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#53811 - 11/30/09 06:49 PM Cam timing on a 250 chevy inline 6
Vman Offline
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Registered: 10/13/08
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Loc: CA
I was wondering if any one has messed with the cam timing on a 250. I was reading an article that this guy was advancing the timing on all his vehicles and getting much better low end power and mileage and run cooler. but he said he only did it to 1975 and newer vehicles that were normally retarded due to smog. So I don't know if it would work on an older. I have looked high and low online and there is no info on anyone else actually doing this on older engines. Any experts out there have first hand knowledge of doing this? the idea is just to advance the cam gear one tooth.
Photos of my unit
http://photoman.bizland.com/1966/index.htm


Edited by Vman (11/30/09 06:50 PM)
Edit Reason: add text

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#53813 - 11/30/09 07:11 PM Re: Cam timing on a 250 chevy inline 6 [Re: Vman]
CNC-Dude #5585 Offline
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Most of the aftermarket timing gears have multi-keyways in them for this purpose. The Cloyes timing sets we used in all the 292 dyno testing recently were all degreed in, in this manner. But before you actually start just assuming you need to advance the cam, you need to degree it in first to see where you are at to begin with. If you are using an aftermarket camshaft, you can simply look at the cam timing specs on the card to determine what needs to be done. If you have a camshaft of unknown specs and no cam spec card, it is still fairly easy to determine how to degree it and at what point it will yield the best performance, even with no manufacturers data. This latter method is a little different than the traditional centerline method and involves a few more steps to perform, but it puts the cam in where it will make the most power everytime. However, since the Cloyes timing sets for the 6's will only allow you to move the cam 4+/- from straight up, you might not be able to dial it in and get the same results as timing sets that allow you to move the cam in 1 increments as in SBC, for instance.
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#53814 - 11/30/09 07:27 PM Re: Cam timing on a 250 chevy inline 6 [Re: CNC-Dude #5585]
Vman Offline
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Registered: 10/13/08
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Loc: CA
Well I am dealing with just the stock cam. I'm looking to just do a cheap adjustment without buying parts so it gets a little more low end power. I drive the car around town mostly so low speed getup and go and mileage is what I am after. do you think there is any advantage to doing the cam advance like that or is it better to just leave it alone.

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#53815 - 11/30/09 07:35 PM Re: Cam timing on a 250 chevy inline 6 [Re: Vman]
CNC-Dude #5585 Offline
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There definately is an advantage, but you have to use the Cloyes style timing sets to do it, and they are over $100 bucks.
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#53822 - 11/30/09 08:09 PM Re: Cam timing on a 250 chevy inline 6 [Re: CNC-Dude #5585]
Vman Offline
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Loc: CA
Here is the article where the guy was doing it on his vehicles and he only just did it when replacing the timing chain and advancing the chain one notch.

http://www.panacea-bocaf.org/camtiming.htm

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#53825 - 11/30/09 08:23 PM Re: Cam timing on a 250 chevy inline 6 [Re: Vman]
CNC-Dude #5585 Offline
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Thats assuming you are at least 10 or so retarded to start with, and you only end up at around 8 advanced from straight up, or in other words you are moving the cam 18. Like I said, you need to see where you are to start with, before you assume you need to move the cam. Advancing a cam that much is a good way to bend valves. When you advance a cam, you lose intake valve clearance with the piston. Be careful, I wouldn't do as this person has done....
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#53873 - 12/02/09 09:35 AM Re: Cam timing on a 250 chevy inline 6 [Re: Vman]
Ks Fats Offline
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V-man, years a go I worked as fleet manager and we had some 300 cid trucks; we found the o.e.m.cams to average 8 degrees retarded....when the engines were refreshed we used an offset woodruff key to advance the cam accodingly....I haven't used one in years but they may still be available.......I just checked an 8-1018 straight gear set for the chevy and it has 54 teeth on the cam gear; that computes to 6.66 degrees per tooth...as dude pointed out you need to know where you are first before proceeding....fats
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#53877 - 12/02/09 10:25 AM Re: Cam timing on a 250 chevy inline 6 [Re: Ks Fats]
Winter Offline
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Ks Fats, would that be 6.66 degrees x 2 for 13.32 crankshaft degrees? For everyone 360 degree rotation of the camshaft, the crankshaft rotates 720 degrees.

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#53878 - 12/02/09 10:41 AM Re: Cam timing on a 250 chevy inline 6 [Re: Winter]
64NovaWagon Offline
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Vman,

On a 1966 engine, the factory cam timing shouldn't be reterded. They were still running a normal amount of advance in '66, so I think you may be spending time thinking about a problem that may not exist. Unless I've missed something in your posts, the engine in your Chevy is the original one, so the cam timing shouldn't need to be advanced any more than it already is.
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#53888 - 12/02/09 02:03 PM Re: Cam timing on a 250 chevy inline 6 [Re: Winter]
Ks Fats Offline
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Registered: 05/14/07
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Yes thats correct, at the crank it would be 13.32....the 6.66 reflects the change at the camshaft based on the tooth count of the cam gear.....having said that; I have found that when you roll out a camshaft using the multi groove lower gear the "4" at the crank does not always come out to be 2 at the cam....I've always attributed that to manufacturers tolerance variations....I'll also go out on a limb here and say that when racing on dirt tracks I didn't find much gain or loss @ 2 degrees....over the years I developed a correlation between intake lobe center placement and the rod ratio ...that seemed to work best for me....fats
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#53899 - 12/02/09 07:03 PM Re: Cam timing on a 250 chevy inline 6 [Re: Ks Fats]
Vman Offline
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Registered: 10/13/08
Posts: 49
Loc: CA
OK thanks much for all your help , everybody. I think it wolud be wise for me to leave it set at factory then. Much appreciated for all your help.

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