exhaust/header length

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frederick
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exhaust/header length

Post by frederick » Mon Oct 01, 2018 8:28 pm

I understand the type 4 exhaust pipes are 1.75" / 44.5mm. I know motors (especially smaller displacement) are sensitive to length and diameter...too short or too long creating poor scavenging or not enough back pressure possibly reducing hp and (the fun part) torque. While sexy as heck, just wondering if the long pipes on the Trikings are affecting performance in any way, and if so, is there is an optimum length.

Frederick

westendguzzi
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Re: exhaust/header length

Post by westendguzzi » Mon Oct 01, 2018 9:53 pm

Hi Frederick
I had a problem with my exhausts, you may care to read through the topic I just copied from the old site entitles Back to Dellorto carbs.

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frederick
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Location: san jose

Re: exhaust/header length

Post by frederick » Tue Oct 02, 2018 12:16 am

thanks for that...unfortunately the pics didn't stick with your text.

You spliced in a baffle at the head end of each pipe? That's a trick we Harley guys use to put some back pressure in for straight pipes, but the motor is still trying push out that long column of gasses each exhaust stroke. I'm just wondering if a shorter "tuned' pipe is going to help the stock motor breathe better. For kicks I just wrote these guys: http://www.ghezzi-brian.com/en/tuning-m ... t-systems/ asking the optimum length for a 1200 Guzzi 1.75" dia header and silencer. We'll see if they answer.

westendguzzi
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Re: exhaust/header length

Post by westendguzzi » Tue Oct 02, 2018 7:54 am

Found a picture of the home made baffle.
Attachments
DSC01919a.jpg

Doverhay
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Re: exhaust/header length

Post by Doverhay » Sat Oct 06, 2018 3:52 pm

What you don't want is back pressure, what you do need is exhaust velocity. Over size the exhaust system and the exhaust gases slows down hampering the scavenging effect, undersize the system and you get the unwanted backpressure which doesn't allow full exhaust evacuation of the cylinder. Get it right and the speed of the forced out exhaust will cause a depression behind it to help scavenge the cylinder. Well this is how I understand it!

westendguzzi
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Re: exhaust/header length

Post by westendguzzi » Sat Oct 06, 2018 5:58 pm

Rubbish.
You do need back pressure.
If you just want noise then you won't get maximum power over the rev range.
Tune the exhaust!

Doverhay
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Re: exhaust/header length

Post by Doverhay » Sat Oct 06, 2018 6:33 pm

I agree to the tuned exhaust, but not to back pressure. Check one of the YouTube clips I found and there's plenty on the subject. https://youtu.be/jjPeP_Nn2B4

westendguzzi
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Re: exhaust/header length

Post by westendguzzi » Sat Oct 06, 2018 8:04 pm

In a nut shell we need adjustable diameter and length of pipe.
Trial and error.

EricStarmer
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Re: exhaust/header length

Post by EricStarmer » Sat Oct 06, 2018 11:44 pm

A tuned exhaust only helps at certain RPM ranges - at other RPM's it is a detriment because instead of relieving the back pressure it increases it. Ideally the exhaust pipe(s) should be different lengths for different RPM's - difficult to achieve, although when I was an apprentice at DeHavilland (RIP), one of the other apprentices was using the workshop to build a tuned exhaust system for his car, which consisted of trombone-type pipes the length of which could be changed by a lever inside the car. Don't know whether it boosted the power output, but it sure sounded great !

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