Technical advice needed: Timing chain and gears

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Doug The Dog

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1973 Convertible, 351CJ, 5 Speed. Currently being restored. Projected finish date is some day.....
I remember when I built this engine in 1990 or 91, that I installed a Lunati camshaft and Ford Motorsport timing gear set. I know that we degreed the cam. What I don't remember, is why did I set the crankshaft gear to 2 degrees retarded? I had a machinist friend helping me, and we got the timing marks on the money. What are the advantages/disadvantages of advancing or retarding the timing marks? What is the best set up for the best low end torque from a 351 4V engine? In the for what it's worth category, I have open chamber heads, milled .050. Mild cam, stock exhaust, 4speed, wide ratio trans, 3.50:1 tractionloc rear diff.

Google has not been my friend tonight finding the answers to my questions. Hopefully, someone can refresh my memory. (I think the hamster fell off the wheel).

Thanks,

Travis (AKA Doug The Dog)

crank gear.jpg

 
I remember when I built this engine in 1990 or 91, that I installed a Lunati camshaft and Ford Motorsport timing gear set. I know that we degreed the cam. What I don't remember, is why did I set the crankshaft gear to 2 degrees retarded? I had a machinist friend helping me, and we got the timing marks on the money. What are the advantages/disadvantages of advancing or retarding the timing marks? What is the best set up for the best low end torque from a 351 4V engine? In the for what it's worth category, I have open chamber heads, milled .050. Mild cam, stock exhaust, 4speed, wide ratio trans, 3.50:1 tractionloc rear diff.

Google has not been my friend tonight finding the answers to my questions. Hopefully, someone can refresh my memory. (I think the hamster fell off the wheel).

Thanks,

Travis (AKA Doug The Dog)
Travis,

I am no expert here but my cam is advanced 2 degrees. I believe that you want the LC between 108 and 112 degrees. This is how I have my engine set up:

CR 10.44 : 1

RPM Range: 2500-6800

Advertised Duration: 290/290

Duration @ .050: 225/235

Lift: .530/.550

Lobe Center: 110c

Total advance distributor = 34 degrees.

I believe that a 2 degree retard will up your top end performance. Don't take this as gospel and I would also like to see what others have to say. Cam dynamics is still an area that I am learning. Do you have your cam specs, I am curious what your advertised LC is.

-john (jbojo)

 
Last edited by a moderator:
Here are the specs from my cam:

•Advertised Duration (Int/Exh): 276/276

•Duration @ .050 (Int/Exh): 221/221

•Gross Valve Lift (Int/Exh): .524/.524

•LSA/ICL: 110/104

•RPM Range: 1500-5600

 
Here are the specs from my cam:

•Advertised Duration (Int/Exh): 276/276

•Duration @ .050 (Int/Exh): 221/221

•Gross Valve Lift (Int/Exh): .524/.524

•LSA/ICL: 110/104

•RPM Range: 1500-5600
I found this:

By advancing the cam, the valves open and close earlier. Duration and overlap remain unchanged. Advancing raises the cylinder pressure (due to earlier valve closing) This improves low end and mid-range torque at the expense of some top-end power. The result is similar to using a shorter-duration cam since the intake valve closing point is more critical than its opening point.

Retarding the cam so valves open and close later has the opposite effect. This should increase top-end power, at the expense of low end, and mid-range torque. Thus: 1) Advance Cam: More low and mid-range torque, 2) Retard Cam: More top-end power.

BTW Advancing/retarding cam has no effect on LC. I read my engine notes wrong. My advertised LC is 110 degree, correcting my earlier post

 
Here are the specs from my cam:

•Advertised Duration (Int/Exh): 276/276

•Duration @ .050 (Int/Exh): 221/221

•Gross Valve Lift (Int/Exh): .524/.524

•LSA/ICL: 110/104

•RPM Range: 1500-5600
I found this:

By advancing the cam, the valves open and close earlier. Duration and overlap remain unchanged. Advancing raises the cylinder pressure (due to earlier valve closing) This improves low end and mid-range torque at the expense of some top-end power. The result is similar to using a shorter-duration cam since the intake valve closing point is more critical than its opening point.

Retarding the cam so valves open and close later has the opposite effect. This should increase top-end power, at the expense of low end, and mid-range torque. Thus: 1) Advance Cam: More low and mid-range torque, 2) Retard Cam: More top-end power.

BTW Advancing/retarding cam has no effect on LC. I read my engine notes wrong. My advertised LC is 110 degree, correcting my earlier post
OK. That confirms what I was searching for. Not really sure why I set the cam up the way I did. I do remember though, going for a test drive and being gutless at lower rpms. At the time I was blaming it on the close ratio 4speed I had in it.

I will do a little more research, but I think I want to advance it. Iwant to be quick from stop light to stop light. Not really concerned about running 140 mph!

 
Here are the specs from my cam:

•Advertised Duration (Int/Exh): 276/276

•Duration @ .050 (Int/Exh): 221/221

•Gross Valve Lift (Int/Exh): .524/.524

•LSA/ICL: 110/104

•RPM Range: 1500-5600
I found this:

By advancing the cam, the valves open and close earlier. Duration and overlap remain unchanged. Advancing raises the cylinder pressure (due to earlier valve closing) This improves low end and mid-range torque at the expense of some top-end power. The result is similar to using a shorter-duration cam since the intake valve closing point is more critical than its opening point.

Retarding the cam so valves open and close later has the opposite effect. This should increase top-end power, at the expense of low end, and mid-range torque. Thus: 1) Advance Cam: More low and mid-range torque, 2) Retard Cam: More top-end power.

BTW Advancing/retarding cam has no effect on LC. I read my engine notes wrong. My advertised LC is 110 degree, correcting my earlier post
OK. That confirms what I was searching for. Not really sure why I set the cam up the way I did. I do remember though, going for a test drive and being gutless at lower rpms. At the time I was blaming it on the close ratio 4speed I had in it.

I will do a little more research, but I think I want to advance it. Iwant to be quick from stop light to stop light. Not really concerned about running 140 mph!
Here is the disadvantage of retarding the cam, as the lifters cup, timing chain wears and the cam lobes wear with age the end effect is the timing will continue to retard even more making low end performance/torque even worse. The motor will get lazier and lazier.

 
When you degreed the cam it may have been ground off-center and you needed the 2 degrees retard to bring it to specs.
Good point. I am going to break out the degree wheel while I have the engine apart and check it out.

 
I ended up setting my cam 7 degrees retarded to get it actually 4 degrees advanced. When we degreed it it was 11 degrees advanced at the "0" location. I will never again install a cam without degreeing it. No wonder the engine detonated severely before the refresh.

Advanced = low rpm power

Retarded = higher rpm power

 
Low quality valvetrain/timing components can add serious error into cam timing. If you don't degree, you will never know. I say 80% of the time you never need to adjust more than 1-2deg to get it to true straight-up. I've seen on Chinese made Summit Racing timing sets add 3-4deg on average because of poor machine tolerances and slack in a brand new chain.

I've found Cloyes True Roller timing sets are about the best value out there.

 
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