Turning in my man card... I want to make the GTRA quieter... best method?

[MarkMc26]

Originally Posted by jmarsey

Sure Mark and good to see some life here. I'll post some pics of the 4-2-1 system I just finished. I thought about a 180deg crossover but would have required modifying the passenger foot box to do a balanced system.


John

A balanced system...what's that? lol...What I'm building is anything but balanced, but it won't matter with the existing Tru-Ram exhaust manifolds that aren't exactly designed for optimum scavenging. Driver side 2.5" crossover will be about 40" longer than the passenger side route to the muffler, but oh well. Before my cam and intake swap, this car made roughly 25-30 rwhp too much for NASA TT3 (10:1 lbs:rwhp ratio) and embarrassingly low torque with the 7500 rpm Victor Jr. intake and some 7200 rpm COMP cam (all installed by the previous owner, as was his 6500 rpm rev limiter). It now has a more torque-friendly COMP cam and a Performer RPM dual-plane intake that should work better in the 4000-6500 range on this 5.3L. I'll post some exhaust pics after it's finished, hopefully next week. They might not be helpful if you don't have an LS in one of these cars, though.

While I'm waiting for another exhaust elbow to arrive, I'm working on a steering column mount for my new Holley 7" digital dash that simply plugs into my Terminator EFI and will incorporate various switches/knobs in an effort to get rid of that center panel over the shifter as well as the redundant gauges/hoses/wiring all over the place. Kill switch and fire bottle pull handle will eventually move to the A-pillar bar for easier access from outside the car. Brake pressure gauges will get mounted to the 1"x1" dash crossbar.

Mark

[MarkMc26]

Posting to a mostly-defunct thread, but whatever...

I finished building the single 3" exhaust for the LM7/LS swap, keeping only the Tru-Ram exhaust manifolds that came with the car, and tested it at Sebring last weekend. It didn't fall off and it was relatively quiet inside the car (the quietest solution so far, anyway); so, I'll file it under "not a failure" for a change. I'm still using Decibullz earplugs, which are physically uncomfortable and need to go. At idle, the loudest thing on the car (by far) is the Bosch 044 fuel pump.

Various 2.5" elbows from Dynomax go from the manifolds to the Y-pipe. A Flowmaster Y250300S Y-pipe that was in my exhaust scrap pile was used to join the 2 sides. I'm still using a Flowmaster 52573 70-series muffler for SUVs/trucks/motorhomes/towing, which comes in 2.5" in/out but can easily be made 3" or larger by trimming the tapered inlet/outlet (although, note that the internal center tube is 3" ID). A stock 1999-2004 Mustang GT 3" OD stainless exhaust tip was repurposed as the side outlet in front of the RR tire. A pair of 3/8" rod end hangers holds the muffler off the ground, while a smaller 1/4" rod end brace keeps it from swaying side-side.

I built a 20 gauge aluminum heat shield where the crossover pipe goes over the bellhousing, to protect the engine wiring harness, with this Thermo Tec reflective heat barrier material stuck to the bottom side of it. The top side of the heat shield is still hot to the touch after a 20 minute session in 80*F weather; I'll be ordering a set of temperature stickers to see how hot it gets. The wiring appears to be fine after a weekend of use, though.

The muffler gets pretty hot...almost every bit of Flowmaster-applied paint (likely "good enough" for SUVs/trucks/RVs/towing) was torched off, and it's down to bare metal now. I might drop the money for ceramic coating once I'm 100% sure that I don't need to make any modifications or repairs.

It's good to not have any noise on the driver's side. It's still a bit loud on the passenger's side, although my bystander buddy said that he couldn't hear the car approaching on track. This is probably as good as it will get without adding a tailpipe (which defeats my intent of keeping the exhaust away from the fuel cell).

Hopefully, I can get the car on the dyno this week to see what I'm working with.

Mark

Driver's side; U-turn from manifold under steering shaft, then up/over bellhousing:


Passenger's side; you can slightly see the pipe angling downward after the bellhousing crossover (no heat shield in this pic):


Passenger's side; both pipes, pre-merge:


Y-pipe in body side tunnel, with rod end hanger and muffler in background (RIP paint):


Rear of muffler, with the other rod end hanger and side brace:

[MarkMc26]

If they are useful, here are some photos of the heat shield above the crossover pipe.

Things that weren't done yet when these photos were taken:

1. The white protective plastic wasn't peeled off
2. The mounting holes weren't drilled
3. The adhesive heat reflective material wasn't installed on the underside

The top of my right shoe felt like it was a bit warm when I got to impound after an afternoon session; I couldn't recall if it was warmer than usual or not. In any case, I wasn't uncomfortable in the car with the heat level.

Mark

Driver's side; shield is attached to the angled 1x1 chassis member on the right with a square U-bolt:


Passenger's side; shield is attached to the angled 1x1 chassis member on the left with a square U-bolt:


View from the passenger's side; 1" to 1 1/2" gap between exhaust and shield for most of it, although there's about 1/2" to 3/4" in a non-critical spot: