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Old 09-07-2002, 03:29   #1 (permalink)
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What's Better? 2V or 4V??

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?
Thanks..
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Old 09-07-2002, 05:03   #2 (permalink)
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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

hope this helps ya
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Old 09-07-2002, 05:15   #3 (permalink)
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dont forget about the 5.4 3 valve setup
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Old 09-08-2002, 01:35   #4 (permalink)
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talking clevo heads here strife.. as much as I wish, the OHC heads aren't going to fit !!

I have ported 2Vs (from COME) on the XA and it has pulled an indentical 1/4 time through the mufflers as my XB did through open exhausts
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Old 09-08-2002, 02:21   #5 (permalink)
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Hrm well i think my 351 has 4V heads, but soon anyway i'm gonna do a complete overhaul, which is why i was asking soi can get things running as good as i can. Thanks for the responses so far fellas..
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Old 09-08-2002, 16:05   #6 (permalink)
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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.
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Old 09-12-2002, 23:27   #7 (permalink)
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depending on how much power you want out of that 51, is where your answer lies..

what HP / ET is your goal if any?

I will need to run 4V's in my XW even if it means its a pig untill 4,000, but who gives a shit really? :)

2V's will get you into the 12 second mark, 11s with NOS, possibly even without it, but thats stretching them to the limit.. and when you port them that much, the walls become thin and they break etc..

Speak to the dude that will build your engine, and work out the combo..

Robbie
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Old 09-13-2002, 00:54   #8 (permalink)
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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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Old 09-13-2002, 01:01   #9 (permalink)
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Oh, if I had 4v heads I would run them !! I certainly wouldn't get rid of them .. just choose your cam wisely.

a nice combo IMO with 4v's is a Crane F246, torker type manifold, 4 into 1 extractors and a 750 DP. A small enough cam that its still drivable but easily capabel of 12s
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Old 04-27-2003, 17:06   #10 (permalink)
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If you are going to use the 4v heads, just remember to keep the diff ratio as low as possible, it will help keep the air speed/torque & RPM's in the right spot to make the best use out of them.
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