Icemastr

A few turbo kits are coming out for the RX-8 soon so I wanted to share a little bit of information and maybe get soem discussion going about how the Renesis will respond to turbos. Hopefully some people on here might have already experimented with turbos and share some information on how the side ports affect turbos which is what I am most interested in finding out.

My knowledge of turbochargers comes from working on a few different turbo charged cars on a few different types of motors and work including making my own custom turbo kits, bending and welding my own exhaust piping, tuning stand alone ecus, and dyno testing. I am by no means a turbo expert but here are some of my opinions about turbochargers from my own experience and research of compressor maps, boost response, dyno plots etc.

When comparing the difference between turbocharging the renesis over the old 13B there are three major factors, the new ECU which is difficult to replace with a standalone ecu like the older rotaries, and is proving to be difficult to reflash or piggyback. The side ports instead of peripheral ports and the higher compression of 10:1.

The ECU is a factor that may be easily changed in time, however the compression and side ports are not things that can be easily changed. Lowering the compression on a renesis is accomplished by changing the rotors to different ones, this in short requires removing the engine, dismantling it, putting the new rotors in, and then rebuilding the motor and reinstalling it. Not something easily or cheaply accomplished. This can easily by a $3000-$5000 job meaning lowering the compression is not something that can be done with a "bolt-on" turbo kit. How does the compression affect things? Well advantage wise it will spool a turbo faster as well as create more HP, making the turbo more streetable, however on pump gas this means you are limited to low boost (7-8psi) where as 9:1 compression rotaries are generally known for running 15PSI pretty safely. Tuning also becomes much more dangerous as there is less margin for error in tuning (as if if wasn't bad enough with the 9:1 compression).

The problem that is most often see with turbo rotaries is detonation casuing the apex seal to break or crack, usually a good piston engine can handle a good bit of detonation before breaking a seal or gasket, however with my experience with rotaries twice it only took one detonation to break the apex seal, thus losing compression and needing to rebuild the motor. Many different materials have been tried to make stronger seals, however there is no seal that has shown up to suddenly be capable of handling more than a tad bit of detonation. In addition with those seals when the motor does blow, most often the rotors or housing will be damaged resulting in a more expensive rebuild because you need to replace more parts. In short no "magic" seal has been found to my knowledge that solves this issue.

Another thing to consider is the side ports and how they will affect turbos, this is the key difference between the renesis and the older 13B's, as they had peripheral ports. For anyone who doesn't understand ports check out http://www.rotaryengineillustrated.com. Side ports are smaller ports that come in through the side of where the rotar spins, where as peripheral ports are just a big hole for the air to directly come in or come out of the rotor chamber. The advantage of peripheral exhaust ports on a turbo rotary was that the exhaust gases were at a high velocity and very hot going right into the turbo. Since the old 13B's only had two exhaust ports you could make a fully divided equal length manifold to your turbo and use a divided inlet (just like the twin scroll turbo on the Mitsubishi Evolution 8, the rotary had it back in the 80's) so each rotor is in effect sending its exhaust pulse to one side of the turbo allowing you to tune the exhaust pulses for maximum spoolup.

Two things thats greatly affect turbos, displacement and exhaust. The exhaust is what gives the turbo its power to spin and force air into the engine. Displacement will allow you to make more power on lower boost. A lot of people overlook this and just think boost is boost but this is an error. Comparing the rotary to a piston engine turbo wise becomes complicated because of the characteristics of the rotary. Previous 13B's displacement wise to me compare similar to a 2.0-2.2L engine in that they make similar power naturally aspirated depending on the modifcations. Both max out in race trim around 300HP. When you put a turbo into the mix, the rotary tends to make the same power using the same turbo as a 2.0L piston engine with the same boost. However what I have found with the peripheral port exhaust the rotary engine spools up a turbo much quicker than the 4 cylinder piston engine.

A GT35R would not even be considered streetable on a 4 cylinder engine because it would not reach full boost until around 4500RPM or more however a rotary reaches full boost with a GT35R around 3200-3600RPM. In fact same turbos on 13B's reach boost faster than even the Skyline RB26DETT 2.6L engine, and the Supra 2JZ 3.0L engine. Boost response is really closer to a 3.8L-4.0L piston engine. Which is great, it means you can run a larger turbo and still have great boost response. However a 3.0L piston engine tends to make around 10-15% more HP at the same boost levels with the same turbo.

This is why I am interested in finding out how the side port exhaust affects turbos on the renesis.

RXE16T

Very comprehensive info you've posted there, Icemastr.
So in theory, a HKS T51R or a Trust T88SPL would almost be a streetable turbo if what you say about rotaries reaching max boost at lower rpm is correct.

Icemastr

The HKS T51R KAI has shown to reach 15PSI around 4000RPM on a street ported 13B, this turbo is generally considered not streetable on a supra, where it doesnt reach 15psi until almost 5000RPM. Big difference, now you can make the decision of what you think is streetable. Some people don't like a turbo that hits peak boost 4000+RPM. Some people dont even like a turbo that starts making boost around 2000RPM and hits peak by 3000.

For reference the T78 on a 13B hits 15 psi just under 4000RPM and is considered a decent compromise between streetability, big power, and cost effectiveness, however a T78 on a supra is not considered streetable because it doesn't reach the same boost until past 4500RPM.

The things I consider important with a streetable turbo are what RPM does the manifold see positive pressure at full throttle, what RPM does the turbo reach peak boost, and if I am in higher RPMS, let off throttle, then step back on it how quickly will the turbo create boost again. These are your key factors in determining the turbos streetability, and people's opinions will vary greatly on what they consider acceptable.

Of course lots of factors including porting, internal engine work, exhaust etc. can all affect boost response. What I am curious about with the new renesis is, does it still have this same advantage with the side ports? If not, it will really suck to run a 60-1 or T04S turbo at 7 psi and only make 300RWHP but not even have the turbo reaching peak boost until 5000RPM. If this is the case to get good streetable you would have to run a turbo sized for a 2.0 4 cylinder, like the GT28RS or T28, something that would see peak boost a little after 3000RPM and be lucky to make 250whp @7 psi. Any of these companies developing turbo kits care to chime in with what they have found so far?

RXE16T

Might I also add that how much useable power band following peak boost is also a consideration of how streetable a turbo is.

For example, no point having a T51R reach peak boost at 5000rpms on a Supra if the rev ceiling is only 2000-2500rpms more.

Icemastr

Pssst... don't tell the Supra guys that!

T77 - Look ma 350whp @ 5000RPM but 800+ by 7000!
http://www.to4r.com/media/jinfurnadyno.jpg

GT42 (Considered streetable on a 13B with 4" exhaust and 9:7 rotors)
http://www.to4r.com/media/peterbdyno.jpg

RXE16T

Is that 1100hp with the GT42 or am I not reading it correctly?

Icemastr

Yeah, hes on the juice too.

RXE16T

That doesn't happen to be your FD does it?
What have you done to get 848whp?

Icemastr

LS1, big turbo, alcohol injection :D

I didn't want a peaky powerband

Thats 18PSI, pump gas, turbo lag is the amount of time it takes to go really fast to ludicrously fast. About 1500 RPM.

RXE16T

That ain't a rotary!

Icemastr

Don't worry I got plenty of rotary power :D I got something special I plan on starting work on next year. Lets just say it has more than a few rotors hehe.

RXE16T

Keep us updated.... it's always refreshing to see what rotorheads do around the world since unfortunately everything downunder consists of dropping in a 20B.

colin204

Icemastr or anybody else


What turbo would you put on a RX8 running 6-8PSI looking for 300-325 rwhp

globi

Icemastr, In order to reduce the compression ratio of the Renesis couldn't you, instead of replacing the rotors, just enlarge the intake side ports?
(If you'd close the intake valve later in a piston engine you'd automatically reduce the compression ratio as well.)

MazdaManiac

iTrader: (3)

Your "out of the box" choices are:

Garrett T04E Super 50
Garrett GT20 (which, I think, is perfect)
Mitsubishi TD04-15 or -18
KKK K16 or RS2

Other possibilities as I see it are a T4/T3 hybrid (an "upside-down" Grand National turbo) or the KKK sK26.

SpeedDemonSoldier

So what all would you have to do to make your 8 run with the Garrett GT20 without any problems?

MazdaManiac

iTrader: (3)

:p

Read "Maximum Boost" and check back with us in the next month or three.

Icemastr

How do you figure the GT20 is perfect? Its a 140-260HP turbo meant for 1.4-2.0L 4 cylinders. It would choke the renesis. The Super 50 is also small, in fact all the turbos you listed are under 300Hp turbos and thats at 15psi.

What makes them out of the box choices? No one has a turbo kit (complete bolt on nothing else needed) out yet which is what I would consider out of the box.

I have seen a Greddy T78 make 315WHP @ 7psi on a mild port 13B-REW. Also seen a GT35R make 285@ 8 psi.

Is this good or bad news? Well the Renesis has tertiary ports which will allow it to flow more air in the higher RPMS, and since it can go to 9000RPM instead of 7500RPM like the older 13B-Ts as long as you can keep the torque up, 200lb ft of torque at 7500RPM = 314HP 200lb ft of torque at 9000RPM = 342HP. The GT35R is considered a fairly quick spooling turbo on a 13B-REW, I think there would be a good chance it could get you into the 300+RWHP range on pump gas with low boost. However the GT35R is a very large turbo for a 2.0-2.5 4 cylinder.

Like I said, how the ports affect turbo spoolup will play a large role in what size of turbo you can use. Running something like a GT28R (which is comparably in spool on a 2.0L to the GT35R on the 13B-REW) you would only be making around 250WHP around 8 psi.

Of course this is all hypothesis based on experience with other motors, I wish I had a dyno at my house so I could test some of this stuff out.

Icemastr

I am a novice on these type of things so I could be incorrect but I have never heard anything about changing the ports affecting compression ratio or allowing more boost on a rotary.

MazdaManiac

iTrader: (3)

Typo, was supposed to read GT28.

I meant out of the box like "out of the starting box", not "bolt on". Implicit understanding of where that expression comes from was assumed. Sorry.

I'm not using other people's past experiences to define what the correct turbo would be. I'm just doing the math and using the compressor maps.
If I used everyone's suggestions (especially the RX-7 guys), I'd be using a T58 or something similarly over-sized.

On that note, the GT20 would actually be a good choice.

The map for 9 psi based on the Renesis flow rates looks like this:



Plenty of headroom to up the boost.

The turbo I am probably going to use is the T3 "Super 60":



Remember, the Renesis only consumes about 20 lbs/min of air at redline. At 9 PSI of boost, that only climbs to 30 lbs/min or so. It is only an 80 cu/in motor. That is a max of 400 CFM or so.

globi

When you enlarge the intake port to a certain extend you compress less air which is essentially the same as reducing the compression ratio. I guess this concept could be considered a miller cycle rotary engine just that the mechanical supercharger is substituted by a exhaust driven supercharger (or turbocharger).
http://www.wordiq.com/definition/Miller_cycle
The advantage of the miller cycle (as far as I understand it) is that the engine still does 10:1 expansion (work cycle) but with a shorter compression cycle maybe (8:1) and therefore allowing more boost without giving up the expansion ratio which is partly responsible for the efficiency of any engine.
I'm sure it has its disadvantages too. It's too obvious that this wouldn't have been considered before.

Icemastr

When considering the 13B-REW engine it comes with twin turbos that allow it to make about 220RWHP @ 10 psi stock, removing the restrictions in intake and exhaust and providing enough fuel you can easily make about 300+ RWHP at 10 psi. 350 @ 15 psi. You say if you used RX-7 user suggestions you would be going with a much oversized turbo, however when you consider how much HP the 93+ RX-7s make on the stock turbos, who is going to "upgrade" to a single turbo to make less HP than the stock twins? A T60 or a T04E don't even flow all that much more air than the stock twin turbos.

I have a GT28R turbo on a 1.8L engine, its making about 200whp @ 9 psi. The turbo maxes out about 15PSI making 280whp.

Now if you are basing sizing and compressor maps off the Renesis being 1.3L how would you expect the Renesis with smaller displacement to make more power with less boost?

I have toyed with the idea of using a GT28R on a 13B-REW for an autocross car, but I don't see how the car would possibly be able to make more than 300whp if that, and thats at 15PSI. Yes it would be amazingly quick spoolup, but it would make quite a bit less power than the stock turbos. I haven't tried this though so I don't have any actual results.

It seems like you are comparing the renesis with piston engines, however they are different animals and the 1.3L of displacement doesn't = a 1.3L piston motor.

Snoochie

Wouldn't fiddling with the intake ports cause overlapping and idling problems?

Icemastr

The intake ports where they open into the combustion chamber are already about as wide as they can go from what I have seen, the best thing to do would be cleaning it up and enlarging the passage, then smoothing it out. Or you can make a bridge and add another port. Once again, I am not an expert on porting, just a tiny bit knowledgeable.

MazdaManiac

iTrader: (3)

I'm not "comparing" it with anything.
The Renesis flows an absolute amount of air. You can calculate this. It doesn't matter what a piston engine does at any given displacement, I am not considering it.

The object is to produce a turbo system that almost immediately produces 7 PSI to 9 PSI and holds it through 9000 RPM. That is all. The net power will be the net power. I'm not building a dyno queen, I am building a system that enhanses the already fantastic drivability of the RX-8. No more. If I only get 50 HP peak that is fine., but I'll bet you that I'll see 30% - 50% more torque across the entire REV band.

The OEM EFI on the RX-8 wont support more than this, so why engineer for it?

The RX-8 isn't an RX-7. Stop trying to use that comparison.
No doubt, the Renesis is capable of a lot of power, but not under the restrictions of the existing fuel system. I am building under these restrictions.

Stop speculating and start looking at compressor maps and use the apropriate formulas.
The Renesis displaces 80 cu/in per rev. That is ~20 lbs/min at 9000 RPM.

BTW, my 1800cc Miata motor only flows 10 lbs/min at redline, so it should be obvious that a 1300cc rotarty motor flows more than an equally-displaced piston motor.