to speculate.
I will offer a point to give some considerastion:
I've read Your COMPLETE post & the facts You relate. Its seams there MAY be a scavange related problem reflecting "FROM" port timming.
Check for "Reversion" or "Stand Off" atop the carb's trumpets, & The Rpm in which it happends.
This may give You some insight as to why the engine is not in RESONANCE at higher revs.
Good luck, & Best Regards,

GT1-20b