327 Dynoruns

[Gene M.]

Re: 327 Dynoruns

What type of exhaust are you using aft of the headers?

Mike

Joe's graph chart at the top says open headers.........

[Joe C.]

Re: 327 Dynoruns

What type of exhaust are you using aft of the headers?

Mike

Mine are custom fabbed units using triple plated chromed steel (not stainless) tips welded to Classic Chambered 2540-VP "VettePacks" welded to 3" mandrel bent turns which are flanged to mate with the collectors. They reside under stock 1965-1967 covers with no shims or spacers. During one of my phone conversations with Eric Sauls, the owner of Classic Chambered Exhaust, I suggested that he develop a combination muffler/resonator system with a 3 1/2" outer shell and 2 1/2" inner tube. I reasoned that a larger contained volume between the core and the shell would attenuate the noise better, which has proven to be the case. The result was christened "VettePack", which he now sells quite a lot of. The system is also equipped with a pair of 3" electric exhaust cutout valves by Quick Time Performance. They dump exhaust gas just aft of the collectors to bypass the mufflers.

Refer to this:

http://www.classicchambered.com/classic/sounds.html

Scroll down about 1/4 way and read the testimonial about my black '65 as well as three video clips taken last year when the engine still had a solid flat tappet cam for a heart. The cam has been upgraded this year, to a solid roller with an additional 20% lift (.600"/.606"), about same durations and tighter lobe centers so overlap goes from 26.5 degrees @ 0.050 lift to 31 degrees.

[Gene M.]

Re: 327 Dynoruns

.......248/254 @ .050 and 294/300.......... The cam has been upgraded this year, to a solid roller with an additional 20% lift (.600"/.606"), about same durations and tighter lobe centers so overlap goes from 26.5 degrees @ 0.050 lift to 31 degrees.

So based on this information and if high point of lift is somewhat symmetrical, the LSA is 110 degrees, right?

That helps the midrange torque from all the information I find. I experience the same wider power band in the mid range but on a smaller level with very conservative grind with tighter lobe centers with older style heads. With a conservative street grind fast ramps cut down on overall overlap @ .006" a lot while overlap @.050" is a bit more.

[Joe C.]

Re: 327 Dynoruns

So based on this information and if high point of lift is somewhat symmetrical, the LSA is 110 degrees, right?

That helps the midrange torque from all the information I find. I experience the same wider power band in the mid range but on a smaller level with very conservative grind with tighter lobe centers with older style heads. With a conservative street grind fast ramps cut down on overall overlap @ .006" a lot while overlap @.050" is a bit more.

That's right. You have correctly calculated the lobe separation angle at 110 degrees.

It's more practical to use tighter LSA (compared with those of the vintage cams that we're used to seeing at 112, 114, 116) with fast ramps because the seat-to-seat (J604d) durations are smaller than those of cams with slow ramps, given equal durations @ 0.050" valve lift, and so the "effective" overlap is less. Modern circle track and drag cams normally use LSA's of only 106 degrees. What you say about more torque in the midrange holds true of any cam with fast ramps as compared to one with lazy ramps. In addition to the boost in midrange torque, the duration of the elevated torque is extended both in the low and the high range, and again, this holds true for all cams with faster ramps as opposed to those with lazy ramps. The reason for all of these benefits is because the 0.050" durations are closer to the J604d durations. Fast ramps reduce the amount of pressure bleed off at low valve lift and allow the engine to develop higher cylinder pressures at all speeds. Roller cams have no downside, other than their higher cost.