Pea Shooters on 1.5" headers

[rambler]

the motor in my cafe has the Shell #1 cam, 9.5:1 750cc pistons, VM34's, Boyer ignition and is mildly ported.

I want to bend some 1.5 inch stainless into headers with a continuous BSA-style curve mounted to Pea Shooter mufflers.

How long should the headers be and does this exhaust system sound like a good street bike set-up for this motor - or would you reccomend a different muffler? Would anti reversion cones be of any benefit?

[xsleo]

I think it should work quite well. I still have the stock in my 750 kitted 75. The 1.5 headers do work well.
For torque cones, cutting the ends off the stock head pipes at about 1.5 inches from the flange. Cut off the outside pipe. This will fit in your pipes. You might try it with and with out.
I think the length should be around 33 to 36 inches long. Measured along the outside of the bends. The stock header is about 32. They also have the crossover to help scavanging. So the bit shorter pipe works ok. Mikes head pipes are 35 inches long. I think getting the exact length is important but sometimes we have to compromise to get them to fit.
I can't say for sure what the BSA style curve is but if it is something like the later Special header is you can have the longer length and still mount the mufflers up close.
I have Mike's 1.5 headers slightly modded and Emgo shorty mufflers sounds good throaty yet not too loud. Runs strong. I have the 1.5 bends to build a set of headers to fit more like I want. I have oil cooler fitings and Mike's headers won't fit around them. I have a stock right side cover on now. When I get the new pipes built and on It may not run better but I'll have the cooler on and it will run cooler.
I think however you get it to fit it will run better than the stock headpipes.

[tomterrific]

Real Peashooters off a Norton Commando are for 1 3/8" pipe. The Brit bikes used to use 1.5" but 1 3/8" gave more power. There are Peashooters made for Triumphs that are 1.5". You can use the original Norton Peashooters by sticking a stub of 1 3/8" pipe in the end of your 1.5" head pipes. Then push the Peashooter over the 1 3/8" and butt it up against the 1.5" headpipe.

True Peashooters are very free flowing, a little too loud on an XS650 but look and sound great. I have them on my XS and another guy bought the exact same ones for his 850 Norton. They sound lots different on the NORTON.

Stock pipes can fool you about their length because some of the pipe sticks into the muffler before ending.

Tom Graham

[rambler]

The peashooters I have are after-market items for Nortons. They have 1 3/8" inlets. I had a muffler shop spread them to accept 1.5 O.D. pipes. Tom, do you agree on the 33 - 36 length for the head pipes?
Does the torque curve go down with header length? In other words will a longer pipe produce peak torque at a lower RPM than a relatively shorter pipe?

[grizld1]

Torque peak is affected by pipe diameter; as diameter increases, the rpm at which the pipe can maximize torque rises. Power peak is affected by pipe length; as length diminishes, the rpm at which the pipe can maximize horsepower rises. Other factors are in play as well. A larger carburetor will move the power peak up the range, and cam timing affects the power and torque peaks as well; retarded timing moves them higher, advanced timing moves them lower. Specific examples of choices made by professional tuners can be found in Craig Weeks' "XS650/750 Engine Modification Guide," available as a download at www.650performance.com for $39.95. It'll save you 10 times that in mistakes avoided.

But back to the specific question; the standard for specifying primary (header) pipe length is length from the center of the valve face to the outlet, as measured on the center line of the pipe. Michael Morse shared a rule of thumb with me which makes life easier; on the XS650, measurement of the pipe from entry to exit on the outside line will come very close to the valve-to-outlet center line length. Bottom line: with the Shell #1 timed with the intake lobe centers at 100*, a pipe length of 34" to 36" would serve you well. I strongly recommend Michael Morse's Exhaust Port Optimizers.

[rambler]

Is the MMM optomizer compatabilty with XSLeo's advice to use the first 1.5 inches of stock header pipe for the exhaust mount flange, (thereby having the stock pipe-to-exhaust port fit and a reduced i.d. in the initial portion of the exhaust header) ?

[rambler]

I bought and downloaded the modification guide, and now I'm scared.

The manuel says the stock rods are soft and break easily.

I know the early models (256) would stretch the small end but I hadn't heard anything bad about the newer (447) ones.

I don't want a hand gernade.

[grizld1]

Re. exhaust port inserts, the EPO's are used alone. Re. rods, the stock units work just fine if you observe the 7500 rpm redline. If you plan to wind the motor up in racing, however, you'll need to install competition rods and have the crank pins tack welded to the flywheels to avoid separation.

[rambler]

Thanks. I don't plan to race it so the stock rods will be fine for me and no worries there. I'm not certain what you mean by "the EPOs are used alone" do you mean that they are used only when the header is not stock or do you mean they provide a benefit no matter what header is used?

[grizld1]

Sorry, I misread your question. I thought you were asking if the EPO could/should be used in conjunction with an insert made from the inlet end of the OEM pipe (answer: no). The EPO is designed for use with single wall aftermarket pipes, 1-1/2" OD (~1-3/8" ID) or larger, not with OEM pipes.

[jack]

Mar 4, 2011 18:25:29 GMT -5 rambler said:

the motor in my cafe has the Shell #1 cam, 9.5:1 750cc pistons, VM34's, Boyer ignition and is mildly ported.

I want to bend some 1.5 inch stainless into headers with a continuous BSA-style curve mounted to Pea Shooter mufflers.

How long should the headers be and does this exhaust system sound like a good street bike set-up for this motor - or would you reccomend a different muffler? Would anti reversion cones be of any benefit?

Ar inserts are a band-aid fix for an ailing exhaust port that exhibits lazy port velocity and for over-sized header primary tube dimensions that slow exhaust gas velocity in the low to mid RPMs or to provide a cushion in tuning the engine for alternative power bands. You be better off working the ports in the head first,then if called for then install the AR inserts for optimum tuning.

[rambler]

With Leo's method the initial 1.5" length of the header would be the same as stock and the rest of the pipe would have a bit larger i.d. than stock, but not a bunch bigger. There might be some turbulance created by the lip where the two pipes meet, but do you see this geometry as a good fit for the motor that I've described? Keeping in mind I'll be keeping the rev range where the stock rods can live a long and happy life.

I appreciate the advice that there is more to be gained from re-working the exhaust port, but I'm really not looking for every oz of power that I can get. I'm thinking around 60 ponys is the cost:beneft sweet spot for a non-race xs650 motor and that's the neighborhood I'm looking at.

Am I looking through rose-colored glasses or does this set up sound like 60 ponys to you fellas?