Topic: Hi-Po mods: Are they REALLY worth it?

[Scott S]

 Working on a '78 CB550. It's smoking a little, so I'm going inside it regardless. Been thinking about some mild port work to go along with the CB650 cam and a 1.00mm overbore.

 I bet I've read this thread a few dozen times, along with the Hondaman stuff in the FAQ's.
http://forums.sohc4.net/index.php?topic=17374.0

 Got a spare head, took it apart and cleaned it up in preparation for porting and was really surprised at what good shape it's in.
 Compared to the pics on that thread (and some others), I have virtually NO ledge at the valve seat. The intakes are nearly perfectly matched to the head (especially compared to the 550 engine that's currently on my stand. HUGE mismatch on those ports/manifolds). Even the casting marks and "boogers" aren't as bad as the pics in that thread.
 I'm really tempted to save my money and just install the cam and go.
 Maybe run a flapper wheel through the intake and ports just to take out the casting "boogers" but not remove any material or mess around with the valve guide "football".

 For a street ridden bike, is it really worth it? I don't want to move all the power UP by a few thousand RPM.

 I am very interested in the advanced timing mod. That keeps the power where I'd personally use it.
 However, will I need a degree wheel, etc., to do it right? Should I spend my time slotting the cam gear and figuring out how to get 3-5 degrees more timing and leave the ports alone?

 And, please, genuine thoughts on this. It's really easy to build an engine on the 'net and say "Oh yeah...go for it!".

 (Pics of my head to come soon...)

[Rigid]

I am a big fan of good compression, low oil consumption, no leaks, easy starts, reliable idle, and a smooth power band.  Just as Honda designed it, stock.  If I can improve upon any of those attributes, I am willing to try it.  If it detracts from one or more, I'll pass.  That is for a bike I will be riding.  If it is a custom bike for sale, the market drives things such as pods, open headers, and the occasional 836 kit. 

[Kong]

My genuine thought on this is that other than cleaning up some port matching that most home (and "professional") port and polish jobs stand about as much chance costing power as producing it.  I don't think its ever worth the time, trouble, and burrs.  The cam makes sense only if its going to make power where you like to play and if you want to ability to adjust your cam timing a few degrees one way or the other to do that then good for you is what I say.  Go for it - but in honesty it will end up being one of those things where there won't much bang for the buck.  By the way if you do it give some thought to eccentrics, not slots.

I think keeping it basic is your best bet for a fun street bike.  Go with the cam, clean up the ports just to the minimum just because you can, put some money in the exhaust, get your carburetors spot on and then drop the front gear 1 tooth.  I think its the recipe to a fun fun bike at reasonable cost in cash and time while holding on to reliability.

[Bodi]

Doing up a high performance engine will never be "worth it" except as a hobby. You can spend thousands of dollars and countless hours to get the ultimate power from your motor and then more dollars and time on optimizing the chassis and tires, yet any modern sport motorcycle will run away from you in a drag race or run through the twisties.
Since you're doing a rebore anyway and will have the head off, I would match the ports to the carb spacers and smooth out the casting marks a bit but major porting would be a waste: it just dares you to do other things to justify it... oversize valves, big carbs, freeflow exhaust, a real big-bore kit (and Carillo rods so your engine doesn't grenade), hot cam (and special springs plus lighter valves with titanium retainers in new guides), high flow oil pump, oil cooler... the list and the associated pricetags goes on and on.
Step onto this path with trepidation... insolvency and divorce are not far.

[Scott S]

 And I agree....

 I learned a lot from my Hi-Po VW days. I have a '63 with a huge stroker motor, awesome heads, big cam, tight gears, etc. I went back into that engine a few times to "dial it back". Big HP is fun, but often useless on the street .
 The last VW stroker I built was a toned down mid-range torque monster that idled like stock and pulled like a monster truck. Big fun.

 I need an overbore anyway. I have the CB650 cam, which is a mild and popular upgrade. I'm mostly concerned about how much, if any, head work is really needed for a mild street bike.

[Scott S]

 Looking into the intake valve seat. Almost no ledge between the port and the seat like I've seen in other pics.

[Scott S]

 Little bit of casting "boogers" on either side of the guide hump.

[Scott S]

 Another shot of the stuff around the guide.

[Scott S]

 Port match on manifold....nearly perfect.

[Scott S]

 What you're seeing in the pics of the manifold and ledge at the valve seat are mostly shadows. If I run my finger across the edge of either of them, I feel an almost imperceptible edge. Very, very close match on both of themright from the factory.