91RX7N/A

i built a 13b pp port timings at mazda racing spec
it has a weber 51 on it and a stock dizzy ima bout to go make locked out
what should i set the timing at and what Jet size should i start out with and what
Emulsion tube???
thx for any help

speedturn

iTrader: (1)

If you machined p-ports into a stock Mazda housing, then set timing at 24 deg BTDC leading, 16 deg BTDC trailing.

Jetting depends on venturi size

j9fd3s

iTrader: (3)

i'd start @20, and work my way up just to be safe.

jetting depends on fuel pressure, venturi, WHICH MFR spec you have, the exhaust, what day it is, which jets you have lying around, etc etc. i'd start rich, and work my way leaner, so start with the biggest thing you have (230ish?) and a well ventilated area.....

Emulsion tube should be F7 or F8 (one is for the 13B and one with the 12A i forget which is which).

as with anything, the tuning will vary, my P port is a 12A, and its all new parts, and it just doesn't want a lot of fuel, so my jetting gives nice mixtures, and it drives really nice, but it looks weird, because i ended up with really small jets.

the engine is happy though, so i'm happy, its just the neighbors that don't like it

91RX7N/A

thanks for the help guys, now i gotta place to start.

what mix do u guys run 100:1 amsoil?
i was planning on using royal purple 25:1 to break it in
how long did your motors take to break in?
is there any special procedure to brake in on a rotary or just let it high ideal till the seals seat (stops smoking)??

j9fd3s

iTrader: (3)

i've been using any TCW3 oil, it doesn't seem to matter. however with the PP, it runs so cold at idle/fast idle that it actually doesn't burn the premix, it comes out as liquid... you may want to use less mix if you are just going to be fast idling it.

i used the carbon apex seals, i gave it a few hours of fast idling and light throttle, but it didn't really seat in until i got to run it around the track a couple laps. lap 1 was a smokescreen cause it burned off all the goo in the exhaust....

mine got a lot of idling and stop start on the break in, also partly because i was tuning the carb

enjoy the ride!

Donovan N.

J9fd3s, you mentioned different Factory P-port timings, is there any where out there where I can find the different specs for factory P-ports and/or which ever port would be best for road racing?

peejay

25:1 is way way way way way too much.

91RX7N/A

25;1 is way to much i use bout 7 ounces to 5 gallons

j9fd3s

iTrader: (3)

there is an SAE paper on it. 900032. shoot Arghx a pm, he has an SAE membership.

anyways there appear to be about 3 different port timings for the intake and 2 for the exhaust.

the early port timing, which was listed on the paul yaw website, and the yamaguchi FC book it
the intake opens @86BTDC and closes @75ABDC, the exhaust opens @73 and closes @65.

the SAE paper mentions an opening of 100BTDC on the intake and closing @80. these ports make peak power @8500, so they optimized the engine to make peak power @9000.

they came up with an intake port timing of 80BTDC and an 80ABDC closing. the exhaust is 73/55. however due to the location of the intake ports and some slight changes in shape the timing is shorter but the ports have more area.

the paper goes into more detail, and in reality they used ALL 3 ports for road racing, its just that the 80/80 intake port makes more power than the 100/80 port.

Liborek

Most interesting thing is, that 80°BTDC intake opening is giving higher VE% above 8000 rpms than 100°BTDC intake opening. Iīm assuming that this is with all other variables held constant. This is probably boundary where interference with exhaust pressure shows its ugly head...

What i really like about VE% curves and dyno graphs in this paper is, that optimized port timing, port area, runner diameter and lenght seems to carry torque to very high rpms and increase in power is still very steep towards 9000 rpms.

This paper just shows how complicated intake and exhaust dynamics of RE are as there are certain things where common sense about intake and exhaust tuning just wonīt cut it.

Maybe "trustworthy"wikipedia info about R26B being able to pull 830 HP@10500 rpms holds some merit

peejay

Interesting that the IPRA engines out of Australia are (allegedly) making close to 400hp with rules-limited "mild" bridge ports and careful intake/exhaust tuning.

And that semi peripheral engines seem to be the "best of both worlds"... you can get the port area of a peripheral port, but with less port timing.

j9fd3s

iTrader: (3)

the rotary is kind of unique because most of the variables ARE constant. you are right about the intake exhaust tuning, well actually the intake seems fairly straight forward, but look at the exhaust! they tried a pipe from .5 meter all the way up to 5 meters long and there isn't a length that works @5000 AND 6000rpm!

j9fd3s

iTrader: (3)

yes, its all about getting the right port area with the right cam timing. even in a piston engine. any old vtec honda makes around 100hp/liter, and idles, but to get 100hp/liter in a V8 with stock heads you need cam that's too big to be even remotely streetable.

we raced with a historic NASCAR group this weekend, and even though its a V8, the P port is WAY more docile, and drivable.

peejay

I've driven quite a few 100hp/l V8s. They're plenty streetable, and with modern EFI they are downright docile. (A 600hp LS2 can idle smoothly at 1000rpm and cruise around town just fine, like it was nothing out of the ordinary)

The biggest problem with a 100hp/l V8 is finding a use for 600-900hp. And once you find a use, getting a drivetrain that will hold up to it.

Anyway, HP/l is trivial... it's ft-lb/l that is difficult! That's where you really need to work hard.

j9fd3s

iTrader: (3)

these things are using 80's cylinder heads, with a 4 barrel carb. they run full throttle just fine, but starting, idle and running around the pits they are almost the worst thing i've ever seen. it makes a P port look like a camry....

maybe they need to spend some time on the carb or something, but i just thought it was weird. they have opening trunks too which is even weirder, why make a custom body tube frame car with a trunk?

not that it wasn't cool to see em

peejay

Well you have to bear in mind, drag race engines are WAY over 100hp/l nowadays.

And yes a good carb is crucial, but good carbs are freakin' expensive. (I call $1000 for an entry level carb to be freakin' expensive) I tell you what though, a good (read: not a Holley/Edelbrock) carb has phenomenal drivability, even on an engine that has only 4" vacuum at 1100.

j9fd3s

iTrader: (3)

these guys need your help....

Liborek

Maybe they do. Probably its not that hard to make 200 lb.ft of torque above 10k rpms. Still it should be interesting to see some solid proof, something like Vbox datalogs from these cars. I think it would be eye opening Even if they do produce such power, Iīm much more interested in torque as nothing seems to surpass full PP. Be it due to sheer VE or better BSFC.

These things arenīt giving me peaceful sleep

Well, in case of semi-pp, actual pp is very small, so we should rather say that it has port area slightly bigger than side port engine, with much earlier intake opening, but with more docile area/degree opening ratio than full PP. I mean, we could get huge port area from side port only, and it still wonīt produce torque of PP.

Question is why mazda didnīt go with this approach in their race engines? They examined combination port, PP as primary, side port as secondary and torque curve was really good. Still they went with full PP and variable intake

What I also like is, that they discussed impact of rotor position during overlap. In pure graph of area and degree overlap, its huge. But when we consider rotor physically blocking path, its not that bad.

Enough of my rant

j9fd3s

iTrader: (3)

maybe the variable intake was cooler looking? i'd say it was hard to add the side ports on like a 4 rotor, but if you've seen pics of it apart, the have a little spot where a port could go.

we thought about doing the semi PP, factory style, that way you can keep the stock intake, so when the cops stop you and pop the hood its all factory....