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as I told you in my introduction thread, I'm a n00b. I bought a C30-94 with a ridicoulus big pulley (110mm) because I'm frightened by torque and threw it on a high milage NB1. At 7200 redline, the SC is at 80k, building ~9 psi with a calculated airmass of ~240g/s.
My goal is to unleash the unused potential of the rotrex and either go significantly down with pulley size (90mm) and stay at 7200 redline OR go a little lower (100mm) and rev the engine to 8k. Usage is realisticly 10% track, 90% street. It's not my daily driver and I don't care about NVH. Power Goal? Estimation? Dunno, sub 400 whp but over 320 whp I think. TDR made 314 whp on a high milage stock NB1 with 90mm pulley and C30-94 so I think it's an accurate guesstimate.
I would like to know which of the both paths you would take under the given preconditions and which choices you would make.
Preconditions:
Rotrex C30-94 (won't do turbo)
AZ6 has to survive!! (won't do BMW swap)
BP Block (won't do K swap)
RacingBeat Header, 200 cpi HJS Cat, 2.5" Exhaust - This combination is somewhat street-legal, Germany things...
Pumpgas (Euro 98, AKI 93-94 I think)
My current setup:
High milage NB1, Flattop, FF640, 68mm TB, TR6 Intercooler, C30-94. RacingBeat Header, 200 CPI HJS Cat, 2.5" Catback. 10 lbs Flywheel, BOFI Clutch, AZ6, 4.1 Torsen. SM QMAX Reroute, Crossflow, Fluidampr, PS Deleted, no A/C, Toyota COPS, Speeduino.
Plan:
NB2 VVT Longblock is waiting to be built. Going from bottom to top, marking parts already bought with *:
ARP Main Studs*
ACL Race Bearings
Boundary Stage 2*
Oliver A Beam Rods*
--> Pistons. I think Supertech is the way to go with Wiseco rings but which compression? Germans are telling me I should go high even with my power goals -> 11:1. Everything I remember from here is: Pumpgas+High-Power -> 8.6:1. Please enlight me.
ARP Head Studs*
MLS Head Gasket
mild bowlwork, deshrouding valves, remove cast imperfections
--> SUB conversion. Only needed for 8k rpm path, I think
CatCams PAC-S90015 valve springs
--> TOMEI cams (252/256, 10.8/10.0) Worth the money?
as I told you in my introduction thread, I'm a n00b. I bought a C30-94 with a ridicoulus big pulley (110mm) because I'm frightened by torque and threw it on a high milage NB1. At 7200 redline, the SC is at 80k, building ~9 psi with a calculated airmass of ~240g/s.
My goal is to unleash the unused potential of the rotrex and either go significantly down with pulley size (90mm) and stay at 7200 redline OR go a little lower (100mm) and rev the engine to 8k. Usage is realisticly 10% track, 90% street. It's not my daily driver and I don't care about NVH. Power Goal? Estimation? Dunno, sub 400 whp but over 320 whp I think. TDR made 314 whp on a high milage stock NB1 with 90mm pulley and C30-94 so I think it's an accurate guesstimate.
I would like to know which of the both paths you would take under the given preconditions and which choices you would make.
I would def vote for the 90mm pulley and 7200redline.
since you can get the same power either way, then it makes no sense to run the 8K redline on a motor that isn’t particularly good at doing so. (It’s no vtec honda)
all the 8K redline will do for you is wear the engine quicker
I think your bigger issue will be gearbox strength if you make it closer to 400hp, even given the more driveline friendly nature of a rotrex.
You’re going to have to do a lot of research. There is a lot of info here, but limited ton only a few truly high-powered Rotrex setups.
Forum member Emilio and Trackdayhookey. Do the searches, it’s worth the effort. USA deals mostly in E85 for consumer purpose and has more knock resistances, so you’ll have to figure out where 98 falls in your power scale. If I recall, Emilio said 11:1 was possible, but must use E85. I could have forgotten though.
Hi, thanks for all the answers. I'll try to explain more of my thoughts and maybe I have a big misconception in my mind...
Gearbox Strength
I thought of a centrifugal blower as a somewhat quadratic function that adds power in relationship to the rpm range. So by widen the rpm range, I ease more on the transmission because even if the power N/A @ 8000rpm is higher than @ 7200rpm, I push the power gains to the upper rpm range and lower the absolute torque. Time for math and a picture:
My 100% guesstimate for 7200rpm is around 334whp which would relate to 326nm / 240lbs. 350whp @ 8000rpm however are only 307nm / 226lbs. Assuming VE linearity, 1:1 ratio of airmass g/s and whp.
2.5" Exhaust
I don't have any datapoints from my own measurements so I can only try to gather sometimes unreliable information on the internet.
TDR https://trackdogracing.com/rotrex.aspx measured 315 whp on a dynojet with no flattop, RB Header, RB mid-pipe (2,375") and RB muffler.
I assume they have the catalytic converter in place because the RB mid-pipe is not a cat-delete.
2.375" diameter -> 4.43 in² area, 2.5" diameter -> 4.91 in² area (10% more @ my exhaust)
Maybe the missing power-adder on the exhaust side makes it possible, even with smaller diamaters.
Here a picture of the HJS cat in comparison to a redback:
11:1 @ Pump-Gas
I surely dont want to begin the blame game but the recommendation came from all sides. Reputable members of the German mx5 forum, SPS and also from the original manufacturer of the kit. I found an German rotrex nb1 who is at 10.3:1 wisecos, pumpgas and in the 300hp range (https://sites.google.com/site/mazda2...mx5/mx5technik). I asked about this recommendation and the answers were nearly identical:
Knock occurs mainly midrange - rotrex haz no torque midrange
Rotrex is easy on backpressure so no heat accumulation
Rotrex is easy on IAT because of low pressure
Maybe the natual laws are not valid in Germany - I can't get my head around it.
I don't want to be knock limited.
Appendix
Thank you for the link to tdh's build thread. I read it again In the last two years I nearly absorbed every rotrex build thread I could find. Dragonfighter, shiz, tdh, dcamp2, GTurbo, ... and also emilios superb contributions <3. Sadly E85 is dead in Germany. We had it but due to specific tax regulations it is nowhere to get since 2016 I think. I could order 99.8% ethanol and mix it on my own OR bite the bullet and go up to 94/95 AKI pump gas but then I had to stick to specific gas stations - no good prospects.
Hi,
as I told you in my introduction thread, I'm a n00b. I bought a C30-94 with a ridicoulus big pulley (110mm)
A few bits of advice based on experience.
-Rotrex's like compression. Your fuel should allow 10.0:1 just fine but 11.0:1 should require race gas on E85. Always better to err on the low side to insure you can reach MBT
- The C30-94 and larger have relatively heavy compressor wheels connected to the planetary gear mech inside. As such they are sensitive to sharp changes in rpm, specifically a hard fuel cut. Be sure to play with ECU settings to
make rev limiter less abrupt.
- Rotrex are incredibly robust.. provided you set them up and maintain them as directed in the destructions. Read everything twice and do everything the docs tell you, to the letter. They require virtually no maintenance other than occasional fluid swaps.
Do something like installing the blower at the wrong angle, mounting the filter at the wrong height, and bang.
-As someone else mentioned, superchargers are less sensitive to engine rpm to make power. The BP has a VE peak with stock cams at around 4800rpm, higher with cams. Be conservative with revs as that's what generally kills BP bottom ends.
- 2.5" is plenty of exhaust. We made 300whp with a C30-74 on E85 an around 9.5psi through a Racing Beat header and full RB exhaust (2.375"). 3" is just louder at that power level. That engine was a 1.9L 11.0:1, CNC big valve head and Tomei cams.
-Cams. Good idea. Rotrex's love cams. Just keep duration as short as possible, like a turbo cam.
- Uprated oil pump. At absolute minimum, shim the oil pump (i
and run slightly heavier oil. The low rod ratio of the BP really hammers the big end and mains with F/I power. Lots oil pressure hurts power a bit, but reduces unplanned block ventilation. Bump 7psi or so with shims
and run 10W40. Keep oil temps below 240° (115c). Better yet is billet oil pump gears and/or blueprinted oil pump. Chances of a direct oil pump failure at 8,000rpm/300whp with a stock OP are not zero.
-There are some things you can do to help keep the AZ6 alive but ultimately, you're on borrowed time. Build a trans cooler, log temps and make sure you stay below about 180° (82c). The aluminum shift forks expand and bind, locking you out of in gears until it cools down.
Case flexes. HD case bolts help here. In the US, a lot of tuners use Walters Motorsports blueprinted transmissions. We have used them with success.
My previous post, before emilio chimed in with his great contribution, was stuck in moderation, sorry for the offensive content Please scroll four posts up to see the whole story.
Originally Posted by emilio700
-Rotrex's like compression. Your fuel should allow 10.0:1 just fine but 11.0:1 should require race gas on E85. Always better to err on the low side to insure you can reach MBT
MBT is always desired. So, 10.0:1 it'll be. In my NB2 longblock, two pairs of 10.0:1 Mazda pistons are resting. Could I get away with those or should I invest into the usual Supertech?
Originally Posted by emilio700
- The C30-94 and larger have relatively heavy compressor wheels connected to the planetary gear mech inside. As such they are sensitive to sharp changes in rpm, specifically a hard fuel cut. Be sure to play with ECU settings to
make rev limiter less abrupt.
I planned to set the rev limiter to an absolute emergency maximum and use a audiovisual signal at the desired shift rev so I should never hit the limiter. At the moment, the limit is ridicously high but the car has not seen any track. On the street it's easy to adhere to 7k shifts.
Originally Posted by emilio700
-As someone else mentioned, superchargers are less sensitive to engine rpm to make power. The BP has a VE peak with stock cams at around 4800rpm, higher with cams. Be conservative with revs as that's what generally kills BP bottom ends.
What are we dealing with @ 8k? Minutes? Hours? 100k miles?
Originally Posted by emilio700
- 2.5" is plenty of exhaust. We made 300whp with a C30-74 on E85 an around 9.5psi through a Racing Beat header and full RB exhaust (2.375"). 3" is just louder at that power level. That engine was a 1.9L 11.0:1, CNC big valve head and Tomei cams.
-Cams. Good idea. Rotrex's love cams. Just keep duration as short as possible, like a turbo cam.
I consulted Jeff David - Honda K20 K24 Supercharger Camshafts - about the camshaft topic some months ago. He developed specific Rotrex camshafts for Honda K engines and he gave me some advise:
As it's important to trap the fuel/air on the valve overlap, higher lift and longer duration NA cams tend to loose power due to blow through. Specific fuel consumption goes crazy as well. On the K22 going from stock to Stage2 NA cams was +50% injector flow. Power was almost the same.
As you widen the lobe centre between the inlet and exhaust the engine becomes less prone to knock. This is a big factor if you have poor fuel and or a relatively high dynamic compression ratio on a boosted car. So wider lobe centers can make more power and reduce overlap.
My approach to the cam design was to try stock, other supercharger cams, then stage 2, model the results with software and then design my own. I ended up with wider lobe centers with less overlap than stock but lift is similar to stage 2 or stage 3 camshaft depending on the vendor. Also plenty of duration at 0.500”.
This is not easy to do while keeping acceleration, jerk and hertizan stress close to OEM.
So I would try the mildest inlet cam you can find, hopefully with more lift than stock. And a stage 2 exhaust cam as a starting point. Fit a venier exhaust cam gear to advance it's centre line. Position based on dyno tuning but 6 degs advanced is a starting point depending on the duration.
The exhaust is harder to know. The Tomei might be a good choice as it is the matching exhaust cam, however from my Rotrex experience I would go much wilder. The only limitation is how smooth it is to drive at low engine speeds or light throttle. With the K Honda we have iVtec, so small and big lobes. I swap at 2800rpm on full throttle or 6000rpm on light throttle to the big cam so avoid this issue.
My general feeling is I would go with the wildest. The Rotrex is forcing the air in. To make power it's got to come out! The SC will create an engine feel with more torque and the big exhaust will help it breath from 6500 to 8000rpm.
Even with relatively wild cams chosen, your lift is very low compared to my GP700 camshafts. The valve open area is also vastly smaller.
I would start with the stock NB2 and then order the Tomei. Maybe I'm curious enough to see what happens with the bigger exhaust cams. Is 10.8mm lift still safe for stock valvetrain / stock valves with uprated springs in the 7200 rev limit case?
No stock pistons. Need to be forged for your power goals. Pick your favorite.
Revving a BP past 7000 shortens its life, getting close to 8k a lot, shortens it further. It's exponentially more destructive as revs rise. A high end, BP expert builder, fully blueprinted engine with all the bells and whistles will last a bunch longer than one built by someone with a lot less experience/resources.
Can't quote you a number of hours, too many variables. Just know that no experienced BP tuner goes into an 8k, 300whp build thinking its going to last a long time.
BP05 has same shallow intake and exhaust port angles. NB heads raise intake port angle which increased intake flow but didn't change ratio of valve area to BP05. Ratio of intake to exhaust flow is important and overlooked. Which is why our old CNC head had +1 intake and +2 exhaust valves. Takeaway is that cams for power on OEM or +1 valves need some exhaust lift too. The Tomei 256° cams worked very well in our C30-74 with a +1/+2 head.
05-24-2022, 04:11 PM
Searching for the holy rotrex grail
0
In the last two years I nearly absorbed every rotrex build thread I could find. Dragonfighter, shiz, tdh, dcamp2, GTurbo, ... and also emilios superb contributions <3. Sadly E85 is dead in Germany. We had it but due to specific tax regulations it is nowhere to get since 2016 I think. I could order 99.8% ethanol and mix it on my own OR bite the bullet and go up to 94/95 AKI pump gas but then I had to stick to specific gas stations - no good prospects.
