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Discussion Starter · #1 · (Edited)
Hi guys,

I will be assembling my sbc soon and wanted to throw something out there that I was thinking about.

Cam timing straight up or advance 4 deg.:confused0006:

The car will be street only and no race track time. If I advance cam 4 deg. how will it effect other stuff?

Will give me more bottom end at lower rpm, will it bleed off compression or help build compression? Ignition timing still be the same? "IF" the engine is 350hp and 350tq with straight up timing, advancing 4 deg will be ? (approximate)
Vacuum not an issue, have manual brakes. Detonation risk higher or lower ?
How about operating temperature?

What else is there to consider to "advance" or "straight up" that I'm not aware of ?

Thanks for any help.
 

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"Will give me more bottom end at lower rpm,"

It will give you more bottom end.

"will it bleed off compression or help build compression?"

It builds a bit of dynamic compression because the intake valve is closed sooner.

"Ignition timing still be the same?"

Maybe, mayb not. Ignition timing depends on a lot of things.

"IF" the engine is 350hp and 350tq with straight up timing, advancing 4 deg will be ? (approximate)"

You might lose 2-3 hp on the top end. You might gain 2-5 ft-lbs and the rpm for peak torque will be 200 rpm or so lower.

"Detonation risk higher or lower ?"

See the answer on timing.

"How about operating temperature?"

It should not affect temperature.

Advancing the cam timing decreases intake valve to piston clearance and increases exhaust valve to piston clearance.

Note that many street grind camshafts are advanced 4º "out of the box". When you look at cam specs, look at intake centerline vs. lobe separation angle. If they are 4º different (intake centerline smaller), the camshaft is manufactured with 4º advance.
 

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I'll stick with advancing to help the low end. That's the way it is.

Thing is, it's splitting hairs. Putting the cam in straight up or advanced 4 degrees isn't going to make or break your combination.

You didn't mention the cam specs or the rest of the engine combination. That would influence what you should do IMO. You don't make each tuning choice in a vacuum, everything relates to everything else as a system.

That said, I never install a camshaft without "degreeing it in". They can build a perfect camshaft as far as the lobe grinding goes, but they still can blow the advertised timing by drilling the dowel pin hole in the wrong place. I've seen it before and probably will again. So there's two things here - what they intended to make and what they really built.

You didn't say whether the cam is already installed and whether the engine is in the car either.
 

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Probably could use more info like compression, cam specs, intake, etc.

Personally, I'd advise you pick the cam you want and install it straight up and be down the road. The cams are good enough today that you can find something that will give you the low end torque you want.

Unless you already have a cam and are trying to make it act differently, why mess with it? 5 extra foot pounds isn't going to make any big difference.
 

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I like your combo, sounds like a decent street/performance package.

Myself, I would install it straight up, put a degree wheel/dial indicator on it to verify that's what you have, and put it together.

I would also check the retainer to top of the valve guide/seal clearance carefully, as well as verifying that the installed heights and spring pressures are where they should be.
 

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My recommendation has always been to start with the specs on the cam card. And some cams are not quite as accurate as advertised - not necesarily the cam's fault - but the entire valve train. Sometimes setting the intake timing makes the exhaust a degree or two off - in that case I like to split the diff to get back to an average event timing.

Varying from the cam card is a tuning issue - and I have never been able to tune (and know of no other experienced builders who can) without first establishing a baseline to compare your changes to - in otherwords tuning before the baseline is known is WAG-ing (wild a$$ed Guess). I have seen things play out on the dyno that were not quite as expected - it becomes even harder to anticipate what happens by the time all the stuff goes through the gears getting multiplied and divided many times over!

There are timing sets and covers that make cam timing after install easy - just make sure during assembly that you clearance check at both extremes of the available timing first - would hate to find that adding or taking valve lead eats up that clearance and has the piston getting overly intimate with a valve!
 
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