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1250cc heads. How much more can they flow

5K views 31 replies 10 participants last post by  lbrown 
#1 ·
Over the winter my project is to install my BOSS NOSS system but talking to a few people it's been said I can make a big power change on head work. I already have Screamin Eagle II cams installed SO does anyone know what the heads flow with the cams & how much more can I flow? From what I read the factory heads are already C & C ported?
 
#2 ·
Easy answer is YES, you can make them flow much better. How much more power you can get varries from bike to bike, supporting mods, tune, ect. The heads are definatly not CNC from factory. (Only the SE heads were CNC) The 08 and later 1250cc heads are all sand cast.

I think Fitzgerald still offers CNC headwork, you will have to contact them to inquire about potential gains. You will probably also a require larger throttle body. With shipping, throttle body, tune and everything, you are probably looking in the $3k range for maybe 10-20 hp gain.
 
#3 ·
600-800 for head work for 3-5 hp not worth it.


just add the NOS and be done.

Keep the 53 mm TB's for now.

if you go BB the go to 58's
 
#4 ·
I agree with RSC on this one, even though with my big bore I port polished and had over sized valves put in, but if your just putting in NOS no sense it stripping the motor to just have head work done.

64mm Throttle body?!? What the head would he need that for?? Most that big bore them only go up to 58mm.
 
#6 ·
That's like putting a Dominator carb on a small block Chevy. Bigger is not better. You might make more peak hp, but torque and driveability will suck.
 
#7 ·
That's like putting a Dominator carb on a small block Chevy. Bigger is not better. You might make more peak hp, but torque and driveability will suck.
69 Camaro with small block with a 1050 dominator carb. Bracket car and runs amazing.



Since he is running nitrous, the larger tb may be better. I cant tell you how many small block nitrous motors I have seen running up to 1400cc carbs. (usually in the 1050-1100 range though).
 
#8 ·
Few people I talked to the 53mm TB's at full sing don't max out on flow. with nitrous you don't need a bigger TB (Or carbs for some) because N2O is it's own source of oxygen. If your primarly racing were your wide open more then part throttle I can see bigger TB's being a advantage. As for head work I would of hoped the heads would be C & C ported then casted. Maybe just removing them and polishing the ports might give good results?
 
#10 ·
Ever notice how those 1000-1400 cc carbs on small blocks idle like crap too. you have to "burp" the throttle to keep it running. I think even Big Bore kits you can get away with the 53mm . For the cost of heads a Big Bore might give better results for the cost
 
#11 ·
It is so easy to overcarbuerate. When I built the 355 for my truck, I originally had a Holley 780 carb... ran strong, but was sort of flat in the mid-range. I downsized it to a 670 Street Avenger, and the motor came alive.

If I was building a motor for my V, since I have an 1130, I'd go with my original plan to use a Destroyer crank, CP pistons at a 1250 bore, and have a 1302. I sold all the parts when I went turbo, but that's what I'd do.
 
#16 ·
What about a Destroyer crank. I seen a post somewere were someone posted the difference from a stock 1250 crank to a Destroyer crank. It was slightly longer. Obviously I would have to take the engine apart but to have a stroker engine would be nice
 
#20 ·
I have a guy that does head work. BUT if I can get away with a stroker engine then all the better. I found a old post on CC/Stroke differences

Stock stroke = 72mm
Destroyer stroke = 75mm


1250 with Destroyer Crank = 1298.9cc

I MIGHT be lucky that a friend MIGHT have a Destroyer crank on hand. Only thing I wonder is will it work with factory parts and will it raise the compression too high were it would need race fuel? I believe the compression on a stock 1250 is 12:0:1
 
#28 ·
I've searched for Stroker engine posts. Most I see are people doing it to the 1130cc engines or just full on Big Bore packages. I have someone very close to me (family) that was involved in the devlopment of the Destroyer before he retired from HD. i'm trying to do my own research before he will work on the project :deal:
 
#31 ·
We have proven this numerous times that 53 to 58mm is a difference not mainly in HP but more TQ and the rate of the climb to redline. Heads done properly with Stage II cams and tuner will walk all over a stock setup. Is it worth it that is up to you.

A destroyer crank in a 1130 makes it a 1177 and in a 1250 it will be a 1302. You will need to do a little clearance in the bottom case half where the rods come around. A 1302 with heads and cams will scoot no doubt. I have one with over 7k miles on it and I beat the tar out of it.
 
#32 ·
you can have your crank stroked 1/4 in by falicon for less than the 1/8 in stroke destroyer crank... a big race motor could use 64mm tb`s ....a stock 1125r buell has 62mm tb`s...it would have to have a very good cyl head and big cam to need tb`s that big...
 
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