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WRAWRRR, BEAR CLAW!
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I want to ask this of you guys publicly, so we can educate the masses as we discuss.

Being that our wagon has the Borla cat-back on it (edit -- it is a 2.5") -- do you believe we'd see significant gains if we chose a 3" exhaust?

Ken - What is on your orange L3 beast?

Walter -- same for your built black hatch

Thanks for your help... we just got a new system, but I hesitate to install it if it's going to hurt hp. (it's only 2.25"
)

K
 

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EAT MORE CORN DAMNIT!!!!
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Borla is 2.5 inch & keeps the cat (unless yours is special...
)
 

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Mr Know-It-All
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They are referring to the second cat - the one found under the car. Early Borla systems deleted it, whereas newer ones force you to keep it in place.

Walter has a 3" on his Black Beast unless he has changed it recently. I recall that Ken said the Orange Beast wears a Borla right now too, as their own exhaust was not available when they built the car.

I would not put a 2.25" exhaust on a Level 2 Cosworth car - it needs more than that. If you plan to go even further with the car it will surely hurt the performance. This engine likes to breath and the bigger the tubes coming in and out, the better.

>8^)
ER
 

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Good question, I just went with 3" on my mustang because 2.5" was just too small for making past 500hp. As soon as I switched to 3" (*with cats*) I saw a increase of almost 20hp. Which I really didn't feel but the torque went up across the band, which I really did feel! But its a much bigger question since the duratec head, cams, engine managment are completely different than a old pushrod 5.0ish engine...

-bix
 

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I want to ask this of you guys publicly, so we can educate the masses as we discuss.

Being that our wagon has the Borla cat-back on it (edit -- it is a 2.5") -- do you believe we'd see significant gains if we chose a 3" exhaust?

Ken - What is on your orange L3 beast?

Walter -- same for your built black hatch

Thanks for your help... we just got a new system, but I hesitate to install it if it's going to hurt hp. (it's only 2.25"
)

K
It would be educational to dyno the car as is with 2.5" at MD Automotive and then swap out to the 2.25" and redyno. That would answer all the questions regarding pipe size. I just don't know if you've got the time.
 

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I'd like to have someone drive a car with a 2.25", 2.5" and 3.0" and don't tell them which is which and have them comment on power, well how the power feels to them. Maybe have the windows up with the music on just a bit loud. Maybe I should see if FocalJet would do this kind of test. Aside from a dyno of course. Sometimes the dyno doesn't tell the whole story, like how the car feels while launching and low RPMs at part throttle and then you punch it. Is it responsive or...?
 

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Yes, the Cosworth car has a Borla exhaust system.
 

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I've got a healthy set of cams and a 2.5"borla that remvoved the second cat.

The car has never fealt boggy or lacking punch and is always a pleasure to drive. btw, induction noise from the cams is sexy and it also significantly increased exhaust noise.

Randy, how hard do you think it would be to setup a mini exhaust shootout? Have 2 2.25" and 2 2.5" and maybe borrow the 3" from Walter. Do it on 2 cars, have be just an intake and the other have like a header and cams. Swapping the exhaust doesn't seem to be to big of a chore on this car either.
 

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Official [FJ] Distinguished Advisor
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That's right. Most of it comes down to your application.

Purely street driven? Or a trailered open-track car?

It's all about exhaust gas velocity.



Walter has posted in this forum that his 3" doesn't hurt torque; but his motor's been rubbed on quite a bit.

I've spent some time pondering these things for a few years now after having Flowmaster specify a system for my 347 inch smallblock that worked incredibly well; they revealed some interesting factoids...

I would think that the best system for a Level 2 car would be as follows:

Header with 3" collector > 3' pipe > 3" stealth muffler (FocusSport, Borla, a perforated core straight-through) > 3" pipe > another 3" muffler of the same type as the first, then, at the rear axle, use a long, smooth reducer to reduce exhaust system diameter from 3" to 2.5" from the rear axle to the rear bumper. Here's why:

Exhaust gas temps are a certain temperature as they leave the cylinder head port. By the time they reach the rear axle (arbitrary point for the sake of illustration) they have cooled somewhat in temperature. Flowmaster suggests that at that point, one should reduce exhaust system diameter in order to maintain exhaust velocity.

Interesting stuff.
 

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I like your thinking, Z63R. At least, the part about no cats running two straight-through mufflers. Give me another few months and I'll have a setup quite like that. I may keep a high-flow cat just 'cause.
 

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I've got a healthy set of cams and a 2.5"borla that remvoved the second cat.

The car has never fealt boggy or lacking punch and is always a pleasure to drive. btw, induction noise from the cams is sexy and it also significantly increased exhaust noise.

Randy, how hard do you think it would be to setup a mini exhaust shootout? Have 2 2.25" and 2 2.5" and maybe borrow the 3" from Walter. Do it on 2 cars, have be just an intake and the other have like a header and cams. Swapping the exhaust doesn't seem to be to big of a chore on this car either.
It wouldn't be hard to do, however I would just be worried that if it wasn't some kind of official FJ thing that whatever the outcome was, it might be condidered biased if any sponsor had anything to do with it. I dunno.
 

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I've got a healthy set of cams and a 2.5"borla that remvoved the second cat.

The car has never fealt boggy or lacking punch and is always a pleasure to drive. btw, induction noise from the cams is sexy and it also significantly increased exhaust noise.

Randy, how hard do you think it would be to setup a mini exhaust shootout? Have 2 2.25" and 2 2.5" and maybe borrow the 3" from Walter. Do it on 2 cars, have be just an intake and the other have like a header and cams. Swapping the exhaust doesn't seem to be to big of a chore on this car either.
It wouldn't be hard to do, however I would just be worried that if it wasn't some kind of official FJ thing that whatever the outcome was, it might be condidered biased if any sponsor had anything to do with it. I dunno.
Hey guys, don't forget that the size of the exhaust is only one part of the equation. As we found out in the original exhaust shoot-out, overall system design tends to be just as important if not more important. Remember how some 2.25" systems did great (Focus Sport for example) but other 2.25" systems did really poorly(I won't mention names here)?

Not that a Duratec exhaust shoot-out wouldn't be a great idea. I just think that it would be a good idea to do it in a similar manner to the Zetec shoot-out and with all the systems available. You can't test one 2.25" system and say that all 2.25" systems will perform the same as the one tested. And you can't test one 2.5" system and compare it to one 2.25" system then say that one SIZE is better than the other size for a certain application. But yea, you CAN say that that in the two specific systems you tested, one is better than the other for the tested application.

But then again, it doesn't seem like there's quite the number of systems out there yet. How many are there?
 

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Our Orange car has a Borla. Our 2.5" exhaust was not
ready when we built the car. However, the engine in the
orange car is coming out next week for some upgrades
and we will install the Cosworth exhaust at that time.
On the Borla, we did add an additional glass pack style
muffler as it was too loud without it.

Ken.
 

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WRAWRRR, BEAR CLAW!
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Discussion Starter #17
I want to ask this of you guys publicly, so we can educate the masses as we discuss.

Being that our wagon has the Borla cat-back on it (edit -- it is a 2.5") -- do you believe we'd see significant gains if we chose a 3" exhaust?

Ken - What is on your orange L3 beast?

Walter -- same for your built black hatch

Thanks for your help... we just got a new system, but I hesitate to install it if it's going to hurt hp. (it's only 2.25"
)

K
It would be educational to dyno the car as is with 2.5" at MD Automotive and then swap out to the 2.25" and redyno. That would answer all the questions regarding pipe size. I just don't know if you've got the time.
I'd hate to go through the trouble of installing the smaller system and have it not work out.


But it is a good idea.

I like Randy's idea of a 'shootout' as well. Now we just need a manufacturer to participate in such fun. At least with the proper mufflers and tips. We could either do it at FS, or at MD, which is convenient with Ace Muffler right next door!
 

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OK, I think this might be something worth pursuing.

There aren't THAT many exhaust systems available yet for the duratec so now would seem to be a good time to do it.

I'd propose a 2 car test, one lightly modded, the other somewhat heavily modded. For the location, if it were to be at FocusSport I'm sure we could get a few people from the contributing sponsors to come and watch and verify that everything is on the up and up. I'm sure there are also various other locations available if that isn't agreeable.
 

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Header with 3" collector > 3' pipe > 3" stealth muffler (FocusSport, Borla, a perforated core straight-through) > 3" pipe > another 3" muffler of the same type as the first, then, at the rear axle, use a long, smooth reducer to reduce exhaust system diameter from 3" to 2.5" from the rear axle to the rear bumper. Here's why:

Exhaust gas temps are a certain temperature as they leave the cylinder head port. By the time they reach the rear axle (arbitrary point for the sake of illustration) they have cooled somewhat in temperature. Flowmaster suggests that at that point, one should reduce exhaust system diameter in order to maintain exhaust velocity.

Interesting stuff.
Agree and disagree. I think a 3" exhaust would be a little agressive for NA engine, 2.5 " would be ok for up to 200whp and anymore than that a 3" would be appropriate. But if the engine is going to have any sort of power adder then a 3" would be the way to go....
Take it easy
-bix
 

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Chris, to do what you're talking about right we'd need to use some temp. probes placed in the exhaust every six inches or so. If you did that you could use a combination of the ideal gas law and the venturi eqn along with something to measure exhaust velocity at the tip and you could figure out relatively easy how the gas changes volume and how the velocity changes.
 
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