Lschiavo

So far, nobody has tried to go as high in PSI as the engine can go due to the fact that it cost a lot of money to replace the engine and the hassle to do all the work on the car (plus the time you won't be driving your car because it will be in the shop, this is probably the most horrible). Now, we are not sure how much boost the renesis can hold, some people say 10 psi, some others say the renesis is good for 13 psi, etc... There are different theories and different numbers. I wont assume this is true until it is proven but, of course, almost nobody is willing to take a bullet for the team.

Now, here is my idea. There are many people willing to go F.I in this forum. This forum has around 18,000 registered users. Knowing that many of the Rx8 owners are starving for more power (let's face it, the car is underpowered) and assuming only 2,000 (that's about 10%) to be conservative are interested in going F.I, that would be only around 4-5 bucks each to pay for one engine rebuilt and the work on the car.

I am willing to pay the 4 or 5 bucks if anyone is willing to commit to this. I know many people is thinking the same way I do. At the end I prefer to pay 4 or 5, even 10 bucks for something that can cost me $8,000. This way we will discover the true potential of the renesis and know what its limits are, and tune it properly without worrying of future blow ups.

If nobody is willing to do this experiment, but many people is willing to jump on this campaign, I will take the shot for the team and I will do it on my car.

Let me know what you guys think and help me organize this if you are willing to cooperate with this issue.

Fanman

So, you're voluteering to test the engine at 12 psi :D . Go for it ! Good luck collecting $4-$5 from the 2,000 people.

LittleJohn

Yeah.. nice idea.. but atm, the real issue is cracking the ecu, trying to make it play ball and do what we want it to do..

Lschiavo

I know it is hard to do, but is a win-win for everybody..i think... I would try increasing the boost until it goes boom.. LOL

Sigma

It's not so much how much it can hold, but how much it can hold long-term. That guy in Puerto Rico did, what, 19psi for a short time? And even if you found a number where yours blew up, a sample size of one doesn't really mean anything. You could volunteer to give it a shot and have your engine blow up at 8psi because it was a weak one from the factory not because, across the population as a whole, that's all the Renesis can take.

Sapphonica

More's the pity, 'tis not statistically significant to test only one.

...hmmm, if income also follows a bell curve in this group, then there should be a sizable group that could afford as many Renesis rebuilds as needed. That would yield sufficient data points.

Too bad I'm not one of them!!!

Lschiavo

Good point!
I guess I tried to make it work, I will have to retract from my idea. LOL. Thanks guys.... I'll keep thinking about a solution...

rotarygod

If I come across as agressive here, it isn't because I am trying to be mean or flame anyone. It is just frustration because both myself and Richard Paul have spent so much time saying this same thing over and over and over again on this forum only to have no one actually listen when they are told how forced induction actually works. Here it is once again. I guarantee that I'll still have to bring this up again in the near future.

Boost pressure is NOT what hurts engines!!!!! How many times do we have to say this??? Over and over again this gets mentioned and the how much pressure question always pops up again. Get pressure out of your heads people. Pressure is absolutely irrelevant. It's airflow that counts, not the pressure it is at. The Renesis will max out with how many psi with what turbo? Intercooled or not? Air/air intercooled on a hot day or a freezing day? With an air/water intercooler with ice in the tank and water injection? Methanol? Just to put this into real world perspective, 15 psi on the Greddy turbo is NOT the same as 15 psi on a 60-1. This is because the 60-1 would be flowing more air into the engine than the Greddy at the same pressure. How could this be? Remember that a turbo needs to spin faster to flow more air. This is true regardless of it's size. As air travels through a turbo, it gets compressed. In order to hold it at a certain pressure level and still provide the right amount of airflow to hold it at that pressure as rpm's rise, we control it's rate of spool with a wastegate. The turbo does need to spin faster as rpm's rise to supply the needed amount of air in cfm at a certain pressure. A small turbo can only flow so much air. The faster it spins however the more pressure it is making. This is a byproduct of internal compression. The intake manifold will equalize to this pressure but the flow won't necessarily go up. With a larger turbo, it needs to spin slower to supply the same amount of air. A slower spinning turbo is making less pressure since it is compressing less. It is still flowing the same amount though. Again, the pressure in the manifold will equalize to that of the turbo but airflow will be the same as the smaller turbo at a higher pressure level. It's all about flowrates. Knowing this, how would pressure be the deciding factor as to what would kill the engine? The different speeds of these turbos will also mean different efficiency levels in terms of heat produced. What about exhaust housing size? As a general rule, it takes 2 psi of boost to cancel out 1 psi of exhaust backpressure. This means a smaller turbo will need to make more boost since it is restricting the exhaust worse. This is also more heat. There is so much more to safe power levels than just boost. Boost is the LAST thing anyone should think of as it is the least important. Boost level tells you nothing important but is fun to use to brag about or sell product.

Here's my favorite analogy to get the point across. I've used it before but I'll say it again. My air compressor in the garage is at 120 psi right now. That's what the air inside the tank has been compressed to and is being stored at. It has 0 cfm of airflow and therefore has 0 potential to make any power. Why? It's got 120 psi! So what right? What if I bleed some pressure off? There is now airflow which means that work can actually be done. But in order to do this the pressure is going to go down inside the tank. Greater airflow regardless of pressure equals more potential to do work. Less total airflow regardless of pressure equals less potential to do work.

While I'm on my rant and spouting off things that many people don't understand with turbos, I may as well address something else. Heat does not spin them at all. It is not important to get them spinning. Stick a turbo in your oven and see if it spins. If it does you just invented perpetual motion! If heat were important, it would spin wouldn't it? Heat is an important factor in sizing though as it determines how much room a molecule of air takes up. A colder air molecule is a more dense and therefore smaller one. A hotter molecule takes up more space and needs a larger housing to fit through in order to maintain the same amount of restriction. That's why heat is important. It is what it does to the molecule, not the turbo. A rear mounted turbo such as the STS uses a smaller turbine housing. Some people say this is more restrictive. Why? The cooler exhaust this far away takes up less room since it is denser. Mounted at the engine it would be a big restriction but not this far away.

These 2 things are the biggest mistakes people make in terms to how turbos work.

Lschiavo

LOL, sorry. My biggest apologize for my ignorance...
Then what we would want to find out is how many "airflow" units can the renesis hold? ok, then forget about the 60-1, the garrett or the super pink panther turbo, we want to find out how much pressure, or better how much airflow the engine can take with this (not the 60-1, or the super pink panther turbo, but the greddy T16Z or whatever the serial might be. SOrry for my ignorance about the pressure or the airflow, butif we talked about the same turbo only without including other variables then pressure and airflow would not be relative to anything, if the engine blows up at 14 psi, (no matter how many cf, kg, kpa, mm, mts or lbs) of airflow, it will blow up at that point independently of how much airflow we have right? another point would be almost nobody want to use methanol, super refrigerated intercooler, super water or gatoraded intercooling pipes liquid or anything like that, we are talking normal conditions. Not to mention extreme situations like "With an air/water intercooler with ice in the tank and water injection? Methanol? and living in the north pole (where santa claus is) at -70 F or in the desert at +80 C (x2). Even though we get those temperatures (-35 C) in some countries, it would be stupid to go and run the **** out of a turbo in those conditions. I don't know if i make sense, but i am trying to make everything simpler and make more sense without comparing my mother's in law hairdryer against the greddy turbo and the 60-1 turbo you mentioned. What if i put the hairdryer on the car, how many psi or airflow units (whatever you want to measure on, maybe solar years) would it take to blow up the renesis? well we will have to make calculations to compare it to our greddy kit in order to remember that airflow is not boost and everything is different because everything blows different amount of air and some people will put their beers in the gas tank with some ice to freeze or maybe in the intercooler tank...LOL
If someone does the hairdryer calculation let me know since that will give me a hint how to setup the greddy turbo, and remember not to do only boost but airflow, temperature, molecules per second, nanoair, millicelsius and the rest of useful info.
Thanks!!! :D don't get mad at me LOL. I really appreciate your help and now understand that probably the hairdryer at 30 psi won't blow the engine but the greddy at 7 psi might do it. (the hairdryer is hotter air i guess, unless I store my six pack of bud light in the intercooler tank with ice on it) :D :D :D

Dragonrider

Thank you very much for the insight. That I think help me at least better understand how and why some turbo systems seem to help a lot while other almost not at all yet the psi boost was the same.

It is so basic you would think one could see the common sense of it that it is cfm not psi that is required to figure what is going on.

Your insight is very much appreciated.

recsate

Correct me if I am wron but dont cfm and Pressure go hand and hand?? I agree that CFM is the component in any turbo application. But if the engine cannot consume the entire volume of air it is being fed it responds by building pressure (PSI). Under pressure every intake stroke of the engine is force fed a denser more powerful charge (higher CFM) creates more power. Arent pressure and velocity directly related? Velocity and time are related as well. Now wouldnt that mean that the same CFM's of air could be forced into the engine in less time, therefore more CFM's would be fed into the engine in the same timeframe under pressure??

IMO. PSI is directly related to power production.
However whether or not our T618Z turbos can support the flow requirements to hold 12 PIS in the upper RPM range would be my concern.

Like I said I could be wrong..

Sapphonica

Thanks again for all the great info, RG!

One minor point of clarification: the size of molecules is pretty much constant as temperature varies. As temperature goes up, the amount of kinetic energy per molecule goes up as opposed to the volume of a molecule.

There is a thermal expansion coefficient, which is the measure of how volume changes as temperature changes.

rkostolni

I have to agree with recsate. Ultimately it is CFM that create power, however, higher psi means higher CFM UP TO A POINT at which the turbo becomes so inefficient it just cannot flow anymore. But the Greddy turbo is flowing more air at 7 psi than at 3psi, and likewise more at 9 psi than at 7psi.

Imagine blowing through a small pipe with a smaller hole at the other end. The harder you blow the higher the pressure in the pipe and the higher the air flow that will come out the other end.

I think the best relationship, ignoring the efficiency considerations, is of voltage and current. It is current that actually does the work, but increasing the voltage(pressure) does increase the current through a device.

I know their is no way the Greddy turbo can flow 19psi efficiently, but I would guess, although it is impossible to say for sure without a compressor map, that the turbo would still be making more power up to 12-15psi. I for one would love to see someone pushing 15psi go to the track and make some runs and would definitely pay $4 to see that. Assuming of course there were videos!

khtm

I'd pay $5 and I don't even have a turbo nor plan on getting one soon. I just like advancing "science"!

Dragonrider

PSI and CFM are not the same. Pressure is the force exerted against the surface area. PSI can be increased by simply exerting pressure like in a tire. The amount of air in the tire can remain constant but add heat to it and the PSI goes up, in some cases beyond the capacity of the tire to contain the volume of air.

PSI is the expansion on gas while CFM is the flow. Increase the size of a pipe and the cfm remains constant but the psi drops, decrease the size of the pipe and psi increases, decrease the size of the pipe even further and psi continues to increase but the cfm will go down. Just look and a nozzle on a garden hose or better yet a fire hose. By decreasing the diameter of the opening the psi at the nozzle is increased but the flow of water through the nozzle is decreased. Raising the psi will increase velocity, but to increase velocity volume must be restricted. How much air gets to the intake is a matter of flow, velocity is a matter of pressure. High flow with low pressure would result in higher horse power.

So on the exhaust side forcing the exhaust gas through the turbine to reduction vanes to increase the velocity of the gas to turn the compressor psi is increased a bit to force the volume of exhaust gas through turbine at a higher rate of speed, but the compressor is moving cool air at a slower velocity psi at a higher CFM than the hot exhaust side. In both cases it is all a matter of flow not pressure. The only reason psi is a factor in to achieve velocity. Static pressure does not cause anything to flow, and that is what TG reminded me of.

You see, while in the pipe low volume and high psi looks like you are really doing something until the forced air enters the intake, the larger area drops the pressure drastically because there is no volume. So say if is a turbo that is 10 psi is only moving 150 cfm but one say at 8psi that is moving 300 cfm, the one at 8 psi would provide twice the boost. Now by putting twice the volume in the combustion are at a 10 to 1 compression, which turbo could possibly cause over pressure in the engine? The turbo that is 8 psi that moves 300 cfm would be the one to be concerned with.

So by decreasing heat in the compressed gas, increase the volume capacity of the pipe while the compressor speed stays the same, cfm will increase but psi would decrease providing more volume which is the real point in forced induction isn't it. So hopefully you now see, the real issue that needs to be understood is what the cfm is not the psi. It is the volume of air in the intake that will cause the problem not how fast it gets there, for once the intake closes it is the compression that must dealt with, therefore volume is the only real issue.

rotarygod

My molecule size analogy was a little off. What I meant was that hotter molecules are spaced farther apart from each other since they move more and colder molecules are spaced more tightly together. This is why size differs for turbos based on heat.

Yes pressure does play a role. Don't think based on what I said that it has no importance. It just comes second to actual airflow. That's all we care about anyways, how much air actually gets into the engine. Let's just say that on a perfect day of 14.7 psi atmospheric pressure we are running an engine that ingests 400 cfm at 8000 rpm and it makes 200 hp. If we had a perfect sized compressor that had absolutely no loss to it we should theoretically double our airflow at exactly twice the pressure which would be 800 cfm at 8000 rpm at 14.7 psi of boost over ambient would be 400 hp. This assumes that we have a turbo that flows 800 cfm at 14.7 psi of boost. What if we have a turbo that only flows 650 cfm at 14.7 psi of boost? That would only be about 300 hp at the same boost level. This is only for illustrative purposes so please don't think I am spouting off actual numbers. It takes a certain amount of air to make a certain amount of power. What if this smaller turbo flowed 800 cfm at 23 psi of boost? That's the same amount of air as the larger perfect turbo. Yes I am completely disregarding temperature and everything else relevant. It suddenly becomes obvious that we have 2 turbos that can flow the same amount of air but they can only do it at different pressures. Suddenly pressure wasn't the issue, airflow was. That's the point.

There is a limit though that you can keep getting air into the engine at a certain pressure. I used the example of the perfect compressor of perfect size exactly doubling the airflow with exactly double the ambient pressure. Don't think however that going larger still will give you more power with less boost. It won't there is a limit. As an example, we can't double our horsepower with only 8 psi. Even if a turbo that flows 8 psi has twice our initial airflow numbers. This is because the air that came out of the turbo will back up in the manifold like the air out of a roots blower. It will compress itself in the manifold and while the turbo may only be compressing internally to 8 psi, the air is further compressing in the manifold to 15+. A bad byproduct of the air getting compressed in the manifold itself is that it heats up worse this way. It gets a little confusing.

There is alot to think about when it comes to forced induction. Yes pressure is important but only from the standpoint that you need to know how many cfm your turbo is flowing at your intended power level.

WantedTwo

iTrader: (4)

my head hurts

Richard Paul

iTrader: (5)

Both of you seem to know what your talking about but your explaination leaves a little to be desired. I'm not the one who usually clears these things up. I never claimed to be the professor, I'm no good at it. If I were I'd just be on campus somewhere looking at coeds for a living.

First of all let's clear it all u by ditching CFM. Replace it with "MASS". This will the gas by it's weight. Next lets get the molecule thing over with because this in itself tells you why you have pressure period.

The mols themselves stay the same size, they just speed up and slow down. If the get hot they speed up therefore hitting each other and the container around them with greater force. Thus more pressure. Colder is the oposite.

They tell us that if there was no heat at all meaning absolute zero the moles would be still. Then sound would not travel at all. Therefore the moles are traveling at the speed of sound. Gets clearer now right?

The analagy about the flow and pressure doesn't work right either as the pressure you see at the turbo is the same as you see in the manifold once they are conected. If it takes x psi to put y mass into a given engine at z temp then that is that. You can adjust these things around the efficeincy and particulars of the installation but fact is fact.

So that's why you are right and wrong. Sure a given compressor map shows xxx compressor flows 400 cfm at zz psi you can't just say my engine will make more power with that comp then with one that flows less with that psi.

You are already starting with the biggest compressor in the world. Said comp will put unlimited cfm into your engine at 14.7 psi. Guess what? it already does, it's Mother Nature. You can't get a more eff comp with more capacity. It's the best and the biggest. If the engine would take more mass just because the compressor can produce it then the first engine would be using it all and we would all be sucked into said engine with it.

An engine will take so much more depending the resistence of itself. The only way to get more mass with the same pressure is to have it cooler. The only way to get it coller is better efficeincy. Remember anything that gets hot used energy to get there.

Now for some lab work. We have here a box that has around it a water jacket. There is a pressure gauge and temp gauge in the chamber. First we clamp the lid on and there is zero psi by gauge. We now pressurize the chamber to 10 psi while filling the jacket with crushed ice. So there is 10 psi at 32f. Next boil the ice at 212f and we have without opening or changing a thing 19 psi. BUT THE SAME MASS IS IN THERE.

Next fixture has a chamber that can vary in size with say a piston sliding in it. We again start with the ice filled jacket and find 10 cu ft in the chamber. with a given pressure of say 1psi. Boil the ice to 212f and in order to keep the same 1psi the piston must slide out to develop 13.6 cu ft in the chamber.
THE SAME MASS IS IN THERE.

It's all down to that little mole. There is no free lunch. A good install is a lot of work. You must understand the science first, then be a good fabricator. My best advice to most of you is to buy a well engineered kit and tune it like it should be then leave it alone. Beware, there are a lot of people building kits that don't have all the resorces that they should have. I don't mean facilities, I mean brain trust.
On the other hand there are a lot of homemade one off installs that work just fine.

Moral of the story is to know as much as you can before you buy. Take advantage of other peoples screw ups. Don't believe everthing you read in ads. For that matter read between the lines of magazine reports.

Jon

Since everyone already explained all the important key points I would just like to put in my 2 sense.

Tuning would be a VERY important part of determining the renesis motors potential. Some people can make more power than others with the same setup just with better tuning. At one point a REALLY REALLY REALLY long time ago people thought that 500hp was the max that a Supra could make. BOY WERE THEY WRONG!!! I believe that it will take a very long time to see the full potential of the renesis motor. Motors will blow and people will think thats the limit and then one brave soul will test the limits again and get a little further and a little further until that one blows and so on and so forth. Anyway thats all I wanted to say.

Good explanation RotaryGod and Richard, it is always good to see people willing to give out information to assist people with there decisions.

Jon
PTP Motorsports
512-834-8771

If we ever get word back on our new engine management maybe I can assist in the answering that potential power question ...

rotarygod

Richard, that's what I was trying to explain but the words wouldn't come to me properly. It's that damn "mass" thing! Thanks.

swoope

iTrader: (5)

no,
knowledge is power, kinda like airflow is like mass. i said kinda. psi is not related to a and b. but it is.

great thread. wordy yes, but it had to be.

beers

MazdaManiac

iTrader: (3)

Why are you guys getting all worked up trying to explain pressure and flow. It is irrelevant in this case.
An absolute amount of fuel will make an absolute amount of power. Run out of fuel - stop making more power.
The RX-8 runs out of fuel at 300 crank HP plus or minus 20. Pretty much end of discussion.
Now, if your little fund will cover all of the work needed to run up the fuel to meet whatever amount of air will pop the motor, you've got my attention.

swoope

iTrader: (5)

jeff,
i have pissed away money on dumber stuff, and i dont gamble.
you figure it out and i will **** away money, just need a video. still am waiting for the rp action. obscure, small, well thought out. the horror.

btw if you guys need a comp while messing this stuff up let me know, got stuff laying around.

beers

Dragonrider

Could you enlighten us on factual basis of this little tidbit? I have seen older rotaries at well over 300hp so you comment is interesting.

tazzydnc

Dont you get 5 bucks for getting someone else to sign up for paypal? Lets all just do that - problem solved :D