Topic: Engine Building Goals

[MRieck]

Engine building goals... to make a lot of noise and kick some hitech ass on
the way.Simple as that

You doing that all by yourself Juha???

[Leino]

You doing that all by yourself Juha???

Nope.Some weird fellow from Boston is helping me occasionally... 
Most of the time I mess things up and he solves the problems. 

[JMURACN]

Well I'm currently working up two builds almost at once.

Motor1: (it will be purchased next weekend from a salvage yard)
stock CB750
stock carbs with pods
custom 4:1 dump exhaust
obviously it will be tuned and the jets redone.

the object is just to get the bike a running motor asap.
-----
Motor2: (to be bastardized from three non running motors i have in the garage)
836 kit
stock carbs with pods
mild cam
port and polish
deck the head (just a smidge to make sure its true)
custom 4:1 dump exhaust
heat coat exhaust valves and piston tops
low friction coat the cylinders, bearings, and cam

i'd like to get a little more "top end" but really keep the mid range beefy.  I commute to work just about every day on a bike.  Every day i battle traffic with the old men and hippies in their econo box hybrids.  I dont really want to invest the money in the head to get it to spin nice and high... i log too many miles on my bike in a given year to have to keep replacing titanium valve retainers (yes they are a wear item... at least they are in cars!) and things of that nature every year.  A nice stock redline with some more scoot should do the job. 

plus next years winter project is going to take the 836 motor and add a snail

The goals of my CB build is to meld the classic cafe look and style with modern technology into a bike that best suits my personality... well that and i'm pretty sure my dad is going to drop on off at my house one day and have me just restore it will the millions of parts i am not using from my CB build.

[mlinder]

Many bikes run 11:1 or 11.5:1 on street gas. I'm not terribly worried about it.

   Here in California, street gas only goes as high as 91 octane. This seems to be just at the margin of compatibility with my 10.25:1 pistons with .012" decked off the head (sorry, don't know final comp. ratio). Just did a test yesterday and bumped to 93 octane using Toluene, man what a difference

That probably puts you over 11:1, if you haven't changed the heads combustion area.
I'll be getting some (hopefully good) advice on exact chamber shape for the pistons I will be using to make this very high compression on 92 octane possible.

[scondon]

Many bikes run 11:1 or 11.5:1 on street gas. I'm not terribly worried about it.

   Here in California, street gas only goes as high as 91 octane. This seems to be just at the margin of compatibility with my 10.25:1 pistons with .012" decked off the head (sorry, don't know final comp. ratio). Just did a test yesterday and bumped to 93 octane using Toluene, man what a difference

That probably puts you over 11:1, if you haven't changed the heads combustion area.
I'll be getting some (hopefully good) advice on exact chamber shape for the pistons I will be using to make this very high compression on 92 octane possible.

  The 91 octane is "do-able", just requires a lot of carb fiddlin' and running out of the optimum AFR/ignition timing. And really, I am just a finicky bastard when it comes to getting all I can out of a performance built motor. California is the only state that doesn't go higher than 91, as far as I know. Whenever the talk turns to high comp engines running on pump gas I feel it's my duty to put the *results may vary in California* in

   I've often felt compelled to move out of state just to get 92+ pump gas on a daily basis. If only I didn't have to give up all this fresh, sea level oxygen and thousands of miles of good , twisty roads

[paulages]

i just read an article about brazil and their sugar-cane ethanol industry. 115 octane at the pump.  now that would be nice.

mark--i'm guessing you're gonna want a dyna 2000 with compression that high, so you can dial in the advance curve.

[mlinder]

I dunno Paul, I'll see how it does on the dyna-s with my homemade rev limiter. If I have to get the 2000, then I guess I will eventually.

[scondon]

  If that homemade limiter works with the Dyna-S then I'll take a dozen

[mlinder]

Well, I'm trying to figure out if my simple way of limiting revs is the best.
I'm just going to have it cut power at the limit. No more power.
Dyna makes a rev limiter, but it says it "randomly deletes ignition pulses to hold the engine exactly at the desired rpm".
Dunno if I have the skill to emulate this. Dunno if it's necessary. I just don't want to blow up my engine again. Cutting power would keep the engine safe, at least.

[MRieck]

I dunno Paul, I'll see how it does on the dyna-s with my homemade rev limiter. If I have to get the 2000, then I guess I will eventually.

I think it will be case. You will need some control over the advance curve.

[eurban]

Compression ratios of 11:1 and higher are common place on modern water cooled engines that have alot of engineering invested in being detonation resistant.  In my experience on my 836 10.25-1 cr engine (78 750K engine as the starting point) detonation isn't far off even with 93 octane gas.  I use a Dyna III by the way.  Installing colder plugs, retarding the ignition timing a bit, fine tuning the carburetion, and installing an oil cooler has pretty much taken care of things but I will eventually upgrade to a Dyna 2000 I think.  Like I said before CRs approaching the 11:1 range in the SOHC type engine would seem likely to require gasoline with a higher resistance to detonation than is typically available on the street. . . .

[Bodi]

Re rev limiter - completely cutting the ignition is not good.  A lot of fuel will get passed into the exhaust in a short time at high throttle/high RPM (when you'd need a rev limiter...) and it will be ignited as soon as the revs drop and spark is restored. This can really explode your muffler (with shrapnel and a fireball).
There are two ways to do it with carbs (EFI can easily skip injector pulses). Either retard the ignition or skip every second or third ignition pulse. Both will create a lot of extra heat in the headers but there won't be any damage unless you ride on the limiter for a long time.

[MRieck]

Re rev limiter - completely cutting the ignition is not good.  A lot of fuel will get passed into the exhaust in a short time at high throttle/high RPM (when you'd need a rev limiter...) and it will be ignited as soon as the revs drop and spark is restored. This can really explode your muffler (with shrapnel and a fireball).
There are two ways to do it with carbs (EFI can easily skip injector pulses). Either retard the ignition or skip every second or third ignition pulse. Both will create a lot of extra heat in the headers but there won't be any damage unless you ride on the limiter for a long time.

Yes. Absolutely correct.

[mlinder]

Re rev limiter - completely cutting the ignition is not good.  A lot of fuel will get passed into the exhaust in a short time at high throttle/high RPM (when you'd need a rev limiter...) and it will be ignited as soon as the revs drop and spark is restored. This can really explode your muffler (with shrapnel and a fireball).
There are two ways to do it with carbs (EFI can easily skip injector pulses). Either retard the ignition or skip every second or third ignition pulse. Both will create a lot of extra heat in the headers but there won't be any damage unless you ride on the limiter for a long time.

Roger that.

I think I can handle that.

[seaweb11]

.....and we need all this why?

[mlinder]

.....and we need all this why?

.......what?

[paulages]

.....and we need all this why?

i don't need nothin but a pair of sandals and a toga, man.

[seaweb11]

.....and we need all this why?

.......what?

rev limiter

[paulages]

.....and we need all this why?

.......what?

rev limiter

mark wants to build a cb750 engine that will spin to 13 grand. guess he doesn't want to slip the clutch and blow up his new motor like he did the last one. not a bad idea if you plan on pushing the red line at all if you ask me.

[mlinder]

Oh. Yeah, what Paul said.