Hey guys, just wanting to know what the difference is between the 2V and the 4V heads, and which one would be better for performance?
And also what do you think is better: Open or closed chambers?
2 and 4 V heads are both good depends what the intended use is the best phrase i ever saw about clevo heads said 4V heads are great if you are pushing 7 grand down conrod, but for street they are overkill - that actually came out of street machine
a good thing bout 2 V heads is you can port em between mild to wild a mate had a decent 351 that only had 2 V heads he took em off and gave em a 'dags off' port and they went a damn site better than before.
after that he got bored and whipped em off and had em dome at c.o.m.e. in melbourne and whoa!!! what a farking difference great all round performance great low end throttle response (much better than 4V headded cars ive driven) and they reved out to 6 grand ok he has taken em to 7 but 6 or 6,5 is a nice rpm to go to
There are open chamber and closed chamber versions of both types of heads to just to add to the confusion. Generally open chamber is the go (unless you have special dished pistons) otherwise you will have too much compression to run properly on normal petrol. The closed chamber 2V heads came out on the 302 Clevos while the open chambers came out on the 351 Clevos.
4V heads can be identified on the car by a raised "4" cast into one corner of each head. Off the car it is even easier by looking at the massive ports and valves.
You know, somebody actually complimented me on my driving today. They left a little note on the windscreen. It said, 'Parking Fine.'So that was nice.
I don't think anyone has yet answered your original question re the differences between the 2V & 4V heads - The major difference is that the ports in the 4V heads are much bigger than those in the 2V heads & as a result have slower air flow (but higher volume) through the ports, resulting in poor low RPM torque, but great mid to high RPM power with the right combination of cam, intake (carby & manifold) & exhaust. The 2V & 4V designation comes from the original intended use of the heads - the 2V heads were originally intended for use with a 2 venturi (or 2 barrel) carby & the 4V for a 4 barrel carb. This doesn't mean that this was the case in production & doesn't restrict you to using either carb. In fact, for a street engine you are probably much better off (as suggested in another reply) using 2V heads with a port job, concentrating on the Exhaust ports, as it is widely recognised that the Clevo heads have a great intake port design, but a relatively poor exhaust port design, which ultimately restricts the power the engine can make as what comes in must also go out! With regard to the open & closed chamber question, the major difference here is the combustion chamber volume & if my memory is correct (I used to have an XB GT with "relieved" closed chamber 2V heads) the compression ratio of 2V closed chamber heads on a 351 clevo is around 11.5:1 (much too high for petrol). if you want to have a higher compression ratio than open chamber heads (approx 8.9:1 on a 351 clevo I think), you are best off getting a head specialist to relieve the chambers (ie. remove some material to increase the volume) to achieve the ratio you need for the cam, carb & exhaust setup you are going to use. (cam lift & overlap has a big effect on cylinder pressures & can make a big difference to what static compression ratio you are able to run without detonation).
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