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FYI
A Miller-cycle engine is very similar to an Otto-cycle engine. The Miller-cycle uses pistons, valves, a spark plug, etc. just like an Otto-cycle engine does. There are two big differences. First, a Miller-cycle engine depends on a supercharger. Second, a Miller-cycle engine leaves the intake valve open during part of the compression stroke, so that the engine is compressing against the pressure of the supercharger rather than the pressure of the cylinder walls. The effect is increased efficiency, at a level of about 15%. |
The supercharger is there mainly as a check valve so the reversion isn't so bad.
Crane Cams was developing an "Economizer" setup for V8s in the early 80's... it was just like a Miller-cycle engine, with LOOOONG intake duration extending far into the compression stroke, but instead of a supercharger they used sky-high compression pistons (14:1 as I recall). The engines only made 200hp out of a 350 which was barely better than stock at the time, and there was so much reversion that carb tuning was quite difficult (and EFI was still extremely expensive) BUT... the engines had a cruise BSFC on the order of .30 lb/hp/hr! For reference most rotaries are around .65, most gasoline boingers .50, most diesels .40. Mazda was experimenting with something called TISC, Timed Induction with Supercharge, for their rotary engines about this time. They had a very very late opening and closing port that was to recieve timed air from a blower pumping 30psi boost. (Note that the rest of the induction path was N/A - only this small port would get pressure, and only part of the time) |
Originally posted by BLUE TII Wow! I never thought I would say this, but Ted you are incorrect. The Miller Cycle engine DELAYS the closing of the intake valves further into the compression stroke and depends upon a strong S/C to provide compression and stop reversion. Typically Millers are 15% more efficient per displacement. I knew something was wrong with what I said. :) -Ted |
Originally posted by peejay You're only losing velocity if you open up the runners a huge amount! Only open up the parts that are a restriction and leave the rest alone, and get max velocity with minimum volume. Then you start making stupid-big power at decent RPM! window of the port isn't critical to velocity... it's more critical as it relates to opening and closing timing. Look at it this way, the airflow is going from high velocity in the runner to very low velocity/large volume when it actually gets in the chamber, you're going to want to make that as smooth a transition as possible so you need to open up the port window BESIDES the obvious benefits from increased port timing. With a good Bridge or a Peripheral the air has more of a straight shot into the runner versus the two or three right angles that the air must make with a stock port or even some badly done street ports. -Ted |
Originally posted by RETed Oops, brain fart - thanx for the correction. :) I knew something was wrong with what I said. :) -Ted just for the record i dont see you making HUGE numbers or running impressive times on the strip either..... i do believe on your webpage it says on a turbo'd rotary you dont want to make the intake ports open any earlier than they do from the factory, yet this is one of the ways people double the stock HP output, care to clarify that statement??? |
Originally posted by RETed This is a bit too general of a statement to be making; the intake/combustion cycle is a super complex system that goes way beyond my knowledge. The intake doesn't stop right after the intake port, but goes through 1/3rd of a revolution around the rotor housing before getting ignited by the spark plugs. I'd bet the intake port is not the restriction in the intake system (my bet is on the intake runners in the intake manifold), so you get weird compressions and expansions in the intake path... -Ted I have to disagree with something though - yes the intake DOES stop after the port closes, as far as that rotor is concerned - we are now in the compression phase. Between going from high velocity/low volume of the port runner to low-velocity/high volume of the chamber, to getting forced around and squeezed from a roughly D-shaped slug of air into something more resembling a flattened M with a trough in the middle, there is so much turbulence in the combustion chamber that any effects from the resonances in the intake manifold would be minor at best. And as the rotor turns the charge gets squished from one side of the "m" through the trough to the other side as the rotor moves past the pinch in the chamber! Weird compressions and expansions in the intake path... yeah, it's called resonance tuning, or "how to get max VE at a given RPM"! Most boingers use it to stunning effect (that's how 5.0 Mustangs have such incredible torque numbers for engines of their size and compression ratio they have over 104% VE at peak torque in stock trim!) and fuelie rotaries do too... and it works even better when you tune it right with more overlap because you can more easily scavenge the chamber of exhaust gases by the incoming intake charge - which is where this all goes back to on-topic.... |
damn how did it turn into this? all i know is a bridgport IS streetable!
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Originally posted by soul assassin damn how did it turn into this? all i know is a bridgport IS streetable! |
half bridge, here is my pic of the porting
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i would estimate that in NZ there would be around 500-1000 daily driven rotary's with either Bridge ports, J Ports or PP's in them......................
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Originally posted by HWO just for the record i dont see you making HUGE numbers or running impressive times on the strip either..... i do believe on your webpage it says on a turbo'd rotary you dont want to make the intake ports open any earlier than they do from the factory, yet this is one of the ways people double the stock HP output, care to clarify that statement??? -Ted |
Originally posted by RETed I never claimed I did; you are the one claiming so-and-so works cause so-and-so has done it. Why would I need to run "impressive" times to back myself up? I guess I need to remind you that I don't build cars for the 1/4-mile - I've gone through that phase, and I find road racing a whole lot more complex and challenging. -Ted |
I shouldn't try to speak for Ted, but he probably means if you don't have direct firsthand knowledge from personal experience do not express your opinion as fact or even strong opinion. You will note if Ted posts "this is how it is" he always has a direct personal experience to back it when someone asks. Look at the Miller post-he prefaced it w/ doubt. There is way too much misinformation seeping into this forum from what Posters have "heard" or "seen" on others cars-but you in no way even close to the biggest perpetrator of this HWO; You'd probably find a few stupid posts by myself if you searched, I'm sure... Anyways, strong opinions and statements of fact should be from firsthand experience in my opinion! Of course "how streetable a bridgeport is" is only going to be opinions and dependent on soo many variables.:)
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Originally posted by HWO I dont build cars for the 1/4 miles either, i am building mine up for hill climbs, circut racing and autocrosses, but the way you go on about it, it seems that you think i need to 'prove' myself to you before anything i say on here can have any true meaning............... The Racing Beat catalog says not to increase overlap on a turbo engine. "How to Modify Your RX-7" book by Jim Downing says not to increase overlap on a turbo engine. Now, with those two "tuners" saying otherwise, why would I want to try increasing overlap?  I didn't say it couldn't be done, but sorry to disappoint you that I don't have the money to experiment with such mods.  How you know that Rice Racing and crispeed would actually make MORE power without increasing overlap?  It's a "what if" question - something that will take a lot of time/money to prove otherwise. Any now you're telling us to ignore such advice because Rice Racing made 600hp?  That's some twisted logic.  Every claim you've made that I've challenged was answered with:  "so-and-so has done it so it must me true" or some twist to that reply.  Replies like these don't count in my book - this is why I rag you so hard. :D -Ted |
damn!! calm down fellas!
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Originally posted by RETed It's cause you're basing your information on other people's work.  I don't know if you've never seen these references before, but... The Racing Beat catalog says not to increase overlap on a turbo engine. "How to Modify Your RX-7" book by Jim Downing says not to increase overlap on a turbo engine. Now, with those two "tuners" saying otherwise, why would I want to try increasing overlap?  I didn't say it couldn't be done, but sorry to disappoint you that I don't have the money to experiment with such mods.  How you know that Rice Racing and crispeed would actually make MORE power without increasing overlap?  It's a "what if" question - something that will take a lot of time/money to prove otherwise. Any now you're telling us to ignore such advice because Rice Racing made 600hp?  That's some twisted logic.  Every claim you've made that I've challenged was answered with:  "so-and-so has done it so it must me true" or some twist to that reply.  Replies like these don't count in my book - this is why I rag you so hard. :D -Ted How is passing on infomation which i have learned from others who have been open enough to pass on some of the stuff they have discovered over their years of playing with rotary engines, any different to say an school teachers - teaching stuff to their pupils? most of the time they haven't learnt what they are teaching from first hand experience - however i dont see people - such as yourself, dissing school teachers with comments of "you haven't experienced that first hand so you dont know sh1t" there is no real difference. the difference is guys like Peter and Cris are great guys who are willing to share some of their knowledge with other rotary fans who are wanting to learn the pro's and con's of all the so called "basics" of the rotary world. They are guys who have challenged the "basics" as they were and have discovered that HP can be made in ways which a few years ago , older 'set in their ways' rotary 'experts' would have laughed at the idea's and said it couldn't be done. As one of the aussie guys said - a couple of years back the top drag guys were running T04's which now days every 'tom dick and harry' is running on their 13B, give it a few years and every 'tom dick and harry' will be running T72's and T76's and the drag guys will all be running thumper sized snails on their 13B's. times they are a changing, weather one wants to move with the times is truely up to the individual, but as technology grows, more advancements in rotary engines and turbo rotary engine HP are made. Now it is up to each individual weather they want to grasp the new idea with two hands and go with the new way of thinking or if they want to stay set in their "you cant increase overlap" ways and stay where they are. I could continue on to tie religion into this same sort of issue that you seem to be having but that would open up another huge kettle of fish which would lead this to become completely off topic and the other members of the forum would gain no info to do with rotary's let alone HOW STREETABLE A BRIDGE PORTED MOTOR TRUELY IS............... |
What Peter says, GOES :D. From what I see, HWO is knowledgeable and re-iterates what he's learned when Peter isn't around (which he's very busy). I don't think he just regurgitates info, but actually understands the concepts he's talking about. Maybe he doesn't go into the kind of technical detail, but what do you expect? Peter is a mechanical engineer, that has done tests, and has hard factual data, on nearly any setup you can imagine. When I see Peter say overlap makes power, I believe him, and will continue to, until he can't backup his claims with facts (which he always does).
So in conclusion: What Peter says, GOES ;) |
Could someone please translate this thread into english. And while you're at it, delete all of the nonsense, and replace it with nice remarks about how much everyone admires each other. We need our tech's to get along.
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Originally posted by RETed The Racing Beat catalog says not to increase overlap on a turbo engine. Look at it this way... A BP or PP works well with ~14.7psia manifold pressure. (aka atmospheric pressure) Why shouldn't it work even better with 20, or 30, or more psia manifold pressure? Or do BP/PP engines stop making power once you're below sea level? |
Originally posted by peejay to find out where this "no BP/PP on turbo" fallacy started. "Fallacy" is from boingertech. Too much overlap causes intake charge to be pushed out the exhaust, reducing VE of motor. Ever seen a turbo'd ITR w/ stock cam running >10 PSI boost? Big black cloud of smoke upon cam change out tailpipe. (still big power, but mosquito fogger too) FWIW, this whole thread started as "is a bridgeport streetable?" My answer remains "if you're hardcore" :D Brandon |
sorry to bring this back from the dead but i have a few questions becuase the rebuild is comeing soon... i am thinking about a bridge port but i do drive it a lot on the streets and cant drive around 4000-5000 all the time... if i get one done how much power am i looking at around 3500-4000? same as i have now or will i lose a lot of power down low? and does anybody have any experience on the 1/2 Bridge Port? seems like a good way to go? thanks..
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bump... any ideas
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I drive my full bridge TII almost every day.
The first time in each drive that I get on the car to make big boost, it seems that the plugs are fouled. I first got the normal driveablilty good then, began to tune for boost. When I get on it the first time during each drive, it seems to need to clean the plugs and spits out a lot of black smoke and doesn't want to haul like I want. After that first time during each drive, it's fine. I like my BP. I hope I can overcome the issues that I have but, after driving around long enough to feel comfortable that it's warmed up enough, the first ass-hauling does not much more than spit black smoke. |
Originally posted by 13B2QuIcKNy First of all this is my first post.. and would like to say what up to all the fellow rx7 lovers out there.... about the bridge port... ive known many 12a and 13b's with it and it doesnt give any problems...u lose some low end torque but the high end is incredible.. my friend just sold a white 86 wit 13b housings and 12a side housings. bridge port, exhaust porting.. no cats and 2 1/2 exhaust piping, racing beat intake manifold , holley 650 4 barrel with a turbo II hood, and a bronze clutch and he use to run 14.5 constant.. and had no problems... it did swallow more gas.. but it got more than 10-12 miles a gain.. he got almost 210 miles a tank driving in traffic with the idle bouncing from 1000 to 1200 constant... and he never had problems.. the car was solid.... |
Re: bridgeporting a street car
Originally posted by bcty what are your guys oppinions on bridgeporting a street car? will it be driveable? and is it only reccomended for a turbo or can us N/A guys do it to. thanks. You will use up to double the amount of fuel in low load low rpm "street" point A to point B mode. You will have a LOUD car when exhaust is set to get full benifit of the porting, which may WILL cause many hassles with cops, RTA, Neighbours (pick any or all of these !) The pluses are... You will have a wider power range, you will use less fuel under high load/high rpm "racing" You will make more power for the same boost level compared to side ports For a true "street" car that you want to still get good economy out of and have perfect road manners/drivability then a side port is realy unbeatable for this design criteria. Partial or even Full Peripheral ports are totally drivable ! but they do use a LOT more fuel and are as a package a lot more complex and expensive to get running to their full potential. As I mentioned, I ran a full Peripheral Port for over 4 years driving every day and covering around 30 000km a year so I think I can give you some long term impressions on this topic, I loved it ALOT, but when waying up the hassel from the extra fuel costs to the constant worries about noise it took away some of the fun. For a weekend car, if cruizing economy is not an issue, I would run my road car as a BP or PP turbo no doubt about it :D But for the economy and the power I make with a street port it realy is a better option for me here in Australia, even if it is a soft cock option ! |
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