Wrencher

Like the title says, anyone done this? I build lots of engines, but I've never been brave enough to change the basic timing on the double roller sets I typically use. I get that retarding the chain 4 degrees generally adds low end torque, and 4 degrees advanced adds mid and top end horsepower. I worry about detonation with an advanced cam, but anything else that folks have experienced? I'm currently building a 327/350 HP clone with a Lunati 00210 Hydraulic flat tappet cam with 10.5 - 1 Keith Black pistons, 461 heads, good dual plane intake and long tube headers. I'll use better fuel in this in a 3200 pound car, just asking about real world experiences. Thanks in advance!

Hans

Engage

Retarding timing adds top end power........ advancing timing adds low end power!!!!

Wrencher

OK, learn something new every day. Any personal experience, sort of seat of pants feel? I'm especially curious regarding the effect on pre ignition ("pinging"). I would expect worse detonation with an advanced cam? Thanks for the response!

Hans

resdoggie

Yes, advancing the cam timing is the wrong direction in preventing the onset of detonation. Retarding the timing will bleed off pressure due to the intake valve closing later.

lars

The advance and retard features available on many timing chain sets can be used for 2 purposes:

1. When you "degree" a cam and find that the parts tolerance stack-up of your particular engine results in the cam not being "at spec," you can use the + and - degree feature to correct the out-of-spec issue to get the cam to it's "in-spec" degree specification.
2. When you have your engine on an engine dyno and you have firm dyno data and curves with engine torque and power, you can advance and retard the cam to see the shift in the torque & power curve, thus tailoring the cam to your most desirable power curve. You have to have actual dyno data to see if either shift is desirable or not.

Randomly either advancing or retarding the cam, without a reason to do so based on degree data or dyno data, is completely pointless. I will typically dyno test an engine with the cam installed "straight up," as well as advanced 4 degrees and retarded 4 degrees to see the effect on the torque and power curve in order to maximize engine output in the usable rpm range. The changes in peak power and torque from the advance and retard positions compared to the "straight up" position are usually less than 10 horsepower, which you cannot feel in the "seat of your pants" in a 3400+ pound vehicle. So just do an accurate "degree" process on the cam and assure that it is installed to the cam grinder's specs, using either the timing chain degree options or offset crank keys to achieve the correct spec. You don't use cam timing to control detonation - you use ignition timing curve and fuel octane to control detonation.


Lars

gkull

You must have quite a dome to get 10.5 out of a 327. The majority of my custom cams were ground 4 degrees retarded compared to equivalent comp cams extreme line of off the shelf cams valve events.

I've played around with DCR VS Static Compression ratio calculators. You can input the valve event numbers with + or - 4 degrees and see where you are at.

I've only built one total detonation motor. I had everything to detonation proof my I think it was 10.8 383 . .038 quench -7 cc forged flat tops Swain tech ceramic thermal barrier pistons. Aluminum heads . Crane adjustable vacuum advance set to under 8 degrees additional. 32 degrees max mech timing just like the afr heads said. All in at 3000 rpm. going down a freeway at 65 mph it would just rattle away on california 91 octane. I ran octane boosters.......... The solid roller 232/238 cam was the problem. I just went up to 236/242 and the motor ran like a champ for many years.

Jebbysan

You will never notice the difference.......don't waste time, money or energy on it.....
A third reason to move the cam around is if you are very close on piston to valve.....moving the cam + or - 4 degrees can get you in spec if you have already installed the pistons and fly cutting valve pockets is not an option....not really the right way, but if you are out of time and have to get to the track tomorrow....it can save your ***.

Jebby