2 valve vs 4 valve

[bhuff30]

This is just to satisfy my own personal curiosity...

I've always heard that the advantage of more valves is more low speed torque production... meaning a 4v should have a more flat torque curve than a 2v with the same peak power. Something to do with the smaller valves of a 4v engine maintaining higher velocitys at lower speeds than a comparable 2v. Any truth to this in the 4.6 engines? Do the 4 valves generally have flatter, broader power bands?

Next question, which do you think has more usable peak power, the 4v or 2v 4.6? Seems like there aren't any aftermarket cams available for the 4v, but the 2v has LOTS and lots of cams and ported heads. Seems to me like it would be easier to make a wicked 2v combo... just run long tubes, well ported PI heads and a set of lumpy cams. But would this kind of combo be useless below 3500rpm?

Well, give any experience or input you have. Talking about NA only in this thread.

 

[mustang50v8]

im speaking from personal knowledge, and i may not be right...


4v's make more power up top, but i do believe that it is because of increased air flow that the extra valves allow.


there are more cam options available for the 2v'ers simply because there are so many more of them on the road than any 4v ford. if im not mistaken though a ported 2v still doesnt flow as much as a stock 4v but that will probably change when the new trickflow heads come out. however, a port job on a 4v head will put the advantage back onto the 4v heads over the trickflows.


oh and above all, a 4v motor looks so much sexier in the engine bay than the 2v.

 

[NO BRAKES]

+1 for the 4v

 

[CobraRed_96_GT]

Ported 2V's can flow more than 4V's, mine flow more than 3V's same as B head 4V's and more than C head 4V's and easily outshine all on the exhaust side. Doesn't mean they'll make the same ore more power though - volumetric efficiency, and design of chamber that allows mixture and optimal position of the spark plug all allow it to outshine regardless of cfm.

 

[mogs01gt]

This is just to satisfy my own personal curiosity...
I've always heard that the advantage of more valves is more low speed torque production... meaning a 4v should have a more flat torque curve than a 2v with the same peak power. Something to do with the smaller valves of a 4v engine maintaining higher velocitys at lower speeds than a comparable 2v. Any truth to this in the 4.6 engines? Do the 4 valves generally have flatter, broader power bands?

Not at all, their power curves are normally "peaky" while 2v's are more linear

Next question, which do you think has more usable peak power, the 4v or 2v 4.6? Seems like there aren't any aftermarket cams available for the 4v, but the 2v has LOTS and lots of cams and ported heads. Seems to me like it would be easier to make a wicked 2v combo... just run long tubes, well ported PI heads and a set of lumpy cams. But would this kind of combo be useless below 3500rpm?

2v's have a more usable power band and they have more power under the curve. Its only up top in the RPM band where the 4v shines.

With the new Trickflow heads coming out, there is no reason to go with heavier and expensive 4v setup.

 

[04GTMustang]

its not really about number of valves though its airflow thats all. you put a really good 2v head on a 2v that out flows a stock cobra 4v and your going to make more power. but stock for stock the 4v is better cause it does flow better. that is the only advantage to 4v over 2v.

to make power you need air, fuel and spark thats it so increased flow = more power

 

[CatmanJJ]

There are plenty of cams available for the 4v but you are basically paying for 4 cams instead of 2 which makes them more expensive and a less desirable mod to do. I'm doing them in mine along with LTs though since I'm having the motor rebuilt but otherwise I wouldn't go that route.

 

[Stan Weiss]

its not really about number of valves though its airflow thats all. you put a really good 2v head on a 2v that out flows a stock cobra 4v and your going to make more power. but stock for stock the 4v is better cause it does flow better. that is the only advantage to 4v over 2v.

to make power you need air, fuel and spark thats it so increased flow = more power

This is true up to a point. You do not race flow benches just like you do not race dynos. I have seen flow bench numbers and dyno tests where a engine made more power and ran slower are the track. There is a difference between peak and average power produced.
If you can not control the one large valve at the RPM needed to make power from the head's flow than that flow is of no use. It is easier to control 2 smaller lighter valves which have the same or more valve area. Air Flow, velocity (CSA), and port shape are all factors in how much power the engine will make.
What some companies do is use a secondary throttle blade so only one of the 2 intake valves is used at part throttle which improves the velocity through the bowl / valve area.

 

[bhuff30]

It sounds like the 2V, surprisingly, has more area under the curve and a more usable power band. I hope that is still true after adding a lumpy cam.

Personally, I like the look of the 2v. The 4v is just so rediculously huge, much bigger than even a big block.

My 10 year plan is to build a factory five cobra, and I would probably go with a 2v 4.6. The car would be so light and simple and the 2v would just fly. I was thinking ported PI heads on flat top pistons for about 11:1 compression, an aluminum block (maybe the 01+ cobra block since I won't make rediculous power), a very lumpy cam and long tube headers. Clean up the vacuum lines, electrical wiring and ditching most of the accessories and it would be a screamer. I'm sure aftermarket rods would be a must with the rpms she would take. Maybe 400hp at the crank and a weight of 2500lbs. Pure light weight NA V8 simple fun. With an aluminum block, aluminum 2v heads and no accessories, it wouldn't be rediculously heavy.

 

[mogs01gt]

My 10 year plan is to build a factory five cobra, and I would probably go with a 2v 4.6. The car would be so light and simple and the 2v would just fly. I was thinking ported PI heads on flat top pistons for about 11:1 compression, an aluminum block (maybe the 01+ cobra block since I won't make rediculous power), a very lumpy cam and long tube headers. Clean up the vacuum lines, electrical wiring and ditching most of the accessories and it would be a screamer. I'm sure aftermarket rods would be a must with the rpms she would take. Maybe 400hp at the crank and a weight of 2500lbs. Pure light weight NA V8 simple fun. With an aluminum block, aluminum 2v heads and no accessories, it wouldn't be rediculously heavy.

Stop coping me!! I already have it priced out!

though, my engine is ready to go!

 

[CobraRed_96_GT]

its not really about number of valves though its airflow thats all. you put a really good 2v head on a 2v that out flows a stock cobra 4v and your going to make more power. but stock for stock the 4v is better cause it does flow better. that is the only advantage to 4v over 2v.

to make power you need air, fuel and spark thats it so increased flow = more power

More cfm doesn't not mean more power than a 4V head - it just doesn't. You're assuming the greatness of a head stops at the ports - while all the important stuff happens inside. Sure it gets the air there easily, and takes it out the same - but that's just step #1.
Think about why many porting companies have gone back to keeping the low rpms emission ledge on PI heads after porting, taking it off allows for a few more CFM, but according to Mark owner of MMR

it is there to help promote combustion effeciency and we have seen losses from removing it, the reaon the Trick flow heads do not have it is because they have changed the valve location making an artificial swirl in the head.

Powerheads agrees as well.
So if something as little as the ledge makes more cfm but reduces power potential think about a whole new design of a 4V vs a 2V. It's not even close.

 

[bwahl602]

should have bought a 4 valve.... :'(

 

[CatmanJJ]

For sheer badassness of the exhaust sound alone yes.

 

[LaserSVT]

4V>2V /thread

 

[mogs01gt]

4V>2V /thread

negative!
2v>4v

 

[Stan Weiss]

More cfm doesn't not mean more power than a 4V head - it just doesn't. You're assuming the greatness of a head stops at the ports - while all the important stuff happens inside. Sure it gets the air there easily, and takes it out the same - but that's just step #1.
Think about why many porting companies have gone back to keeping the low rpms emission ledge on PI heads after porting, taking it off allows for a few more CFM, but according to Mark owner of MMR

Powerheads agrees as well.
So if something as little as the ledge makes more cfm but reduces power potential think about a whole new design of a 4V vs a 2V. It's not even close.

Maybe someone put it on a wet flow bench and it showed why Ford used it in the first place.

Stop drinking the 4v kool aid

 

[CobraRed_96_GT]

Maybe someone put it on a wet flow bench and it showed why Ford used it in the first place.

Stop drinking the 4v kool aid

So 2V heads that flow the same as 4V make the same or more power and can add just as much timing? That's convenient.

So I can put on a stock 03 blower set-up and make as much as a 03 cobra, cool! Actually more, i have aftermarket cams.

 

[02nightmaregt]

2v rules all

 

[CobraRed_96_GT]

2v rules all

This, however, is teh truth. Most fools wont mess with a cobra - no matter how slow (ish) it might be. Plenty willing to play around with a GT and get served a plate of pwnage.

 

[LaserSVT]

4V>2V /thread