Dyno Mule question for Mr. Brown

[allrightmike]

   I have taken much info from your book and thank you. Now the question is, I have noticed that the cam timing on the dyno mules was set at 4 degrees advanced. For what particular reason was this done?

[jayb]

It was either specified to do that on the cam card, or if not it was to optimize the DCR (dynamic compression ratio) for pump gas, since the engines in the book were all designed primarily as street engines.

[allrightmike]

     Aside from altering DCR would a change from straight up to four degrees advanced cam timing have a noticeable effect on torque production in the 2,500 to 4,000 RPM range?

[blykins]

Changing the cam timing doesn't do as much as everyone thinks it does.  Very rarely does it make a big swing in power or torque.  Mostly single digit changes. 

[allrightmike]

   Well I guess I was one of those everybody's but I am now up to speed, thanks.

[blykins]

It's interesting to see what gets perpetuated around the internet.  We've always heard that advanced cam timing gives low end torque and takes away from high horsepower.  We've also heard that retarded cam timing does the exact opposite.  It really boils down to the individual engine combination. 

Daniel Powell was telling me about a dyno test he did several weeks ago.  Same exact engine combination, swung the cam timing both directions.  It was down to low single digit differences. 

Engine builder buddy of mine used to run NHRA SS with a SBM engine.  After many cam changes, cam timing changes, etc., it made the most power on a 98° ICL.  Turning to ~8500.

[Qikbbstang]

Unexpected/defies logic changes in power are often common.  There is a dyno analysis w/tune on a GT350 Coyote Voodoo on Y-T. They swapped X-pipe configurations and numerous exhaust configurations noting power and sound changes. The final addition of high dollar "Cooks" stepped headers vs factory Ford headers was a surprise in that little more the car's sound changed / single digit power changes up/down.   

[Rory428]

Plenty of times I have seen things that were supposed to be worth "X amount" of HP, or more importantly, to me, ET and/or MPH at the dragstrip, that simply did not deliver as claimed.  On my Fairmont, with the 428, when it still had a C6 in it, I tried moving the cam around 4 times at the same track on the same day, from 4 degrees retarded, straight up, and 4 and 8 degrees advanced. The car ran the best at 4 advanced, but other than at 8 advanced, which hurt the performance noticeably, the difference between 4 retarded and 4 advanced was only .004, so just under 1/2 tenth in the 1/4 mile. Now keep in mind, my car had a transbrake, and I left at WOT , which the torque convertor went to 5200 RPM. So low RPM drivability and of idle response was not a factor, so what helps at higher RPM, may hurt at lower RPM, so that needs to be kept in mind. Much like camshafts, often to much attention is focused on peak  HP, and ignores losses down low. More than once I had cams that lost more in the first 330 feet, than they made up during the last 990 feet, so the net was often a slower ET, with a higher MPH. Same with carb spacers, collector extensions on headers, intake manifolds, etc, everything needs to work in harmony. Thats why I have to laugh when somebody asks "Whats the biggest cam that I can put in my stock 390 in a 4000 pound car, with 3.00 gears and a stock torque convertor, and wonders why he ends up with a sluggish, gas guzzling pig, but at least, it SOUNDS "fast"!

[Barry_R]

When doing EMC development I would often try different cams and, with the belt drive, make cam timing changes for each looking for improvements.  Usually the gains at one end of the curve were offset by losses somewhere else - and they were incremental.