jayroc

Does anyone know a website where I can get some good general knowledge about owning/tuning/breaking in a bridgeport? I may be coming into one soon and I'd like to know more about their behaivor.
(too lazy to search and compile)

RotorMotorDriver

iTrader: (1)

Well, I suggest that you become un-lazy rea quick like because sofuckingmany people are gonna tell you to search its not even funny...lol.

Although, come to think of it, I dont know where you would find such a website covering those items. Just a description of what the port is, not how it acts day to day, tuning, etc...

~T.J.

peejay

There's a nice description in the FC section. Someone laid out the recipe for the bridgey he put in his RX-3. Allegedly it makes decent power (~250 at flywheel) and gets over 20mpg on the highway.

The trick is he only takes the eyebrows down half of the height of the intake port. This does two things... it reduces the chance of the bridge cracking, and it reduces the overlap enough that it's more tolerant of a quiet exhaust system, while still having enough overlap to fatten the midrange nicely.

12abridgeport

People always talk about cracking bridges with boost, i can make the biggest bridge port and make the bridge strong enough to withhold 40 psi if i wanted to. That would be like the least of my concerns.

As far as 20mpg with a small full bridgeport, i've had one and i was getting like 11-12mpg on highway. Of course that would depend on what it's tuned for, what kind of carb you got, and if you have msd boxes (i didn't).

peejay

The bridges crack from the stress of the rotor sliding past it, especially at higher RPM when things start really wobbling around in there like they aren't supposed to, and especially when you make the bridge pretty thin for minimal cross-section and long when you make for high overlap. I do not see at all how making intake manifold pressure higher than atmospheric can cause a bridge to crack. Seriously.

My guess is, his car was fullbridge also (didn't really specify) but the reduced overlap compared to typical "make um real big vern!" ports made the difference. hell even a decent streetport is sensitive to exhaust backpressure with respect to idle/low load running quality.

edit: Found link... https://www.rx7club.com/forum/showth...94#post1944894

DriveFast7

iTrader: (1)

Has anyone actually seen a cracked bridge? I've talked to many owners and builders of bridgeports and they havent had a prob with that. it's usually carbon apex seals or bearing dying that causes failure.

12abridgeport

That's a good link, i read some of it.

I've never heard of cracking bridges from high rpm though. I don't see how that would be possible unless the whole rotating assembly is totally out of balance and the bridge is extra extra thin. Never happened to me and i know i've hit 11k a few times. Some people say they crack their brides all the time, where as, others say they never cracked one. It must be a mystery...
Boost however, would put a lot of stress on all the engine plates that's why people put extra dowel pins to prevent vibration under extreme loads. Of course it would take a lot of boost to do that.

peejay

You've hit 11k a few times... do you run at 7k-10k for 2 straight hours in a race, though.

Dowel pins aren't to prevent vibration. Dowel pins are to prevent extreme combustion pressures from successfully forcing the rotor housing (momentarily) into a circular shape, breaking or ripping the upper dowel pin out of the rear rotor housing in the process.

WackyRotary

I cracked the rear dowl in my mildport 12a turbo blowthrough in late May(not from detonation, from excessive combustion pressure!). I am now dowling it now for being able to handle 15psi-16psi-which was VERY impressive and enough power for me. I did note a siamler sliding rotor housing on sideplates image that was like in the mazdatrix "overboost results", no coolant loss or inner rotor housing seal failure occured thankfully. Also, I guess S4 TII endplates are good for 15psi before dowling is nessessary according to someone I know, and S5 can handle more yet.

High combustion pressures is the limiting factor till I get this done. I don't plan on using more then 10psi on this stock 12a I'm using now to prevent rear dowl cracking and associated oil leak you get with it.

Also, I never had a bridge break on me. And I took my 12a bridgeport out several times for unrelated failures, and I am sure boost isn't going to break it before something else breaks first.