scathcart

I think its possible. The secondary runners receive little to no air under light throttle since the secondary butterflies are closed, so the secondary runner porting should have limited effect on emissions.

RETed

I guess I'm the only one who thinks they are a waste of time then?



What I've always wondered is these BP's are not back-cut correctly, and they do very little to added flow.



I think you got dyno graphs of another BP motor running, and it clearly shows that the BP does very little to add to the power.







-Ted

TYSON

I've seen dynos of 2 cars built by the same builder with the same turbo, etc. Only difference is street port vs half bridge.



One made 425 hp @ 15 psi, the other made 463 hp @ 15 psi.



They work. Whether you can do the same thing with a more aggressive street port may be possible.



I believe you already had this argument. Let's not start it again here.

BDC

I originally thought it was a waste of time myself, Ted. I was originally against the idea until a friend of mine all but cornered me into doing this on his engine a long time ago. Even with lousy bridgeport cuts then, it turned out to be very effective. At first blush, they may not appear to work to you, but trust me they do. I honestly wouldn't go through the trouble and the hours involved in punching these things out if they weren't beneficial in some way.



B

j9fd3s

maybe if you disconnected the secondary throttle plates so they stay closed? i'd be amazed if it could be done , we have a visual too

RETed

Oh, I didn't say it wasn't going to do anything.

Maybe I should reword it to state that if the BP was done "properly", it would've made a whole lot more power.



Not start it here? Are you afraid one of your gurus is perhaps wrong?

I'm surprised no one has said anything this long, since I know there are competent BP porters out there that'll laugh at the BP that BDC is cutting.



Maybe I should just use pictures...



This is what I'm talking about - BDC uses no backcutting on his BP's.





The backcutting profile is one of the most important points for (any) porting. If you're ignoring this fact, you're got a lot to learn about porting in general.



If BDC would kindly post one of his dynos off his BP motors, you'll see the little "tail" in the dyno graph at the tail end of the run. That's his BP's effectiveness on the power band. If you've ever seen a turbo'd BP, the dyno graph is significantly different - it basically just shoots up with no sign of dropping off on the top end.



If you guys want the truth, you need to be able to comprehend what I'm saying. If you want to stay in your own little world, then I'll just shut up right now.





-Ted

RETed

See previous reply...



Your BP's are basically only effective if the main port gets overloaded. Your BP then takes over any "overflow" that can't efficiently flow through the main port. I had my suspicions on your ports initially, but I couldn't prove anything; your dyno sheet confirm my suspicions[sp?]. You should try and compare your dyno runs on your BP's with other turbo BP's. There is a big significance in the curve. Other BP's have a flat, climbing torque line, while yours do not. You can easily analyze your curve to confirm my suspicions that your BP does not flow until way up in the RPM band.



Without the backcutting, there is no easy path for the intake charge to go through. Through fluid dynamics, we know that the air intake charge will tend to flow straight and hit the wall of the main port before taking a bend into the combustion chamber. Look at the BP port pic I just posted - you can see the how much easier the intake charge can flow to get into the combustion chamber. With the nil backcutting if your BP's, there is no easy way for the intake charge to get through the BP unless the main port is overloaded.





-Ted

banzaitoyota

Do you have a dyno sheet to go with that picture of the BP?

BDC

The above comments you've made Ted are the very reason why there's so much animus against you in the Rx7 world. There's absolutely no reason for the abrasive and caustic remarks you've made continually against me nor is it necessary here. I'm just like the next guy who's looking to build a better engine and do things better the next 'go around', but this kind of taunting and language from you does nothing to further your technical points; Infact, it will make people look at you like the jerk you really are and question anything you have to say, even if you are right. You're alienating yourself on rx7club.com and it'll quickly happen here, as well. I've seen some of your porting work that I didn't necessarily agree with but I didn't go off and lambast that work or make you appear to be blatantly incompetent in public or on one of these forums here. Instead, I'll salute you on the effourt done and look forward to good results. There's so sugar-coating or infidelity here; it's the truth.



Guys like you make my blood boil because of how arrogant and self-righteous you come off on these forums as if you're the "know-it-all" with next to NOTHING good or positively constructive to say to anyone about what they do. Perhaps you should post some of your bridgeported housings' pictures, from various angles, with explanations to the application, to substantiate just how skilled you are and why everything you say should be listened to.



If you had bothered to read the original posts, you would have learned that this bridgeport is done _conservatively_ as a way to add a little extra mid-range and top-end power plus give the bridgeported notoriety to the vehicle. I've done much more radical than this with the aforementioned "back cutting" you're speaking of. I'll let a photo illustrate:







Backcutting of the short radius of that eyebrow cut *was* done at two different points:



-) On the combustion chamber side, it was done with the same grinding stone I use to fine-edge the sides and bottom of the cut as well as tapering the closing timing. The angle isn't done sharp because the width of the eyebrow cut prevents nearly anything from getting in there.

-) On the port tunnel side, it was done there as well.



There was backcutting done. It's standard for me to do. Had I taken a picture from the perspective of the port tunnel, you would have seen it. You're mistaken and you're a jerk for the way you've come off. Nobody is going to "laugh at my BDC bridgeports" because those that are better than me see that I atleast have a solid idea of what I'm doing. Plus, they see that I'm out looking for constructive criticism to make improvements in my skill in doing them. Only a guy like you, who seems to thrive off the angered responses in threads like this, will even bring the subject up and try to turn a technical and mostly-enjoyed by the community hobby and trade into a veritable "pissing match". It reminds me of the bully kid in elementary school that tries to knock someone right back down that's trying their hardest to lift themselves up above their circumstances.



By the way, while we're on the subject Ted, where's the pictures of your bridgeports? Where's your cars that you've setup that you've learned from and experimented on to produce the best results you can? I managed to 499rwhp and 399.7ft/lbs of torque at 22psi of boost out of this car (two weeks after this dyno was done) with a *much worse* bridgeport (that had zero backcutting or closing timing tapering) than the ones you've seen posted here:







Where's yours?



B

nyt

not for nothing, ted, but youre failing to take into consideration the drastic difference of the start of the intake cycle. These bridge ports may look small, but make a LARGE difference on when air can start flowing into the combustin chamber. I have a BDC bridgeport in one of my cars. The plate is 'backcut' as you call it. It makes more power than my last HUGE streetport motor.