By using the same algorithm I came to 55.4% increase in power using 8 psi. So, 248.64 hps on the mazda v6.. Guess there isn’t that much magic to this after all.

 

The suspense is KILLING ME!

Can't wait to se the dyno figures, and how they compare.............. :D

 

I want to know the 1/4 ET and maybe the 0-60 if possible too.

 

I give up................................................ .

 

Let's all just go to the pub an grab some beers... it's friday.. let's get drunk.

 

dam were they at ????

 

yeah - 248hp at the wheels - A side note, I had 17hp MORE in 4th gear, than in 3rd, during most dyno pulls.


Remember....the V6 had a 1.2L more displacement. That may affect things. 7psi on my 1.6L Miata (with tiny turbo, no FMIC, though) took it from 100whp to about 150...so I dunno.


Still, I'd rather be pessimistic - if you expect the worst, you won't be dissapointed.

 

Now I will tell you again why you can't tell hp gain from pressure.
Go to the first few pages of the axial flow thread or search for the plots produced by Turbine_pwr.
Here he shows you the mass flow for different efficencys.

I'll give you a simple equation to show what gets into the engine, it's called: density ratio. As opposed to pressure ratio which is what you guys are using.

P2/P1 = Pr
Pr x T1/T2 = density ratio or the actual amount of additional mass entering the engine.
Temps are in degree R, or absolut F. Or ambiant plus 460.

Given a Pr of 1.5 which is roughly 7.5psi. Then given an efficency of 65% we can calculate the temp rise.
Pr to the power of .283-1 gives the y factor
So 1.5 ^.283-1=.1215
this times the tempR at std cond=520F
=63 F at 100 % eff.
divide by eff so 63/.65=97 temp rise

so 520 + 97=617 therefore 520/617=.84
.84x1.5=1.26
so if you want to use your 14.7 std times 1.26 you now have18.6
or 18.6-14.7=3.88psi worth of air.
So you really are getting 3.88 if it were a perfect world that is what you would need to produce to get the same results.

So use your 3.88 times whatever power you had to start with and you will be closer.
The question is how much does the ren produce? And what is the real eff of the turbo. As that is a big part of the equation.

If It is what I said and you were getting say 170 WHP mult it by 1.388=235 WHP
Lets see how close that number is. I'm betting a bit less because i think the eff is less due to heat transfer from the turbine side. Which is never figured into the compressor maps.

Next I'll tell you why you might get more then the math says you will. But I have to go to work so save it for later. Or you can go back and study the math provided at the start of my thread.

 

I hope no one Broke an apex seal

 

yeah - that is all great and stuff, but it means nothing to me.

I have learned there are three types of HP.

1st is the "Planned HP" where ppl make predictions, based on experience
2nd is the "Mathematical HP" where ppl like you write up equasions to PROVE their predictions
3rd is "The HP the car actually makes" where people sit around and scratch their heads because their experience, their math all seemed in order, but the result was different.

 

Over and under hummmmm

i'll say 210 for Jeff untuned
and 235 for John using the greddy map.

 

Exactly. A friend of mine (Dreamwarrior) was telling me that people were complaining about the turbo that came with the Greddy kit was too small. I told him it was probably unfounded, and unless you were running BIG boost, there was no reason to have a big turbo.

On top of that, a modern "smaller" turbo can still be efficient until relatively high boost levels.

You really have to look at compressor maps to make any judgement calls.

 

Too bad none of that explains ANY direct correlation between pressure and power output nor does it explain how a rotaries theoretical power output can be figured based on what happened on a Mazda 6. If those are the only "3 types of hp" your own reasoning of power output would seem to be unjustified.

Planned horsepower output is the goal that is hopefully to be attained.
Mathematical horsepower is in fact what is determined by years and years of equations based on actual testing in order to determine what would on paper appear to be the best route to take in order to reach said planned output.
The hp the car actually makes is only finalized after testing. It is in fact true that a design on paper can vary from the real thing. This is usually a fine tuning issue but on occassion can mean going back to the drawing board. If this is the case then it would seem that there was an incorrect equation used in the math part so in reality the math is not flawed but the variables used in the original equation were. When done properly, the math can and does exactly prove the outcome. Now you know how products are designed, tested, retested, finalized and put into production.

They can't get a good product to the market with pure speculation that it "should" be this much power based on how much another car or engine had at the same psi level. That's irrelevant. That means nothing. The only thing of relevance is that exact product combination and not another one that is merely a resemblance.

 

question why does his turbo make his exhaust pop so much i hate to be driving that thing farting up a storm everywere i go.

 

i say 253hp 212tq at the wheels.

although Jon is a little late...hope nothing broke!

 

I wish more people understood this. On the RX-7 forum all you ever see is the same question over and over again. "What is the largest turbo I can use with...?" That is the single dumbest question anyone could ever ask. A better question would be what is a good turbo for my intended application? The response to that should be "are you being honest in what the car will actually be used for or are you telling me what you are dreaming that it was to be used for?" This is another area that people are unrealistic. Small turbos can do more than most people think they can and many times are better at the cars intended power level than a larger turbo. Of course a small turbo doesn't have the physical bragging rights but oh well. It's not what you have it's how you use it!

 

the map runs very rich to keep the egt's within reason, and all that unburnt fuel is ignited in the hot exhaust system. the car is basically backfiring, but the cat and mufflers arrest most of the flames. ours cars do it stock too.

 

My 3 types of power doesn't attempt to explain correlations between pressure and power output, nor does it attempt to predict what power the Rotary will have compared to the mazda V6 I had boosted prior.

Here's my point; I think you are over-engineering the issues:


With a similiar sized turbo, (as on the GReddy) my 2.5L engine made 90 hp more than before boost, at 8psi. Most people are predicting about 235-250hp for the GReddy turbo system on an RX8 at close to the same boost. I contend, similiar sized turbos, similar boost, a lower displacement engine will make LESS power.

 

Is there a way to fix this... or do you think Greddy would release new maps? I for one would probably not know how to tune it to minimize the backfire so I would rely on Greddy. Is backfire a bad thing, other than sounding ugly?

 

I like to use statistical data to predict output. History has a tendency to tell us what's right.

 

Everyone please stop and read this article, then please continue this thread:

http://www.rx7.com/techarticles_displacement.html

Using the RP displacement calculation the 13b is equates to roughly a 2.6L 4-cylinder 4-cycle engine. This is a pretty logical assessment from a knowledgable source.

Carry on with the bench racing now...

 

Why do you compare it with a 1.3l piston engine? A 1.3l 4 stroke piston engine displaces 0.65l per revolution and NOT 1.3l per revolution.
Besides the rotary engine has no air restricting valves and larger intake ports so it might even pump more air than a comparable 2.6l piston engine (higher volumetric efficiency). Also the intake cycle lasts longer 270 degrees compared to 180 degrees on a piston engine.

 

I compare them because they are two engines I have, or have owned. I don't know much about the volumetric efficiency of either - but I'm pretty certain in my belief re: similar turbos/similiar boost/ higher displacement engine will make more power. Again - I doubt I could 'prove it' but I think I'm right. We'll see, maybe, when the dyno's are published.

 

EXCELLENT info...thanks - I'll read that

 

A little side note on the crank hp. Since RB had an engine dyno the numbers should be pretty accurate. Secondly, if the rx8 had 25% drive chain loss then it would open up for some nice aftermarket parts to reduce parasitic loss. Since it's down to "only" 15% it makes me sleep better at night at least.