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Forced Induction choice for a street project

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Hello there,

I've got a Mazda RX-8 with a V6 (2.5L KL-DE). The engine is coming from my previous week-ends car which I took for street driving, open track days and category-free racing events (prototype ?). So the usage for the RX-8 would be around the same line.

I'm trying to make my car a little relevant and bring the horsepower to somewhat 280-350hp given the weight of the car. The engine is known for producing a little less than 160bhp stock and given the CR (9.2:1), lots of suggestions I've received from peers was to go forced induction for the usual reasons: cost benefit, quick and easy power. I didn't challenge much of it as while discussing with KL owners told me the NA way requires to get a Japanese version of the engine (KL-ZE) which bears more aggressive camshafts and a more aggressive CR (and i'ts hardly expensive to get one).

Currently the engine isn't modded and is only rebuild since the swap, for the exception of Coil-on ignition plugs with an added camshaft sensor replacing the original ignition distributor to facilitate tuning afterwards.

However now comes the question of supercharging vs turbo and it's hard cycling through the heresays on the internet, so I'm asking the place I've learnt most of it here. 😊 I initially thought of supercharging as a mean to keep a flat torque curve which covers up for the removal of VICS/VRIS (one of the two systems in the stock intake that provided two paths for intake to provide torque at both ends), and having less additional piping required hence taking complexity out. Although from what I read, the power gains would be far from the objective I've set. For a turbocharged system, given the engine layout I guess it would be easier to run two small turbos on each side but given the engine revs up to 7600, I guess I'd be going way off the compression chart and eventually damage them while losing power right ?

Thanks a lot,

Anouar

Anouar,

The compression ratio itself is relatively low, so not a concern by itself.

Either super or turbocharging could supply the airflow to achieve your power goal.

Either can create a linear torque curve if that's what you desire. With turbos you would just use boost control to generate a boost curve that creates the torque curve you're looking for.

Supercharging doesn't necessarily involve exhaust piping work, but requires creating or adapting a drive system, and I would intercool with turbo or supercharger, so there's a bit of work either way. I'm more partial to turbocharging as it's more efficient, but again, either could hit your power goal.

The COP and cam sensor updates sound great.

Since your goal is to double stock output, I'd just verify the physical components in the engine can support the increased stress and heat, but otherwise with careful building and tuning this sounds great.

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