[scott70]

RARE makes a 3" mandrel bent down pipe thats made to hook up to their 2.45" RA manifolds. Would there be a decent power increase over a 2.5" down pipes? Assuming you would extend the 3" downpipe with 3" pipe,,,at least back to the front of the muffler. And then leave the 2.5" mufflers and tailpipes.

[Formulajones]

Speaking of that area of the exhaust in particular with these manifolds, that very first bend right off the manifolds is critical and a HP killer if it's a crush bend. It's been dyno tested a bunch of times and a mandrel bend there is a pretty substantial improvement.
With that said, going to a larger than 2 1/2" pipe for that mandrel bend can only help the situation. Wish I had a pair of them last time at the dyno, I could have back to back tested them against the 2 1/2" mandrel setup.

[scott70]

Yes,,,I meant to say compared to 2.5" mandrel bent headpipes. Only difference would be in size. Obviously not ideal being the exhaust manifold outlet is only 2.5" compared to the 3" pipe but Im curious if there would be a power gain and just guessing how much would it be? Just seeing what peoples opinions would be if it would be a worthwhile thing to do. The picture of the 3" headpipes it looks like they just had a stubby piece of 2.5" and just welded it to a 3" pipe.

[Formulajones]

I figured that's what you meant.
I wouldn't think going to 3" right out of the 2 1/2" manifold would hurt anything and shouldn't be an issue. The larger pipe can only help that first 90 degree bend which is the real restriction. I have seen going the other direction (necking things down) be a big issue though if the transition is abrupt.

Like a 3" header collector that quickly necks down to a 2 1/2" exhaust system right off the collector with those cheap adapters. That affects power output. It's always best to make that transition gradual and there are 12" long merge collectors to do that. But that's a different subject.

[ScumOne]

Not sure if I can help, but my RARE exhaust manifold down pipes are going to 2.25" pipe to the mufflers tomorrow. I was just told to taper it evenly.

[Murf]

I used them on my wife’s 64. Can’t say anything about power difference. I used them cause they seem to not hang down as low as his 2.5 headpipes. Better ground clearance. I ran them to a 3 inch x pipe then went 2.5 the rest of the way. The connection at the manifold is a little bit of a pain. I ended up using Allen head bolts & ball type wrench to tighten them up. It’s tight in there.

Murf

[Skip Fix]

I am assuming they still use a 2.5 flange at the manifold? Even the 2.5 it was hard to tighten all the nuts easily on mine.

[scott70]

Originally Posted by Skip Fix

I am assuming they still use a 2.5 flange at the manifold? Even the 2.5 it was hard to tighten all the nuts easily on mine.

From their picture on the website of the 3" down pipes it looks like the same 2.5" flange but quickly jumps to 3" . Thinking about ditching my 2.5" X pipe system and trying the 3" downpipes then go back to a 3" X pipe and then use a 3" to 2.5" reducer cone and leave my 2.5" dynomax ultraflows and 2.5" tailpipes. Trying to make the exhaust as efficient as possible without actually using headers. I used to have this exact setup on another car but did use headers but his time I want to keep the RA manifolds.

I come up with these crazy ideas because I just cant leave it alone but I hate wasting time and money if Im not going to get anything out of it or actually decrease power. My current mandrel bent pipes arent that great if you ask me. My old dr gas x 3" mandrel system had perfect bends and the 2.5" tailpipes were perfect but when I ordered my current 2.5" headpipe/xpipe system the mandrel bends were crushed more than a mandrel bend should be.

[OCMDGTO]

Scott,
I picked up 2/10 by adding the RARE 3" to 2.5" before the mufflers( with X). I had a crush bent 2.5" headpipe w X to 2.5 mandrel bent system an went 12.1. I put mandrel bent 2.5" headpipes on and stayed at 12.1. Then I did the whole RARE system above and got to 11.9. Hindsight being 20/20 I would have gone all 3". So yes, it's worth it. As stated, the bolt access really sucks but is doable on the 3" and no problem at all on the 2.5".

[Formulajones]

Since you want to go from 3" headpipes to 2 1/2 after the X, and since you aren't happy with your current X, and you like dr gas stuff, he makes it very easy to go from 3" to 2 1/2" with his X setup. It necks down on the outlets of the X.
This is actually the preferred way to do something like this and is what I've used on header systems that have 3 1/2" collectors that need to be necked down to a 3" system.

I know, more money 😁

[scott70]

Originally Posted by OCMDGTO

Scott,
I picked up 2/10 by adding the RARE 3" to 2.5" before the mufflers( with X). I had a crush bent 2.5" headpipe w X to 2.5 mandrel bent system an went 12.1. I put mandrel bent 2.5" headpipes on and stayed at 12.1. Then I did the whole RARE system above and got to 11.9. Hindsight being 20/20 I would have gone all 3". So yes, it's worth it. As stated, the bolt access really sucks but is doable on the 3" and no problem at all on the 2.5".

Just what I wanted to see! Thanks

[scott70]

Originally Posted by Formulajones

Since you want to go from 3" headpipes to 2 1/2 after the X, and since you aren't happy with your current X, and you like dr gas stuff, he makes it very easy to go from 3" to 2 1/2" with his X setup. It necks down on the outlets of the X.
This is actually the preferred way to do something like this and is what I've used on header systems that have 3 1/2" collectors that need to be necked down to a 3" system.

I know, more money ��

Shows you where Ive been,,,I thought they were out of business and havent googled their company since.

[scott70]

So its prefered to use a 3" to 2.5" X junction over a 3" by 3" X junction to a 3" to 2.5" reducer cone before the muffler?

[Murf]

Originally Posted by scott70

So its prefered to use a 3" to 2.5" X junction over a 3" by 3" X junction to a 3" to 2.5" reducer cone before the muffler?

No , that’s how I did it. IIRC. Going all the way with 3” should be better in theory. IDK if you’d ever notice the difference on a street car.

Murf

[Formulajones]

Originally Posted by scott70

So its prefered to use a 3" to 2.5" X junction over a 3" by 3" X junction to a 3" to 2.5" reducer cone before the muffler?

Well, 3" all the way would be best for sure.

But if you have to absolutely neck the exhaust down at some point through the system, the best way to do it is with the "X". There has been testing on that deal as well and it works better than just sticking a swedged adapter on there.

Where you find this most commonly used is when someone has headers with 3 1/2" collectors, because no one runs a complete 3 1/2" exhaust. Everyone would just neck down right at the collector and bolt on their 3" exhaust.

Decades ago Dr. Gas came out with an X that did this for you. So you could keep the collector size of the header the same size to the X, which is where it counts most. But this has been done on 3" collector headers as well for those that want to run a 2 1/2" exhaust out the back. Dr Gas makes those too.

However putting an exhaust adapter all the way back after your 3" X may not affect things as much since exhaust gasses aren't moving as fast back that far in the system. The point I'm trying to get across is everyone puts an exhaust reducer right at the header collector, and that's a bottleneck. I know you aren't doing that but wanted to point out "X" cross overs are made to accomplish this so you don't have to fab up an exhaust like that, and having this done toward the rear of the systems where exhaust gasses aren't moving as fast is more beneficial and don't affect power output as much. I wasn't trying to sell you on it because it sounds like you already have a system to work with anyway.

[scott70]

Back in the day I used 3" up front and I think a 3" to 2.5" flowmaster reducer cone that was probably a foot long and into the muffler.

[Formulajones]

Originally Posted by scott70

Back in the day I used 3" up front and I think a 3" to 2.5" flowmaster reducer cone that was probably a foot long and into the muffler.

Yep those are the reducers I referred to earlier. Best way to adapt if you need to.

Those cheap little 3" or 4" long reducers are abrupt and nothing but a swedged pipe.

[OCMDGTO]

Scott,
Here's a couple pics of mine. It took some cutting to fit, but uses quality materials from RARE like usual. Hope this helps

[scott70]

Looks like you went with 3" oval? I was thinking just going round.

[OCMDGTO]

First 3 feet coming off the manifold are round, oval for the X and the back to round 2.5" before the mufflers.