[chevy302builder18]

ok i heard strange things about performance on this application, i heard back pressure on these ford V8s make em more fuel efficient and give em better hp? Is this true cause i wanna do dual exhaust

[1931 steve]

You should be fine as long as you use cat converters. Plenty of aftermarket cats out there that flow better than stock.

Steve

[Valkyrie5.7]

Don't expect to gain a lot of horsepower with a decent exhaust system on these cars, although they do sound nice with set of mufflers. T-bird should already have a factory dual exhaust, albeit one branched from a y pipe. The 2v npi 4.6L isn't known for it's low end torque (factory rated 285ft lbs at 3500rpm IIRC), so don't add to the problem by forgetting to include a crossover pipe (H or X).

Avoid shorty headers too, just stick with the stock manifolds if you're not going to step up to full-lengths.

I'd start with a 3.73 or 4.11 ring gear and a PI intake if it were my car though.

[chevy302builder18]

thanks guys, i already knew the exhaust manifolds were factory headers, so the manifolds wont be an issue this car is wicked fun, great gas milege, 15 to 20 in town, 25-30 highway (thanks to overdrive), i drive it almost everyday purring, just i wanna hear it rumble, the X pipe wouldnt be bad or the H pipe?

[Valkyrie5.7]

Originally Posted by chevy302builder18

thanks guys, i already knew the exhaust manifolds were factory headers, so the manifolds wont be an issue this car is wicked fun, great gas milege, 15 to 20 in town, 25-30 highway (thanks to overdrive), i drive it almost everyday purring, just i wanna hear it rumble, the X pipe wouldnt be bad or the H pipe?

You're not going to see much of a difference power wise. Don't go any bigger than 2.5" pipe for duals. I've been told the X pipe will sound more raspy and H pipe will sound deeper. I personally don't really hear a noticiable difference between the two so just do whatever fits easier, with two high flow cats and a pair of your favorite mufflers

[chevy302builder18]

yea its got that IRS system in the back, good for top speed but i heard some half shafts like corvettes irs could go out if to much power is this true?

[Valkyrie5.7]

All I know about the Thunderbird IRS is this:

The v8 and S/C v6 models got an 8.8" differential, The IRS unit is all iron, and very heavy. It's extremely similar to the one in the Lincoln Mark VIII (it's MN12 platform sibling) and that a lot of the Mark VIII's lighter aluminum components swap over.

I don't know anything about it being good for top speed other than the fact that it might be more stable because it's independant, but I do know that it rides a heck of a lot better than the log wagon ride you get in the mustangs with the SLA 8.8"

I'm not very well versed on the MN12 Platform, just the Modular motors but I've personally never heard of half shaft issues. On the other hand, I've not heard of very many fast MN12 birds either compared to the Panther and SN95 platform cars.

[chevy302builder18]

ok now thats some good news