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OK, I'm in the process of doing a PI swap, and in the process doing some P&P heads, Comp cams (262AH), etc...So it won't be a stock PI when I go to install it. My current frustrations have to be that I live in a crap emission state. I know there is a problem with lack of back pressure, what happens with too much? If I use the stock exhaust?
 

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Nick said:
OK, I'm in the process of doing a PI swap, and in the process doing some P&P heads, Comp cams (262AH), etc...So it won't be a stock PI when I go to install it. My current frustrations have to be that I live in a crap emission state. I know there is a problem with lack of back pressure, what happens with too much? If I use the stock exhaust?
Not enough back pressure will cause a loss of torque Too much will cause a loss of overall performance - I found that my 97 liked the stock manifolds and cats w/ a dynomax catback
 

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Discussion Starter #3
Thanks for responding. I'm wondering if I'd be shortening the life of the engine by putting on the stock tubes. Since I'm having some P&P work on the heads and larger valves, and cams put in.
 

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You're not really gaining a whole lot by PnP the heads and swapping the cams if you're just going to choke it down to the stock exhaust system. I'd bet you'll be giving up in the neighbourhood of 30hp and nearly an equal amount of torque, by doing so. As it sits, the '96-'97's are already down 10-15hp over the '96-'98 Mustangs because of the difference in their exhaust systems. Now you're going to try to force even more air through the engine, but still have the cork in the outgoing end.
 

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Discussion Starter #5
yeah, my problem I pulled the pin before thinking. LOL go figure. I have been planing the PI swap and sent off for the engine work, then decided to look at the exhaust setup. Well, long story short, I live in California, and it seems to maintain emissions legal, I'm screwed. I post much of it in the exhaust forum.

Why I posted here was more of a concern, if I was doing damage to the engine by restricting it.

I ordered the Kooks headers, but again not legal...so I might be tossin them up for sale to get the JBAs in the near future.
 

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I'd suggest having a better exhaust system made and holding on to the stock exhaust so you can swap them out when its emission testing time, but I have a feeling its not that simple.
 

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Mod Motor Cat said:
You're not really gaining a whole lot by PnP the heads and swapping the cams if you're just going to choke it down to the stock exhaust system. I'd bet you'll be giving up in the neighbourhood of 30hp and nearly an equal amount of torque, by doing so. As it sits, the '96-'97's are already down 10-15hp over the '96-'98 Mustangs because of the difference in their exhaust systems. Now you're going to try to force even more air through the engine, but still have the cork in the outgoing end.
Don't the mustangs have like...6 cats and two mufflers? I didnt think their exhaust was THAT much better. I understood the hp gain was due to tuning and a solid axle..
 

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weswing04 said:
Don't the mustangs have like...6 cats and two mufflers? I didnt think their exhaust was THAT much better. I understood the hp gain was due to tuning and a solid axle..
Yeah, some year mustangs had 6-cats (a couple of them were resonators), but it's still a true dual, larger diameter exhaust. The Mustang before '98 would have been tuned nearly the same as the MN12 and no real performance gain would have been gained there. Only in '98 did they get a more aggressive EEC tune and slightly freer flowing exhaust....which gave them another 10hp, for a total of 225, to the MN12's 205.

The drive train (transmission, rear end, transfer case, etc) would only affect a vehicle that was being rated at the rear wheels. The factory SAE numbers are not and therefore the Mustang having a solid axle over the MN12’s IRS won't post any different horsepower numbers.
 

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Discussion Starter #9
I think I saw an ad in MM&FF by Kenne Bell, stating with there 14psi blower on a mustang gt would be over 500HP with stock exhaust. I know the GTs run more cats than us, but do they have that much more flow? I'm wondering if I could get away with 300HP with stock exhaust.
 

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Nick said:
I think I saw an ad in MM&FF by Kenne Bell, stating with there 14psi blower on a mustang gt would be over 500HP with stock exhaust. I know the GTs run more cats than us, but do they have that much more flow? I'm wondering if I could get away with 300HP with stock exhaust.
A blown car and a N/A car are too totally different stories though. You might eek out 300hp at the flywheel in N/A trim with the stock exhaust and all the bolt-ons along with a full PI swap, but you'll never see that amount at the rear wheels. Not choking through the stock system from the manifolds back anyway.

....and Kenne Bell adds should be taken with a grain of salt. The 500rwhp GT they claim also runs their full induction components, with 100-octane gas and 23* of timing. Not something your average owner could even consider using on the street for daily driver usage!
 

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I dunno, my 98 GT had 6 cats and that was one crappy exhaust. I think the biggest gain over the bird is that it had a better setup after the cats and it was shorter.
How much work can you do to the exhaust after the cats and get away with?
 

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Discussion Starter #12
I think after the cats I should be able to toss on any 50 state legal muffler for the most part.
 

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Mod Motor Cat said:
The drive train (transmission, rear end, transfer case, etc) would only affect a vehicle that was being rated at the rear wheels. The factory SAE numbers are not and therefore the Mustang having a solid axle over the MN12’s IRS won't post any different horsepower numbers.
this is true... i feel stupid now, wasnt even thinking of that :)
 
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