Planning my exhaust

Topic: Planning my exhaust (Read 3212 times) previous topic - next topic

Planning my exhaust

June 02, 2012, 03:39:26 AM

I'm looking at 2.5 inches to bumper, no cats, shorty headers. Am I going to run into trouble adapting mustang catback parts (extension of the intermediate pipes and extension of the tails), and will I have a problem running 2.5 inch tails?

Any parts recommendations are welcome, what's worked well for you guys? I don't want super loud, just good flow.
:burnout:

Planning my exhaust

Reply #1 – June 02, 2012, 01:20:10 PM

You will have to hang your own hangers.

Read up the coolcats.net article. Couple of little things you might have to do.

I would run some 1 5/8th primary headers, matching offroad h/x pipe, and 3" or larger tail pipes, depending on what engine plans you have planned out.

Stoc a mustang had 2.25", my crown vic has dual 2" from the factory. I don't think t would be out of line for you to go 2.5 or even 3".

Planning my exhaust

Reply #2 – June 02, 2012, 02:37:53 PM

Watch your pipe diameters!!! If they get to big HP will drop. Normally somewhere around 2 1/4 is ball park for an NA engine. Cats are a PLUS and with cats you can eliminate the lers for more PONIES. You just may want to consider a ler shop with a BLUE BOY!!

:hick: :burnout:

Planning my exhaust

Reply #3 – June 02, 2012, 03:32:04 PM

I've got some generic 1-5/8" headers, BBK 2.5" off road X, and flowmaster american thunder cat back, also in 2.5", sounds great, bolts together fine, but the tails aren't in yet. In fact, I'm about to head out and take the cat back stuff off as well, since it's only held on by a couple of coat hangers right now. I need a welder....

The reason it's cobbled on right now: I just wanted to hear what it sounds like. I've got serious issues with my TC rear...the diff is full of a near perfect (or rather, imperfect) ratio of oil and water. F*ck.

So yeh, might as well pull the new pipes back off while under it. Thankfully I have a Mustang 8.8 that just so happens to have 3.55s in it as well, which I discovered by accident when I opened it up to pull the axles last weekend. Score. It negates the shiznitty feeling I had when I pulled the cover of my TC 8.8 and milk ran out of it.

Now..back to our regularly scheduled thread. This announcement has been brought to you by your local ThunderbirdSport302.

Planning my exhaust

Reply #4 – June 02, 2012, 05:43:42 PM

Quote from: TOM Renzo;391321

Watch your pipe diameters!!! If they get to big HP will drop. Normally somewhere around 2 1/4 is ball park for an NA engine. Cats are a PLUS and with cats you can eliminate the lers for more PONIES. You just may want to consider a ler shop with a BLUE BOY!!

:hick: :burnout:

If you want to show off dyno numbers then yeah go for 2 1/4 or 2.5" exhaust.

If you want it to accelerate or run quicker at the track, then go bigger. Going from stock 2 1/4 to 3" exhaust will drop hp peak numbers on a dyno, but will run faster at the track, even faster after a tune.

Planning my exhaust

Reply #5 – June 02, 2012, 10:54:18 PM

Quote from: Haystack;391336

If you want to show off dyno numbers then yeah go for 2 1/4 or 2.5" exhaust.

If you want it to accelerate or run quicker at the track, then go bigger. Going from stock 2 1/4 to 3" exhaust will drop hp peak numbers on a dyno, but will run faster at the track, even faster after a tune.

God I hate posts like this ... this is not true ,, if the COMBINATION is correct it is ..but just bolting a huge exhaust on a stock motor will NOT make it perform better , either on a dyno OR the track
The whole package has to work together

Planning my exhaust

Reply #6 – June 02, 2012, 11:11:08 PM

Quote from: hypostang;391349

God I hate posts like this ... this is not true ,, if the COMBINATION is correct it is ..but just bolting a huge exhaust on a stock motor will NOT make it perform better , either on a dyno OR the track
The whole package has to work together

Spot on well said. AND 100% CORRECT. We have dun extensive testing on exhaust diameter and HP. Bigger is not always better. Tuning exhaust is a complicated equasion. By the way HP IS HP either it is their or it is not. Thanks

Bigger is not better???

Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off .Also pulses wont line up correctly after they leave a header with large diameter pipes. Cats keep the exhaust gases hot. They also have a tendency to allow exhaust gases to expand rapidly and keep the flow pulses lined up. This increases flow. Once the pipe diameters cause a cooling effect flow is actually restricted with an increase in diameter. CATS ARE YOUR FRIEND. Better believe this it is true. Removing a good flowing modern cat will cost you HP im most cases.Thanks

BIGGER IS NOT ALWAYS BETTER. Old WIVES TALE

Planning my exhaust

Reply #7 – June 02, 2012, 11:48:51 PM

I have 1-5/8" shorties and a 2.5" offroad H-pipe with Flowmaster lers for a fox Mustang. Made my own hangers out of pieces of steel and 1/4" rod that I bent to go through the rubber ler hangers. I also have LX style tailpipes but they are on the shelf....can't seem to get them to fit but need to play with them some more. At this point I'm going to put turndowns on it just to get it on the street.

Planning my exhaust

Reply #8 – June 03, 2012, 12:25:42 AM

My ultimate goal is 410 NA horsepower. My future plans include MAF conversion, then aftermarket heads, cam and intake. For where I wan't to go, 2.5 stem to stern seems optimal, and I only want to build out the system once. The cats are taking a hike more for cost reasons that for any supposed performance advantage. Tom, I agree that cats are an important part of flow management, and that good modern cats don't offer a measurable flow penalty, however, my car is now 25 years old, and even if Michigan were a sniff state, I'd now be exempt. No, My current Mark VII h-pipe has older cats that are in poor health, and If I'm paying for that much new pipe, I'd like to avoid paying for new cats. I spent a lot of years working in ler shops, and am familiar (and also skillful) with a pipe bender, I just don't like the compressed bends. In my mind, ler bender bent pipes are good for rednecks who want loud exhaust on their trucks, and for piss-poor people who can't pay for walker or similar pre-bent pipes, but they don't make real "high performance" pipes (Loud exhaust is not, by default, performance exhaust). Good smooth bends also prevent 'hot zones' which you can always find on several year old custom bent pipes by the appearance of bends that are rusty where they shouldn't be. Also, through the years I've noticed that high quality mandrel bent performance pieces usually seem to be made from thicker material, although this is merely an observation of their appearance, I've never measured wall thickness between the two. I custom bent my own 2.25 tails for my 87 V6 T-Bird years ago when I had it, and I had a hell of a time getting bigger than 1 7/8 tails in place (although, I was only 25 when I made them). My current car came with just that from the factory on BOTH sides (so at least I have hangers), but I was hoping somebody would be able to tell me how 2.5 mandrel bent tails would fit up in there.

Planning my exhaust

Reply #9 – June 03, 2012, 06:58:07 AM

Quote from: TOM Renzo;391351

Spot on well said. AND 100% CORRECT. We have dun extensive testing on exhaust diameter and HP. Bigger is not always better. Tuning exhaust is a complicated equasion. By the way HP IS HP either it is their or it is not. Thanks

Bigger is not better???

Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off .Also pulses wont line up correctly after they leave a header with large diameter pipes. Cats keep the exhaust gases hot. They also have a tendency to allow exhaust gases to expand rapidly and keep the flow pulses lined up. This increases flow. Once the pipe diameters cause a cooling effect flow is actually restricted with an increase in diameter. CATS ARE YOUR FRIEND. Better believe this it is true. Removing a good flowing modern cat will cost you HP im most cases.Thanks

BIGGER IS NOT ALWAYS BETTER. Old WIVES TALE

Actually quite the opposite. Ever watch performance drop with egr temps on a deisel? I wonder why that is...

Restricting flow will probably never help your performance. If you plan anything more then a stock h.o. upgrade, I don't see why you wouldn't run 3" exhaust.

Having cooler exhaust because of extra flow means there is less energy being converted to heat, and therefore wasted in the exhaust system.

Why would the exhaust pulses change timing because of the header primary's? If you have the air under 10psi, its not going to exit much faster then 11psi, but it does have to over come the extra back pressure.

Also, if restricting flow increases power, and opening up the exhaust doesn't, why do a lot of newer cars (including the vette...) have butterfly's that dump exhaust bypassing the ler?

Planning my exhaust

Reply #10 – June 03, 2012, 08:26:32 AM

Diesel EGR temps matter because it's being fed back into the engine to cool combustion. They have EGR coolers for this, just like our 5.0L's. Tom is saying that keeping the exhaust hot improves flow because it keeps the rate of expansion up. Cooler exhaust expands out more slowly and results in lower cylinder scavenging. But this is mostly a mid to high rpm issue. Smaller pipes, and slightly more back pressure will always aid low end torque some, but hitting that sweet spot in the set up gets good low, but better mid to high. There is no point to having bigger tails when you have smaller lers or mid-pipes (H or X and intermediates) because the system will only flow as much as the smallest pipe. It would be better to have 3 inch mids and 2.25 tails than the other way around. At any rate, the only large expansion I want is in the lers so they can do their job, and some fine tuned expansion in the ends of the tails for sound tuning (but the custom tips I build are my secret recipe, and I give no details).

Planning my exhaust

Reply #11 – June 03, 2012, 08:59:14 AM

Also, if restricting flow increases power, and opening up the exhaust doesn't, why do a lot of newer cars (including the vette...) have butterfly's that dump exhaust bypassing the ler?

Because LERS RESTRICT. I dont build systems with lers. I explained that several times

Restricting flow will probably never help your performance.

And a 3" exhaust cant retain heat and i explained why that is BAD. So do as you please and build a exhaust system and loose HP.

Planning my exhaust

Reply #12 – June 03, 2012, 10:45:28 AM

Case in point, my Coupe is a NA 306 with Edelbrock Performer RPM heads, a nice Comp Cam, and a bottom end that with the heads is a 10.5:1 compression ratio. The induction is an 80mm MAF, 75mm TB, Edelbrock RPM II upper and lower, and 42 lb/hr injectors. There is also a SCT dyno tuned chip on the car to make all of this work with the A9L EEC. The car makes 318 rwhp and 324 ft-lbs of torque with 3.73 rear gears. I have two X-pipes, one with cats for regular driving and one without for the track. I will tell you that the car runs much better with the off road X than the catted X on the track. Hits the RPMs faster and pulls harder coming out of the corners. I have not put it on a dyno an compared the two as I was not going to pay the dyno time for something as trivial as that.

With all of that said I always thought that this was just a sign that the 2.5" exhaust was too small. My suspicions were confirmed when both Ed Curtis (http://flowtechinduction.com/) and the guy that does all of my machine work both said the exhaust was too small for a NA motor like mine. I have an Ed Curtis custom ground cam for the car but it being installed are contingent on three things: the heads being ported, the lower intake being ported, and moving up to a 3" exhaust. If I do all of this Ed was comfortable with the car hitting the 375 rwhp mark but he and I both agreed that the area under the curve would get fatter and there would be more usable hp and torque in the 3,000 to 6,000 rpm range.

Tom knowshiznit stuff for sure and is on the money when he is talking about the system as a whole and balancing it. When you are getting up in the large hp numbers with a small displacement naturally aspirated engine there is only one way to get it and that is move more air. This is done by opening up the engine via larger valves, port jobs, more induction, and larger exhaust. Another way is to leave everything alone and increase the pressure with a turbo or super charger. We have all seen how a stock 5.0 with a blower or turbo and stock exhaust will hammer out 400+ hp numbers. Change the exhaust and presto, more hp. Take the same stock 5.0 and put 1-5/8" shorties on it and a full 2.5" exhaust and you are lucky to gain 25 hp. Does it hurt, not really. Should you spend you money elsewhere first, up to you. I put the exhaust on the car first because it was cheap, made the car sound great, and it gave me some room as the bolt-ons happened. Now I am out of room so the 2.5" will eventually be replaced with a 3" system.

To the OP, one other thing I forgot to mention is the cost difference between a 2.5" system and a 3" system. It is a wallet beater so be sure that is what you want to do as with your current setup and a lot of bolt-ons down the road the 2.5" system will do you proud.

Darren

Planning my exhaust

Reply #13 – June 03, 2012, 11:31:25 AM

I won't be getting back in the engine for quite a while, so i feel like anything bigger than 2.5 would be overkill. Maybe 3 would be just fine on my finished product, but 2.5 would be adequate also, and not overlarge for my current setup. Aerocoupe, thanks very much for your insight on how to reach my goals, Tom, thanks for showing up and being helpful.

Planning my exhaust

Reply #14 – June 03, 2012, 03:17:25 PM

2.5" will be fine for your setup. The only thing you will need to ask yourself is shorties or long tubes. With the AOD I would go with the shorties as the LT's can be a pain in the ass to install with the wider AOD, been there and done that. Also, the shorties allow better access to the starter. LT's will net you some low end torque and a couple more hp but its all up to you if the effort to install is worth it. The Mustang X-pipes and H-pipes will bolt right in but there is a little bit of wheel base difference, 100.5" for the Fox Mustang and 104.2" For the Fox T-Bird. This can be made up with the intermediate pipe from the X or H to the inlet of the ler. As far as tail pipes go, the Fox Mustang units will hang under our cars just fine but they are shorter i.e. the end of the tips are way under our cars. If you run the GT tips then this is not a big deal but if you want the stainless look of the LX Mustangs then its an issue. Some of the guys here have simply welded a slightly larger tip to make it work out but that was not something I liked the look of, to each their own. I had a ler shop order some stainless tube and I spent a Saturday up there helping my buddy bend and weld the longer pipe on. We made them just long enough where the weld was behind the tire and had to but a little bend on them if I remember correct. My buddy's family owned the shop so we were able to mess around with it all day and he did a couple other cars off what he did on mine. That was years ago (1995 or so) and I no longer have that system on the car, whet to 3" in 1998 and he sold my system to another guy with a Bird the next day.

Darren