Valve size. When is enough, enough?

[dave571]

I've noticed looking at other BB heads (like 454gm, or 429 ford, 351 clevland 4bbl ford) That these engines have very big valves. Biggerthan BB mopars.

Yet...they don't make more power.

Why?(all things being equal..)

Is it worth the work/money to install bigger valves in a factory iron head, when the smaller ones seem to work?

Are the bigger valves in aftermarket heads just selling features that don't improve performance?

[Don]

But they aren't equal...the head ports are different as are the combustion chamber designs.

I started to say something real smart ass but decided I better not......

[dave571]

I'm assuming an application that varies from a 13 second car down to an 11 second machine.

So are you saying that because of superior head design, an iron mopar head does not require bigger valves to perform as well as a brand X head?

I guess why I'm asking, is a lot of sources suggest that bigger valves is the first step to building a race motor(sources like mp catalog buildups...I didn't say reliable sources)

In modern crate motors(all makes), the valve size seems to be more under control. I read an article about a 1000 hp boat motor. BBC based. It was nearly 600 cid, and the exhaust valve was a mere 1.80"

So does a 440 really need a valve bigger than 1.74"? Keep in mind I'm not flaming those who have done it, I'm simply trying to debate the issue intelligently

[Chryco Psycho]

long rod engines respond differently to valve size & small high velocity ports can flow more air especially if they are designed to swirl as the big block Mopar heads are even with smaller valve size

[Don]

Hey Chyco.....Good to see you here....

Gentlemen the tech knowledge on this board just doubled

Thanks for joining us

Hows my Buddy John the NY Dentist these days....LOL

[Chryco Psycho]

Hey Don
Thanks for the invite to this board , it looks great!
John is well , he had a setback with a bad roof & some frozen pipes to fix with the cold weather , but as soon as his cash flow recovers it looks like he will build an engine for the Cuda

[Don]

He's quite the character....I enjoyed our Chats...he would advise me on my dental care and I would try and help him out with his Mopar.

You should invite him over here if you have his email.

Don

[Chryco Psycho]

I have his email & will shoot him a link

[Coil]

Are you serious about your engine? How serious? Serious enough to have the heads flow tested? With proper flow of the intake runner in head "A" with smaller valves.....there is the potential to make WAY more power that with poor flowing head "B" with HUGE valves. The key.........is.........volumetric effiency (i know, its spelled wrong). The more volumetric efficent your engine runs, the greater the output.
Example: When washing the underside of your early model Power Wagon that has 3" of mud. The first hose you use has no nossel, just the open hole at the end. Spray the mud......not much happens. Now, put a nozzel on it and direct the stream....what happens? Removal of mud. Did you spray more water? No, the hose still flows the same ammount but its how you are using it and how it flows that made the difference.

[Don]

Ya...what he said....if Coil says it, it's right....I taught him everything he knows....LOL ;D ;D

[motorhead446]

it makes alot more sense when explained that way. Thank you coil

[Don]

"Bidding on a set of big block mopar 452 heads,heads have had a competition valve job done and have been fully ported and polished,they do have the stock valves 2.08 and 1.74,I bought these heads from a buddy who works at a Maryland machine shop for $750 a year ago,I never got to use these heads on the car (the porting work looks real good thu)I never went ahead with my project.There are no flow numbers with these heads ,but I was told from the guy I bought them from he said that they flowed around 270 cfm at .600 lift"

So my questions are:

Competition valve job...lay a straight edge over the valve tips ...are they with .005 from highest to lowest?
Stock valves....do you mean they still have the 3/8 valve stems?

Looks real good?...OK Superman, I won't argue with a super hero who has x-ray vision.

It looks to me like they did alot of work to the floor.....not a good sign, you want to work over the roof and the short turns, cut the bowl behind the valve and then blend the roof to it. By cutting away the floor your sharpening the short turn making it worse. The floor should only be deburred. How about the term "Raised Runner"....that's why they raise the runner, to reduce the short turn and that's really what portings all about.

I tell all my customers that 75% of their gain in porting is going to happen in the first 3-4 hours, after that you've got a 100 hours to gain a few more % points and your risking the integrity of the head.

Ported heads must be matched to the engine, as you increase the port you reduce the velocity over the valve, you need to add compresion, cam duration and operating RPM as you go bigger and bigger. Ported heads reduce low end tork, driveability and street manners.

We always recommend a bowl hog, blend, minor gasket match, 11/32 stems and a good set of components, SS valves, Titanium retainers, 10* locks. Just basic good stuff, too much requires too much RPM to take advantage of the $$$ spent.