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I’ve been lurking and hopefully learning about this RX8 marvellous car. What I’m planning may offend members but think of it as a resurrection of sorts. I like building stuff and cars, vehicles are a hobby and truth be told I have way too much stuff that absorbs a lot of my time, but I’m a gear head addict.
To the subject at hand. I want to do a car from scratch and choose to build a tribute to the Alpha Type 33 Spyder version. It is consistently voted as one of the most beautiful examples of automotive art and it appeals to me. My build must adhere closely to the specs of the original, 90” wheelbase, 60” track and weighing 700kg. The 33 Stradale had a mid engine lightweight twin cam v8 redlining at 10000 rpm, producing 270 bhp. That brings me to the 13b MSP as it’s not going to be possible to source a 2 litre V8 without paying a kings ransom. In fact both the front and rear suspension clips of the RX8 appeals to me.
As my user name suggests I like to feel power when I drive and initially thought a normally aspirated rotary would do but after thinking on it more I’ve reached another conclusion and that’s forced induction.
Turbo charging at first light seems the logical choice but I don’t like the heat soak that comes with it + a few complication. The heat though is the main objection and I think from what I read heat must be removed from the engine bay ASAP.
Super charging is great for increasing power lower in the rev band and I’m inclined to go with a clutched supercharger that disengages at X revs. I don’t know what X is and throw that question out there.
I like the idea of replacing the high revving V8 with a rotary. Make sure you source a 6 port engine as they have the better redline. This engine is better to supercharge because the exhaust porting in the 13b-MSP is terrible for a turbo setup. Since you only need 270hp it's possible on a Renesis.
Make sure the engine is compression tested first. You dont want a low compression Renesis, it wont make the power you need.
Thanks. I guessed that a 6 port would be the best candidate engine. I figure my best approach is getting a totalled wreck. Because of the resale/repairs cost involved in collision repairs insurance companies declare plenty of write offs and that should offer up some good candidates. I think sending the engine out to an experienced rotary shop and getting it prepped is a good 1st step.
Im JimV8 because I put a built LS1 into a Porsche 968 and it’s a special thing. The Type 33 project is an entirely different animal, super light and nimble. Before choosing the 13b msp as candidate engine I considered the Honda 4 banger, K24 and the BMW N54(?) 6, both are light, rev nicely but almighty complicated. The rotary is lightest and smallest and the power match goes nicely with the lightweight 5 speed Boxster transaxle I’ll be using. And two moving parts and who cares if it needs regular care and feeding. At most it will see 2-4K of summer driving. Most of that be will on the twisties where I live and maybe a couple of tracks days so I can humiliate my friends in their 911s.
It always make me smile when people think a Renesis is a good idea because it has "two moving parts".
That idea is so simplified as to be completely inaccurate. The eccentric shaft moves. The rotors move. The apex seals move. The side seals move. The whole S-DAIS system moves at 4 different locations. The OMP moves.
Sure, it's small and compact but it's hardly simple and the options for power beyond stock are limited and expensive. Not only that, but the number of people that actually understand how different the Renesis is from previous 13B designs is very small.
If you want a small, compact powerplant with a high specific power, go for it but don't pick this engine because it's going to be easy.
An LM4 isn't significantly heavier and can make 400HP for $1500, including the motor. And if you want a fizzy, high-rever, you can always destroke it and upgrade the top end to have it spin to 8k.
Building a car isn’t simple. It takes tons of planning and thinking just to consider which parts should go in it.The 968 in my garage weighs a hair over 3000 lbs and the engine isn’t much heavier than the Porsche 4 that originally fit in it. It is built as a streetable track car and can smoke the 295/18s in 3rd at 100mph. I know what a V8 can do, but the idea of rotary in a tribute Type 33 seems quirky enough to catch the spirit of the original car. If you’re interested in the back story just YouTube Targa Florio, circa 1972.
Anyway I’ve graphed the Renesis engine RPMs against the Porsche transaxle gear ratios and have an idea how that might translate in real world driving. But I’ve never driven an RX8, (I did test pilot a turbo RX7 a long time ago).
so I’m wondering how you folks drive your cars? I’d be interested to learn RPMs at normal launch and at gear shifts. Cruise speeds in which gear. That sort of thing.
Thanks.
On a series 1 renny, good cruise is between 3 and 4k. 2-3k is usable, but you don't get a lot of pickup. Highway cruise in 6th puts you around 3800. Series 2 cars have a different final drive, but idea is the same.
Gear shifts are personal preference, but I upshift around 4500 in regular street driving. 8500-9000 trackside.
No idea on launch I've never dragged the car. Enthusiastic takeoffs for me are maybe 2500.
Alright, well, since you won't see reason... some useful answers.
Launches will depend heavily on the tire, surface, suspension, and temperature.
Autocross launches in my RX-8 on cold (40-ish˚F) asphalt with 255/40-17 Bridgestone RE-71R tires were around 3k-4k. Up the temperature to 80+˚F and it would be closer to 5-6k. For Hankook RS-4 tires, I generally dropped about 1.5k from RE-71R launches. If I was fighting wheel hop issues, I found it smoothed things out just to roast the tires more (sacrificing tire to save the axle/diff because I couldn't get it tuned out with damping) so 7K+ on RE-71R.
For normal driving... I can't remember because I mostly did it by feel after almost a decade of ownership.
Renesis power tends to drop off after 8600 RPM so I only wring it out past that if there's some other reason to (turn is coming up and the time cost in shifting greater than what I'd gain). You might be able to reduce the power drop-off if you can find a magical way to make the exhaust breath better (and no, enlarging the ports won't help because the main restriction is in the hard 90˚ turn between the side plate ports and exhaust manifold).
IIRC, highway cruise at 70 mph in 6th gear is between 3500 and 4000 rpm (as Loki said). When accelerating up to highway, the sky is the limit and depends mostly on my mood. Around town, I kept mine between 3k and 4k. Sometimes rolling at 2k in quiet neighborhoods to be polite (I really hate ******** who have to show off how tiny their ***** is in residential neighborhoods).
Of course, all of these RPM quotes will be of limited use if you go with forced induction.
My strong recommendation to you if you're planning on going with a turbocharger from the start is to go with a 13B-REW. It's already turbocharged and works much, much better in that application (and responds much better to various mods). You can use a Renesis but if you aren't starting out with an RX-8, there's no reason to. There's a huge body of knowledge spread all over the place (kind of like bomb debris) here: https://www.rx8club.com/series-i-maj...r-upgrades-93/
There were supercharger kits from Pettit but they are out of production so you'll be waiting on a used one to show up. https://www.rx8club.com/series-i-maj...owners-127674/
You can try to roll your own supercharger but I can't think of a single person who has so you'll be blazing a trail with very little support.
Edit for punctuation and the following thought that was late to the party:
TeamRX8 (easily one of the snarkyest and most knowledgeable people on the forums) had an idea he was batting around of using a 4-port motor with a turbo with a different focus than most of the 6-port big power guys on here. https://www.rx8club.com/series-i-maj...thread-266951/
Sadly, he had to abandon his plans before finishing (for reasons unrelated to the build) but it was something that I thought had some serious merit. It was a smaller turbo concept that provided good grunt in a usable range without having to downshift a ton. It also eliminated some complexity by eliminating most of the S-DAIS system (I think he kept the aux ports).
Last edited by NotAPreppie; 01-05-2020 at 12:42 PM.
Thank you. As for reasonable it may well be a certifiably insane thing to do. All options are on the table right now but I think building a three or four rotor engine will be outside of the scope of an amateur builder. I thought about the exhaust issue you described and because this all starts on a fresh sheet of paper it will be possible to build a long radius header going into a Venturi collector to accelerate the pulses. It will take a lot of modelling but I know from the work I did on the 968 project that tight bends act as a restriction to exhaust flow.
The problem is internal to the engine. You can't resolve it without completely redesigning the side plates themselves.
Picture this:
The exhaust ports are on the three iron plates in between the two aluminum rotor housings.
The exhaust has to travel sideways out of the chamber through those ports. Those ports then feed into an immediate 90˚ angle inside the iron plates. From there, they exit the irons into the exhaust manifold.
This configuration is different from the 13B-REW which had its exhaust ports on the periphery of the rotor housings. In this scenario, the exhaust travels out of the combustion chamber along a straight path to the exhaust manifold.
You can see in the image below. The top row, from left to right is rear iron, rear rotor housing, middle iron, front rotor housing, front iron.
The lower tapering holes on the faces of the irons are the exhaust ports. These pass the gas through the rectangular openings on the sides of the irons.
So, you can see, the combustion gasses have to pass through the ports and then make an immediate hard turn to leave the irons.
The round indentations on the two rotor housings are where the exhaust ports used to be on earlier 13B designs.
The upper tapering holes on the iron faces are the intake ports. The large black plastic thing on the left is the upper intake manifold (UIM). It feeds air to the lower intake manifold (LIM) pictured down and to the left of it. The two cylinders poking out of the LIM are the electrically-driven auxiliary port valves and they insert into the holes near the top of the front and rear irons.
Last edited by NotAPreppie; 01-05-2020 at 03:04 PM.
If you want something totally awesome ....... buy a billet aluminium rew 13b engine and slap an efr 7670 on it ........ possibly the best engine you could have in there....
Lightweight an easy 350-400 whp with awesome spoolup.
A number of people have speculated that you could hybridize the engine and use peripheral ports and side ports together but I'm not aware of anybody that has gotten it to work reliably for more than a few dyno pulls. Not saying it hasn't happened, just that I haven't seen one reported to last a long time.
I have enquires out on weight/cost of a b13 billet engine. Im seeing consensus that the Renesis is suitable as a stock drop in engine for the project but beyond na power it’s much better to go with an REW or similar. I see JDM rotaries REWs for sale asking 5 ish Canadian and there’s a built long block in the classifieds in Canada asking $ 14K. The question that I need to answer for me is whether this project can live with a 200 hp engine or does it need 400 hp. The Porsche 5 speed weighs 91 lbs and easily can handle 200 hp. For 400 hp I’d go with a close ratio 0E1 Audi 6 speed and that weighs 175lbs. I believe it was F. Porsche who said ‘every ounce has to accelerated and then braked’ so lightness is a very important part of the build. Realistically if my answer is HP then I’d look more closely at the BMW engine. Thanks for your interest.
I have enquires out on weight/cost of a b13 billet engine. Im seeing consensus that the Renesis is suitable as a stock drop in engine for the project but beyond na power it’s much better to go with an REW or similar. I see JDM rotaries REWs for sale asking 5 ish Canadian and there’s a built long block in the classifieds in Canada asking $ 14K. The question that I need to answer for me is whether this project can live with a 200 hp engine or does it need 400 hp. The Porsche 5 speed weighs 91 lbs and easily can handle 200 hp. For 400 hp I’d go with a close ratio 0E1 Audi 6 speed and that weighs 175lbs. I believe it was F. Porsche who said ‘every ounce has to accelerated and then braked’ so lightness is a very important part of the build.
You said Initially that you only needed to make 270hp which the Renesis can do. If you need more you would have to get a 13b-REW and a good single turbo setup. That is if you are still considering a rotary. Its definitely the most expensive option.
The Alfa 33 specs show 267 bhp so I expect that’s engine not RW. So could you point me to where I can find 270? That number and 700 kg will have it in the zone.
Cayman is talking flywheel hp not whp ......also that would be a full race build and more likely 260 tops if done well.
270 doable on a Renesis. Even at the crank. Will require FI. You are correct that it will be a full race build and will be expensive. Even if you got the engine for free.
Last edited by CaymanRotary; 01-06-2020 at 05:53 PM.
Brett, looks like you're correct, for once .
Now don't let it go to your head! Back to the patent mines!
Meh, the Renesis would make enough power for him. Hes not looking to break quarter mile records. 270ish HP possible with a 6 port. I think that car would be bad *** honestly. I say do it!
Meh, the Renesis would make enough power for him. Hes not looking to break quarter mile records. 270ish HP possible with a 6 port. I think that car would be bad *** honestly. I say do it!
I think you’re right. Looking at the charts, and based on the examples of how you guys drive your cars and from YouTube this car will be mostly a 2nd and 3rd gear affair and there’s plenty engine in the rev range to put and keep a grin on my face. So thanks again, now I can get on with the details. Here’s a pic of the inspiration and you’ll see why the rotary is a great match.
01-04-2020, 10:59 AM
some useful answers.
.