My HP 1.6 Scirocco is too close to the sound limit for comfort so I need to revise things.
Right now it's running an L shaped system, 2.25" pipe, exiting in front of the left rear, with a short bullet glasspack (Dynomax) in the short leg of the L and a turndown on the exit. Turndown is within (barely) the car pan view, basically right under the rocker.
My local track, Summit Point, has sound on the left as many do, thus presumably much of my problem. But the fuel pump etc live in the same area on the right, making a right exit less attractive.
Would ideally prefer to minimize changes that could affect engine tune as things are running well as is. Car is a few pounds heavy so would prefer to minimize weight gain. Car is closed and I prefer not to breathe much exhaust gas. I'm also a cheapskate whenever possible.
Rules allow exhaust exit anywhere aft of the halfway point of the wheelbase as I read them, which I presume means directly under the car is OK as long as far enough back.
One simple light option would be to swing the muffler inline with the car and dump the exhaust straight down or even slightly to the right, close to the car centerline just ahead of the rear axle. I'm not sure how much this would lower sound readings, though I've heard that it does and it stands to reason that it should. I'm probably more concerned that it will result in my breathing more CO than I want to....?? Or maybe I'm just used to seeing exhausts running to the car perimeter..???
The other option is to run the exhaust in the stock location, up and over the rear (twistbeam) axle and out the back, presumably with a RH turn on the exit. There's plenty of room under the rear for the muffler (where the stock one lived) and I assume that's where I'd put it. This adds a bit of weight and a fair bit of length to the system.
A third option is to add a second glasspack to the existing layout, in the fore-aft section in front of the existing L bend. Tech support at Walker estimated that this would take 2-3dBa off existing reading which seems like enough. For reference, he estimated that a longer similar glasspack instead of the current one would only help by about 1dBa which seems inadequate.
Also - the cavity in front of the axle, where the current muffler sits, is fairly large (stock fuel tank was here) so a bulky alternative muffer is a possibility as long as it is light.
One question - has anyone played much with secondary (ie tailpipe length) on LP Prod engines w/ minimal mufflers? Are they very sensitive (wrt power curve) to changes in length?
Thanks for any thoughts!
Al Seim
HP VW Scirocco 1.6
Right now it's running an L shaped system, 2.25" pipe, exiting in front of the left rear, with a short bullet glasspack (Dynomax) in the short leg of the L and a turndown on the exit. Turndown is within (barely) the car pan view, basically right under the rocker.
My local track, Summit Point, has sound on the left as many do, thus presumably much of my problem. But the fuel pump etc live in the same area on the right, making a right exit less attractive.
Would ideally prefer to minimize changes that could affect engine tune as things are running well as is. Car is a few pounds heavy so would prefer to minimize weight gain. Car is closed and I prefer not to breathe much exhaust gas. I'm also a cheapskate whenever possible.
Rules allow exhaust exit anywhere aft of the halfway point of the wheelbase as I read them, which I presume means directly under the car is OK as long as far enough back.
One simple light option would be to swing the muffler inline with the car and dump the exhaust straight down or even slightly to the right, close to the car centerline just ahead of the rear axle. I'm not sure how much this would lower sound readings, though I've heard that it does and it stands to reason that it should. I'm probably more concerned that it will result in my breathing more CO than I want to....?? Or maybe I'm just used to seeing exhausts running to the car perimeter..???
The other option is to run the exhaust in the stock location, up and over the rear (twistbeam) axle and out the back, presumably with a RH turn on the exit. There's plenty of room under the rear for the muffler (where the stock one lived) and I assume that's where I'd put it. This adds a bit of weight and a fair bit of length to the system.
A third option is to add a second glasspack to the existing layout, in the fore-aft section in front of the existing L bend. Tech support at Walker estimated that this would take 2-3dBa off existing reading which seems like enough. For reference, he estimated that a longer similar glasspack instead of the current one would only help by about 1dBa which seems inadequate.
Also - the cavity in front of the axle, where the current muffler sits, is fairly large (stock fuel tank was here) so a bulky alternative muffer is a possibility as long as it is light.
One question - has anyone played much with secondary (ie tailpipe length) on LP Prod engines w/ minimal mufflers? Are they very sensitive (wrt power curve) to changes in length?
Thanks for any thoughts!
Al Seim
HP VW Scirocco 1.6
