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So I have benign looking around and find old post on the subject. As I have read the typical argument agent HBP is fuel MPG drop for a street car, Noise and not worth bang for the buck.
Some advantages for HBP is less stress on the engine, lower boost pressure requirements for 450 + rewhp, small turbo requirements.
Then I read mpg not drastically effected with HBP If tuned semi correctly.
Addressing your question from the other Single Turbo form thread:
Originally Posted by TeamRX8
the one thing you might consider for the BP is asking them not to extend the bridge opening so far to the closing end of the intake cycle. Imo that’s been overlooked some for a streetable BP application. Because even though they may look equally positioned on the closed timing end, the bridge ends up closing later than the adjacent main port due to it’s position relative to the rotor. It’s one thing to have overlap at idle, it’s another for the compression cycle to be blowing back through the bridge opening into the port runner. You can get away with that at higher rpm/velocity/momentum, but not at idle.
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Originally Posted by swif
Is this something to worry about with a half bridge?
to a lesser degree but yes and potentially the same for a large street port depending on how extreme the closing timing point
in the quoted diagram and description below, note the closing face position of the rotor tip/apex seal relative to the main port; this is what I’m referencing in the copy-replied post above. Not only is the intake cycle compressing into the runner through the BP opening, but exhaust overlap on the other side as well.
Originally Posted by Compliments of Paul Yaw & Yamamoto Kenichi
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Intake Cycle Event #5 45° ABDC - The chamber has started to decrease in volume, and with the exception of a stock US model 12A, which has an (primary) intake port closing of 40° ATDC, the intake port is still partially open. At high rpm, the intake port is still flowing in the forward direction due to inertial supercharging. At low rpm, airflow in the port has reversed, and some of the intake charge is being squeezed back into the induction system by the pressure of the intake chamber which is decreasing in volume. This is the result of the low velocity in the induction system. This is a very important point to consider, as this alone affects the operating range of the engine more than than any other factor.
I’m not a big fan of BP for turbo myself, consider this example from Kevin Blantz:
The one exhaust port template I favor is from Kyle Mohan (below); barely touches the closing side/overlap, but advances the opening timing significantly. I might not even alter the OE closing line at all except to smoothen flow exiting it into the port cavity. If doing your own porting, it’s entirely within your discretion to alter some of these details wrt opening and closing timing features. If anything, the average person tends to trend too much on the racing side of the balance scale and then pays the piper for it. Having some basic understanding and trending conservative is likely to yield better idle and drivability manners without costing too much of the total performance gain potential.
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(apology for going into the Renesis diatribe, but some this all interrelates)
interesting to note that the factory 6-Port Renesis Primary port closes at 65° ABDC, but the key factor being the Renesis has no intake/exhaust overlap and relies heavily; in fact “solely”, on intake resonance. Because though while still not fully understood or accepted by many people, exhaust resonance is virtually nonexistent without intake cycle overlap/momentum flow to carry it through i.e for all intents and purposes there is none on a Renesis. Performance-wise, a header offers nothing on a Renesis over a big open manifold and exhaust system to absolutely minimize backpressure.
The lack of overlap allows the Renesis intake ports to be placed in the extreme early opening points and also interesting to note how the Aux serves as a high rpm extension to the Sec port. Effectively this all making it the same as closing the LSA on a camshaft to the extreme. Which I’m a 100% believer in the David Vizard view on piston engine camshaft timing with LSA being the #1 key component to camshaft selection for a particular engine parameters and then establishing overlap relative to the application wrt Street —> Performance —> Race. Most people and camshaft companies are doing it the reverse way. Unfortunately fixed ports and water passages on a wankel engine aren‘t as easily manipulated as poppet valve events with a camshaft.
Which is why the Renesis hybrid concept; the addition of the peripheral exhaust port rotor housing to a Renesis engine, pretty much results in it falling on it’s face. It essentially becomes the equivalent of a full PP engine; except with all the bad traits and none of the good due to both the intake and exhaust all being split up into multiple flow streams of differing and often conflicting timing events and all the compounding efficiency losses that result from such.
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Hit just over 700 rewhip but is boosting to 30 psi. Isn't that a lot of pressure for the engine? If I recall correctly this engine is studded correct?
What is scalloped rotors, does this increase overlap? If so overlap increase with HBP or BP correct?
the build is impressive for sure. I m not sure I want to hit 30 psi. From what I have read so far a proper large street port will also effect omg, give brap brap to a point and can also give characteristics of a bridge.
Will definitely share with builder to get more input.
1st link is interesting for hp with a bridge port. Id think more power would be available.
The 2nd link is crazy to run pump gas (91)and hit power at that psi with out worry.
both guys were doing track days for years at that level with no real issues. its possible. Max tests EVERYTHING before he puts it on the car. its surprising how many new fancy aftermarket parts fail
both guys were doing track days for years at that level with no real issues. its possible. Max tests EVERYTHING before he puts it on the car. its surprising how many new fancy aftermarket parts fail
Over the years I have seen many people advise not to boost at those levels with pump gas. In many cases AI was recommenced at the least.
Talking with builder tomorrow and see what his thoughts are. Again I am looking for mid 500s but not stressing the engine so much. Maybe hit 22 psi.
His engine builder cant really tell him if the noise, nhv increase and mpg decrease of turbo half bridge vs mild street port is "worth it" to him.
Its subjective.
I dont really have an opinion. When Im in the mood for a rowdy car its fun and when Im not in the mood its onto a trailer or take a different car for the trip?
if you have a builder then why are you even second-guessing them and jumping the forum through these same old hoops again?
because you wouldn’t be asking if you knew enough yourself, which then also leaves you open for not knowing enough to discern the replies either.
just sayin’ is all … do you trust your builder or not?
if the answer is no, then that ought to be a big red flag waving in your face.
If yes, then go with what they recommend.
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So you make this post then about 10 minutes later on the other thread you stated, "not trying to be derogatory...."
1 Not second guessing my builder
2 Asking question to learn is part of the process. As a person learns they learn how to discern the information.
You are clearing researching my post, you will see that I posted about builders in my area and I did research on them. You will also see that in many of my post with question I have understood replies or ask further questions.
You will be happy to know that I spoke with my builder this last Saturday and I am going with their original suggestion of a half bridge for my goals and driving experience.
His engine builder cant really tell him if the noise, nhv increase and mpg decrease of turbo half bridge vs mild street port is "worth it" to him.
Its subjective.
I dont really have an opinion. When Im in the mood for a rowdy car its fun and when Im not in the mood its onto a trailer or take a different car for the trip?
Who has FD as only car in 2022?
I am fortunate enough to have the option of when I will drive my FD. it will be for the most part a weekend driver. That being said I also have the option to drive a V8 sports car to get a completely different experience with a sports car. I also have a family car.
Because of these options Im not too worried about mpg, but also don't want to have something that is 8 mpg. My V8 if I get on it with about a 30 mile drive I can see about an 8th of a drop on the gage.
And my limited understanding is that bridge ports assist with moving air to allow for higher HP with out the need for so much boost pressure. A bridge port can/is streetable with proper tune.
Lots of folks run Bridge ports on the street and they work fine if set up properly. If any of you ever go to true Rotary car events like DGRR or Seven Stock you would see a TON of brapping rotaries. Some of you need to get out more! lol
I can’t wait to get rid of the BP engine installed by the previous owner
the whole brapping thing is overhyped by the attention harlot crowd, even if you can get it to idle at a lower speed it’s still annoying to a hydrocarbon-stenching fault, and more importantly not necessary at all with a turbo either. If you’re going there then semi PP makes more sense on every level.
funny to be reading your responses now like you have it all figured out before having even gone there, but then glossed right over the example I gave you for a large street port. That engine at 25 psi would be in the low 600 whp range. In other words, right where you were looking to be in the 22 psi range.
what you still didn’t grasp fully yet is that the terms street port, bridge port, etc are only words. What ultimately matters is the opening and closing timing points. There’s a lot of undefined variation out there …
I can’t wait to get rid of the BP engine installed by the previous owner
the whole brapping thing is overhyped by the attention harlot crowd, even if you can get it to idle at a lower speed it’s still annoying to a hydrocarbon-stenching fault, and more importantly not necessary at all with a turbo either. If you’re going there then semi PP makes more sense on every level.
funny to be reading your responses now like you have it all figured out before having even gone there, but then glossed right over the example I gave you for a large street port. That engine at 25 psi would be in the low 600 whp range. In other words, right where you were looking to be in the 22 psi range.
what you still didn’t grasp fully yet is that the terms street port, bridge port, etc are only words. What ultimately matters is the opening and closing timing points. There’s a lot of undefined variation out there …
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I will take that BP off your hands!! lol
I agree with you on a turbo engine, i would stick to Street port. The BP is fun with NA though.
I can’t wait to get rid of the BP engine installed by the previous owner
the whole brapping thing is overhyped by the attention harlot crowd, even if you can get it to idle at a lower speed it’s still annoying to a hydrocarbon-stenching fault, and more importantly not necessary at all with a turbo either. If you’re going there then semi PP makes more sense on every level.
funny to be reading your responses now like you have it all figured out before having even gone there, but then glossed right over the example I gave you for a large street port. That engine at 25 psi would be in the low 600 whp range. In other words, right where you were looking to be in the 22 psi range.
what you still didn’t grasp fully yet is that the terms street port, bridge port, etc are only words. What ultimately matters is the opening and closing timing points. There’s a lot of undefined variation out there …
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So now you interject personal opinion (not fact based or scientific based) for "whole brapping thing".
Idling at lower RPM from what I have read can be handled with bp porting and placement (opening and closing timing points) along with proper tuning. As far as hydrocarbon-stenching fault, running E85 takes care of that problem. Of course I will run pump fuel to assist with avoiding corrosion from E85 so I guess I will have that concern from time to time.
Its funny how you assume I have it all figured out with your lasted post yet prior you stated I didn't trust my builder? Which is it?
I did not gloms over your example of street port hitting 600 hp on pump gas. I found it interesting and I have seen a couple other examples. I question it as it does not seem to be the norm. Yes people say street port pump gas no AI can get those numbers. Yet how safe and are there pushing the car to that level often or was that just a tune to say it was done? Keeping with AI I am aware of people hitting close to those numbers with AI but they suffer in drivability.
"what you still didn’t grasp fully yet is that the terms street port, bridge port, etc are only words", interesting take. So a street port vs a BP or PP is only words no physical difference at all? If these terms are only words then your statements are worthless as the various porting mean nothing and changing opening and closing points is the only key. Yet the various ports effect just that and each one has variation with in them selfs.
Someone elses car is always going to annoy you. Especially if you are a crotchety old ****.
Get the large turbo brap porting. I mean a full built sickarse sportscar isnt supposed to be sensibke ffs
not that it’s about me or ever should be, but regardless of who it is; it’s not the first time some guy on the internet thought he knew and understood more about somebody else better than he does his self … people are often much deeper than what a few words on the surface, which possibly the true intent of weren’t fully comprehended, can define …
which one day though you ought to let me tell you the story about my father; who by all worldly standards was a very successful man that started with him graduating #1 of his class at the Dale Carnegie “How to win friends and influence people” doctrine, what he told me as a teen, and why later as an adult when the meaning of it was fully understood, I rejected it for myself.
then you might actually know something real and truthful about the person you’re speaking of. And now back to you’re regularly scheduled internet forum show …
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Idling at lower RPM from what I have read can be handled with bp porting and placement
mostly this is tuning, my Peripheral port idles ~900rpm, like the manual say it should. this is with a carb and locked distributor too, so with EFI, you should be able to idle around there with ease.
the engine is capable of idling lower, but the carburetor is my limitation
As far as hydrocarbon-stenching fault, running E85 takes care of that problem.
sort of, you smell like potato chips, which is better. if you say go dyno, breathing the fumes will still turn your head to mush though, just like regular gas.
E85 is nice though, we ran it in a miata, and just by dumping it in the tank we got 3-4hp, which is really good for that. it also would tolerate hot days better.
but they suffer in drivability.
they shouldn't, again that is a tuning problem. a bridge or PP won't be happy at mid rpm (2-4k) and low throttle openings (if you are behind a prius), but other than that it should start and run and drive like stock. a street port should run like stock.
if you have a bigger turbo and more boost, it should just shove you in the back harder
we have fancy ECU's now, we can make the engine happy all the time
Exhaust porting is where you can really ruin driveability of a turbo car in my experience.
I would leave stock FD exhaust ports stock up to ~550rwhp level.
if you over port the exhaust (anything "up or wider") it makes it harder to get going from a stop- gotta abuse the clutch.
If you are idling at 2,000rpm like most poorly tuned bridges and semi p-ports it probably has no/little negative affects though.
I really noticed the downsides from 800rpm idle to 3,000rpm on an overly large street port.
Here are the ports I had.
Keep it more like the Left if anything- just down a bit for earlier opening/better spool and shaped for flow. The Right where it was larger and ported up was doggy off idle.
11-30-22, 11:13 PM
