PaulFitzwarryne

I am thinking of getting a 12AT rebuilt and ported, while upgrading to a 13BT turbo.

There has been adverse comment on the forum about the small size of the 12AT ports. Unfortunately none of it gives specifications as to what is needed.

On the list of prices for modifications by a tuner there is a distinction between a turbo port and a street port.

Are there any real differences between the porting needs of a turbo as against a NA. The exhaust ports could be the same but is there any need for differences on the inlet side to cope with differences of intake pressure?

Is there any difference between the 13B and 13BT?

MIKE-P-28

iTrader: (1)

I get lost in all the lingo with ports too. Seems every tuner/builder has a different name for it. Maybe they call it something different cause they have a personal touch that is tried and true only to them?

I think you know the difference between a 13b and 13bt. the 13b is 6 ports and the T is 4

diabolical1

iTrader: (3)

aside from the 4 vs. 6 thing, i believe the primaries on the 13BT are slightly larger as well.

i guess the best place to start is find out what the differences are from that guy you mentioned, to see what he does differently between "turbo" ports and streetports.

my guess is maybe he matches the exhaust port size with the turbo that's going to be used????

Directfreak

iTrader: (2)

AFAIK,

Turbo port is designed for Turbo use, so they make the port opening larger, but don't necessarily move the port up or down, to prevent possiblitly of overlap.

I personally know that a good friend of mine does Turbo bridgeports, and while they are a bridge, they look totally different from his N/A bridge ports.

If I say any more, he will kill me, so let's leave it at that.

MIKE-P-28

iTrader: (1)

Say more, so I can the fastest forum rotary FB in the US..

Notice I said, forum and US..

Think about it, if you die, I win LOL Negotiable losses

j/k

PaulFitzwarryne

I was thinking 4 port differences as the 12AT is also 4 port, the 2 extra ports were primerely to improve emission problems.

Diabolical- the reasons given were that the turbo port shape was due to 6 port NAs being more difficult to optimize, and all exhauts should be matched but not necessarily on the inlet.

Mike- I thought that with the turbo higher inlet pressure there would be no need to enlarge the port as the extra fuel/area required for the increased power would be acheived by that pressure. Which way would you go, increasing the boost or increasing the port size for the same power target?

fatboy7

Obviously, a "turbo" port would have less overlap, cause unless you've got a large(read HUGE) divided housing turbine, your turbine inlet pressure is going to well excede your intake pressure, this is like reversion times ten, overlap bad..... large ports good. Notice you can actually lower your overall compression ratio too, by causing the intake ports to close later, just somthing to consider.

You know, I'd love to see those "turbo" bridgeports.... Mmmm.... C'mon, just email it to me, I won't tell a soul

RICE RACING

Paul

There is no difference between "turbo ports" and a street port.

It is realy a BS excuse used by alot of engine builders in Aus that spout some crap from reading to many Fast Fours articles I suppose ?

When I do an engine, I make the ports as large as they can possibly be on a 4 port engine that is not bridged, this includes the exhaust ports. You cannot make them to large and any excuse offered as to too much overlap is plain Bull **** (excuse my language).

Make sure who ever you get to build your engine knows what the porting limits are (ie so no water or oil leaks into the engine & no seals drop out of the ports) and you will be fine, you will end up with a motor that will have a nice peak speed increase and a broader peak torque point, all without loosing that fantastic low speed low load fuel efficiency of a side port (non bridge).

If you want some more detail, feel free to PM me.
Who is your friend who does partial bridge Turbos?

RICE RACING

Search the forum, there are proven styles of partial bridges and Partial PP turbos, and they are no different to the N/A couterparts !

Soul Assasin had a nice photo of one which crispeed helped him with, I would say his experience with partial bridge turbos is second to none

fatboy7

Ok, Ok, I want to believe you, as you have a ton more expirience at porting and tuning than most.... Just throwing out a hypothetical here, but assuming you could get two ports of equal flow properties (may be an immposiblity in our rotaries, but humor me), one with less overlap (like a huge street-port), and the other with tons of overlap (full BP/PP), which one would have the ability to make more power, run more boost, and be less prone to detonation?

Basically, why is it that you think the overlap issue is complete BS? Is it because there is only so much material that can be taken out without resorting to increased overlap? Is there actually more power to be had by increasing the port size beyond what would be capable in a low overlap situation? Is it that the turbos your tned to use are large enough to have a near NA exhaust port pressure to intake pressure ratio? I'm just curious......

I only have a few personal expirences with turbocharging, none on a rotary (but soon will), so my understanding on how turbo rotaries differ from turbo-piston engines is somewhat limited. But I'm a believer in physics, and it seems flawed that more overlap in a turbo charged car would have anything but a negitive impact on the detonation margin for a given application. Enlighenment appreciated, please...

PaulFitzwarryne

Rice Racing- it was Directfreakwith the friend who does turbo bridgeports.

Going back to fatboy's question can you increase port size without increasing overlap? If so is there an'ideal' ratio? Is it different between a turbo and NA?

When I first turboed a car some 30 years ago, a Lotus 47, we played around with valve size and cam profile which are the piston eqivalents, along with boost and compression ratios. Never came up with any theories except to believe the dyno. We were getting 300hp plus net SAE from 1.6 litres which was not too bad on a lightweight street machine.

RICE RACING

To answer your question on resistance to detonation, ANY time you increase the effective BMEP in the engine you will edge closer to this point when running on pump fuel.

You can increase the BMEP in a number of ways, either by retaining std restrictive ports (either NA or Turbo, of which there is minimal difference), and using more turbo boost pressure, or you can increase the VE of the engine (porting and sub systems "manifold lengths, IC eff etc") If you start using too much boost you will be more prone to detonation due to a high charge temp prior to the compression stage in the motor. Or you can port the engine and get a good balance of increased VE and use not so much boost pressure to achieve the BMEP gains you are chasing (Engine BHP).

The benifit of overlap is that you will get a wider peak torque spread and if set up right you will get an increase in usefull RPM range + you will get an increase in BSFC in the higher rpm ranges wich is benificail if you are racing the engine. The down sides? the engine will be less intolerant to "excessive" back pressure ratios, where the exhaust manifold pressure exceeds the intake manifold pressure, this is more of a problem on partial bridge motors and greater but even they can tolerate a bit of this and still make exceptional power. However it is best to set them up the way they were ment to be to take advantage of the increased efficiency of the porting and run them with a 1:1 or less ratio.........select the right size turbine combination.

The reason why your charge does not get blown out the exhaust because of the overlapo is because of complex and I mean complex! wave interaction between intake & exhaust ports + manifolds that push the charge back into the combustion chamber while at the same time using pulse or wave pressure charging to dynamically fill the chamber with more air and fuel ! This is why they have VE's of well over 110% in some cases even at revs of 2000rpm (if tuned for this rpm range).

The one and only down side to increased overlap in increased sensitivity to exhaust back pressure, and in the other major one is a loss in low engine speed and low load fuel efficiency. The street port (or largest side port you can run) is one of the best compromises for this situation in that it allows you the best of both worlds. I use my daily driver as an example here, I get exceptional fuel economy (13L per 100km city and less than 9L per 100km highway), I have dynoed at 472 rwhp (dynapack which = about 490rwhp dynojet) or around 560bhp on 19.9psi boost while running an air filter, 3" exhaust "quiet for rotary" and 98ron fuel. My ports in this car are the biggest you can fit in a 4 port engine, I have progressed from std to mild to this point and this is the best out of the three in my opinion. I do not see the problem with increasing the overlap at all, My exhaust port is so large that people just laughed at it when they saw it (you will find pics under porting on my website link) The ONLY downside is a little higher idle 1150rpm and a loss of power compared to the small ports below 4k, after that though there is no negatives, only postives to running the larger port combo (more correct large timing combo, earlier opening later closing for both intake and exhaust).

The biggest tip I can give you Paul is even if you do not want to increase the timing overall is to get rid of the 12AT center plate and use a normal 12A RX7 one this will give the primary ports the same or similar opening and closing timing to the secondaries and will let the engine breath alot better, I strongly recommend porting the exhaust ports as they are stupidly restrictive and were designed to work with the small factory turbine combo, at minimum open these up to the limits of the exhaust sleeve, you will be happy you did

regards

Pete

MIKE-P-28

iTrader: (1)

damn peter you just lost me way back there

AdrenalifeRX7

it would be easier to just go 13B turbo

fatboy7

Wow, that was even better than I expected Ok, I think I get what you are getting at. The more overlap, the worse the low load, idle fuel consumption, and a loss of VE in the low RPM, just like a NA engine would act.

You speak of BMEP (brake mean effective pressure), or the amount of pressure that when sweeping over the displacement, would make do the same work as the combustion in one cycle, right? As I understand it, this is a figure that can be used to compare the state of tune for a given engine. Its understandable that this would be closely related to detonation, as the higher specific output the closer to that hairy edge you become. I agree with you that the interactions of pressure waves when both the intake port and exhaust ports are open are very complex, and of course relize that the effect overlap has on reversion is RPM, and Intake/exhaust pressure ratio dependant, as well as other factors.

Heat as we know is a primary cause of detonation, exhaust in the intake would seem to add a lot of heat, as well as lowering the VE of the engine. Wouldn't this effectively lower the torque and therfore the BMEP of an engine (BMEP = 2*pi*torque/Displacement...) at a particular RPM, not increase it? It seems to me that detonation margin is not only dependent on BMEP, but thermal management (highly effecient IC's tend to push the detonation margin farther even though it makes a more dense charge, allowing possibly more boost and even higher BMEP) has a huge play in it as well.

What I'm comeing to conlude is that the overlap issue isn't an issue so far as the pressure differential is small, and the port interaction is good , especially near the torque peak (highest BMEP). So a street port that produces the same torque as a bridge will be less detonation prone. But due to the fact that bridgeports have torque peaks higher in the RPM's, where the mere fact that overlap exists is overcome by the complex port interactions, means that brigeports are less streetable, but are not much more if any more prone to detonation. In low RPM's their VE is low enough that the added heat from reversion doesn't cause much alarm.... Am I getting warmer?

RICE RACING

As the BMEP goes up or the average power goes up the likley event of detonation goes up, you need to run less ignition advance and higher octance fuel.

Nitrous is a good example of this, there is no heat associated with it's introduction to the intake charge yet even when the fuel mixture is correct it still needs attention in these areas Higher octane and reduced spark advance to avoid detonation.

It is a common principle when tuning engines to use less spark advance at or near peak torque because of the highest BMEP figures near this point, yet spark can be advanced after this point, independant of the charge temperature, so BMEP does play a big part, as does charge temperature in regards to the fuel if it has a lower autoignition point.

BMEP realy tends to follow a good trend with the peak combustion pressure which gives a good indicator of what is going on in there, Unless of course you are using water injection in which case the peak pressure drops or even reduces ! but the BMEP goes up (another topic). So in short there are many ways to skin a cat !, it is just as easy to get in trouble with lower boost/more overlap as it is with more boost/less overlap, but the odds are with the lower overlap engine you will strike troubles having preheated the air too much (too much boost) to match the peak BHP of the ported "lower boost" rotary, you may match the peak power but you will have a less efficient engine with a narrower power band, but it will be better on fuel for stop start traffic and periods of long idle time.

It is horses for courses. There is nothing wrong with a "maximum side port engine" I am yet to met someone who wishes they had a stock ported motor after running one of these, unless of course they were using the dead stock turbo charger, in which case, the std porting is a great match for that crazy 180 odd BHP of power

fatboy7

Yea of course, water dosen't expand as quickly, so peak pressure is lower, but eventually expands more, later in the combustion cycle, so it still does work raising BMEP.

I think I'm on the same page now, thanks.