I think it can be agreed on that a true dual exhaust is better than the catback that are normally offered for our cars....but is it the best possible design?

Specifcally and descriptively why is it better, and which is better an X pipe or H pipe? What are the advantages of each as far as RPM and amount of peak HP and TQ. Its always a debate as to whether a 2.5" or 3" system is better. Outside of those two what advantages or disadvantages if any would a dual 2" or 4" system have?

Is there a "perfect" exhaust design in general? How is the design of the exhaust affected by the cam, specifically the exhaust duration?

Just trying to dig a little deeper than usual "loss of backpressure" and too "free flowing" of an exhaust.

 

Some thoughts on exhaust systems for 500+ hp F-cars:

1) Exhaust has to be matched to power the engine is producing. If you have a 500+ FWHP 383, and don't want to lose 10-15% of that power, you need a system equivalent to a dual 3 in diameter non-restrictive system. More below.

2) If you are willing to use two properly installed cut outs (noise is no problem for you) when you are running hard, you can fabricate a system that is about zero hp loss with cutouts open, but is still fairly good (maybe less than 50 hp total loss) thru the large muffler. I've never seen this design for sale, but I'll show it to you if you wish. 3 inch back from the Y would be good if a high flow muffler was used.

3) Generally the muffler flow, or restriction to flow, is a much bigger problem than pipe size. Unless you have flow numbers for a muffler, stick to those like Dynomax Ultraflo welded, where flow numbers are published.

4) If I couldn't (or wouldn't) use cutouts, and wanted most of my 500 hp useful on the street, with a reasonable noise level, I would consider this: 3 inch, mandrel bent pipes behind the 3 inch collector headers. These would "Y" into a 4 inch single pipe back and over the axle and then thru a 4 to 3-1/2 reducer cone into maybe a Ultraflow 17224 (3-1/2 inlet and outlet VERY high flow) muffler. Outlet would be on 3-1/2 mandrel bent elbow, thru a 3-1/2 to 3 in reducer cone and a 3 inch resonator (24222 Bullet) and a 3 inch tip on the left side outlet. This would be the most expensive street system, but you rarely get what you don't pay for.

5) A 4 inch tube flows within 90% of TWO 3 inch tubes, so a well designed 3s-into-4 Y pipe works.

6) As gas cools off from 1200F or so at the head to maybe 300F or less at the tailpipe, the volume decreases a lot, so as it cools along the system you really need to keep decreasing the pipe size to keep the flow at the same speed. That's why the reduction from 4 to 3-1/2 for the muffler and 3 inch tailpipe, which also helps noise. Hey, if you are above 550 FWHP, continue the 3-1/2 outlet, 3-1/2 bullet resonator and tailpipe.

7) Bends cause lots more restriction than straight pipe, so that's why the 4 inch until it's over the axle.

8) As far as true duals dumping out in front of the wheels, ground clearance would be my big concern. Again muffler restriction would be the problem; I'd use UltraFlow welded 17220s on each side. I know that 2 will support about 600 hp without much loss. A 2-1/2 or larger H-pipe would help both power and noise. An X-pipe might be marginally better, but if it didn't fit, or had extra bends I'd use the H-pipe. We're only talking a couple of hp here. With all that dumping under the doors, the noise would be pretty annoying, IMO. Of course, this would be the easiest and least costly good-flowing system.

9) IMO, cam duration, etc. doesn't change exhaust system design unless you are using merge collectors or 180 degree headers. I don't think either of these are in the picture, right?

10) Remember that we're talking about power levels almost twice what a stock LT1 kicks out. All of the stuff above would be overkill and mostly a waste of $ for a basically stock engine.

My highly-opinionated $.02.

 

Very informative and thorough response.

Well I ended up going with a true 3" dual set up exactly like this one. I used to have a 3" mufflex y pipe to a 3" catback with cutout....and without cats it was LOUD. This system shouldnt be as loud but I do like loud exhuasts so I can deal with the noise.

Dont loud pipes save lives?

 

I like most of the above comments, but I have a few more thoughts to add.

I'm not a fan of "in front of tire" exits. There tend to be annoying if driving near any walls or Jersey barriers since sound is reflected directly back to the side window. I like to hear my stereo & not smell exhaust fumes. I had these on a few "limited" street drivers & was glad I didn't have to drive this way every day.

True 3" duals to the rear bumper are a tight fit above the panhard rod & require some mods to fit. 3" duals are not generally required over 2-1/2" tubing unless over 450hp. Dropping a size smaller for tail pipes will reduce noise substantially & ease fitment. I have a 3" dual system that is 100db at idle. Setting off car alarms in parking lots is common. No tickets, but expecting one everytime I drive the car. Full throttle sound is comparable to a Harley with drag pipes. Inside the car is loud, but somewhat livable. There is not much room for mufflers except at the rear bumper location & only small straight thru units fit here. Quieter mufflers are available & ground clearance is fair, but admittedly there isn't much room under the left side of the car for exhaust. Doing it again, I would probably go with a single 4" with dual 3" tips.

A dual 3" y-pipe into a 4" single will result in nearly the same flow with substantially less noise & no clearance problems under the car. This does not require a H-pipe, X-pipe or any other fabrication.... plus they have a nice sound.

Thought I would share my experiences.

 

one thing i haven't read about yet is WEIGHT....needs to be taken into account also when doing an exhaust system

otherwise i've learned a bunch

 

Good point.

How about this math:

3500 lb gross weight / 500hp = 7 lbs/hp

If exhaust frees up 50 hp, that's worth 7 x 50 = 350 lbs ???

Let's say the suggested system wieghs 80 lbs more than a minimal system. (that's high really. 8 feet of 4 inch exhaust tubing weighs 21 lbs). 80/7=11.4 hp. If the system gives 12 hp more, it's a push. Besides putting stuff behind the rear axle not only adds rear weight, it removes front weight!

OK, more weight IS harder to accelerate, but big 50 hp gain is probably worth the weight penalty.

 

WHAT DID YOU SAY? CAN'T HEAR YOU OVER MY IMPALA'S PIPES.

 

That pic looks oddly familiar

And ill throw in Chucks old comparo for some good dyno results:

 

if you running a true dual set up weather it be 2.5" or 3" what is the true need for the x pipe or the h pipe? just for equalization or just sound?

Kmook- i bet i've seen that pic atleast 200 times now. that vid of your car is awesome too.
Rob

 

Yes my exhaust is modeled after kmooks. I should have cited that in my post, but that pic is common place now on the board.

Anywho the weight difference between the dual set up I have(which is the same as in the pic), and a mufflex y, flowtech cutout, and flowmaster catback I used to have is 14lbs...with the duals being the lighter of the two.

 

Reading Chucks post and talking with Old Stroker about it is interesting.

One thing I think that will work well with your new engine and exhuast is that the exhaust timing should like the duals. That's a good benefit.

Bret

 

That setup in that pic should probably have the turn downs turned in rather then out. It would be significantly quieter and less annoying on the street when driving by surfaces that reflect exhaust sound.

I’d bet that most of the HP differences between that dual/X-pipe setup and the 4” cat back is in eliminating the part that goes over the axle… bends suck for exhaust flow. If you made something like the setup in that pic but at the location of the x just put a nice y-pipe and then a single 4” with a 4” muffler of the same design and turn down you’d make better power then most.

Remember, exhaust restriction depends on surface area of the tubing, so you’ll get more flow out of a single larger pipe then dual smaller pipes with the same cross sectional area.

Of course, single exhausts never sound as good as duals