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Topic Review (Newest First)
05-31-2014 08:13 AM
dyn085
Quote:
Originally Posted by Buildist View Post
You are neglecting the significance of the heads and intake (manifold). Everything works as a whole. Sure, the cam grind will set the performance parameters of the engine, but if the head design is not to the needs of the cam it is all over. So too is the significance of the intake manifold and header design to support the head and the cams. Exhaust is a trickier thing than many people think. The engine is not merely an air pump because that air changes temperature drastically and the thermal dynamics introduces additional physics elements to be considered to make the engine perform at peak performance.

You are right, the exhaust can only hinder the efforts of the headers. However, in most everything in the world, the "If some is good more must be better" mentality doesn't work, or at best only works up to a point.





Steve
I'm actually not forgetting about anything forward of the header, I'm simply omitting it due to the fact that this is an exhaust thread. Out of all of the dyno sheets I've seen on this forum, the only ones that showed a loss anywhere in the rpm range were due to the intake, and that loss was in comparison to another intake-not the OEM design.




Quote:
Originally Posted by Buildist View Post
I wasn't comparing a V8 to a 4 cylinder, other than to say most V8's cannot benefit from a 3" exhaust, I don't know how people think a 4 cylinder, N/A with no building, can.

My whole contention was exhaust velocity and torque across an RPM range. A 3" exhaust will reduce both while allowing more HP at top RPM, which is not useful on the street.


Steve
A 3" exhaust will benefit the Mk3 with no other engine building. If the header remains the same then the torque curve will not move in one direction or the other. You won't give up anything anywhere in terms of power. There are no before/after dyno sheets that I am aware of, especially with 3" because I've only seen or know of two Mk3's that have had 3" installed.

Will it benefit more in any significance when compared to a 2.5" setup? If everything else is OEM, most likely not. If the intake is aftermarket, probably a little. Add a tune, probably a little more. But no matter what is or isn't added (outside of the header), it will not hurt power at all anywhere.
05-30-2014 11:52 PM
Buildist I wasn't comparing a V8 to a 4 cylinder, other than to say most V8's cannot benefit from a 3" exhaust, I don't know how people think a 4 cylinder, N/A with no building, can.

My whole contention was exhaust velocity and torque across an RPM range. A 3" exhaust will reduce both while allowing more HP at top RPM, which is not useful on the street.


Steve
05-28-2014 07:41 AM
Briggs I love how these threads go from simple exhaust pictures to comparing a V8 to a 4 cylinder.

So 2 side exhaust and no videos??
05-06-2014 10:58 PM
Buildist
Quote:
Originally Posted by Seminoles View Post
If this is true why did Ford use cams that put the torque @ 4450 rpm and horse power @ 6500 rpm ( if I shift @ 4450 people think I racing them, why not 2500 rpm max torque ) if you add this to comparing your two V8 engines they would be full blown race engines at these rpm's. These four banger's are high efficiency motors I believe in one of the Ford write ups about direct injection it was said cylinder salvaging was not needed as much unlike other engines as in no EGR valve.

Four cylinder engines have to rev higher to make their power (N/A) than larger engines, this is why the peak torque is at 4450 rpm. Big block V8's are known for their low end torque. This is why you have higher revs in your Focus at cruising speed compared to larger engines. Four cylinder engines only get good torque numbers down low when forced induction is used. The torque curve in our engines are pretty flat, which is good. Notice that peak torque comes in at a good rpm if accelerating onto a highway, when it is needed most, but otherwise our engines don't go there much, but there is still a very useable amount of torque.

Horsepower is a calculation, not a measurement. It peaks at 6500 again because it is a small displacement engine and relies more on revs to help make power than an engine of larger displacement. V8 engines usually peak around 5240 rpm, if I remember correctly because of the calculation method and displacement, give or take 50 rpm or so.

Engine design for the mass market, to please the widest range of their customers, is a balancing act. There needs to be sufficient power for most types of driving while also not sacrificing fuel mileage in a very competitive market. Emissions are also a factor as well as NVH.


As for the exhaust on my wife's 66 Mustang, it has no cross over pipe. I will be putting in an H-pipe, it is just low on the priority list of things that need to be done right now. I don't want the affect to the sound of the exhaust that an X-pipe gives. The other engine will not be built for a while yet.

Quote:
Power and power bands are really determined by the cams and Header design and the exhaust will mostly only hinder the efforts of the headers, they can't really make it any better, unless the header design is really poor. So more exhaust flow is usually better.
You are neglecting the significance of the heads and intake (manifold). Everything works as a whole. Sure, the cam grind will set the performance parameters of the engine, but if the head design is not to the needs of the cam it is all over. So too is the significance of the intake manifold and header design to support the head and the cams. Exhaust is a trickier thing than many people think. The engine is not merely an air pump because that air changes temperature drastically and the thermal dynamics introduces additional physics elements to be considered to make the engine perform at peak performance.

You are right, the exhaust can only hinder the efforts of the headers. However, in most everything in the world, the "If some is good more must be better" mentality doesn't work, or at best only works up to a point.





Steve
05-04-2014 04:55 PM
Juicedz What size exhaust tips are on the ford Escape? I was looking at a pair yesterday wondering if it would look good tucked into the rear valence or if they would be too big. I do like the slash/rounded cut tips.
05-04-2014 01:46 PM
dyn085
Quote:
Originally Posted by evilO View Post
Off topic for just one sec... I am sure I can find it somewhere but what exhaust are you running? 2.5" Custom? Magnaflow? TIA
2.25" from the flange to a 14" Magnaflow 2.5" center-center, 2.5" mandrel bent from there over the axle into a Jones Camaro muffler and into dual 3.5" resonated tips. Mine is deep and mellow while Injected's was deep and raspy (the good kind of raspy).
05-04-2014 01:16 PM
evilO
Quote:
Originally Posted by dyn085 View Post
Fwiw, the best sounding Mk3's at FocusFest last year were mine and Injected's (depending on whom you talked to, obviously, but many agreed), so that's a 3" setup and a 2.5" dual exit setup. Ymmv.
Off topic for just one sec... I am sure I can find it somewhere but what exhaust are you running? 2.5" Custom? Magnaflow? TIA
05-04-2014 01:15 PM
mustang0 You won't get an argument from me, Duane is right. Iv'e have had my car on the dyno two times and seen good improvements from fairly simple mods. I might do it a third time yet.
05-04-2014 12:56 PM
Seminoles ^^
Like he said...
05-04-2014 12:22 PM
dyn085 There is a lot of misinformation and old-school thought processes dominating the automotive world these days. You can either live in the past or you can embrace technology and science and move forward with the rest of the world.

Backpressure is a myth in the way people think of it. It doesn't make horsepower in any way and only hurts an engines ability to breathe, at least in the way most people here are discussing it (cat-back). Primaries and secondaries (header design) size/length/design are what affect powerband. Cat-back is just a situation of diminishing-gains in the fact that one you've gotten it large enough to effectively remove spent gasses then you will not see enough of a gain to justify the added material cost or work to make it fit.

Exhaust design is a compromise. The most power may not sound the best. The best sounding won't give the best performance. Either of those may not be the best solution financially.

There is a wealth of information available on the internet. You have to do a little research and work to sift through what is true and what isn't so don't just take my word on it. But on top of not taking my word I would also not recommend taking the word of those that still think removing backpressure in the cat-back portion of the exhaust will hurt performance.

Backpressure is the enemy.

Fwiw, the best sounding Mk3's at FocusFest last year were mine and Injected's (depending on whom you talked to, obviously, but many agreed), so that's a 3" setup and a 2.5" dual exit setup. Ymmv.
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