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im new to v8's so i dont really know what sizes are apropriate for exhaust. but im trying to figure out what size exhaust piping im going to need on an n/a 4.6 2v. going to be full straight piped with an x pipe. otherwise theres going to be no resistance to the exhaust gasses. theres 3 options i have of running right now. 2.5", 2.75", and 3" i could go bigger or smaller but thats just what i was aiming for.

2.5"- is it too small for the amount of air the engine is going to be pushing out? i dont want a ton of back pressure.
2.75"- dead center of the 3 sizes. only concern is it could be too small for the engine and still be too much back pressure.
3"- not sure but i know 3" is way too big for N/A on 4 cyls no idea on v8s though?

im not aiming to be loud im aiming to get the best performance out of it.
 

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Are you building your own exhaust or piecing together aftermarket exhaust?

Anyway... go with 2.5 all the way back. These engines don't have the cubic inches to benefit from 3" exhaust. Almost all aftermarket exhaust pieces for our cars are 2.5".


Best power gain will be from switching out the midpipe. Go o/r (no cats) if you can get away with it in your state.

Also, it's going to sound like **** with straight pipes and you're not going to gain much (if any) HP from it. Go with a nice aftermarket muffler. With the Xpipe I'd go with a straight through muffler like an SLP LMII, Borla Stingers, or Magnaflow Magnapacks
 

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Discussion Starter #3
Are you building your own exhaust or piecing together aftermarket exhaust?

Anyway... go with 2.5 all the way back. These engines don't have the cubic inches to benefit from 3" exhaust. Almost all aftermarket exhaust pieces for our cars are 2.5".


Best power gain will be from switching out the midpipe. Go o/r (no cats) if you can get away with it in your state.

Also, it's going to sound like **** with straight pipes and you're not going to gain much (if any) HP from it. Go with a nice aftermarket muffler. With the Xpipe I'd go with a straight through muffler like an SLP LMII, Borla Stingers, or Magnaflow Magnapacks
im building my own.
the engine is going in a 240sx. not a mustang so i cant really just buy an exhaust.
 

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im building my own.
the engine is going in a 240sx. not a mustang so i cant really just buy an exhaust.
Oh wow, yeah I don't think the Mustang to 240sx exhaust conversion kit is offered on AM yet haha.

I'd stick with 2.5" all the way back, or even go with 2.25" if you need to save a little room. The exhaust really isn't too restrictive on our cars when you take the stock cats off.

How much power are you planning on pushing out?
 

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King Trashmouth
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im building my own.
the engine is going in a 240sx. not a mustang so i cant really just buy an exhaust.
Congrats on what sounds like an awesome project. I expect lots of pictures. ...partially so I can send to my friend with his RB26dett swapped 240sx.

But as far as exhaust sizes go, 2.5" is probably your best bet. It's not so much backpressure as flow velocity that you want. Higher flow velocity = better exhaust scavenging = more power. Basically you want to optimize flow velocity (and consequently flow rate) and pressure differential to yield maximum power.

Straight pipes is also a poor idea. Aside from sounding like garbage the loss in resistance from the mufflers decreases flow velocity, particularly at low RPM causing a loss in low RPM power/torque. If you're going to spin the motor at very high RPM it could be an advantage, but that is unlikely, so I would reccommend keeping mufflers. Cats can go though.
 

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Discussion Starter #6
well its 260 stock so im aiming for 330ish with full bolt ons and a tune. probably more then possible.

i wasnt even looking for a swap kit actually. im just building it all myself lol.
 

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Congrats on what sounds like an awesome project. I expect lots of pictures. ...partially so I can send to my friend with his RB26dett swapped 240sx.

But as far as exhaust sizes go, 2.5" is probably your best bet. It's not so much backpressure as flow velocity that you want. Higher flow velocity = better exhaust scavenging = more power. Basically you want to optimize flow velocity (and consequently flow rate) and pressure differential to yield maximum power.

Straight pipes is also a poor idea. Aside from sounding like garbage the loss in resistance from the mufflers decreases flow velocity, particularly at low RPM causing a loss in low RPM power/torque. If you're going to spin the motor at very high RPM it could be an advantage, but that is unlikely, so I would reccommend keeping mufflers. Cats can go though.
car is mainly a drift car so its going to spinning it at high rpms is very likely haha

but would throwing glass packs on there be a little bit better then just full straight pipes? wouldnt mind a little bit better low end if i decide to cruise around.

and i have a build thread up just still trying to hunt down an engine lol
 

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King Trashmouth
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Glass packs are ok for flow characteristics, but they sound very out of place on anything other than an old truck or old muscle car IMO. There's tons of alternatives, I'm sure lots of guys can guide you on that one.

And if you're looking for closer to 330hp (not sure if you mean bhp or rwhp), you might want to look into a 3v or 4v motor. There's a few debates on which is better going on, so take your pick. Then there's all sorts of different options as far as NA, FI, s/c vs turbo...etc. You've got your research cut out for you.

Or if you have the budget get a termi motor. I'd love to see a terminated 240sx make some import kids cry. :D
 

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So you're making you're own exhaust, but is it going to be duals all the way back? If it is, then use 2.5" all the way back. I have a y I made for my mustang, and it's dual 2.5 into a single 3" back into a single muffler. You probably going to want mufflers on it, as it will sound like **** without.
 

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I would match the diameter of the pipe to the exhaust ports on your manifold?
 

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I agree that 2.5" sounds about right, but in my experience you won't necessarily get the most power from the least backpressure. Unless your car is built to be a full race 1/4 mile car, full open straights are probably not the way to go.
 

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Too Soon, Junior!
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Acoustically tuned exhaust manifolds will give you the biggest increase in performance since you're going to be spinning at the higher RPMs. The Ford modular 4.6 2-valve heads don't breathe very well at the higher RPMs so you may consider porting them to achieve better flow characteristics. Go with any diameter of exhaust you'd like, as the power gained from optimizing the exhaust diameter is a function of both exhaust gas discharge velocity and flow restriction due to the piping diameter. The momentum of the exhaust gases will play a big role depending on what type of performance you optimize for. Smaller diameter will give you slightly more torque at low RPMs, and larger diameter would be better at the higher upper RPM range. This is going to be a sweet project, hope you keep us updated with some pictures :yes
 

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I would look into pressure wave tuning, and pressure wave termination boxes, it's a topic commonly covered by david vizard. Definitely do not do straight pipes. A properly tuned exhaust will benefit you @ roughly 10 times the rpm range of a properly tuned intake. Utilizing pressure wave tuning you can determine exactly where to place the pressure wave termination boxes, and with some engine specs the volume of the pressure wave termination boxes can also be determined for whatever engine you run. I'm more than willing to help you out on this but would need to know the specs.

As for exhaust pipe size the general rule of thumb is for every inch of cross sectional area of tailpipe you can support 115cfm and you need 2.2cfm per 1HP. Therefore if you are planning around 330HP then your bare minimum would be a Diameter of 1.289in.
Keep in mind these are general rules of thumb, however and given the application may/may not work for you in your situation.
pm me or email me at [email protected]. if you would like more info on the matter.
 

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well its 260 stock so im aiming for 330ish with full bolt ons and a tune. probably more then possible.

i wasnt even looking for a swap kit actually. im just building it all myself lol.
Ha, that was a joke about the swap kit.

If you're building a drift car then I'd start off with an aluminum block to shave 80 lbs from the front end. Doesn't matter if it's Teksid or WAP since you won't be shooting for tons of power.

I'd also stick with the 2v heads, either have yours ported or buy some stage 2/3 heads from the aftermarket. 2v heads are going to be quite a bit lighter than 4v heads and will be more than capable of handling what you need for power.

I really don't know too much about drifting from a power curve standpoint, whether you'd rather have an engine that can spin up to 8k or whether you want something that will have lots of torque... I guess either way would have advantages/disadvantages.


And if you're looking for closer to 330hp (not sure if you mean bhp or rwhp), you might want to look into a 3v or 4v motor. There's a few debates on which is better going on, so take your pick. Then there's all sorts of different options as far as NA, FI, s/c vs turbo...etc. You've got your research cut out for you.

Or if you have the budget get a termi motor. I'd love to see a terminated 240sx make some import kids cry. :D
No need for 4v heads, blowers, turbos, etc on a drift car. Definitely no need for a termi motor. Too much weight on an already noseheavy car. The main reason a stockish GT sucks for drifting is that it's noseheavy and has a **** rear suspension. It has more than enough power to drift with.



Anyway, back to exhaust. These guys are throwing out some pretty technical ideas, but honestly I'm not sure if you need all of it unless you're looking for every little last HP in your setup. If it were me, I'd keep the stock manifolds (for space savings) and get a used o/r x pipe (almost all are 2.5") that you can chop up to suit your needs. After that I'd just build a catback out of 2.5" that somewhat mirrors how a Mustang catback is set up. Throw some magnapacks or lm2's on there and call it a day
 

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King Trashmouth
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If you're building a drift car then I'd start off with an aluminum block to shave 80 lbs from the front end. Doesn't matter if it's Teksid or WAP since you won't be shooting for tons of power.

I'd also stick with the 2v heads, either have yours ported or buy some stage 2/3 heads from the aftermarket. 2v heads are going to be quite a bit lighter than 4v heads and will be more than capable of handling what you need for power.

I really don't know too much about drifting from a power curve standpoint, whether you'd rather have an engine that can spin up to 8k or whether you want something that will have lots of torque... I guess either way would have advantages/disadvantages.

No need for 4v heads, blowers, turbos, etc on a drift car. Definitely no need for a termi motor. Too much weight on an already noseheavy car. The main reason a stockish GT sucks for drifting is that it's noseheavy and has a **** rear suspension. It has more than enough power to drift with.
I was kidding about the termi motor, I mean the thing has a cast iron block. Though I would love to see one in a 240.

Aluminum blocks will definitely be your friend.

As for the whole 2v/3v/4v, that is going to be up to you. Each has it's own strengths and weaknesses, and I don't think any of us can definitively say what is best.

One edge you have over the GT's is you have an IRS.

All of this is straying away from the exhaust question though. Good to see we have so many people who understand compressible flow.

And no need for FI or 4v's in drifting? Come on.
Exhibit A:
Doug Van Den Brink has possibly one of the most badass drift Mustangs ever.
 

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This guy isn't building a drift Mustang though, he won't need gobs of power. How much power does an AE86 corolla have? Like 150 at the flywheel? Those things drift like nobody's business
 

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Discussion Starter #19
alright i had to read over alot of this stuff lol.

4v is more than likely out of the question being the heads are going to be too big for the engine bay and i really would rather not cut apart my strut towers. stock manifolds im going to have to see how they work since im not sure what will fit around the stock s13 steering column, after looking into alot of things until like 4am it seems some/most 2v gt's are aluminum block and actually weigh almost the same as the stock KA24DE that the 240 comes with. i can slide mine around completely fine with just a 6 puck clutch and welded diff. somehow i ended up off topic too lmao.

but the 2 thoughts for now
1)headers -> catless x-pipe -> blast pipe style exhaust going out the back of the car.
2)headers -> Y-pipe -> single 3" catback with typical n1 style muffler.
neither will have a cat. my car is a 90 or 91 or 89 idk anymore its got too many mixed and matched parts. either way i dont need to pass obd2 i just need to get someone to say heres a sticker. lol

if i had the budget of a race team i would be putting in a completely built engine not a stock-ish one with mild bolt-ons and a tune so pressure wave tuning is kind of out of the question. just a bit more then im looking to spend on a weekend fun car haha.

and i thought doug drove the ASD mustang? unless he changed it idk.
i was pretty sure he was with ASD when he was doing streetwise. also i think he was with them at XDC nj unless theres a couple 4th gens in the group.

and ae86 has like 9 hp =P
nah its got i think 120ish crank last i checked. varies with the model.

oh and the heads are going to be ported. slightly larger valves and a bit higher profile/duration cam. i was looking at dyno charts from mustangs and ls1 camaros and the curves all seem very similar just the power output was really the only difference. i might try to focus the power band/torque curve up a little bit in the 3k-6500 range. if you do it right you wont even touch the rev limiter mid drift.

back to my hunt for an engine though. this is the one thing thats really holding up the build.
 
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