Exhaust velocity/restriction question • The Dodge Challenger Message Board

by **Goldenblack440** » 10 Oct 2009 13:45

I want to swap exhaust tips (Rallye tips). The exhaust is a twin 2 1/2" and the tips at the moment are 3" pipe tips, i want to pull these off and keep them for my 440 project and swap them for some smaller 2" pipe Rallye tips. My question is, if i get these smaller diameter welded on, can i assume that there will be be no restriction to be concerned about here, right at the end? Since the exhaust gases have lost a lot of their velocity by then due to cooling? Thanks.

by **dave-r** » 10 Oct 2009 16:36

Correct. They will not restrict anything.

by **burdar** » 10 Oct 2009 17:11

I have a hard time believing that going from 2 1/2" to 2" won't be a restriction. Ontop of that, the factory tips are installed into the end of the muffler. To do it right, you need to have the same size all the way through the system. The tip end should be swedged to 2 1/2" ID and installed over the end of the muffler. 2 1/2" stainless steel tips are available.

That being said...it will be a restriction but I don't know if you would ever notice it. But if you are going for maximum HP...every little bit counts.

If you really want to get the most out of your exhaust system...you should be running a full "mandrel bent" system. A 2" mandrel bent system will out-flow a 2 1/2" convensional system.

by **Goldenblack440** » 10 Oct 2009 17:22

thanks for quick answers. I'm with Dave on this as firstly i don't have a factory twin system (ie, no resonators or mufflers next to the fuel tank), i am only running two straight through turbo mufflers after an X pipe (too keep it legally quiet) just behind the trans X member. My system is mandrel bent, so there is about 7 foot of free flowing pipe from the muffler to the tip -well enough time for it to be slowed and cooled to a point where a half inch will not make a discernable difference. On top of that, i rarely rev my engine to the area where there will be max power. Its street driven, there is plenty of cops around here and up to 4000rpm that diameter difference will not be felt.

by **dave-r** » 10 Oct 2009 18:06

burdar wrote:I have a hard time believing that going from 2 1/2" to 2" won't be a restriction.

If that was a reduction at the header end of the pipe you would be correct. But not at the tail end.

by **patrick** » 10 Oct 2009 21:40

I'm with Dave! :thumbsup:

by **Jon** » 11 Oct 2009 2:29

On my 340 small block there is 2-1/4" to the mufflers then 2" beyond to the tips. I think the smaller size is not a problem after all the muffler back pressure. :nod:

The 2'' pipe has a rather long 4'' swedge to fit the tips in so no leaks at all. I wouldn't weld them on (tips) as some adjustment is nice to have around the valence cut outs.

Here's something to look at. :s004:

by **Goldenblack440** » 11 Oct 2009 7:39

Thanks Jon! that's exactly how i want mine to look. The A hole who did my exhaust had them pointing down at an angle and sticking out so far you could see the spot welds holding them on. Plus one tailpipe hits on the shock absorber and generally a rushed job and little care for top dollar. But i will get another exhaust place to put these other tips on. How do you recommend them being held in position? With an exh U clamp? As long as the clamp can be rotated so that's its not visable. Its true, that to get them sitting as right as possible, that some movement and adjustment is good to have.

by **burdar** » 11 Oct 2009 13:34

Does anyone know if those tips were installed at the factory or if they were in the trunk to be installed at the dealer? If they were installed at the factory...is there any paperwork describing how far the tips should be sticking out the back? I see cars with the tips at all different depths.

by **Jon** » 11 Oct 2009 14:29

Sorry to hear about your experience, there are bents on bents to deal with, and the larger diameter pipe is that much more difficult to fit.
The guy that did mine spent most of the day on it. He was the best in town at the time. I lucked out.

As for the hangers he used this rubber insulted U-clamp set up bolted to the stock holes in the trunk. I recently had to move the over axle section back to fit a sway bar and the adjustment provided was a real lifesaver.

by **Goldenblack440** » 12 Oct 2009 10:06

Thanks Jon, those hanger adjusters are great. Nice big photo too ! I have not seen those over here, although i'm sure they do have them. I spoke to another exh shop this afternooon, he said the easiest way to graft on the 2" pipe tips to the 2.5" tail pipe was with a flange arrangement. But i can't see why they can't just swage a 4"length of tube as an intermediate between the two.

by **burdar** » 12 Oct 2009 14:42

Going from 2 1/2" to 2" kind of tuff to do. I know they do sell the reducers but they were always hard to make when I did exhaust for a living. We used aluminised pipe that was seamed. On more than one occation, the seam would split if you tried to expand a 2" OD piece to 2 1/2" ID.

by **Goldenblack440** » 12 Oct 2009 20:19

yes i suppose swaging that much diameter difference in a very short length is difficult. The trouble with the flange arrangement is that it is an abrubt change, so there will be a ledge, unlike a smooth transition. I might ask other places and see what else they suggest

by **dave-r** » 12 Oct 2009 21:23

Oh you do need a smooth transition otherwise you are talking a lot of back pressure after all.

by **Jon** » 13 Oct 2009 1:07

Maybe transition into the back muffler with 2-1/4 over-axle, then reduce the pipe to the 2" tips.

As for maximum flow, the 2-1/2 inch tips probably are better as Burdar suggested .They just don't look right IMO though. :s022:

by **Goldenblack440** » 15 Oct 2009 14:16

I don't have the back mufflers -just two straight through Turbo style behind the X pipe. Anyway, problem solved today. Took them into another exhaust place. Unlike the first fellow who said they would split and wanted to make a meal out of it by using two flange arrangements with bolts etc, this guy said no problems, and simply swaged the 2" pipe up to the same ID as the 2 1/2" on my tailpipe. So they will fit inside and just clamp up. Easy for $10. However, back to the restriction question - as you can see by the pictures, there is a deflector/splitter welded inside there which is supposed to deflect half the gas to the other side. But it looks to me like it would be the very same type of restriction we are talking about! It would not be noticeable in my application but they probably not necessary unless on a very cold morning you like people to see steam coming from all four outlets!

by **Jon** » 16 Oct 2009 3:40

Nice looking stainless tips there. :thumbsup:

Glad things worked (swedged) out for you.

I'm curious if that material is more malleable then regular exhaust pipe.

So you are keeping the over axle pipes and installing the tips in place of the 3" ones? How does the offset on these tips work out with that?

As for the diverter, I would guess it does have some additional back pressure and you are right noone would ever notice it if removed.

by **Goldenblack440** » 17 Oct 2009 17:26

Thanks Jon, yes, interesting you say that, because as i was watching him use the expander, i could see how elastic the metal was. It was amazing watching it expand, then when he released the pressure, you could see it go back down a little. These were made in Australia, copies yes, but at least they were lovingly copied here, not mass produced in China, like the 3" ones on there now. The stainless steel they used was probably a marine grade stainless. It was quite malleable. The exhaust fitter said that pipe is just rolled and formed sheet. The pipe can 'split' along that seam if it is expanded too aggressively or too much. But luckily these ones didn't.

The reason i am swapping them around is so i can keep the 3" ones for my 440 '71 Challenger. This will be running twin 3" system. And will be more of a performance motor. This '73 360 is more of a nice tractable street car, so a tiny exhaust restriction at the end will not be noticed.

Not sure what you men by 'offset' but i am hoping they will fit into position the same as the others, in relation to the tailpipe and the valance opening

by **Jon** » 18 Oct 2009 2:38

Looks like nice material. Those welds are perfect too. Glad it's going well.

What I meant by the offset was, I thought you had straight thru tips, aftermarket ones. Sounds like they were larger repros so things should line up pretty well. :thumbsup:

by **Goldenblack440** » 18 Oct 2009 16:03

Yes these are copies of some genuine ones. The welding is good, isn't it...? Fully welded. Better than the imported ones on at the moment. They only spot welded them in about 5 places around the join. The only drawback with these ones is the pissy 2" pipe he used.