Maxxx

Just a general mod thread.

Like did the exhaust you fitted gain any power or u just love the sound.

Does the air filter system you have installed make any power gains.

Anyone perform any port work to their RX8, with results. Hypotheticals.

Any FI experience to compare the peripheral and side exhaust ports. Hypotheticals.

Inlet manifold design and modifications. Hypotheticals.

Any input what so ever, basicaly a brainstorming and comparison session.....lets see what we can collectively come up with. Some of us have more experience than others so it will be interesting to see where this goes..........we need many curve *****.......

Maxxx

With the forced induction issue........peripheral exhaust ports have been the key to massive power gains on the RE....now that we have 0deg inlet/outlet overlap we may have an issue for conventional shool of thought as far as turbocharging goes.....the main reason i have held off too see how Hymee and Rotormaster SC kit were going to work......

On a peripheral exhaust RE you could spool very larger turbos for massive power gains due to the fact that you had substantial inlet/exhaust overlap......with increased combustion chamber volume on the lower comp engines.......also they were very fuel inefficient...........

With the renisis i belived that that advantage is now lost......so any restriction in the exhaust system, cat, turbo, bad muffler, would result in greater engine inefficiency..... From what i have been reading there are small gains to be made on NA exhaust systems........only gains to be made with exhaust would be after some form of FI.......that tells me Mazda has realy done their homework....... If you were to compare a piston engine with zero valve overlap you would have no power what so ever............the renisis makes the power with the revs.......

On the dyno graphs that are poping up both turbo and superchargered, things are starting to make some sense.......has anyone else picked up on it?? or has opinions??

timbo

Good topic Maxxx

I think Hymee's your man on this -- that's why he went s/c; presumably Rotor Master, too which is why he moved from t/c to s/c (but Joe doesn't post )

A big issue is obviously staying legal in terms of emissions. There's been some speculation about what happens when you remove the cat and in fact replace extractors all the way back. But we have to live within the EPA rules given that for most these are our daily drives.

That suggests to me that unless you are going FI, the only other gains might result from tinkering with the ECU. Again, some good early work has been done here (Canzoomer) and now people are starting to bring forward other systems (MoTec).

Overall, there's not been a lot of dyno-ing, simply because you need to trick the ECU to dyno it properly (it goes off when it sees the back wheels moving but not the front) Someone post what the trick is, 'cos I can't find it!

Maxxx

EPA regs can be overcome quite easily for a street driven car........iv'e had my cars offten tuned for emissions testing.......the only problem with it is depending on the setup you have, running lean could be a reliability issue if the engine is boosting within the load range for testing.....again depends on your individual setup.....slightly on the rich side is ideal....although the RE love lean.......lean is mean...

auzoom

I had a conversatiom with Gomez when I went to see off the Vic guys/girls to the nationals about the gains to be had through more efficient Air/Fuel ratios (AFRs).

A lot has been said about the loss of power in the Renesis purely because of the issue of CAT life and Mazdas response of burning rich. Gomes mentioned (i think this is correct) that there are people close to being able to reflash/reprogram the ECU (on a retail basis) and as such come up with more efficient AFRs. I also recall reading (but it could be my imagination as well) people who have been able to do this so far have found double digit hp gains (again i "recall" around 20hp)

Andrew

rotarenvy

why do you need overlap to spool a turbo?

Maxxx

the main reason i belive is, the engine does not breathe in the low rpm's and then it would choke in the top end if there is a restriction in the exhaust..............the Mazda exhaust is perfect you can't gain much with after market cat back system, 5Hp if your lucky, extractors maybe 10-30Hp.................staic comp is high..but dynamic comp is lower...........and you need exhaust gas (mass flow) to spool a turbo................with timing overlap in a peripheral exhaust RE you get a great deal of cylinder scavenge which provides mass low...and the staic comp is low but dynamic is higher............also of some help (depending on the state of tune) is the air/fuel mixture that bypasses the combustion chamber and goes straight in the exhaust............don't help emissions, but..........PP Turbo.....hmmm
i belive this can be helped to some extent in the renisis............but you would need to tear the engine down and do some nifty port work.................

thats why im an advocate for supercharging over turbocharging on the renisis engine............

opinions??????

Maxxx

Apparently Mazda's official position on the MazdaSpeed RX-8.......

http://rotarynews.com/node/view/466

intersting...........

takahashi

Sound argument
ehmmm... without putting my foot into the deep hole:

I heard some massive figure in the US (remain nameless but he is pretty high up in the human chain) that the restriction of outlet air flow is at the exhaust port. So in fact we are spending so much money on the extractor, hifo cat and cat back is mainly for sound, since the limiting step is not addressed.

Porting is an idea but no one has idea to port so it is: 1) still have correct timing and ignition setup with tuning; 2) emission standard; and 3) fuel economy.

I wish there is an answer for porting and some are doing it in the US.

There are someone in the background doing research locally. But I ain't brave or have enough money to do that... all I can do is listen really

In the meantime, I may just have to squeeze mini-seconds from my best lap time with what I have got

Revolver

Oh man, it's just been too long a day to get my head around any of this.

Wake me when you've worked it out.

Maxxx

you may be rite with the exhaust port.................the port timing alone is a big issue.....................custom side plates.........hmmm........i'd like to see that............... or just PP the exhaust........LOL

rotarenvy

I have read where overlap helps intake tuning effects but nothing that it helps spool a turbo. with overlap you are less worried about Air and fuel entering the exhaust you have to worry about exhaust gas entering the intake. Exhaust entering the intake air destabilises combustion and forces richer mixtures which would lead to the poor fuel economy and worse emissions.

I would agree that overlap helps with exhaust tuning on a NA car but the exhaust impeller is such a restriction you always have a bottle neck on a turbo and high pressure in the manifold.

I would suggest a peripheral port has a higher exhaust velocity than the more convoluted exhaust path on a side port, hence a turbo will spool better on a peripheral port. then there is the ability to split pulse the exhaust turbine on a peripheral which can't be done on a side-port due to the Siamese centre port.

timbo

I tend to agree based on both your analysis and the fact some pretty experience rotary engineers have shifted away from t/c to s/c. In particular, while there have been many early installs of t/cs (including multiples of the one type, eg, GReddy) in the US, documented power/performance improvement claims remain very conservative. Methinks these guys are having problems getting much more out of the motor using t/c's, and the OEM port design is the reason. Whereas this is not as much of a restriction for s/c's.

But, as we know, it's still early days for the Renesis.

Maxxx

if the pressure from your turbo manifold is just exceeding your inlet manifold pressure...........that means you have just about maxed out the turbine..you will make some power but very low................

if you have a lower exhaust pressure that inlet ...then you will have the ability to make more power...supply more mass air flow at lower inlet manifold pressure............rite??

the issue with no overlap would be that your dynamic compression ratio is lower that static...........so during lower RPM there is not enough mass flow to spool the turbo up..............as the revs build............your exhaust pressures would climb as the engine volumetric efficieny increases with RPM............so there would be a short power band as either the compressor goes into choke or more likely (to be tested yet) you have exceded the turbine flow relative to the presure ratio.......... the power would just roll off quicker then it came on...........so the exhaust pressure would be higher than your inlet pressure (again..to be tested..it makes sense to me..don't mean im rite)...........

so more boost in the inlet will net less power because the engine can not breathe..you are only adding heat that can mke things much worse.........as boost is the product of the engines inability to breathe and the compressor efficiency............generaly speaking larger flowing compressors are more efficient.... so will make more power for less boost.....as long as there is less restriction on the exhaust...........and a larger turbine harder to spool......joy...

ideal forced inducton engine is large compressor mass flow (regardless of what the boost is) with free flowing exhaust.........but with the renesis and a turbo there is a some what complicated balancing act that may be possible to resolve with a variable vane turbine..maybe ........ don't know enough about the technology...............

all the dyno graphs that are poping up seem to point in that general direction..... the Rotormaster graph shows power all the way to 9,000rpm at 7psi.......the other turbo graph rolls off after 6,500 @ 13psi............and the SC makes more power.......i have seen other turbo graphs that are a little better.........but the RM SC graph is by far the best i've seen......actualy it is ideal as far as power delivery goes...would like to see it with more boost......well mass flow....you know what i mean......

this was the reasoning i used to come to the conclusion that a supercharger is a far better option fo the renesis.............the more efficient the supercharger the better i guess.............

rotarenvy

I'll have to think about this ome more. I agree with a lot of what you have said but there are a few things I need to get my head around.