outcastcat

The more i learn about the 13B Renesis, the more i dream of one day building a RX-7 with it. Ive searched some of the threads but havent found this SPECIFIC topic, so im opening one up. Whats interchangeable, whats not? Whats worth interchanging? Can you swap the Renesis into an old FC (it might require some custom exhaust work)? What exactly makes the Renesis so much better?

Heres what I already know:

Rotors can be swapped, offer a better 10.2:1 compression (good if you're willing to spend more $$ on gas and stay N/A). THey are also lighter providing better rev characteristics.

Housings has side exhaust vs peripheral exhaust, and this is perhaps the biggest single advantage of the reworked 13B

Question: With custom exhaust work, could an old RX-7 13B be converted to something much closer to the higher output (207 or 247 depending on tranny, either way a significant unboosted gain) Renesis? And would this be worth it considering price (since RX-8s are still fairly new this engine isnt easy to pic up used)

Because its a 13B how interchangeable is it to put into a NA FC? Its power makes most STREET, RELIABLE, DAILY DRIVEN, N/As dream.

Because its a 13B can the tranny be swapped? And is the 6-sp worth it?

Thats about it. Ill assume ECU stuff is un interchangeable, and that probably the engine can make better numbers in the old FC because u could remove SOME emissions stuff. But overall the engine doesnt seem like it wants to give up a whole lot of power to tuners (atesting to Mazda's good engineering).

Jager

iTrader: (10)

Search actually. The Renesis engine was covered in depth about a month ago.

Also you can search for the 6-speed thread. There was on recently.

andrew lohaus

side exhaust is only an advantage if you are trying to reduce emmisions and extend apex seal life, it is not advantageous for power. you need custom mounts, and IIRC the only aftermarket ecu that can run it properly outside of an rx-8 is a motec (BIG $$).

even disregarding the cost of obtaining a renesis core, you will have more power for less effort and money spent by either swapping in and/or builiding up a 13bt. or if you want to stay n/a, massage an s5 n/a to as much if not more power using a big port, custom manifolds, and a carb or EMS.

mcnannay

from what i've heard, im going to disagree, anyone feel free to correct me.

The fact that there is zero overlap (and actually a dwell) in the renesis' exhaust and intake ports is actually "advatageous for power" especially considering the higher compression rotors. I would think torque, mostly low end would benefit significantly from this.

tweaked

iTrader: (4)

I thought the side port exhaust was a disadvantage because the middle ports are not separate so you can't tune for the pulse from each rotor.

NZConvertible

10.0:1 actually, or about 3% more than S5 NA rotors. Not really worth getting too excited about.

250hp is fairly easy to achieve with any old 13B with the right mods, but that's only peak power. Compared to a Renesis it would have a far narrower power band (all up top), it would be noisy, thirsty, and have zero chance of passing emissions. It's average power would be far lower.

IMO no. Until the cars and engines become far more common, a 13BT offers a far better bang for your buck. Even a stock 200hp S5 13BT (more likely 220-230hp due to basic intake and exhaust mods) would result in a faster and more flexible package. You'd have to really want to stay NA, and be prepared to pay for it, to pick a Renesis over a S4/5 NA 13B. That's not to say it shouldn't be done, as long as you understand what you'll get at the end.

Correct. You'd need a fairly high-end ECU to run the Renesis anywhere near as well as the Mazda ECU (three injectors per rotor, multiple intake valve, electronic throttle control, etc).

Sorry, but that's BS. Side exhaust ports allow the intake ports to be considerably larger without the overlap you'd get from a peripheral exhaust port. How else do you think the Renesis can make over 50% more power than a S5 NA while being quieter, more economical and greener?

RETed

BUY THE MOTOR FIRST, and THEN come back and ask us questions.
Else, you're wasting our time...


-Ted

Snrub

iTrader: (1)

The Renesis ports are larger when fully open, but if one takes the area of the ports over the time that they're open, the "classic" periperhal exhaust seems to have the advantage. http://www.geocities.com/jeffguilfoil/renesisports.html

The Renesis seems to be fairly unresponsive to exhaust mods. I'm certainly no expert on the topic, but to me this would also seem to suggest that the engine has a greater restriction in the exhaust ports. Comparing side exhaust ports to a periperhal exhaust ports sort of reminds me of how the ports on a flathead engine restrict power compared to a conventional engine.

Not that the Renesis isn't a big step in n/a power, but ~215-220hp compared to 160hp isn't a >50% increase.

I definately agree that from a bang for the buck perspective a TII engine is the better route. A mild exhaust put my S4 TII engine in Renesis range for peak power and a lot more low-mid range. http://www.geocities.com/jeffguilfoil/dynoresults.html

ddub

Name n/a engines that ARE very responsive to exhaust mods. You'll find almost all are the same unless it was way too restricted stock. The stock rx8 exhaust is already fairly well made, but midpipe and catback while still smog legal can produce around 6rwhp (probably max) and still be using the stock exhaust manifold. Turbos show bigger changes with exhaust, but I bet you wont find many n/a engines out there (again unless very restricted stock) do much more than that.

Snrub

iTrader: (1)

I'm just suggesting that others are more reponsive, I'm not saying any are "very responsive."

It seems like a FC 13B is more responsive to exhaust mods than the RX-8.
A RX-8 gets 21rwhp with a high-flow, no cat exhaust (presumably that's a best case claim). http://rx7.com/RPGReddyRX8exhaust/ That would be a little under a 10% improvement and would put it in the 200rwhp range.

Kahren made 178rwhp with stock ports, right? Others have gotten say 10hp less. He had an exhaust, custom intake manifold and Haltech. RX-8s gain virtually nothing from a performance ECU. I don't know if you read the RXTuner article where they found performance ECUs were gaining little on some cars and losing on others. So if anything the addition of a Haltech for the S5 creates a comparison of apples and apples. The RX-8s also gain very little power from an intake filter and I have a hard time believing much would be gained on the RX-8 the intake manifold. If anything I would expect more could be improved upon from Kahren's. Feel free to add an extra 5hp (intake filter) for the Renesis on top of the 21rwhp gain from the exhaust to make it comparable. The point is that a S4/5 13B will have greater gains from exhaust than a Renesis. In stock form there's a ~35% performance different, modded up there's a little over a ~10% difference.

ddub

See the problem with all of that is that you're comparing two VERY different setups. Mazda spent great lengths of time and money developing everything on the rx8. The intake system alone is one of the craziest and most tuned stock ones I've seen, that's why you see little to no gains from aftermarket intakes. I believe the RB one is the best one out there right now for the rx8 for mid/high ranges while keeping the drivability and torque curve smooth.

You just can't compare these two engines in the ways you seem to be, that's all I'm trying to say. If Mazda had spent the amount of time, ingenuity, and had the technology of today on an s5 n/a, you'd probably see some very different stock results. And like I said before, the rx8 stock exhaust seems to be very well sized for the engine as is, and that's why you don't see great gains.

Racing Beat is doing a lot of research on the renesis engine and how things respond to the rx8. They have found that intake and exhaust can add little gains, but you wont see major ones due to how well it works stock. A lot of people seem to think all of the power is in the tuning with minor bolt-ons. The rx8 runs pig rich stock, and timing can be taken further than it is. Also, the ECU of the rx8 is too smart it seems. It compensates for modifications and sometimes ends up running richer than before, or changing the maps. This can take away from some of the expected power gains from mods since it ends up changing the fuel maps again as it learns the new changes to the car. The best thing to do would have some type of customizeable aftermarket computer and tweak the maps after each modification AFTER the learning period is over.

Oh and the problem I've seen with the ECU upgrades is mainly that not everyone's rx8 is the same, not everyone's driving habits (how the ecu learns how you drive) is the same, and not everyone's modifications are the same. Therefore an ECU that works well on one car might not work well on another. ECU upgrades on the rx8 need to be customizeable like the Canzoomer with programming software. This way you start with a base map and have the ability and freedom to tweak the fuel and timing maps as needed for your car. Plus, after future modifications you can retune it easily.

That's my .02 on the rx8 I guess :|

Snrub

iTrader: (1)

I agree that the comparison I've made are of two very different setups. My take on the RX-8 is the same as yours, that they spent a lot of time and effort perfecting it. Essentially if one wants more power without N20, forced induction or porting they've got a maximum of ~25hp to gain. Perhaps as you've suggested the ECU "learning" adversely effects some of it. How much can it possibly adjust anyway? Everyone says the stock RX-8 ECU runs rich, but as I mentioned, from what I've seen attempts at leaning it out have not resulted in much change in output.

The bottom line is that I don't think the stock port n/a Renesis shortblock produces a massive amount of power over the stock S5 shortblock. I think the perfected intake, exhaust and ECU are what makes the big difference. To me it takes something away from the Renesis and the side exhaust ports, in that after 15 years the short block has been made emmissions complient and had only an incremental power increase.

ddub

There's definitely a lot more research and work done to the rx8 before the full potentials can be realized. From what I've seen and heard on rx8club the Canzoomer ECU seems to do well, as well as the tuning aspect. I saw some before/after dynos with AFR's for simple upgrades. The power increase wasn't anything special, but what was interesting is that the AFR's got RICHER than before. It seemed like the ECU was overcompensating, which is kinda crappy. A full standalone might be beneficial with the renesis, but you'd need to figure out ways to control some of the things.

Anyways.... To the original thread starter sorry we got off topic slightly there, but I don't think the swap would be worth it. For the exact same cost you can get a lot more power.

NZConvertible

The 6-port Renesis makes considerably more power than that. It makes 238hp in US-spec and up to 247hp in other countries. 238hp is 49% more than 160hp, and 247hp is 54% more. Even the 4-port Renesis makes up to 206hp, 29% more than the S5 6-port motors. You can't say that's not a big step for an engine that hasn't changed in size and meets much tougher noise and emission regs.

Snrub

iTrader: (1)

It's still overrated @ 238hp, dyno results show that it makes more like ~215-220hp. I haven't seen any non-North American results, but I'd be quiet interested in looking if they made a true 247hp. I can't recall seeing any 4-port results.

As I suggested earlier, I think it's the manifolds and ECU that have been optimized to get that power.

ddub

You're assuming a 15% drivetrain loss still, though. It seems like the rx8 loses more than that, like somewhere around 20-25% loss through the drivetrain, which would equate to what stock rx8's are getting on the dyno. Mazda overrated the US version initially because we have different emissions regulations so the ECU flash is different than say the JDM one, however the 238 at the flywheel rated power seems to be right. Like I said, it just seems that it has more loss through the drivetrain than 15%, 15% is a good "guess" for an average car, but it doesn't work the same for all vehicles.

Snrub

iTrader: (1)

Why do you think the RX-8 drivetrain losses more than other cars? I realize different cars have different drivetrain losses, but I'm not aware of anything that would add substantially more friction or weight to the RX-8's drivetrain. (I'm willing to use say ~17.5% to get the 220hp number ) Seeing as manufacturers optimize everything to acheive the absolute maximum performance and fuel economy, why would Mazda implement a drivetrain that was 1/3 worse than what is common in even 20 year old vehicles?

I'll also appologize for going a little off topic, but I think it's important for people to understand that while the Renesis is a good engine, it's not some mystical end all and be all.

ddub

I've heard a LOT of talk about modern cars having more towards the 20% or more drivetrain loss. I have no idea why, but it seems to be common with a lot of newer cars. The Honda s2000 has similar issues with the rated flywheel HP versus rwhp on the dyno as the rx8, and seems to have higher losses through the drivetrain. I can't explain why, this is just what I've heard and observed.

Icemark

Nah most cars, have about a 20-25% loss... I know there are people that claim only a 15%, but I personally think they are smoking.

ddub

Ah, well that's good to know

Proves even more so that the rx8 really isn't underrated for fwhp.

Snrub

iTrader: (1)

The S2k has higher losses? Here's one stock with 206rwhp. http://www.flyinmiata.com/tech/dyno_...99TvsS2000.pdf Considering RX-8s produce results typically more than 20rwhp less than that and are rated by Mazda to have a mere 2hp less than the S2k, I'm not sure how that arguement flies. I guess if an RX-8 has 238hp then so does my car.

SonicRaT

iTrader: (6)

Why not get an engine dyno and stop this rather dumb arguement? Nobody here can specifically tell you the drivetrain loss between each vehicle, and any guess is just speculation. You'll never know until they're ran on an engine dyno where you have no loss at all to compare the TRUE bhp.

banzaitoyota

I do know this, based on Dyno testing performed at SDJ last week, an engine was run on S5 NA Rotors, disassembled and reassembled with Renesis Rotors. Net gain was 8HP.

ddub

I never said higher, I said "similar issues."

EDIT
I see where you misunderstood me. By "higher losses through the drivetrain" I meant higher than 15%, just like the rx8
/EDIT

And yes some people produce significantly less, but there was a guy on rx8 club that dyno'd 200 rwhp completely bone stock, and that was after correction. This was at a NW rx8 dyno session, and in fact an s2k attended as well and put down less, I think, hp than the rx8. So it varies. Was that car you're quoting corrected at all?

The point is that the 15% loss is really not true, and Mazda didn't overestimate the rx8. I don't know why this is such a hot topic in this thread when it's merely about doing the swap, but oh well

outcastcat

Wow this got off topic in a hurry. There was good stuff, specially on modding S5's to get within 10% of modded Renesis stuff. My question basically concered using the millions of dollars of research Mazda put into the RX-8 by applying some of that technolofy to older 13Bs in order to bring them to a better place. I was looking for a way different than simple boltons.

I admit i need to search more.