I've been reading up on drilling the cam gear to get a 71/2 degree advance. Any advice making this mod? Is it really worth the effort? I'll be using a Prus head and stock cam on this motor. PK
7&1/2º is a 1/2 tooth difference.
Here's a pic of the place to drill the 2 extra holes to get 7&1/2º advance.
That picture looks to be 15 degrees judging from my eyecrometre (Which has not had a calibration test in a while).
48 teeth divided by 360 degrees is 7.5 but that isn't the end of it. The extended center line of the stock timing position is 2 teeth away from the timing mark. The advanced line up is separated by 1 and 1/2 of 1 tooth. If one tooth is 7.5 from the other, then one half is 3.75 degrees as measured on the cam. We know the crank has to travel twice as far which is why it is 7.5 degrees (3.75 + 3.75). Valve timing is expressed in crankshaft degrees.
3.75 at the cam gives you 7.5 at the crank. Be sure you know what timing your cam has at the crank. If it is around 10 deg like the Stipe cam or a stock Ford cam, you can definatelly improve the low end performance.
Do you loose on the top end then? I read that you need less advance with high compression heads, true? PK
With a good std cam retarding the cam timing is less needed than with a reground cam. The higher compression in your head helps at hill climbing and you may have a good running car without any change to the timing gear.
Whether you want it depends on a lot of factors - what gears do you have in the rear end, do you have any accessory transmission and what's the type of terrain you'll drive the car?
In my example I have a reground 3/4 race cam from Spokane, 3:1 rear axle gears and a 0.100" planed Prus head in a light car. I live in an area with some hills and mostly 50-55 mph roads. So to avoid slowing down too much uphill (No accessory trans) I've installed a 7.5 degrees retarded aluminum timing gear. It makes the engine stronger in the low rpm range where you'll need it when pulling hills and changing from low to high gear, while you loose some at high rpm - but my car will still top out at 53+ mph with a NH carb, so the small trade off is certainly worth it ;)
I can't get my head around this. Can't the gear just be installed "incorrectly" at 7.5? Why drill it?
Charlie B, if you move the timing gear one tooth, it will change the timing 15º.
Roger, Pat K was asking about advancing the cam timing, now you're talking about retarding it. Please explain.
Retarding the cam will kill you on the low end. There are many reground cams and they are all ground different so you can't make a blanket statement about reground cams. . You have to know what you have before making a decision about advancing the cam. Our reground and new cams are optomized for street use with both a good low end and a good high end. Typically, advancing the cam or decreasing the lobe separation between intake and exhaust lobes will increase low end torque and horsepower. increasing lift and duration increases the high end.What we have done is find the combination of the four parameters noted above to give you the best performance at both ends without hurting the other end. The stock Ford cam has a good low end but a moderate high end. Our cams have a better low end and high end than the Ford cam. If you want to contact me I will tell you how we did this.
I run .280 Chaffin cams in my T's and they are very satisfying on the low and high end with and without high speed rearends. Glen seems to have a good option. Mike
Sorry, I was mixing up terms there - Glen is of course right about *advancing* the cam shaft for better low end at a small trade off in the rarely used top rpm end.
My " blanket" statement is about many popular reground cams that was available before Stipe came with his new cams and a lot of new research was done in Model T camshafts. There may indeed be new profiles that doesn't gain as much from retarding as earlier regrinds did.
So if I want to run down the highway 45 mph, would I be better off with stock advance? Most of my driving is on state highways as county roads are only local. We also have a lot of hills. PK
With hills and stock cam, advance it. You'll be pleased with the result on the hills.
If you advance a stock or Stipe 280 cam 7,5 deg they will perform about as good as our reground and new 280 cam on the low end. Our cams high end can do at least 50 MPH., But they are not for the Montana 500. All you want there is better high end. I have a lot of guys who buy our finished but unground cam and put their personal high speed grind on them.
Great info guys! I love these threads full of good information. PK
I have a few spare cam gears and would like to try this modification. Is there anything out of the ordinary that I should know about before tackling this job? From what I can see I should be able to do this with the engine in the car. What about ignition timing - will this be affected, and lastly - I live five and a half thousand feet above sea level...will I benefit from this mod at this altitude?
Paul in Johannesburg.
I helped my buddy Bob advance his cam gear and install a Z head. He says its like a different car now. Lots more power.
I have a little over 1500 miles on the motor now and it really pulls hills good. The other day I was running down Hwy 200 at 48 mph on the flat. I have noticed that the advance is not as much as before. I just drove over Bear Tooth Pass which is just under 11,000 feet, all I did is lean out the mixture some and it ran real strong pulling the grade up. PK
The timer rod will need to be re-bent same as installing a new timer. If you don't re-bend the rod, the timing will be off when trying to start and could damage ones arm or the starter.
Many argue that this doesn't affect ignition timing however, on battery, the rotor attached to the cam will now make contact 7.5 degrees sooner than before. Should this cause spark to occur before top dead center and you're hand cranking, there is a good chance you won't like the result.
Bend your rod so it buzzes the coil a few degrees after TDC with the lever all the way up. Same as setting up a stock arrangement.
Be aware that some of the cams from Chaffin's are already ground advanced:
I should have said that if you advance the cam 1/2 tooth (3.75 deg) you will advance the valve timing 7.5 deg. That is what you want. So don't advance the cam 7.5 deg.