1999 18hp Vanguard to 1996 DS ?s

cclingma · 08-07-2018, 08:02 AM

The 420cc clone that has been in our DS for 10 years gave up a while back (cracked block) so I started searching for a replacement. Found a Vanguard 18 and decided to give it a try. Making some nice progress with the install but as always have questions.

Exhaust and performance. I splurged and put a rev kit and cam in this motor and purchased parts to build headers. The headers have me concerned. It appears that my pipe is 1” OD while the exhaust ports on this motor are 1” ID openings. So, if I use this pipe I’m going to have a fairly significant step down in size right as the exhaust leaves the cylinder. About 3/16”. Do you guys usually have this reduction or try to use 1”ID pipe?

Thanks!

Rooster59 · 08-07-2018, 12:50 PM

Just my opinion but I think I would have gone with 1.25"OD tubing. Still smaller than the ports but 1"OD seems pretty small. Although I believe that engine is only 570cc. Which means two cylinders of 285cc displacement pushing exhaust gases out the ports. Exhaust tubing 1"OD might be OK. Even so, I might prefer to have a free flowing exhaust and adjust back pressure at the muffler end of the system.

This advice is worth what you paid for it.

cclingma · 08-08-2018, 07:22 AM

Thanks for the reply.

I believe I agree with you that I would rather have 1” path. I hadn’t even considered the part about really having two cylinders of 285 each and I see pretty small headers on my other 300cc and under engines. That thought combined with my desire to slow the money spend on this project and the fact that my parts aren’t returnable says I’m probably going to try the smaller pipe.

Thanks

Rooster59 · 08-08-2018, 10:24 PM

You should be fine. Vegas Carts supplied a 1.25" OD header for my 625cc single cylinder engine. It might run better with 1.5" but it does just fine as is.

Steve390Gold · 08-09-2018, 11:58 AM

I would try to find a header material that closely matches or is slightly larger than the port. Keep in mind back pressure in a 4 stroke engine is only counter productive and it should be totally eliminated if possible.

On a 2 stroke however, one is best served with a well tuned helmholtz resonator on either the exhaust or the intake.

08-07-2018, 08:02 AM	#1
cclingma Getting Wild Join Date: Jan 2008 Posts: 147	1999 18hp Vanguard to 1996 DS ?s The 420cc clone that has been in our DS for 10 years gave up a while back (cracked block) so I started searching for a replacement. Found a Vanguard 18 and decided to give it a try. Making some nice progress with the install but as always have questions. Exhaust and performance. I splurged and put a rev kit and cam in this motor and purchased parts to build headers. The headers have me concerned. It appears that my pipe is 1” OD while the exhaust ports on this motor are 1” ID openings. So, if I use this pipe I’m going to have a fairly significant step down in size right as the exhaust leaves the cylinder. About 3/16”. Do you guys usually have this reduction or try to use 1”ID pipe? Thanks!
cclingma Getting Wild Join Date: Jan 2008 Posts: 147

08-07-2018, 12:50 PM	#2
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: 1999 18hp Vanguard to 1996 DS ?s Just my opinion but I think I would have gone with 1.25"OD tubing. Still smaller than the ports but 1"OD seems pretty small. Although I believe that engine is only 570cc. Which means two cylinders of 285cc displacement pushing exhaust gases out the ports. Exhaust tubing 1"OD might be OK. Even so, I might prefer to have a free flowing exhaust and adjust back pressure at the muffler end of the system. This advice is worth what you paid for it.

08-08-2018, 07:22 AM	#3
cclingma Getting Wild Join Date: Jan 2008 Posts: 147	Re: 1999 18hp Vanguard to 1996 DS ?s Thanks for the reply. I believe I agree with you that I would rather have 1” path. I hadn’t even considered the part about really having two cylinders of 285 each and I see pretty small headers on my other 300cc and under engines. That thought combined with my desire to slow the money spend on this project and the fact that my parts aren’t returnable says I’m probably going to try the smaller pipe. Thanks
cclingma Getting Wild Join Date: Jan 2008 Posts: 147

08-08-2018, 10:24 PM	#4
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: 1999 18hp Vanguard to 1996 DS ?s You should be fine. Vegas Carts supplied a 1.25" OD header for my 625cc single cylinder engine. It might run better with 1.5" but it does just fine as is.

08-09-2018, 11:58 AM	#5
Steve390Gold Not Yet Wild Join Date: May 2018 Posts: 69	Re: 1999 18hp Vanguard to 1996 DS ?s I would try to find a header material that closely matches or is slightly larger than the port. Keep in mind back pressure in a 4 stroke engine is only counter productive and it should be totally eliminated if possible. On a 2 stroke however, one is best served with a well tuned helmholtz resonator on either the exhaust or the intake.
Steve390Gold Not Yet Wild Join Date: May 2018 Posts: 69

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