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Thread: Piecing a Rotrex kit, need some input

  1. #11
    Lepton cvjoint's Avatar
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    Won't fit. You need the 3.15" pulley, lovingly known as Stage II. See:
    https://www.arielatomchat.com/forums...html#post15956

    Oh, and check your fuel injector sizing as well. You might need to get larger ones to go with the smaller diameter pulley.

  2. #12
    Gluon
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    Quote Originally Posted by cvjoint View Post
    Won't fit. You need the 3.15" pulley, lovingly known as Stage II. See:
    https://www.arielatomchat.com/forums...html#post15956

    Oh, and check your fuel injector sizing as well. You might need to get larger ones to go with the smaller diameter pulley.
    cvjoint, thank you for your advice! I bought a CTE kit (new, but missing some parts) from a Honda kid, with the aftercooler, which I immediately listed for sale. I'm working a trade for the KTUNE 90mm mechanical throttle body for a J37 unit with the adapter so I can keep the throttle by wire. The guy also said he'd throw in a 3.6" pulley.
    I am selling the aftercooler to another guy who has an extra 3.15" pulley BNIB, so I'll likely pick that up from him. I was hoping not to run that much boost! My 750cc injectors will be fine if I stay with 93 octane, but I'm torn about the long term longevity running 10 PSI on that 3.15" pulley... might be forced into E85, which would be annoying and I'd end up having to get it tuned twice!

    It will be a couple of weeks before I'm ready to start wrenching. Hope I didn't hijack your thread too badly, but you've definitely got a leg-up on me with all of this.

  3. #13
    Lepton cvjoint's Avatar
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    Since you already bought some parts I'd say you're the one leading at the moment! I was so close to buying the CTE kit, there was one on ebay that went for 2,800 new with 3.15 pulley and I nearly bid on it. The best part about the Eaton is that it is bulletproof. I don't expect a Rotrex to have anywhere near the same lifespan.

    The engine will last a long time on 10 psi as long as you cool the charge. If you are going to do track duty I'd say you need two radiators and an oil cooler. It sounds like a lot but we don't have the heat exchanger surface area that production cars do. If you go the TMI sidepod route one will be air to water HE for the charge, and the other will be a second radiator.

    What's the deal on the throttle body? Is that the largest that works on a K while keeping the DBW?
    Last edited by cvjoint; June 7, 2018 at 11:42 AM.

  4. #14
    Gluon
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    Quote Originally Posted by cvjoint View Post
    Since you already bought some parts I'd say you're the one leading at the moment! I was so close to buying the CTE kit, there was one on ebay that went for 2,800 new with 3.15 pulley and I nearly bid on it. The best part about the Eaton is that it is bulletproof. I don't expect a Rotrex to have anywhere near the same lifespan.

    The engine will last a long time on 10 psi as long as you cool the charge. If you are going to do track duty I'd say you need two radiators and an oil cooler. It sounds like a lot but we don't have the heat exchanger surface area that production cars do. If you go the TMI sidepod route one will be air to water HE for the charge, and the other will be a second radiator.

    What's the deal on the throttle body? Is that the largest that works on a K while keeping the DBW?
    So, my plan was no charge air cooler, like the factory superchargers were... my goal was to get away without any additional cooling. With the 3.6" pulley, the Honda guys don't use any charge air cooling. With 3.15, I am scared I may have to go to bigger injectors and E85, which is about 15-20 minutes from my house to the nearest station with E85.

    I haven't seen anything concrete that the 3.6" pulley won't fit, other than a couple of people repeating it. I hope they're wrong, but I doubt it. The 3.6" pulleys are easy to find used, and I have a line on a 3.15" pulley if the 3.6" pulley won't fit. Maybe someone can chime in with a picture showing that there's no way in hell to fit a 3.6" pulley? Come on... it's less than a quarter inch of additional radius!

    I'm in North Carolina, which is stupid hot, but I am not sure I'll be tracking it, more likely just autocross and a lot of street miles.

    My understanding is the J37 throttle body, which comes off of some bigger engine Honda car is the largest drive by wire throttle body, and should be plug-and-play (with tuning obviously). I am in the process of trading a guy a J37 throttle body and the Merc Racing inlet to fit it to the CTE MP62 supercharger.

    I will know way more in two weeks when I've got more of the parts, and I can start taking the car apart.

  5. #15
    Lepton cvjoint's Avatar
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    Quote Originally Posted by Mitchell View Post
    So, my plan was no charge air cooler, like the factory superchargers were... my goal was to get away without any additional cooling. With the 3.6" pulley, the Honda guys don't use any charge air cooling. With 3.15, I am scared I may have to go to bigger injectors and E85, which is about 15-20 minutes from my house to the nearest station with E85.

    I haven't seen anything concrete that the 3.6" pulley won't fit, other than a couple of people repeating it. I hope they're wrong, but I doubt it. The 3.6" pulleys are easy to find used, and I have a line on a 3.15" pulley if the 3.6" pulley won't fit. Maybe someone can chime in with a picture showing that there's no way in hell to fit a 3.6" pulley? Come on... it's less than a quarter inch of additional radius!

    I'm in North Carolina, which is stupid hot, but I am not sure I'll be tracking it, more likely just autocross and a lot of street miles.

    My understanding is the J37 throttle body, which comes off of some bigger engine Honda car is the largest drive by wire throttle body, and should be plug-and-play (with tuning obviously). I am in the process of trading a guy a J37 throttle body and the Merc Racing inlet to fit it to the CTE MP62 supercharger.

    I will know way more in two weeks when I've got more of the parts, and I can start taking the car apart.
    That's how I would go about it as well. Get a 7 PSI pulley and run without aftercooler. Then if you ever want more there is the option of another pulley and aftercoolers.

    I am also resisting the alure of fancy gas. There is 100 octane at literally every track I go to. If you are willing to pay the $10/gal that is. I would much rather optimize the car for 91 octane which is dirt cheap and can be found even cheaper on the street before entering track ground. As long as there is a way to get more power out of 91 I will mod for that first.

  6. #16
    Gluon
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    We've got 93 everywhere, so I'm a hair better off, but I think 93 with no aftercooler is pushing my luck with that 3.15 pulley. I'll have to talk to my tuner as we get closer, assuming the 3.60 won't fit.

  7. #17
    Gluon
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    I just thought up with a new plan. If I can't fit the 3.60 pulley, I'll run the 3.15 and look for a smaller crank pulley to underdrive the supercharger pulley! Apparently the one off a K20 is smaller, and I'm sure I could find one for chump change.

  8. #18
    Lepton cvjoint's Avatar
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    That would work for the supercharger. What about the other accessories? Wouldn't you underdrive the water pump and alternator?

  9. #19
    Gluon
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    I'm cool with that. It's barely at all, and I'm pretty sure we run the stock alternator, with probably only 30% of the load of a normal Civic. As for cooling, I'm really only slowing things down about 5%, and our radiator is so small, I figure coolant flow speed could afford to be slower without issues.

    I put this together based off of the available crank pulleys found on a link below. I am out of town and can't measure my Atom's stock pulley, but I'm assuming it's the same as a 9th gen Civic, at 6.37" diameter. Anyone want to confirm with some calipers?

    I made this neato spreadsheet just now:

    Crank SC Redline SC RPM
    5.46 3.6 7,600 11,527
    5.98 3.6 7,600 12,624
    6.37 3.6 7,600 13,448
    5.46 3.15 7,600 13,173
    5.98 3.15 7,600 14,428
    6.37 3.15 7,600 15,369

    The red is where I'd be on supercharger RPM if I used the 3.15" pulley with what I believe is the stock crank pulley diameter (aftercooler territory). I think I'd like to be closer to 14,000 RPM for 93 octane (pulling this out of my ass), assuming I'd want to be halfway between the 3.60" pulley and the 3.15" pulley SC RPMs, so at 14,428 RPM on the 5.98" pulley Honda P/N 13810-RRA-A02

    I'm using a lot of info from these guys... but keep in mind they're working with a 8600 RPM redline on those K20s that were in the 8th gen Civic. Our redline is 7600, right?
    Blower RPM 101 for the MP62 - 8th Generation Honda Civic Forum

    I foresee a lot of time picking out which belt I'm going to have to run. But if all of my assumptions are correct, I think this is my ideal solution!
    Last edited by Mitchell; June 8, 2018 at 06:16 PM.

  10. #20
    Lepton cvjoint's Avatar
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    I've been working off the 162mm or 6.38" inch crank pulley measurement. That's what I got from boosted guys on 9th Civic forum. 9th gen Civic is the one with the K24Z7.

    My redline is 7,200 from factory on my SRA. I saw in the manuals that the street Atoms are spun to 7,600rpm. At that RPM you get the same piston speeds you get in a 2.0l S2000 at 9,000 rpm. With higher revs you wear out the piston rings faster even if the engine is operating safely.

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