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I forget you're here in SoCal as well. You're in the Burbank area if memory serves correct? You're about 1-1/2hrs (west) from me. Perhaps you can provide some insight as to what to do / have done to keep your mods CA legal.
Well, I lower my expectations (hahaha), mostly from reading about how expecting 400+hp from these 2v 4.6s is a pipe dream. I go with what is listed as smog-legal here. So the JBA shorty headers were the only option, as was the Magnaflow cat pipe replacement, though that thing flows better than the stock set-up for sure (90 degree bends at the cats stock). Same with the headers, and they sound waaay better. Add the dual exhausts (after the 3rd cat) with Flowmaster mufflers and it's the best that stock-approved is going to get. I could go with 3" pipes after the cats but what for, I'm not racing this thing. I'm only trying to get it to where Ford should have had it new (larger Mustang). To that end I also got the transmission J-modded, I have a Truetrac rear, bigger radiator, urethane bushings almost everywhere. Up next is the Mustang hubs and rims and a 1-piece driveshaft.

My biggest move will be getting '97 NPI heads and getting them ported with new cams. From what I've read PI heads are much better than NPI heads stock but ported NPI heads are better than PI heads, and as good or better than ported PI heads. So I will go that route. Around 300hp at the end? That better be enough for me because to try for more requires loads of money for something that I will, again, not race. I assume I will have to reprogram the computer at that point. Eventually I will get a new block/forged crank/rods when I'm in the mood to have everything torn out and put back in. Not ready for that nightmare yet. Maybe new pistons especially if compression is an issue.

I want a cool driveable car. That means it's comfortable and sane driving to and from work or on the road for 2 hours. I can't live with a shaking overheating beast that's too loud for my music. A car that my mom or uncle can ride in if we go visit friends somewhere but doesn't bore the **** out of me. Not an embarrassing "What?!" conversation because my passengers can't talk over the roar of the car and the road bumps keep shaking **** loose from their hands because my suspension is set for a racetrack. No thanks.

For the oh **** this thing is scary car I still hold out hope of building up a modernized '71 Dodge Challenger, though if I stuck with Ford I'd get a '70 Torino (Cobra), the car that our Thunderbirds are actually descended from (these MN12s don't say "Thunderbird" at all to me, not like the 2002 reboot). If you look at a '95 Thunderbird and squint you can almost see a modern Torino. I'm even thinking of getting rear window louvers because of the similarity.





One slight change to the passenger side windows shape, a different front bumper/grille/headlights style, it would totally be a modern Torino.
 

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1994 Cougar XR7 DOHC/5-Speed
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Slow loud cars still piss me off. If you're going to sound like you're at the dragstrip, could you at least move faster than the Prius in the lane next to you so I can be on my way?
I guess it depends on the relatively of speed and just how loud we’re talking. I don’t like open headers loud on street cars at all, that’s all noise, and I don’t like POS junkers with no exhaust or holes in it, that’s just disrepair, but the sound of headers + H pipe and flow master 40s on a basically stock 5.0 Foxbody Mustang is A-ok to me, regardless of its high likelyhood to get get beaten by a new V6 Camry with nearly 100 more horsepower on tap.

When EVs get truly mainstream popular and most accelerate like Teslas should every moderately powered gas powered performance car of the past still on the road cork their pipes because they’re “slow” by new standards?
 

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My red car was a straight pipe until it got to the rear mufflers, which are still stock SC mufflers. Besides that, LT heads and open pipe straight back.

@MadMikeyL couldnt believe I still had stock mufflers on when I took him for a ride. It does sound decent.


But those are getting removed in this new build.
 

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Well, I lower my expectations (hahaha), mostly from reading about how expecting 400+hp from these 2v 4.6s is a pipe dream. I go with what is listed as smog-legal here. So the JBA shorty headers were the only option, as was the Magnaflow cat pipe replacement, though that thing flows better than the stock set-up for sure (90 degree bends at the cats stock). Same with the headers, and they sound waaay better. Add the dual exhausts (after the 3rd cat) with Flowmaster mufflers and it's the best that stock-approved is going to get. I could go with 3" pipes after the cats but what for, I'm not racing this thing. I'm only trying to get it to where Ford should have had it new (larger Mustang). To that end I also got the transmission J-modded, I have a Truetrac rear, bigger radiator, urethane bushings almost everywhere. Up next is the Mustang hubs and rims and a 1-piece driveshaft.

My biggest move will be getting '97 NPI heads and getting them ported with new cams. From what I've read PI heads are much better than NPI heads stock but ported NPI heads are better than PI heads, and as good or better than ported PI heads. So I will go that route. Around 300hp at the end? That better be enough for me because to try for more requires loads of money for something that I will, again, not race. I assume I will have to reprogram the computer at that point. Eventually I will get a new block/forged crank/rods when I'm in the mood to have everything torn out and put back in. Not ready for that nightmare yet. Maybe new pistons especially if compression is an issue.

I want a cool driveable car. That means it's comfortable and sane driving to and from work or on the road for 2 hours. I can't live with a shaking overheating beast that's too loud for my music. A car that my mom or uncle can ride in if we go visit friends somewhere but doesn't bore the ** out of me. Not an embarrassing "What?!" conversation because my passengers can't talk over the roar of the car and the road bumps keep shaking ** loose from their hands because my suspension is set for a racetrack. No thanks.

For the oh **** this thing is scary car I still hold out hope of building up a modernized '71 Dodge Challenger, though if I stuck with Ford I'd get a '70 Torino (Cobra), the car that our Thunderbirds are actually descended from (these MN12s don't say "Thunderbird" at all to me, not like the 2002 reboot). If you look at a '95 Thunderbird and squint you can almost see a modern Torino. I'm even thinking of getting rear window louvers because of the similarity.

View attachment 46193

View attachment 46194

One slight change to the passenger side windows shape, a different front bumper/grille/headlights style, it would totally be a modern Torino.

The NPI block with PI heads gives a compression boost over an inch of Mercury. That's a minimum 4% power gain over the entire power curve.
I would think that negates the NPI ported head flow gains.
I understood a PI swap, done right to be pretty much a 75 to 100hp gain and a net 300hp 2v with a stock short block.
Am I wrong?

I don't see any way to get a 2v to 400 HP without a major power adder and probably rotating upgrades.
Just as I don't see a 4v getting to 500hp any other way. A 400hp NA 4v is likely possible I think, but 500 is out of reach.
 

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How about these options?

So what about capping off my TruBendz kit with a set of original stock:
95 Cougar 4.6 mufflers
97 Mark VIII base mufflers
Or:
I have the resonators from both cars, they can be used as mufflers with some pipe added.

I know I need mufflers, it is VERY LOUD now.
 

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1991 Mercury Cougar LS 5.0 in restoration
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The Cougar mufflers have to small of inlets and would choke the exhaust at the end. You don't want to do that. If you want relatively cost effective, thrush welded mufflers at a local AutoZone, pepboys, etc. They're decent for around $40-50 each. Basically a cheaper flow master. Just make sure you have tips just past the bumper
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I understood a PI swap, done right to be pretty much a 75 to 100hp gain and a net 300hp 2v with a stock short block.
Am I wrong?

I don't see any way to get a 2v to 400 HP without a major power adder and probably rotating upgrades.
A PI swapped NPI will net at most a 50 HP gain over a factory NPI when properly tuned. Massaged heads, a fatter cam, and other supporting mods are needed to approach 300.

It is possible to get a 2v to 400 HP N/A. TFS heads makes it much easier than it was before they came to market, but it will still need to spin north of 7000-7500 to do it.
 

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Well, I lower my expectations (hahaha), mostly from reading about how expecting 400+hp from these 2v 4.6s is a pipe dream. I go with what is listed as smog-legal here. So the JBA shorty headers were the only option, as was the Magnaflow cat pipe replacement, though that thing flows better than the stock set-up for sure (90 degree bends at the cats stock). Same with the headers, and they sound waaay better. Add the dual exhausts (after the 3rd cat) with Flowmaster mufflers and it's the best that stock-approved is going to get. I could go with 3" pipes after the cats but what for, I'm not racing this thing. I'm only trying to get it to where Ford should have had it new (larger Mustang). To that end I also got the transmission J-modded, I have a Truetrac rear, bigger radiator, urethane bushings almost everywhere. Up next is the Mustang hubs and rims and a 1-piece driveshaft.

My biggest move will be getting '97 NPI heads and getting them ported with new cams. From what I've read PI heads are much better than NPI heads stock but ported NPI heads are better than PI heads, and as good or better than ported PI heads. So I will go that route. Around 300hp at the end? That better be enough for me because to try for more requires loads of money for something that I will, again, not race. I assume I will have to reprogram the computer at that point. Eventually I will get a new block/forged crank/rods when I'm in the mood to have everything torn out and put back in. Not ready for that nightmare yet. Maybe new pistons especially if compression is an issue.

I want a cool driveable car. That means it's comfortable and sane driving to and from work or on the road for 2 hours. I can't live with a shaking overheating beast that's too loud for my music. A car that my mom or uncle can ride in if we go visit friends somewhere but doesn't bore the ** out of me. Not an embarrassing "What?!" conversation because my passengers can't talk over the roar of the car and the road bumps keep shaking ** loose from their hands because my suspension is set for a racetrack. No thanks.

For the oh **** this thing is scary car I still hold out hope of building up a modernized '71 Dodge Challenger, though if I stuck with Ford I'd get a '70 Torino (Cobra), the car that our Thunderbirds are actually descended from (these MN12s don't say "Thunderbird" at all to me, not like the 2002 reboot). If you look at a '95 Thunderbird and squint you can almost see a modern Torino. I'm even thinking of getting rear window louvers because of the similarity.

View attachment 46193

View attachment 46194

One slight change to the passenger side windows shape, a different front bumper/grille/headlights style, it would totally be a modern Torino.
Man that car looks great! This is exactly my plan for my car. What wheels are those? How did you get the paint to look that good? Did you even have to repaint it?
 

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I guess it depends on the relatively of speed and just how loud we’re talking. I don’t like open headers loud on street cars at all, that’s all noise, and I don’t like POS junkers with no exhaust or holes in it, that’s just disrepair, but the sound of headers + H pipe and flow master 40s on a basically stock 5.0 Foxbody Mustang is A-ok to me, regardless of its high likelyhood to get get beaten by a new V6 Camry with nearly 100 more horsepower on tap.
Oh, I'm not talking about legitimately loud cars with headers like musclecars, I mean more the ricer cars, the coffee-can mufflers, and the modern Challengers/Mustangs/Camaros with the obnoxious exhausts but otherwise no faster than before. And I mean specifically those drivers who insist on being the loudest but are more or less the slowest on the road. Get in the slow lane!

When EVs get truly mainstream popular and most accelerate like Teslas should every moderately powered gas powered performance car of the past still on the road cork their pipes because they’re “slow” by new standards?
Depends. The louder and more "race car" you sound, the faster you better be compared to the other cars around you. Regular "loud" cars that are really just hearing the engine itself (headers + mufflers), like old-school musclecars, are fine, that's how they should sound. Not near-silent but not RRRROOOOOOOORRRRRRGGGLLRLRRRRRLLL, either.
 

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Man that car looks great! This is exactly my plan for my car. What wheels are those? How did you get the paint to look that good? Did you even have to repaint it?
Sorry, didn't mean to mislead, that blue Thunderbird isn't mine, though I think that's what my first Thunderbird looked like new (minus the rims). I just found that pic online and it's the perfect representation of a blue Thunderbird like mine was. I crashed my blue one (hydroplaned on the freeway years ago) and have since replaced it with another '95 Thunderbird, this time silver. Hate that color, I will paint it a 2005 GT color, I believe. I will also get Mustang SVE Mach 1 rims because they're the closest thing I can find to Magnum 500 rims that will fit my car with a hub swap (so, similar to that Torino's rims). Just have to decide, 17x8 or 17x9? Seems that there's an issue with offset for our cars? I can't tell yet.
 

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The NPI block with PI heads gives a compression boost over an inch of Mercury. That's a minimum 4% power gain over the entire power curve.
I would think that negates the NPI ported head flow gains.
I understood a PI swap, done right to be pretty much a 75 to 100hp gain and a net 300hp 2v with a stock short block.
Am I wrong?
That's why Part 2 of my eventual engine plan will involve different pistons with a compression bump. I don't suppose there's much to be gained with thinner head gaskets (if that's even possible, don't know how thin they are already). I am against milling heads or blocks for compression changes because that's irreversible and alters where the heads sit on the block. Much better to change the piston shape. Much harder to change pistons, I know, so that will get done when I'm in the mood for the connecting rod/crank/block upgrades. I can wait, I'm not racing this thing. I assume that piston design for the 4.6s has improved since 1995. It would be sad if it hasn't.

From everything I've read/heard, ported NPI heads flow as good or better than ported PI heads, and definitely better than stock PI heads. The compression drop is the issue but with the cams and different pistons it will be what I want.
 

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A PI swapped NPI will net at most a 50 HP gain over a factory NPI when properly tuned. Massaged heads, a fatter cam, and other supporting mods are needed to approach 300.

It is possible to get a 2v to 400 HP N/A. TFS heads makes it much easier than it was before they came to market, but it will still need to spin north of 7000-7500 to do it.
A stock 99 GT nets 260hp.
Add an inch of compression and it's no longer a 260hp engine is.
How can that math work? What am I missing here?
an NPI makes 210
add 50 for PI heads to 260net
add 4% for compression bump for 273+ net.
I assume a good degree job, a couple bolt ons like headers, TB, CAI, UD, and a good tune and Bam that's 300hp.

I must be missing something, what is it?

Along that pattern, what do you suppose my DOHC output is?
I have a 0.75 UD Cobra spec(so it says) Harmonic balancer.
I have the factory manifolds, but full dual exhaust. Other than that, stock.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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A stock 99 GT nets 260hp.
Add an inch of compression and it's no longer a 260hp engine is.
How can that math work? What am I missing here?
an NPI makes 210
add 50 for PI heads to 260net
add 4% for compression bump for 273+ net.
I assume a good degree job, a couple bolt ons like headers, TB, CAI, UD, and a good tune and Bam that's 300hp.
The GT also has a vastly different program, exhaust manifolds and cat-back system than an MN12. :)

The top-end bolts ons, as Matt has said, do nothing for power. The restriction is the heads themselves. I had all the bolt ons plus stage 2 ported heads and cams, and barely made it to 300 crank HP.
 

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Point taken.
Those bolt ons only contribute in conjunction with accompanying components and proper integration(tune). That said, they are not worthless extra weight, but taken alone, yeah you are right.
 

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1994 Cougar XR7 DOHC/5-Speed
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Those bolt ons only contribute in conjunction with accompanying components and proper integration(tune).
Still nope.

The stock TB and plenum simply aren’t restrictive for the flow capabilities of the PI intake itself. If the intake tract becomes a roadblock for making power it’s going to be the manifold, and any manifold that is going to actually flow better than a PI intake(eg not the typhoon) won’t accept the TB, plenum, intake tube anyway, they’ll be outgrown at the exact same moment. A tune doesn’t magically make them make power either, there’s a reason these fall into the “bolt ons” catagory, and it’s because all that’s involved in their installation is to literally just bolt them on.

Throttle body “upgrades” only have the seat of the pants effect of changing transient throttle response, since for every bit of pedal travel a larger diameter blade creates a larger opening than before, at wide open does it really matter if the throttle body is the size of a manhole if the manifold hole is only about 65mm in diameter? Plenums are misleading to begin with since they’re really not plenums at all, they’re simple 90° elbows on the way to the actual manifold plenum in the valley of the engine, theoretically they can increase plenum volume but what kind of meaningful volume can truly be be added in that little space? And what would it even do since it’s still not technically in the plenum chamber of the manifold?

This is all a problem created by aftermarket companies who made their names with 5.0 Fox and SN95 Mustangs and tried to stay in the late model market when the 4.6 came out, and applying the logic that worked for the 5.0 never really worked because few of these companies really cared to understand the 4.6s. CAI kits, TBs plenums, UDPs and headers were all there was available for the 4.6 for almost a decade, cams seemed to come around in the mid 00s but heads and intake limited the potential of hotter grinds and, the best heads and intakes were all Ford engineered(SVO, Bullitt) and not supported for long, Trick Flow is still a newcomer to these engines and the twisted wedge heads came out, what? Ten years ago?

Magazines in the 2000s perpetuated the “10-20 horsepower” from bolt ons gains, and just so happened to advertise every product they tested, hmm. I used to have a subscription to MM&FF before I even had a license at the time and even then it made me laugh when they’d take an older SN95 to do all this stuff to and gently brush past the fact that the original plugs and wires had 120,000 miles on them when demonstrating the gains of their MSD coil packs and wires, or changing out the factory intake tract including the dirty old air filter and replacing it with the shiny new chromed metal pipe, oiled cone filter with a marginal heat shield(or not) and dyno the car with the hood open to see the mad 15 horsepower gains. Wow! Adding a tune on top of this stuff doesn’t prove anything either, it’s well known the factory tune leaves power on the table, usually commanding too much fuel at WOT and “safe” spark to avoid pinging. Apply the same the same tune to a 100% stock car and you’ll see indistinguishable results from the one with those bolt-ons.

Note that I have had all of these parts in a combination of “see for myself” and underhood looks(hey, I never said aftermarket plenums/TBs don’t “look” better. I kept running underdrives on my current engine because the damper is the SFI type and doesn’t hurt anything and to simply slow down the accessories a little for longevity, and even that I’m skeptical of the difference they make.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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^^ The man speaks the truth! :)

FWIW, when I was first tuning my H/C/I combo over 8 years ago, I had the factory TB/plenum on the car. I had measured airflow at WOT many times and knew exactly what the airflow at WOT at a given RPM would be. When I put a P&P'd 70mm TB and plenum on the car I naturally measured airflow data to compare to the stock parts and........ no difference. Sure enough there was an increase in throttle response due to the greater opened surface area for a given blade angle... but the data proved absolutely no power gain, even on stage 2 heads and cams.
 

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Still nope.

The stock TB and plenum simply aren’t restrictive for the flow capabilities of the PI intake itself. If the intake tract becomes a roadblock for making power it’s going to be the manifold, and any manifold that is going to actually flow better than a PI intake(eg not the typhoon) won’t accept the TB, plenum, intake tube anyway, they’ll be outgrown at the exact same moment. A tune doesn’t magically make them make power either, there’s a reason these fall into the “bolt ons” catagory, and it’s because all that’s involved in their installation is to literally just bolt them on.

Throttle body “upgrades” only have the seat of the pants effect of changing transient throttle response, since for every bit of pedal travel a larger diameter blade creates a larger opening than before, at wide open does it really matter if the throttle body is the size of a manhole if the manifold hole is only about 65mm in diameter? Plenums are misleading to begin with since they’re really not plenums at all, they’re simple 90° elbows on the way to the actual manifold plenum in the valley of the engine, theoretically they can increase plenum volume but what kind of meaningful volume can truly be be added in that little space? And what would it even do since it’s still not technically in the plenum chamber of the manifold?

This is all a problem created by aftermarket companies who made their names with 5.0 Fox and SN95 Mustangs and tried to stay in the late model market when the 4.6 came out, and applying the logic that worked for the 5.0 never really worked because few of these companies really cared to understand the 4.6s. CAI kits, TBs plenums, UDPs and headers were all there was available for the 4.6 for almost a decade, cams seemed to come around in the mid 00s but heads and intake limited the potential of hotter grinds and, the best heads and intakes were all Ford engineered(SVO, Bullitt) and not supported for long, Trick Flow is still a newcomer to these engines and the twisted wedge heads came out, what? Ten years ago?

Magazines in the 2000s perpetuated the “10-20 horsepower” from bolt ons gains, and just so happened to advertise every product they tested, hmm. I used to have a subscription to MM&FF before I even had a license at the time and even then it made me laugh when they’d take an older SN95 to do all this stuff to and gently brush past the fact that the original plugs and wires had 120,000 miles on them when demonstrating the gains of their MSD coil packs and wires, or changing out the factory intake tract including the dirty old air filter and replacing it with the shiny new chromed metal pipe, oiled cone filter with a marginal heat shield(or not) and dyno the car with the hood open to see the mad 15 horsepower gains. Wow! Adding a tune on top of this stuff doesn’t prove anything either, it’s well known the factory tune leaves power on the table, usually commanding too much fuel at WOT and “safe” spark to avoid pinging. Apply the same the same tune to a 100% stock car and you’ll see indistinguishable results from the one with those bolt-ons.

Note that I have had all of these parts in a combination of “see for myself” and underhood looks(hey, I never said aftermarket plenums/TBs don’t “look” better. I kept running underdrives on my current engine because the damper is the SFI type and doesn’t hurt anything and to simply slow down the accessories a little for longevity, and even that I’m skeptical of the difference they make.

All good points and very well written. Thank you.
I have always viewed building a car as more of an excersize in reducing hysteresis, and improving efficiency. Because you are right, putting headers on gains no power. It only frees up what power it's design superiority allows over the stock manifold. It's the same with most "performance" bolt on parts.
My bOlt on examples in the previous reply were pretty poor examples for the point I tried to make.
Without getting too wordy here, I can also affirm that the UD sheaves in my application are specifically intended to save on accessory life. And UD also gains nothing no Power wise, it only moves the load about.
 
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