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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 ! |
Dude, you're talking about FC owners who complain about gas prices going up 10¢ a gallon!!! :D
-Ted |
You're also talking to Australians, the continent of rotorheads who find a cheaper way of getting power with anything they do, just to afford to spend more on gas and get lower MPG :)
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Originally posted by RETed Dude, you're talking about FC owners who complain about gas prices going up 10¢ a gallon!!! :D -Ted I would like to refine it a bit. Potential BP or PP people ask your self these questions. A: Do you worry about how much fuel costs and how much you use through the week? If you answer yes, then you do not want a bridge or peripheral for the street simple as that. If this is answer NO then got on to B B: Do you have concerns or do you think that you will be fined (by police or RTA) for "very" above legal exhaust noise? If you answer yes, then you do not want a bridge or peripheral again. It realy is as simple as that, ask yourself these two questions, and remember to give an HONEST answer that is applicable to you or the area you live, as ALL our circumsatances are different. |
man good info, i didn't want this thread to end
james |
my only consern is that i have a n/a... i dont want to bridge to really hurt my car because i only see it being run on turbos... i am getting the 10lb flywheel and 4.30 gears so that might help with the lower end a bit... i just need to know if anybody has run a BP on a n/a? or would if even matter?
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Okay, take notes - I'm only got to go over this once! :D
The lines on this graph pretain to my street port '87 Turbo II 13BT versus the KSP Engineering twin-turbo bridge port monster. My dyno graph can be seen here:  http://www.fc3s-pro.com/pics/dyno1.jpg The KSP FC is this the pink FC, which can be seen here:  http://www.fc3s-pro.com/pics/FC3S/KSP/kspfc1.jpg The KSP FC has it's power units in "PS", but this is very close to "HP".  The graph was plotted in MS Excel and overlayed over each other... http://www.fc3s-pro.com/pics/spbpcompare.jpg If you can believe it, my car makes MORE power than this KSP beast under ~3,800RPM or so.  My car only made 253hp at the wheels; the KSP beast made over 580ps at the wheels - that's over TWICE as much power, yet my car made more power under 3,800RPM!  If the race was restricted to 3,800RPM, I would win. :) Of course, this is not realistic, and above 4,000RPM that thing would walk all over me like I was standing still.  I believe RICE RACING is produce power in this range - I'll race you RICE RACING up to 4,000RPM! :D THIS is what I mean about losing the low end power.  The BP is just not efficient down low as an SP - imagine if the turbos were the same type!  This is a measly T5/T6 compressor upgrade up to 15psi versus a PAIR of HKS GT-2835 BB turbos pushing up to 20psi of boost!  The SP would produce even MORE power over the BP if the turbos were the same! This is POSITIVE PROOF the BP can't match the SP under 4kRPM or so.  I'm surprised the power difference was this bad to tell you the truth... :D -Ted |
10 views and no one says anything? :D
-Ted |
I accept that my engine makes less power below 4k rpm than it did with the street port. I cruise around at 2-2.5k rpm. I won't race from that rpm.
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to use one of Peter's favourites - this is a PRIME example of WHY cars have Gearboxes and Diff's
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Originally posted by HWO to use one of Peter's favourites - this is a PRIME example of WHY cars have Gearboxes and Diff's We're not driving race cars here.  I dunno about you, but I'm getting almost too old for that shit.  I can "tool around" in 5th gear at 2,000RPM around town and not have to downshift for more power; just giving it a little gas gives me enough power for 99% of my needs.  Lower RPM means lower EGT, lower temps, lower revs, lower wear&tear, lower stress on the engine - we're talking street car here.  I got NOTHING against a race car running a BP motor.  I think street cars outnumber the races cars very easily on here.  You can live with the disadvantages of a BP motor for a daily driver like MikeL, sure go for it!  I'd bet 90% of the people have no clue what it's like driving or owning a BP rotary - you're giving them a false sense of facts by telling them it's okay; my graph clearly shows the SP motor puts out significant power at low RPM's. Hell, if you're going to scream at me why I'm driving under 4,000RPM, you're wasting your time.  The exhaust gets stupid loud at that point (at least mine does).  The heat difference is really obvious, as I pointed out earlier.  Your mileage goes to crap; I can regularly get 20mpg driving like a grandma around town - any BP owners can claim that on 50/50 city/highway mixed driving? Need I even remind that when that bridge does break (and it will), you're looking at a really big price tag to rebuild and replace at least a $400US+ rotor housing! Your arguments are looking pretty weak.  The graph practically shut the door on any doubts on what makes better low end power.  Imagine if the turbo set-ups were the same... -Ted |
Ted,
Please, try not to be offended by anything that I write below. It's not my intention to offend, only to tell you how this old fucker feels about his full BP TII in daily driving. I can't yet relate much about ass-hauling with it. That will come later. Even with me at 2-2.5k rpm driving around town, with the a/c running, either in 4th or 5th gear, this BP seems to have more power than my SP when I go to accelerate without downshifting. I think the reason for that is that while cruising, the vacuum reading is very low, very near boost at about 7-8 on the gauge. The slightest pedal press gets me into boost. I think that if the turbo wasn't there, I would absolutely hate the BP but, since I can boost at 2-2.5k rpm in ANY gear, I feel more power down low with the BP. I'll post again after I begin to tune for boost. Mike |
I'm not offended at all - in fact, I'm looking forward to the dyno sheet from you MikeL!
The beef was more pointed to HWO since we both go way back on this SP versus BP argument... Sorry to have dragged you into all of this. :( -Ted |
I might be able to do a dyno in a month or two. I just passed 1000 miles with the engine.
My financial situation has been very bad for almost a year. I can't afford to break anything, especially an engine. I just can't afford to be a race car driver right now. When I do dyno, the T-66 will see only maybe 15 psi, but, since the debate here is low rpm, I could still get us some good information and, the dyno operator will overlay previous runs with the SP onto the BP dyno sheet. I don't think we can get much better than that for a comparison. |
Originally posted by RETed Oh, come on...you're never going to admit it, and you're still making excuses. We're not driving race cars here -Ted speak for yourself, but my car has no carpet, no sound deadening, no extra's which aren't needed to either a) make it go faster or b) keep it road legal c) my car might see a trip to work once a week on a saturday, approx 3km down the road, just to give it an airing, otherwise it will be driven to events - approx every 3rd or 4th weekend average over the year and it'll be rung out hard. launch and ride the clutch a bit in 1st, i might see under 4000rpm for a second or two, but after that it wont see under 4000rpm until i cross the finish line weather it be an autocross, a circut sprint, a road sprint or whatever. It has a full rollcage, two race seats, 2 harness belts, is generally loud to ride in and the ride comfort certainly isn't high. so i'd say my car IS a race car, cause it certainly aint a daily driver. |
i have a BridgePorted Engine, ive had since last year of march of 2001, ive driven the car 15,000 miles, the engine was rebuilt and given too me, No problems , i baby it like my own son, i got 205HP stock and 279Torque at low RPM, about 4500, i luv this engine :)
oh yeah its 89 T2 |
Originally posted by DrunkenMaster i have a BridgePorted Engine, ive had since last year of march of 2001, ive driven the car 15,000 miles, the engine was rebuilt and given too me, No problems , i baby it like my own son, i got 205HP stock and 279Torque at low RPM, about 4500, i luv this engine :) The thread is here:  https://www.rx7club.com/forum/showth...threadid=78869 -Ted |
Originally posted by HWO speak for yourself, but my car has no carpet, no sound deadening, no extra's which aren't needed to either a) make it go faster or b) keep it road legal... I smiled when you wrote all of that, cause I've been through it myself.  Just wait till you hit the age when your eyesight, reflexes, and patience all take a shit.  Trust me, age is going to catch up to you, just as guarantee as "death and taxes". Enjoy it now - it is all over in a blink of an eye... -Ted |
Originally posted by RETed Your facts are suspect...that V8 is running nicely in your FC... The thread is here:  https://www.rx7club.com/forum/showth...threadid=78869 -Ted |
what do u think the main cause for the bridge breaking is? boost? abuse? and is there any way to keep the bridge a little thicker? and is a 1/2 bridge port the same as a partial bridge?
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Gidday,
My old b/p was angle cut at about 45deg to the face of the side plate. This give heaps of meat under the bridge, so the chance of cracking is minimal. That was the best engine i've ever had in my Rx2, i'm getting rid of the turbo engine now and going back to the b/p i think. It was only 250hp, but the throttle response was awesome and much much less complex that my current motor. |
any pics of what that would look like?
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Okay, i'll see if i can dig some old housings out and take some pics.
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A page from tonights datalog.
I was cruising at 1760 rpm in 3rd gear. I pressed the go-fast pedal down. In less than a second and by 1940 rpm, I had boost. Before I got the pedal down all of the way, I was into boost. Full BP TII. http://brfoundation.com/RX-7/Images/rx7forum1.jpg |
You may have had boost before that, just because it was still in a "vacuum" does not mean it was not on boost, if you think in terms of absolute pressures, you will see what I mean..
I do have a question though Mike, how do you get screen captures like that??? Max |
here's the pics of my old bridgey. It's gone a bit rusty, but you get the idea. For those who are interested
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