pengaru

I'm with you on the short runner length for the aux ports, but you'd have to tune the length properly to take advantage of the pressure waves between the ports and the plenum... the ports you want tuned for higher rpm will obviously be shorter, exactly what length though you have to do some math.

j9fd3s

this is when you put the motor on an engine dyno and start playing with lengths



mike

mazdaspeed7

That spreadsheet than you enjoy so much will do the math for you. Just punch in a few numbers, and viola, you now know the proper length. The idea behind calculating the runner is so you have a good starting point. And Im sure what works best on paper will also work best on the dyno. Physics works.



Shorter runners are needed for higher rpm, BUT, the runners for a bridged port need to be considerably longer than the other ports in a n/a motor, EVEN if its tuned for a higher RPM range.

Travis R

Explain more please. Don't be afraid to use big words... I'm an Inguhneer.

slvr7

This is a great topic - mazdaspeed thanks for your insights. I have been sitting around pondering this route - [bridge on the aux. port] - as well, thinking it would a 'cake and eat it' scenario. Retain low rpm torque, emissions, but above ~4000 rpm the breathing would improve with earlier opening and later closing of the aux. Seems it is not the case?



The only 'documented' instance I have seen of this kind of approach is the Grassroots Motorsports magazine folks. They built a S4 13B powered Spitfire (car, not WWII fighter!). The motor was built by Tri-Point Engineering with both a bridge on the aux, and slightly extended timing of the aux. However, the sleeves were removed and it runs on a standalone with a pair of TWM throttlebodies on a Weber type manifold. Apparently makes around 220 hp (which is plenty in a 1400 lb car!).



Having working aux. actutators is means there's a lot of obstruction in the airflow path, with the lumpy boss in the runner, and the actutator shaft, cross pin in the sleeve.......not to mention the sharper turn the air must make in the runner to get to the upper sleeve port.

If it's not worth it, what is the best 'mild' approach to porting a 6-port motor?



Curtis

'86 GXL autox'r

mazdaspeed7

You said you have the excel sheet. Take a look at that. Especially the chart on page 3. Like they say, I picture is worth a thousand words.

White_FC

Well I guess the guys here in Oz that race in improved production and are just cracking 300rwhp on their bridgeports have their inlet runner length all *** about then aswell hey?



I can't see how having a longer runner would benefit a bridgeport to make more power, I don't care what a excel spreadsheet says, it doesn't happen like that...

White_FC

While we're sort of on the subject, how does everyone here prefer to start the new port on their side plates?

Just use a center punch and then drill some pilot holes along the way?

Or just start grinding straight away instead of drilling some guiding holes first?



My engine will be out and pulled appart tomorrow, so c'mon guys, anyone here that can actually back up the claims of a longer inlet runner making more power (per RPM of course..) than a short one on a BP motor? I just can't see how it is possible... but I am willing to accept it if I see some real proof before I make up my inlet manifold....



and mazdaspeed7, you mentioned somewhere back it was because of the earlier opening was it? I can't remember..



Mazda's tech paper on the lemans R26B would tend to agree that a shorter runnger = more high end torque... that was a PP but the basic principal is the same.

Travis R

Sorry, but that doesn't tell me why a longer runner is needed for a longer duration. Reverse engineering your formulas is a little difficult. I don't know what all of your constants mean.

I just want to make sure we're talking about the same thing too... In your spreadsheet you have "primary" and "secondary" ports listed. The primaries are the four ports that are always open and the secondaries are the two actuated by the rotary sleeves?

Thanks

j9fd3s

yah mark where you want the port and then drill a couple/few holes and then you can get your bit in there.



i'm thinking that after a point it might be better just to loose the 6 ports altogether and go for a bp 4 port, you can get similar port size with less crazy port timing, but thats just conjecture



mike