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Delkevic Header C14... getting your torque back

Steve in sunny Fla

Iron Butt
Industry Vendor
If you've followed me for a while, you know I dislike the light throttle torque loss associated with the addition of headers, particularly big tube headers. I have been working on a cost effective way to get the torque back. I have hit on a system / formula that works, and won't cost much money or any peak HP.

Please read the instructions to the end.

1) Source an automotive exhaust reducer that has an entrance OD of 2.375" or entrance ID of 2.25" and an exit side OD of 1.875" or ID of 1.750" . You can find this easily at many auto parts stores, or order online at Rock Auto, Jegs, etc etc. You can order an AP exhaust reducer # 8931 and it will fit the bill. Usually about 5-6.00 dollars.

2) Cut 1.125" off the entrance end (large diameter end) Clean the cut with a file, die grinder, etc.

3) If there's any crimps or metal around the exit, (1.750" end) clean it with a file or die grinder.

4) We're going to be inserting this into the adapter pipe just after the header collector. We want it snug in the pipe. You can test fit it per the pic below, but an easy way to make it snug is to go down the INSIDE about 1/4" from the leading edge the large end, where you cut, and using a hammer / punch, punch 3 or 4 divots from the INSIDE of the pipe towards the outside. this will make little high spots on the outside of the reducer that will prevent it from slipping in the adapter pipe. If you flatten the "roundness" a little when punching, round it back out with a peaning hammer. If you're doing this mod, I don't need to tell you how to use your tools.

5) Insert the reducer into the adapter pipe as per the pic below. You should have to tap it to be flush with the leading edge of the adapter. It's a good idea to bevel the internal "lead in" edge, so there's not a sharp edge for the exhaust to impact.

6) Reassemble the exhaust and go ride your bike!

7) Many thanks to Justin Bowman for creating the graphic!

8) All the information you need is here. I'm not going to get sucked down the internet wormhole answering questions. This modification will cost you 30 minutes and less than 10 dollars. It works. It works with any flash, it works with no flash. Do it, don't hit me with the ordinary 10,000 questions. Do it, and then post up about it. Remember, this will help your throttle response and torque just ordinary riding, and not take anything away from WOT performance.

9) Yes, I've already done this for the Black Widow header. I will post up about that soon, I'm trying to source an adapter that I like a little better, just for convenience sake. DO NOT hit me with the posts about "what about the Black Widow" ... I'va already answered this.

10) If someone with an area p pipe is interested, post up and PM me. You will need to do some measurements. I'll see if I can find a reducer for it, too. BTW, IF someone posts up that they will measure the area p header, that's it, everyone else can relax, I don't need 50 PM's.




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This is great Steve! I purchased a full Delk system for my 2013 Concours and THEN read the forums and found the issue with the loss of low end torque. I thought "m'eh", not going to really notice it, as I am not that hard of a rider anyways. I was wrong! That low end torque is really NICE to have when navigating surface streets, or even riding two up. The bike felt like it was asleep until about 3k and then it would wake up. After some conversations with Steve, we tried this modification. I was leaning towards removing the Delk header, and this was a last ditch effort before undertaking that tedious task.

After about 30 minutes, with minimal parts removal, and a little trimming of the reducer it was all back together. I rode it two up for 280 miles Sunday; uphill, downhill, in town, fast, slow, you name it; we did that type of riding. I have been commuting on it this week, 55 miles each way from Northern Colorado to Denver as well. The lag from a stop is gone, and the bike feels like it has torque to spare, even loaded with two riders. The delivery is smooth and continues all the way into the upper rpm range. Much like Steve's MRP did for the stock bike, pairing this mod with his flash AND a full Delk system was the best thing I ever did.

I was frustrated with the loss of torque from the big pipes, but loved the high end power and the finished look, and thanks to Steve and his continued work to improve the experience for his fellow riders, he has been able to deliver a solution that almost anyone can do relatively quickly with very little cost.

Thanks to Steve for the long phone calls, it is greatly appreciated!


I'm surprised that there isn't any discussion on this?
Sounds like a useful (almost free) adjustment to your Torque range.

This may be related;
When I first installed my ZX headers, I used Muzzy Mufflers and Mids.
They were too loud, I kept dragging the mids in the turns, lots of peak power, but it seemed like the bike had less low end/mid rpm torque..
Biggest problem was; the bike was awful at parking lot speeds. {Felt like I was in a car with a very lumpy cam..}

So I removed the Muzzy's, and installed Area P Mufflers/mids.
"Everything" got better, particularly the parking lot speed performance.

One big difference in the 2 systems was;
the Muzzy Mufflers had 2 1/4" OD Mid pipes and muffler ID.
the Area P Mufflers have 2" OD Mid Pipes and muffler ID.

So, maybe (??),, my muffler/mid pipe change did the same thing as this reducer?

Ride safe, Ted

Steve in sunny Fla

Iron Butt
Industry Vendor
A lot of people have very little understand about exhaust system dynamics

Bigger isn't always better, velocity is where it's at. Even the infamous backpressure statement doesn't always apply.
I have to agree with that. I'm not an authority on exhaust by a long shot. With the help of my dyno I'm learning. I've been running experiments. There actually is a formula I've developed. I also have taken into account HP and flow from the stock systems. I don't think I'm learning anything new, only new to me. there is a huge amount of information to be learned by disecting a stock system, as to flow potential and what they deemed important.
Folks with alot of tuning experience know "bigger isn't necessarily better"... although I think when building a product you want to sell, THEN "bigger is better" is important, because in most hotrodder consumers minds, the bigger the exhaust is the better it will work. That's not true. My experiments were "how small can I go and not lose power". Going smaller brings back the flow velocity and torque. The trick is to get all the torque and all the peak HP at the same time. This exhaust reducer does that, though I'm sure many who have never done the hard work and experiments will dismiss this.