smaller ports = better power?

I have been thinking about doing some clean up porting on my 650 head before putting it on the bottom end I am building. I want to run bs34's and I wanted to at least taper the runners to match the new boots...

then I read this:

www.mototuneusa.com/think_fast.htm


I tend to really like this guy and I think he knows his stuff, but this sounds so different from everything the folks who do this for a living claim...

Has anyone here tried anything like this? I am interested to read what they pros think about this.

That guy is right in certain respects, but he also knows very little about engine port airflow. A lot of people who do porting end up killing your velocity, and in that respect he's right. But, a well done porting job will increase both your velocity and peak airflow.

So, if you leave most of your port as stock, you'll be fine, but I think matching the port to your intake boots is a good idea. You could end up with some pressure pulses in the worng spot if you don't.

i believe Larry C and myself have said this same thing more times than we'd like to remember,bigger is not always better.smaller higher velocity ports tend to work better on street driven motors that run at varying speeds,versus a dragbike that has the throttle pinned from start to finish! same thing goes for carbs

when i port heads i always look at the guy's combo and what he is doing with it, as plummen said for a low compression (under 11-1)and mild street cams i'd be inclined to keep port sizes on the small side, mostly what i'd do is a good blend in the valve seat area and match the intakes then do a good clean up of the port. getting rid of casting flash that sort of thing in this situation i wouldn't be conceren about horsepower so much i'd be looking to improve throttle responce and driveabilty. now if the guy has a 1400 with major compression big cams and 40mm + carbs then definitly out comes the epoxy.

What compression, valve work and more specifically which performance cams are you planning on... What's your riding style... Statements more than questions, things for you to think about...

I'm with the others on this one... As I have mentioned numerous times, when researching for engine build and for this subject matter, the head work I had in mind. In discussions with both Buzz @ Dynoman and Larry, I was asked the above questions (plus other questions including riding style) and for which carbs I had planned on....

Now the following came for two different ppl that I had never spoken to ever...

Buzz:
"I'll sell you what ever you want but from what your planning on, those 34's won't be the right size for your build"...

"Those Mik 34's are a great carb... for RACING that is so unless you plan on riding WOT most of the time, not for your build"

Larry: Pretty much the same word for word...
"For your planned build, you'd require a J head to truly benefit from using a set of 34's otherwise, waste of time and money for they just won't perform to expectations in your build"...

Then throw into the mix Plummen and I started our friendship and followed with the same statements as the others... Then Timebomb comes into the friendship mix and says the same...

Ok, this was getting really weird or was it these guys just truly understand these KZ engine builds... :laugh:

NOTE: Whoa, did I luck out with these friendships for I have learned soooooooo much from these guys... Not to mention they're just damn good ppl....

As for the head P&P... Larry had me send him the camshafts (w/spec sheets), the intake manifolds as well to match the combination's... Then he measures for CFM and air velocity insuring minimal turbulence at the ports... I'm sure there's a hell of a lot more to it then this including valve sizing, overlaps/cam durations that all make power....

All in all, more than just slapping some big ass carbs on there and taking a dremel to the ports...

Follow the link to Larry's site has good P&P info there.... Good luck in your venture...

www.flowbenchtech.com/porting/CRH/porting_method.htm

OMR

hardr0ck68 wrote:

I have been thinking about doing some clean up porting on my 650 head before putting it on the bottom end I am building. I want to run bs34's and I wanted to at least taper the runners to match the new boots...

then I read this:

www.mototuneusa.com/think_fast.htm


I tend to really like this guy and I think he knows his stuff, but this sounds so different from everything the folks who do this for a living claim...

Has anyone here tried anything like this? I am interested to read what they pros think about this.

10mm larger carburators than stock with ports gobbed full of epoxy isn't a combination that makes much sense.

Filling in ports can work. It all depends on the whole combination of parts and what you're after with the motor.

I had to go back and search your posts. You were after the ultra high RPM 650 based motor. Try it if you think that's the hot setup. Nothing ventured - nothing gained.

at it again ehhh.....


huk huk huk.......

get an r-6 .f3,6rr,like i said last time...and be done with it...:woohoo:

I am preping two heads, one is a 650 head ther other a 750 head. I plan on putting as set of 750 valves in the 650 head. Both heads will also get new valve seals and get the valves / seats re-cut both will also get the runners blended for the bs34's (which were stock on the gpz750's so they cant be all that bad). On the 650 head I will try the epoxy and leavy the 750 ports stock. I am thinking about having a mm or 2 removed when I get them surfaced as well.

Try it and see... the worst that can happen is I mess up one of my 4 650 heads

I wasn't planning on touching the top end this year, but I can't resist at least a little head clean up! And it is very tempting to try it on my own.

sounds interesting, and like you said, whats the harm

my take on it is:

smarter ports = better power

and sure, smarter isn't necessarily bigger

first thing to consider is your existing valve size, you should be building/planning from that dimension up stream.

current theory is that you should aim for a continuous taper of just a few degrees.

One thng that helped me lots with my porting was making rubber castings of the current port. really lets you "see" where the port is wrong, where to remove material, and sometimes, also where to add!

see how strangled the stock porting on my sohc honda 500 was near the valve guide area! before on the left, after on the right

TG

turboguzzi wrote:

my take on it is:

smarter ports = better power

and sure, smarter isn't necessarily bigger

first thing to consider is your existing valve size, you should be building/planning from that dimension up stream.

current theory is that you should aim for a continuous taper of just a few degrees.

One thng that helped me lots with my porting was making rubber castings of the current port. really lets you "see" where the port is wrong, where to remove material, and sometimes, also where to add!

see how strangled the stock porting on my sohc honda 500 was near the valve guide area! before on the left, after on the right

TG

Thats what She Said...:laugh:

Here's a Pro Stock Kawasaki Head