dlnoss

We ran some unscientific tests, mainly to check the 'even' cooling properties of the head. It ran 55 degrees cooler than an stock head on a hot day doing sand drags. I don't know any numbers on other brands of heads.

That would be good. If you were at sea level and the timing was also at +4, I'd probably run 100 or above. Over 1500', 50/50

Yes there is....10% which makes a silver head and domes $234.00 + shipping.

If 4000' is the minimum elevation you ride at, you could install some 19cc domes. Your bottom end power would increase a lot. If you went on a trip to a lower elevation you would need to increase the octane some.

Check the compression. It should indicate if the head gasket is blown.

I wouldn't run pump gas with 19cc domes.

If you don't find some used ones, I have new ones for $58.50 + shipping after the BHQ discount.

Jack, I'm going to try to be there. I don't have any stuff for the Predator. I would like to develop some stuff but don't know what would be good to make for them. And didn't know anyone,,,,,,,,until now,,,,,, that had one. I don't know if my Banshee would do well there unless I took the plus a-arms and axle off and put the stock length ones back on. I haven't ridden the Gold rush before. Is width a problem? I could ride the Z400 if I promise Jaylee that I'll fix it if I tear it up.

Here is a flyer for the 2005 Gold Rush. It's a really fun event. It's for beginners, novices and pros. Gold Rush Flyer

Each side should have the full compression....170 for example. I remove both plugs and hold the throttle wide open. You should be around 155 - 165 with your setup. The part of the compression checker that threads into the dome (cylinder) should be the same length as the thread length on the spark plug for an accurate reading.

It looks like 978' for Highland, MI according to Google, less than that in som areas of MI

I've been on vacation for a week and logged in a couple of times from a nearby library. Sorry I didn't respond but it looks like you got good answers. -David

You are probably okay at that elevation with premium pump gas and 20cc domes. I'd check compression and make sure it is 155 psi or less with the timing advance. If not, I do swap out new domes for the cost of shipping.

It would probably be best to ask GRR since they did the porting. Like Brad said, there are lots of variables. Your timing, porting, and compression all play into it. When in doubt though, run high octane. My gut response would be that 103-104 would be okay at 175psi or less.

Try JH Racing at 918-371-0101 I just bought a set from Johnny. Paid a good price and got them quick.

You don't usually need to rejet but you should check jetting after installing the head.

I know my opionion might seem biased but I have both. I felt like my throttle response was a little snappier with the vforce reeds. I had a substantial power increase with the head.

I am curious why you want to do this.

It depends on your other mods. If your timing isn't advanced, you can probably get away with 160-165 psi with premium pump gas with stock porting and bore. A little less if the timing is advanced. Elevation will change the compression you get from a given size dome.

I'd probably increase the octane a little to be on the safe side. Maybe 10% to 20% race or av gas mixed with premium pump gas.

Jetting usually doesn't change with a different dome size but I always recommend checking it with any mod (or season change). The stock chamber size is 22cc to 23cc.

It installs in an hour or two. No other mods are necessary if you keep the compression under around 180 psi. It's a good idea, as with any mod, to check jetting afterwards but the jetting doesn't usually need to be changed. It's a quick, easy, relatively inexpensive mod for the difference it makes.

What is the bore size on the 420?

Air filter mod Pipes Head or head mod

Glad to hear it Andy