Originally Posted by cbtlr
This may be an old thread but does anyone no anything about the zh-446 head.This is the head that pbu uses for their sleeper kit.I have this kit.The bottom and espeacialy mid is great.Top end,cant get her to rev out.Jet pro 1st pipe,ada fiber glass reed,rocket key,stack and filter,72 main jet,needle in 3rd position.2nd position engine dies 4th position engine boggs. 6/63 gearing gets 35mph.Have I tach'd this head out or besides the dual boost ports can this head be modded for more power.Any reviews about this sleeper kits porting or duration?
I have been unsuccessful so far at getting over 10,000rpm with a highly modded engine. See post for info on mods.
I have messed with the transfers and the exhaust and the boost ports and nothing seems to make any diff. Since my cylinder is already messed up I am trying everything because I have nothing to lose as this cylinder is useless to me the way it is. My port timing is 129 transfers and 170 exhaust.
I have also reworked the boost ports so they are squarish and angled the roofs so they are pointing at the plug.
I am wondering if the transfer ports are just too small on the 44mm head.
The stock 40mm head has much larger transfers than the 44mm.
Since my cylinder is useless I might try making the transfers deeper to see if there is any diff.
As for the carb, I made sure that the pump pop off pressure was set correctly. The walbro carbs are always set incorrectly stock(pressure was set way to high). Still no diff.
Another thing is you should get rid of the Rocket key. I tried advancing and retarding and still no diff. Advancing caused the motor to run hot and lose power. Just for the heck of it you may want to try putting the rocket key in backwards/retarding and see if it will rev higher. I have read somewhere that advancing gives more low end and retarding gives higher rpm. I did not see any differences in top end though.