scottly 475 Posted March 28, 2013 hey guys, been looking around at many stroker combo's as i plan on getting a alloy head roller cammed 408 cleveland built for a street car. i have started gathering parts but along the way i have noticed not many poeple are using the alloy 4v heads, they all seem to be running alloy 2v or or chi 3v heads why is this are the 4v's getting out performed by the smaller heads or? alloy heads are new to me any info would be great on this thanks scott Share this post Link to post Share on other sites
Trev Vaa 1,185 Posted March 28, 2013 smaller ports and higher air velocity. Dion runs 10s with a 408 which you can pretty much buy every component off the shelf. bottom end, cam, heads, intake, only thing custom is the carby i'm pretty sure. he uses afd 2vs Share this post Link to post Share on other sites
gerg 10,871 Posted March 28, 2013 The CHI 3Vs have the advantage of 30 years of experience in port design, with the bonus of having been designed with computer modelling. Looking at a cross-section of 2v, 3v or 4v ports, the difference is profound. The original 3v opening sits higher, straightening out the flow, and the short-turn is nice and smooth and the pocket is nice and round too, giving the mixture a straighter shot into the cylinder. There are versions with the lower standard ports, able to be used with any 2v manifold. By comparison, the factory iron heads, while excellent in their day, have lots of compromises. The opening is tall but low, forcing the mixture to squeeze tightly up the ramp in the floor, then turn around about 110 degrees to get round the short turn. The pocket is deep and looks to be a bit of a dead spot, causing loss of velocity and turbulence. 2v and 4v suffer the same problems, but much exaggerated in the 4v. They discovered that filling the port floor in a 4v with epoxy filler straightened out the flow and actually picked up horsepower, despite the port being smaller. This is the principle behind 3vs. Again, factory clevo heads flow much better than most other smallblock heads around at the time, particularly Chevs. They were as good as factory iron heads could be in the late 60's. The secret to 3vs flowing more despite being smaller is in the velocity, having higher speed through the port keeps momentum up and fills the cylinder more efficiently. Being made of Aluminium alloy allows them to carry away much more heat from the combustion chamber, enabling higher compression before detonation is a problem, generally around 1 point more. They enable the engine to warm up more quickly. They're also much lighter, about half the weight of iron. 2 Clevo120Y and SMIKXF / YEABRA reacted to this Share this post Link to post Share on other sites
scottly 475 Posted March 30, 2013 cheers for the replys boys, is dions the red xd408? those chi heads a very popular with dandy engines and pavtek on there stroker combos and man some of those engine make good numbers lol. i have been looking into the alloy head stroker combos more and im kinda getting a better idea now, but i think ill talk to a engine builder when its time to buy the heads Share this post Link to post Share on other sites
Trev Vaa 1,185 Posted March 31, 2013 yep thats dion. Share this post Link to post Share on other sites
