Bonneville America Forums Forums Technical Forums Exhaust Crossover pipe

Just a simple post here about a simple mod. For anyone wanting to plug the crossover pipe between the headers I was pleasantly surprised to find a 1 1/4" frost plug fit's PERFECTLY in there. I added a small bolt to the equation making it easy to remove should I change my mind.

Here is my nieve question of the day. Why would I want to eliminate the crossover pipe?

Oh yeah, I guess I should mention why I'd do such a thing. People do it to achieve a better sound... a better exhaust note. The sound coming from the cylinders won't mix so apparently you get a more distinct sound. It seems logical but I won't know for sure until I fire 'er up (that ain't gonna happen anytime soon... my bike is all torn apart).

Anyway, it's said not to do it if yer running restrictive pipes 'cause the crossover allows for better breathing. But if you have open pipes the breathing thing becomes a non-issue. There's plenty of reading on the topic in the following link, which has links that lead to more info and so on.

http://www.bonnevilleamerica.com/forums/...part=1&vc=1

Ok Keith.... now I'm looking under my beloved's belly...I see the cross over pipe, I'm running sceptors....and life was good until I saw this post.....exactly how much "better" does it sound on a scale of 1-10 (1 being no diff and 10 being "wow").... is this something I need to get excited about in your opinion ?

You can regulate the blockage by using a proper fitting washer as well, as that is what I have done, BTW, I'm running EPCO s. To me it makes my bike sound more towards a non cross over '50-'60s 650 Bonnie, a little louder of course.

I would agree. It sounds more like a old school Bonnie (50's-60's 650). Someone at one time put my sound clip on the site but I guess the link is not working anymore. It just gives you an idea. The clip did no justice to the in person sound.

My vote is a good 8.

I like mountainman's mod. If you did not like the sound or wanted to go back to stock you can. I do not have any plans on returning to the crossover.

Do you still have the sound clip?

I did it to mine...I can't tell the difference, but I haven't ridden with any other triumphs

Daniel, I can't tell you how it sounds with the x-over pipe blocked because I have yet to fire up my bike since I did it. AND it will be a while before I can start 'er up 'cause she's all apart sitting in my house. Interesting to hear what others are saying here though.

Btw... if you do this, pull the right side header... that's the side you want to plug just because of the way the x-over slip joint works.

I cut mine off and welded it shut, I like the sound difference. I say maybe a 6.I run gutted stock pipes, no baffles.

The crossover pipe is there for a purpose. It mainly improves scavenging of the burnt gasses = more efficient fuel burn = more power ... they didn't just do it for freer flow (but that extra flow also helps the power gains).

I have not noticed any power difference....the bike seemed a lot quicker...the only other change was going from D&D to BC cocktail shakers

It would seem turning gases at abrupt 90 degree angles would cause turbulence and encumber the flow, I do know that it's a concern with live steam feed to turbines and their efficiency, perhaps an engineer could chime in with an opinion. Any mech. engineers out there? As an aside thought, engineers put the cross overs on our bikes.

You are correct about the turblence of the "tee" in the main pipe..it will create a system loss.

removing that cross over changes the sound, and isolates each cylinder. So you can hear or do an exhaust gas test with out the minor effects of the other side. For the most part its extra work for nothing.

I do understand that without a free flow exhaust you will lose power. That has been reported...Those who have free flow exhaust report that there is no change in power, just sound. I had my pipes off to wrap them so I said why not and put the freeze plug in..

Yes, 90 degrees is not desirable for gas flow turbulence but better than not having it. But it's not just the flow of gasses that is important in performance exhausts: ... There is the pressure wave which travels extremely fast (very much faster than the gasses or sound waves) which is significant in assisting with gas scaveging from the cyclnder ... IF it is at the correct tuned length. We assume they got it right.

I ran my bike on a dyno before and after the cross over pipe was cut out and there was no change in HP or TQ. I have plenty of room for the exhaust gases to escape since my pipes are totally open except for the reducer cone at the header end of the pipe.

"no change": ... yeah, practical testing sometimes defies technical theory - and certainly trumps it - I yield.

When I say no change the small change was with the margine for error or difference in climate that day. The numbers were slightly better after I cut the cross over out but I don't attribute that to the mod.

The pipe is going down ( bonzi shooting icon here) if nothing else, I'm really noticing it now and want it gone for aesthetic reasons

I agree that the crossover should probably be left in place if there is enough restriction that the exhaust gases need somewhere to go. In my cases they don't, thus no change (small for the better but as I stated not attributing that to the mod), on a more restricted exhaust it may well change the power but I'm not so sure of that one.

Yeah, but it's not JUST gas flow to consider, the pressure wave from the opposing cylinder and reflections of the evacuating cylinder plays an important role too.

I am aware of that and still not convinced.I could see it under a higher performance situation.

I figure it's worth a try, even with my TORS. As shown in the pictures I posted it's easy enough to go back to a x-over. I understand the thing about back pressure and exhaust needing a place to go but soon enough (I hope) I'll have SS pipes on there which should work quite nicely with a plug in the x-over pipe.

No, he is talking about turbulence and reversion waves coupled with the ability to evacuate exhaust gases from the combustion chamber. Then you can add in the pulses working for each other and the scavenging effect, again I am not convinced of any of this with an open exhaust given the performance level of our engines and the dyno results I had.

Ian is right. These bikes aren't dragsters or even race bikes you can get some power out of them but at what point are you spinning your wheels and getting nowhere.

Ian is right. The pressure wave has a vacuum between the peaks. The object is to time this vacuum to coincide with the latter stages of the exhaust port opening. The resulting vacuum left in the cylinder when the port closes aids the speedy fill of the incoming a/f gas and also increases the volume of the a/f burn - and perhaps also the explosive power of the burn as the a/f is mixed with less residual exhaust gases.

This tech is not just the domain of high performance engines: ...

X-over-pipes, 2-into-1 systems and manifolds (3+ into 1) are designed to exploit these pressure waves. Most modern engines exploit this. Short straight drag pipes are a tuned length to maximize the reflective pulse. They have a very large expansion chamber - the universe.

Triumph don't put the x-over there on a whimsy and it's not there for the sound either - but it does push some gas through the other cat (on recent models) so maybe it's a little cleaner as a result. However that doesn't explain why they put the x-over on the earlier models.

However, practical testing without the x-over is the bottom line- your results may vary.

Exhaust Scavenging. I think that's what it's called.
We've talked about this before.
The cross-over splits the exhaust pulse between the two
stock restrictive mufflers.

You make a very good point and my thinking was kind of narrow. I am running a 790 with the 790 cams and no cat and basing my results and statements on that. I actually don't know enough about the 865 to speak as to how the cross over removal would effect them. Your intake and exhaust will effect the outcome as well. I can really only speak for my set up on my size engine and cam timing/duration. Wendy's 790 with gutted slash cut exhaust showed no change mine with cannons a slight increase. Again given a small margine for error no change to either. I would do it again that is for sure, I am not running a race bike and even if I had a small loss in power I like the sound.

And MOST importantly, don't forget that removing the cross-over pipe will definitely change your motor oil requirements.

I didn't dyno mine before and after...but my butt dyno says no change

Robert what oil are you using in your mufflers

I built mine by using a square of expanded metal, bought at Home Depot, rolled it into a 1 1/2" tube, and wrapped with packing material from J.C.W.

Brazed a round end piece on it, and viola!

Here's a pic of my baffles next to the stock baffles (from the J.C.W. pipes)

Their modeled after the FMF Powercore mufflers on my Yamaha's.







Total cost didn't hit $20.

Used to call them "glass-pacs"
Bet they sound great!
Uncle Charlie

Now that's resourceful.

Robert, no I didn't.

You must have skipped the word when you were reading it.

Thats cool, I can't even find my Mason jar now.