b2fast007

Trying to find out if any one has tested a two stroke style header with expansion chamber on the renesis.It seems to me that the scavenging effect caused be the pressure pulse could help overcome some of the losses of the restrictive port runners . This could help to bring back significant amounts of the missing hp mazda claims our cars have. obviously im not talking turbo applications just n/a versions. A well tuned pipe for a 650 stand up jet ski can increase power output by 15% . Thats like 36hp based on mazda's claimed numbers and it basically eliminates the drive losses our cars suffer from any thoughts.

paimon.soror

iTrader: (15)

Odd harmonics from expansion chamber. - RX7Club.com

RIWWP

iTrader: (2)

What "scavenging effect"?

This isn't a piston engine.

alnielsen

iTrader: (4)

There isn't a scavenging effect in a 2 cycle engine either. That is specifically why they use expansion chambers.

b2fast007

In automotive usage, scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel/air mixture for the next cycle.
This process is essential in having a smooth-running internal combustion engine. If scavenging is incomplete, the following stroke will begin with a mix of exhaust fumes rather than clean air. This may be inadequate for proper combustion, leading to poor running conditions such as four-stroking.
Scavenging is equally important for both two- and four-stroke engines. However it is more difficult to achieve in two-stroke engines, owing to the proximity, or even overlap, of their induction and exhaust strokes. Scavenging is also equally important to both petrol and diesel engines.
Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.
To increase scavenging potential, the entire path from intake to exhaust (i.e. all powertrain parts) to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of this exhaust gas is what will hinder the scavenging potential.
For example, fast flowing heads and a tunnel ram intake combined with a poorly planned camshaft and exhaust system will cause the air to "slow down" and "speed up" throughout its journey, thus reducing its scavenging potential. So, to increase scavenging potential, the air must maintain a positive linear acceleration curve.
There are three types of scavenging on the basis of the flow of air:

so you are both telling me that these basic physics of internal combustion engines do not apply to the renesis. OK

b2fast007

As riwwp loves to point out every time someone posts anything the renesis is not a piston engine unfortunately the terminology still has applications. On that note why use a standard piston engine exhaust why has no one developed something application specific as the formulas for calculating the exhaust design no doubt come from piston engine technology and are sub standard for our applications. Think outside the box for once thats how innovations happen.

RIWWP

iTrader: (2)

The exhaust port is closed for a given face before the intake port open, there is no overlap on a renesis. The principal simply can't be implemented.

slvrstreak

iTrader: (3)

Doesnt work like that
The Renesis is a zero overlap engine

paimon.soror

iTrader: (15)

Before you can 'think', you must first 'understand'.

Spend time understanding the dynamics of the renesis before you act foolish

b2fast007

so when the gasses enter the expansion chamber they expand decreasing pressure and causing a pulse wave that travels down the length of the chamber as it does so it pulls the exhaust gasses from the chamber. When the pulse hits the end of the chamber it bounces back towards the cylinder in the process it pushes back any intake gasses that are pulled thru by port overlapping (2 stroke piston engine) we cool my facts seem on point. so here is the thinking outside the box part if the pipe is tuned so the back pulse hits the port when it is in the closed position the shock front will be traveling away from the combustion chamber as the port re opens further assisting the expansion chamber at pulling the exhaust out. This would increase the over all exhaust efficiency would it not.

b2fast007

a hypothesis without a proof is just an opinion. Albert Einstein

always question what you understand it increases ones understanding

logalinipoo

When one exhaust closes, the next one almost immediately opens in the exact same place. two faces might even be exhausting at the same time. So the "back pulse" would then be impeding the flow of the next exhaust pulse.

On top of that a tuned pulse would probably work in a very specific RPM range. The rest of the time it would be out of sync with the engine. This is great on a engine that is running at a set rpm like most two stroke engines do, but it in something with a wide operating range it would be useless.

Charles R. Hill

iTrader: (7)

Part of the problem with an expansion chamber exhaust manifold on the Renesis is simple fitment. There is very little room for one as the engine is installed in the RX-8. A secondary concern arises as, which has been stated previously, the Renesis has nearly zero overlap. In order for effective scavenging to happen, there MUST be at least some appreciable amount of overlap. Piston-port two strokes use expansion chamber exhausts so to assure negative pressures in at least some portion of the RPM band, which makes those particular engines rather "peaky" in terms of their torque peak. Modern piston engines (2 and 4 stroke) used in PWCs, snowmobiles, and motorcycles, will often employ active exhaust system tuning methods in conjunction with variable intake runners and active camshaft timing. All this is done in an effort to keep the intake charge and exhaust gas velocities at their peak to benefit efficiency.

Several years ago I, like the OP, pondered such expansion chambers but decided it was not worth pursuing. Interestingly enough, and certainly counterintuitive in this case, what has been shown to benefit the Renesis engine is the use of longer primary pipes with each exhaust port and a straight 3" exhaust collector. There are two other features that I will be using with my long-tube header but I will not disclose them at this time.

b2fast007

thanks for the reply i was hoping to get at least one response from a fabricator not a theorist. The opinion of one who actually builds components for our cars carrys more weight with me to many people on this sight use empty facts with no testing or research data to back up their points to be taken seriously.

RIWWP

iTrader: (2)

It's interesting that you only consider the facts as facts now that Ray has supported them as such. The engine design hasn't suddenly changed since he made his reply. Have you considered that perhaps we learned this information from Ray previously? By your apparent logic, it will be impossible for anyone to learn anything from you, which would make suggestions like the original one rather hard to get people to accept. By following your own example, no one would ever accept an idea you have.

It is good to be cautious of what information you accept to be accurate, but it is also dangerous to belligerently reject information that has been understood years, or decades, prior to you even being aware that it's fundamental concept might exist.


It is also worthwhile to consider that such a basic concept of exhaust design has been known for very very long, and that if Mazda had been able to see any gains from it, they would have implemented it. For example, the same principle is the one that forms the basis of variable intake runner length? Every single feature of the intake system for the RX-8 uses this principle to maximize every bit of intake air velocity possible. It's used in the 1999 Miata's intake. It's a huge facet of the SkyActive header design.

With a little bit of thought, you would have realized that there is a very good reason why it doesn't exist on the exhaust side of the Renesis, and some minor research, or even looking at a picture of the engine components, could have enlightened you to why.


Try to tone down the belligerence. It serves you no benefit and garners you a fair degree of harm.

Charles R. Hill

iTrader: (7)

Thank you. Another great source for this topic was/is Eric Meyer as he hosted a lengthy thread wherein this particular matter was discussed and he was quite open as to what he and his team discovered on the dyno with different versions of headers he was having built. The Grand-Am teams were another great source (to whatever extent they would discuss it) but the interesting part is that they all ended up with very similar findings and results. There were some who thought a venturi collector would help but I tried that and a straight 3" collector on the dyno, within minutes of one another, and discovered the venturi collector to LOSE about 3-5 lb./ft. of torque anywhere above 6,000 RPMs.

The strangest thing, in a way, is that I was skeptical in the early days of any kind of header being useful for the Renesis due to the lack of overlap (like most of us were). Meyer and the Grand-Am teams demonstrated that not everything with the Renesis is obvious or intuitive.

One last point; as far as fabricators and theorists are concerned, one major lesson I have learned in my past five years as a product developer is that theory is useful...... to a degree. After that, practical application prevails. I used to (and still do) love and admire all the same rotary-centric companies as everyone else on this forum. On the other hand, having spoken with them and sharing experiences/tech discussions in private/etc., I have come to realize (as I once had as a professional musician, too) that we are all mere human beings and none of us holds the "magic" that makes the performance aftermarket operate such that it does. We are all mere mortals. LOL

TeamRX8

iTrader: (25)

dwalker claims to have made it work on their race RX8s

Amusing commentary just the same

b2fast007

funny I asked a first hand question and wanted a first hand answer. I got what I wanted as for RIWWP we have had dealings in the past and no I do not Value your opinion SORRY. You come in here ripping on me as an idiot and don't even say a word about your fellow moderators post containing false information. So I will continue to use the information I deem reliable If that's ok by you If It's not sorry you can have this thread deleted too.

Mazda had to change the exhaust prior to production to meet the 100,000 mile catalytic converter warranty requirements. For all any of of know those changes were to the header mazda isn't going to tell us how to undo it or if they had some awesome new design mazda isn't talking

I'm a chef and reading 1,000,000 cook books and watching the food network still doesn't mean you can or should cook. If you want to be a good cook learn from cooks not books.

J8635621

iTrader: (10)

Who told you this?

slvrstreak

iTrader: (3)

What's funny is you talk about this...like you read it in a book
By all means if you have an idea implement it but there are many people who have already been down this same road and know you're spinning your wheels from experience
Some of us are...how you say...cooks

b2fast007

mazda press release pre-launch to 2003 rx8 model. original mazda release date was pushed back to make mods to comply with us regulations.

hey you know who Chris Fishetti is he put a supercharger on a Kawasaki 650 stand up jetski. every one told him it was stupid it wouldn't work. guess who won the IJSBA championship that year blowing away all competition myself included that year. So it won't work, but stranger ideas sell millions like the turbonator and it doesn't work either. Had to ask the question was never a statement of fact.