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 Post subject: Engine performance mods ?
PostPosted: Sun Feb 08, 2015 12:42 pm 
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Joined: Wed Feb 04, 2015 9:30 pm
Posts: 34
I've always wondered why we never hear about anybody doing things to gain more power from the PC800.

The PC800 has a relatively low compression ratio. That's a simple thing to increase.
Are big bore kits available for the PC800?
What about work on the valves?

If you've got to do an engine rebuild or a swap, it seems like a good time to consider boosting the power a bit.

Have any of you done any engine mods?


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 Post subject: Re: Engine performance mods ?
PostPosted: Mon Feb 23, 2015 11:54 am 
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Joined: Tue Jul 22, 2014 6:13 pm
Posts: 74
Location: Long Island, NY
I remember reading someone swapping a VT1000 motor into the PC.
http://pc800.co.uk/cgi-bin/mwf/topic_show.pl?tid=723

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Brian
1997 Honda PC-800
1980 Honda CB750F
1982 Honda CB900F
1977 Honda GL 1000


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 Post subject: Re: Engine performance mods ?
PostPosted: Tue Feb 24, 2015 12:42 pm 
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Joined: Wed Feb 04, 2015 9:30 pm
Posts: 34
The VT1100 is looks like an air cooled engine. Seems like that could cause problems.


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 Post subject: Re: Engine performance mods ?
PostPosted: Wed Feb 25, 2015 4:42 pm 
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Joined: Tue Jul 22, 2014 6:13 pm
Posts: 74
Location: Long Island, NY
GlennR wrote:
The VT1100 is looks like an air cooled engine. Seems like that could cause problems.

Like anything, it takes time and money. From what I've read, swapping in the VT1000C motor is used as the mounting points and shaft drive are the same. That is, it's pretty much a bolt in/on project. However, that doesn't mean that there aren't any problems. Personally, I don't think the added horsepower to PITA ratio is high enough for me to try it.

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Brian
1997 Honda PC-800
1980 Honda CB750F
1982 Honda CB900F
1977 Honda GL 1000


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 Post subject: Re: Engine performance mods ?
PostPosted: Tue Mar 03, 2015 6:32 pm 
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Joined: Tue Oct 08, 2013 6:31 pm
Posts: 42
I haven't made any changes to my PC800, but based on my experience with modifying other motorcycles and cars, I would offer the following advice. First start with the easy stuff that gets you the most bang for the buck. The stock bike is restricted on the intake and exhaust. Remove the large exhaust chamber under the bike and the stock muffler. Purchase two Supertrapp units and install them one on each side of the bike. This means custom mounts for them. Fabricate two exhaust pipes to connect them directly to the stock header pipes. The supertrapps are adjustable for flow and you will need several discs to get the flow you need. Obviously, the bike will be louder. In order to realize any gains from the new mufflers you MUST rejet the carbs richer. I have no data on how many sizes larger you would need on the main jets, but it would be substantial. Research information on CV carb equipped 400cc dirt bikes for jetting starting points. Also, I would raise the piston needle about 0.050" with a small washer and drill the holes out on the carb constant velocity piston to 30% larger. The air inlet under the headlight needs to be enlarged. I would remove the small neck and holesaw out an opening as large as possible without damaging the airbox. These mods, when properly executed should net you much better midrange response and noticeably stronger high rpm pull. Bottom end torque may be slightly lower. When you start going further than this, you are into things like high compression pistons that get costly and labor intensive. Bumping the compression to 10.25 would be noticeable but you are faced with boring the cylinders, fitting the pistons and rings, gaskets, hours of labor and high test gas. I'll likely never bother changing mine as I like the quiet sound and don't drive this bike fast anyway. If anyone goes to the effort of making similar mods, I would be interested in hearing about the results, just out of curiosity.


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 Post subject: Re: Engine performance mods ?
PostPosted: Tue Mar 03, 2015 9:23 pm 
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Joined: Fri Sep 26, 2014 10:07 am
Posts: 151
Why not just buy a crotch rocket?

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Bob Carr
Stem NC
IBA #56949


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 Post subject: Re: Engine performance mods ?
PostPosted: Sat May 30, 2015 6:09 pm 
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Joined: Sun May 24, 2015 6:02 pm
Posts: 12
Location: Moon, VA
If you want more speed and better acceleration, try an ST1100 or an ST1300. I have a PC800 and an ST1100, and while they are similar, the V4 engine is loaded with torque. Ride one and you will understand what I am saying.

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Seth Anderson
Moon, VA

1990 Honda PC800
1991 Honda ST1100
2012 Honda NC700X
2008 Honda Ruckus NPS50
2003 Honda Ruckus NPS50
2003 Honda Metropolitan II
2005 Yamaha Zuma 50


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 Post subject: Re: Engine performance mods ?
PostPosted: Sat Jun 18, 2016 8:18 pm 
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Joined: Tue Oct 08, 2013 6:31 pm
Posts: 42
Reposted from ADV site for those who may be interested. Additional background is also there on previous pages.

Here's some information on the changes I made to enhance performance. In this post, I will try to attach the drawing
of of the new muffler and photos of the air box and muffler. There is not much point in a bunch of photos of the new
muffler. It mostly looks just like the stock one. A black steel canister. However, the internals are a LOT different.
The design of the new muffler is dead simple. Not quite straight through, it has a baffled entry that I wanted to create
controlled backpressure over the entire rpm range without restricting airflow. It works.

Please note that ALL THREE of the modifications work together and must be done at the same time. Failure to do so
will result in engine damage or destruction.

Modification no.1: New exhaust muffler. Construct as shown. Build a jig using the original resonator/ muffler
to establish dimensions and angles before you cut things apart. Cut apart the resonator from the muffler at the welded seam.
I lowered my muffler apx 10mm to provide extra clearance between the muffler and the bottom of the trunk.Use the original
chrome cover as a template to weld on the new mountings for the chrome muffler cover. While you have the assembly off the
bike, it's a good time to check for cracks or other problems. Look at the left side resonator mount. It's notorious for failure. Check the seams as well. I sandblasted mine while I had it off. Sure enough, I found a crack and welded up several
seams that looked suspect.

Modification no. 2: Rejet the carburators. This is the most current setting I have. Install a #40 pilot jet in both carbs. The carb feeding the front cylinder will need a no. 155 main jet and the needle will have to be raised 0.094" with a shim. The carb feeding the rear cylinder will need a no. 152 main jet and the needle raised 0.094"with a shim. I made my shims
from small metric nuts that I drilled out to fit. IMPORTANT: In order for the shims to fit under the needle,
the plastic post on the needle retainer must be cut down to 50% of original length. This works fine, but must be
done carefully.I used small sharp sidecutters from 3 three different angles. Do not drill out the vacuum bleed
ports in the carb pistons unless you really know what you are doing. I didn't do it. It works sweet without it.

Modification no. 3: Modify the air box. See photo. Remove the top snorkle from the air box. Replace the stock
filter with a K&N air filter. Carefully cut open the existing inlet opening in the air box to a size that is
apx 3 times larger than stock. Look at the photo again and duplicate. Minor changes in the opening size will
change jetting requirements. I installed galvanized wire mesh over the opening to stop mice from nesting in the
air filter. I live in the Canadian woods and it's a big problem here.

Do these things and your PC800 will come alive. It changes the bike from mild to "Bitchen". If you go to the effort of doing these changes, I recommend that you check over your brakes. And clutch too. I had a heart stopping moment on a corner doing a test run. The sharp turn was only a mile away from home but I underestimated my speed. Afterall, I "knew" where the turn was and how long it took to get there. However, I got there a lot quicker and was on the corner before I realized that I was MUCH faster than I should be. The only thing that got me through it was remembering that old adage "NEVER give up on your turn". I lost 5 years in 5 seconds. Won't forget that for a while. Good luck and have fun.ImageImage


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 Post subject: Re: Engine performance mods ?
PostPosted: Thu Aug 11, 2016 5:07 pm 
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Joined: Tue Oct 08, 2013 6:31 pm
Posts: 42
UPDATE August 11: I have changed both of the main jets to #158 and it improves the mixture ratio and performance. Background: I wanted more fuel during the 1/8 to 1/4 throttle opening so I ordered a set of needle jets for a Honda VT1100C thinking that the solution might be easy. I measured the jets when they arrived, and to my surprise discovered that they were LEANER than the stock needles that came in the PC800. A waste of $50. However, instead I did install a pair of #158 main jets and it helped quite a bit. I'll keep you posted as the process continues. Is anybody out there making the mods? Seems quiet around here......


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 Post subject: Re: Engine performance mods ?
PostPosted: Wed Sep 28, 2016 10:13 pm 
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Joined: Wed Sep 28, 2016 9:56 pm
Posts: 1
IMaScot, thanks for the info.
KD8FQM & drseth, most people don't have a brace of motorcycles awaiting their use. People on this and other forums ask about adding power to their rides because they want to have more fun on the bikes they already have. We can probably all agree that if we all had an ST13 and a sport bike, our PCs would collect a lot of dust. Unfortunately buying, registering, insuring and maintaining another bike is just out of reach for most of us.
Gator


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