Topic: Worth the $ to bump compression from 9 to 10.5?

[eworth]

Hey all,

Here's where my project stands and I'm interested in all your opinions on whether the next step is a waste of money.

1977 CB550F.  CB650 Cam,  Heads ported and matched to the intakes, 4-1 Jardine exhaust and Dyno S ignition.

The top end is apart and the above is just about done (Head will be back soon)

How much extra "Kick" am I going to get buying the Dynoman 592cc pistons / 61mm bore??

Is it worth the $800 or so dollars for the kit and cylinder work to make it happen?

How much difference should I expect in horsepower going up to the 592 from the improvements above that already been made?

Is this a waste of money or would there be a significant boost in hp and torque?

Thanks all,
Mark

[dave500]

with the crappy fuel you get in the states i wouldnt go high with the compression.

[Stev-o]

I wouldn't do it, not worth the cost.

By the way, are you planning any suspension or brake improvements?

[luap]

looking at those last night on that website your 650 wont work, you also need to buy the cam he sell another what 250 bucks an then I believe the stock valves wont "work" either another 80 bucks an then the stock retainers wont  work again need the machines stainless ones he sells for 180 bucks, seems like one works off the other

[eworth]

Thanks Daven and Steve-O.      Had been on the fence and then started second guessing my decision to go through with it.

Steve-O.   Front brake rotor drilled, rebuilt caliper, new pads and new upgraded master cylinder and SS lines.   Rear is stock.

I'm thinking just the 650 cam and headwork will be a nice boost.     

 

[bwaller]

Let me offer this, take from it what you will. Someone here years ago planned to increase the power of his fairly low mileage 550 and ran it on the dyno first...36.8rwhp. I never saw that he returned with an "after" report.

I did up a 592 with 10.1:1CR, matched the inlet tracts plus did some mild porting, added a WebCam 58a, modified the cam sprocket then degreed the cam. It uses the stock PD carbs plus the air plenum (no box) with a single large K&N. It has a 4-1 also. The result is 51rwhp, a 28% increase in this case.

To just install a bigger bore without cam and/or head work will not live up to the power expectations. As an alternative, to tidy up ports with a different cam may deliver similar power to that bore increase alone.

There is an immediately obvious synergy improving the whole package, and done correctly, I don't believe you'll experience any problems at 10.5:1. However if there are wallet constraints, then I think you've followed the best path for the buck. 

[eworth]

BWALLER: 

Your reply is really appreciated. Thanks. To this point, headwork, port match, 4-1, Dyna S and CB650 cam will be a nice improvement.  Glad I chose well. 

Sounds like our set ups are similar except for compression and bore size increase.

I'll never race this engine but did want a bit more "uummmphh" out of her.     Maybe I'll just put her back together and see how it feels.     Can always do the 592cc upgrade down the road if I'm not satisfied in the current set up.

Cheers, Mark

[Stev-o]

Or sell and upgrade to an 836!  (that's what I did)

[eworth]

oooooooo, tempting........ but I love my CB550.   

[Stev-o]

oooooooo, tempting........ but I love my CB550.   

And I miss my 550F. Will probably sell my K4 (not the 836) when I find a 550 that I have to have!

[eworth]

They just nice little engines and they sound great too!!

[Rgconner]

Might want to check out some of the recent posts about DynaS and problems with wiring:

http://forums.sohc4.net/index.php?topic=98305.0

and failures:

http://forums.sohc4.net/index.php?topic=98483.0

There are several other ignition options available, some made by members of the forums.

[eworth]

I've run the Dyna S since  April.  No problems yet.  But thanks I wlll check out the posts  you mentioned.