JK5S

iTrader: (2)

Has anyone done this build? I'we searched the Google and the only things that pop are Rx8's with 20b swaps. I am interested in using Rx8 irons, housings and rotors with 20B e-shaft and counter weights (blue printed). Obviously custom intake manifold, exhaust manifold, standalone management system and oil pan. Theoretically 360+hp naturally aspirated.
I hope to see one already made with lots of good info to report.

j9fd3s

iTrader: (3)

can't be done, there is no renesis thick center plate, unless you want to make one.

JK5S

iTrader: (2)

Thanks, makes more sense now.
So then the 4 rotor would be the only realistic option.
Has anyone built the quad rotor from 2 rx8 engines and a custom 5K crankshaft?

sinned2545

iTrader: (7)

Why Go through all that effort when 3 rotor motors already exist???

If you havent seen these links...

Gordons car I believe uses rx8 rotors.... but thats about it..... Its a AWESOME 20b NA.... his car is like if mazda did a 2011 NA rx7..
https://www.rx7club.com/showthread.p...hlight=Gmonson

And there's this from Define autoworks....
This thing is all sorts of BAD ***
https://www.rx7club.com/build-threads-292/non-turbo-428rwhp-fd-build-up-history-937570/

RX-Heven

iTrader: (1)

Has been done.
Afaik, they used a short crank 20b e-shaft. The car was a drift car I believe in the UK or EU. There are videos of it but unfortunately, I don't know any more about it than that.

JK5S

iTrader: (2)

Thanks RX, i did stumble upon that thread in the RX8club and it looked solid. Although I'm not sure of the term 20B short crank??? Is that a custom billet crank, or is it a modified Cosmo 20B crank? There was also a controversy on the center rotor not producing enough power due to exhaust ports of the two center irons being too small.

RotaryEvolution

iTrader: (30)

alot of people lean away from the RX8 rotors because they are actually more difficult to generate more power from, they do make it easier to get a better torque curve though.

JK5S

iTrader: (2)

the ppl from above build claimed to have generated 250 whp at 6000 rpm and predict another 100 hp gain at 8500rpm.
300+ hp all motor is plentiful for me, I'd take that.

RotaryEvolution

iTrader: (30)

for the amount of work involved in those builds, i would not.

t-von

iTrader: (8)

Yes it's a ton of work but the car can always be highly modified at a later date after the swap. Far too many people think 20bs should be ***** to the walls right out the box to justify all the work involed.

RotaryEvolution

iTrader: (30)

well not exactly but for a custom job i would expect it to perform a bit better.

problem is that the RX8 rotors are designed for a specific set of conditions, simply tossing in higher compression rotors will help with response and torque but not so much with peak power. yes you build an engine for certain criteria such as road racing or drag racing where the power curve is critical.

my point is that just because they fit doesn't mean they are better all around. to get you have to give, with compression differences that high you will likely be sacrificing your top end power for mid range torque. a number of people who build high revving motors usually opt for lower compression rotors with big porting.

largest problem with the side port engines though is the side seals get cooked handling the exhaust gasses. it's also the main reason that the renny doesn't take to forced induction well, but getting a bit off topic now.

JK5S

iTrader: (2)

Thanks for that, It makes sense. Now is the profile of the RX8 rotor chambers or is it the higher compression that makes it condition specific?

Trots*88TII-AE*

iTrader: (11)

^A rotor's combustion chamber profile and compression are one and the same, the higher the compression, the shallower the combustion area. I can't speak from experience but I think it has more to do with the RX8's bathtub than compression, I have never heard of higher compression limiting top-end performance of an engine unless you experience pre-ignition.

Liborek

Not exactly.
There are several designs of rotor recess: MDR, LDR, TDR etc. Middle deep recess pocket (which is AFAIK used in all modern 13B´s Renesis included) gives the best performance in the whole rev range and especially in very top-end granted there is ignition on both plugs.

So its not just about CR and flow through recess but also about ignition configuration, physical spark plug arrangement, timing, split etc.

But in case of Renesis rotors vs. everything else, poor performance lies in poor seeling of side seals and consequent low dynamic compression. Maybe some people who are truly experienced with building Renesis engine know how to create several very important angles on uncut side seals to achieve better sealing, but I think that it still won´t be on pair with classical side seal design.

Just a note, compression ratio number means nothing without knowing intake events and total nothing when engine is poorly sealed.

RotaryEvolution

iTrader: (30)

i wonder if the 8 would have benefitted more from a dual side seal design such as the old 12A 6mm carbon rotors used.

this is also a good example of the differences in bathtub design as the old rotors used to have the angled pockets(even though i haven't heard those terms before, most common rotors are universally deep and supposed to be uniform in shape).



but i digress, these shouldn't be big concerns with the stock RX8. it is mainly an issue for high mileage out of warranty 8's and those that have been modified running leaner AFRs, more timing advance and higher EGTs.

j9fd3s

iTrader: (3)

all of the 68-73 and 76-85 12A engines have a LDR (leading deep recess) rotor. 74-75 are MDR like a 13B.

there are plenty of graphs of mazda's testing of different chamber shapes in the kenichi yamamoto rotary engine book, but on a 12A the LDR offers slightly better flame speed and slightly better low speed efficiency.

there are also plenty of piston engine examples where higher compression pistons make the chamber shape so strange that power goes down.

from http://www.expeditionlandrover.info/...ompression.htm

Kas Kastner is the Jim Mederer of the Triumph world

"Also from Kas Kastner:

The issue of popup pistons has come to the fore several times over the years and the information never seems to be saved or passed. To wit: I made a series of engines for exp. purposes in the early 60's to view the effects of compression ratio increases.

In a nut shell here is what I found on an honest engine dyno with an operator that didn't lie to himself (me). The 13:1 popup piston that entered the combustion chamber confused the flame pattern in the combustion chamber so much that the measured BHP was the same as an engine with flat top pistons and 10.25 ratio.

The slightly domed pistons were better than the popup by a considerable measure but NONE were as good as the flat top. The combustion chamber in the wet sleeve engine series is so ancient that there is not room for a decent flame front to progress.

Look at the tops of your pistons if you have the popup or domed type. See if the carbon is a reddish or off color brown instead of black and that there are swirl type patterns on the piston top as opposed to a flat covering of carbon. Generally you will find exactly that as I have described. The flat top piston allows the flame front to progress evenly to the back of the combustion chamber and reach there before the end gas has time to heat up and explode on its own (detonation). On the flat top pistons you should see that the carbon is thinnest or maybe even nonexistence on the squish area side of the piston and closest to the exhaust valve because this is where the detonation is going to occur.

I ran cast pistons for years and years in these engines both the stock 83 mm,86 mm and the Hepolite 87 mm. The Hepolite in my opinion was a great deal better as it was a lot lighter than the stock castings. When we ran forged pistons they indeed had the longevity but did not produce the power as the bore clearance was twice that of the cast pistons and they were quite a bit heavier. The thing here being that if you control the detonation you can run a cast piston. Of course I am speaking from efforts 30 years ago but gasoline still is supposed to burn not explode so maybe some of this is still true.

The best and most powerful engine I made were done with 87 mm cast pistons, chrome compression ring and .003" bore clearance. To eliminate the run in time and additional wear on the engine I lapped all the rings into the individual mating sleeve and had the highest effective compression immediately and it showed on the racetrack. With all my work in these areas I have a small caveat that must be remembered, and this is that I was only interested in something to last the weekend not the year and there is the "wolf in the bush" Kas."

peejay

Modern Wedge heads surpass Hemi heads because a true hemispherical combustion chambered head requires pistons with a lot of popup, which makes the combustion space pretty crappy, and modern ways of doing things have us able to surpass the hemi head's moderate gains in airflow with the wedge head's superior combustion.

Hemis are mainly used nowadays where rules mandate them, or where 6:1 compression is acceptable.

Scottish#1

Yes the rotors are the same size and the higher compression from the Rx8 rotors is perfect for na use in your 20b build. just machine the rotors to take bigger apex seals. as for the side seals, they fail due to poor cooling,poor lubrication and high boost but for na, no side exhaust port and lower rpm you will be fine.trust me i flog the **** out of my 8 on the track with 40 min 9k redline sesions all day with no problems.

as for Hp just add bridge port and haltech and bingo bango estimated 350whp.There is a 20b build with Renesis rotors going on as we speak on the Rx8 club. http://www.rx8club.com/showthread.php?t=199903

as for reliability of the renesis it is down to poor build quality,bad maintance and bad tunning.we have boosted 8's on the forum that run a reliable 425 whp with no issues.(see www.Turblown.net)

rotaryB-2000

anu updates on this rx8 3rotor ?

YaNi

iTrader: (2)

I was under the impression that the issue was with the side seal springs weakening due to the excessive heat and not the seals themselves.

jaggermouth

iTrader: (1)

So if you used rx8 rotors, the groove just needs machining?
And is it only possible to use the RX8 plates and housings with a custom shaft?