Topic: CB650 Surface Turbulence™

[Pinhead]

I've finally started acquiring parts for my '79 CB650 rebuild project for the winter. A lot of people will probably call me crazy but I decided that Metric Mechanic's Surface Turbulence™ will best help me meet my goals.

My friend and I left Kansas City Saturday morning at about 9 am. About 200 miles. We took our time, stopping more than a few times to stretch our legs and enjoy the ride. We got to Metric Mechanic's shop at about 3:30pm. Hell of a guy. He showed us around the shop, showed us a few of his specialty pistons (and boy are they special!), showed us some cylinder heads and explained what they do. After it was all said and done, I got my cylinder head bead blasted, cleaned up the bowls and short sides of the ports, and added Surface Turbulence to the chambers. My valves were converted to ST valves as well and the piston piston tops will get the same treatment as the valves (done by me, though). We finally left at about 7:30pm. He could've gotten the job done a lot faster if I weren't asking so many questions.   Unfortunately I don't have any before pictures, but you should be able to easily spot the modifications.

EDIT: This project has evolved much further than I had initially planed. I'm running '78 CB750 pistons with Surface Turbulence domes machined by Soos. I've also installed Surface Turbulence valves, ST modded combustion chambers, and Power Lynz'd intake ports. I've omitted the cylinder base gasket to raise the compression a hair, and tighten the perimeter squish in the chamber.

Compression ratio is between 10.5:1 and 10.7:1.

Ultimate goal: 100mpg at highway speeds and more power than stock. 

I'm doing all of the mods outlined in THIS thread.

[KingCustomCycles.com]

Smooth vs. turbulated combustion chambers....the mystery lives on.

[Soos]

Interesting...

Have come across this post elsewhere.
Are you doing a before and after dyno runs or anything to compare against?

Interesting to say the least.
I don't see how it would hurt, or hinder performance, not sure whether it gives a gain. Never tried it(yet?  )
Post the results either way good or bad.


I would watch for carbon buildup on those ridges.
Mabey pull a spark plug once every oil change and inspect the piston near TDC.
Carbon buildup can turn into pre-detonation over time with a lean engine.


l8r

[Pinhead]

I don't think a before/after dyno run would be fair because it would be comparing against a worn engine. However, it would be easy to compare the after results to a typical stock stock CB650. I won't be changing the cam or pistons so the only difference will be the chambers, valves, and piston top surfaces. Also note that I'm not necessarily aiming for better power; efficiency is my ultimate goal.

[Soos]

100mpg is what you're shooting for right?

Good luck!
I hit 60+mpg once with the stocker carbs, nothing modified on my 650... before I started tinkering with it. 



l8r

[Soos]

SO any progress with this pinhead?



On the note of efficiency, would a cb550 cam in a 650 motor help with MPG?


l8r

[cb650]

Or the German low profile cam.   I have gotten a best of 67  but usually 57 or so.

[Pinhead]

Not much progress yet... I need a few things before I get everything buttoned back up. Specifically, a small valve spring compressor, all of the o-rings, and a thinner base gasket to raise the compression and squish just a hair. It's been slow-going this winter since higher priority projects, such as replacing a blown tire on my pickup, have taken precedence.

[Pinhead]

I'm finally getting my CB650 put back together but ran into a little snag... I lost one of the inner valve spring seats (tiny flat washer). It's the ONLY part I need to finish rebuilding my engine!

PN 14776-107-010

It's the same PN as the CB500/550.

I only need one and am trying to get it before Tuesday when I can work on the bike again. None of the bike shops in the area are open on Sunday or Monday so I can't go pick the part up. Ordering it online would get it here after Tuesday unfortunately. :/

Does anyone in the KC area have a spare they'd be willing to part with?

[Pinhead]

And some pictures for those who are interested... These are the intake ports.

The modification is called "PowreLynz" which were developed by Mike Holler (mpgmike on various forums). The modification greatly increases fuel homogenization and vaporization, and therefore increases efficiency and lowers detonation tendency. So much for "polishing" the ports.   

Sorry about the quality; my phone isn't good at taking close-ups.

[cb650]

If I have one handy I'll mail it out to you.    I'll look when I get home.

[Pinhead]

Thanks man!

[Pinhead]

It's amazing what progress can be made with 4 hours of work.  

[Pinhead]

I got the bike 99% put together and got it back home... And then it rained ice and snowed. Here's the most recent picture thus far.

Things left to do:

• Install Ignitech Ignition
  -Build brackets to mount Ford COPs
  -Install GM MAP Sensor for Vacuum Advance
  -Program Optimal Ignition Curves
• Find optimal Jetting
  -Lean out idle
  -Slightly lean Cruise
  -Maintain WOT mixture
• Re-Wire Alternator
  -Install 3-phase rectifier to replace existing 2-phase rectifiers
  -Relocate Regulator to make room for Ignitech box

[Pinhead]

I decided to run GM HEI coils instead of the Ford COPs since the COPs stuck out too far and looked like crap. The Ignitech ignition allows me to select between high and low resistance coils. Two coils came out of an early '90s Chevy Cavalier to light the fire which throw a LOT bigger spark and should widen the A/F tuning windows.

So far I can see that I don't have to run the choke for nearly as long as with the stock ignition. I haven't yet widened and side-gapped the plugs which should help even more.

[Pinhead]

I got the GM HEI conversion 99% done; all that is left to do is decide on plug cap resistor values. I'm currently thinking 10k ohms or more on each plug cap. The HEI has plenty of power available to use a high resistor value which lengthens the spark event. This will more consistently ignite leaner mixtures.

If anyone was ever worried about their spark not being strong enough, go with a GM HEI conversion. These coils easily throw a big, fat, bright blue, two-inch spark when the wires are disconnected from the coils.

[Pinhead]

I got a relatively undeveloped ignition map made for the bike and took it for a spin today. I initially had some slight pinging between 2500 and 3000 rpm in 4th when rolling on the throttle. A few changes to the advance map and the ping is gone. I'm running the stock centrifugal advance (10° initial and 28° at 2800 rpm) and am adding advance in the map on top of that. Got the rev limiter set to 10,500 rpm.

It seems like there is a slightly lean spot at about 3/4 throttle but above and below that throttle position runs great. I may need to increase the main jet by a size or two and lower the needle, though these carbs don't have adjustable needles. Other than that the bike runs really well. The very low RPM performance is much better than it was before the rebuild; I can take off in 1st at idle (1100 rpm) and not kill it.

Speaking of idle... I've got it to idle as low as 550 rpm (according to the Ignitech's digital tach) though it's not real smooth at that speed and I'd guess the oil pressure is just barely adequate. At 900rpm the idle sounds like a cammed-up V8.

[Pinhead]

I think I solved the lean spot... I forgot to install the carb boot clamps on either side of the carbs. Now it seems almost perfect.

I had to go back to the stock ignition, though; it seems that my Ignitech box took a dump. Stock ignition stil works, but I have to choke it for longer and it doesn't idle nearly as smoothly as it did with the Ignitech/HEI combo.

[Pinhead]

As of today I am running GM coils and 7-pin HEI modules on my '79 CB650 (couldn't find the 4-pin modules at the junk yard).

The idle is absolutely amazing. The bike starts up extremely easily. Very little choke is needed (impressively so, considering the generally "cold blooded" nature of the CB650). The bike can take off in 1st gear at idle without dying. The low-end (1000 to 2500 rpm) is as smooth as my CM400 that has CV carbs.

I'm running Iridium plugs which are gapped at 0.060 inches. As of right now, I'm not using any resistors in the plug boots (the resistor plugs are ~5k ohms each).

With my highly modified engine at 10.7:1 compression ratio, there is no detectable ping even going up a steep hill at 35mph in 5th gear.. Even if I go to WOT. (This is more-than-likely a function of my engine configuration more than the ignition.)

With the stock ignition I would have definitely been forced to down-shift as the engine would bog down otherwise (verified by a ride with the stock ignition earlier today).

I'd say the HEI conversion is definitely worth a try, especially since a pair of HEI modules and coils cost me less than $30 at a salvage yard. 

[cb650]

though these carbs don't have adjustable needles.

Funny u say that too someone argued with me about how they did have adjustable needles. 
When you do the 100 run what speed you going to use?    I've always gotten my best mileage at 40mph in 4th.

[Pinhead]

though these carbs don't have adjustable needles.

Funny u say that too someone argued with me about how they did have adjustable needles. 
When you do the 100 run what speed you going to use?    I've always gotten my best mileage at 40mph in 4th.

I'll probably do a few at different speeds and document each. I suspect the best mileage would be somewhere around 45mph and a little over 3000 rpm (so the ignition is fully advanced).

BUT I'm not running the Ignitech box which means I don't have any vacuum advance. This will be a large contributor in MPG so my initial numbers won't be as high as they could be.

[Bankerdanny]

This is an interesting thread and I look forward to seeing what mileage you get. That said, I can't help but point out (I'm a semi-cumpulsive commenter/meddler  ) that 45 isn't really highway speed.

[Pinhead]

This is an interesting thread and I look forward to seeing what mileage you get. That said, I can't help but point out (I'm a semi-cumpulsive commenter/meddler  ) that 45 isn't really highway speed.

I concur. But it won't hurt to have multiple data points for later optimization.

[cb650]

Nor are the new car ratings at anything near real conditions.   If you out on a 2 lane you could get by at 45.

[Bankerdanny]

Hey, 100mpg at a 45mph average would still be outstanding and probably translate to 70+ at 70+ I bet. Which would also be an outstanding figure for more typical open highway speeds and far better than any car or stock full-size motorcycle.