The Myths of Porting and Polishing!!

[duaneage]

I see posts all the time about hopping up 550's and 850's when the real answer is to move to a larger engine and be done with it. And if an 1150 is not enough potential for you I recommend a ZX14, that won't leave you hungry.

Porting alone won't do much. Now if you change the cam profiles to take advantage of more port flow and target a specific range for improement, your on your way. Then you have to change the exhaust to move gasses so that you don't lose what yuo gained. At teh end of the day the low end suffers so around town you will find yourself downshifting more and reving higher,

That's why my little 650 is bone stock and will stay that way.

[Mike_H]

BTW, its the same reason 600 repli-racer are so high strung. Yes, they develop Gobs of power for such a small displacement, but they also spin to 13000 RPM to make it. They are very flat performer, unless you wring their necks all the time.

[Hoomgar]

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.

Well mine is being done anyway

[Boozy Creek Beast]

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

[drhermanstein]

You Got it Pontiac, clean up the short side radius, get rid of gobs, bumps, machining/casting meet points etc. and leave the essential design alone. If you knife edge the intake port where it splits in a 4valve chamber you'll help as well. Keeping velocity up is the absolute key. POLISHING looks good but does little if anything. Why does a jet airliner get dirty? wouldn't the immense airflow keep it clean? The phenomenon known as laminar air flow is what prevents the air immediately next to the polished surface from moving at all.

Herman

Re U.P. Dragracer 1st page post

[renobruce]

Well mine is being done anyway

Mine for the Beast came ported. Looks like a nice job, too. Nice and smooth.

[Billy Ricks]

I had Britt Turkington do my head for me. He's been around enough top notch tuners to know what to do. All new valves and guides checked when he did it. Matched the manifolds to the ports and cleaned things up.

[49er]

DRH
You are right about that laminar air flow. I saw some pics of a highly polished port where atomised fuel was reverting back to fuel droplets while passing through the port area. If you decide to port, leave the finished surface as if it had been rubbed with some 320 wet and dry paper. That's slightly finer than than Suzuki leave their port surfaces standard.

[Graeme Sydney]

A lot of interesting comments. My observations;

1/ When you talking improvements always define what you need from the mods. Drag racing or road riding etc.

2/ Even on 25 year old bikes the manufacturers did an amazingly good job of meeting a wide range of performance criteria including reliability, rideablity and tractability.

3/ Manufacturer tolerances can be improved (or blueprinted). For most street bikes this is normally the most productive and most cost effective.

4/ an engine is an air pump. The more efficiently it moves air the more power more easily. The two easiest areas to improve OEM are intake (filter/airbox) and exhaust – but both will probably come at the expense of noise.

5/ Because the OEM allow for great variance in fuel quality, good and cheap improvements can be made with higher compression – but you better be prepared to seek out reliable source of hi qual fuel or put up with detonation (and associated potential damage).

6/ Measuring peak anything (HP, airflow etc) can be misleading – even in drag racing 100hp over 6,000 rpm can be faster than 150hp over 1,000 rpm.

7/ The engine works best as a package. Since about 1975 (GS750) the OEM engineers have done a remarkable job in getting a package that works well in unison. Vary too far away from the standard specs and you better be prepared to vary other specs of the package (and you better know what you are doing or you might actually go backwards).

8/ In the past 25years engine tech has moved on, especially in porting and electronic ignition and EFI. It would be more ease to apply the electronics than the porting improvements.

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?

I’ll finish my resto first but I’ll have enough bits left over for a ‘hot rod’. I might muck with the porting then. But I think I’ll start with the EFI for the simple reason that EFI will make mucking about with the jetting after the porting mods so much easier (I think:-D ).

Cheers, Graeme.

[crag antler]

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.

How much work would you need to rebuild the components of the head not including valves,springs,seals,etc. on an 82 GS1100ED ?
Looking at polishing of the body while not knowing if I require porting
No smoking and only slight blow-by on cyl. #3.
My Parts.

I am only having the work done as I felt at 41,000 miles and I have the head off to repair a leak, why not get the top end freshened up?\\/

I ride moderate to occassionally fast, sport-touring GSR style
, usually averaging 37-45 mpg on a bone stock motor.

[duaneage]

I would be cautious about doing a valve job on an engine with 41K on it since your liable to get more blowby from the restoration of compression. Typically a car engine won't tolerate a valve job after 40K because the rings become beveled and restoring the compression increases ring pressure. I would go with new rings since your practically there anyway with the head off it.

[duaneage]

A wise man once said: don't make a racehorse out of a mule.

Some heads and engines were designed for mudane performance and reliability. Not everything can be hopped up. Not only does the bottom end need to handle the added stress of increassed power the head and intake are critical. The ratio of the rod length to stroke is important because it affects the amount of leverage the engine has. This translates to an engine's ability to respond to changes. Another factor is the ratio of bore to stroke. Short stroke wide bore engines respond to high rpm power better than long stroke small bore combinations. THe latter gets better emissions because the spent gas cools more as it expands. Long stroke motors make good drivers at the expense of nascar performance. For 90% of the time that is the better choice.

[crag antler]

I would be cautious about doing a valve job on an engine with 41K on it since your liable to get more blowby from the restoration of compression. Typically a car engine won't tolerate a valve job after 40K because the rings become beveled and restoring the compression increases ring pressure. I would go with new rings since your practically there anyway with the head off it.

Thanks for the advice.
I was planning on replacing the rings,piston clips,have the bore and pistons checked for critical measurments.
My compression before the teardown was similar across the board with good numbers.
No smoke or running issues.

[ducpilot]

Hi, the article is right on. Back in the early seventies I had a Suzuki Hustler built into a very, very fast racer which had a factory race kitted engine. The ports were HUGE and were they ever ROUGH. I could not believe they were so unfinished and figured I would clean them up and polish them. I was told very emphatically to LEAVE THE BLOODY THINGS ALONE!
Basically, if you want more power in a street bike - iether buy a more powerful bike or have your present engine blueprinted. Another way to improve performance is to shed weight off the bike-or yourself. A change to lightweight wheels (real magnesium) will make an astounding change to the handling of most bikes.
Cheers,
Mike

[49er]

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.
For me, the intreging part was the test on the Yamaha R6 after the inlet ports size had been reduced by 30%. The improvement in HP was evident over the complete rev range and the increase remained steady at 5 hp from 8000 - 12750 rpm over the stock port size.
It reinforces my decission not to enlarge the ports on my 850. Blueprinting and blending in any casting lumps, should do the job.
Very few tuners would consider reducing their exhaust port diameters. Makes you wonder how many standard exhaust headers are above optimium size as well.
When a tuning combination is working really well on your road bike, it often pays not to tinker with it. It's easier to loose 5hp when trying to gain 10hp.
Cheers
Ian