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Message started by backroadbozo on 10/17/20 at 15:32:56

Title: Custom Exhaust Fabrication
Post by backroadbozo on 10/17/20 at 15:32:56

Hey y'all,
I'm looking to get a new header made. I'm going to run it in the same location as stock. The main reason for going at this is I want to open up the ID for better exhaust flow. The stock inner pipe is 1.5 inch if I'm not mistaken? I know that really the max ID anyone wants to go on these savages is 1 5/8 inch or 1.625 inches. The main question is if I get a 2 inch OD tube with a 1.625 ID that will put the tubing wall thickness at about 4.75mm or .188 inch. When is wall thickness too thick for an exhaust? For one, I can guess that that dimension of steel tube will probably be heavier than the stock header and harder to bend. I want to go this route because I had just purchased a straight thru muffler that is 2 inch ID. I cut off the old mounting point for a muffler and ran it on the outer tube of the stock exhaust. It looks great and sounds great but now I want my whole exhaust system to perform great.
Does anybody have info to share? Has anybody gotten a new pipe made and what dimensions did you go with? What was the outcome?
I do plan on doing hi-comp piston, cam from lancer, and carb upgrades as well. I'm just trying to gather as much info as possible so I can knock it all out at once. The exhaust is the last piece to the puzzle... for the engine anyway.

Title: Re: Custom Exhaust Fabrication
Post by verslagen1 on 10/17/20 at 17:04:47

42464F5A5345030F360 wrote:

The stock inner pipe is 1.5 inch if I'm not mistaken?

I believe Lancer said a 1.5" ID was about right. The current pipe is about 1.375" For the sake of convenience, 1.75" OD is about what you'll end up with and that'll fit any HD muffler.

Quote:

The main question is if I get a 2 inch OD tube with a 1.625 ID that will put the tubing wall thickness at about 4.75mm or .188 inch.

;D math is funny. That's what our stock pipe is, but it's double wall. You'll want somewhere between .03 and .06" wall

Title: Re: Custom Exhaust Fabrication
Post by backroadbozo on 10/17/20 at 17:47:39

What exactly does a thicker wall affect? I've read a few articles on the inter web that most exhaust tubing is between .030 and .060, but what if you went thicker? I haven't found any info that explains an answer. The only thing I can think of is that the exhaust won't be able to dissipate heat as quickly or effectively. But then again, most people wrap their headers with heat wrap so does it really matter that much about heat dissipation? I'll keep looking around. I think if I went with the dimensions I mentioned above the header will be way to heavy without additional support and I aint really about heavier. After all, bobbing means shedding weight, not adding it back on!

I just got done reading DragBikeMike's 97mm build and he used a Mac header which is 1.73" ID and OD is 2" I believe. That would put the Mac header wall thickness at around .140. No exhaust wrap though.

Title: Re: Custom Exhaust Fabrication
Post by Fast 650 on 10/18/20 at 10:20:05

A thicker wall doesn't affect performance other than adding weight. As far as diameter and length go, the available cams for the Savage have zero or near zero overlap so pipe tuning has no advantages that you can feel with the butt dyno. You will feel a difference going from the stock 1.3" ID to a 1.5" ID or bigger pipe due to reduced restriction. But from 1.5" to 1.75" ID there is no appreciable difference. Those are nominal dimensions, exhaust pipes will vary a few thousandths one way or the other. I have a preference for 1.75" OD (which gives an ID of about 1.625") because the exhaust velocity is in the sweet spot at the peak HP RPM, and there is a greater choice of mufflers available for that size.

Title: Re: Custom Exhaust Fabrication
Post by backroadbozo on 10/18/20 at 11:50:05

Thanks Fast650. I was trying to go 2" OD just for the fact of keeping my reverse cone muffler I just bought a few months ago, but to get an appropriate ID with 2" tubing will put the header at way more weight than I want. I wish I would have done more research before buying muffler. Knowing what I know now, I would have just bought the 1.75" version. Oh well, I'll just have to bite the bullet and buy the 1.75 version. Anyone want to buy a slightly used 2" reverse cone muffler? [smiley=lolk.gif] I'm going to go with 1.75" OD with the ID of 1.625. From what I'm reading, and from what you said, that seems appropriate for our bikes with a stage 3 cam and vm38 carb.

Title: Re: Custom Exhaust Fabrication
Post by Fast 650 on 10/18/20 at 23:35:06

You can still use your muffler with 1.75" OD pipe if you get an adapter to go from 1.75" to 2". Check your local auto parts stores. I haven't looked recently but that used to be a pretty common item.

Title: Re: Custom Exhaust Fabrication
Post by verslagen1 on 10/19/20 at 07:48:12

All you need are 2 strips of material .060" thick rolled to fit.
And slip them in between the header and muff.