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Discussion Starter #1
I had some heads done by a reputable port guy and he started with my 323 at .600 and now they are nearly 50 cfm more. Is there a formula to tell how much more HP potential I have?
I know taking it to the dyno or track will tell me that but I just ordered rods and was just wondering how much more over the 825 I already made before it broke will I get...... I have been told so many things so far I cant figure out who to believe. Ive heard like only 50 HP to 150hp I tend to think the 50 is right but then today I heard 2 hp for every cfm.. anyone want to chime in?
 

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Could make less if they weren't done right. To quote Darin "a good head flows a lot of CFM, the bad news is a bad head can also flow a lot of CFM"
 

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I had some heads done by a reputable port guy and he started with my 323 at .600 and now they are nearly 50 cfm more. Is there a formula to tell how much more HP potential I have?
I know taking it to the dyno or track will tell me that but I just ordered rods and was just wondering how much more over the 825 I already made before it broke will I get...... I have been told so many things so far I cant figure out who to believe. Ive heard like only 50 HP to 150hp I tend to think the 50 is right but then today I heard 2 hp for every cfm.. anyone want to chime in?
was [email protected] peak flow or did they keep going after that?

might be worth listing you old flow numbers and your new numbers.
 

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To actually answer your question...yes there is a ballpark calculation...but it's only a potential of possible power gains. cfm x 2.4=h.p. potential max , or cfm x .257-.320 x 8 cyl. (higher end stuff will see the larger side of that range .257-.320)

See while others have stated that a bad port can still flow a lot of cfm...they're right... BUT...
if you size a port based on demands for airflow of the displacement underneath it and you keep making it bigger within those
design parameters and it keeps gaining cfm...it's a win-win...always! It will never become too large or lazy. Its when you grind continuously and don't gain that it's a problem!!!
Hopefully your porting guy is sharp...that's a big gain. Good luck!! Johnny
 

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Well, he did ask for a "potential" gain. Not what it would actually do. Potentially 100+HP. But its dependent on many things. How much did the low lift numbers improve? Were you maxing out the cylinder head to begin with? Can the intake flow near what the heads are capable of? Are you changing cam to take advantage of the cylinder head work?
 

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To actually answer your question...yes there is a ballpark calculation...but it's only a potential of possible power gains. cfm x 2.4=h.p. potential max , or cfm x .257-.320 x 8 cyl. (higher end stuff will see the larger side of that range .257-.320)

See while others have stated that a bad port can still flow a lot of cfm...they're right... BUT...
if you size a port based on demands for airflow of the displacement underneath it and you keep making it bigger within those
design parameters and it keeps gaining cfm...it's a win-win...always! It will never become too large or lazy. Its when you grind continuously and don't gain that it's a problem!!!
Hopefully your porting guy is sharp...that's a big gain. Good luck!! Johnny
So true and so many people miss this, .. can't just go by a port volume for
X size engine.

Very true, a great flowing head can make crappy power, .. ...
had a deal recently where one of my heads made 30+ hp more then a set of heads flowing 50 cfm more!
Geometry, port shape, valve locations, chamber, mixture motion, ..
ALL are critical and often MORE then JUST the cfm number.

I'd think you COULD make another 1.8 to 2 hp per cfm IF the rest
of the combo was held back strictly by head flow.

Curtis
 

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Discussion Starter #9
Ok I have the actual numbers in front of me

before at .500 was 322 cfm now its 336

before at .600 was 324 now its 361

before at .650 it was 323 now its 363

So I have a 40 cfm gain officially in the intake side
 

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Discussion Starter #10
This engine is a 535 ci that was dyno'd at 826 HP and 801 torque.
 

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To actually answer your question...yes there is a ballpark calculation...but it's only a potential of possible power gains. cfm x 2.4=h.p. potential max , or cfm x .257-.320 x 8 cyl. (higher end stuff will see the larger side of that range .257-.320)

See while others have stated that a bad port can still flow a lot of cfm...they're right... BUT...
if you size a port based on demands for airflow of the displacement underneath it and you keep making it bigger within those
design parameters and it keeps gaining cfm...it's a win-win...always! It will never become too large or lazy. Its when you grind continuously and don't gain that it's a problem!!!
Hopefully your porting guy is sharp...that's a big gain. Good luck!! Johnny
Johnny knows what hes talking about. Trust me!
 

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Ok I have the actual numbers in front of me

before at .500 was 322 cfm now its 336

before at .600 was 324 now its 361

before at .650 it was 323 now its 363

So I have a 40 cfm gain officially in the intake side

What is your max intake lift @ the valve?


This engine is a 535 ci that was dyno'd at 826 HP and 801 torque.
► 826 / 324 = 2.54938 HP per CFM

Stan
 

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Discussion Starter #13
It's a roller cam .62x lift
 

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This engine is a 535 ci that was dyno'd at 826 HP and 801 torque.
Judging by the tq and cubes I'd guess it's a compression motor and peaks pretty low (56-5800ish)?? If the new port work can move the curve up ~500rpm it could be a nice gain (80+) assuming the intake is up to snuff. :cool:
 

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A simple WAG - based on if the motor can use the increase in CFM

► (826 / ((324 + 322) / 2)) * ((361 + 336) / 2) = 891.2 HP

Stan
 

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Discussion Starter #17
Judging by the tq and cubes I'd guess it's a compression motor and peaks pretty low (56-5800ish)?? If the new port work can move the curve up ~500rpm it could be a nice gain (80+) assuming the intake is up to snuff. :cool:

4600 torque and 6200 was HP rpm
 

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Discussion Starter #18
Is this engine NA, because I am having a hard time with 826 hp out of 323 cfm and .62x lift.
It is a NA engine yes. Gary Stinnett Dyno'd it a few years back when it was fresh.
 

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Discussion Starter #19
OK I just found the build sheet on the cam spec for those who are interested

Gross Intake .638 duration at 50 254
Gross Exhaust .637 duration at 50 253
centerline is 107

Not sure what all you want to see
 

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OK I just found the build sheet on the cam spec for those who are interested

Gross Intake .638 duration at 50 254
Gross Exhaust .637 duration at 50 253
centerline is 107

Not sure what all you want to see
Well I can answer for myself. There is no use in looking at .650" lift flow numbers if the cam does not open the valve that much. I interpolated to .550" lift for my calculations.

Stan
 
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