MIME-Version: 1.0 Content-Location: file:///C:/EB63AA96/carbsSUHS6.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" H6 vs HS6

H6 vs. HS6

Some clas= ses of vintage sports car racing require that the competitor stay with the origina= l SU carbs. In fact, over the years we have found that there is really no advant= age to using anything else. However, there does seem to be a lot of discussion about what type of SU and what manifold to use. We’ll talk a bit about that here.

We conced= e that the TR4A long manifold is superior to the shorter rake-style that was used = in the earlier four-cylinder engines. However, the current practice of using t= he long intake manifold with the long H6 carbs is counter-productive. <= /p>

I put a f= lowed TR4A cylinder head on the flow bench and attached a TR4A long inlet manifol= d. I then attached first a long H6 carb with the piston locked at maximum lift a= nd took air flow readings at every .100" of valve lift, up to maximum. I = then duplicated this procedure using a short HS6 carb and found that the HS had a 2-3% flow advantage at every step. While there might be some possible ram effect advantage with the H6, it would seem that the tuned length would be = the worst of all worlds.

On the tr= ack, the HS6 has demonstrated its advantage on every car it’s been tried o= n. There could be more to this than just the carb, though. Some of that advant= age might be that the shorter length of the HS6 allows room to use the very lar= ge and aerodynamically clean Hurts Air Ram Bells.

Both test= s were conducted on carbs whose pistons were not modified in any way. It is possib= le to carefully shape the leading edges of the pistons to streamline and thus increase the flow of air to the manifold. In conclusion however, it may be = said that regardless of the combination of parts that we tried, the HS6 gave a better flow under any and all conditions and is the obvious choice for maxi= mum performance.