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Thread: Piecing a Rotrex kit, need some input

  1. #21
    Gluon
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    You're right. 6.37" is the correct number... it was even on that link I posted to 8th Gen Civic. I transcribed that incorrectly when I was building my spreadsheet. I'll go back and edit that post so nobody references the wrong details in the future. Still pretty close I go with the slightly smaller pulley.

  2. #22
    Gluon
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    It's been coming along slowly. Didn't have everything I thought I needed, and then USPS lost one of the parts I had in the mail which set me back a couple of weeks. I ended up getting the wrong injectors from the kid who sold me the kit, so I had to fork out $450 for Injector Dynamics ID1050X injectors, which are good for 400HP on E85 if I ever go that direction.

    The factory intake is absolutely AWFUL. There's a choke point where it goes into the fiberglass box at only 2.375" diameter, which is really restrictive... on top of that dryer vent tubing with 180 bend, I am going to have to get some fabrication work done to build a new intake. My plan is to go from the throttle body underneath the shock and out just in front of the left rear tire. That would avoid cutting the tray above the engine.

    The 3.60 pulley MIGHT fit, but I didn't even try it, since I had the 3.15 and I'd already installed the smaller crank pulley. There's less than 1/4" clearance with the 3.15" pulley to the shock mount. You have to install the belt before the supercharger, because there's literally not enough room to fit the belt between the shock mount and the supercharger pulley.

    Speaking of belts... what a pain in the dick. The factory belt length apparently didn't exist in a 7-groove belt, so TMI bought a 8-groove belt and cut a groove off of it. I'm still experimenting with which belt will fit with the tensioner I'm running. I went with the newest iteration of the CTE tensioner, because I couldn't stomach what MercRacing charges for a tensioner ($400), and MercRacing's reputation for communication and timely delivery is terrible. If the belt I ordered doesn't fit today, I will have to do what TMI did, trimming a 8-groove belt into a 7-groove.

    I am abandoning the J37 larger drive by wire throttle body at the suggestion of my tuner. He is insistent that the larger throttle body can cause issues with drawing too much current from the ECU. There's a Hondata thread about this issue, and I think at 300ish HP, I should be ok with the factory throttle body. Our TB is actually a 64mm TB, which is larger than the older K20 TBs, which were usually 60mm (I think). So, the K24s have what the tuners refer to as the TSX throttle body.

    This week, if everything goes right, which it hasn't at all so far... I'll get the intake tubes bent and installed, and get the car back together for the tune later this week. The tuner I've chosen to work with is a remote tuner.

  3. #23
    Lepton cvjoint's Avatar
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    Quote Originally Posted by Mitchell View Post
    It's been coming along slowly. Didn't have everything I thought I needed, and then USPS lost one of the parts I had in the mail which set me back a couple of weeks. I ended up getting the wrong injectors from the kid who sold me the kit, so I had to fork out $450 for Injector Dynamics ID1050X injectors, which are good for 400HP on E85 if I ever go that direction.

    The factory intake is absolutely AWFUL. There's a choke point where it goes into the fiberglass box at only 2.375" diameter, which is really restrictive... on top of that dryer vent tubing with 180 bend, I am going to have to get some fabrication work done to build a new intake. My plan is to go from the throttle body underneath the shock and out just in front of the left rear tire. That would avoid cutting the tray above the engine.

    The 3.60 pulley MIGHT fit, but I didn't even try it, since I had the 3.15 and I'd already installed the smaller crank pulley. There's less than 1/4" clearance with the 3.15" pulley to the shock mount. You have to install the belt before the supercharger, because there's literally not enough room to fit the belt between the shock mount and the supercharger pulley.

    Speaking of belts... what a pain in the dick. The factory belt length apparently didn't exist in a 7-groove belt, so TMI bought a 8-groove belt and cut a groove off of it. I'm still experimenting with which belt will fit with the tensioner I'm running. I went with the newest iteration of the CTE tensioner, because I couldn't stomach what MercRacing charges for a tensioner ($400), and MercRacing's reputation for communication and timely delivery is terrible. If the belt I ordered doesn't fit today, I will have to do what TMI did, trimming a 8-groove belt into a 7-groove.

    I am abandoning the J37 larger drive by wire throttle body at the suggestion of my tuner. He is insistent that the larger throttle body can cause issues with drawing too much current from the ECU. There's a Hondata thread about this issue, and I think at 300ish HP, I should be ok with the factory throttle body. Our TB is actually a 64mm TB, which is larger than the older K20 TBs, which were usually 60mm (I think). So, the K24s have what the tuners refer to as the TSX throttle body.

    This week, if everything goes right, which it hasn't at all so far... I'll get the intake tubes bent and installed, and get the car back together for the tune later this week. The tuner I've chosen to work with is a remote tuner.
    Richard B. also found the same thing as you did re. the intake. He abandoned the stock box and went with a pipe. This is one reason I won't mind yanking out the stock airbox in exchange for an air to air HE for the Rotrex. Though I'm sure if you put enough resources to develop a proper intake box in the stock location it will work really well, as that's what all the top open wheel and LMP cars do.

    Is there a way to quickly swap a new belt on if it fails or will you have to re-install supercharger? I guess the CTE setup is fairly reliable but other blowers do shred belts often.

    I might be able to give you a part no. for a belt that fits the car without cutting. But, i'm guessing it won't be useful since you have to get one that works with the CTE tensioner.

    The whole intake manifold/TB setup is hard to improve upon from my research. There is an RBC manifold that does flow better, and even an OEM polished version of the RBC called RCC but both require cutting the Atom frame for fitment. Since I don't want to cut the frame I'm staying stock. 4 piston racing will port and polish a Skunk 2 Ultra manifold and match it to a port and polished head. That manifold can use spacer to increase plenum volume so you can swap spacers to maximize plenum volume but not exceed the engine bay room and keep the frame untouched. If I mess with the tb/manifold at all in the future I would go that route and just get whatever TB matches that manifold well.

    I'm stalled with my setup for another 4 months. I had the surge tank cap go bad and the shop misdiagnosed and spent a chunk of money changing the headgasket for no reason.

  4. #24
    Gluon
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    I am giving up on the stock box right away.

    Quick belt change would require unbolting the supercharger from the intake manifold. I don't think there's any way around it. I'm still experimenting with belt lengths. I should know today exactly which one I will need.

    I wish I had waited until winter to tear the car apart. By the time I'm done, I will have lost a month of my driving season.

  5. #25
    Lepton cvjoint's Avatar
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    Oh, no doubt I will have it done off season. I already nearly missed a track day over the surge tank issues. Not to mention, shops are busy in the season, sometimes having to get their own cars working.

  6. #26
    Gluon
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    I swear somewhere I saw a car where the guy routed the intake underneath the LH shock and out in front of the rear tire. I can't figure out a way to make that fit, but I'm trying to find those pics. Otherwise, I may just have to cut a hole in my engine cover and just have a cone filter right behind my head.

  7. #27
    Lepton cvjoint's Avatar
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    Quote Originally Posted by Mitchell View Post
    I swear somewhere I saw a car where the guy routed the intake underneath the LH shock and out in front of the rear tire. I can't figure out a way to make that fit, but I'm trying to find those pics. Otherwise, I may just have to cut a hole in my engine cover and just have a cone filter right behind my head.
    I would peruse TTS's Facebook page. I found all sorts of one offs they make for their customers.

    The hard part is anticipating future mod compatibility. Will you still be able to fit sidepods, wings, Laguna Seca pipes, etc.

  8. #28
    Gluon
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    Just a note, the Honda RBC and the RRC manifolds do fit the K20 engine in the Atom, but do not fit the K24 due to interference with the bulkhead frame. The k20 block is 19mm shorter (deck height) compared to the K24 . The 19mm allows the the larger of the two manifolds, the RBC, to fit with about 5/16 space between the intake and the frame.

    The RBC has slightly longer runners than the RRC. The RRC has shorter, but bigger runners--allowing more flow at top-end

    On a 2.0, the RBC makes anywhere from 5-12 hp, and 4-5 lb/ft. of torque, more than the stock PRB manifold. The RRC may make 1-2 hp more, but will typically only break even on torque numbers, while giving less "area under the curve."
    On the 2.4 engine, it is a different story--the RRC outperforms the RBC by about 5hp and a few foot/pounds due to the larger, but shorter runners.

    The RBC intake will run you about $200, but the RRC costs about $550

    Note: I have seen an RRC installed in a 2.4 Atom, but the mounting flange--to the head--was machined to about 1/3 its original thickness and the plenum was ground for clearance.
    cvjoint likes this.

  9. #29
    Lepton cvjoint's Avatar
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    Quote Originally Posted by jeff8407 View Post
    Just a note, the Honda RBC and the RRC manifolds do fit the K20 engine in the Atom, but do not fit the K24 due to interference with the bulkhead frame. The k20 block is 19mm shorter (deck height) compared to the K24 . The 19mm allows the the larger of the two manifolds, the RBC, to fit with about 5/16 space between the intake and the frame.

    The RBC has slightly longer runners than the RRC. The RRC has shorter, but bigger runners--allowing more flow at top-end

    On a 2.0, the RBC makes anywhere from 5-12 hp, and 4-5 lb/ft. of torque, more than the stock PRB manifold. The RRC may make 1-2 hp more, but will typically only break even on torque numbers, while giving less "area under the curve."
    On the 2.4 engine, it is a different story--the RRC outperforms the RBC by about 5hp and a few foot/pounds due to the larger, but shorter runners.

    The RBC intake will run you about $200, but the RRC costs about $550

    Note: I have seen an RRC installed in a 2.4 Atom, but the mounting flange--to the head--was machined to about 1/3 its original thickness and the plenum was ground for clearance.
    Wow, that's a lot of good insight. Someone has been thinking about intake manifolds in their sleep!

    It's nice to know the RRC would fit with some machining. Do you trust that the RRC will not crack given the treatment? All in all, having looked at the dyno results in several applications I think there is a chance RRC will make more power than a ported Skunk 2 Ultra, it's just that good. Shame it doesn't fit unaltered on a k20/k24 frank.

    I don't plan to ever rev over 7,600 rpm on the K24 bottom. From what I've seen the RRC always beats the Skunk 2 Ultra under 7,600 rpm.
    Last edited by cvjoint; August 3, 2018 at 12:10 PM.

  10. #30
    Gluon
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    So, I'm essentially done. My dyno time is scheduled for Thursday, but already it pulls like a beast with my street tune. I'd like to guess from my seat of the pants guess that I went from my 176whp I had on the dyno, to 240whp... I'll confirm on Thursday. But the sound... it's so good.

    For the belt, I had issues with a bunch of the tensioners, and regretfully had to go with one from MercRacing. The guy has absolutely garbage communication and customer service, but he makes the best tensioner, and it's ungodly expensive. I would recommend trying to source it used, just so you don't have to deal with him directly. Had to take the factory top idler pulley bracket to a machine shop to have them shave a bit off of it so the tensioner would align up properly with the supercharger pulley. I also found a way to fit the belt on, if I rotate the supercharger, I can squeeze it through between the shock mount and the bolts on the supercharger pulley... it's tight, but I won't have to pull the blower to swap the belt. I believe I ended up with a Continental 4070695 belt, which is 69.5" 7 groove. I must have bought a dozen belts with all the different combos I tried before I settled on this one.... which of course is specific to my crank pulley and tensioner combo.

    A few of the little finer points I had to do. I ditched the MAF, and wired in an IAT sensor from a Honda B-series, it's a shielded IAT, and it was easy to mount to the side of the intake with just tapping a couple of #10 machine screws and a hole in the center. Cost was about $25 and I got the pigtail for the connector too.

    The fucking Ktuned coolant bypass adapter thing that you need for a K24 when you're using a K20 head. It's a piece of shit! It has some spring bullshit on there that is supposed to keep pressure on the coolant port to keep the seal, using one of the bolts. Don't try to use that gay ass spring shit, it will leak. Drill and tap the head with another bolt, you'll need to buy a bottoming tap. I just used a #10 machine screw and bottoming tap. If you've got a K20, don't worry about any of this, you won't have that extra coolant port to block off.

    For the intake, I ended up going with a K&N Filter just attached directly to the stock TB, it managed to fit in there. No pics right now, but it was a RU-0950 5.5" diameter, 4" tall with an offset inlet. Was a tight fit, but cleared the shock mount and has significantly larger surface area than the stock filter. I haven't put a temp gauge there, and based on my street tune, my tuner wasn't thrilled with my Intake Air Temps, but he's OK with them.

    As for the tune, I worked with a guy remotely, I think he works out of the west coast somewhere, his name is Tony, with 2nrs of Springfield... the dude is a K-series encyclopedia... highly recommended. Basically, so far, I've hooked up to the FlashPro with the laptop, and drive around with a wifi hotspot as he makes adjustments through TeamViewer on my computer. Just for the street tune, he's uploaded at least a dozen different tunes, smoothing it out. He's put in a few hours of his time so far, and then we're hitting the dyno on Thursday, where he'll remote in again.

    I'll update with my final dyno numbers on Thursday, but my hope is 270whp.
    Atommatt and cvjoint like this.

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