my thoughts on the upper manifold
 

im posting this here so i dont hijack someone elses thread....

The upper intake is designed for N/A applications and that’s why all the turbo kits crap out at higher rpm when the aux ports open, there are too many pathways and it upsets the turbo trying to force the air in there. Since the exhaust drives the turbo, the exhaust is not fixed to the turbo blades so it is possible for the exhaust turbine to fight the exhaust because the intake tract on the renney puts resistance on the whole set-up and the turbo gets slowed down from this.... well not slowed down but more like held back.

This is why the supercharged dyno looks better, the belt forces the air in and the resistance on the intake path can not slow down the supercharger because the supercharger is mechanically driven.

The intake mani is a big restriction for turbo because it was designed for N/A.

Until mine, or someone else’s replacement comes out for the upper intake mani, POWER WILL BE LIMITED!!!!!!

yeah.. it sounds funny, it's tough to explain a visualization

Seriously, it might be funny.. but the upper manni will limit you to a certain point... im not talking 300.. 400hp.. im talking more in the 500+ whp range....

Really, think about it, you have to take turbulance into affect at a certain point.

If someone knows more and can prove why the upper mani is not a restriction at high power levels please post why.

It is a vacuum design... now we have boost vs. vacuum.

Post your comments.

I disagree.

I'd actually like to know why you think something that flows more air than the ports themselves can is such a restriction. My perfect "turbo" intake manifold would be longer than stock which on a flowbench would appear to flow less! There is one thing you need to take into account when it comes to flow and that is, the greater the pressure, the more flow you can get through the same area. If an engine is trying to do all the work to pull air in, this air will be at lower pressure which means it needs a certain sized manifold. An engine that has air that is being compressed forced into it will be able to get more through the same path at a lower restriction level or as a different way to look at it, can get more air through a smaller orifice with the same total restriction. (That came out a bit weird so hopefully the example is understood.) You need to know pressure. What this means is that your logic is in fact backwards!

Up at the 500 hp level, the manifold's ability to flow air will be irrelevant as you'll have long hit a host of other more important issues not only in terms of engine strength but airflow. It's not the intake that anyone needs to worry about when it comes to flow.

+1 I think the holiday weekend is affecting people.

I think people confuse a drop in manifold pressure with a reduction in flow.
When the APV opens, the flow increases.
This causes the pressure to drop.
Its simple thermodynamics.
Now, if the turbo is properly sized, the pressure will work its way back up, but it is a massive increase in turbine speed that has to happen to make that so.

MM & RG,

In a piston engine application, ('98 SVT Cobra), it was common to remove the butterflies in the intake (opened only at higher RPM) when supercharging. The computer was then tuned accordingly.

In the RX-8, would it be possible with a positive pressure system to have all the ports open all the time, and size the compressor / tune for this 'new' intake? Wouldn't this solve the changing flow problem? Also, I would imagine that it would be more useful for s/c, as you have more pressure at lower RPM.

Thoughts?

TIA.

^Charles. A thousand apologies!!! You are most certainly allowed.

Sorry!

I can fix that.

Charles, what do you think?

You can absolutely leave everything open full time if you choose to and tune accordingly.

An easier way would be to change the opening points to a specific calculated load range via the AccessPORT.
Just pop them open in boost and let them do what they do naturally everywhere else.

That seems to make the most sense. +1 for the AccessPORT. (& good tuners).

Is it fair to say that a turbo kit developed with the A/P in mind would be appropriately sized to flow properly with all ports tuned to open at lower rpm/boost pressure?

Charles, thanks for your reply. I think I would want to go through the hassle if I could be shown that there was a benefit to having more air in the engine at a lower RPM. I've looked quite hard at all of the power-adders, and (like others) I am looking for "gobs 'o torque"tm at the lowest possible RPM. Ya know, just the holy grail of the Rotary Engine :bowdown:

It's also fair to say that I am waiting for said kit....

thats an excellent idea! you two put way too much time into this stuff already

thank for your explinations, i need to better explain myself to what i feel are drawbacks in the stock systems.

i am just trying to say that the stock upper mani can be improved for turbo app, i know its more then enough for N/A

and ofcourse, obviously i am no where near some of you guys as far as the rx8 design goes, however i am learning..

if i'm wrong great, id rather be told am wrong and why then to have someone just look at me and shake their head...

who knows, maybe one of my crazy ideas might spark something in someone elses head who will know how to make what ever it is work.

so back on topic, and this is in regards to the turbo app, how come there are no turbo kits that build power to redline like the s/c kit.

efficiency range?
must be more then this?

why do the turbo kits fall off at high rpm?

it's the VE of the engine. That is how the engine functions.

What you're seeing is the inefficiency of the SC. It's unable to feed the engine enough till near redline (since it's rpm based). With a turbocharger, we can feed it power pretty much anytime after 3.5k rpm. So if we want 10 psi, we get it right away. That's why every single turbo kit for the rx-8 makes more torque than the pettit SC.

also I don't know how many actual pettit customer dyno charts you've seen, but most of the one's I've seen make 240-260 whp range. No where close to what's displayed on the dyno compare thread. But the same could be said of the greddy kit results. Most people on that make around 230-250 whp on emanage and 260-280 with the int-x/ap type systems with increased boost.

*shaking my head*

Benjaminz, what would you do to the intake? What are you looking to gain? I'm curious.

Dipping an oar back into this one...

In general, my understanding is that the *problem* with the rotary is that it doesn't make torque anywhere, and it needs to rev like crap to make horsepower. (don't flame me).

Intakes and exhausts don't seem to do much to address this problem in the Renesis. I haven't see any real flow-data to support or dispute the stock reality, or anyone else's proposals.

There seem to be two general solutions to the Rotary (imho). Add rotors to increase displacement, and/or force feed air into the mixture. Porting has in the past shown amazing gains - but unfortunately the Renesis doesn't want to play.

Until the RX-8, most of my research shows to be that turbocharging seems to be the way to force feed. Aftermarket, this approach would generally ignore the low-end and focus on adding lots of horses to the top. I have driven an rx-7 racecar like this. Brilliant within that 3,000 rpm band - but I wouldn't like to drive it on the street.

With the RX-8, it looks like the aftermarket has brought the supercharger into play to try to do something at low revs. It works, too.... The problem seems to be that at higher revs, the S/C just can't flow all the air that the engine seems that it can use. So, we now have a broader powerband, but (relatively to turbo) poor performance where the rotary seems happiest.

Adding insult to injury, the Renesis has significantly higher compression that prior engines, causing engine builders/tuners to have to work with significantly lower boost pressures for safety reasons.

Ideally, I would like to have a solution that can feed extra air to (an otherwise stock shortblock) engine at low revs - just off idle, please; and keep feeding this air until redline. I had great hopes for the Axial Flow unit, and am quite interested in the Hymee s/c. Perhaps a 2 speed S/c will come out, or a new engine entirely with seperate 'scavenging' rotors as was discussed in another thread the other day.

However, I am a realist. This is a rotary and there are almost NO aftermarket dollars thrown at R&D. End-users are the guinea pigs. That is such a shame, and we all owe a debt to those who have grenaded engines, or spent after-tax dollars in this pursuit.

I think that the best bang for my buck within the next six months will come from a turbo system that is more integrated with the engine / EMU than the bolt-on solutions of the past. This isn't an ad for MM & BHR, its just that they seem to have a similar (w)holistic approach to this.




(Note that before posting the above, y'all could only guess at my ignorance - now you know!, LOL at myself). :lol:

The upper intake manifold is actually the single LEAST restrictive part of the entire induction system! The stock manifold is holding nothing back anywhere on either n/a's or forced induction. Yes it is that good.

I'm actually not going to get into the efficiency side as others will and hopefully they'll do it without resorting to the whole turbo vs supercharger debate.

I will comment on one more thing. The reason the rotary has little torque is not due to the fact that is is a rotary. It is solely based on the fact that it is small! All small engines have little torque. You can't change that. They can have power by revving them up high but torque they can not have without forced induction. This is not a problem unique to the rotary. It is a problem associated with all small engines.

Torque is based on 2 things and they are displacement and efficiency. Obviously the more efficient we are, the higher it can get. Once we max out efficiency though it ultimately means we are limited by displacement. Since torque doesn't mean anything useful in moving a vehicle, this isn't a problem as long as we increase rpms. Even an F1 engine at stratospheric rpms and horsepower levels still makes little torque due to the fact that they are relatively small engines.

All small engines need to rev high to make naturally aspirated horsepower. That's physics. There's no "problem" at all with the rotary. If it did make lots of torque, then there'd be a problem! A small engine making torque is getting help from somewhere and it's doing it not based on size but based on efficiency. Forced induction to look at it in simple terms adds efficiency that the naturally aspirated engine lacks. FI can easily get efficiency (I'd better mentions it's volumetric before someone rebuts this) well over 100%. Nitrous also adds efficiency. If they didn't, power wouldn't be gained.

RG - instead of 'problem', I should've said 'reality'. Don't get me wrong, I didn't accidentally buy a rotary. I'm well aware of the ~1.3 litre displacement & all of the realities that entails. The stock Renesis is indeed a marvel at what you can get out of two rotors NA.

I also realize that I am asking the improbable in wanting the powerband to start lower and keep going at higher rpm's. Never hurts to ask, though. :)

When you say that the intake is the least restrictive part (I am putting words in your mouth a little), may I assume that you mean the restriction is in the porting/housings? I think I have read your writings in this regard before.

Thanks again for your thoughts, I'm always learning.

Silver06.. i would like to see a modification to the intake system that will compliment the turbo set-up so that it rises in power damn near to redline... i klnow it can be done, just needs more thought.. more R&D

The upper intake manifold is actually the single LEAST restrictive part of the entire induction system! --- rotarygod

ok, note taken and learned something new... so then the manni itself has stored air in it since the restriction is the intake port? it seems that this stored pressure will cause resistance on the turbo.. this is still what im trying to get at.

ummmm.... ok i want to ask this then, this is still in reference to the valve opening inside the manni at the 7250 rpm, the one in the primary pathway.. the last valve in the sequence

i am still thinking that somehow either it being the ports which are more restrictive as noted before by rotarygod or something else not deeply being looked into is backing up the turbos at higher rpm

i still think something is being missed

as for us (the rx8 community) being the test mules for R&D.. I have been blessed with an opportunity to pick up a fantastic website that will be up soon and i have a "little" bit of capital to play with

have any of you guys seen the yellow feed car where the took out the upper mani and the have a set-up that goes directly to the lower mani... makes 288ps

so if it is proven that the upper mani is and or the pathway to the lower mani is perfect, where can the capital be invested to make a product that can be sold globally (the other countries with rx8's) and the appropriate people getting the returns?

so, anyone care to explain the VE of this engine in more detail?

p.s. this thread was not ment to be turbo vs. supercharger... it was ment to be what is causing the turbos to die off at the higher rpms.

I'm all for experimentation and trying new things. I've tried many things that haven't worked out all that well. That's a good way to learn. It is true that the Renesis manifold was designed around natural aspiration. That's why it has all the bells and whistles. A turbo doesn't need all of this but it's not to say that it still isn't effective with them.

Here's how I personally would go about a new turbo intake manifold as I think what you want to do isn't so much to remove a perceived restriction but rather optimize an induction system for turbo use. Fair enough. It can be done. You do also need to take turbo sizing into consideration as it is equally important.

Back to the manifold. I would actually keep working auxiliary ports (somehow) but instead of them being rpm dependent, they would be opened solely at the onset of boost. No boost, they stay closed. Boost, they open. Simple. Next I'd remove the VDI system. Leave it closed. I know some would rather see it stay open but bear with me.

With only working aux ports as the only functioning concern we can now design the rest of the manifold. I want longer runners than stock! Lengthen them if you can. Shorter is for people who don't know what they are doing. The manifold needs to be designed to good low end power. Top end power is completely irrelevant in forced induction intake manifold design as far as I'm concerned. You want as much low end as you can get as early as you can get it. This really goes counter to what most people do with FI but then again a single Lemming will jump off of a cliff and the rest of the population will then proceed to just follow him right off so go figure.

So now you're probably curious as to why I would possibly want a longer manifold that tunes lower. The answer is actually quite simple. What is an inherent weakness in ALL turbo systems? Lag. If you don't have lag, you don't have a turbo. Period. You can't eliminate lag completely but you can greatly decrease it. You are waiting for the engine to get enough exhaust energy out so that it can spool up the turbo. Until this point the engine is running naturally aspirated. If we have closed aux ports (which keeps intake velocity up among other things) and have longer runners that tune lower, we are helping the engine develop more power on it's own. If you can get the engine to make more power sooner, that's more exhaust energy to spool up a turbo sooner and quicker. When this happens you can trade off a little bit more and run a larger hot side on the turbo for more flow which will help top end power. Typically people will either run larger hot sides and suffer greater lag on the bottom end or small hot sides for good low end at the expense of some top end. You can have the best of both worlds (within reason of course) if done properly. Longer intakes and larger hot sides on the turbo are how to do it.

If this sounds like what you are going for, what's stopping you! Go do it!

thank you very much
 

Rotarygod, you just explained what I was trying to explain except it was understandable, thank you, I’m very sorry that I am not good with words in explaining things, I just hope that what I have to offer as far as products to the community will speak for themselves.

I want to thank everyone for being open minded to this thread, I appreciate it.

I gotta work on a few other products before i get too deep in this one.

I want to make a few working models and just try it with nothing to fancy, a basic greddy kit should be great to use a base turbo kit for the different configurations.

In the future (realistically next year) i will post here with updates on working models, until then I would still like to hear everyone’s thoughts.

Again thank you all to who have given their comments and opinions.

Rotarygod,

I agree the stock upper manni is more then enough in N/A for the renny

I’ve been thinking about what you said on the additional ITB’s for the aux ports, there have been many configs going through my head, a couple written down, but it would be easy to have a servo or a solenoid to open the aux ITB’s via vacuum pressure or a electrical signal.

Anyways, I too have been thinking about using the 787b variable length idea for the primary set-up and when the tube retracts it will be shorter along with the aux port set-up. The factory TB will still be retained to keep simplicity and cost down, but the factory TB and additional ITB’s will be downstream from the intake manni. (like a sr20det Gtir set-up) and the maf will be at the entrance of the intake manni. the variable length set-up could some how be designed to work within this set-up.


this are just ideas to show where im going but it is for turbo app only.. well thats what im intedning it to be for...lol

Also it was kind of funny, another forum member on here, I think its getreadytogreddy.. the yoda with the green hat guy, mentioned something about the exhaust set-up for a twin turbo app that I was thinking of too. Using the siamese port to power a small turbo for low rpm, and then the outer ports to spool a larger turbo for higher rpm. I know that if you have a properly sized turbo it good too, but the twin turbo set up with give you a broader power band, “more power under the curve”

Have a good memorial day everyone, ben

When it comes to twin turbos, don't think in parallel, think in series. Scroll down a little bit and enlarge the diagram on the right. This is how you do 2 turbos. Parallel sucks!

http://www.greencarcongress.com/2005...eils_opel.html