Honda VTX Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
129 is my top speed and I am a little miffed about it. When the bike was stock I was able to hit around 140 mi/hr. My mods are: Techlusion Fuel Injection (TFI), V&H big shots and Thunder Tear Drop. Since doing the mods I gained torque and HP when hammering thru the gears (as expected) but I guess that I lost the back pressure needed for top end speed (not expected).

I am thinking about updating my cams thinking it will help.

Anyone have any experience and/or thoughts on this?

I have not had my bike on a dyno yet.
 

·
Registered
Joined
·
1,123 Posts
hmmm, I thought it was the other way around. More air is better for top end. BAck pressure is for low end torque. You might possibly be running a wee bit lean on your upper end?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #3 ·
I added the air kit a year after the pipes and got nothing more at top end. I don't think that I'm running lean but I can't totally rule it out.
 

·
Registered
Joined
·
9,766 Posts
Did you happen to add a speedohealer, change the size of the rear tire? Either would effect speedo readings. Or add a windshiled, bags, etc.? 129 is about right for top speed. my 02 C would run an indicated 140, considering an average error of 8% that was about 129.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #5 ·
I do have a honda windsheild and bags which have been on since day 1, so not the cause.
 

·
Registered
Joined
·
172 Posts
rayr,

What are your settings on the TFI? Have you changed them since you ran 140 mph?
 

·
Registered
Joined
·
9,181 Posts
Very respectfully, are those last few MPH that important to you? By no means am I saying that you're not entitled to them if that's what you want, but the bike is limited on the top end mechanically - it can only go SO fast because the motor and rear tire are tied together physically. Once you hit the rev limiter in 5th gear you're done - and the absolute top end is in the 140's somewhere (I forget the exact #). So my question is simply, are those last few MPH worth spending oodles of money on? That's the question you need to ask yourself. :wink:
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #9 ·
Bare, yes it is important to me... not so much to ride at that speed, but to know that it can and it is running the best that it can.

Paul, the bike was completely stock motor-wise when I was able to get 140 the TFI was added shortly after I added the V&H.

I will play aroung a little with the TFI this weekend. I can't remember exactly what the settings currently are. If I remember correctly it's something like 3:30, 2:30, 2, 4.
 

·
Registered
Joined
·
172 Posts
rayr,

You've got your's set about where mine is. Mine is 3-2-2-4. Seems to work the best for me. I've run 130 mph and still climbing and I am 300 lb. (A Harley and a Victory were behind me.)

To set it back to stock with throttle wide open try 3-1-1-4. The 1 O'clock position is off. Maybe the bike is running too rich at high RPM's?

good luck
 

·
Registered
Joined
·
958 Posts
What about grade of road and wind. It may seem like it wouldn't matter, but a 5 mpg tailwind would give you about a 10 mph difference on back to back runs if you went back the way you came on your second run. That is why most top speed records do a average speed from two runs. Down and back. I remember NASCAR was over revving engines at Kansas Speedway last year because of a high tailwind. The cars were running must faster than expected at the end of the one straight a way due to a 20 mph tailwind.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #12 ·
72chevman said:
What about grade of road and wind. It may seem like it wouldn't matter, but a 5 mpg tailwind would give you about a 10 mph difference on back to back runs if you went back the way you came on your second run. That is why most top speed records do a average speed from two runs. Down and back. I remember NASCAR was over revving engines at Kansas Speedway last year because of a high tailwind. The cars were running must faster than expected at the end of the one straight a way due to a 20 mph tailwind.
What you said is true but I've done it a few times on different days and different rodes. Roads were pretty flat.

Paul, I'm going to go up first and if that doesn't work I will wire brush the spark plugs and start over at the bottom settings. plugs are new (bosch +4 hot)
 

·
Registered
Joined
·
6,536 Posts
From 30 years of racing Formula Vee cars with VW motors I would guess that:

1: Forget about the pipes.

2: not enough fuel flow at top end,

3: OR the valve springs have gotten weak. That is a #1 cause of loss of top end with our cars.
It's like you hit a aero wall.

I would not go the the trouble of changing cams.
You hit 140 with those cams before.

Larry
 
1 - 14 of 14 Posts
Top