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Hello,

I'm looking into the options for a forced induction K24 to put into a Lotus Elise. I'd like to know some things about the K24/K20. As it's going to be a track car (not dragstrip), i'd like to have a relatively quick spool and reaction time if opting for a turbo. What kind of turbo do I need to get it spooling from about 3500 rpm max, and have a decent reaction time? And what kind of power would that make? And what kind of power will a stock K24a3 bottom end with a stock K20a2 head take? From what i've heard about 450 whp? Is that correct?

I know it depends hugely on the rest of the setup and tune, but i'd like to have something of a guideline.

Thanks in advance
 

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Gt3076r Good for 400hp and pretty responsive on a 2.4. Might be a little choked up at the top of rev range. Manifold design seems to be the main factor in turbo response. Some reading I've done suggests the shortest runners spool the quickest. contrary to popular belief, cheap Log design manifolds seem to be the quickest spooling.
 

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Arouse the DAMPFHAMMER!
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Manifold design seems to be the main factor in turbo response...contrary to popular belief, cheap Log design manifolds seem to be the quickest spooling.
Yes, I agree too. A quick spooling of the turbo needs roughly two things, a positive pressure drop from intake to exhaust and a highly rate of dynamic pressure wave force.

The first is depended on the turbine/compressor map combination with respect to combustion porperties, valve timing and other systems of the engine. Deciding the right is not simple, OEM's do 1D/0D-simulations for it to see the matching of the turbine setup with the engine. Aim is to have the working point curve of the application main operating field crossing the map sections of biggest efficiency. I did this process for a 1200 hp drag engine project, took me a couple of days to find the right matching. So here the easiest procedure would be taken the advantage of experience of existing similar setups.

The dynamic force utilization could be an more easy job, as a rule of thump 1st priority is to combine primaries right into the merger of the turbine inlet. What is right depends on setup. For a good spooling it is definitely good to combine runner 1+4 and 2+3 into an extra turbine inlet port. This guarantees two things, highest velocity of gas (= high impuls to accelerate the turbine) and lowest damping as according firing order of the K20 engine (1-3-4-2) of each exhaust pipe gas flow by another pipe gas flow. This approach needs an double inlet turbine, like the BMW twin scroll design has it. It is correct that short runners support this, as a small volume of the runners give can give a stronger impuls, but also important is the ID. It should be on the smaller side for spooling improvements. Regarding length, the rule of thump is, the short as possible, the long as necessary for matching all runners to exact the same length!
 

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Both thanks for your answers, will definitely keep that in mind when building a manifold. I'm planning to play around with the backhousing as well to see what that does.
 

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also keep in mind that the gearbox won’t take 400+Nm of torque without upping its internals.
it will lunch 3rd or 4th gear first time you floor it on the OEM gearbox with any kind of slippy diff. Traction level in the Elise is much higher than in a FWD car inducing much higher loads on the gearbox.
Charge cooling is also a huge challenge at this power level in the Elise platform.
Next challenge you have to overcome is tire width. Most folks doing 400-600HP in an Elise opt for wider tires and wider clams. You only get so far on 225 rears.
A laggy turbo makes the Elise very hard to drive on track. I’d consider trading off a few top end ponies for a more responsive turbo. Some remap their turbos to limit boost in the mid range for more controllability.
 
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