Can anyone get me close to a pipe length. I have the older style Silver Bullet pipe and a Silver head Rossi O/B 3.5 running 60%. The motor is stock.

Thanks.. Chuck

I can only tell you what was suggested by Silver Bullet Pipes about my K/B 3.5 SS Air Cooled Outboard.

With the Silver Bullet Header and the Late Style Pipe, the header pipe should be cut approximately 1/2" from the end point of the radius.

I had to call and speak to him about it, because there's really nothing as far as instructions on tuning, and this was the first time with me working with outboard pipes.

Sorry, I can't be more help to you, but what I understand there's a common length to cut the header, and the rest of the tuning is left up to the length of the coupler.

My plan is pre-marking the cutoff points at 3/4", and removing 1/16" at a time with a file and running it after each cut. Hopefully I can tell where it starts to drop off and have enough smarts to stop cutting. This will keep the gap between the header end and the pipe to a minimum, which will be easier to adjust when it comes time to replace a coupler.

Either way, for me it's going to be a lot of guesswork and testing. It sure would be nice if the header pipe fit into the pipe opening like a trombone slide, and just use a coupler to lock it in place, but it's the same size.

I hope someone else that has more knowlege than me will write.

Jetpack.. thanx for the info. That's about where I had it and I'm not very happy with the outcome. It sounds like the pipe is still to long and I can't cut it any shorter. I think I'm going to try a Irwin and see how it runs. I always had good luck with the Irwin pipes but thought I would try something different. I thought I was doing something wrong, but I guess not!

Do you have the Bullet Header? You can get those copper fitting headers that are shorter....

I have a Rossi header that came with the motor. Looks like the same as the Bullet headers.

Here Chuck let me share my notes with you maybe they can help. Click on that pic and I have written a general table to look at.

While your thinking, remember when a motor comes up on the pipe its tendency is to go lean, so always start with a fat setting with your starting length, and go through the needle first. Then move the pipe in and go through the same process with the needle.

This is where the third-channel mix is nice.

That pic I threw in is one of those copper fitting headers I've seen around. I am not sure where to get them or who makes them.

I would say give it another shot with a longer piece of coupling, and work that needle more. I think with what you said about being too short already, and running 60% nitro, you might have started too short to begin finding it, and its choked on the pipe. Drop a prop size too, get the load off the motor so its easier to tell when it jumps on the pipe.

I've played with all those settings, props, fuel,etc. My other tunnel is running in the high 40's, and if you guessed its a K&B your right.
Everyone tells me this motor should go faster but after playing with it for a half of last summer its not running very good, high 30's.
My goal this year is to break the big 50 mph this year. I have been playing with tunnels for some 15 years and I still ask questions.
I see Mark (HTB) has a new pipe out and I'm just wondering what is the difference between new and old pipe. Got to get this boat running. Got a new Octura Y-537 that I'm going to try. Always trying new things for the quest of speed.

That pictures looks like a newer HTB pipe. Yes or no?

When I started looking at what pipe to buy, I had called Mark and asked what he thought I should run. I told him my setup and what fuel I'll be running. KB SS and nothing above 40% nitro - maybe just 25% most the time, so he suggested I get the standard (original) pipe. He built the larger HP pipe for high nitro, and come to think about it he did mention some of the guys were having trouble with the original with high nitro, so thats why he started with the HP.

I decided not to get crazy with buying nitro, so I chose the original pipe and just left buying the HP for when I do decide to jump up over 40%.

They almost look the same, except if you go to the website there is a slight difference...

The original is more slender on the secondary cone, look close at the outside curve of the weld. The HP seems more stubby at the second cone, maybe more wider.

If you want to compare pipes, heres what kind of eyeball measurements I have with the pipe standing up straight as I can put it on the bend:

It is 6" to the root of the stinger tube, and 2 5/8" to the top of the inlet tube. I'm almost sure he would use a welding jig to hold the parts, so they should be pretty close to each other.

I used my calipers to measure the fattest part of the pipe before it flares into its welding lip and its about 1 3/8" wide, and across the two halves its 1.300" thick.

If you can, measure your's up and post it because I would like to make sure mine is what was sent, not the HP. It's too hard to verify what I have with just the webshots.

Here ya go.. I used my calipers also and they don't lie!

6.625 root to stinger tube
2.625 inlet tube to stinger.. same
1.140 fattest part of pipe before weld to weld fattest across pipe weld to weld 1.710
1.240 fattest two halves
1.500 mounting post .. center of post to stinger
8.00 overall pipe length.. weld to stinger end.. not including J
3.210 overall width.. header end .625 across J to weld
12.500 overall length .. .625 end around to stinger end (outside)

I sure hope you understand this! Because it sure looks funny if someone reads this.

Looking at the two measurements I would guess you have the HP pipe but not sure.
Also are boat club (Marquette Boat Club) is having are IMPBA race July 1st at 167th Cicero Ave, Oak Forest, Illinois. Not that far from you. I will be one of the judges for the race.

Did you check your zero before you measured?[sm=omg_smile.gif] LOL sorry, that's just a shop joke.

I am glad you went the extra step checking that pipe for me and sending me back to my bench again with my calipers, square, piece of string, another hand.....

Let me see what I can come up with. That pipe came in a Silver Bullet bag with a label, but the label only had thier logo and address on it, no model number, so I been kept curious about what pipe I actually recieved...this will help.

I've been up to your Oak Forest pond and you guy's have a really nice setup going there. No corn fields to have to cut through, no overpass traffic noise, and no old tires to dodge in the pond, ect ect....

When I started into building my Dumas Eagle, I hit every race that was sanctioned on the list in all three states that summer, and got to know some of the guys and what they were running just to educate myself.

I'm sure I'll be able to make it up there, even if I don't have a boat ready to race. I like just being there and hearing six boats clip the line. It's too close of a race for me to not go to.

I knotted one end of a string, and tugged it against the .625 tube end to start, followed it around the outside of the pipe in the flair-bend radius, inch wormed my finger all the way to the very end of the stinger tube and came up with 12 inches right on the button.

Mine is a half-inch shorter overall on the outside curve, .060" fatter across the halves, so it must be the stumpy HP.

I'll try and snap a good pic with a tape measure with it, maybe you can pick something up that I have missed.

If I knew this morning I was going to be holding a camera I would have backed off the coffee.

This is the squarest image I can come up with and the best focus my webcam can muster.

Your pipe has a bigger and longer J bend. I wouldn't put book on it but I would say its a hp pipe and I'm stuck ith this low nitro pipe.
Maybe all this time this is my trouble. Irwin here I come. I'll take off my Irwin pipe off my other boat and give it a try.

I think your right Chuck. I guess there was some confusion over the phone when I ordered it after I had talked to Mark, because I did go back and forth a bit as we talked about the pros and cons of each.

I guess my 40% will be happy to hear I have the HP pipe. I would swap you pipes but I might as well hang on to what I have here and see how my motor likes it before I go jumping around with things.

It might be that earlier pipe was discovered to have not enough volume and perhaps thats why your struggling with yours. Lets hear how your Irwine turns out on your combo, maybe you will have an easier time with it.