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This thread was about a N/A to turbo conversion, without changing any internal engine parts, but we are all curious about cams, which can be aquired and changed easily. My conversion is running close to stock boost for an OG900T and there is seldom any boost cut by the APC even using 87 octane fuel.
People have been turbocharging N/A engines ever since turbochargers became affordable and readily available in the smaller sizes, without making any internal engine modifications. From everything that I have read stock N/A cams do work well for a turbo conversion. I'm sure these cams aren't the best answer, but for normal use they seem to be a good choice. I'd tend to believe that using N/A cams would not be the main reason an engine failed after a conversion.
You're still not really saying anything here. I do understand static and dynamic compression ratios, tell me how that relates to the cams we are talking about.
Dynamic compression ratio may actually increase using the turbo intake cam (although effective CR is less), when the engine is under boost. The intake valve closes 12 degrees later, if boost pressure is greater than what the cylinder pressure would be, had the intake valve closed 12 degrees sooner, then the dynamic pressure would be higher.
Take the Miller Cycle engine for example, it uses a blower and very late closing of the intake valves (70 degrees ABDC), to increase cylinder filling. This can't be directly compared with a turbo engine, because the engine isn't alway under boost, but it shows my point. N/A engines do not, do well if the intake valve closes to late, because the intake charge will backup into the intake manifold before the intake valve closes. Turbos and blown engines can have later intake closing because the intake pessures are higher and keep the intake charge in the cylinder until the intake valve closes.
Increased overlap (itake open to exhaust close), would be a larger concern from my veiw point, not because this would kill an engine sooner, but because it would effect the efficiency of an engine under boost. If you look at the cam data for stock cams, you'll see that with the exception of the '85 turbo cams, overlap runs 29-31 degrees, no real difference there.
I'm still looking for someone that can give me some real info on what cam specs work for a performance street turbocharged engine. I'd like to hear anything specific that you can say about conversions, performance cams, etc.
posted by 206.105....
, Fri, 17 Aug 2001 22:38:56
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