kahren

overlap begins here

kahren

another

kahren

overlap ends here

kahren

another

kahren

the pics above are the overlap start for teh bridge ofcourse and the overlap end is for the stock exhaust port closing.

mazdaspeed7

Youre going to need a lot of extra area with your intake port to match up the the larege increase in intake flow. You can port out more than down, and youll have the flow with a shorter duration, and a lower torque peak, rpm-wise. But there will be more of an issue with the apex seal warping from having to pass over a wide opening. Extending the port down will result in a higher torque peak.



Bridgeports are extremely sensative to backpressure. Youll notice it the worst at low rpm, when the engine is out of the powerband. Youre going to need a very well setup exhaust to meet your goals with this engine. The diameter and tuned lengths will need to be carefully considered, as they are goign to have a profound effect on how your car drives with the intake porting. Intake manifold design will play an equally important role.



Ito, wanna chime in on the exhaust port shape? Anyone have personal experience with both? Mines more rounded, and it has a very strong midrange, and that goes along with what Ive read. Rounded ports have a broader torque peak, with the peak occuring at a lower rpm than a squared port. Squared ports make for a mor eprominent top end.



Bottom line on the exhaust port, though, is it just needs to flow enough. The manifolds are what will determine your powerband. Dont be afraid to go big. A properly done large port will work better than a port thats too small. Your intake ports are going to pull in a hell of a lot of air. Make sure your exhaust ports can keep up.

kahren

racign beat NA exahsut is 2.5 inches, i was also thinking abotu that that i might have to go with a 2.75 or mayeb a 3 inch, but i really dont want to make the car really loud. i might just **** it all and just go witha single 3 inch exhaust

Travis R

I was thinking about this style of intake port the other day, and the intake tuning that would go along with it. Since the aux. ports are connected to the main port, would the stock intake work well? Maybe grind out the barrier between the ports on the intake so that they would see the same pressure wave? MS7 your thoughts?

mazdaspeed7

The stock manifolds are too restrictive to use with a full bridge. Im having problems with the VDI manifold on my SP engine. It simply cant keep up with the airflow the engine is trying to pull, and performance is really suffering.



N/a's are very sensative to the intake and exhaust manifold. Very much moreso than turbo engines. If youre looking for ways to save money, a n/a engine isnt for you unless you want it relatively close to stock. For anything past a street port(intake and exhaust), I would recommend non-OEM manifolds, and in the case of the exhaust, custom. Im sure it will run with the stock intake manifold, but power and drivability will suffer. Same with an exhaust thats too restrictive.



Kahren, youre going to need to seriously rethink your exhaust plans, else youll be very disappointed once everything comes together. The sizes you listed were way too small. You should have 0.025 in^2 of exhaust area for each hp. Say youre going for a relatively modest 300 hp(240 rwhp). You will need to use 2.25" .065 wall pipe for the headers, and 3" .065 wall pipe at the collector. Do a little math. Multiply your goal hp at the flywheel times 0.025. This is the cross sectional area necessary for proper flow. For the headers, divide by 2, since there will be two pipes, then determine the diameter. Take the number you got, divide by 3.14 and take the square root of the result. Then multiply by two to get the diameter.



Travis, the pulse tuning will be shifted to a higher rpm with the stock intake manifold because the ports are open longer. But that isnt so much the problem as the narrow runners. The stock intake manifolds simply cant support the necessary airflow to match the engine.

j9fd3s

todds bp used a 750double pumper holley, its 4x40mm chokes. on a rb manifold thats been cleaned up (casting is poor)