Author Topic: Head flow 390  (Read 18771 times)

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Offline rotten ron

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Head flow 390
« on: January 28, 2011, 11:00:36 pm »
Today we flowed a stock head that has not been touched yet,got 97 CFM @ .500" lift but we used a valve that has been backcut and polished,so with a stock intake valve it would have been a few CFM less,I will post what happens when I get a larger seat in it and port it

Offline fx28

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Re: Head flow 390
« Reply #1 on: January 29, 2011, 08:32:24 am »
A question Ron? I know there has been a lot of developement on the 390 in the last year. Is the 390 able to run .500 lift? I have ran one for a long time and my stuff is still strong but dated to say the least.

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Offline fordman21

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Re: Head flow 390
« Reply #2 on: January 29, 2011, 05:51:12 pm »
You better look into that Rotten, before you go hogging the head out. You might have to fill some in instead.
 After looking at the GX390 head it looks really nice, (meaning it has potential) but I was surprised that it didn't have much at the lower lifts or overall for that matter. I think the port opening is already too big for the available camshafts, but it needs bigger valves.
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Offline Old Goat

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Re: Head flow 390
« Reply #3 on: January 30, 2011, 02:19:07 am »
I think the port opening is already too big for the available camshafts, but it needs bigger valves.

I'm working on one now (GX390), and am going to put a bigger intake valve in it. Do you think it should have a bigger exhaust valve too? The reason I'm asking, last year, on a briggs single ohv, I put larger intake and exhaust valves in a head. I kept the same proportions as the factory valves. I lost all my bottom end. Top end ran good, but it wouldn't come out of the turns very well. So I went back to the stock exhaust, with the same larger intake and it worked a LOT better.
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Offline rotten ron

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Re: Head flow 390
« Reply #4 on: January 30, 2011, 02:49:01 am »
I am changing the intake seat and using a larger valve.I am using about .125' larger exhaust valve .I am planning on having 13 to 1 compression,after I get the new seat in I will be able to tell what size intake valve I can use but it will be a bit longer before I get that far

Offline Old Goat

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Re: Head flow 390
« Reply #5 on: January 30, 2011, 03:57:20 am »
13 to 1!!! Dang, a little bit more and you wont even need a spark plug! Just make it a diesel!
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Offline Rooster

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Re: Head flow 390
« Reply #6 on: January 30, 2011, 09:12:19 am »
or run it on alcohol maybe?
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Offline fx28

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Re: Head flow 390
« Reply #7 on: January 30, 2011, 01:06:04 pm »
There are some guys on the left coast that are putting in larger valves, 1.6 to 1.7 on intake. Not sure on exhaust. That would depend on what the intake could achieve as far as flow to see if needed. They also were running 12.5 to over 13. to 1 comp. They claim you will start having block issues on circle racing over 12.5. I dont know where my ratio is at but after several years the block did crack under the cylinder at the side cover.  I looked last night for their posts for info but looks like the site purged at the first of the year.


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Offline zach87cp

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Re: Head flow 390
« Reply #8 on: February 03, 2011, 10:55:56 am »
How do you get 500 lift with 13 to 1 compression,We have too run a 305 lift cam just soo the valves dont hit the piston but we have a little over .250 shaved off the block and head.
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Offline George Herrin

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Re: Head flow 390
« Reply #9 on: February 03, 2011, 12:37:36 pm »
You eyebrow the pistons for valve clearance
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Offline bountyhunter

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Re: Head flow 390
« Reply #10 on: February 12, 2011, 10:02:02 pm »
I was told becarefull not to take 2 much off head as this weakins them use plan b  alsol at what lift does it stop increasing in flow any wat im not up on flow *s so how does this compair to say and intec single head

Offline fordman21

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Re: Head flow 390
« Reply #11 on: February 18, 2011, 07:52:02 am »
I never had an intek single head on the bench yet Ferris.
I'm going with a 1.65" intake and 1.33" exhaust in the Honda head.
Ryan Kerr  519-332-9532
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Offline Rooster

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Re: Head flow 390
« Reply #12 on: February 18, 2011, 07:36:03 pm »
How do you get 500 lift with 13 to 1 compression,We have too run a 305 lift cam just soo the valves dont hit the piston but we have a little over .250 shaved off the block and head.
What ratio rockers are you running?


Ohh wait, I forgot I don't know what those are..
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Offline Old Goat

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Re: Head flow 390
« Reply #13 on: February 18, 2011, 08:06:40 pm »
What ratio rockers are you running?


Ohh wait, I forgot I don't know what those are..

Yup, you got a fat head,  :omg: Ooops, I mean a flat head!  :D
I'm also going  to use a 1.65" intake. I wonder if a stock size stainless intake valve could be used as the exhaust valve?
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Offline Rooster

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Re: Head flow 390
« Reply #14 on: February 18, 2011, 08:24:18 pm »
Yup, you got a fat head,  :omg: Ooops, I mean a flat head!  :D
I'm also going  to use a 1.65" intake. I wonder if a stock size stainless intake valve could be used as the exhaust valve?
Guess I got no use for these then?

Anybody want them, will trade for Moon Pies, chocolate cake or pictures of OG getting beat by an Opposed !
Bert stole my cookies!!
 I think he used them to bribe Ed into something naughty?

http://www.cutlooseracing.com

 

anything