cabaynes

iTrader: (4)

Ok so I have always wanted to build an NA motor, whether it is a 13b or 20b isn't really my first concern so for this post we'll assume I want to use a 13b.

This motor would probably see only 1200 miles or so on the street a year (if that) and would be mainly for track events.

Based on what I've read about a few well-built (well in my opinion) NA motors, I've compiled a list of my ideas. Tell me what is good, what is useless, and what I should do different... and perhaps, why. Please excuse my newbishness today-

- D-shaped perphial port with EFI 55mm IDA throttle bodies
- Lightened rotors (but which rotors? S5 NA, or standard FD 13brew?)
- 4 550cc injectors
- custom intake/exhaust manifolds (obviously, but is there a preffered design?)
- Bosch ignition coils
- Autronic ECU
- dry sump oil system (reason being for the track days)

Like I said, I don't claim to know anything about building an NA motor so if I'm just rambling, tell me. This list obviously isnt everything but the main components I'm curious about are the periphial ports, what diameter they should be, and circular or D-shaped? and the rotors, should I use NA rotors from the S5 or would the standard FD rotors be adequate?

Any info is appreciated-
Thanks guys
Charlie

dubulup

S5 N/A rotors have the highest compression 9.7:1...FD is 9.0:1. I'd go with S5.

you probably want to have a set of those lightened.

lightest flywheel possible (counter weights balanced with rotors)

maybe run a ZERO split ignition...two FC leading coils firing off the trailing signals 'might' be enough...they are pretty beefy (TII same as N/A)

and dual EGT is a must.

I can't comment on P-Ports, sorry.

cabaynes

iTrader: (4)

Thanks for the info. Is there any particular reason to run the ignition like that with an NA motor?


Anybody else familiar with p-ports, dry sump, and manifold design?

speedturn

iTrader: (1)

I have been road racing P-port motors for 9 years now. I sometimes sneak my race car out on the street to test it just to make sure everything runs right before I load it up on a trailer and tow hundreds of miles to a road race.

A p-port engine is not for street use. You would not enjoy trying to drive a p-port engine for 1200 miles a year on the streets. Like I say, I have driven street port engines on the street and it is not fun when you are in traffic.

Street port engines are for street use.

Dry sump adds at least another $2500 to the cost of your engine.

cabaynes

iTrader: (4)

While I appreciate your experience and comments, I'd still like to learn more about them and the motor I'd like to build. Whether it is suited for street use or not is my problem once I build it. I am also aware that a dry sump system is rather pricey, but that was not my concern. Your post is very negative, do you have anything positive to add based on my original questions regarding port size, intake/exhaust manifold suggestions, oil system suggestions, etc?

RX*Guy

A great port that worked wonderful for me, this is back in carburator days, was a large street port on the side ports, and a P-port. I had to make my manifold, as a matter of fact I still have the manifold. I ran the primaries on the center side ports and then the secondaries on the other two side ports and the P-Ports. The
P-ports were only about and inch and a half diameter. But it would idle well and go like stink! The only draw back was building the intake. Making the P-Port was easy.

Bob

cabaynes

iTrader: (4)

Sounds cool - do you have any pics of the manifold or the ports?

RX*Guy

I can take some pics of the manifold since I still have it. That motor and car left my hands about 26 years ago. (I'm and OLD rotor head). It was a 12A in a RX3. I'll try to do the pic tomorrow.

BTW. I later installed a turbo on that car and I just bolted a RB/Holley manifold over the P-Ports. the new owner dont even know that motor has P-ports.
I did try the turbo with this port system and it did not work very well due to the timing overlap.

speedturn

iTrader: (1)

Mazda tried the combined P-port and side port motor on one of their race cars back in the late '60s and gave up on the idea. I don't know of any races being won with a combined side port and P-port motor.

The '89 thru '91 N/A rotors are light and have decent compression ratio; they make good power for me. I use carbon seals with them on my P-port race motor since it lives at high rpm.

Sorry to sound negative - it's just that your P-port motor sounds like a bad idea for a car that will get 1200 street miles of use every year. Sometimes my tounge is too sharp. I am not very good a letting people save face.

dubulup

I've read ZERO split is the proven set-up for the most power out of an N/A motor.

some 600+hp turbo 13B's use zero split as well.

turdbo

im also into na...im getting a 13b from an 86 im curiouse if those rotors are light and good for N/A because they have the highest compression ratio...sorry for the thread jack

dubulup

86 is a series 4...I believe those rotors are 9.4:1. Series 5 are 9.7:1

speedturn

iTrader: (1)

turdbo - no

_______________

dubulup : Spark Timing - timing depends on the rotor housings used. The trailing spark plug location on MFR PP housings are in a slightly different location than Mazda production street car housings. MFR PP housings like no split. PP rotor housings made from Mazda street housings (like Racing Beat and Rotary Reliability & Racing PP housings) will have the trailing plug in the street location, and those home made PP housings like a small amount of timing split. I use PP housings ported by Nick at Rotary Reliability & Racing. They are almost identical to Racing Beat Housings - yet Nick will make them for a little bit lower price. Nick's PP motor set a Bonneville Land Speed Record back in the '80s, so he has the speed record to prove his horsepower.

cabaynes

iTrader: (4)

so what sort of split do you use with your housings?

Also, are MFR housings still around?

dubulup

just the stock L & T holes (I believe they are 19* apart)...is that what you are asking?

if you need an AMP you can NOT use a multiple spark discharge or rapid fire, as the trailing rapid fire duration will cause idling problems.

cabaynes

iTrader: (4)

I was wondering what the split on speedturn's spark was since he said that his RR&R PP housings like a little split when compared to MFR housings that use no split.

dubulup

gotcha...I missed that part of his post. Looked like his signature, haha!

cabaynes

iTrader: (4)

Haha I see.

Does anyone know if MFR housings are still availabe?

Also has anyone here ever installed/run a dry sump on rotary before?

speedturn

iTrader: (1)

part # 4801-10-100 housing, rotor, peripheral port 13B, price $1862.35 each. Currently out of stock at Mazdaspeed Motorsports Development (the new name for MFR stuff.)

RR&R will turn a new stock housing (that you or he buys) into a PP housing for $500 labor charge. This turns out to be less than 1/2 the price of MFR PP housings; that is why they are popular. The RR&R price used to be $50 less than the RB price. When setting up your engine budget, remember you need quantity two of everything. If you are going to run a high rpm PP motor, you will need better stat. gears and race bearings too.