is 6 degrees advanced too much?

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Dec 6, 2002 | 06:20 PM

71roadster

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is 6 degrees advanced too much?

When I checked on my short block the other day the machinist told me he installed the cam at 6 degrees advanced. I understand the rational of advancing the cam to move the torque curve to lower RPM's but 6 degree's seems excessive. Its a comp cams xe274h. It is ground 4 degrees advanced and the crank sprocket allows 2 degree increments. The engine is a 383 with 6 inch rods and 10.5:1 compression. Someone on another forum suggested that my dynamic coompression ratio may be to high but I don't have the cam card to calculate those values at this point. He suggested I may want to run an even larger cam because the increased duration and overlap will result in a lower dynamic compression or at least retard the cam 2 to 4 degrees.

Any thoughts?

Thanks
Chris

PS The engine is still at the shop waiting for the heads to perform a valve clearance check so now is the time to figure this out.

Dec 6, 2002 | 07:55 PM

sinistervette

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From: the corner of walk and dont walk

Re: is 6 degrees advanced too much? (71roadster)

I'd give comp cams a call, their CAM HELP line is 1-800-999-0853. They are available from 8am-8pm cst mon. thru fri. To me 6* adv is too much, but that is just my opinion. If they were trying to desolve some compression, I'd think that they would have to retard the cam not advance it. If I remember correctly adv. the cam will increase not decrease compression. Give comp cams a call, they will definiately set you on the right track. :cheers:

Dec 6, 2002 | 08:17 PM

Vetterodder

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From: Fountain Hills AZ

Re: is 6 degrees advanced too much? (71roadster)

I don't think you'll have any problem with it advanced only 2º more than it's straight up position but I do agree it seems unnecessary in a 383 unless it's pulling tall gears or in a heavy vehicle. I'm runing the XE274 in my `65 with 331ci, installed straight up, and I'm happy with it's low end. If I were installing the same cam in a 383 I'd probably retard it 2º. If, after driving the car, you decide that you're willing to give up a little bottom end power in exchange for a little more higher up, you can always readjust it later.

Dec 6, 2002 | 09:09 PM

CORKVETTE1

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Re: is 6 degrees advanced too much? (Vetterodder)

if you had a 5.7 rod you could probally leave it at 6 but with those longer rods in there your piston speed is slower and the piston is hanging out at top dead center longer with more of a chance of detonation so back it bak down some 2-4 degrees total :cheers:

Dec 6, 2002 | 11:08 PM

gkull

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Re: is 6 degrees advanced too much? (71roadster)

In the past I ran cams really straight up. So if it had 4 deg. ground in I retarded it 4. I always ran the best roller chains and never planned slop into the future equasion. A high compression 383 should have no problem with a XE274. I had one in a hot 355 ci. Every degree might alter the peak TQ rpm @100 rpm. At lower rpm a highly advanced cam is going to cause intake reversion

Dec 8, 2002 | 10:53 AM

CORKVETTE1

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Re: is 6 degrees advanced too much? (gkull)

gkull is right if you were road raceing like he is you would probally be bettter off at straght up but for max effort street and strip advance it 4-6 degrees :cheers:

Dec 8, 2002 | 01:03 PM

Stingraycrazy

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Re: is 6 degrees advanced too much? (CORKVETTE1)

I agree with Gkull, "at a lower rpm a highly advanced cam is going to cause intake reversion". In a running motor if you must advance a cam to 6 deg over spec It's probably to big a cam for your application. The XE274H or XE284H would be a great street cam for a 383. I would install the cam as spec in the cam card and then make adjustments from the base line after the engine has been run & evaluated. Move the advance or retard in 2 deg increments from that base line. Thats the only way in my book, I just think 6 degs as a start is way too much. I'd pick the XE274H with 2 deg total advance and 1.65:1 intake / 1.5:1 exhaust rocker ratios :crazy

Dec 21, 2002 | 03:47 PM

The Money Pit

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From: Orrtanna Pa.

Re: is 6 degrees advanced too much? (Stingraycrazy)

For my 2 cents worth I ran the XE-274 in the 406 straight up and felt it had a ton of low end power (easy 30 foot burnouts) and after it went flat due to improper break in on my behalf,I went with the XE-284 and 1.60 rockers. This combo lacks the low end punch as would be exspected,but cruises without effort at 75 and will pull to 120+mph in around 4 seconds with no sign of fading at the top. My advice would be to install the cam straight up and use a two piece cover if you think you may be inclined to tweak the advance later.
Also I've found that playing with the ignition timing will have a huge effect on how the engine feels. Even 2-4 degrees will make a measurable difference in the seat of the pants.