There's no difference in the bottom part of '95-later
883 and 1200 engines... it's all the same from the
cylinders on down, including the starter, primary,
clutch, and transmission.

The only difference between a factory 1200 cylinder
and one that's been bored to 3.498" is the casting
mark on the front of the jug. One says 883, the
other 1200. The outer diameter of the steel liner,
as well as it's thickness, is the same. Harley DOES
inspect all new cylinders for porosity to a depth
of .030" to ensure they can take 3 overbores. Some
say that it's better to buy new 1200 cylinders than
to bore 883 cylinders to avoid possible porosity.
I've never even heard of a porosity problem with
bored 883 cylinders. All this being said, if new
1200 cylinders are used in a conversion, even the
casting stamp will be the same.

The 1200 cast pistons weigh a whopping 517 grams with
rings, wrist pins, and circlips. Because of this
weight, they can't be revved as high as lighter
pistons, such as the 425 gram 883, or Wiseco 883/1200
pistons, without cracking, or overstressing the rods,
main bearings, and crankpin. This also causes engine
vibration to occur at lower engine speeds, which
would be at a lower road speed. So to get the
vibrations back up to the same road speed as the 883's,
higher gearing (a 29 tooth front belt sprocket vs the
27 on an 883) has to be used. This sacrifices
acceleration.

Also because of the much heavier pistons, the factory
1200 has a lower rev limit (5,200 rpm) in the
ignition module than the 883 (6,000 rpm). Certainly
either engine can be revved to 6,800 with a SE
replacment module, but the heavier pistons produce
more wear and tear on the factory 1200 lower end.
The modules also have different advance curves that
suits the combustion chamber they are used with.
That's why a stock 883 module works well with the
883/1200 conversion.

Wiseco 883/1200 pistons weigh about the same as the
stock 883 pistons, so they don't have the vibration
problems of the heavy factory 1200 pistons and
require you to sacrifice acceleration with higher
gearing. And as forged pistons, they're MUCH stronger
than the factory cast pistons.

While the factory 1200 heads do have larger valves,
they have a huge, 3.5" wide inefficient combustion
chamber with no quench (squish) area above the piston.
IMO they are the poorest design put on a Sportster in
recent years. To improve upon them for performance
requires welding in a lot of metal and then machining
it, while with the 883 heads require only machining
to remove material, and they also provide a 1/4" wide
quench ring all around the top of a 1200 piston,
resulting in very efficient combustion. The SE heads
used on the 1200 Sport are much better than the
factory 1200 heads, which couldn't tolerate the
higher compression.

It IS possible to do an 883/1200 conversion using
factory 1200 pistons, but this brings with it the
vibration problems, and it requires grinding out
the quench area of the 883 head to lower compression,
making them as poor as the factory 1200 heads in that
respect. And it is even possible to acquire used
1200 heads additionally. Those who've tried this
route eventually have to sacrifice acceleration with
the larger front belt sprocket to raise vibration
speed.

Ignoring the 7% torque multiplication advantage of the
883 gearing, a Wiseco 883/1200 conversion has a 9.6:1
compression ratio with stock HD 1200 gaskets, and over
10:1 with thinner aftermarket head gaskets. This
added compression produces significantly more torque
at lower and midrange rpms than a 9.0:1 factory 1200,
and the additional compression of the conversion almost
exactly offsets the advantage of the larger factory
valves at higher rpms. The 883/1200 and factory 1200
engine

 

Does anyone make high compression pistons for the std. bore 883? Seems to me that if you built a higher compression,more efficient version of the 883 that you could produce the same power gains of the conversion to 1200. I don't know, I could be wrong...I am fairly new at the bikes, however I have been building race engines for years. Sometimes the bigger fight comes in the smaller dogs...y'know?...I am aware that a larger bore flows and breathes better, but on the other hand head and portwork and nasty a$$ cams can go a looooong way. The higher the compression the more tame the nasty cam becomes(in any engine).Sooooooo...,Is anybody doing this? Basically I'm bbrrrrrrooooooke and tryin' to go fast. I have time. I have skill and tools. any answers would be greatly appreciated.

 

Old post, but interesting, if you're still on the forum, thanks

 

If you're keeping it stock, the answer is the same. 1200. Over 20 hp. More like 25. Plus you can do a simple cam change for a considerable boost in power with Hammer's 570 cams that are designed specifically for a stock 1200 meaning no other work necessary. Good for close to a 90hp ride then. Even the 560s are bolt in. You'll spend a lot of money on headwork alone, plus cams to even come close to 80 hp with an 883. In stock form the heads in a 1200 are in a whole different league. Not to mention the clutch will slip without a better diaphragm spring.

 

Im questing some don't know that early 883 heads are much different than later models.the castings are different. Just like Earley 1200 heads.the valve train on pre 04 heads isthe same.same springs,same angle valve pockets.even the valves are the same,with exception ov the diameter.they both can use cams up to 500 lift.the original s.e.bolt in cams were designed for the 883.they also give good usable power in a conversion,even with stock 9:1comp.my favorite all time 500 lift cams are andrews n8.on my 883 i used the s.e. head gaskets.they come with 3 10s and a twenty riveted togeather.you drill the rivet out and use any combo you like.when i took the heads off to port them the pistons at tdc came up 10 thousandths below the deck.i replaced the stock 50ths with 10s.the same as shaving 40 off the heads.the n2 cams I used have lots of piston to valve clearence so taking 40 off isn't a problem.i knew 20 is cutting it close on the deck.but I've put 26000 miles on it without a tick.i too searched high and low looking for high compression pistons for 883 with no results.when you Google it its like asking for a unicorn.so if I ever get too much time on my hands,pistons with deeper valve pockets would alow more comp. And enough piston to valve clearence.

 

because a basic 1250/1275 kit will make more power than an 883 with cams ect.

 

I posted the gains of the 883 in full detail prior to those of the 1200s.the point being the 883 heads have alot more potential then given credit for.also: i have the advantage of years of road racing,porting and building high performance road race and drag race motors.the only expensive part of the 883 project was the cams and head gaskets.

 

clapping 👏 bravo haha