Reply With QuoteI always advance it 2 degrees if using a chain to componsate for stretch and with that big of boat you can use more bottom end!..
I have ended up with a camshaft that I am not used to, it is my first boat cam, and I have a quick question about how much advance, 4, 5, or 6 degrees?
This roller cam was specced out by Reed Oliver at Crower Cams.
Some quick info before we go further:
26 foot Caribbean Daycruiser, its gotta be 4000 pounds at least.
Top speed on GPS 43-44 with bonestock Volvo 255hp 350 and a 21 1/2 prop.
Now has:
Small block Chevy 406, ported WP Sporstmen 2 heads, 9.5:1 pistons 0.038 deck clearance, Gil exhaust, ported GM marine intake with Quadrajet. Hopefully 440 hp.
cam specs
adv duration 264 intake, 539 lift
adv duration 273 exhaust 525 lift
intake open -3.5 atdc, closes 36.5 abdc
exhaust open 48 bbdc, closes -8 btdc
This is obviously conservative, as Crower is concerned about reversion etc.
The lobe centers are very far apart at 114, so the recommended 4 degrees advance is intake lobe centerline of 110, but I'm thinking 108 would be better? That would be a full 6 degrees advance, but with a max rpm of 5100, this might be the best cam timing. :idea:
Any one with more experience than me care to comment???
thanks for looking, Jay
I always advance it 2 degrees if using a chain to componsate for stretch and with that big of boat you can use more bottom end!..
And I will add to that....my experience with moving camshafts has been 6 degrees moved one way or the other...the overall performance suffers.
A word of caution here, I have ran into camshafts that were ground "up" by the cam company. If you also advance one of these cams you may be playing with piston to valve clearances that could be very tight. As always, check the piston to valve clearance several places before and after TDC. Both valves..........Another note, cam "bumping" is usually an attempt to improve performance, but to just bump it the first time it is installed is trying to out guess the engineer that designed it, and may not be the best way to evaluate its possibilites. Even advancing/retarding using a desk top dyno program to measure performance doesn't always give you the straight poop...If the cam card recomends advancing, I would question the amount of research that went into the development in the first place..............MP
I neglected to mention that I already dialed in the cam, and indeed it was right on the money. Installed with no advance or retard, it was actually 4 degrees advanced (with a new tight chain)
I went ahead and added 2 degrees, so after chain stretch I am going to be about 5 1/2 advanced.
This decision was made with the advice of a friend of mine who said: "Its not like you're ever going to get the thing to rev anyway"
The plan is to shoot for 5200 rpm, 55 mph, and keep adding prop to try to make it happen . The current 44mph is actually at 4300 rpm, so its got too much prop for the stock motor anyway.
Thanks very much, Jay
I cant upload a pic, but click on this link to see the motor.
http://www.ground-control-store.com/...ky12_25_dp.jpg
I'm with Fiat. We never move a cam 6 deg. If it needs that much it is the wrong cam. A small block needs torque in the correct rpm range to move a hevy boat. I would put the cam in at the grinders spec of 110. That is already a fairly small cam for 406 CI. Just my .02
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