thunder bigbore kit

[blowndodge]

Bill. You could "cam" the Nomad for more bottom end like the "255se" cams that you can get on the 103 HD's.

The problem I see is that more bottom end would mean higher pressures and/or heat in the lower rpm region. Seems to me the pinging most of us get would be exascerbated by that.

I'd almost perfer thje rpm ceiling be raised to 6900 and get a little overlap in so at least when I reved it up some it would get moving quickly.

[ponch]

Originally Posted by Blowndodge "Darksider"

Bill. You could "cam" the Nomad for more bottom end like the "255se" cams that you can get on the 103 HD's.

The problem I see is that more bottom end would mean higher pressures and/or heat in the lower rpm region. Seems to me the pinging most of us get would be exascerbated by that.

I'd almost perfer thje rpm ceiling be raised to 6900 and get a little overlap in so at least when I reved it up some it would get moving quickly.

And then we have a weak clutch spring design, so while we are at it, replace that too...It never ends, especially when the design limits are pushed.

[ringadingh]

I think you said it best Jim, the Nomad is what it is and big hp gains are not practicle. Buy a different bike if the power has to be increased.

[trosco]

I asked a wizzard (ie the harley 1/8 mile drag motor guy I know) about kits that bore out engines like ours for added power. He said he did not particularyly care for kits that do nothing to strengthen the bottom end of motors. He said cheap kits often use a longer rod and replacment pistons with a higher wrist pin location. Combined that is a cheap way to leverage the existing stroke's torque producing capabilities but it adds stress to the crank and speeds up wear in cylinder walls and piston skirts.
He said that a bore expansion on our 1600's really wasn't going to yield a lot because the heads on our bikes are what he called "veloscity" heads meaning they moves air at high velocity in relatively low rpm situations. He says that design make good (not great) power down low and also the restricted quanitity of air flow prevents high rpms so helps engine life. He also said that our engine has relatively low piston speeds for it's displacement because of the short stroke design and that is also good for durability.
He said that he'd expect our motors to be long lived but he'd not be able to build a lot of power from one until the after market started to offer different heads and stroker cranks for them. So in his own way he said what ponch said, our motors are bulletproof, but they will never be faster than a speeding bullet so love them for what they are.

[blowndodge]

+1 Trosco.. I think it's a waste of money.

[Sin City Stan]

Originally Posted by MAS Tequila

I think you should check your facts Stan.

426 hemi 4.25 x 3.75

Boss 429 4.36 x 3.59

454 4.25 x 4.0

Oversquare, or short-stroke engineAn engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length - giving a ratio value of greater than 1:1.

For example an engine which has 100 millimetres (3.94 in) bore and 80 millimetres (3.15 in) stroke has a bore/stroke value of:

100 mm / 80 mm = 1.25:1
An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

The reduced stroke length allows for a shorter cylinder and sometimes a shorter connecting rod, generally making oversquare engines less tall than undersquare engines of similar engine displacement but wider and longer (for engines with vertical cylinder axes).

By changing the crankshaft and modifying the connecting rod(s), piston(s) and/or engine block an engine can be "de-stroked". This reduces the displacement and consequently the torque of the engine, but can allow it to run at higher speeds and in fact develop greater peak power.

[edit] Oversquare engine examplesOversquare engines are extremely common, including both Chevrolet and Ford small block V8s. Most Boxer (horizontally-opposed) engines (such as those built by Volkswagen, Porsche, and Subaru) feature oversquare designs since any increase in stroke length would result in twice the increase in overall engine size.

Undersquare, or long-stroke engineAn engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.

For example an engine which has 90 millimetres (3.54 in) bore and 120 millimetres (4.72 in) stroke has a bore/stroke value of:

90 mm / 120 mm = 0.75:1
At a given engine speed, a longer stroke increases engine friction (since the piston travels a greater distance per stroke) and increases stress on the crankshaft (due to the higher peak piston speed). The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. Because these factors favor lower engine speeds, undersquare engines are most often tuned to develop peak torque at relatively low speeds

The Chrysler Slant-6 engine, in its most common 225 cubic inch (3.7 litre) version, is a massively undersquare engine, with a 86 millimetres (3.39 in) bore and a 105 millimetres (4.13 in) stroke, producing most of its power right on the peak of its torque curve. The Achilles heel of this engine, otherwise known for its exceptional durability, is being over-revved by inexperienced drivers. Red line for a factory engine is under 4,500 revolutions per minute (rpm); red line with aftermarket connecting rods is about 5,500 rpm. On the other hand, a well-maintained Slant-6 can be made to idle as low as 75 rpm (though this is not a recommended speed - neither the alternator nor the oil pump will function adequately).

MT

Given, I typed "over" when I meant "under" square when referring to the 1700. ;) However, your examples other than the Boss 429 have a longer stroke to bore ratio than the venerable small block 350 Chevy, which is true of most big blocks. I still maintain top end torque is made by stroke not bore. The small blocks are known for roaring off the line at insane RPMs but the big block strokers catch up and blow by on the top end.

The 225 brings back old memories. I helped install an Oldsmobile F85 turbocharger on it in a Dodge Dart about 1970. It was a fun project.

[ponch]

I prefer the Rocket 350. 4.057" bore, 3.385" stroke. Those engines last forever and have their own sound with that crossover exhaust manifold. The 455 on the other hand had a 4.125" bore and 4.250" stroke and it was a torque monster...Unlike the Chevy, their wasn't so much difference in the big and small block Olds block, primarily deck height and bearing journal size.

[Sin City Stan]

Originally Posted by ponch

I prefer the Rocket 350. 4.057" bore, 3.385" stroke. Those engines last forever and have their own sound with that crossover exhaust manifold. The 455 on the other hand had a 4.125" bore and 4.250" stroke and it was a torque monster...Unlike the Chevy, their wasn't so much difference in the big and small block Olds block, primarily deck height and bearing journal size.

Did that Rocket 350 have Ultra High Compression?

[ringadingh]

Originally Posted by ponch

I prefer the Rocket 350. 4.057" bore, 3.385" stroke. Those engines last forever and have their own sound with that crossover exhaust manifold. The 455 on the other hand had a 4.125" bore and 4.250" stroke and it was a torque monster...Unlike the Chevy, their wasn't so much difference in the big and small block Olds block, primarily deck height and bearing journal size.

Ive Got my pals Olds Cutlass with a Rocket 350 in the garage right now, Its over for some work and Im talking him through it the last couple nights.

[ponch]

Originally Posted by Sin City Stan

Did that Rocket 350 have Ultra High Compression?

Some had that label. After 1970, nothing had high compression for a long time.

[ponch]

Originally Posted by Ringadingh

Ive Got my pals Olds Cutlass with a Rocket 350 in the garage right now, Its over for some work and Im talking him through it the last couple nights.

Cool. What year? When I was a senior in HS, I could have bought a 1970 W-30 for $1500. Damn. Can't touch one for 50 times that now. Not anything decent.