i dont remember where but i heard on a site that its not good to have a turbo-bridge ported motor... but why? that doesnt sound right. i mean its just more air right? as long as you get the fuel to back it up... i was thinking about doing a mild bridge-port and havea turbo set up next year when i get the motor done... good idea?? my town is overrun by gt's and cobra's and im tired of it

oh yeah and what about a p-port motor with turbo?? wich would creat the best power ??

Well, for p-port turbos, I've heard that you can blow boost out of the exhaust port because of the overlap. But I guess that all depends on how big your p-port is and where it's located.



Owen

this gets into the area of 'its possible, but what are you after'.



There are a number of ways to view a turbocharged engine. If you just look at the turbo as a torque multiplier on top of a naturally aspirated torque curve, then it follows that any engine can be turbocharged provided it can withstand the BMEP increase without exploding.



And this is the crux. If you have a high revving engine with very high overlap that does not produce much low down torque, then adding a turbo will not overcome that fundamental torque curve. This is why in general you start with a low overlap engine with wide and flat torque curve, then add as much boost as possible. This gives the best canvas on which to build boosted power.





So the BP turbo can be made to work, but boost will tend to build later than with a street port. You also need to focus a lot harder on reducing back pressure in the exhaust and realise that the overlap means that a larger turbo is needed to deal with that additional airflow, as you end up blowing a lot of air straight through the rotor and out again. Not a bad thing per say, as you get cooling of the turbine, and if you can get the EBP below the inlet pressure, then you get pressurising of the clearance volume. In laymans terms this allows you get get more power out for the same amount of boost.



However, to get to that level you end up with a motor that is not suited for the street. Lound, late spooling and them horrendously powerful. TBH a large streetport would be a better way to go unless all the local cops are deaf or its a trailer queen.

You'd have to have a REALLY good turbo setup for that to be a problem. Generally speaking, the exhaust pressure will be about the same as or higher than the intake pressure.



If you do blow air out the exhaust port, it probably won't hurt anything. You'd know at that point that you are evacuating ALL of the exhaust gases from the chamber. More likely, you'd only be blowing exhaust gases out and no actual intake charge.

What sort of turbo would that be? The REALLY good one? For that to be a problem, it would be one that flows a lot at low rpm, in which case overlap duration is longer and you'd be blowing intake charge out of the exhaust port, rather than building boost charge. At higher rpms, the overlap is less and more intake charge goes where it's supposed to, into the combustion chamber. Correct?



I understand the need for a larger turbo with less backpressure, or two turbos whose combined exhaust area exceeds the area of a large single. So what kind/type of turbo would that be? This is getting interesting. Oh, I'm talking p-ports here, not bridge, if it matters any.

You can split the forum in half with a debate like this...

I would like to hear from people with turbo bridged and see how they feel about it.

think about it. the turbo is adding a restriction in the exhaust, so if anything the exhaust is going to go out the intake. a REALLY good turbo in this case would be one where the exhaust backpressure is as close to intake pressure as possible.



look at howard colemans setup, he's got 2 turbos and i think he's running about 21psi backpressure @15psi boost. imagine how big his turbos would have to be on a pp motor....



https://www.nopistons.com/forums/ind...howtopic=54978

I believe the physics of the situation makes it impossible for the exhaust pressure to be less than the charge pressure regardless of boost. Is what Corky Bell says anyway. So you will always end up with exhaust gasses in the intake charge with large overlaps.



With a bridge port or p-port you will always end up with charge dilution to some point which compromises low end driveability and power. However the gains from mid to top should more than make up for it.

Not necessarily. There are plenty of documented situations where exhaust manifold pressure is lower than intake manifold pressure.



Exhaust gases necessarily have a lot more velocity than the intake gases, and a lot more volume. This can be exploited.

Actually Bell does make reference to situtations where P2/P1 <1. It's not generally dwelt upon, as in order to get it you end up with something that is a pure race engine with all the drawbacks that entails.



I have some evidence off some of the australian race engine builders that they have this situation quite freqently on high boost rotary drag race engines.

Well, there you go. I don't even plagerize correctly. https://www.nopistons.com/forums/pub...IR#>/smile.png

OK, got ya. And yeah, howard's setup is the one i was referring to, couldn't remember the name...

So...what if I wanted a PP engine, turbo(s), 400-500hp on pump gas...I would either have to get a huge turbo or get a smaller responsive one and suffer all thr drawbacks of high backpressure, right?



If this were just a "I did it cuz I wanted to car" and not a hardcore racer or anything, what would be good turbo choices for single and twins? A laggy turbo for a street ported 13B would spool better on a p-port?



Owen

if you only want 400-500hp then pp is prolly not a good choice. people make that with a street port, or stock ports and higher boost.

I've said before and I will say it again. The only drawback to running a half bridge turbo on the street is NOISE. After running the bridge and stepping back down to the side I can say this.

Well that means bridgy's for everyone!!! Well for meee!!

OR - You can go to the third option:



Bevel the rotors.



http://208.62.166.66:82/guest/pics/9...-timing153.JPG

I agree. I'll post more on this topic as well.



B

Regarding the turbocharged bridgeport idea ...



There's been alot of debate over this for atleast the past couple of years or so. I believe much of the negative stigma associated with bridgeporting comes from the normally-aspirated world where problems with overlap are evidenced clearly. However, when throwing a turbocharger into the equation, it becomes a monkey-wrench and things don't turn-out as one would expect. Prior to any of the BP-turbo stuff I delved into, I only knew of one person (John Duarte/Boostn7) who'd experimented with it and ran it for awhile. He eventually went back to a street port for unbeknownced-to-me reasons. Before then, I'd never heard of anyone who was running any kind of BP-turbo setup on any well-tuned EFI system, let alone anywhere. That doesn't mean it never existed; I'd just never run across anyone doing it. So, as best as I can figure, prior to about three years ago, it wasn't an alternative that many would consider viable. The norm was doing your typical street-port variant with a different turbo. Not quite three years ago, I started experimenting with the half-bridgeport turbo platform. I was initially against it and for many months prior to being "arm-twisted" into doing it on a friend of mine's car. My opinions about the setup pretty much echoed Bill Shurvington's. I was adamantly against it and was sold on the idea that it wouldn't work. Well, I turned out to be wrong about it. As many other times in our rotary history, this was yet another discovery that wouldn't seem to work well at all on-paper but, surprisingly enough, turned out to be not only a viable alternative to street porting but a significantly-improving one. I was amazed by the results -- better turbo spool, much better mid-range, and a high-end curve that didn't fall off. I've been working with these ever since (going on 2 1/2 years now) and, like a few have already said, I won't go back. Throughout my research and experience with these setups over this 2 1/2 year period of time, I've found that the bridgeport-turbo combination can yield higher power output figures with lower boost levels and can run a larger-than-normal turbocharger while still maintaining the feel of a street-port turbo combo (all things remaining constant). These positive effects have been echoed over and over again by those that have chosen to experiment with this setup. It seems to be quite a worthwhile option to those that want to delve into it. Many of those people are now BP-turbo advocates where they once may've been skeptical.



The bridgeport-turbo platform isn't without its complications or downsides, however. It does pose a much greater need for fine tuning via a good standalone EFI system. There's just not much getting around this with the exception of having a linear-run vehicle like a straight-line drag setup. I've spent this entire time working on making better fuel curves and leading/trail-split ignition maps for these setups and am still not considering them to be perfect. From what I've experimented with and done over this time, I've come up with ignition stuff that's fairly more radical (in places) compared to your typical stock or street port setup. Another downside associated with these has to do with the difference between half and full bridgeporting. I'll admit that I've not yet experimented with full bridgeporting on a turbo setup, but I suspect the effects are the same -> a "pushed up" power-peak, earlier spool of a turbo and thereby earlier and more aggressively building torque curve, etc. However, the more overlap that is added in to the equation, the more loss of very low-end (below 1500rpm) is found. This is yet one more factor that a stock injection system can't account for very well and one that further emphasises the need for a good, tunable EFI system and professional tuning. Another thing I have found that gives rise to potential tuning issues is how little of a change in shape, width, and heigth the bridgeport cut can exacerbate drivability problems. Even just the smallest change can add a significant amount of overlap into the equation which makes it all the more difficult to tune for tip-in and for idle. I am not sure of what this would be like on a full-bridgeport; only a half. What I've personally found is to go for the half-bridgeport in using two smaller-sized cuts. The benefits of better spool, better mid-range and exceptional high-end (along with the cool, lopey bridgeport idle) are in their glory yet are not diminished by the tunability issues. Here's an example of that:



http://bdc.cyberosity.com/v/Porting/NeerajTandon/



The work done on this motor is what I call my Spec-C half-bridgeport. This particular one was done on a 13BREW just recently. It's my old "mainstay" of a scheme that has proven to work well for street use. The cuts aren't very long or wide at all with comparison to that of some of the more radical bridgeporting schemes that are floating around out there. To be greatly effective, they don't need to be large. They also don't need to be so big and all-encompassing that they threaten the water jacket o-ring land or march into it requiring some sort of hack-job on the o-ring. The o-ring cutting as well as the issue regarding making the actual iron bridge too thin is what creates the reliability issues that many have risen against this setup. When sticking to smaller cuts such as the ones these alleged reliability issues are a moot point.



In my business, I have alot of questions posed to me about this setup. While I am pro-bridgeport turbo all the way, I do tell my customers that "you've got to have your i's dotted and t's crossed if you want to pursue this setup". Extra care needs to be taken in selecting and matching up a properly-sized turbocharger to the application. A good deal of focus also needs to be applied when looking at heat-elimination type things such as heat-blanketting the turbine housing, ceramic coating exhaust pieces, better intercooler, ceramic coating of intake manifolds, etc. I suppose much of this is true for any good setup but I feel that it needs to be more of a stressed point in this case. There's also the noise factor that's been brought up -- depending on the size cuts done on the housings for the bridgeports, there will be a dramatic increase in exhaust noise (to the tune of 50% or greater loudness).



On a side note Sureshot, the rotor beveling job you did looks very good. However, I've got my concerns about its efficacy as a port-modifier as well as the effects on crank balancing. I wouldn't mind hearing more about this as I do not know a whole lot about it.



B

ive driven a well sorted na full bridge car and the only downside is the idle/cruise, everything else is better. the full bridge na, made more power from 2000rpms, than my gsl-se's do. it just bucks under 4500rpms, making cruising a pain.



the car had enough muffler under it that while you could hear it coming, it wasnt louder than say a honda with a fart can....

I know of one guy running a cosmo 13B turbo with a full bridgeport. He has two piece apex seals from Adam @ RX7 specialties in calgary. He Dyno'd at 705 RWHP. The car has a microtech lt8 management system. My father in-law in going to be running the same set up as Forcefed Performance has except that he will have a smaller turbo than marko. But should still be making 500+ rwhp in a full drag car set up. The corner seals are larger than others being produced so that as they wear down they wont fall into the bridge and **** your engine.

I think the air/fuel charge that escapes into the ex-manifold has a big part in the mid-range power gain. I think it contunues to burn in the turbo and manifold adding to heat and exhaust gas volume.

In japan they have been using bridge port huge j ports and pp engines with turbos. Revolution uses big street ports with 32mm pp . They make a intake manifold which splits the secondaries to both factory secondaries and pp, with t51 spl 680ps at 1.2kg. Before Scoot switched to a 4 rota there demo car 13b streetport primaries and pp seconaries ( factory pp size ) made 720ps at 1kg with t51spl.

I have made manifolds for s4 engine which used factory primaries and pp secondaries, The shop i made them for is yet to complete there customers cars.

Later this year i should get my own project engine for my car going. Its going to be like the Revolution port setup.

Knightsports was playing with Jports for awhile but that was sometime ago. The revolution car made 625 at 1.6 kg/cm3, the main reasoning for the configuration was that it was a legality trick for racing class rather being superior to other setups, not sure the cost would warrant anyting you would gain over other porting with stock manifolds It works pretty well, but the same effect can be had with a half bridge and the power band is very similar. KKM did a 8mm bridge and made 619 at 1.5kg/cm3, which is right on par with the crossport car, both cars did that on premium pump gas. The scoot car was making 710 at pressures around the 2.2 kg/cm3 mark, the T51 spl has to be run at pretty high boost pressures to make power, its a huge turbo..

I know RE wing has gone to a bridgeport with a T88-38gk and is now over the 700 mark, they are the fastest street tired fd in Japan currently, in the 1/4 mile according to the gossip mill there.