TOPIC:

loudhvx wrote:
From what I've read, I don't think the ZR400C had 4-valves. That auction says ZR400C, but then look at the strange valve cover. It appears to have plugs for adjusting lash screws. I don't think a two-valve head would have lash screws. Maybe it's for measuring lash without removing the valve cover, but still uses shim-under, so you have to remove the cover to adjust the lash? Not sure.

As near as I can tell the Zephyr X (also called the Zephyr Kai, and zr400G) is ALSO called a zr400C!! It's confusing, but it seems that numbers after the "zr400C" into the 300 range indicate a Zephyr X (e.g. 16 valve). The screws on top of the valve cover are the giveaway (though I didn't know what their function was until your post). They correspond to a cover that I've only seen on parts diagrams for zr400G's, with associated differences in the head and cams. I'll see if I can dig some of those diagrams up.

Yeah, $500 isn't cheap, but buying the head and all the other parts separately would be in the thousands. I don't know if this would be worth the time and money, but it sure would be fun.

Zaddict wrote: Yeah, $500 isn't cheap, but buying the head and all the other parts separately would be in the thousands. I don't know if this would be worth the time and money, but it sure would be fun.

Nah, you want a used head with the valves and cams still installed.
I gave less than $100 (shipping included) for a GS1000 head for my dad's bike, and it still had the cams in it. Of course, this was shipped from here in the US, and the GS1000 was a MUCH more common model than the Zephyr X.

Here are some parts diagrams for a 2008 ZR400 G8. Note the bolts on top of the valve cover.

Zaddict wrote: Here are some parts diagrams for a 2008 ZR400 G8. Note the bolts on top of the valve cover.

Those screw into the tops of the cam caps to hold the valve cover on, something you see on more modern designs, not peekaboo holes to adjust lifter screws.

Yeah, that just occurred to me as it appears there are no mounting screws near the lip of the cover.. Seems strange that you'd stress the cam caps to mount the valve cover, but maybe it somehow holds the cam caps more securely. Or maybe it's just fewer bolts that way.

Long time no posting here from me. Thanks for the e-mail about this thread, and thank for the plug, but I have only learned what i know from reading the Factory Manuals, actually working on my GPzs, and help from this and other sites. I believe Lou has more experience than I do.

I'd have to agree with above. If you are just itching to install a 16v head, then go right ahead. You can have a lot of fun and reliability with the Wiseco box 615cc kit, larger cams, pod filters, and aftermarket exhaust(stay clear of Mac Exhaust). Oh by the way the CV32 Carbs from the GPz600('85-'87)/ZX600C Models will work using the CV30 Intakes. The CV30 from the ZR550 and the 600 models above, use the same throttle assembly and cables, so just a jet kit and tuning is needed. Leave the CV30s in place till you at least remove the air box, and open up the exhaust.

Have fun and be safe.

Thanks Corey.

I have a few questions about your GPZ build.
First - was it worth the effort (including learning/fun involved?)
Second, from the dynos you have online it looks like you maxed out at about 65 hp. I was surprised about that given that those bikes theoretically came with that hp after 1984. Or maybe that's the difference between hp at the wheel and at the crank?
Lastly, I've heard that pods with CV carbs are a nightmare and to stay away, but it seems like you got them to work just fine. What was the trick (maybe there is a thread where you describe the jet sizes/other parameters you used?). Also, how does the GPZ ride after all that work? Is it still smooth and comfortable for street riding?

Thanks!

Zaddict wrote: Thanks Corey.

I have a few questions about your GPZ build.
First - was it worth the effort (including learning/fun involved?)

Yes it was very worth it, and I'd do it again, but have the short-cut route now. I could street ride the 615 race engine in the condition it was in, before it blew, and the bike caught on fire. I am still thinking about doing it to one of my 2 existing commuters.

Second, from the dynos you have online it looks like you maxed out at about 65 hp. I was surprised about that given that those bikes theoretically came with that hp after 1984. Or maybe that's the difference between hp at the wheel and at the crank?

Yes the dynos do show actual rear rear wheel horsepower, and that is usually about 27% different than at the engine of the factory manuals. Just for added information, Stock TK27, Stage 3 Jet Kit, Pod Filters, and 4-1 Moriwaki Exhaust, only nedtted about 53 hp and 27 torque my first dyno. Yes, I was hoping to get closer to mid-70 hp using the Wiseco 12:1, 615 Pistons which was my next modification.

Lastly, I've heard that pods with CV carbs are a nightmare and to stay away, but it seems like you got them to work just fine. What was the trick (maybe there is a thread where you describe the jet sizes/other parameters you used?).

That is Horse-Poop!!! Pods and CV Carbs have no issues on my GPz550, and I have not heard of anyone having issues with this combination either. I don't know about other larger displacement bikes, but start up cold were and have been just fine, and restarting hot never gave me any issues either. Yes, nothing wrong or difficult to tune them in for racing or street.

Also, how does the GPZ ride after all that work? Is it still smooth and comfortable for street riding?

I haven't ridden the 615 and Megacycle 478-60 Cams on the street yet, but if it is anything like out on the track, it will be a hoot, with a lot of mid-range and top-end power. There never was a loss of bottom end either. Current stock bore and stock ZX Cams with 4-1 Kerker and Pod Filters with dyno-jetted CV32 Carbs work very nice. Still no issues on cold starting or hot restarting. Fun factor has me at a loss of about 5 mpg. 16/40 Gearing is my choice over the sock 16/38.Pulls hard and strong.
Thanks!

CoreyClough wrote:

Zaddict wrote: ...Lastly, I've heard that pods with CV carbs are a nightmare and to stay away, ...

That is Horse-Poop!!! Pods and CV Carbs have no issues on my GPz550, and I have not heard of anyone having issues with this combination either. I don't know about other larger displacement bikes, but start up cold were and have been just fine, and restarting hot never gave me any issues either. Yes, nothing wrong or difficult to tune them in for racing or street.

I run dual-flange oval K&N pods on Mikuni BS34 constant velocity carbs on my 750. I can pull my carbs in about two minutes if I want to tweak my float levels or whatever.

The 1100 I'm building will get the original air box with new rubber at both ends, with a nice new factory filter. I'm trying to tune it for a strong midrange.

guitargeek wrote: I run dual-flange oval K&N pods on Mikuni BS34 constant velocity carbs on my 750.

Did the pods change the character of the ride much? More top end less bottom end?

Yes it was very worth it, and I'd do it again, but have the short-cut route now. I could street ride the 615 race engine in the condition it was in, before it blew, and the bike caught on fire. I am still thinking about doing it to one of my 2 existing commuters.

This sounds like a sad story. What happened?? So how many GPZs do you have now?

Yes the dynos do show actual rear rear wheel horsepower, and that is usually about 27% different than at the engine of the factory manuals.

So that means your engine mods netted about 30% hp gain, correct? (since now you're getting 65 at the rear wheel versus the claimed 65 when new which was actually at the crank). I'm wondering what that percentage gain would feel like. I think I could probably be happy for the rest of my life with a light bike like the Zephyr that puts out that kind of power.