Drago86

also ive only ever seen even numbers for the r value,... usually 2, or 4,.. im not sure if odds work out right. 2 is a very good number if you want a good peak performing manifold tho, whereas 4 would give you a boost at half your target rpm aswell.

White_FC

I don't know what you mean tunned for a lower R value that makes no sense to me, i have no idea what 'R' is in this respect....



I believe you that a long runner is need for a longer port duration, what I want to find out is HOW much long per port duration we're talking about here.



Now I wouldn't be that suprised the aux port closes a tab bit later than a PP, however a bridge on the aux port definatly wont come anywhere near close to opening up as soon as a PP...



Lets see some numbers really quickly here..

Total port timing:

6-port = 32deg. After Top Dead Center -> 70(or 80)deg. After Bottom Dead Center.

MFR PP = 86deg. Before Top dead center -> 75deg. After Bottom Dead Center



Now the PP closes either 5deg. AFTER a 6-port motor or 5deg. Before depending on wether its a early or late 6-port, yet it open looooooooooooong before the stock ports which is obviously not suprising...



What is a bit suprising is that a 'Racing Beat "J-Bridge Port"'

has a port duration of:

115° Before Top Dead Center -> 72° After Bottom Dead Center

Now I admitadly don't know much when it comes to all these rotor timming things but to me it looks like this J-bridge still does not have as long duration as a MFR PP? is this right?

(info thanks to http://www.yawpower.com/dectech.html)



And if your going to tell me your aux bridge design has longer port duration than any J-bridge, I will not believe that.... because there is no way a aux bridge will open up anywhere near as early.



Anyway, this is all really a mute point... I just wanted a formula.. now its there, and i'll take it as red that is works..

but Drago86 you just brought up something else i've been interested in for a while since this thread started, when you want this pressure wave to arrive at the port/rotor.

Why is "25-30ish" a good starting point? just curious.

Drago86

R is the refractive value, i think the r26b uses 2, wheres the stock car uses 4. 4 resluts in a longer manifold for the same tune, and also has the benifit of being tunned at half the tunned rpm (3250 in the care of the stock care assuming a 6500 rpm tune, which is quite close to the torque peak), however the strength of the pressure wave is lessed because they go thru 4 reflections, which is why racing vehicles usually use an R value of 2, they dont need the low rpm grunt, and the added high rpm power helps out.



formula for port duration is: 720+BTDC+ATDC

so stock s4 is: 720+ -32+80 or 768

a BP is 720+115+72 = 907

a PP is 720+86+75 = 881

a full bridged 6-port would be: 720+115+85= 920

an aux bridge would be 720+~70+85=875



So you were right about jsut the aux not having more timming, but its close.

The reason a BP can get away with opening earlier then a PP is that the eybrow is much smaller then the big *** hole of a PP, thus the velocity is much greater in the first opening stages of a bridgeport, so they can get away with opening it earlier without losing effeciency and getting backflow. a J-bridge and regular bridge both open at the same time, the only differance is the j-bridge has more flow thru the eyebrow. Moving the bridge up or down will effect its timming, but not moving it furter into the water jacket, as its allready being opened by the apex seal.



I said 25-30 is a good startign point because thats wht they use as a value for piston motors, it may be slightly differnt for a rotary, only dyno time will tell. in any case it will only throw the tune off by a few hundred rpm anyhow



http://www.rotaryengineillustrated.com/RE1...4-ports101.html - also has some timmings, look at the j bridge, and the regular bridge and youll see what i mean about them sharing the same timming.



also dont forget to use the port runner length in your calculation for when you actually make a manifold.

toyotaownsyou

ok....i'm completely new to this whole aux. bp idea....but had heard about it and it sounded good to me until i read this.....see i was thinking of running it n/a with something like a weber 48 ida setup.....would the aux bp work then???.....if so what kind of power do you think i could expect it to make?

mazdaspeed7

Im selling my aux bridge motor if youre interested. PM me if you want info.

Judge Ito

Pic of the port I did and the 6 port bridgeport engine.The engine is still running a year later and running hard I might say..

Baldy

how does the idle on a full-aux bridge compare to a 4-port bridge? I mean, I always hear that the bridge requires a high/rough idle, is that less of an issue with the 6-port engine? Or about the same?

Judge Ito

because this is a totally bridged ported 6 port engine the idle is the same as the regular bridged 4 port engines. Vosko has a video of this 6 port bridgeport at idle. Brap,brap,brap,brap

j9fd3s

yeah its neat, brap brap brap. how do you thnk it would run if you did the streetport part of that and just didnt cut the bridge?

j200pruf

Hey Ito, if you were to do the bridges on just eh aux and secondary ports could you block them off and make a different fuel map to get through DEQ, or is that just a stupid idea?