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Porting and polishing? 8 years 2 weeks ago #11406

  • Ledkz1300
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I just dropped the head and cylinder block off at the machinist today. Getting the cylinders bored and honed for the big bore kit, as well as new valve seals, cleaning and checking the valves etc.

I asked them to see if there is anything else they think they can do to get a little more performance out of the old girl.

Are there any advantages, or warnings, regarding the porting and polishing of these heads? Is there anything else I should or shouldn't get the machine shop to do?

These guys are wizards with cars. Building race engines is what they specialize in. They have a great reputation in the Nascar and drag racing circles. However, motorcycles are not their usual cup of tea but then again... no one else around here would even touch it and they will.

Any advise out there would be appreciated. Some things can't be undone.

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Porting and polishing? 8 years 2 weeks ago #11407

  • Kawboy
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Our member "Tyler" is the one you want to chime in here. He's done a big bore with JE custom pistons and port work. Check out his build on KZ riders.com . www.kzrider.com/forum/11-projects/367864...-kz1300?limitstart=0 Port work to be done right needs someone who specializes in it. You can really mess it up if you don't have a flow bench to work with and you don't know what you're doing. The best you can do when you don't have a flow bench is clean up the casting burrs in the ports and leave the intake runners slightly rough to assist with laminar flow and keep the fuel in suspension with the air, and the exhaust runners as smooth as possible to assist with the flow.
you're not going to get a lot out of the porting because the intake runners are too long and the flow path is far from ideal. Be happy you have a torque monster.
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Porting and polishing? 8 years 2 weeks ago #11408

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Thanks Kawboy. This is exactly the input I'm looking for. These guys do have a flow bench but are you saying it won't matter much anyways because of the intake runners?

And I'm thrilled to have a torque monster. Anything else I can do to jack it up even more? :)

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Porting and polishing? 8 years 2 weeks ago #11410

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Kawboy pretty much covered the issue of porting and polishing, and the whys and wherefores and what-nots of it. Polishing is not hard to do at all, but you do need to know where to polish and NOT to polish, as Kawboy mentioned. Porting is something else altogether, and it's an art form. It also requires a lot of specialized equipment, set up time, adapters and tons of extremely dirty, tedious labor. The gains, as Kawboy said, will not be significant enough to warrant the expense. unless the "artist" doing the job has experience on several 1300's, he won't really have a handle on what the best shape should be, so you will be getting a compromise. It might be better than stock, but certainly not worth the expense. And, he also won't know enough about the head's casting to be damn sure he doesn't make a area too thin!

I've done a lot of porting on Honda GL1000 heads for myself (long story!), but I ruined three heads learning just how non-uniform they can be! And, I would never even consider doing a 1300 head for somebody who only has one to work with and in the end will only be running it on the street. Porting is just too expensive, labor-wise, to reasonably consider for the street, unless you are rich, willing to cut up two or three more heads and a serious street racer.

A lesser known process (except to a porter) you can have done to improve your top end power is to "unshroud" the valve pockets. I won't go into that too deep here because it would take too many illustrations to explain, but it involves some careful removal of material right around the base of the valve seat to help direct the flow of mixture into the cylinder for a better "swirl-effect", which means better combustion, which means better efficiency of what fuel air you do get into the cylinder.

Some guys just have the talent for porting from years of experience, but the danger still exists that their lack of casting thickness knowledge can get them into trouble if they don't have several heads to work with.

Unless you are looking for all out top end performance, as Kawboy said, leave the casting rough near the valves to maintain the mixture in a vapor state rather than condensing on smooth walls just before entering the cylinder. If you intend to run high rpm's a lot, then polish the hell out of the whole intake area, run a wild overlap cam and put up with the low end roughness!

Your big-bore kit will give you the biggest gains per dollar (or pound, or yen, or lira, or euro, or whatever you have!). Nothing beats cubic inches, as we say here in the U.S.!!!

FWIW, if you want a really smooth running engine, you might have that shop cc the combustion chambers to be sure they all match perfectly. It's easy to do and not too expensive. Everything they can do to make sure that each cylinder is the same will help smooth out the power. Polishing the combustion chambers (during the cc'ing process) and the tops of the pistons will also help prevent carbon buildup.
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Porting and polishing? 8 years 2 weeks ago #11411

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I just read Tyler's whole build thread and must say, that is the best build I have ever read. VERY thorough on his research and a very impressive approach to the porting issue. Ledkz1300, you would do well to copy just what he did! I would! Thanks for the heads up about that thread Kawboy!

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Porting and polishing? 8 years 2 weeks ago #11414

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This is exactly the insight I am looking for. I also read that thread about Tylers build and it was very informative.

Thanks for responding fellas!

So, minimal gains vs cost and risk for porting. I have a spare head but I am not rich enough to throw it away for practice. I'd rather keep it as a spare if something ever goes wrong or maybe another member will someday need it more than me.

I'll talk to them about this. Perhaps print the threads so they can have something to refer to.

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