650R cylinder head

[iestrada]

I want to replace the cylinder head, i had mine ported and didn't like the outcome. So i'm lookig for a used cylinder head before, might get it cheaper than servicehonda... So does anybody has one for sale?

[drop]

What didn't you like about the port job?

[HawkGT]

Yes, please share your experience.

[iestrada]

the main reason is power drop. When I'm riding a loose sandwash i need to start downshifting, when with the stock head and the stage 2 hotcam i could stay in, let's say, 3rd gear. now I need to drop to 2nd rev it then 3rd and then again 2nd rev it ....

What i did like is that each gear was looong. 5th gear lasts for ever.

I've been playing with jetting but couldn't get the way i like it. lso i'm reluctant to cut the air box cover, do you think that can help me? May be an edelbrock...

[Billahjack]

Porting is a touchy modification. You need a constantly decreasing cross-section of the intake/exhaust ports from the outside going in towards the valves. If you get this wrong, then you lose big time on power.

Polishing intake ports can also reduce low-end power because the air is not turbulent enough. Most race engines (F1, Indy, Nascar, etc.) use the heads in an "as-machined" condition with the tiny ball mill scallops on the port walls for better air flow.

Match porting is the best port modification that you can do for most engines. This is matching the mating surfaces of exhuast to the exhaust cylinder head port or intake manifold to the cylinder head intake ports and carburetor. This removes a sharp edge and blends the tract where mating surfaces do not match.

[Nailpounder]

I always bead blast my intake ports an polish the exhaust ports.

I've seen a lot of poor porting jobs in my life. People think all they have to do is hod metal out an presto, you have more H.P.

[porterdog]

Agree with the above posters regarding the relative finesse required in a porting job, one car guy stated that "Any magic in the motor resides in the porting of the head...".

Your situation may be recoverable without resorting to a new head, though- you could add epoxy back in and have another go. This is not a revolutionary technique, check out this page from MotoMan

[HeadTrauma]

Portwork is indeed a touchy procedure to do right. Something else to remember is that Honda typically has very good port designs to start. Good ports are even harder to improve upon making the portwork an even more specialized process. Most garage mechanics don't have the skill, knowledge, or equpiment to do this.

the main reason is power drop. When I'm riding a loose sandwash i need to start downshifting, when with the stock head and the stage 2 hotcam i could stay in, let's say, 3rd gear. now I need to drop to 2nd rev it then 3rd and then again 2nd rev it ....

What i did like is that each gear was looong. 5th gear lasts for ever.

I've been playing with jetting but couldn't get the way i like it

Before I recommend you spend a bunch on a new cylinder head, I have a few questions.

1.) Who did the portwork? An XR specialist, or some bike shop that does general porting?

2.) What cam are you using in the ported head?

3.) What's your overall setup and mods?

4.) What do you mean you couldn't get the jetting the way you "like it."?

Based on the information already provided, I'm suspecting that the portwork is either poorly done or it's fine and there is a midrange power deficit somewhere.

[iestrada]

1.- the portwrk was done in a shop that does port for 1/4mile and offroad racing engines. They do have the flow bench.

2.- i kept the stage 2 hotcam

3.- uncorked, T4 full system, hotcams stage 2, 15/47, cant remeber de jetting right now

4.- i have poor low end and poor fuel range compared vs the same bike with stock head.

Porterdog,

I've read almost all the pwer news. And my problem is just like the one MM mentions in thet link you post. I'm considering using J&B weld.

[HeadTrauma]

1.- the portwrk was done in a shop that does port for 1/4mile and offroad racing engines. They do have the flow bench.

2.- i kept the stage 2 hotcam

3.- uncorked, T4 full system, hotcams stage 2, 15/47, cant remeber de jetting right now

4.- i have poor low end and poor fuel range compared vs the same bike with stock head.

1. 1/4 mile and offroad what engines? Automotive?

2. Alright.

3. Part of the problem is your top-end gearing coupled with the reduction in low-end torque. The ported head shifted the whole powerband upward and it will feel doggy if you can't easily keep it there. Have you tried something like 14/47 or 15/49-15/50?

4. Heavy portwork will do that. The low-rpm port velocity took a dump and fuel atomization followed suit. All of that means more fuel for the same power until you open it up or spin it faster.

They didn't give you a before and after flowchart for the head, did they? I think there are other factors coming into play, but I moderately suspect the portwork. There's more than one way to wreck drivability while picking up port flow.

[Nailpounder]

You get most of your power from port work un-shrouding the valve.

Not making the ports larger. A good three or five angle valve job is all you need.

[iestrada]

1. Yep, mostly automotive engines. Hes been dealing with motorcylce engine just por 2 or so years.

3. nope, haven't played with gearing. Should I expect higher speed with the portwork and gearing like the ones you suggest vs a stock head and 15/47?

4. So with the portwork i'm supposed to keep the engine in the higher rpm's?

HeadTrauma, what do you think of the link of the reduced ports with J&B Weld?

[HawkGT]

"velocity" porting is a legit concept. Here's what Yamaha did to the 06 YFZ450 head vs. the 04/05 head:

If I dare speculate: the bits and pieces I've picked up regarding XR650R head porting leads me to believe that only heavily R&D'd port work is appropirate. I've got to believe that the stock ports can be imporved upon. But I question how many porters (even generally excellent ones) know what the XR650R head really needs. I could be way off base on that, but this isn't the first time I've heard anecdotally: "I had my XR650R ported and wasn't happy with the results".