Author Topic: Head CFM vs. HP per c.i.?  (Read 4885 times)

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Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #25 on: December 31, 2017, 05:23:01 AM »
Most of the posts mention the importance of velocity, How much velocity do we need?
What is the proper way to calculate intake air velocity?
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Offline pwmorris

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Re: Head CFM vs. HP per c.i.?
« Reply #26 on: December 31, 2017, 07:21:41 AM »
Jessel rocker/S&S pro stock top ends and SA cases aren't really standard fare around here.
Apples and oranges. But I get the point.

Just thinking out loud...
No, apples and apples. My 91 octane, pump gas, no PMS, daily driven street bike motor was the example I mentioned, and yeah, it is ALL S&S (except for CP Pistons).
Principles still apply though-street, strip, dirt, or on the lake or in the snow.

Offline Matt C

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Re: Head CFM vs. HP per c.i.?
« Reply #27 on: December 31, 2017, 08:16:50 AM »
Jessel rocker/S&S pro stock top ends and SA cases aren't really standard fare around here.
Apples and oranges. But I get the point.

Just thinking out loud...
No, apples and apples. My 91 octane, pump gas, no PMS, daily driven street bike motor was the example I mentioned, and yeah, it is ALL S&S (except for CP Pistons).
Principles still apply though-street, strip, dirt, or on the lake or in the snow.

Yep. The same principles apply whether its a Briggs&Stratton or a Top-Fuel dragster. Its not rocket
science.

Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #28 on: December 31, 2017, 08:26:45 AM »
"Never hang on to a mistake just because you spent time or money making it."

Offline build it

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Re: Head CFM vs. HP per c.i.?
« Reply #29 on: December 31, 2017, 09:20:09 AM »
Interesting conversation.
My youngest son, 17, has an interest in being a Mechanic and the other day he stated something about Air Flow being important, got me to thinking he's actually read/studied some on the subject. He's not the best at the righty tighty lefty loosey stuff but he's pretty good on Math etc and I've thought he'd be better off more on a design/Engineering path  . . . anyhow I've sent him an email directing him to this thread and bought the book referenced on the matter, and another on Engine Formulas.

If your son is serious about making power he should read fluid dynamics textbooks and practice with a grinder, I’d recommend air. These forum discussions, specifically on air flow have little to no value. The correlation between static flow at 1psi and performance is tenuous at best, and will lead him down the wrong path at worst.  A lot of cylinder head shops produce results in spite of what they think they know.

Make sure he knows how to measure and take molds. If he goes down this path, not recommended, his ability to measure and track performance will be the sole indicator of success.

The best tools he can have access to are a dyno, burette, indicator, mold making materials, and an ass load of burrs and cartridge rolls. The dyno can wait for now, but track everything typically mentioned in a dyno sheet and CSA. Comparing sheets from one hand port shop to another is a waste of time.

I’d also suggest visiting the local university that has an ME program and ask them what textbooks they use.
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Offline Matt C

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Re: Head CFM vs. HP per c.i.?
« Reply #30 on: December 31, 2017, 10:04:31 AM »
 :agree:
Making molds and sectioning them is a great way to see the shape and measure the various sections (number them).

You'll need access to a seat and guide machine as well. You can't do airflow research without being able to cut seats
and try different shapes. (a flowbench helps too).

PS: An engineering program/degree will open up all kinds of doors. Even if it's not directly related to this specific subject,
the job opportunities will be far greater in the long run.
« Last Edit: December 31, 2017, 10:13:39 AM by Matt C »

Offline build it

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Re: Head CFM vs. HP per c.i.?
« Reply #31 on: December 31, 2017, 11:09:54 AM »
:agree:
Making molds and sectioning them is a great way to see the shape and measure the various sections (number them).

You'll need access to a seat and guide machine as well. You can't do airflow research without being able to cut seats
and try different shapes. (a flowbench helps too).

PS: An engineering program/degree will open up all kinds of doors. Even if it's not directly related to this specific subject,
the job opportunities will be far greater in the long run.

He can farm s&g out for now. Right now he needs grinder and measuring time, nothing else. If the kid is disciplined and has a good work ethic he’ll go far.
Not everything’s a nail.

Offline Matt C

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Re: Head CFM vs. HP per c.i.?
« Reply #32 on: December 31, 2017, 11:28:34 AM »
Good point (I take that part for granted). You have to walk before you run...

Since he's good in math, I'd try to steer him into an engineering program. But that's
just the old man in me talking. That was the best thing I ever did for myself (next to
marrying my high school sweetie).

Actually, my parents talked me into school. But man, it paid off big.
« Last Edit: December 31, 2017, 11:35:01 AM by Matt C »

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #33 on: December 31, 2017, 12:51:25 PM »
The BIG Picture-
Textbook answers are ok .
But the devil is always in the details.
I have worked very hard at discovering more then what is says on say page 93.
The guy that has applied all of that and 1000 other pages in details will win.
I am not sure what he will win, It is just personal satisfaction for me.
Everything (all most) that will make your engine perform better will never make it last longer.
The novice wants a hi-performance guaranteed to go hundred thousand mile engine.
That is upside down and not going to happen.
Narrow seats, steeper angles, shorter narrowed guides, will outperform the textbook answers.
I have arrived at the 20K mark .
By this I mean I will sell out miles for performance if it will make it 20K mark.
That is about two years for me and just long enough to make me forget all the frustrations last time.
So, guys and gals pick your poisons.

D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.

Offline FXDBI

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Re: Head CFM vs. HP per c.i.?
« Reply #34 on: December 31, 2017, 01:09:58 PM »
The BIG Picture-
Textbook answers are ok .
But the devil is always in the details.
I have worked very hard at discovering more then what is says on say page 93.
The guy that has applied all of that and 1000 other pages in details will win.
I am not sure what he will win, It is just personal satisfaction for me.
Everything (all most) that will make your engine perform better will never make it last longer.
The novice wants a hi-performance guaranteed to go hundred thousand mile engine.
That is upside down and not going to happen.
Narrow seats, steeper angles, shorter narrowed guides, will outperform the textbook answers.
I have arrived at the 20K mark .
By this I mean I will sell out miles for performance if it will make it 20K mark.
That is about two years for me and just long enough to make me forget all the frustrations last time.
So, guys and gals pick your poisons.

Well I disagree to a point, a well built high performance engine should make 50k+. Brother did up a 103 HQ kit years back. 117 tq  111 hp . Engine has 60k on it now and still running strong compression still 210 a cylinder.  Good parts, good recipe good tune and attention to details will get you there. 20k is just enough time to show all the short comings of your endeavors and if it needs a rebuild by then something wasn't done right.  Bob

Offline Ohio HD

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Re: Head CFM vs. HP per c.i.?
« Reply #35 on: December 31, 2017, 01:13:18 PM »
The BIG Picture-
Textbook answers are ok .
But the devil is always in the details.
I have worked very hard at discovering more then what is says on say page 93.
The guy that has applied all of that and 1000 other pages in details will win.
I am not sure what he will win, It is just personal satisfaction for me.
Everything (all most) that will make your engine perform better will never make it last longer.
The novice wants a hi-performance guaranteed to go hundred thousand mile engine.
That is upside down and not going to happen.
Narrow seats, steeper angles, shorter narrowed guides, will outperform the textbook answers.
I have arrived at the 20K mark .
By this I mean I will sell out miles for performance if it will make it 20K mark.
That is about two years for me and just long enough to make me forget all the frustrations last time.
So, guys and gals pick your poisons.

Well I disagree to a point, a well built high performance engine should make 50k+. Brother did up a 103 HQ kit years back. 117 tq  111 hp . Engine has 60k on it now and still running strong compression still 210 a cylinder.  Good parts, good recipe good tune and attention to details will get you there. 20k is just enough time to show all the short comings of your endeavors and if it needs a rebuild by then something wasn't done right.  Bob

Agree Bob, I pulled the 117 out of my bike with over 40k, hard miles. Still was running like a top. Only removed to make way for the 124 I built.
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Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #36 on: December 31, 2017, 01:15:58 PM »
The 20K is an arbitrary number.
Pick one that works for you, and transparently you did.
The bigger point is performance numbers are not linear in longevity.
Sort of like- how long will a dragster engine last compared to your go to town car.
I always get a tickle when the dude says I want this, this,  and that and how long will it all last..............
It is a slippery slope.
D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.

Offline Barrett

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Re: Head CFM vs. HP per c.i.?
« Reply #37 on: December 31, 2017, 01:22:02 PM »
I expect my built S&S engine to last longer than what I had..
Mine isn't on the extreme edge but it will get it done. I hope..
Don't know how much my heads flow but they look good...

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #38 on: December 31, 2017, 01:34:10 PM »
S&S is not really a HIPO engine.
It is a better engine.
Again John Q Know nothing Public,  would be pissed as hell if he bought a real performance engine
 and it needed a top end every two years.
There is no way a very narrow seat way to the top of the valve going to go 50K.
I think that example is agreeable?
D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.

Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #39 on: December 31, 2017, 01:34:19 PM »


This thread sure took a turn. How many bike shows should you be able to do before you need to rebuild a performance street engine?
"Never hang on to a mistake just because you spent time or money making it."

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #40 on: December 31, 2017, 01:36:05 PM »
I am not sure as I have never done a show......LOL
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Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #41 on: December 31, 2017, 01:37:07 PM »
How wide is a very narrow seat and what is your spring pressure and cam?
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Offline build it

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Re: Head CFM vs. HP per c.i.?
« Reply #42 on: December 31, 2017, 01:39:04 PM »
I think a performance oriented HD can make more power and last longer than 20k. 50° seats and Ti valves are standard in OE environments, they aren’t bleeding edge by any means.

No one is saying the textbook can replace experience. Experience and rigorous study will get you there though, as far as the specific individual can go.

Forums are good for experience based knowledge, IME.
Not everything’s a nail.

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #43 on: December 31, 2017, 01:45:33 PM »
I will run right out and measure it for ya...
LOL
Actually Just took it apart and I can give you just a couple number cause I can't remember everything.
I believe the seats are 2/32  way at the top.
Cam is DM 530 with his spring set.
  I measure it about 2.5 years ago..  Brain farts
I am now going to a 50 deg seat angle with perhaps a 3/32 seat..I will not know until a few other items are solved here.
(I need the rockers back from Basily )
Like i said
Don't do what I do if you want a 5oK (mile ) engine.
D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.

Offline FXDBI

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Re: Head CFM vs. HP per c.i.?
« Reply #44 on: December 31, 2017, 01:55:28 PM »
I will run right out and measure it for ya...
LOL
Actually Just took it apart and I can give you just a couple number cause I can't remember everything.
I believe the seats are 2/32  way at the top.
Cam is DM 530 with his spring set.
  I measure it about 2.5 years ago..  Brain farts
I am now going to a 50 deg seat angle with perhaps a 3/32 seat..I will not know until a few other items are solved here.
(I need the rockers back from Basily )
Like i said
Don't do what I do if you want a 5oK (mile ) engine.

Well your doing something wrong if it cant make 50k. Tell us more so we don't make the same mistakes....Bob

Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #45 on: December 31, 2017, 01:59:16 PM »
I will run right out and measure it for ya...
LOL
Actually Just took it apart and I can give you just a couple number cause I can't remember everything.
I believe the seats are 2/32  way at the top.
Cam is DM 530 with his spring set.
  I measure it about 2.5 years ago..  Brain farts
I am now going to a 50 deg seat angle with perhaps a 3/32 seat..I will not know until a few other items are solved here.
(I need the rockers back from Basily )
Like i said
Don't do what I do if you want a 5oK (mile ) engine.

So how many horse do you honestly feel all this will yield at the rear wheel?
Sounds like a lot of work to give up longevity and gain little.  :scratch:
"Never hang on to a mistake just because you spent time or money making it."

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #46 on: December 31, 2017, 02:06:41 PM »
Like I said, I do this for my own satisfaction.
I have no clue what TQ/Hp is as there is no dyno available here.
I could travel a 100 miles...I guess I am not that interested.
Next-milage
I have no clue how long the TBO would actually be, But my goal is always at least 20K miles.

Everyone says a Harley cannot beat a Honda F6
I own one and this POS Road king makes it look like it is going backward.
Ths F6 is so wimpy in comparison i seriously considering selling it.'Quite disappointing really.
« Last Edit: December 31, 2017, 02:11:04 PM by thumper 823 »
D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.

Offline 1FSTRK

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Re: Head CFM vs. HP per c.i.?
« Reply #47 on: December 31, 2017, 02:22:33 PM »
How would you know if something you try makes an improvement?
"Never hang on to a mistake just because you spent time or money making it."

Offline pwmorris

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Re: Head CFM vs. HP per c.i.?
« Reply #48 on: December 31, 2017, 02:30:39 PM »
I think it's great Thumper that you are out there, testing, testing, testing and more testing stuff. Fail, succeed, fail, succeed-No Dyno, no problem. Sure it would be a lot easier to evaluate changes but, shit, Just take it out on the open road or a track and rip it-you will learn what works, and what doesn't. BTW, there was an AHDRA pro stock champ who never put his bike on the Dyno during his championship year run...
You are actually exploring the possibilities and potential of your motor, not playing keyboard commando and never doing anything.
Depends on many factors how long they last, but my current street bike motor lasted about 30k hard core miles till it needed a rebuild....must have been all the "shows" the bike was in that wore it out- :hyst:

Offline thumper 823

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Re: Head CFM vs. HP per c.i.?
« Reply #49 on: December 31, 2017, 02:35:46 PM »
I a not here to Bragg.
THE BIKE  goes like hell.
I will dyno it this summer after back together as I have done enough changes to warrant the cost.
Speaking of my 20K mark.......
i installed a 12 lb ring pack thinking this might be my biggest mistake .
Truly I was on the fence about it .
I have been to Sturgis twice with it same rings and about 2oK all told.
It uses a QT in about 2500 miles .
Now some people would say that is HORRIBLE!
I say that is freeking    TERRIFIC!
This engine sees at least 15 lbs less friction then most.
D Troop 3/5, - C/16 ,162AHC, Mekong delta.
Amateur engineering with bad math.