Disappointed magnum head flow numbers....

[Brooks James]

Read that stock magnum heads flow 222 with some touch up
Another place 232
What’s the deal???
I want to know for sure before I buy aftermarket heads!!!!!

 

[toolmanmike]

You may never know. 2 ports on the same head may flow a different number and different flow benches can definitely flow different.

 

[Brooks James]

You may never know. 2 ports on the same head may flow a different number and different flow benches can definitely flow different.

Ballpark numbers will be good

 

[dano]

Flow benches and dynos are tools you use to compare change and they will differ from each other even if the same make and model then add an operator can skew or alter numbers based on setup, which isn't bad, you just need to test the same way every time. So ideally you want to measure a set of heads then port and measure again to see gains.

Are you buying ported heads or buying something bare and doing some home porting?

 

[Brooks James]

Flow benches and dynos are tools you use to compare change and they will differ from each other even if the same make and model then add an operator can skew or alter numbers based on setup, which isn't bad, you just need to test the same way every time. So ideally you want to measure a set of heads then port and measure again to see gains.

Are you buying ported heads or buying something bare and doing some home porting?

Looking at the price of aftermarket heads I’m inclined to get mine ported
But have reservations if the stock ones are ported or do it myself
Especially if the stock heads ported will
Flow as much or more than aftermarket
That’s why it’s so important that I have a ball pArk flow numbers on stockers

 

[dano]

Looking at the price of aftermarket heads I’m inclined to get mine ported
But have reservations if the stock ones are ported or do it myself
Especially if the stock heads ported will
Flow as much or more than aftermarket
That’s why it’s so important that I have a ball flow numbers on stockers

Thanks, I think that will help folks give you a more direct answer.

 

[Cuda416]

There are other advantages to aftermarket heads. Factory heads are prone to cracks between the seats for instance.

 

[Scody21]

And not many people will do full port jobs on iron. You might get some clean up porting but that’s about it. As a lot of guys here have said Speedmaster heads are where it’s at for price point of Alum heads..

 

[33IMP]

Google Stan Weiss cylinder head flow data. He has results from about a thousand flowbench tests for just about any kind of performance engine.
From a cursory look at the LA section, looks like iron magnums look like 225 cfm stock, 250-260 ported.
Now for personal opinion. If you want to play with learning to port (or even if you are not a novice), work on a set of magnums that you know are not cracked. I doubt that i would pay someone else to port used iron heads. I would rather put that money toward a set of aluminum that already flows better than a ported set of iron.

 

[beanhead]

Well one of the best Mopar head porters around has been known to drop in from time to time...
He's even got 'Porter' for a last name!
@PRH

 

[GTX JOHN]

My vote is to go with Aluminum Heads.
Porting the old Iron Heads is expensive and
not an easy Do it Your Self Deal if you do not
have extensive experience!

 

[Cuda416]

Nowadays i think the only reason to do extensive port work on iron heads is "stock" class requirements. I'm talking about the uncommon stuff like 427 hi rise FE heads, "W" heads, "T/A" heads etc. I knew a family when I was a kid who raced nothing but 66/67 fairlane wagons with 427 FE's. They buy anything of that flavor for good money, cracked or not.

You'll never get enough metal our of the way at a "reasonable" cost to make it worth it in my opinion. When you get get a set of TF's for the price they are.... it's almost a no brainer. The cost of an extensive port job adds up really quick as I understand it. Those folks don't work cheap.

 

[Rolling_Thunder]

Google Stan Weiss cylinder head flow data. He has results from about a thousand flowbench tests for just about any kind of performance engine.
From a cursory look at the LA section, looks like iron magnums look like 225 cfm stock, 250-260 ported.

Was going to say the same thing - he has factory truck iron magnums 1.92/1.625 heads at 214/147 @ .600" lift

 

[Brooks James]

Was going to say the same thing - he has factory truck iron magnums 1.92/1.625 heads at 214/147 @ .600" lift

Did I miss something Stan Weiss website only 143 cfm @ .500 lift. !!!!!
On stock magnum heads

 

[dartfever]

My magnum heads were 215-219 stock and 242 @.500" after porting on the intake. Exhaust were surprisingly good at 163 stock and 180 after porting. All at 28". I will the casting quality between the 2 heads were very different ends of the spectrum! One was a nice smooth finish, the other was very rough. Both gave the same #'s in the end though.

 

[Krooser]

Thank God we didnt know iron heads were junk when I was younger....

 

[rumblefish360]

The Stan Weiss site has less than reputable porters posting there results that he just slams in the list.

 

[33IMP]

The Stan Weiss site has less than reputable porters posting there results that he just slams in the list.

Kinda agree. Numbers are just numbers if you dont know the reputation of the porter, and the validity of his bench. Kinda just like chassis dynos. Unscrupulous operators can post any numbers they want, and big numbers usually mean good business.

 

[Brooks James]

So the question I was leading up to was: how much at 225 cfm how much hp will the they allow to be made until the are kaput. 9:1cr @550 lift
stock cc

 

[33IMP]

The general rule i have seen, is two hp per cfm is possible. I think that kinda depends on how much motor is under the heads. I doubt a 273 under 225 cfm heads will run as well as a 408.
Forced induction throws that (very!) general rule way out the window.

 

[512Stroker]

So the question I was leading up to was: how much at 225 cfm how much hp will the they allow to be made until the are kaput. 9:1cr @550 lift
stock cc

We need to see a head flow chart at cam lift points, not just the max flow.
Cam choice will be very important.
Dont expect much with that low compression ratio?

 

[Brooks James]

The general rule i have seen, is two hp per cfm is possible. I think that kinda depends on how much motor is under the heads. I doubt a 273 under 225 cfm heads will run as well as a 408.
Forced induction throws that (very!) general rule way out the window.

Ok let’s throw in a150 shot of nitrous. The cam was ground by a guy who worked for crane and went on his his own. It was ground for a nitrous engine. I lost the card.
All I remember was intake 498/274 exh 512/286 lsa i113.5 hydraulic roller. I asked for extra on the exhaust as I’m running 340 manifolds

 

[Bewy]

Yup, normally aspirated, max hp can be about double the intake port cfm flow @ 28".
A rough guide.
Buuuuuuuuuut, that assumes that the rest of the combo is mutually supporting to support that amount of power.

 

[rumblefish360]

Very true. Rough, but a accurate estimate of what can be done without going nuts. I see the 2hp per cfm math as what a really good street machine or bracket racer can produce themselves without going crazy on an engine.
It is not the ceiling.

Now the CID X 2 for HP is another story, but yet again, not the ceiling. Also, of course, what the head is capable of on the engine and its size is a constant variable to what can be done easy or with pushing it.

A 360 cubic inch engine at;
CID X’s 2 = 720 hp.

Cylinder head flow at;

220 x 2 = 440 hp
280 x 2 = 560 hp
300 x 2 = 600 hp
Etc....

While the cylinder head numbers suggest a possible certain amount of power possible, it would be easier to make the possible power on a larger engine rather than a smaller engine.

 

[66fs]

The general rule i have seen, is two hp per cfm is possible. I think that kinda depends on how much motor is under the heads. I doubt a 273 under 225 cfm heads will run as well as a 408.
Forced induction throws that (very!) general rule way out the window.

The general rule applies whether 273 or 408. However the other general rule also applies pertaining to rpm. Will your valve train and short block handle the required higher rpm to make that power? And both are very simplified generalizations.