The Myths of Porting and Polishing!!

[Boozy Creek Beast]

I found this article on the web about Porting and Polishing the head. I had been thinking of doing it to my 1980 1100E since I completed my 1166 up grade. I was wondering what everyone thinks. Do you agrees or disagrees.

http://www.motorcycleproject.com/motorcycle/text/cows-porting.html

Thanks
The Beast

[80GS1000]

If porting/polishing is good enough for God (Pops Yoshimura), it's good enough for me. Sounds like the moral of the story is to have an experienced engine builder (APE etc) do the job.

[fatkid89704]

basically i think they are saying that you will never run a street engine hard enough to justify the time and expence of porting your head.

[Road_Clam]

basically i think they are saying that you will never run a street engine hard enough to justify the time and expence of porting your head.

Thats EXACTLY what they are saying. I've been around racing, and race engine builders for the past 25 years. The smartest thing a gung-ho garage performance engine tinkerer can do is just leave your engine ALONE. The pro engine builders all agree, If you have to ask on the internet about what performance upgrades to do, then you don't belong inside the engine anyway. In the process of a novice trying to gain 3 hp, he will almost always end up loosing 7 hp....

A perfect example of my stupidity and ignorance in my youth was when I built my own hi-po 350 Chevy. $2700 in reciepts, and I was putting down a pittifull 237 net RWHP. A bone stock 1981 Z28 350 would put out 224. From that point on, every engine I built thereafter I built bone stock. If I needed more HP, I simply bought a BIGGER engine!

[Big Jay]

basically i think they are saying that you will never run a street engine hard enough to justify the time and expence of porting your head.

Didn't read the article, but doesn't sound like someone with much experience with high performance engines.

With the GS1100 / 1150 motor, the heads are so bad stock that there will be a good power increase when the head is done right. Even on a stock motor. Those heads are about the equivalent of modern 600s.

Jay

[Road_Clam]

With the GS1100 / 1150 motor, the heads are so bad stock that there will be a good power increase when the head is done right. Even on a stock motor. Those heads are about the equivalent of modern 600s.

Jay

True.... BUT the added port work will only shine if you are versed at jetting, setting up a good exhaust, proper timing........ and so on. Again, and I agree, in most cases the average street engine will never reap the complete benifits of extensive mods. "An engine is an air pump, the more air in, the more air needs to be let out...... I am no 1100/1150 guru, but I highly doubt if JUST a port job will yield significan gains.

[BadBillyB]

I think the article basically is warning people that if they do not know exactly what they are doing, the results are going to be disappointing. Just because a shop has a flow bench, it does not mean they are going to provide you with good results. This I know first hand. The statement, quote...."porting without a flowbench is akin to luck", I do not agree with as it implies that the flow bench is critical in making a good flowing port. It is not. Knowledge and experience will outperform any novice with a flow bench.....If you want to try porting your own cylinder head, I would suggest getting your hands on every thing you can find about the subject, and reading it over and over until you know exactly the game plan, than search some more......I have been porting 2V Suzuki cylinder heads for almost 25 years and I can assure you, I have done my homework....Modern port work has been eclipsed by Serdi machines and CNC machines, so if you are not sure exactly how to modify your ports, have an expert do it, it's an investment if properly done. I cringe when I see a cylinder head for sale thats been ported by "some dude" on Ebay etc........Have a pro with credentials do it for you, or get busy reading and studying how to do it yourself (could take years).......BadBillyB

[U.P.dragracer]

I must add that a good bowl blending and valve job will wake up just about any engne . most bike , car , ATV , engines are not finished well in the area behind the valves .
Most porting mistakes are made by the good old Joe racer trying to hog out the ports thinking he will get tons of air pumping through the engine by going big .
most of the time the port shape is ruined and and variences between cylinder ports kill any gains that might be had . I've seen some pretty goofy stuff done to automotive race engines by wannabe cylinderhead guru's

My best advise for the home porting fella's is just do a nice smoothing job in the bowl area {remove the machining marks } match up the manifolds to the port , and just remove some of the harsh casting flash etc. in the ports . get a nice radius on the port short side {bottom towards cylinder} as it goes towards the valve . Keep it simple and consistant from port to port :-D

[fatkid89704]

your right i know nothing about performance.i just learned how to turn on my computer yesterday.but i would interested in some real time numbers from a before and after dyno sheet showing all this amazing horsepower you can get from porting.as far as my past tries,it does little or no good to the average person riding on the street.if you run at full throttle all the time it is worth the money and time to do it.other then that save your money.

[U.P.dragracer]

If you can increase flow numbers at lower valve lifts RE: mild porting bowl blending multi angle valve seats . that will give you seat of the pants results .
The valve spends more time opening and closing than it does at full valve lift so it makes sence to me to keep high velocity and efficiant ports .
Just get rid of all the goobers and notches .
any time air flow has to change direction or size it will lose energy along the way :?

[fatkid89704]

i do agree witht that to a point but to spend a bunch of money on 2 or 3 top end horespower its not worth it to the average guy on the street.

[U.P.dragracer]

i do agree witht that to a point but to spend a bunch of money on 2 or 3 top end horespower its not worth it to the average guy on the street.

I agree LOL!!
but for the mechanicly inclined folks who want a little edge and have some tools . what the heck buy a gasket set and tear into it LOL!! it's a hobby :-D

[Mike_H]

Just a port job will not grant big gains...unless the heads are very bad. They would have to be the most restrictive part of the engine in order for them to yeild major results. Guess what, head are not the most restrictive part of the air flow path. That would be the air filter, and exhaust. Thats why every magazine, hotrod shop, and gearhead say to get the most bang for your buck, change the intake, and exhaust. And yes, you will most likely have to rejet to gain the maximum potential from any airflow change to maintain proper stoicheometric balance.

The article makes sense, you want to reduce restrictions to air flow, not merely make the ports bigger. Most port jobs (on cars) I have seen just blend the intake and exhaust manifolds to the head, to get rid of the inevitable lip that is present due to manufacturing tolerances. The lip will create all kinds of flow anomolies that potentially will slow the intake charge, which, you all guessed it, reduces the amount of fuel and oxygen available to burn. There is a book, called Scientific Design of Intakes and Exhausts, that explains all this in excrutiating detail. It was a required read for my Internal Combustion Engine class in college. There is some good stuff in it, and I would recommend it to anyone who is considering having work done. If nothing else, it will explain why this work cost so much money to have done properly, due to the amount of time involved and the type of equipment required to properly benchmark an engine.

[earlfor]

Didn't read the article, but doesn't sound like someone with much experience with high performance engines.

With the GS1100 / 1150 motor, the heads are so bad stock that there will be a good power increase when the head is done right. Even on a stock motor. Those heads are about the equivalent of modern 600s.

Jay

I dont see the point for street use. A stock 1150 has considerably more go than proabably 99% of the riders are capable of using.

Earl

[49er]

There has been some good advice given here.
If you're tuning for road use don't get carried away with porting.
When the time comes for a re-ringing job, consider boring oversize and moderately increase the compression ratio. You will gain more lower to mid range punch with this approach.
Most times you wont even need to change your 4-1 if it's a well designed unit. Leave the cams standard as you always end up trading some bottom end perforance for increased top end.
While you have the head off, blend any ridged machined areas in the valve pocket areas, particularly just below the valve seats. Also, make sure that the internal radius closest to the valve pocket has no sharp ridges and is smoothly blended towards the valve seat.
Check that the inlet boots are correctly aligned to the inlet ports. The same goes for the matching of the exhaust pipes to ports.
If you want to go racing, do your homework before porting, and be prepared to loose some/alot of your present reliability.