kahren

i was wondering if those who are experinced in doing bridgeports, what/how do you port the exhaust port when doing a half bridge engine concentrating on mid range power. since the bridge opens so much earlier then the reglar port and adds lots of overlap i tend to think that you dont want to port the exahust port up any. adding overlap is good for makign power but it also means that even when tuned the realized power will be up top.

so any advice from some of the gurus?

93BlackFD

square exhaust ports give midrange power

Lynn E. Hanover

The "Gurus"seem to be busy, so, allow me to speculate:



Since this is (i'm guessing) a street driven car, it has to have quite a bit of muffling, and thus close to stock amounts of back pressure. The overlap from the new port will be a change of from night to day as far as drivability. Poor off idle and once the clutch is clamped up solid in first, not much power until the revves are up pretty high. You could tire of this thing very quickly. The back pressure will make it all worse, so if you get it together and the performance is just unacceptable, before you scrap it all you might try a few laps, or autocross runs with minimal muffling, just to get an idea as to what kind of power might be available. A big stainless Borla or a Flowmaster. The flowmaster must be kept well near the *** end of the system. They tend to melt and swell up like a big pillow.



A friend dynoed his 13B with very mild bridge ports (no "J") with 44MM chokes in a Weber 48IDF, and got it up to 259 HP under 9,000 RPM. So getting well over 200 should be possible. Extended visits would require hardened stationary gears, and more than stock oil pressure. Nothing over 9,000 for steel apex seals, and not for long even then.



But until it steps up on the (cam) above 4,500 or 5,000 it just isn't going to make you happy.



Leaving the exhaust timing stock while improving exhaust performance is the goal. My opinion is that I would leave the upper (closing) event stock, except that I would make a nice radius, about 1/16" all around the top and sides. You don't want any more overlap. The bottom (opening) I would make the radius a little bigger which would by just a hair open the port earlier. The big polished radius at the bottom is to help the hypersonic flow remain attached to the bottom of the port until outside the engine.



Another thought: If a 4BBL were used, it could be set sideways on the manifold and just the inner ports opened with the primaries, so that low speed performance might be better with the big overlap. I don't know that for a fact. Just speculation.



Lynn E. Hanover

j9fd3s

thats how they are setup.

kahren

thats kinda what i was thinking, no more oeverlap , and just smooth off the edges up top and open teh port some earlier. i guess looking at th eintake ports woudl be a better idea to determine the seize of the exhaust. here are a couple of pics.

this car will be running a custom intake manifold with teh stock throttle body, and i have currently on the car racign beat exhaust with the street header which will prolyl need to be changed and the collector palced at diffrent length.

the car made 165 at wheels before with a crappy street port on the secondaries with stock primary runners. i foudn myself shiftign at 3500 most of the time and i drive the car pretty hard on teh street so i visited teh redlien of 8500 everytime i got the chance.

i am not buidling teh car to rev passed 8500 due to $ and noise issues. this is a daily driver car oriented to road racign, i also dont want a impossible to deal with low end. i can sacrifice some of it to get the top end i am lookign for.

kahren

intake ports

kahren

another

kahren

secondary

kahren

another, the secondary port is unfinished and will eb gettign some devcon steel putty up top of the port to smooth out the flow.

kahren

another