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Cam help?

  • Daryl

    Sept. 7, 2008 10:27 p.m. Daryl

    I am building a Datsun Roadster R16 pushrod stroker motor (1600 up to 1800cc) with EFI.

    When it came to the cam I was steered toward a 270 duration, 108 LSA cam. It was good thru the powerband, but I couldn't get a decent idle below 900 rpm, and then it was sort of rough.

    I've pulled the engine apart, and another "grinder" has steered me to a 112* LSA cam with the same advertised duration. I understand I should get a better idle and a wider powerband, less peak power......

    The head has been thoroughly ported with oversize valves and a jump to 10:1 compression.

    I have also read where displacement can have an effect on the LSA you may want to use.....

    Unfortunately, none of the info I can find is really applied to our little old 4 cyl engines.

    Is there anywhere on the net to figure out how duration, LSA, powerband, lift, and compression ratios will work together?

    IE: the differences say between a 270* cam with .400" cam lift, and 108* or 110 or 112 LSAs?

    I have read where some newer, stock oem cans have as much as 116* LSAs.

    Why the big differences? What works well with what?

    Thanks Daryl

  • Sept. 10, 2008 5:23 p.m. Jack SuperDork

    I'm happy with the 280/105 cam in my TR3 at 9:25:1. It's kind of similar.

    My engine is a bit lopey under 1,000 RPM, but the power up higher is worth it. With 10:1 compression, you can certainly benefit from the bigger cam.

    I don't think you will find enough in the way of relationships between all of the factors for you to pick a specific cam, without an engine specific group. Bigger cams like more compression, bigger valves, etc. but for details you need specific experience. Have you checked the Datsun boards?

    You may also get more detailed cam info on the GRM board. Classic or modern, a cam is a cam and the GRM boards are more active.

    Jack

  • trboost

    Sept. 14, 2008 5:56 p.m. trboost

    LSA, Lobe seperation angle is the seperation in degree's between the intake & exhaust lobe centerlines. An LSA of 108-110 will work best for most street applications. Larger LSA's will give a smoother idle decreasing overlap. It is the valve overlap that will affect idle vacuum. You will usually see wider LSA cams used with forced induction motors. The idea is to trap the intake charge from blowing out through the partialy opened exhaust valve. You can also experiment with advancing the cam by using an adjustable timing gear.

  • foxtrapper

    Sept. 16, 2008 5:23 a.m. foxtrapper SuperDork

    You're not going to find one single perfect source of "the answer". As you've noticed, the experts in the field continue to disagree on the subject of the perfect cam lobe shape and such.

    Instead, I'd suggest read, read, read. Start at the various cam makers web pages and read what they right. Isky and Crane both have some good stuff, as do many others. Continue to read, including some of the stranger things. For as you learn you can understand what they are saying in the stranger posts.

    Your engine is not terminally unique. In fact, it's essentialy half of an old american V8. The same thinking and philosophies will apply to your engine.

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