1250 kit info
Road Master
Joined: Jun 2009
Posts: 933
Likes: 1
From: Indianapolis
You should have quite a significant gain over a relatively stock 883. Top speed is mostly a product of horsepower, so with a lot more horses, top end will be a good bit higher as well. The 1250 including good flowing heads and cams will easily make up for your top end gearing. It'll launch nicely off the line. Shift points will change too. After your install get a good dyno tune and a tachometer. For for fastest ET shift about 100 rpms before the point where your bike is making max power.
Last edited by fox4; Jun 1, 2012 at 10:02 PM.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
Take a look at the NRHS website, where there is a comparison of several power curves for a stock 883, their kit, plus headwork etc. If you really do not expect to exceed 100mph then a straight 1250 kit on its own will probably do very nicely. That is what gives the biggest low/mid range gains. Headwork and cams give more top end.
Last edited by grbrown; Jun 2, 2012 at 08:15 AM. Reason: Added link.
Top Speed has nothing to do with HP. It just changes how quickly and efficiently you get to the top speed the vehicle is geared to. It is all in gearing. His top speed will not change a bit if he doesn't change the gears. I could make a 20HP motor go 200 MPH if I added enough taller gears. It would just take years to get it up to that speed. The only other way he could get more top speed is by bumping up the redline which will be bumped to 6500 or 7000 after his build, but that is no more speed than if he bumped his stock motor's redline to the same.
Seriously, I understand your point regarding tall gearing and there is validity to it. I do not know know the top speed of his bike or the RPM he is turning when is at top speed, but frequently, a motor will not have the power to push all the way to red line in top gear. There is a lot of drag on an object moving through the air at 100+mph.
It takes power to turn the gears (and push the air) The more power, the faster they turn. Look up some vehicle top speed numbers. Frequently, a vehicle will reach a higher top speed in 5th gear then 6th. (and when in top gear, often at an rpm well below redline) Why do you think that is? The reason is, it takes lot of horsepower to push an object to very high speeds. There reaches a point, that the available horsepower combined with the extremely tall gearing can only push the object so fast through the air. (It actually takes a certain about of HP just to move an object through the air and that amount of HP increases with speed, think of driving a snow plow through the snow) There are a few ways to increase the top speed, reduce the gear (shift to 5th, or reduce overall gearing), reduce drag (a fairing perhaps) or add more HP. Reducing gear can only help so much, as quickly you will reach redline.
When my Street Glide had it's Stock 96" engine, it could barely break 105 mph, now with the 120R it's still pulling strong through 125 (Haven't gone faster than that, but I feel 140 may be within reach) I haven't changed the gearing at all. Can you explain a reason other then the increased HP for it's increased top speed? Oh the 120R still has the same 6250 Redline as my Stage 1 96 had.
Last edited by dgdamore; Jun 2, 2012 at 08:57 AM.
Club Member
Joined: Feb 2007
Posts: 16,320
Likes: 306
From: Boynton Beach, FloriDuh
Congratulations. You may have just won the stupidest comment ever award! Oh, and I'd love to see that 20HP motor go 200mph!
Seriously, I understand your point regarding tall gearing and there is validity to it. I do not know know the top speed of his bike or the RPM he is turning when is at top speed, but frequently, a motor will not have the power to push all the way to red line in top gear. There is a lot of drag on an object moving through the air at 100+mph.
It takes power to turn the gears (and push the air) The more power, the faster they turn. Look up some vehicle top speed numbers. Frequently, a vehicle will reach a higher top speed in 5th gear then 6th. (and when in top gear, often at an rpm well below redline) Why do you think that is? The reason is, it takes lot of horsepower to push an object to very high speeds. There reaches a point, that the available horsepower combined with the extremely tall gearing can only push the object so fast through the air. (It actually takes a certain about of HP just to move an object through the air and that amount of HP increases with speed, think of driving a snow plow through the snow) There are a few ways to increase the top speed, reduce the gear (shift to 5th, or reduce overall gearing), reduce drag (a fairing perhaps) or add more HP. Reducing gear can only help so much, as quickly you will reach redline.
When my Street Glide had it's Stock 96" engine, it could barely break 105 mph, now with the 120R it's still pulling strong through 125 (Haven't gone faster than that, but I feel 140 may be within reach) I haven't changed the gearing at all. Can you explain a reason other then the increased HP for it's increased top speed? Oh the 120R still has the same 6250 Redline as my Stage 1 96 had.
Seriously, I understand your point regarding tall gearing and there is validity to it. I do not know know the top speed of his bike or the RPM he is turning when is at top speed, but frequently, a motor will not have the power to push all the way to red line in top gear. There is a lot of drag on an object moving through the air at 100+mph.
It takes power to turn the gears (and push the air) The more power, the faster they turn. Look up some vehicle top speed numbers. Frequently, a vehicle will reach a higher top speed in 5th gear then 6th. (and when in top gear, often at an rpm well below redline) Why do you think that is? The reason is, it takes lot of horsepower to push an object to very high speeds. There reaches a point, that the available horsepower combined with the extremely tall gearing can only push the object so fast through the air. (It actually takes a certain about of HP just to move an object through the air and that amount of HP increases with speed, think of driving a snow plow through the snow) There are a few ways to increase the top speed, reduce the gear (shift to 5th, or reduce overall gearing), reduce drag (a fairing perhaps) or add more HP. Reducing gear can only help so much, as quickly you will reach redline.
When my Street Glide had it's Stock 96" engine, it could barely break 105 mph, now with the 120R it's still pulling strong through 125 (Haven't gone faster than that, but I feel 140 may be within reach) I haven't changed the gearing at all. Can you explain a reason other then the increased HP for it's increased top speed? Oh the 120R still has the same 6250 Redline as my Stage 1 96 had.
So no, without gearing changes, there will be no significant increase in top speed by doing a straight 883 to 1250 conversion.
That's all well and good if you're riding a barge, but a basic stage-1 883 in 5th gear, hits redline at ~110 mph, and under decent conditions is capable of hitting that.
So no, without gearing changes, there will be no significant increase in top speed by doing a straight 883 to 1250 conversion.
So no, without gearing changes, there will be no significant increase in top speed by doing a straight 883 to 1250 conversion.
Road Master
Joined: Jun 2009
Posts: 933
Likes: 1
From: Indianapolis
Congratulations. You may have just won the stupidest comment ever award! Oh, and I'd love to see that 20HP motor go 200mph!
Seriously, I understand your point regarding tall gearing and there is validity to it. I do not know know the top speed of his bike or the RPM he is turning when is at top speed, but frequently, a motor will not have the power to push all the way to red line in top gear. There is a lot of drag on an object moving through the air at 100+mph.
It takes power to turn the gears (and push the air) The more power, the faster they turn. Look up some vehicle top speed numbers. Frequently, a vehicle will reach a higher top speed in 5th gear then 6th. (and when in top gear, often at an rpm well below redline) Why do you think that is? The reason is, it takes lot of horsepower to push an object to very high speeds. There reaches a point, that the available horsepower combined with the extremely tall gearing can only push the object so fast through the air. (It actually takes a certain about of HP just to move an object through the air and that amount of HP increases with speed, think of driving a snow plow through the snow) There are a few ways to increase the top speed, reduce the gear (shift to 5th, or reduce overall gearing), reduce drag (a fairing perhaps) or add more HP. Reducing gear can only help so much, as quickly you will reach redline.
When my Street Glide had it's Stock 96" engine, it could barely break 105 mph, now with the 120R it's still pulling strong through 125 (Haven't gone faster than that, but I feel 140 may be within reach) I haven't changed the gearing at all. Can you explain a reason other then the increased HP for it's increased top speed? Oh the 120R still has the same 6250 Redline as my Stage 1 96 had.
Seriously, I understand your point regarding tall gearing and there is validity to it. I do not know know the top speed of his bike or the RPM he is turning when is at top speed, but frequently, a motor will not have the power to push all the way to red line in top gear. There is a lot of drag on an object moving through the air at 100+mph.
It takes power to turn the gears (and push the air) The more power, the faster they turn. Look up some vehicle top speed numbers. Frequently, a vehicle will reach a higher top speed in 5th gear then 6th. (and when in top gear, often at an rpm well below redline) Why do you think that is? The reason is, it takes lot of horsepower to push an object to very high speeds. There reaches a point, that the available horsepower combined with the extremely tall gearing can only push the object so fast through the air. (It actually takes a certain about of HP just to move an object through the air and that amount of HP increases with speed, think of driving a snow plow through the snow) There are a few ways to increase the top speed, reduce the gear (shift to 5th, or reduce overall gearing), reduce drag (a fairing perhaps) or add more HP. Reducing gear can only help so much, as quickly you will reach redline.
When my Street Glide had it's Stock 96" engine, it could barely break 105 mph, now with the 120R it's still pulling strong through 125 (Haven't gone faster than that, but I feel 140 may be within reach) I haven't changed the gearing at all. Can you explain a reason other then the increased HP for it's increased top speed? Oh the 120R still has the same 6250 Redline as my Stage 1 96 had.
I could most definitely make any power motor go as fast as I want with enough gears. Why do you think semis have 18 gears? They would have to have massive amounts of HP (which they do not) to get up to speed with just 5 or 6 gears.
So your comment is the uneducated stupid comment of the day..
Ultimate HDF Member
Joined: Mar 2008
Posts: 7,604
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From: Landrum, SC , elevation 986'
Now, put in an ignition with the capabilities of increasing your REV limit and all bets are off. lol 
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Ultimate HDF Member
Joined: Jul 2006
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From: Nashville, TN
Significant increase in power and torque. No change in shift points, and no change in top end speed. I still hit the rev limited at 114 mph. But, I can get there a hell of a lot quicker, if I choose to do so.
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Tourer
Joined: Sep 2008
Posts: 474
Likes: 1
OK, thank you all for clearing that up. After totaling the cost for 1250, heads, cams, and exhaust I think I might just hold off and look for a used Dyna or softail. Gotta see if I can swing both or sell the Iron and find an older sportster to build for fun.