Ok, I had a 2010 SG with the 120r motor. Performance was great, when the bike was running. The motor was one of the first built by my local, in kit form, and just never seemed RIGHT...I could go on and on about it, but it no longer matters. Anyhow, something I did enjoy about the motor was how fast the thing would spool up under acceleration...seemed to rev as quickly as a dialed in Evo motor.

Decided to sell the bike after several weeks of it being in the shop. I still have my 08 SG and I'm now researching a motor for it, narrowing it to a crate 120r OR an S&S 124. In my research here, I've seen comments on the 124 not spooling up very quickly, so, to my question:

Does anyone/can anyone tell me their experience with an S&S 124 and how the thing accelerates, or should I say, spools up? I've had a bike (twin cam) that doesn't spool up very quickly (as we probably all have) and realize the enormous effect that has on acceleration. Quite honestly, if it takes (what seems like) FOREVER to get to XXX hp/tq as I'm accelerating through the R's, that has an effect on acceleration.

Thoughts?

 

Like any longer stroke engine the rpms will take slightly longer to get there. Vtwin were not designed to be fast revving engines like those in a crotch rocket. With that said it doesnt mean a Vtwin wont be quick. Most long stroker engines that are built to make big power will shred the rear tire.

Controlling that big power comes with other problems to work through. Beefing up your clutch,transmission might need to be swapped for a stronger unit, the rear belt will most likely have to swapped out for a chain drive, swing arm modifications may be needed and building the exhaust that will give you max power from your engine


Here is some good reading on Vtwin Torque & Horsepower from a guy ( sadly he passed away the beginning of March ) who knew his stuff >> http://www.hemrickperformance.com/Pages/engine.aspx

If you know what you want I would suggest speaking to a few engine builders who can answer your questions.

 

I don't think there are that many 120R or 124 owners on here, so you may be a bit light on useful replies. You already know the 120R, although it is disappointing you didn't stick with getting it sorted out. There are not that many threads about them on HDF and IIRC most contributors used motors, not kits.

I wish I had your problem! I personally would go with Star Racing and one of their S&S 124s, built for touring. Amongst others, they do a build using the 585 cam that I particularly like. If you need a little more fire I'm sure they can oblige!

 

the S&S 124 crate motor is a deal with 1 year warranty - you are correct about the spooling up - but with a 124 hit the gas and it's going sideways -- keep the compression at 10.5 with a 585 / 600 cam and you will be good

 

The 120r and the S&S 124 both have the same 4.625" stroke. The difference in the bore is pretty small too. Most of the difference in these motors will probably lie in cam choice or other mods. In general most big inch motors will take a little more time to get breathing, but I doubt the difference in these 2 is much at all.

Ive ridden a Road Glide with a 124" with the S&S .640 cam. The bike winds up fast, and keeps pulling. It has that neck snapping, tire spinning, front wheel pulling type of power and its still not soft at all on the top end. I was thoroughly impressed. Also, take into consideration that the S&S motor comes COMPLETE (minus exhaust), TB, intake, ignition system, all there. It also carries a 2 year warranty. I'm not a rep for s&s or anything, just been an extremely satisfied customer for years. Never been dissatisfied with products or support from them.

With the popularity of these big inch crate motors increasing, there are plenty of off the shelf aftermarket exhausts now available that can support them.

As far as other mods I agree with FLTR2008TRIKE on the clutch, definitely going to need some attention. A chain drive may be warranted depending on your riding style. For only $300 to convert, I would recommend it. Some guys don't have a problem with belts, but I ride to aggressive for a belt on a 100+hp motor. I think swingarm, frame, trans mods are probably overkill unless your gonna build this thing to 150hp and put it on the track.

 

The 120 and 124 do have the same stroke, but the S&S 124 is slightly taller. S&S pin placement for the connecting rods is farther out from the center line of the crank.

 

Moving the crank pin further to the outer diameter of the flywheel would in fact increase the stroke... You could have a taller motor with longer connecting rods and the same pin placement on the flywheel. If you move the crank pin out on the flywheel means that the rods are going to travel further up and down (longer stroke) throughout the rotation of the flywheel. That's all an increased stroke crank is, the pin is moved further from the center of the crank.

Also, if the overall height of the motors is different for any reason, its negligible because they both fit in a stock frame.

 

I know that my S&S 124" uses a 7.677 connecting rod with 5.033 tall cylinders. The SE 120 uses a 7.575 connecting rod ( not sure of the cylinder height ) and a taller piston with the wrist pin placement below the oil control rings ( S&S 4.125 pistons the wrist pin bore cuts through the oil control rings )

Both do fit in a stock frame but the S&S being taller there is less room between the rear rocker cover and the frame.

As Im building my 124" engine it has come with some issues to deal with

1) I had to swap out my HPI reworked stock throttle body with a HPI 58mm throttle body that has longer runners to fit the cylinder spread of my 124
2) The 124 requires longer head bolts ( depending on which heads you use HD or S&S there are 2 set to select from )
3) Exhaust fitment requires 2 guys pulling apart the head pipe to get it to fit. Or you have to cut the lower fins on the heads to mount a headpipe, or modify the pipe you want to use, or get a custom made exhaust to fit.

My 124" engine is being built for my trike. Its going to be a moderate compression build that I want to run well with out it wearing out the the valve train with a high lift cam and high compression. I dont plan on trying to win races or do burnouts, I wanted a engine that makes torque to move the pork!! LOL

If the OP decides he wants a all out 124" then he would want to look at a 124" with the B2 heads. Doing those heads with a 124" would require cutting the frame and modifying it to get the engine to fit because of the height of the B2 heads

 

I misunderstood you there partner. When you mentioned the crank center I thought the "pin" you mentioned was the crank pin. Yes indeed you can have the wrist pin lower/higher on the piston and that will make a taller/shorter motor with the same stroke.

As far as the problems you listed, the crate motor comes assembled, so you don't need to change throttle body or head bolts. The S&S heads also have clearances in the fins for exhaust installation. The Bassani road rage slipped right on when I helped install one... IMO, the crate motor is a good deal for reasons like those. Also, the 2 year warranty with the IST ignition isnt bad either.

I understand your reasoning for buidling your own though thats exactly what I did with my 96" evo. Built it myself peice by peice to make over stump pulling torque at 2500rpm rather than just a peak hp number. It may not meet the peak hp number of the crate motor, but itll pull them off the line

 

I tried the 2 into 1 exhaust when I first put my trike together. The diameter of the Propipe I used would drag when the suspension was compressed hard enough. Then I really fubared it when I rode to California from SC and toured San Francisco. Those street are steep!! I dragged my pipe so hard that on my return ride home the collector pipe in the front of the muffler cracked and eventually broke from the dragging stress I placed on it. Half of the front muffler pipe was gone when I got to Illinois.

I have a V&H Power Dual head pipe I am modifying for my trike for the 124". I plan on cutting the head pipe sections to adjust it for length and welding in a collar for each pipe to give me the ease of installation. Also since I have a reverse gear setup I also need adjust the pipe for the offset of the transmission side cover.

I didnt realize what I was stepping into when I decided to move up to a 124" from my 117", but hey its a challenge and I will overcome it