[04FX4]

I want to up grade my exhaust. I do not want to loose any hp or tq.I am leaning towards magniflow but what is better. SI/SO or SI/DO? I see bill always saying SI/DO so which one is best?

[Power Hungry]

From my experience, either single in type is fine. The exit is personal preference as to whether you want a single pipe out the passenger side or duals out the back/corners/sides.

Anyone else have any thoughts?

[JackandJanet]

Originally Posted by Power Hungry

From my experience, either single in type is fine. The exit is personal preference as to whether you want a single pipe out the passenger side or duals out the back/corners/sides.

Anyone else have any thoughts?

Back in the bad old days, before most of you were born, duals with straight pipes that were tuned properly (you didn't want interfering pressure pulses) were supposed to "scavenge" the cylinders better during the exhaust stroke so that they were "cleaner" for the next intake charge.

I imagine, with the introduction of catalytic converters, EGR valves and the like, that these ideas sort of went the way of the dodo.

You'd need a bigger capacity exhaust system if say, you put a blower on the engine (conservation of mass again), but I doubt there's too much reason for changing it otherwise (beyond looks or sound). Possibly you can get a slight power increase with a less restrictive exhaust system, but I doubt it is going to be a significant change on anything beyond your wallet. My

[cleatus12r]

I changed the exhaust on my '73 2wd about a year ago. It's had a few different setups since I started modifying it about 14 years ago.

The one I have now is the one that's staying until it gets turbocharged.

I picked up so much more midrange and top end (as if 4000 RPM is high) that it was scary for the little bit I actually did to it. (dyno proven)

My recipe for success:

Single exhaust. Sure it sounds terrible but it works. The headers never changed....neither did the first 6 feet of 3" dual pipes or the dual dynomax welded mufflers. However, immediately after the mufflers, I joined the two pipes with a "y" (not a "Y") and ran a single 3" pipe out behind the left rear with very little arch over the rear axle.

Instead of losing torque at 3000 RPM, it held absolutely rock steady up until 4000 RPM. For reference, the dyno graph for torque hit 353 ft. lbs. at 1800 RPM and stayed perfectly flat until 3500 RPM. The old setup began dropping torque at about 2600 RPM....even though it SHOULD have had better breathing.

I'm a firm believer in smooth exhaust flow....I've seen it help so many vehicles. For example, a friend's 66 Chevelle with a worn out 327 (45% leakage past the rings on most cylinders) with long tube headers, dual 2.25" pipes and glasspacks dumping in front of the front axle was a complete turd at all RPMs...it was terribly doggy.

Then (against advice from EVERY exhaust shop) he installed 3" pipe from the collectors into *cough* Flowmasters *cough* and did side exits in front of the rear tires. Did he lose any power? No. From idle all the way to redline (nearly 6500 RPM most times) he gained. It sounded terrible due to the Flowmasters, but it ran like a mad chief after the exhaust job.

You DO NOT want backpressure at all. It's a myth. If backpressure was good, stuffing a potato in the tailpipe would make your front wheel drive car do wheelies. You don't want stagnant flow either. Once the flow slows down too much, the engine has to work to push the exhaust out of the pipe.

[kokopellimotorsports]

Cleatus, this is why I am upgrading my exhaust. I will be putting on high flow cats (magnaflow) to a si/do corner exit MBRP exhaust.

To the OP, when you are ready for exhaust let me know, I have access to many manufacturers.

Ty

[JackandJanet]

Nice post, Cody! Everyone can ignore my final comment about exhaust mods only changing your wallet! :o

- Jack

[cleatus12r]

Oh, and I wanted to add that YOU DO NEED SOME SORT OF EXHAUST SYSTEM.

Some folks think that open headers are awesome (and sound good ) but they really hurt performance until the exhaust pulses are often enough (read: high RPM) that there is no atmospheric pressure reversion into the collector or primary tubes.

An exhaust system CAN be too short and it CAN be too free-flowing. Don't get my original post wrong....I re-read it and can see where it might sound like I condone huge pipe that's only six inches long.

Unfortunately, tuning the exhaust is very difficult to do. To do it right, both pipes on a "v" type engine would have to be the exact same length and that's tough when both pipes run down one side of the truck. They should have equal bends (both angle and length) and we know that is impossible. There's always a compromise.

Jack, you're right, most aftermarket exhaust systems or custom exhausts are only for asthetics and sound....let's face it, if it doesn't sound bad-***, it probably isn't. Besides, factory exhaust is not visually pleasing. No disrespect meant to your last comment.

On edit:
The most disheartening thing I see when it comes to exhaust is the pipes people will have installed at an "exhaust shop". As a diagnostic rule, the new Chevy trucks are designed FROM THE FACTORY to have a backpressure to not exceed .5 PSI (one half of a PSI) of backpressure at full load redline. That is VERY LOW. It would be hard to beat that with ANY custom job. The factory pipes on the 2500/3500HD trucks with the 6.0L or 8.1L gassers are 3" and they go into a dual inlet/dual outlet muffler then "Y" into a 3.5" tailpipe that has nice, smooth bends over the rear axle. These people have the dual 3" Inlet/Outlet muffler removed and have two 2.5" pipes/mufflers welded in with tight non-mandrel bent pipe twisting all over the rear axle to avoid the spare tire. Under certain conditions, the backpressure in the pipes will actually cause a passive EGR effect (reversion back into the combustion chamber) and set misfire codes. UGH.

The exhaust from reputable companies (that our vendors sell) are good in the flow department and usually sound really good. Power wise.....maybe a little. But they do look nice with a polished stainless tip!

[JackandJanet]

Cody, no offense taken at all! I was, as usual, being my normal opinionated self and making a broad, sweeping statement that could not possibly be right in all respects. You pointed out holes in it (in a very diplomatic way, I might add) while at the same time supporting other parts of what I said - you just said them better!

Exhaust mods were really a big thing back when I was young. And, you had to be careful with them. You run into many of the same problems I was concerned about in intake mods. Airflow engineering, especially in ducts, is a VERY tricky, poorly understood, science!

- Jack

[88Racing]

Two questions you should ask yourself:

1) How much noise am I or everyone in the truck going/willing to put up with?

2) Are you going to pull any trailors?

Fords are supposed to have quiet steel? On a real long trip the sound may get to you. Especially if your married. "I told you it was going to be to loud"

The trailer question is that it depends what type.
Straight out the back are good with flat beds and most of the time with "V" and round noses.
I would not recomend them when pulling flat nose type trailers such as campers. The sound echos back at the cab.

I recomend some system with side discarge then you don't have to worry about the above.

Lars

[88Racing]

Forgot to add this in.

How long are you keeping the truck?

I only ask that because up here up where I live some of the galv steel kits rot out in 3 to 5 years due to road salt. So I went with with stainless did not want to spend the money again. But it is easily justified if the truck needs a new look again.

Lars