Cylinder Heads

Hello Shah; Since you are wanting to keep your top rpm range relatively low "5,000", the Aussie 2V head is your friend, as it primarily is a case of port velocity.

The Aussie 2Vs will give you better low end throttle response & torque due to superior low RPM port velocity.

Think of it this way....you have 2 garden hoses both 50ft long. 1 garden hose is 1/4 inch ID ( inside diameter) the other garden hose is 1/2 inch ID.

You turn on the water in both hoses at the same time with the same water pressure supplying both hoses.

The 1/4 inch hose will fill faster & have more velocity coming out the end of the hose vs the 1/2 inch hose.

Now think of the water being a gasoline/air mixture following through small Aussie 2V head ports vs following through the LARGE Cleveland 4V ports...Mark

the 2V heads will never do what the 4V's are capable of at 2500 rpm much less 5000, the beauty of the 4V cylinder head is that it IS capable of doing what the 2V head does and then some

is the goal to detune the DeTomaso to compete with a Datsun for MPG, or do you want to keep that ~ 100hp ?

quote:

Originally posted by 4V & Proud:
the 2V heads will never do what the 4V's are capable of at 2500 rpm much less 5000, the beauty of the 4V cylinder head is that it IS capable of doing what the 2V head does and then some

is the goal to detune the DeTomaso to compete with a Datsun for MPG, or do you want to keep that ~ 100hp ?

Your statement I find interesting.

If there were 2 exactly identical Cleveland engines, the only difference being 1 had 4V closed chambered heads & the other engine had Aussie 2V heads, I wonder what engine would propel a DeTomaso Pantera faster in a 0-60 MPH standing start race?!

I would place $$$ on the Aussie 2V headed engine!...Mark

You can use the Mind Train headers on either cylinder head because the exhaust manifold flanges of the Australian 2V head are large enough to provide a seal around the larger 4V headers. So that's not an issue. If your Pantera is equipped with an engine having dished pistons (1973 - 1974 Q code) installing a set of Australian 302C heads is a slick way to achieve 10:1 compression without having to replace pistons. That is an important consideration.

The intake ports of both heads are tuned more or less to fall within the power range you've described (2500 to 5000 rpm). The 2V heads are tuned for 1000 to 5000 rpm. The 4V heads are tuned for 2000 to 6000 rpm. The power range you've described is therefor in the top end of the 2V head's power band, and in the bottom portion of the 4V heads power band.

Power potential is one of the two differences between the heads. The 2V heads cannot take advantage of camshafts which lift the valves more than 0.500". Un-ported the 2V heads flow 195 cfm at 0.500" lift, and that's as much as they flow, period. Un-ported 4V heads flow 245 cfm at 0.500" lift, but air flow continues to increase as the valve opens further, 275 cfm at 0.600" lift.

Power characteristic is the other difference between the two heads. The Cleveland 4V cylinder head design was chosen by Ford because of its suitability for endurance racing, it provides an unprecedented wide and flat torque curve and a power band characterized by a strong mid-range rush. Power at lower rpm with the 4V cylinder head is peppy, smooth and linear. As long as it is not "over-cammed" the low rpm power and throttle response of a 4V motor is every bit as strong as the low rpm power of a 2V motor. A 4V motor can "light-up" the rear tires at low rpm with little effort. A 4V motor builds "steam" with engine speed and then hits a strong mid-range rush which is like the afterburners of a jet engine kicking-in! From that point on a 4V motor pulls harder and harder as the engine speed climbs (as long as the carburetor is big enough). This is an ideal power characteristic for a high performance street car, a sports car, or a GT car. Over the decades I've read reports praising the engines in high end sports & GT cars such as Ferrari, Lamborghini, Mercedes and Aston Martin for having similar power characteristics.

Some street performance and sports car enthusiasts prefer the low rpm biased power characteristic of the smaller cross-section 2V ports. The mid-range rush of an engine employing 2V cylinder heads is not as pronounced as an engine with 4V heads therefore the power characteristic of a 2V motor seems somewhat more sedate. Those who prefer the power characteristic of a motor with 2V heads feel it is more "refined" while the 4V motor is "brutish". A motor with 2V heads also lacks the endless high rpm pull of a motor with 4V heads. The 2V cylinder heads are better choices for low rpm torque applications such as towing and hauling vehicles, off-road and rock crawling vehicles and heavy vehicles in general. But I might argue such power delivery is "too typically American V8" and not as desirable for a sports car like the Pantera.

A 2V engine with its smaller valves and lower rpm tuning is a little more forgiving than a 4V engine. The 4V engine is a high performance engine, it is equipped with racing cylinder heads. The important thing with the 4V engine is to avoid "over-camming" it, set the static compression at 10:1, and make sure the carburetor and ignition are tuned well. Failure to do these things lead to unhappiness with the 4V engine.

I could live with an engine equipped with either cylinder head. As I get older I question sometimes whether or not I'd be happier with the somewhat more sedate 2V power characteristic. But then again I think I'd miss the way the 4V motor accelerates. I do not have a desire or need for a motor producing more horsepower than what can be achieved with the 2V cylinder heads, but I prefer the power characteristic of a motor equipped with 4V cylinder heads ... I've lived with it most of my life. The Pantera is an ideal vehicle for an engine with such a power characteristic, I find far easier to use the power "safely" in the Pantera than I ever did in my Mustangs.

quote:

Originally posted by PANTERASHAH:
For a strictly street driven car with the motor operating between 2500-5000 rpms which is a better choice, 4V closed chamber heads or Aussie 2V closed chamber heads?

I have both 2V closed chamber and 4V closed chamber on almost identical 351c engines and i can tell you without a doubt that the 4V with the correct intake manifold and carb or injection setup will out perform the 2V, all other things being equal, in every way from 1000rpm up.

You would choose the 2V over the 4V if you were perhaps seeking to squeeze some extra MPG out of your car and your car was heavy. But there are not many MPGs in it.

The 2V of course has smaller ports and valves and also higher compression ratio so with a very heavy car the 2V may give you some extra throttle response at very slow RPM such as in city traffic and slowly plodding around the suburbs.

Although once the RPMs get up and with a lighter car like the Pantera the 4V heads as i say with the right intake setup should not have any appreciable throttle response difference to the 2V in a heavy car.



2V heads vs 4v heads tend to give the engine a different feel (character).

The 2V will give more of a linear feel to the engine eg: twice the RPM feels like it is twice as powerfull.

The 4v wll give more of a logarithmic feel to the engine eg: twice the RPM feels like it is four times as
powerful.

The choice depends on how brutal you want the car to be and how hard you drive it.

Thanks for all replies. It seems that 4v heads are better suited for high performance applications. Performance wise are 4V closed chambered heads much better than 4V open chambered heads with all other things being equal?

Agreed 1000% with what those two guys said.

The 4v has plenty of power off of idle to spin the tires all the way into third gear "off the line"...THEN it hits it's rpm "sweet spot" and absolutely explodes with another 200 ft-lbs of torque. Almost as though it is a dual over head cammed engine, and the secondaries just opened?

The 2v heads are much like small block Chevy heads are. Very linear and predictable up to their peak...which is right in the 5,000 rpm area.

DEPENDING on what camshaft you have in a 4v, the "sweetspot" is in the 3,500 to 4,200 rpm range. At that point is has similar characteristics to a big block.

The "autocross" guys absolutely LOVE the 2v primarily because the courses are so tight and they never get much over 40 mph or out of second gear.

I "attempted" to autocross with a "Boss 351 engine replica with 4v iron heads" and simply couldn't drive the car as a stick.

The only way I could even contemplate being able to handle the car would be with a version of the current "PK" type paddle shifted transmission like in the current Porsche?

Go with the 4v iron heads. They are good heads but you need a measured static compression ratio with them of about 10.5:1.

Over that you WILL run into detonation unfortunately with premium pump gas and under about 9.5:1, the engine looses it's crispness.