At 11:41 AM 6/12/02 -0400, Rob Christopher wrote:
>Hi again everyone,
>
>Based on the responses from my first question on this topic (thanks to
>everyone Hugh, Randall, Bob) I had another shot at the cam last night
>using 'Method 1', crankshaft to 112 ATDC, find max intake lift on #1 and
>chain together.
>
>Now, the question is how close is close enough. I am using the original
>cam sprocket so I have the 1/2 tooth adjustability using the two sets of
>holes, and there is some slop in the bolts holes on the sprocket so
>there is a little adjustment there as well.
>
>Using the 'centreline' method in the cranecams.com document Hugh pointed
>me to, I get the following results:
>
>1st set of holes, moving the cam within the slop of these holes, I can
>achieve 104 to 109 ATDC for max lift on #1 intake.
>2ns set of holes, moving the cam within the slop of these holes, I can
>achieve 114 to 117 ATDC for max lift on #1 intake.
>
>Note, neither of these gives me the 112 ATDC the spec calls for. So,
>which of these two would be the better choice? 109 ATDC or 114 ATDC? I
>think as the chain stretches, the 109 would slowly become 110, 111...
>
>Should I just drill a new set of holes 1/4 tooth away from the others?
>Create a little more slop in the current holes? Or stiffle my
>engineering gene that won't allow me to accept 'close enough' and bolt
>it up at 109 or 114?
>
>Rob
>74.5 TR6 CF28217UO (now on the 5th hour of indexing the camshaft....)
If you are using a stock cam sprocket, you can make an adjustment by using
the other set of holes, as you know. You can also change THAT adjustment by
half, by flopping the sprocket over front-to-back.
I will share with you some data acquired on the engine dyno a couple of
years ago on the vintage race engine I was running at the time. The info
I'll give you is true for 6000 rpm horsepower, 32 deg ignition advance,
very very rich mixture, 11:1 compression ratio. I was running an Isky TR666
camshaft which is spec'd at 33-73-73-33, modified for .488 lift.
For the dyno runs, we fitted an adjustable sprocket and a timing cover with
a removable plate to allow camshaft timing to be adjusted without
disassembling the engine. The camshaft was spec'd at 111 deg. Here's how it
came out:
baseline run at 111 deg
identical hp at 114 deg
4 more hp at -- 109 deg
1 additional hp at -- 108 deg (and of course it can be argued that dyno
runs aren't accurate to one deg)
Your hp may vary. My current engine is much better but still has the same
cam timing, but don't tell anybody. I'm off to Mid-Ohio to see if I can run
with the big dogs.
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