diyman25

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.

diyman25

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

geargrabber

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.

diyman25

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 .

FxF

What about exhaust diameter?

-Fanis

BMS2004

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.

turbojeff

iTrader: (30)

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.

diyman25

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

BMS2004

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

Ron

oregano

iTrader: (1)

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?

diyman25

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

speedturn

iTrader: (1)

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.

DriveFast7

iTrader: (1)

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.

13btnos

iTrader: (1)

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.

DriveFast7

iTrader: (1)

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.