MazdaManiac

iTrader: (3)

No. The engine is the most efficient compressor in this equation up to and slightly beyond the maximum flow of the engine.

Rote8

Wow, it's is amazing how many folks on this know things without testing, better than those who are actually doing; no matter what results the rest of the world publishes.

Now we find out that certain model turbos are not even as efficient as the non turbo 200RWHP engine at gas compression.
So, we should all just drop forced induction and raise the compression of the rotor, who cares about static/dynamic compression ratios and detonation/pre-detonation issues the entire rest of the world experiences when running high compression in a force induction engine.

I will stick with Racing Beat's opinion on this matter.

bse50

I won't and the reason is simple.
From the moment they quoted pressure\boost and not flow as an inherent limit of a high compression rotary engine they lost ALL their credibility.

Plus:
Engine management options vary with time and the resolution you can achieve nowadays was impossible with the first engine management options (8\16bit crap pcms). Distributors anyone? twist the disty and pray wasn't a saying?

Math doesn't change (nor my understanding of it does, that's why I often follow the empirical way) but technologies and variables do as others have stated.

All in all we are missing this thread's point:
Is a lower compression ratio needed to achieve a stable 300rwhp goal? The answer is: No.
Then if you have an inefficient compressor that may overheat air, a crappy tune etc the answer may vary. For sure if the compressor is not up to the task you'll only spend a shitload of money for an expensive bandaid that won't really do much!

olddragger

iTrader: (3)

bse ...friend,
boost and flow although two different things, are used a lot in the same reference by many people in America. Its not totally correct, but dont discount RB because of that. They have probaly done more flow studies than most other major engine builders out there.
I know I am talking about 300 whp with a goal of a reliable 50K miles of daily driving and about 3-4 track w/e's a year. With track type maintainence of course. And, I really dont care if power goes down a little over that time.
I really dont know of anyone that has done that with this engine?

At this point it seems to me there are 2 options:
1- low CR rotor set up.
2- convert to E 85.

Now MM has stated that a dual map set up with a Cobb unit would work ( I now have one!!) when you run into those situations in which its hard to find E85--but I am not sure about that.
I just dont know much about it. E 85 would require a different pre mix oil type etc etc.

Maybe a thread needs to be started about what milage others have gotten at 300rwhp?
Think I will.
OD

Rote8

Boost PSI / Flow/ Resistance to flow...

Remove any one and the remaining 2 are meaningless.
I am sure those spamming the tread with how it will never work and the rest of the world is wrong, know how flow/resistance/boost combine.
Those who dare...

Increase boost (while resistance remains the same) - increase flow.
Increase Flow (while resistance remains the same) - increase boost PSI.
Lower the resistance, (while boost stays the same) - increase flow.
Lower the resistance, (while flow stays the same) - decrease boost PSI.

Lower compression ratio = less resistance to flow.

Charles R. Hill

iTrader: (7)

For a given engine, once mass airflow and intake air temps delivered into the engine are determined, the rest is rather moot. Before the advent of high-resolution mass airflow sensors, manifold boost data was used as a presumptive to determining actual airflow. Now that we have rather accurate airflow sensors we no longer need to assume airflow by calculating it from manifold boost data.

How does lowered compression ratio equate to less resistance to flow? I am rather curious about that one.

zoom44

well thats just ridiculous rhetoric. as kane has said and jeff just wrote up to a point the engine is the most efficient. you can't "drop the forced induction" because you are using it to "raise the compression of the rotor,"

"the rest of the world" ? did you read the articles i posted previously? what was your take away?

you are free to stick with Racing Beat. Im one of their most ardent admirers. But I know that article is wrong as written. For what Denny wants its absolutely a waste of his money. He's going to do it anyway because he will "feel safer" and thats fine. but its not necessary.

MazdaManiac

iTrader: (3)

Uh, no.

TeamRX8

iTrader: (25)

bse50

I would still worry more about the tune and the compressor than the compression ratio

So you admit that talking about psi only is meaningless. That's why you need to talk about flow and not merely pressure ratios. That's also why RB's paper is irrelevant since it doesn't address flow.
Nobody's spamming here, we just keep in mind OD's goal and the renny's design when discussing this subject.
I didn't want to say that but if you started off with a wrong compressor and need to chase your tail finding the solution elsewhere it's not our fault. Get something that breathes efficiently, tune accordingly and be happy with it.

TeamRX8

iTrader: (25)

it's not the difference between running vs not running, but it is an important difference on determining max output/efficiency none the less

but srsly, this thread has reached a critical state of tiresomeness, some people just aren't ever going to get it regardless, the OP in particular

MazdaManiac

iTrader: (3)

These threads always behave like they exist in a vacuum. At times it is amusing, but ultimately it is pretty sad.
There are just a few things that get interjected over and over again - torque is all that matters, flow is all that matters, etc. - but no one is willing to connect the dots.

olddragger

iTrader: (3)

Ok guys---- I am a learning---no doubt I am not an expert. So I appreciate yalls patience.
From reading other posts it seems that no one is mentioning realiability?
yes I do understand efficency and reliability can be the same, but they can also not be? Which reference is being made?
Some have said that with a good compressor ( the pettit kit has a good compressor when used for the flow it is rated for), good tune and all the other parameters controlled like heat etc then I should be fine with the 10:1 cr with 93 octane gas and no water meth?
Now some thoughts in my pitifall head---there are a number of blown FI renasis engines---why? Do they all have a bad tune? Bad compressor??
Why did Mazda drop the CR on the turbo models they produced?
Does this make sense..... "a lower compression engine will have less stress on the internals during off boost time and the combustion chamber static compression while on boost will have a more gradual build and release cycle than an engine with higher compression, given approx the same power output numbers while on boost. ".

Sorry guys---this does seems to be going around in circles--maybe thats why I am dizzy.

Zooms idea of E 85 is looking better and better lol. And a hell of a lot less confusing.

dannobre

iTrader: (3)

The low compression engine will have less power...so your foot will be in it till you have the same power that you would with the higher compression engine

So basically you will have less power off boost......and with the same everything else..you will have less power at every point on the curve.

Up till something happens that it goes boom And then you will make less

Question is...is there any majical way that lowering the compression will keep that from happenning.....Not likely from my point of view

Charles R. Hill

iTrader: (7)

Yes, you should be fine. There are plenty of F/I'd (super or turbo) RX-8s that are not using alky injection, use 91-93 octane fuel, and have not had the problems you are seeking to avoid.

zoom44

hey wait - this is my thread

zoom44

because they had to offer a warranty and had no control over the fuel the customer would use. also up until "recently" they weren't using MAFs.

Rotary Inspired

iTrader: (1)

I think you know the answer to this.

Rote8

I ran standard rotors for a long time and have found low compression gives me lower temps and more flow with less boost (I did raise the boost later).
Low compression means less resistance to flow and less heat in the intake from boost. (IC temps are down)

These are the hard results I have found, not some abstract idea of what someone thinks should be.

Racing beat, Kenne Bell, Magnuson, Whipple, Gale Banks; too many people who do test (a lot) have already been trough the high compression low boost vs low compression high boost, yet, some on this board know better than all these leaders of the industry without performing any testing.

I have never said I will make more power, but my low comp engine can withstand more boost than a higher compression engine with the same tune.

As for the "confusion" that seems to happen a lot here.

Rote8

You do get it exactly right.
Less compression does mean less power, unless the boost PSI is raised back where it was before the low comp rotors, an S/C is a fixed amount of air per rotation.
I also think the turbo guys should be all over testing this, due to the fact a turbo can remain at the same boost pressure when the flow increases so radically that boost pressure drops 3 PSI.
(but the turbo would need big enough, to flow enough air, to sustain the boost PSI.)

Two glasses of beer, one a 12 ounce and the other a 16 ounce; which holds more beer per refill cycle?

PhillipM

The problem with that statement is that the leaders in the industry are producing daily drivers with warrenties that are pushing 36psi through engines with 10:1 compression.

olddragger

iTrader: (3)

Team----sorry you think I will never get it. But come to think of it do you have any real experience with a boosted Rx8 engine? If you think theory is enough then please dont ever come into the medical field as you will kill someone.
For the rest of you thanks for all the discussion, seems there will always be two camps. It is good to have choices and I do understand that the power curves are different between the 2 and why.
I have to believe that when reliability is my main goal with FI the low cr engine makes more sense. Its all about heat. The lower cr engine makes less, until you want more. The high cr engine--you dont have a choice. In my little mind that is the best way to kinda sum it up.

Hey Zoom---i never knew you would never get it! Lol.

bse50

I see your points
However let me poke on the heat issue! A more efficient compressor builds up less heat
Sorry, I really couldn't resist!

How are you involved in the medical field?

olddragger

iTrader: (3)

for the last 33 yrs --trauma/neonatal/psy --now have a desk job working with quality/insurance crooks/discharge needs and program developement.
Couldnt resist---lol--i know that feeling.

bse50

Cool stuff, i'm trying hard to find an experienced biomechanical engineer. Obviously to no avail

I'm looking forward to reading your new build thread btw!