Scissors

I know a few folks have good information. Any word on a change in firing order? I know that the change from the LT1 to the LS1's order resulted in a (according to many) inferior exhaust tone.

LT1/LT5: 1-8-4-3-6-5-7-2
LS1: 1-8-7-2-6-5-4-3

RandyB

1-3-7-2-6-5-4-8

Hehe, sure sounds good in the 'other' brand. Personally, I like the sound of the LS1 over the LT-1/LT-4, particularly the Z06.

logansowner

They are saying the fire sequence allready? :crazy:

SWCDuke

Firing order has no impact on sound. Regardless of the firing order option selected, it's always going to be the inner two cylinders on one bank and the outer two on the opposite banks at 180 degree intervals.

Duke

LymanSS

Duke,
I've been wondering about this. Everyone attributes a lot of sound to firing order, but from what you say, it sounds like it has minimal impact. What (other than exhaust) has the biggest effect on exhaust sound? Valves? Number of cylinders? Anything else?

Scott

Light84vette

probably displacement compared to the size of the exhaust pipes. and maybe back pressure, yeah its back pressure, take off your cats and you'll wake up everyone in the neighbor hood. :yesnod:

SWCDuke

The basic sound of an engine is a function of the number of cylinders and how those cylinders are bunded into separate pipes and the relative firing orders.

The sound of any cruciform crankshaft V-8 will be about the same depending on exhaust configuration. For example, a vintage 327 FI has a more gutteral sound because there is no exhaust crossover in the exhaust or via the heat riser, so you hear the uneven firing interval from each bank. Modern V-8s have no heat riser, but almost always have a crossover to allow all eight primarly pulses to reach each side of the exhaust. This results in an even and higher frequency, which is more "pleasant" to the ear and better for passing the EPA and state noise standards. A Ferrari V-8 has a flat crank, so each bank is like a four-cylinder engine with 180 degree exhaust intervals, and the two banks together are essentially two fours 90 degrees out of phase.

In a cruciform crank V-8 each isolated bank has uneven firing intervals of 0-90-180-270, or a variation of this.

Beyond this details of the exhaust system design such as pipe diameter and muffler configuration affect the quality of the sound.

A big factor in the amount of noise is the rate at which the valve opens - the quicker it opens, the steeper the initial blow down shock. That's why a rotary will practically blow out your ear drums as the exhaust port is uncovered very quickly relative to the rate of flow area increase in a poppet valve design, and four-valve engines typically have a steeper initial shock than a two-valve because the expose exhaust flow area quicker

Duke