PORTING (making sense of it all)

[JayDee]

Oh yes, now your talking

Life racing f88 I think

[PGiljevic]

^That is a common mistake most mechanics make.QUOTE]

I am sorry Peter but you are wrong. It is a common misconception that people fall into the trap of especially on turbo engines due to swept volume being the same but potential on turbo engines volume increases.
When the compression is lower the actual chamber volume increases but the swept volume does not due to the combustion chamber still displacing in one steady revolution the same amount.
Think of a piston engine for example, a low comp piston will be physically lower in the cylinder at TDC which means that it will correspondingly be lower at BDC(Meaning same swept volume), but the point is that when at BDC the amount of volume is greater than a high comp piston in the same engine, the only difference is that because the engine runs lower compression it makes less power in N/A form,but as soon as you a strap a turbo on you have a variable compression ratio once above 0 bar N/A and thats where it becomes exciting cos by running higher boost you effectively can make more power by getting more charge mixture into the chamber. Boost level determines whether this is succsessful or not in contrast to higher compression rotors.

"Swept Capacity" is the TDC-BDC volumes. Therefore changes in compression ratio do not do in reality or theory what you are saying regardless if it is turbocharged/supercharged at any boost level you care to mention. I explained it all before, you need to re read it and look up some information on the subject, rotary piston etc. It is a hard concept for newbies to get so don\'t feel bad (dont take that as an isult either) as I know lots of people who make this fatal mistake.

[PGiljevic]

^That is a common mistake most mechanics make.QUOTE]

I am sorry Peter but you are wrong. It is a common misconception that people fall into the trap of especially on turbo engines due to swept volume being the same but potential on turbo engines volume increases.
When the compression is lower the actual chamber volume increases but the swept volume does not due to the combustion chamber still displacing in one steady revolution the same amount.
Think of a piston engine for example, a low comp piston will be physically lower in the cylinder at TDC which means that it will correspondingly be lower at BDC(Meaning same swept volume), but the point is that when at BDC the amount of volume is greater than a high comp piston in the same engine, the only difference is that because the engine runs lower compression it makes less power in N/A form,but as soon as you a strap a turbo on you have a variable compression ratio once above 0 bar N/A and thats where it becomes exciting cos by running higher boost you effectively can make more power by getting more charge mixture into the chamber. Boost level determines whether this is succsessful or not in contrast to higher compression rotors.

Just though of this to help you:
In Layman\'s terms, think of a cylinder only going half way up the tube then stopping (don mega sized head spacer LOL = low compression from hell!) now you revers the direction and go on the inlet stroke and you only breath in the difference between the TDC volume - the BDC volume, this is why the capacity of an engine does not change regardless of what you do the the compression ratio
Now anyone who has actually tested an engine knows that volumetric efficiency (how much of this volume is used) does not change when you cange the compression ratio, boost pressure is a seperate element added ontop and accounted for (as is air density etc, I list it in my figures, again people need to re read it all and take notes), and if you look into it deeper with any level of personal expereince you will know first hand that most turbo systems run more exhaust pressure than inlet pressure, so the ballance of gases want to stay in the dead area rather than go out it by the action of boost (like you claim) so in effect its even worse for the engines efficiencey and without getting into the engineering behind it all I will say is that it is indeed worse the more you lower the compression ratio.

So in summary please do not get upset, the aim is to shcool people who otherwise are mistaken and have no idea how engines actually work thermodynamics is the hardest engineering subject for a reason most people do not get the concepts.

I think what would make most sense to you is this:
Build a motor and tune it to MBT on 9.0:1 rotors (use race fuel) so you are not limited (by spark timing or air fuel ratio).
Pull it apart and then run it on the same boost! and tune it to MBT, you will find if you use lower compression rotors it will always make less power regardless of the boost pressure, 2,3,4,5 bar or more
The opposite is true, fit up some 9.7:1 high comp NA rotors and watch the power go up
The capacity has never changed through this process, but the thermal efficiency and power do.... go run some test if you don\'t trust the qualified words of others or F1 engineers

[matt p]

Life racing f88 I think

Bloody hell, those things look mental!.

[PGiljevic]

Yeh, think I should move these posts into a seperate thread. Peres I to is good, you can learn things from the stuff he posts. You should see the ecu he\'s using now. It\'s insane!

Lets have a separate discussion topic around engine compression, I\'d be happy to contribute as can Carl and others on the topic with examples and engineering data of others etc etc.

Same for other off topic discussions around air density or anything to not do with porting.

I generally make the mistake I am talking with engineers, and this is my fault that I think people are on the same page about the actual topic being discussed, and it is all to easy for these to be derailed with (honest questions) from people are confused about the other contributing factors. All legitimate questions btw, they should be addressed but not in a topic where the main point is porting or whatever subject. It just dilutes the discussion is my thought on it.

[Grant Monkhouse]

I will see what I can do and try clean thread up a bit to keep on subject

[Mir]

Sorry, not impressed with the Life racing ECUs.

Mir

[Erdin]

Rice, am i correct in saying, if you take a engine and change the compression, The displacement stays the same but what dose changed is the amount that can be compressed at TDC.?

[PGiljevic]

Rice, am i correct in saying, if you take a engine and change the compression, The displacement stays the same but what dose changed is the amount that can be compressed at TDC.?

ZERO as you have increased the clearance volume, the engine is starting from a lower point (down the bore) to use a reciprocating term you can picture. You can never properly empty the clearance volume (as defined by Volumetric efficiency) Some porting types have higher volumetric efficiencies in certain rpm ranges, but changing the compression ratio has no net positive effect on this aspect. In fact its proven to reduce power for the reasons I gave, this is universally well known.

[senodlo]

What a lot of hog wash kind sir \'RICE RACING\',I have worked out your mathematical  \'google\' calculations here at Nottingham Uni.,actually they hold no concrete evidance to sustantuate your \'beliefs\'. It seems your are most deluded when it comes to Engineering,as a matter of fact you are not even one of the leading ROTARY specialists in Aus.Sorry to say but all your posts are just drivel and you are trying to find an audiance for your ramblings.

[cona2k]

After spending the past bloody hour reading this thread I have to agree with carl and a lot of rice racing seems a mixture of copy and paste.

[cona2k]

Also is this a video of your expertise
http://m.youtube.com/#/watch?v=CqTMYytvfjk&desktop_uri=%2Fwatch%3Fv%3DCqTMYytvfjk

[HaywardRotary]

Rice, am i correct in saying, if you take a engine and change the compression, The displacement stays the same but what dose changed is the amount that can be compressed at TDC.?

Yes but potential volume under boost can be more than with high compression engines. Thats why in F1 turbo engines low compression eg 7.5 to 1 was used which kept det at bay and allowed much higher boost than higher compression engines could take.If high compression was the answer then F1 teams would have done that.EG BMW in the 1980s running 1300hp in qualifying trim in a 1.5 liter 4 cylinder piston engine.
This does not apply to N/A engines where SWEPT volume is a constant no matter what the compression ratio (Apart from the days air pressure)

Look at it this way.
If I was running 7.5 to compression ratio and then was able to run 3 bar over normal air pressure or alternatively was able to run 15.0 to 1 compression but only able to safely run 1.5 bar over normal air pressure which engine everything else being the same including swept volume would make more power?

All that happens with a higher compression engine is the total charge is forced into a smaller space at TDC, the charge then is more likely to to det cos it is alot hotter than a lower compression engine, conversely a lower compression engine can take in more charge at a higher boost level cos when it is compressed it does not get up to the same temp of heat as it would with a higher compression engine. In fact if both engines ran at the same temp once the engine is at TDC you would see more power from the lower compression engine due to alot more air and fuel mix entering the engine which means more BTU\'s are in the charge.
This is for everything else being equal including the det suppression quality or knock level of the fuel. Ontop of this there is more potential room for a greater charge mixture to enter the engine UNDER BOOST.

A big disadvantage of lower compression is that the engine feels lazier off boost and higher boost levels need to be run to get the real potential out of the combination.

[Erdin]

What a lot of hog wash kind sir \'RICE RACING\',I have worked out your mathematical  \'google\' calculations here at Nottingham Uni.,actually they hold no concrete evidance to sustantuate your \'beliefs\'. It seems your are most deluded when it comes to Engineering,as a matter of fact you are not even one of the leading ROTARY specialists in Aus.Sorry to say but all your posts are just drivel and you are trying to find an audiance for your ramblings.

Mate, I think you will find rice knows what his talking about. I know for a fact he has been working on rotary\'s for a very long time. I my self have been into rx7 for well over 10 years and he was given advice and help well before that.

His calculations are a guide. I dont believe he is saying this is what your car will make, its to give you an idea.

[PGiljevic]

Normal set ups like people would run here, 9.0:1 rotors V\'s 8.5:1 S4 rotors or modified S4 rotors you will always see a power drop when reducing the comp ratio. *remember variables held same so you can ascribe the loss in power to reduced engine compression)

To justify the lower compression you really need to using a very knock limited set up (very poor quality fuel) no water injection etc.

Which is covered in the "tuning caveat I mention in the first few posts :cheers