Author Topic: 28 ohv port redesign  (Read 5582 times)

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Offline Sodslinger

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28 ohv port redesign
« on: January 15, 2012, 10:01:11 pm »
hey i have heard of guys successfully reshaping the intake ports of various heads with different types of puddies, for example duraglass or jb weld, they said it works great, what do you guys think of doing this to a 28 head?
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Offline blasterracer817

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Re: 28 ohv port redesign
« Reply #1 on: January 15, 2012, 10:09:07 pm »
In motor theory a smaller more straight intake runner will flow more than any "hogged out" intake. the reason they use putty:epoxy, jbweld etc. is because when it dries its easy to form and make smooth. so what im getting at is Yes if you had a flow bench and time your intake with the small straight runner filled with epoxy will flow more cfm than a hogged out intake. But if you have no access to a flow bench starting with a Hog port as i like to call it will give you more cfm than a stock port. and the bonus to that is when you do have access to a flow bench, your intakes ready for the epoxy.
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Offline Burwell555

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Re: 28 ohv port redesign
« Reply #2 on: January 15, 2012, 10:14:30 pm »
CFM is just a number. Just cuz it flows big numbers doesn't necessarily make it a choice piece.
Zach Burwell
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Offline blasterracer817

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Re: 28 ohv port redesign
« Reply #3 on: January 15, 2012, 10:30:59 pm »
Zach I agree, but cfm is velocity, and velocity and intake speed is what makes a motor. some may disagree with me but if you dont have your air and fuel moving at a fast enough velocity it wont make power. Im sure ec's carbs have better cfm and flow than a stock carb. and yes I would believe they're carbs have a larger throught than stock, BUT the thing that makes them flow is smoothing out the carb and a good velocity stack to increace cfm. please correct me if I'm wrong.
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Offline Burwell555

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Re: 28 ohv port redesign
« Reply #4 on: January 15, 2012, 10:36:07 pm »
I guess it all depends on what ya want. I won't correct you, but I won't say anymore.
Zach Burwell
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Offline fordman21

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Re: 28 ohv port redesign
« Reply #5 on: January 16, 2012, 09:03:12 am »
I use JB weld, but you have to use the slow stuff, the quick curing stuff is no good and won't take the heat. The slow JB weld will need about two days to cure before you can really work with it.
I agree that big cfm numbers are not always the answer.
I also agree that velocity and air speed sometimes are.
It all depends on the application.
If you know what you are doing there sure is a lot of room for improvement.
There is a fine line between gaining 1cfm and loosing it, its usually in the finest details.
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Offline bountyhunter

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Re: Re: 28 ohv port redesign
« Reply #6 on: January 18, 2012, 04:26:58 pm »
Don't it depent on engine head, design some need opened up were others need smaller(some you can only get so much out of because of design) and isn't it a lot of making the port uniform in size to make flow
Good and round square corners
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Offline Rooster

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Re: 28 ohv port redesign
« Reply #7 on: January 18, 2012, 10:28:07 pm »
CFM is just a number......
as is ...CID, HP and Torque, Lif , duration, LSA, timing, gear ratios, tire size, air pressure, rpm, CHT, EGT .....

Numbers are important things...learning how to use them makes allll the difference in the world.

1st is a number.....last is not!
Bert stole my cookies!!
 I think he used them to bribe Ed into something naughty?

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Offline Ron Atchison/A.C.E. Race Engines

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Re: 28 ohv port redesign
« Reply #8 on: January 19, 2012, 09:51:36 am »
CFM is just a number. Just cuz it flows big numbers doesn't necessarily make it a choice piece.

theoretically speaking it takes roughly between 3.2-3.4 cfm per horsepower. So that being said, hp is just a number. To most successful builders, port cfm numbers are the foundation for a particular Hp goal.
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Offline Otto

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Re: 28 ohv port redesign
« Reply #9 on: October 30, 2013, 01:31:53 am »
With the guide location in a briggs overhead valve cylinder head there is no way of getting enough valve in it to properly feed that bore.then there is not enough cross section in head or manifold to feed the valve it needs.a good engine should make 2.2 to 2.6 hp per cubic inch.there is no where near enough csa in a briggs port layout to achieve this.so in short term and rules allowed and clearance available the briggs ohv is maxxed out way before potential the bore is capable of.jmo
3 Cfm per hp in todays world is one inefficient slug.1.6 to 2 Cfm per hp is where its at if your going to have any success.look at 358 inch nascar engine.400 Cfm head makes 880 hp on dyno.limited sprint engines/290 Cfm making 700 plus hp.its all about efficiency.

Offline willenglish

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Re: 28 ohv port redesign
« Reply #10 on: October 30, 2013, 02:17:39 am »
A good RACING engine may make 2.6 hp per cubic inch..but a production industrial engine like we run will not. A racing engine..NASCAR for example...is not a stock based engine. Nearly every parameter of those engines has been optimised to make maximum hp and maintain reliability. Bore...stroke..cylinder spacing cam position have all been changed.The cylinder heads are specificly made for racing....everything about them are designed to make power. This type of engine will produce that 2.6 hp per cubic inch. Our engines come from the factory making just about  1/2 hp per cubic inch. There is a physical limit to the modifications that CAN be made to them...in observation of the "as cast" rule.  When you get a Briggs model 33 up to 80 horsepower....within the rules....let me know.
William L. English, jr.

 

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