The Myths of Porting and Polishing!!

[lecroy]

Another way to improve performance is to shed weight off the bike-or yourself.

This is the route I am taking. Very cheap, just stop eating so much and get off the couch.

[BadBillyB]

Having said that I’m very interested in the following article.

http://mototuneusa.com/super_sonic_nozzle.htm

What do you guys think of these porting mods?


Cheers, Graeme.

Graeme, heres an old thread discussing the mototune article
http://www.thegsresources.com/_forum...ghlight=school

[duaneage]

Graeme
You make some very valid points.
A very thought provoking article. Quite controversal, but many a performance advantage has been gained by tuners taking a punt outside the square.

yeah, we went round and round on that one. The greatest gain is had by raising the floor, that's always been known. In 1962 Ford had a 260 V-8 at Indy in which the intake flow was straight through the valve cover right into the chamber. The carb throat was lined up with the cylinder. It was the ultimate in breathing capability since there was no turn in the intake path. They used 8 carbs.

Reducing the port size does all that wonderful stuff but it will limit the maximum rpm of the engine, it's no different than not opening the throttle all the way. Port mods are best done with cam changes that take advantage of the new tuning effects. Changes in the port accompanied by more aggressive cam timing can get you big gains in SPECIFIC RANGES. If you adjust your riding to suit those changes (change gearing for example) then the net result is a +.

It's interesting to note that they don't state how small is too small or why those dummies at Suzuki made them the size they did. I'm sure Mr Motoman is real clever and all that but I like to think a company like Suzuki ws hell bent on getting the most out of their engines while having them be streetable and well behaved on the road. Remember, you only use 90% of an engines power 5 % of the time anyway.

I feel things are best left alone since I spent many weekends on cylinder heads, carbs, and all that stuff with cars. I also think it's easier to buy a bigger bike and if that isn't enough buy a bigger newer one. When you get to a Busa or a ZX14 if your still not satisfied then join the air force and try a F-16. 48,000 lbs of thrust kind of beats all.

[duaneage]

I found this little ditty on his site particularly amusing and narcissitic. I don't think he "knows something nobody else knows", especially about Japanese Motorcycle Companies like the nonsense about next years improved model.


"MotoMan" Has A Brief Conversation With
"Hearing-But-Not-Actually-Listening-Man".

H-B-N-A-L-M:If smaller ports really do make more power, then why wouldn't the manufacturers make the ports the correct size in the first place ??

MM:By gradually reducing the port size in small increments each year, they can easily add more power and thus offer the "new and improved" version with a few
more horsepower than last year's model.

H-B-N-A-L-M:No way... the manufacturers would all have to agree to that, because if one factory broke out and made the ports really small, business competition would force the others
to make their ports smaller also.

MM:They cooperate with each other, the competition is mostly an illusion.

H-B-N-A-L-M:No way ...sorry, I just can't believe that.

MM:Okay, well then you've got to believe that back in 1991 one guy working out of his house for 3 months with a $2,000 flowbench out smarted 4 industrial giants that have employed thousands of the world's finest engineers doing 50 years worth of R&D with billions of dollars at their disposal and they still haven't figured this all out yet.

[U.P.dragracer]

8-[ I must say I am very interested in some of the stuff motoman has to say I myself have found many of his theories to be true . I have built circle track engines , and mud race engines , as well as many all out small block chevy drag engines as well . I usually farmed out all the machining work with the exception of the cylinderhead work wich I was equipped and did them myself .
I was always skeptical of flowbench numbers , for the simple reason of . hey , cam timing and max lift needs to be in the equation when doing a cylinderhead . not to mention what type of flow does the engine actually need to make big power at what specific RPM ????

Hmmmmmmm ? well the circle track engine needs to make some serious mid range power to get off the corners . {4500 to 8500 RPM}sb chevy's I built a few

the mud racer needs to make good power off the converter and pull hard to the top RPM . {428 cu in ford I built ran 8200 RPM}:shock: with a 2800 stall converter it would damn near snap your neck LOL!!

The drag engine needs to pump big air at high RPM . this was the easiest engine to build LOL!!! I got a nice big set of CNC ported Dart Machinery heads and did a bowl blend with a little epoxy as a air foil heading towards the valve guide on the intake port . 377 cu in 735 HP on the dyno @ 9800 RPM {this engine tossed a old school 1964 street driver chevelle to 10.36 @ 132 MPH} the heater radio and wipers still work 9" wide slicks 4 speed }
I also had a camshaft custom ground for this bomb

in all I have just recently started my motorcycle engine building I have my own bikes and just love em . most likely I will never do any race engine work on bikes for anyone else . but I can't help myself for grinding and tearing up my own bikes LOL!!!

I'm not a part's buying kind of guy and I like to experiment on my junk . heck even my chainsaw has a port and polish job on it .{yeah it rips }

:-D

[renobruce]

Port mods are best done with cam changes that take advantage of the new tuning effects. Changes in the port accompanied by more aggressive cam timing can get you big gains in SPECIFIC RANGES. If you adjust your riding to suit those changes (change gearing for example) then the net result is a +.

Exactly. At least as I understand it (so far).

buy a bigger bike and if that isn't enough buy a bigger newer one. When you get to a Busa or a ZX14 if your still not satisfied then join the air force and try a F-16. 48,000 lbs of thrust kind of beats all.

That's funny!

I found this little ditty on his site particularly amusing and narcissitic. I don't think he "knows something nobody else knows", especially about Japanese Motorcycle Companies like the nonsense about next years improved model.

The Japanese are a very shrewd people. I wouldn't put anything past them. If they came out with the "most improved" bike one year, what would they do the next year? But then again, there are some GS models that have the same performance specs for a few years. Stock GS's are definately over built and under powered.

I just bought a ported head with a fresh valve job for my new project, a '78 1000. I am going to try and take advantage of what I have with some aftermarket cams and better carbs. I need to learn a bit more about cams. I don't yet fully understand why you lose bottom end while gaining mid-range or top end.

[U.P.dragracer]

I just bought a ported head with a fresh valve job for my new project, a '78 1000. I am going to try and take advantage of what I have with some aftermarket cams and better carbs. I need to learn a bit more about cams. I don't yet fully understand why you lose bottom end while gaining mid-range or top end.
__________________

Well I learned tons about cam selection from reading book's and also monkeyin around with PC programs like Desktop Dyno 2000 even though it is a automotive oriented it is all for the same end result and concept :-D most of today's high performance cam technology had humble beginnings as trial and error LOL!!!

[Commodus]

I found this little ditty on his site particularly amusing and narcissitic. I don't think he "knows something nobody else knows", especially about Japanese Motorcycle Companies like the nonsense about next years improved model.



MM:Okay, well then you've got to believe that back in 1991 one guy working out of his house for 3 months with a $2,000 flowbench out smarted 4 industrial giants that have employed thousands of the world's finest engineers doing 50 years worth of R&D with billions of dollars at their disposal and they still haven't figured this all out yet.

Yeah I dunno, I don't think that's so incredible. I mean, motorcycle history is full of engineers who've done amazing things with little funding and sometimes little formal training. Look at the Britten, for a modern example. Look at Scott, or even Vincent. On a different, related note, look at Ducati, who competed on a comparatively tiny budget with seemingly old-school technology. Money doesn't always equal success - big companies are good at developing things that exist, sometimes not so good at chasing new ideas - there can be a lot of bureaucratic inertia involved.

I do, however, find it very hard to believe that there's a worldwide conspiracy going on here. Keep in mind, it's not just the Japanese big four that would have to be on board, after all. Yep, that's absurd.

I also find it a little odd that nowhere on that guy's site does he have a simple, straightfoward: "here, engine A with dyno; compare it to engine B with dyno with X mods performed. There's my evidence." I mean, he clearly has the equipment to do so. Unless I missed it...?

[Big Jay]

Again the engine is an air pump. The more in and out, the more power. Any of you guys ridden a GSXR1000? What is the difference powerwise between it and a GS1150? The 1150 has 150 more cc's, but the 1000 has a cylinder head that breathes nearly twice as much as the 1150. It also has probably twice the power.

The only thing that makes a ZX6R more powerful than a GS1150 is a head that flows and electronic fuel injection.

Jay

[ehra]

Here are a couple of pictures of a 16V GS head on a 1400+ cc all motor pro-mod, runs mid 7’s at 175mph. This head is $5000+ to have done and makes 200+hp (they won’t tell me the actual number). It is all about how efficient the port is not the size of the hole in the head. They fill the floor with epoxy to improve the flow by reducing the turbulence from the short side of the port.

Glenn

[ehra]

Next picture.

[Dan Ruddock]

I need to learn a bit more about cams. I don't yet fully understand why you lose bottom end while gaining mid-range or top end.

The condensed version, it's about port velocity, inertia and when the intake valve closes although the other three events effect power band also but to a lessor degree. I would read the glossary on the webcam site which will help you also. Dan

[49er]

Renobruce
You loose bottom end performance because all race/semi race ground camshafts employ greater overlap between the inlet and exhaust valves. This is the time that both valves are open together for a short period either side of TDC. The idea is to try and scavenge inertia from the exhaust valve to increase the inertia at the inlet valve. If you increase overlap dramatically, you spoil the bottom end scavenge with exhaust gases back feeding into the inlet port.
Tuners increase the overlap, opening rate and lift at the valves to gain better cylinder filling and increase their maximum HP. The consequences are a reduction in gas flow at lower rpms, but a major improvement in flow in the mid to top end. The usual increase in port and carb sizes help to further hinder bottom end flow. It is indeed all about gas velocity and accelerating the burnoff rate during combustion.

ehra
Nice pics of that port mod. No valve guide protuding into the port either.

[Dan Ruddock]

Renobruce
You loose bottom end performance because all race/semi race ground camshafts employ greater overlap between the inlet and exhaust valves. This is the time that both valves are open together for a short period either side of TDC. The idea is to try and scavenge inertia from the exhaust valve to increase the inertia at the inlet valve. If you increase overlap dramatically, you spoil the bottom end scavenge with exhaust gases back feeding into the inlet port.
Tuners increase the overlap, opening rate and lift at the valves to gain better cylinder filling and increase their maximum HP. The consequences are a reduction in gas flow at lower rpms, but a major improvement in flow in the mid to top end. The usual increase in port and carb sizes help to further hinder bottom end flow. It is indeed all about gas velocity and accelerating the burnoff rate during combustion.

ehra
Nice pics of that port mod. No valve guide protuding into the port either.

Not true if you increase overlap by using a narrow lobe center cam with like duration the bottom end will improve because the intake is closing sooner. Like I said earlier when the intake closes has the biggest effect on power band. Dan

[skip]

Well thanks for all of the input. I do not plan to race my bike so porting is out. I can see the point if you are looking for a few more HP to shave a couple of .10th off you ET but for myself I can't justify spending that kind of money for that little bit of gain. I have done the 1166 upgrade keeping the engine stock except for the pistons. This year I plan to add Adjustable Cam sprockets, a stage 3 jet kit with pods and a new V and H header. Once that is done I am going to run it on a dyno to make sure that I have max HP. I think these improvements will complete the work on my engine. Now I just have to finish my cosmetic work and start looking for a new project.

Thanks for all of the good advice,
The Beast

good choice for a street bike, plus porting usually removes some of the midrange and bottom end somthing you want in a street bike.