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  #21  
Old 5th August 2017
BrokenIron BrokenIron is offline
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So it sounds like dual plugging may be an option.
My engine has Andrews Y grind cams, but about stock everywhere else, but the efficiency sounded worthwhile enough to do it, then if I do any performance mods it will be there.
Dunno, I'm gonna see if my Indy is experienced with port/polish. But I will research further and see if it's even necessary
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  #22  
Old 5th August 2017
BrokenIron BrokenIron is offline
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Quote:
Originally Posted by Ferrous Head View Post
Good advice.

There are power gains to be had if your heads don't currently flow enough for what you do. If you go racing you will want heads that can flow enough to allow the engine to rev to 7000 RPM.
And that's OK for racing. But on the street you seldom see 7000RPM. You mostly see 2000-5000 RPM. If your heads flow well enough to handle that your OK.
Having heads that flow 165+ is great for a race bike that almost never spends any time at 2000 RPM. or even 400 RPM. Because like everything port flow is mostly a compromise. At low RPMs your engine will generally prefer a smaller port. This is because we need to look at port velocities. There is am optimum port velocity for fuel atomisation to take place. If your ports are too big in other words the port velocity will be too low and the fuel won't "mix" in the required ratio. You will effectively get a lean condition.

as far as I know the heads on the 68 (9 ?) and later Sportsters had different castings and they are better than the earlier ones.

On a stock engine a set of single fire dual plugged heads will work better and be noticeable more than a port job with nothing else added.

professional porters can do wonders when your ports are the restriction in the intake tract. But until you reach the level where your engine needs more air it will make no difference at all unless it harms low end performance (too big a port).

I have always thought the Sportster port passages were too big to start with. Once you increase the engine size (boring/stroking) the ports come into their own. That's part of the reason I suspect is that people rave about bored/stroked engines, the ports are finally closer to the optimum size or the engines requirements. But that's just my opinion, others may disagree.

Professionals don't generally come cheap. I managed to get Dan Baisley to port a set of heads foe me. $2600 more than 3 years ago. I don't think he will ever for another set. His son might.
Also asked Paul O'Keefe (Jerry Branch's partner) if he would do a set. Initial reaction was "No, too much work." But when I told him Dan had done me a set he asked "Whaat did you pay ?" I told him and he winced and said "OK - but only this once".

If someone is going to do this for you they will ask a lot of questions first. Like - What kind of racing will you be doing ? (There's a BIG difference between drag racing, road racing and dirt) What size will the engine be ? What cams will you be sing ? What compression ratio ? What fuel are you using ? and so on.

The idea opf porting and polishing heads for great power gains comes mostly from old time hot rodders who were starting with pretty poor intake manifolds.
Us ironhead riders start with the advantage of a set of very good heads.
First off, thank you for taking the time to post this. It is very helpful and I think you're absolutely right. I'll just leave it be. $2,600 is fkn outrageous and I would never pay that just for the heads unless my motor was built to high fkn heaven!
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  #23  
Old 5th August 2017
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1970 cylinder heads do not need ( or want ) porting for a stock displacement motor.
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  #24  
Old 5th August 2017
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That's good to know mrmom, I have on the shelf a nice set of 60's heads with the small inlet valves, would larger valves be a good upgrade?
.......Davi.
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  #25  
Old 5th August 2017
BrokenIron BrokenIron is offline
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Quote:
Originally Posted by mrmom9r View Post
1970 cylinder heads do not need ( or want ) porting for a stock displacement motor.
Yea that's kinda what I gathered, oh well.
I don't need to have a race bike, but it just seemed so gutless that I want to give it a boost. Now granted, I think a lot of my power loss was from other things. My Indy described some issues that I can't for the life of me recite. But it made sense.
In your opinion, what are things that could rob power from an old 900, other than the fact it's an old 900?
Basic stuff.. any ideas?
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  #26  
Old 5th August 2017
BrokenIron BrokenIron is offline
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My heads have a big intake valve, small exhaust. As you see in the pics. Did someone do that aftermarket? I know they are kibblewhite valves.. so I wonder if the PO put in the bigger valve? I haven't looked to see if a factory 900 had small intake valves originally. But I keep seeing mention of it?
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  #27  
Old 5th August 2017
45Brit 45Brit is offline
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My VT750S Honda had dual plugs, on an engine which supposedly only makes 42 hp.. but it would outrun any 883 Sportster and some 1200s...
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  #28  
Old 5th August 2017
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Quote:
Originally Posted by BrokenIron View Post
My heads have a big intake valve, small exhaust. As you see in the pics. Did someone do that aftermarket? I know they are kibblewhite valves.. so I wonder if the PO put in the bigger valve? I haven't looked to see if a factory 900 had small intake valves originally. But I keep seeing mention of it?
Stock valve sizes for a 70 are 1-15/16 intake and 1-9/16 exhaust. From looking at pictures in another thread of yours ( can't find pics in this thread), It looks like the exhaust is bigger than stock but the intake is stock.
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  #29  
Old 5th August 2017
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Quote:
Originally Posted by BrokenIron View Post
Yea that's kinda what I gathered, oh well.
I don't need to have a race bike, but it just seemed so gutless that I want to give it a boost. Now granted, I think a lot of my power loss was from other things. My Indy described some issues that I can't for the life of me recite. But it made sense.
In your opinion, what are things that could rob power from an old 900, other than the fact it's an old 900?
Basic stuff.. any ideas?
when you say gutless are you comparing it correctly? another iron head or some other bike? A good running iron 883 is generally quicker then most 77 on 1000 iron heads.
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  #30  
Old 6th August 2017
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These heads are on a small stroker that I race. They were ported to suit what I was doing with the engine. That price included a set of his roller rocker (not really necessary and not desirable IMHO on a street engine).
I have about $12,000 invested in this engine. But it should win me an Australian Championship that will provide me with a $15 trophy.

Oh, yeah, I see your point.
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