I found out this is how my motor was ported. Is anyone running a motor like this? What carb setup are you using? How much power are you making? Thanks.

 

What kind of exhaust are you running too?

 

i am surprised that you have a half bridge. there are not many of them around, and after talking with people who know there stuff (amongst others, rob @ pineappleracing), they are not worth the effort

but since you already have one. a 48dco (or equivalent in ida) should be sufficient. 45 may even work.. exhaust should be as free flowing as possible.

 

i've always been curious about the half-bridges. did Rob give any detailed reasons behind them being "not worth the effort ..."?

 

yeah what the hell is a "half bridge" port anyway...

 

half bridges are generally a street ported primary and bridge ported secondaries (or am i wrong on this)..

rob just said that the difference in flow was not that much over a good street port.. the gain is not worth the trouble of porting it, and building it properly.. he did not go that much into detail, since we talked about other options for most of the conversation

 

Told ya it was a half bridge .

~T.J.

 

I've been wondering how a large streeport with some overlap would fair against a bridge.

 

Not worth the effort? Don't tell that to turbostreetfighter or Carlos Gonzalez. turbostreetfighter (Marcus) has his primaries bridged but not his secondaries. Also only 1 intake runner shared between the two primary ports for a total of 3 on the engine. His car is methanol powered and runs in the 8's. May be a race car but the point is clear. I saw Carlos Gonzalez' RX-3 ports a year ago when he had engine problems at the track in Houston. He pulled the engine apart in his trailer. I looked really closely at all of the ports and how he did them. The primary ports were huge. He had the Cosmo 13B center plate streetported and the outers were bridgeported. The magazine articles say that the car is streetported but it is really a half bridge. It is still a bridgeport just a smaller one and therefore should be worth the effort to do. Tri-point engineering does this type of porting all the time. The original question pertained to 12A's but the theory is the same.

 

The primaries are the center ports...Arent they?

~T.J.

 

Cosmos 13 Has alot bigger port than a 13BREW I think its a better engine overall.

Easier to find also.

 

Yep primary, center whatever... The Cosmo engines are easier to find? really hmmm......

 

I dont know if anybodys heard of this but my cousin was telling me somthing about doing a bridgeport to my car but the bridge would be about half the thickness of a regular bridge but the same length. He said I would make the idle not so high and more bareable to drive on the street then a regular bridge. Let me know if you know about this.

This is a VERY rough idea of what I think hes talking about

 

Is your bridge on top of the port or are your artistic skills just that bad j/k The bridge should be on the left. Bridgeports are done in various thicknesses depending on who does them. I like to keep them narrow without intruding into the rotor housings but that is due to the apex seals I use not being one piece. It would still idle rough due to the amount of port overlap. I am currently building a T-II engine with high compression rotors for my GSL-SE with what I refer to as a 1/4 bridge. In truth it is a half bridge but a really small one. The bridge is only half as tall as the main port itself and only on the outers. I think this is more in line with the street driving characteristics you mention. It is a little better than a streetport (worse on emissions) but not as good as a half or full bridge. It is a port style that Paul Yaw uses (or at least used to use) on his Rotary pickup (REPU) for street driving.

 

A half bridge on a 12a is not going to be a headache on the street or require wide open exhaust. I have a 12a street port/half bridge in the build now, only the secondaries will get the half bridge port and the bridge port will be smaller than full width. I have had some good exposure to half bridge port 13bs and 12a, all na for the record. Expect a lumpier idle but a considerable increase in hp over a streetport. If you were turbo than full bridge all day long, but for the street and na a full bridge needs open exhuast and makes terrible power under 3 grand. I think you will be happy with it. The secondaries for the record are the outside ports, primaries are the middles, ciao

Guru

 

for all the feedback guys. Hopefully guru will be right and it wont be a pain to drive on the street. I just got a secondary metering block and new jets for my secondaries. Im off to go and modify my carb and hopefully ill get it started today.

 

It is a pain in the *** to drive on the street. you either have to go full throttle or its gonna run like ****... kinda sux. Im pretty impressed by the power. Its pretty fast. I need to fix my tach, Its not working right now so I dont really know when the power is kickin in. I need to button up some more stuff. hopefully ill have it ready to race at qualcomm next friday.

 

I know I am power hungry, but I personally think if you do a N/A bridgeport, go for a full bridgeport carbon seals, with rotor housings matched, but shy of water seal. The difference I believe between a full streetport/half streetport&half bridgeport/full bridgeport is substanial. The only way I'd ever do a half bridgeport is if it was a turbo setup or was a 4barrel setup so the secondaries would open after 3500rpm or near there.

If you go turbo I think streetporting is best so you can remain with steel seals and just dial up the boost when you want more power and remain with smooth idle and good sealing at part throttle driving. This seems to be a problem for my bridgeport at engine speeds below 3000rpm in 5th gear. The engine ABSOLUTELY wants to be kept at 3500+rpm, which isn't really a problem, since carbon seals work better and keep raw gas from causing build up on the rotors.

As for me and my power hungry attitude, full bridgeport 12a I made seems to get the same milage no matter how I drive it. 14.5mpg. As a result I drive hard all the time, no build up in the chambers, no problem with low rpm, I keep it at 3500rpm when ever I'm moving! Starting from a stop is the only time it drops below this. I have 15,000+miles on the carbon seals.

Oh yeah, I would go with pre-mixing with all of these unless you were to drive like grandma.