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Discussion Starter · #1 · (Edited)
Looking at building a k24 for an endurance series. I have to use a block/head for a k24a1 (for rules on one series) but in another series i want to run, i'm limited to horsepower to weight ratio. So the top teams are building their engines to have a very flat HP curve. So, as soon as the car hits a target HP on the dyno, the dial down the electronic TPS to maintain a flat HP curve.

So with that in mind, i'm looking for the path of least resistance to build something that will last endurance racing. My thought process is to start with the A1, toss in high comp pistons and add some drop-in cams. I'm not sure what this would net in terms of power (DJ). In a perfect world, i'd like to hit 200 hp by 6k RPM or sooner and hold it to 8k. I'm hoping that with proper oiling mods the engine can survive 24 hours revving to 8k. Otherwise i'd have to bump redline down to 7 or 7.5.

Mod list?

k24a1
  1. 12:1 pistons
    1. Required to use 91, so not sure its safe to go any higher than 12:1 for enduro racing.
    2. Also if pistons only buys me like 3 hp midrange then maybe its not worth it. I'd settle for TSX or CRV.
  2. Wide duration drop in cams on stock valvetrain
    1. Could use suggestions on brands
  3. OEM k24a1 intake manifold
    1. To inflate midrange powerband.
    2. Must use an oem plastic manifold. Heard a rumor that a r40 2009 TSX manifold MIGHT fit. If it does, it should be good for a much stronger midrange VS the CRV mani. Would also make the electronic TPS mod more plug and play. Wish i could find someone whose used the r40 before on older k24 heads.
  4. 4-2-1 header. Probably end up with a long tube design like hybrid racing. Also open to suggestions.
  5. Maybe port work? With a mindset on path of least resistance, porting is definitely high resistance.
  6. A friend suggested stroking&boring the block for 2.8L. This is definitely a high resistance path. If the engine can survive 24hrs at 8k rpms i'd really rather not do this.


Side note: The power curve has to AVERAGE at 200 hp for the last 2k of the RPM band. BUT, area under the curve is everything, and the winningest cars in this series are tuned for a FLAT HP curve as it has the most area under the curve.
 

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Why are you stuck with a K24a1?

A K24 at 8k rpm's is not going to live very long in endurance racing. I would recommend not exceeding the OEM rev limit (7,200?) and might even try to limit it a little less, depending on how long you want your engine to survive.

I hear good things about the Drag Cartel Endurance 2.2 cams. You will also want the 50 degree cam gear to help bump the mid range torque. You will need to clay the valves to find your maximum cam gear advance with the cams you chose.

I think you are going to have a hard time getting 200hp over a 2,000 rpm window for an endurance engine on pump gas.
 

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I race in Champcar with a K24A2-swapped 2nd gen Supra. I'm guessing that you will be targeting WRL and AER where they run power-to-weight classes. I believe that WRL requires you to show a dyno sheet from a specific dyno. Below is my current graph from a Dynapack chassis dyno which generally reads lower than roller-types (on a Mustang this curve would max out above 225hp) on 93 octane fuel.



As Ted pointed out above, the K24A2 (or JDM K24A) will provide you with exactly what you're looking for without any internal changes other than the K20 oil pump and 50 degree VTC cam gear. I set my rev limit at 7300rpm for racing because oiling issues are real above 7500. With an engine management system (I use MS3 Pro) a good tuner can play with VTC angle, ignition, and fueling to provide 200hp from 5500-7500rpm. If you limit the cam gear to 40 degrees you shouldn't have any issue with valve clearance.
 

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yes, VTC control will allow you to bleed off power by reducing volumentry efficiency at the top end. It does pretty much the same as a drive by wire throttle body opening limit map common with motorcycles and some cars, e.g. many Toyota. Instead of maximising power, you time the intake cam to maintain the 200HP power limit in the upper rev range. Regarding cam choice, this is tricky as many "stage 2" cams tends to only reach peak torque post 6000 rpm. Honda OEM cams might indeed be a good choice. You might stray into drop in cams, but the OE cams get you a very decent torque spread. 200HP is OE output for these engines anyhow.
And don't rev cast pistons higher than some 7200-7300 in a circuit racing k24.
 

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Discussion Starter · #6 ·
This is a good data point, but it looks like you don't hit 200 hp until 6100 rpm. Additionally, i'll be on 91 octane. My thoughts were to use the lower flowing intake manifolds (CRV/Accord) to help keep peak TQ lower in the RPM band. In order to hit 200 hp by 5k rpm (assuming a 7.2k redline), i'd need 200 ft-lbs by 5000 RPM. Which is 30 more torques than what you're making. That's actually a pretty big margin that i'm not sure can be covered by drop in cams. Unless of course there's something in your setup/tune that is running below your TQ potential between 5k-6k rpm. I have a feeling, and i could be wrong, that even with good drop ins, high compression, and other little tricks i'd struggle to hit 200 hp before 5.5k rpm. Anything i make beyond 200 hp doesn't help the goal at all, and i think that's what some might be fixated on.

The roller types that i'll be dynoing on are properly calibrated dynojets, which as i understand read a few % higher than a properly calibrated mustang. Not sure where dynapacks fit in the mix. I've been able to find dynographs of builds on the internet that do seem to meet my goals but the numbers are so hyper inflated over all of the other builds i come across. I feel like dynos are hard to trust on the internet.... I guess worst case i'll do what i can and try and drop weight to compensate, which would put me at a strong disadvantage at high speed tracks
 

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Good points. I'll be following along to see what you try.

The Dynapack that was used for the graph above is affectionately called "the heartbreaker", for some reason it measures 8-10% lower than the roller dynos in our area. A Dynojet graph would show 200hp around 5500rpm, which is closer to your requirements but still not there. My tuner maximizes everything for safe (endurance) power so I don't think that there's a lot more torque to be had with OE internals. Just for data points: I had my car on a Mustang dyno which showed a peak hp of 203 when this Dynapack measured 181 with the same tune.
 

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Discussion Starter · #8 ·
Good points. I'll be following along to see what you try.

The Dynapack that was used for the graph above is affectionately called "the heartbreaker", for some reason it measures 8-10% lower than the roller dynos in our area. A Dynojet graph would show 200hp around 5500rpm, which is closer to your requirements but still not there. My tuner maximizes everything for safe (endurance) power so I don't think that there's a lot more torque to be had with OE internals. Just for data points: I had my car on a Mustang dyno which showed a peak hp of 203 when this Dynapack measured 181 with the same tune.
Oh wow that is a big difference. Hmmmmmmmm perhaps a set of TSX cams can get me there provided my intake/exhaust mani are setup to emphasize that 5k torque bump. Just for clarification, you currently have the 50 deg VTC installed in your tsx motor? I found this article really helpful Technical Information Tuning the TSX
 
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