3 inch exhaust

[SVTurbo 98]

There are a couple of things that will slow exhaust gas down:

1) A sudden decrease in temperature. This is why auto makers could care less about cooling the exhaust.

2) Going from a small diameter to much larger diameter pipe. A larger pipe will slow the velocity of the exhaust down due to expansion.

Larger is not always better, the larger the pipe - the SLOWER the velocity. It's a balancing act and trade-off.

:nonono:

Now I see where your philosophy is coming from.

2 completely different exhaust configurations. A Turbo will spool most efficiently when there is maximum pressure differential between the turbo inlet and the outlet. The ideal exhaust on a turbo is not having piping or any kind on the outlet of the exhaust scroll. That’s why you see 4” pipes after the exhaust scroll. A turbocharged engine has a substantial amount of backpressure from having multiple cylinders dumping into one or two turbos. A supercharged or NA engine will have more efficient exhaust because they can take advantages of the pressure waves created by each exhaust pulse (when you have a high pressure wave there is always a low pressure wave right behind it and you want to take advantage of that at the next exhaust cycle to help scavenge the cylinder). Turbo’s just pressurize the exhaust manifold to drive the impeller and diffuse the pulse pressure. While I am certainly no expert on exhaust system design I do have first and experience what the effect are if you install to large a system or minimize backpressure. THEY RUN LIKE CRAP! The engine stumbles at low speed and you can never seem to get the engine to run right. Backpressure and optimal exhaust velocity is what you are after something an overly large pipe won’t do.

:bs:
I guess we need to let the NHRA guys know they need to close up there exhaust or else their cars will "RUN LIKE CRAP". :lol:

After the collector, "velocity" means absolutely nothing.

BTW I'm still waiting for you to prove your point using before and after data, rpm vs. time, etc....:rollseyes

 

[SVTurbo 98]

These cars run like raped apes even without headers. Adding headers won't make a dramatic difference in these cars (the blower overshadows everything!). A high boost big hp benefit from headers way more then a mild engine will. On an NA engine they seem to make more of a difference. I have an issue of MM&FF with the Mod-for-Mods article showing dyno'd runs with both LT's and the stock logs and the lines in the graph pretty much overlapped one another all the way to redline and that was done with a straight pipe and no mufflers or cats. There have been quite a few people who were pissed as hell doing back-to-back dyno runs after installing headers. One guy recorded a 5 hp increase after spending quite a bit of dough installing headers. Its surprising how few people are running headers on their Terminators where on other cars it's one of the first mods you make. Go figure :shrug:

So you are taking advise from magazines trying to make their sponsors happy by selling parts....?

 

[SVTurbo 98]

Backpressure is only good off the line

How so?:??:

 

[SlowSVT]

:nonono:




:bs:
I guess we need to let the NHRA guys know they need to close up there exhaust or else their cars will "RUN LIKE CRAP". :lol:

After the collector, "velocity" means absolutely nothing.

BTW I'm still waiting for you to prove your point using before and after data, rpm vs. time, etc....:rollseyes

You seem to know something I don't. Perhaps YOU could explain in detail where I got it all wrong?

op:

 

[cah41]

I know that I have read from a guy who builds these engines that headers are worthless unless you approaching the 700 hp mark with our engines. So that much I am pretty sure of.

 

[SVTurbo 98]

Why don't you first go back and read what you posted and tell me it doesn't contradict itself....

A 3" exhaust will lower the gas velocity reducing the scavenging effect and lower the resonance frequency of the exhaust also known as "drone". I would not consider a 3" system unless I'm making 700 hp and plan on keeping the tach north of 6000 rpm all day. I would stick with a 2 1/2" system. A 3" system is certainly overkill for a small 4.6 with a ported Eaton and will probably hinder your performance somewhat.

It is pretty well understood that an exhaust needs to be sized to promote optimal velocity thru the system to get the best performance. Too small a pipe diameter will be too restrictive and too big a diameter will slow the speed of the spent gasses and not provide enough back pressure. If a 3" system is better then a 2 1/2 wouldn't a 3 1/2" system be even better? See where I am going with this. Imagine all this is going thru the stock cast iron maniford which has a way smaller cross section then even the 2 1/2" pipe. Adding a set of headers only buys you about 10 hp over the stock logs. That crappy non-mandral bent 2 1/4" factory cat back is the worst offender in the entier system.

Yes there are guys who do run 3" systems but some of them actually when back to the 2 1/2" and stated the engine responds better with the smaller pipe if you wanna call a 2 1/2 pipe "small". Like I stated, if I was building a little 4.6 that was going to run high boost and revved to the moon then I might consider a 3" systems. But for the street 2 1/2" is a better choice which is what the vast majority of us are running.

Now I see where your philosophy is coming from.

2 completely different exhaust configurations. A Turbo will spool most efficiently when there is maximum pressure differential between the turbo inlet and the outlet. The ideal exhaust on a turbo is not having piping or any kind on the outlet of the exhaust scroll. That’s why you see 4” pipes after the exhaust scroll. A turbocharged engine has a substantial amount of backpressure from having multiple cylinders dumping into one or two turbos. A supercharged or NA engine will have more efficient exhaust because they can take advantages of the pressure waves created by each exhaust pulse (when you have a high pressure wave there is always a low pressure wave right behind it and you want to take advantage of that at the next exhaust cycle to help scavenge the cylinder). Turbo’s just pressurize the exhaust manifold to drive the impeller and diffuse the pulse pressure. While I am certainly no expert on exhaust system design I do have first and experience what the effect are if you install to large a system or minimize backpressure. THEY RUN LIKE CRAP! The engine stumbles at low speed and you can never seem to get the engine to run right. Backpressure and optimal exhaust velocity is what you are after something an overly large pipe won’t do.

:dw:

 

[cah41]

So you are taking advise from magazines trying to make their sponsors happy by selling parts....?

The quote you took from him stated that there was an article in MM&FF that showed that Long tubes didn't amount to anything; the article wasn't endorsing long tubes, it was showing that they didn't show gains for a terminator below 700hp. So while I would tend to also not just gobble up anything in a car magazine, a conflict of interest can't exist here: if anything the magazine would want to skew their results towards the long tubes showing a significant increase in power, not no increase. That's not the way you make sponsors (who sell LT's) happy.

So you don't think a 3" exhaust would be too large for the 4.6?

 

[SlowSVT]

Why don't you first go back and read what you posted and tell me it doesn't contradict itself....:dw:

This response can best be described as "disappointing" :nonono:

I asked you to explain in detail why I am wrong and this is all you can muster :??: Your not being very convincing.

Try again using more then 1 sentance.

 

[SlowSVT]

The quote you took from him stated that there was an article in MM&FF that showed that Long tubes didn't amount to anything; the article wasn't endorsing long tubes, it was showing that they didn't show gains for a terminator below 700hp. So while I would tend to also not just gobble up anything in a car magazine, a conflict of interest can't exist here: if anything the magazine would want to skew their results towards the long tubes showing a significant increase in power, not no increase. That's not the way you make sponsors (who sell LT's) happy.

So you don't think a 3" exhaust would be too large for the 4.6?

BINGO!

I was only referring to the dyno graph comparing the two and nothing more. That MM&FF article was actually very misleading. They were not running any engine accessories right down to the water pump which showed very inflated numbers.

A more appropriate question would be: if a 3" pipe is good wouldn't a 3 1/2" pipe be "better"?

 

[SVTurbo 98]

The quote you took from him stated that there was an article in MM&FF that showed that Long tubes didn't amount to anything; the article wasn't endorsing long tubes, it was showing that they didn't show gains for a terminator below 700hp. So while I would tend to also not just gobble up anything in a car magazine, a conflict of interest can't exist here: if anything the magazine would want to skew their results towards the long tubes showing a significant increase in power, not no increase. That's not the way you make sponsors (who sell LT's) happy.

So you don't think a 3" exhaust would be too large for the 4.6?

To answer your question, a 3" exhaust is not too large for a 4.6. Magazine articles are very misleading and their "tests" don't tell the whole story. I stopped reading the tech part of magazines for that reason and unfortunately that's where a lot of people get there info from. If I told you two identical cars can share the same horsepower/torque numbers and one car can be faster than the other, would you believe me?

This response can best be described as "disappointing" :nonono:

I asked you to explain in detail why I am wrong and this is all you can muster :??: Your not being very convincing.

Try again using more then 1 sentance.

You should see for yourself that you are wrong by what I quoted in red because you are making statements that are contradicting. First you say 3" exhaust creates backpressure because, as it cools down, it slows down and negatively effects scavenging. Then you say backpressure is what you are after....?

It doesn't take a genius to figure out a free flowing exhaust makes more power than a non free flowing exhaust....meaning the least amount of backpressure. That's why NHRA cars run open headers. Backpressure creates heat and heat will cost you power. It's that simple. I know that may be difficult for you to understand. All I can say is if you don't believe it, then go do your own testing and report back with the results.

Here is a test that shows the importance of exhaust scavenging. It also shows how meaningless horsepower and torque numbers are when it comes to racing. In this test, he is comparing midpipes on a n/a 306.


This is a graph power vs. rpm comparing different exhaust setups. (3" x-pipe, open headers, 3" prochamber)

If you notice, the graph shows that the open headers actually made less peak horsepower and torque by a little comparing power vs. rpms. Most magazines will stop here and make you believe that backpressure is a good thing.

But what if we take a look at those same dyno runs when you compare power vs. time aka ACCELERATION.

The lowest peak HP and torque was the fastest. Peak and average numbers were made at a faster rate, reducing the time required to reach them, meaning the car will accelerate faster and run quicker.


Your next argument is a 3" exhaust is too big if you make less than X amount of HP and the exhaust will slow down. In actuality, the pulse based scavenging is concentrated at the header-extension level after which, an unobstructed flow takes importance over velocity. The vacuum that starts the scavenging effect takes place at the collector. It uses the initial exhaust pressure pulse of the next cylinder in that bank. Anytime an open header or bigger diameter exhaust system setup drops in performance, the cause is not excessive exhaust.....it's a lack fuel/tuning.

 

[FastNick01]

What slowsvt is saying is totally correct!
3' is overkill for a 281
If you have a built motor that sees the strip all day long I don't see 3' being a problem, but for a street car I will stick to 2.5' exhaust

Also in regards to the drag car posts, drag cars don't run 281cu mills, they run beyond 500-600 cubes. Those cars can run 3-4 in exhaust without a problem.

 

[98 Saleen Cobra]

And if your making 600 hp should you step up to a 3 1/2" system? I don't think the GT500 guys are going any bigger the 3" and they got 50 cubes on us.

No that's not the case 3'' systems are great for alot of hp. :beer:

I think that quote you're referring to was in reference to big block chevy's, not a 4.6 modular motor. Thanks anyway

No my quote was from 5.0 mustang magazine. But lets see. Griggs runs 3'' on his cars, and he runs dinky 4.6 motors, if you look at most of the IX/AIX racers and most drag racers I'm sure they run 3'' exhausts as well. If you look Ford made the M55 catback which was 3''. If anything I would run a bigger primary header and if you're worried about a 3'' then just get a 2.5'' collector Even small block fords run 3'' exhaust or bigger even, nascars, drag racers, open track ect. The amount of tq that you is not even noticable if any. The guy asked what he should do, so i put my .02 in:beer:

 

[cah41]

No that's not the case 3'' systems are great for alot of hp. :beer:



No my quote was from 5.0 mustang magazine. But lets see. Griggs runs 3'' on his cars, and he runs dinky 4.6 motors, if you look at most of the IX/AIX racers and most drag racers I'm sure they run 3'' exhausts as well. If you look Ford made the M55 catback which was 3''. If anything I would run a bigger primary header and if you're worried about a 3'' then just get a 2.5'' collector Even small block fords run 3'' exhaust or bigger even, nascars, drag racers, open track ect. The amount of tq that you is not even noticable if any. The guy asked what he should do, so i put my .02 in:beer:

No problem--actually I was the one who asked in the first place. I just actually saw the same thing from an article about big block chevy's.

So if I am reading everyone's posts right--

it seems that while you may lose some peak hp and torque with the larger pipe, you get better power vs time.

I am a little confused about power vs time--if the larger pipe has better power v time but the same (roughly) power under the curve, does this just means it lets the engine rev (climb rpms) faster? That's the only conclusion I can draw. Am I understanding that correctly?

EDIT: and if so, then, by extension, wouldn't it be better to increase to a 3.5" for an even more freely flowing exhaust??

 

[98 Saleen Cobra]

Oh sorry bud I didn't realize it was you asking lol.. I'm not to sure about the all the dynamics that these guys are going into. I've seen dyno numbers and I see and research what racing teams are using so that's what I go with lol. I know that a 3.5'' is way to big and you will lose to much tq and stuff down low. I think they key is finding that sweet spot if you know what i mean for the air getting out but still creating enough back pressure.. I can tell you right now that with a 3'' exhaust its perfect. Maybe you can find someone with a 3'' and a 2.5'' and do some testing?? :beer:

 

[Stalker27]

Holy shit this thread turned into a pissing contest quick.

Here's is the deal. I'm dead set on buying the 3" Mac catback so when i put it on along with tha Mac o/r h pipe ( hopefully by next week) i will report back & tell you guys my impressions so when can put this to rest.

Edit: Well the next week part is out. Just got off the phone with Mac & they don't have any of there 3" catbacks in stock nor the o/r h pipe. If i was to put the order in Wed i would get them 2nd week of Nov

 

[spartansnake]

Even if i had a stock pullied cobra with just an intake. The first thing i would do is big primary long-tubes with a 3" exhuast. Best mod i did to my car is the 1" 3/4 X 3" collectors mated to a 3" O/R X pipe. Im currently getting rid of the 2.5" Bassani and replacing it with a MAC 3". If i could do it over again, it would be 1" 7/8 longtubes. Dont be afraid people, go big or go home. Theres a reason why the fastest Terminators are ALL running longtubes....

 

[cah41]

Even if i had a stock pullied cobra with just an intake. The first thing i would do is big primary long-tubes with a 3" exhuast. Best mod i did to my car is the 1" 3/4 X 3" collectors mated to a 3" O/R X pipe. Im currently getting rid of the 2.5" Bassani and replacing it with a MAC 3". If i could do it over again, it would be 1" 7/8 longtubes. Dont be afraid people, go big or go home. Theres a reason why the fastest Terminators are ALL running longtubes....

I agree that the fastest terminators are running longtubes.

But that is because they are running over 700hp. I have read from trusted technicians who are very experienced with building 4.6 mod motors (read a long, detailed thread over on modular fords. He emphatically stated that the stock tubes are not at all a choking point until ~700hp, and that replacing them before that mark will net nothing.)

So if you plan on getting a whipple 3.4, or a 2.8H with high boost, go for the LT's. But anything less you are wasting your money--again, not my personal opinion, but from what I've read from what I perceived as reliable and knowledgeable sources (I wouldn't make that statement unless I had read it numerous times from several different sources, because I have no first-hand experience with them myself). So for what its worth--

 

[cah41]

Holy shit this thread turned into a pissing contest quick.

Here's is the deal. I'm dead set on buying the 3" Mac catback so when i put it on along with tha Mac o/r h pipe ( hopefully by next week) i will report back & tell you guys my impressions so when can put this to rest.

Edit: Well the next week part is out. Just got off the phone with Mac & they don't have any of there 3" catbacks in stock nor the o/r h pipe. If i was to put the order in Wed i would get them 2nd week of Nov

Well I am probably waiting until after then to do mine anyway, so if you don't mind--let me know what you see from them. And if you bring it to a tuner to get it installed/tuned/dynod afterwards get their input as well (on the 2.5 vs 3 inch deal for 400-500 hp range 4.6's).

 

[Stalker27]

Well I am probably waiting until after then to do mine anyway, so if you don't mind--let me know what you see from them. And if you bring it to a tuner to get it installed/tuned/dynod afterwards get their input as well (on the 2.5 vs 3 inch deal for 400-500 hp range 4.6's).

Will do. I'm installing it myself & i'll probably do a before & after dyno cause i already know that nobody is going to go just by my word & honestly I want to know myself.

 

[spartansnake]

I agree that the fastest terminators are running longtubes.

But that is because they are running over 700hp. I have read from trusted technicians who are very experienced with building 4.6 mod motors (read a long, detailed thread over on modular fords. He emphatically stated that the stock tubes are not at all a choking point until ~700hp, and that replacing them before that mark will net nothing.)

So if you plan on getting a whipple 3.4, or a 2.8H with high boost, go for the LT's. But anything less you are wasting your money--again, not my personal opinion, but from what I've read from what I perceived as reliable and knowledgeable sources (I wouldn't make that statement unless I had read it numerous times from several different sources, because I have no first-hand experience with them myself). So for what its worth--

I understand what your saying, but. Even the fast heaton crew runs longtubes. Most of them dont even make more than 550rwhp. Thats pretty far from a "high boost, big twin-screw" car...
Another thing is dont always go by dyno numbers to come to a conclusion. If you only pick up 10rwhp peak (usually more under the curve) longtubes for me were justifiable because they dropped my boost 2psi, evacuates the heat faster, and makes my car sound like no other v8.
I will always recommend long-tubes to any terminator owner, any v8 owner in fact. :beer: