12a porting ?

[MikeLMR]

After picking up a spare car locally, I've now got a spare motor to exchange for a rebuild in the future :)

I know hurley do a "sports" engine for a not so small fee, but what I want is somthing thats got a nice "lope" to the idle

I have seen the yanks selling "half bridge" ported engines ( stock port primarys and bridge ported secondaries ... does anyone in the UK do these ?

Mike

[Glenn Butcher]

Mike,

I know this is an old thread... I don't think so - if you wanted to speak to someone about porting.

Carl Hayward Carl Hayward (http://www.mazdarotaryclub.com/forums/member.php?action=getinfo&userid=99) knows quite a bit.

[Carl]

Hi Mike,
If you want a "lope" to your engine idle then you really need a full bridgeport, having said that i can build you whatever engine you like from extend ports to a full race bridgeport.
The reason that a 1/2 bridge will not have a brap brap idle is it will be idling on the primary ports that are not bridged but only extended.
For road use a 1/2 bridge is the best compromise for maximum power and still some driveability using any type of carburettor.
At cruising speed on the road the car jumps around like a Kangaroo(sorry Glen)so you are either on or of the throttle all the time,hard work.
Fuel injection with a mapped after market engine management system with sequential fuel injection can make a full bridge port or small periphal port driveable on the road.
Hope this helps

Carl

[MikeLMR]

i think i'm going for a large extend port and possibly a twin webber manifold or a single IDA when it comes to sorting the engine on the ' green monster' :D

I've just been watching some video from the '84 RAC rally and now I'm hooked on the noise a well ported rotary makes ! (that and a 500hp Audi quattro!)

[Grizzly]

Half Bridges Do make the over lap Brap Brap Brap sound?

I have a Video (Suprise of a 13b Turbo Half bridge) if you like.

I would'nt go Bridge for the simple fact the earlyer 13b's and possably 12a's? have a problem with cracking rear plates when producing big hp + the Bridge has to be made well with as much material left on the the bridge part of the port as possable.

If you want to increase the overlap i would rather make the Exhaust port bigger and Extend the Inlet's, this would cause the overlap you want but more tame.

Chris

P.S. Glen if you see this the engine pic i have attached is one of Peter Giljevic's Turbo Engines.

[Grizzly]

^ bit extreme Exhaust but you get the point.

Half bridges, the Secondrys still opens earlyer than the Primary and air is still drawn in so to stop it from running lean you must also put fuel there hence the Brap Brap barp.

if you dont want to get the Brap noise you must use the same opening timing on both primary and secondry.

chris

[Glenn Butcher]

That exhaust port is HUGE! :)

I would imagine that engine would have quite a bit of overlap (BAP BAP sound!).

I believe that a square exhaust port closing provides more snappy type power than a rounded closing on the exhaust port. The rounded closings are good for torque.

One problem with a square exhaust port closing is that there is more strain on the apex seals with they snap shut.

[Grizzly]

That is very extreme! you dont have to have it that shape.

People tend to make the the port more Tear drop shaped to help with the snap shut problem.

^ Peter has run a lot of power of this engine and it sounds like the Silver Fd on the 12a Bridge Thread.

Chris

P.S. note the Exhaust port shape on the P/P pic i have attached.

[catboy]

could someone explain to me the whole bridge port thing?... I have played with rotaries a little, but just tweaking engine management, swapping turbos, intercoolers, etc... ....dont really know much about 'proper' tuning to rotaries
b :)

[Grizzly]

Basicly there are a few diffrent types of porting.

The first and most tame is Street port (Extented) this is usaly only done on the Secondrys, what they basicly do is make the port larger by moving the wide end of the port down 5-10mm (knowing where the water ways are is the key and not going into the Oil/Corner seals part)

The primarys can be extended but there is not much metal between the port and water way.

[Grizzly]

The next step up is geting quite Radical, this is the Bridge.

Bridges have a problem, they have an extra port cut into the plate which increases the port timing and create somthing called Over lap.

Overlap is somthing you want to stay away from if its used on the road, its basicly when the Inlet and exhaust ports are open at the same time, this causes reduced low end power and very bad MPG on low load (every day driving).

Bridges have also got a bit of a reputation for being Unreliable, the problem is the port is so big it needs a "Bridge" for the corner seal to run on, these over time crack and colapse droping the Corner pin into the Port. The other reliability isue is the extra load (Bhp) it runs decreases the life of the engine (wears out). Its the same with any high hp engine the more power you run the less time it will last.

[Glenn Butcher]

Catboy,

Another good site for information on Porting is here:
http://www.mazdatrix.com/faq/portbp.htm

Sample of a J-Port here (larger than a standard Bridgeport):

http://www.mazdatrix.com/faqpics/porting/bp03.jpg


Think of porting as being something very similar to doing "Head work" on a piston engine.

[Grizzly]

The last and most Radical is the Periphral port (P/P).

This is basicly the same sort of thing as Bridging, it has a masive amount of overlap but instead of using the Side ports you make a complete new inlet ports in the rotor Housings and block the side ports off.

This is a Fav for the drag guys as there is no Bridge to brake and the engine has no weak points + its a more dirrect route to the rotors Bath (squash chamber).

I havn't realy gone into detail but you shoud get the genral idear.

[Grizzly]

CatBoy.

http://home.iprimus.com.au/bluey3/portsPage/ports.htm

[catboy]

thanks guys... was looking through the forum the other day, and heard a bridge ported engine ticking over, and was mesmorized!.... ...think its probably out of reach and reason for me tho' :)