Power

hooser said:
Is that an actual RWHP?
Click to expand...

Gary,

I only quote in flywheel numbers - maybe where your confusion has arisen earlier. If it's RWHP, I'll let you know.

It's an accurate model'ed sim of a real life engine.

If you're engines are making power that high with the same CA as a TM-38 offers, then you likely have less CFM per square-inch as a combination I'm working with in that sim. I can't fix the Mach Index - it is what it is. The more CFM per square inch, the higher the velocity and the sooner you'll reach choke flow.

From your plot, looks like you're expecting at least 140% VE.
That's like having a blower with 6 psi boost...
Click to expand...

That is not 140% VE :eek:

Not even within smelling distance of that.
 
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Yes now that we are on the same page , flywhell or what I know a s brake hp is quit a bit higher.. If I remember the stock 650 was quoted to be 56 bhp, which was 43 at the rwhp. Gary
 
My theoretical simulator uses ideal lossless adiabatics in a frictionless environment, and shows a stock 447 engine at 95% VE producing 83 crank horsepower.

Just goes to show how inefficient a 4-stroke can be...
 
toomany That was a lot to take in.....I not the math guy so here is my way of doing things.. take what is available in parts (cam, pistons etc) . port to match ether my Shell head or Rogers Axtell or Andersons 500 head, put it on dyno ,tune for best #'s and run it. When I was racing it work good enough for me , hell I shut off at the corners anyway. If I needed more power I all I had to do is not shut off.
 
I am a newbie with a question for the members that have Mikes Big bore 750 kit from Heiden Tuning. Can you kick start this puppy with the high compression? Well any way higher than stock.. I am asking because it looks like Mikes Big bore (Big Fin) 650 kit comes with standard pistons and I am assuming stock compression.
 
ihaxs650 said:
I am a newbie with a question for the members that have Mikes Big bore 750 kit from Heiden Tuning. Can you kick start this puppy with the high compression? Well any way higher than stock.. I am asking because it looks like Mikes Big bore (Big Fin) 650 kit comes with standard pistons and I am assuming stock compression.
Click to expand...
Yes
 
dlabkeeg said:
How much HP do you pick with that 750 big bore kit?
On a side note, the 78 xs650 has a better power-to-weight ratio, then my 92 883 did. So cool, wasn't expecting that. You guys probably already knew that though.
Click to expand...
Yea you can kick it ok, just have to kick a bit harder. i bored one of mine to 770 and there probably is a few more horses but top speed stays about the same, pulls like a train, but i would not do another big bore, i would much rather a six fifty, smoother and it doesnt shake to bits.......
hooser said:
Yes
Click to expand...
 
willy said:
Yea you can kick it ok, just have to kick a bit harder. i bored one of mine to 770 and there probably is a few more horses but top speed stays about the same, pulls like a train, but i would not do another big bore, i would much rather a six fifty, smoother and it doesnt shake to bits.......
Click to expand...
Cut and install GSXR1100 tapered wrist pins to reduce vibrations or get custom tool steel wrist pins.
 
Re. vibration and piston weight, let's correct a couple of inaccuracies that have crept into this thread here and there. First: forged pistons are heavier than cast pistons for the simple reason that forged aluminum is denser than cast aluminum, which is also why forged pistons are stronger than cast pistons, which is also why performance pistons are forged and not cast.

But heavier big bore pistons won't necessarily cause more engine vibration than stock. The smoothest XS650 motor I ever owned or experienced had heavy 77.5 mm. Venolia forged pistons on a stock 360* crank--no expensive rephase work, crank reweighting, etc. The motor was smooth because we paid attention to the basics. First, we used a very true crank--no measurable runout at the journals, and only .002" runout at the flywheels. Second, pistons were matched for weight on a precision beam balance.
 
grizld1 said:
Re. vibration and piston weight, let's correct a couple of inaccuracies that have crept into this thread here and there. First: forged pistons are heavier than cast pistons for the simple reason that forged aluminum is denser than cast aluminum, which is also why forged pistons are stronger than cast pistons, which is also why performance pistons are forged and not cast.

But heavier big bore pistons won't necessarily cause more engine vibration than stock. The smoothest XS650 motor I ever owned or experienced had heavy 77.5 mm. Venolia forged pistons on a stock 360* crank--no expensive rephase work, crank reweighting, etc. The motor was smooth because we paid attention to the basics. First, we used a very true crank--no measurable runout at the journals, and only .002" runout at the flywheels. Second, pistons were matched for weight on a precision beam balance.
Click to expand...
 
Thanks for that Grizld.Totally agree. Finished My 750 bigfin bike 360 crank that was well trued
attention to the details is the key with any engine rebuild.I would suggest also Judging by all the vibes chat. that a whole lot of engine mounts should be verified with a torque wrench. I also had
spacer sleeves to run the engine mount bolts thru that go between the frame lugs, seems to tighten everything up.Got gimpy old MX knees and She's a bit of a bugger to kick cold, but starts like a charm warm. 2nd gear starts from a stop sign are easy with 3 less T on the rear sprocket.
Matching ports to manifolds,pipes,etc definitely and clean up casting flaws and transition to valve
pockets. Torque like My old Norton commando. If Vibes bug you. fill handlebars with expanable foam and intall old barrel style gp grips.I got badd arthritis and this really helps. Top speed . Get
another bike. The only deal here is the Heiden Overdrive 5th gear. The 650 trans ratios were basically pulled from I believe the old R3 yam 2 stroke, so not the greatest ratios for the old girl.
750 kit is loads of fun. go with 34mm Mikuni carbs from Michael Morse. super response, super
customer service. great guy, Highly recommend His carbs. 1 kick starts.
 
And by reducing upper reciprocating mass will also reduce engine vibs. Forged pistons are heavier cause of the mass under the dome. You only need .160 to .200 dome thickness to prevent melting through the dome. Forged piston mass will also vary depending on forge material and overall piston design. 650centrals long rod piston is a fine example of this and that piston could of have been further lighten. The forged pistons I have in my BMW where 10% lighter than stock and I further lightened the pistons by installing TOOL STEEL wrist pins that shaved off 20 grams of mass.
 
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grizld1 said:
Re. vibration and piston weight, let's correct a couple of inaccuracies that have crept into this thread here and there. First: forged pistons are heavier than cast pistons for the simple reason that forged aluminum is denser than cast aluminum, which is also why forged pistons are stronger than cast pistons, which is also why performance pistons are forged and not cast.

But heavier big bore pistons won't necessarily cause more engine vibration than stock. The smoothest XS650 motor I ever owned or experienced had heavy 77.5 mm. Venolia forged pistons on a stock 360* crank--no expensive rephase work, crank reweighting, etc. The motor was smooth because we paid attention to the basics. First, we used a very true crank--no measurable runout at the journals, and only .002" runout at the flywheels. Second, pistons were matched for weight on a precision beam balance.
Click to expand...
Heavier reciprocating mass puts stress on the bottom end,may not be a street concern but I'd much rather have lighter pistons combined with LW pins. It's possible those heavier pistons corrected the balance factor too. JSmotorsports who sells JE pistons for his long rod Norton engine packages,his pistons average over 100 plus grams lighter than stock and run so much smoother than a stock Norton engine without re balancing
 
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