Author Topic: 10hp cyl headquestion  (Read 7599 times)

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Offline dang107

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10hp cyl headquestion
« on: August 03, 2007, 06:09:17 pm »
I keep hearing to use a 11hp head on a 12hp eng but what about a 10hp I have one sitting around thats in good shape and it bolts on. I am cleaning shop and trying to get rid of the junk. the chamber looks considerably smaller so I don't know if it would be to much comp.for a stock rod and crank or if there would be any other prob. with this combo please help me out thanks

Offline cycloneracer

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Re: 10hp cyl headquestion
« Reply #1 on: August 03, 2007, 06:16:51 pm »
It really depends on the engine size, not the HP.  Many use a 25 cid head on a 28 cid engine.  The 25 is a smaller chamber as you describe.

But there are 2 thoughts on this.  With the 25 head you increase compression, but decrease cylinder volume and flow.

With the 28 cid you don't increase compression, but you increase flow and cylinder volume.

So you decide.

Is the engine stock?  What about cam?

If it is a stocker, swap the heads.  Big improvement.

Cammed?  Well I run the 25 on my 28 with a g-team cam and it seems to run............well..............O.K.

I wouldn't worry about the increased compression for the stock rod.  It will break for some other reason!


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Offline dang107

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Re: 10hp cyl headquestion
« Reply #2 on: August 04, 2007, 09:30:53 am »
thanks for the reply. is there a difference in the chamber of an 11 vs. a10  or are they both 25ci eng the reason im asking is the castings between the 11hp eng and  the 10hp have differnt tin and cooling fin setups anymore insight would be appreciated

Offline allen minaker

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Re: 10hp cyl headquestion
« Reply #3 on: August 04, 2007, 10:33:30 am »
Look at the top of the head , it should have a number casted in to it between the fins . That will tell you what size the head is .
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Offline Don Gienger

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Re: 10hp cyl headquestion
« Reply #4 on: August 04, 2007, 11:37:11 am »
Generally speaking there are about 4 different heads from 22's and 25's. The Briggs starting with model numbers 22 and 25's are the heads you want to use on a 28.
Some heads have a casting number in them and some don't.
Bottom line is those older and smaller CID motors have a .400 depth to the combustion chamber while the 28's have a .500 deep pocket.
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Offline dang107

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Re: 10hp cyl headquestion
« Reply #5 on: August 05, 2007, 01:57:26 pm »
this head was off a really old eng with no markings so I went the measure route and compared it to a known 28ci i'm guessing it is a 25ci another question with so much clearance to the valve does anyone spotface the sparkplug hole to move the plug further into the head to unshroud the plug I know it makes a big difference in other types of eng or is it a waste of time

Offline Squidd

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Re: 10hp cyl headquestion
« Reply #6 on: August 05, 2007, 02:43:32 pm »
Quote
i'm guessing it is a 25ci
25"


28"
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Offline Don Gienger

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Re: 10hp cyl headquestion
« Reply #7 on: August 06, 2007, 11:11:57 am »
 :woo:
Well the USLMRA I am guessing won't alow the mod.
Next why would you want to do that? Move the plug?
The Valves are closed when it sparks so there is No shrouding going on. Also the way the negitive tab of the plug is pointed is more important then anything.
Putting the plug in at an angle is important too but can't do.
Trapping gasses above the piston is super important. But ARC makes a longer rod now and guys think they have to shave the piston for better compression when in affect they may be hurting themselves HP wise.
Cylinder design and flame wave and all that is a WHOLE Nother science so many miss out on.
Just keep it simple..................put the head on and race.
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Offline dang107

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Re: 10hp cyl headquestion
« Reply #8 on: August 07, 2007, 03:07:48 pm »
I guess it seemed odd to me that its so important which way you index the plug if the electrode is surrounded by the threaded hole. If this was any other type of eng. people would say it was a big deal and most of the eng guys I've worked with wont worry about indexing but on acompletly different scale were dealing with a eng were every litte bit adds up so if a simple operation on a mill might benifit such a small ignition system I wondered if it is worth doing both. don't get me wrong I'm not underminding here I don't have much exp. with these eng thats why asked the question. and the head that started all these questions is the top pic. thanks again for the insight guys.

Offline George Herrin

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Re: 10hp cyl headquestion
« Reply #9 on: August 07, 2007, 04:32:57 pm »
Thats another reason I only use 12 hp heads anymore. Oh well nother trick slipped out. But Indexing is important. Least wise I think so. Like you said every little bit helps.
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Offline budd porter

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Re: 10hp cyl headquestion
« Reply #10 on: August 08, 2007, 02:06:41 pm »
OK, indexing is important.  Should the negative electrode be on the valve side or the piston side?  It seems that it should be toward the valve side so that the flame spread would not be blocked between the piston and the plug.

Offline dang107

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Re: 10hp cyl headquestion
« Reply #11 on: August 13, 2007, 07:29:07 pm »
thats a question I've heard multiple answers to. I've heard some guys say with flat head style engs to point towards the valve because of the low velocity in the intake system this would light off the charge that doesnt get pulled into the cyl creating a better flame front towards the piston for the power stroke but with where the plug is located in a briggs head the electrode is shrouded by the valve so it should point towards the piston to light off the power stroke more completely. now the trick is going to see how many guys tell you which way they index and how convincing they are  i'm not being sneaky It just seems that which ever way some one does it is the right way but if you experiment with some wide open plug cuts and examine the plug carefully you will see a difference then you decide

Offline George Herrin

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Re: 10hp cyl headquestion
« Reply #12 on: August 13, 2007, 08:58:36 pm »
Well I am a bit different I guess. I point the open end kind of between the valve and piston. Kinda splitting the difference. Not saying its the best way its just the way I do it. Good bad or indifferent its how I do mine.
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Offline bountyhunter

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Re: 10hp cyl headquestion
« Reply #13 on: August 16, 2007, 08:20:11 am »
 dont understand how valve can shroud the plug when its closed dand 107 can you explain more. thanks

Offline cycloneracer

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Re: 10hp cyl headquestion
« Reply #14 on: August 16, 2007, 09:21:50 am »
I use to index them.  Now I don't.  Haven't felt or seen any difference in hp, torque, response, ect.  There are so many other things that are more important.  I just don't waste my time with it any more.  I worry about proper gearing and carb settings.
Although I have found that when the engine becomes hard to start, a new plug makes a world of difference!  That is why I don't index them, I'm changing plugs often and checking them often.  Don't want to waste time with different shims and washers to get it "just right."  I'd rather spend my time on the carb, or checking all those bolts that can rattle loose!

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