Recommend me a turbo
Discussion
As per the title really - my supercharged K series project has become a turbo charged one, mostly due to packaging issues.
Anyway - 1.8 k series, VVC head, solid Newman cams (PH2 260 degree). I'm looking for something that will give me 250 - 300 bhp (so probably 13-18psi)?
It's been suggested that I consider a cheap eBay GT2871, but I wondered if there was something from a more reputable source that I could consider at a reasonable price? Buy used and get one reconditioned?
All thoughts / experiences and suggestions welcomed!
Anyway - 1.8 k series, VVC head, solid Newman cams (PH2 260 degree). I'm looking for something that will give me 250 - 300 bhp (so probably 13-18psi)?
It's been suggested that I consider a cheap eBay GT2871, but I wondered if there was something from a more reputable source that I could consider at a reasonable price? Buy used and get one reconditioned?
All thoughts / experiences and suggestions welcomed!
In N/A format, with a decent but not outstanding head and cam spec the K series can do about 100bhp/litre at pretty much 7krpm. ie make around 180bhp.
So, for 250 bhp i'd suggest you won't need anything like 18psi of boost, as long as you keep the engine revy, rather than try to make it a boost monster at lower rpms. In fact, due to the construction, i'd avoid massive cylinder pressure loads that come from high boost and aggressive ignition timing. Luckily, the shape of the cylinder pressure curve, and particularly the slower rate of rise of cylinder pressure (charge is burnt at a net higher chamber volume) means a boosted engine is typically less mechanically stressful on it's mechanical support than a peaky N/A one. (it can be much more thermally stressfull however, so good intercooling, and overfuelling to limit EGT is a must!)
So, with the caveat that you want to limit mid range boost / torque and hence peak cylinder pressure, you might want to use a turbo a size too large, which will also have the effect of reducing the thermal load on the engine, but come at the expense of a higher boost threshold.
Having said that, the suggestion to 'get a stake in the ground' with a low cost, known turbo, such as the one off the 225bhp audi 1.8t engine is a good one! That will enable you to get up and running, you can measure some stuff with it fitted, get the engine mapped (careful on the max advance you use, think more boost, less spark if you want to make more torque to keep the pressure curve nice and gentle).
At that point you can look to see if there is a better 'fit' turbo to use depending on what results you get!
So, for 250 bhp i'd suggest you won't need anything like 18psi of boost, as long as you keep the engine revy, rather than try to make it a boost monster at lower rpms. In fact, due to the construction, i'd avoid massive cylinder pressure loads that come from high boost and aggressive ignition timing. Luckily, the shape of the cylinder pressure curve, and particularly the slower rate of rise of cylinder pressure (charge is burnt at a net higher chamber volume) means a boosted engine is typically less mechanically stressful on it's mechanical support than a peaky N/A one. (it can be much more thermally stressfull however, so good intercooling, and overfuelling to limit EGT is a must!)
So, with the caveat that you want to limit mid range boost / torque and hence peak cylinder pressure, you might want to use a turbo a size too large, which will also have the effect of reducing the thermal load on the engine, but come at the expense of a higher boost threshold.
Having said that, the suggestion to 'get a stake in the ground' with a low cost, known turbo, such as the one off the 225bhp audi 1.8t engine is a good one! That will enable you to get up and running, you can measure some stuff with it fitted, get the engine mapped (careful on the max advance you use, think more boost, less spark if you want to make more torque to keep the pressure curve nice and gentle).
At that point you can look to see if there is a better 'fit' turbo to use depending on what results you get!
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