Topic: How'd they do it?

[eldar]

Well clearly, you have not heard of the common 836 conversion. Standard comp is 10.25:1 or so. Just as reliable as stock if you do it right. And you will think, "yeah if done right" but that applies to everything. If you do crap work on a stock engine, it will fail just as easily as anything else. Comp can be increased on our engines as mike and hondaman have said before. With the experience they have, I am inclined to believe most of what they say.

See the problem in not increasing comp, it is find the balance between the comp and heat output. Besides, oil can dissipate ots of heat if cooled properly. Add an oil cooler on the filter, then maybe change the line to provide more cooling.

Point is that there are things that can be done and HAVE been done to increase the comp on these engines.

Why dont you check with elcheapo, he has done some "mods" to his engine such as punching it to over 1000 cc. That removes metal that was used for heat dissipation. He must not have any problems with what he's done, He may not have increased comp but he removed cooling material which in essence will work the same way with heat.

hondaman has reported on a sohc 750 which was able to make 150 hp. that would have required and increase of comp. It was posted here some time ago but I am sure you could ask him about it.

So now that higher comp has been successfully done, reliably, what now? Do you still deny that increasing comp is possible on our bikes? Maybe not so much on the 550 but the 750 is probably one of the most modified engines ever made.

[Noel]

Hey Dusterdude, I hope you're not talking about me. I think stock bikes -- and especially stock SOHCs -- are boring as hell.

But I also think that mods ought to be practical, reliable, and serve some kind of purpose.

[Noel]

Well clearly, you have not heard of the common 836 conversion. Standard comp is 10.25:1 or so.

Maybe I'm imagining things, but it seems that a mildly negative tone has crept into this. I hope not.

At any rate, not being a complete moron, I have heard of the 836 conversion and am aware of the mild increase in compression that goes along with it. At no point have I said that it's impossible to increase compression or that it should not be done.

See the problem in not increasing comp, it is find the balance between the comp and heat output. Besides, oil can dissipate ots of heat if cooled properly. Add an oil cooler on the filter, then maybe change the line to provide more cooling.

  Agreed. And thank you for at least not arguing that increasing compression does not increase heat output.

So now that higher comp has been successfully done, reliably, what now? Do you still deny that increasing comp is possible on our bikes?

Again, I NEVER claimed that CR cannot be increased in an SOHC. My argument is that increasing CR increases engine heat, and that at some point that heat must be dealt with. Somewhere in the neighborhood of 11-1, heat becomes a very serious problem with an air cooled engine, especially one with antique combustion chambers and long heat pathways. 12.9-1 is, IMHO, far too much for an SOHC Honda and will result in overheating, detonation, and engine destruction within a very few minutes.

Now, I could be wrong, as the only information I have on this topic comes from reading and talking to knowledgable people. If someone can SHOW ME a 12.9-1 air cooled SOHC Honda engine that runs reliably for hours at a time, then I'll have no choice but to believe it.

[dusterdude]

Well clearly, you have not heard of the common 836 conversion. Standard comp is 10.25:1 or so.

Maybe I'm imagining things, but it seems that a mildly negative tone has crept into this. I hope not.

At any rate, not being a complete moron, I have heard of the 836 conversion and am aware of the mild increase in compression that goes along with it. At no point have I said that it's impossible to increase compression or that it should not be done.

See the problem in not increasing comp, it is find the balance between the comp and heat output. Besides, oil can dissipate ots of heat if cooled properly. Add an oil cooler on the filter, then maybe change the line to provide more cooling.

  Agreed. And thank you for at least not arguing that increasing compression does not increase heat output.

So now that higher comp has been successfully done, reliably, what now? Do you still deny that increasing comp is possible on our bikes?

Again, I NEVER claimed that CR cannot be increased in an SOHC. My argument is that increasing CR increases engine heat, and that at some point that heat must be dealt with. Somewhere in the neighborhood of 11-1, heat becomes a very serious problem with an air cooled engine, especially one with antique combustion chambers and long heat pathways. 12.9-1 is, IMHO, far too much for an SOHC Honda and will result in overheating, detonation, and engine destruction within a very few minutes.

Now, I could be wrong, as the only information I have on this topic comes from reading and talking to knowledgable people. If someone can SHOW ME a 12.9-1 air cooled SOHC Honda engine that runs reliably for hours at a time, then I'll have no choice but to believe it.

noel,not throwing stones at anyone in particular,just some folks get uptight when the modification threads show up.

[eldar]

Well of course increased pressure increases heat. Adding pressure to almost anthing will increase heat.

If the engine was staying stock and you increased comp, then yes, the engine could only handle so much but you cant increase comp without modifying the engine. mods usually include modifying the heads thus changing the combustion chambers which can then modify how heat is transfered.

One thing though, would you believe anyone if they said it could be done or could show you specs? Or would you need to see the actual engine being tested? cause no one will bringtheir bikes thousands of miles just to show you. You need to find your middle ground on this.

While I myself would never mod my engine that much, an 836 will be happening sometime with head work and such. I do not see heat as much of an issue.

it all comes down to finding the middle ground for everything. the middle ground just changes with different engine designs. That is where the main problem lies.

[Noel]

Ayuh, Duster, I've noticed that. And I don't really have anything against the folks whose idea of fun is to restore and maintain bikes to absolute factory spec. We ought to have a few museum quality bikes around.

I'm just not one of those folks. I love to see a bike modified to suit the individual owner's taste.

[Noel]

One thing though, would you believe anyone if they said it could be done or could show you specs? Or would you need to see the actual engine being tested? cause no one will bring their bikes thousands of miles just to show you. You need to find your middle ground on this.

Whaddya mean, no one will bring their bike thousands of miles to show me? I'm the center of the universe, dammit!

Seriously, I have no reason to distrust any of you guys. If you have one of these engines or have done this (12.9-1) to one of these engines, tell me how you did it and what the results were and I'll shut my face hole. It's just that, as of now, everything I know about these bikes -- and engines in general -- tells me that 12.9-1 is way too much compression for an old air cooled SOHC.

While I myself would never mod my engine that much, an 836 will be happening sometime with head work and such. I do not see heat as much of an issue.

Me either. The road racers are going as high as 11-1, reliably. I have no doubt that 10.5-1 or thereabouts is no real problem, especially if you run an oil cooler.

it all comes down to finding the middle ground for everything. the middle ground just changes with different engine designs. That is where the main problem lies.

I don't disagree with that at all. A few millimeters of overbore, a touch more compression, a cam with a bit more duration... great mods. Punch it up to 1200 CCs, 13-1 CR, and a lumpy cam with a bunch of lift and you've got an unreliable monster with a 500 RPM power band and holes in the pistons.

IMHO, as always. 

[MRieck]

More heat=more power

My point was/is engines are basically heat pumps...period. If an engine doesn't make good combustion heat it does not make power. Engines love compression/heat, right up till the time they explode....always making more power. Guys who ran/run alcohol know this. They can/need to run a lot of compression and run cool. You need to pump a lot of alcohol in there though. Shedding heat is another subject

[Sam Green Racing]

They allways run best just before they blow up. 

[Pinhead]

My point was/is engines are basically heat pumps...period. If an engine doesn't make good combustion heat it does not make power. Engines love compression/heat, right up till the time they explode....always making more power. Guys who ran/run alcohol know this. They can/need to run a lot of compression and run cool. You need to pump a lot of alcohol in there though. Shedding heat is another subject

That may be true, but there are ways to kep that heat from being absorbed into the engine. Basically if an engine was 100% thermally efficient, all of the heat created in combustion would be used to expand the nitrogen in the air to push on the piston. Gasoline endines are nowhere near 100% efficient, but there are ways to push them to higher efficiency than their original design. Basically, the quicker you can get the fuel to burn, the less of that heat will be transfered to the engine. That's what I was trying to get at. And I'm wondering what we would have to do to our engines to make it burn more quickly. Adding squish would be one way. I'm just not sure exactly how to do that, short of welding in the combustion chamber (which is WAY beyond me). Overboring the engine so the pistons would be bigger than the combustion chamber would make a squish "ring" around the ouside of the pison. While this would definately be advantageous, I'm not sure if there's piston kits for my particular engine ('79 CB650). Getting the fuel to burn more qickly will help with thermal efficiency and higher compression ratios aids in raising chemical efficiency.

[MRieck]

Getting these engines more efficient is tough.Welding up the chamber into a bathtub shape might help but you'd need special pistons. Branch does this for big twins BUT there are problems...one is you can only use his pistons. The other is after pouring all that heat into the head it makes it soft as goose #$%* and all sorts of stuff can happen (like valve seats dropping out of the head). His heads run very hot as the Harley heads have limited heat shedding capacity. A second  sparkplug would probably help the Honda head but there is no feasible way you can do it. Changing the included valve angle would help but that's harder than adding a second plug. You are right about larger bore improving squish. It also improves intake fill as the cylinder wall is further away from the intake valve. I think the best we can do is smooth the chamber, mill the head and deck the cylinder. I spend time working on the piston dome too. Coatings for the piston crown, skirts and chamber work well too as long as the people applying it are good.

[turboguzzi]

http://www.motorcycle.com/mo/mctext/h_hon.html

although its about a CB500 dohc twin, this article shows the extent of work needed to perform at really high levels
with an old two valve design

fast two valve moded heads I've seen in old ducati 450's were indeed welded up to bathub shape

would give an arm and a leg to get the 60 hp from my cb500 FOUR that todd's was getting from his TWIN

not planning to go that far with CB500f racer

[MRieck]

http://www.motorcycle.com/mo/mctext/h_hon.html

although its about a CB500 dohc twin, this article shows the extent of work needed to perform at really high levels
with an old two valve design

fast two valve moded heads I've seen in old ducati 450's were indeed welded up to bathub shape

would give an arm and a leg to get the 60 hp from my cb500 FOUR that todd's was getting from his TWIN

not planning to go that far with CB500f racer

i've seen Todd's stuff up close and personal and am good friends with 2 of the men that made it happen. I'm not braggin but......I'm going to take some pics for you turbo of stuff that will interest you.....I promise! I should be able to post them tomorrow.

[Pinhead]

After reading through all of the posts, I'm not sure if I made myself completely clear. I'm not necessarily trying to push a SOHC4 Honda to 13:1 compression... I'm just wondering what they did to deter detonation, and if any of those methods could be used on our SOHC4's. I wold, however, like to run 10:1 or 10.5:1.

[MRieck]

After reading through all of the posts, I'm not sure if I made myself completely clear. I'm not necessarily trying to push a SOHC4 Honda to 13:1 compression... I'm just wondering what they did to deter detonation, and if any of those methods could be used on our SOHC4's. I wold, however, like to run 10:1 or 10.5:1.

10.5:1 can easily be done. I'd recommend a Dyna 2000 digital ignition first so you can adjust the advance curve. Get your deck height tight with the squish around .045" to .040" and smooth the chambers. Make sure the guides are tight etc so no excess oil gets in. That's easy stuff.....

[Pinhead]

So at 10.5:1 you don't have to worry much about preignition? When does preignition generally start on these engines? 11.5:1?

[TwoTired]

So at 10.5:1 you don't have to worry much about preignition? When does preignition generally start on these engines? 11.5:1?

Depends on the octane of the fuel you are using, and the ignition timing.  (among other things)

[Pinhead]

87 octane, stock CDI ignition advance (electronic ignition on the '79 CB650), stock 4-2 exhaust, stock carbs, stock airbox/filter. I'm going to eventually swap out the mufflers for something a little less restrictive and re-jet the carbs at the same time.

Edit: I'm also planning on adding a large external oil cooler.

[TwoTired]

I think you are going to be on the border with your setup.   You may need to use premium fuel particularly when running hard in hot whether.

My 89 IROC has a water cooled V8 with fuel injection, computer, etc. and 10.5 comp ratio, needs preminum fuel.  It will run on regular if that's all you can find.  But, the computer hears the knock sensor and retards timing and changes the fuel mix to keep preignition and detonation at bay.  Note it also has water cooling to keep cylinder temps cool and constant.

Can you retard your spark to keep it from pinging? (Counter productive to horsepower gains, though.)  Does your CDI have an advance control?  Can you get inside it to change the advance curve?  Do you know what it is now?
Your stock carbs do not have "In Operation" mixture control.  Your cooling system (the fins) don't adjust for engine temperature  (Which will be making more heat with the higher compression, and higher power output).

Kind of a guess or extrapolation on my part, but if you are going to insist on regular grade fuel, I wouldn't try more than 10:1 comp ratio, and jet your carbs on the rich side from the start, lean later.  Colder plugs may also help.

Cheers,

[dusterdude]

aaaaaah,another freakin bowtie.god help us.

[eldar]

Well gotta have the bowties around to keep them mopars in line and pull them to the shop when they break down. We all know what trailer queens mopars are!