Header length

mark1122 wrote:

what would i expect to gain ? at low rpms the carbs slide is the restrictor plate? That's would be where i would get revertion ,wouldnt it?
Nascars run wo throttle mostly.arent there plates used for safety,to reduce speed?

You are putting in more fuel then the motor can handle. Yes NASCAR has a big motor with a small restricker plate to slow them. My point was different size intakes have different flow rates. Perhaps it might benifit you to work on the exhaust side of the problem.

mark1122 wrote:

I had my LC at 110 and the intake changed to 112 with the cam stretch. i think i may try 108LC's next.Hopefully the cam has finished stretching.
What were thinking for cam timming?
What is a restictor plate?
why would u think the carbs are the wrong size?
I wellcome sugestions.

I believe closing the intake valve sooner will help with the problem.

You can check out this at Mikuni, it might help.
www.mikuni.com/c-fag.html

Or this is from Isky Cams (It's about cars):


What Causes Intake Reversion?

Two in particular are responsible for perpetuating the "myth" that an earlier opening of the intake valve (even by a mere 2 or 3 degrees) causes the phenomenon known as "reversion". Nothing could be further from the truth! This misconception not only defies common sense, it also establishes a false premise from which other, incorrect conclusions can be drawn. Simply put, those who focus on overlap are on the wrong end of the cam-timing diagram!

Reversion, carburetor/Injector "stand-off" or the general effect of the backing up of the intake Fuel/Air charge normally associated with longer duration high-performance camshafts is actually caused by a Later Intake Closing! How do we know this to be true? The answer lies in the basic principles of physics. For as with geometry and trigonometry, these sacred truths do not change simply because someone chooses to ignore them in an attempt to garner a reputation.

Specifically, when the intake valve opens some 40 or more degrees before T.D.C. at the end of the exhaust stroke, very little (virtually no) exhaust gases remain in the cylinder. The piston is in the vicinity of T.D.C. (only .425" down the hole @40o BTDC - on a typical 350" Chevy with 5.700" rods) and no appreciable threat is posed to the forthcoming intake charge. The "False Reversion Hypothesis" taken to an extreme would lead one to the equally false conclusion that any overlapping of the intake and exhaust valves is totally undesirable. Automotive engineers of the late 1800's and early 1900's used to think this way. They were deathly afraid of overlap, so much so they actually employed "Negative" overlap (minus 5 or 10 degrees) to be absolutely sure none would occur. What was the result? These engines were severely "throttled back" or limited to low speeds and mediocre output. [ Reference: Iskenderian's Tech Article "Cam Degreeing is Simple"] But, more progressive engineers of the early 1920's who performed "brazen experiments" with longer duration cams proved these overlap fears to be only so much "stuff and nonsense", as both power, rpm and performance were actually improved. These engineers demonstrated that overlap did not cause engines to quiver, backfire or lock-up on the spot! Although, the ignorance displayed by their predecessors is easily explained by their lack of experience, (internal combustion engine design being in it's infancy) it was none the less the result of an incorrect hypothesis.

Should you need further persuasion that reversion is not caused by earlier intake opening and the resulting extension of valve overlap, consider this: What happens when you advance any camshaft? The intake as well as the exhaust valves open earlier. Does this advancing of the cam cause more reversion? Of course not. Throttle response and torque are enhanced. Yet, if these theories were correct wouldn't the engine run more poorly, especially at lower RPM? The answer is obviously yes, and because so, these theories are invalid. A brief look at what's happening on the other end of the valve-timing diagram will tell you why.

For when a camshaft is advanced, not only do both valves open earlier but they of course also close earlier - and here in lies the key to reducing Intake Reversion. Close your intake valves earlier and any tendency for the occurrence of Reversion or the backing up of the intake charge as the piston rises on the compression stroke will be reduced. It's not complex, nor is it a mystery. And the circumstances surrounding it's occurrence have not changed. In fact any experienced mechanic could tell you as much, for, as Ed's good friend the legendary Smokey Yunick might say, "Only country smarts are required to solve the problem."

Those are interesting articles and i agree with them.
what they don’t talk about is the exhaust wave. my train of thought has me thinking that the exhaust wave or pulse comes back through the intake during overlap. it is this pulse that pulls the intake charge into the cly. at the right rpm (higher) this helps at another rpm (lower)it will hurt since there are positive and negative waves, and the negative wave will push the intake rather than pull it. Have I got this right?
I still don’t know, if i really, even have a problem. I’m more curious for an explanation of the DIFFERANT AMOUNTS of color in the runners. as reported buy others above, it is common to have discoloration in the intake runners. Do u agree? I don’t have the experience to answer that.
as i mentioned the cam chain stretched. this changed the torque. I felt the bike had less torque.
If I put the cams back to 110 the torque should come back.
I have old RC400 cams. .425” lift. Timing is 20,60 and 260* duration. They are recommended to be set at 108LC.
Larry Cavanaugh ported my head for 34mm carbs.
I have 37.5 intakes(1.5 over stock.) .
My head flows at 155cfm @28” @ 500” lift.
A stock kz is 113.5cfm
J= 117cfm
GPZ = 139cfm

mark1122 wrote:

Those are interesting articles and i agree with them.
what they don’t talk about is the exhaust wave. my train of thought has me thinking that the exhaust wave or pulse comes back through the intake during overlap. it is this pulse that pulls the intake charge into the cly. at the right rpm (higher) this helps at another rpm (lower)it will hurt since there are positive and negative waves, and the negative wave will push the intake rather than pull it. Have I got this right?
I still don’t know, if i really, even have a problem. I’m more curious for an explanation of the DIFFERANT AMOUNTS of color in the runners. as reported buy others above, it is common to have discoloration in the intake runners. Do u agree? I don’t have the experience to answer that.
as i mentioned the cam chain stretched. this changed the torque. I felt the bike had less torque.
If I put the cams back to 110 the torque should come back.
I have old RC400 cams. .425” lift. Timing is 20,60 and 260* duration. They are recommended to be set at 108LC.
Larry Cavanaugh ported my head for 34mm carbs.
I have 37.5 intakes(1.5 over stock.) .
My head flows at 155cfm @28” @ 500” lift.
A stock kz is 113.5cfm
J= 117cfm
GPZ = 139cfm

You can look at ( www.boatheaders.com/reversion.htm ) this talks about about the exhaust wave. 110* is retarding the cam from what RC designed them for. You might think about 106* L/C. You have a head that is ported to run wo! The cams are mid size by todays standards. You may have to live with the problem. I had the same problem on a smaller motor. It's just a loss of efficacy at some lower RPM's........Just keep it WFO!

WFO! YEE HAA!.That is where i useualy end up.Lets face it if u want to accelorate where does your wrist go? WFO.
I realy enjoy getting deep into subjects like this and learning all i can about what makes these thing tick.
Do u have any coments on why the intake runners may have accumulated differant amounts of reversion?
I'm thinking exht tube length diferances?
Can it be cause on the intake side from improper carb sync?

mark1122 wrote:

WFO! YEE HAA!.That is where i useualy end up.Lets face it if u want to accelorate where does your wrist go? WFO.
I realy enjoy getting deep into subjects like this and learning all i can about what makes these thing tick.
Do u have any coments on why the intake runners may have accumulated differant amounts of reversion?
I'm thinking exht tube length diferances?
Can it be cause on the intake side from improper carb sync?

I have no clue, every cylinder is different, the same as every motor is different. If we could only get them to run the same (100%) boy would we have some power. Once the ports are clean try it again, I think the timing change will clean it up or reduce it. It's like Smokey Yunick said "One test is worth a thousand expert opinions" He believed in keeping it simple. I like to keep a couple of different old beatup exhaust pipes laying around. I try each one to see witch one works the best for performance. Most of the time it's the one I least expect, works the best. You can do the math until the cows come home, it doesn't mean it will work best. I don't think carb sync has anything to do with it at all...

Just wanted to say keep this conversation going cuz im learning ........thanks guys

School Teacher wrote:

Just wanted to say keep this conversation going cuz im learning ........thanks guys

I was starting to feel bad because Mark & I have used up the whole page. I thought maybe we should of PMed each other. If no one has a problem with it, I hope the conversion will continue. I hope others will join in. After all, what do we know?

I had heard that Smokey Yunik had a very good book to read with good info on timing. i looked it up on the web and they wanted $52 = $10 shipping, so i didn’t buy it. I ended up getting Kevin Cameron’s book, Sprotbike performance. It is a good read. it tells how the motors frames and suspension have evolved over the years. it is very interesting.
Did u know that the GP bikes have GPS's on them that are tied to the ignition computer? this allows them to automatically adjust the timing differently for every corner of the race track. this allows the rider a smoother transition from braking to acceleration out of the turn, so they don’t brake the tire loose with too much power.
Some pretty cool stuff.
Our old KZ'z are so out of it. but that’s what makes them so sweet. we can still work on them ourselves, with limited knowledge and equiptment.

Mark

I have a couple of more questions for you. I just want to get my head wrapped around this before I let it go.

When you said that the intake cam had moved to 112* lobe center. Did the exhaust cam move any or the same amount? What was it's lobe center?

I just wanted to do some of my Hillbilly garage math.

The lobe centers were 110 each . The intake moved to 112 but the xht stayed at 110 for some reason? doesn’t really make sense that 1 would move and not the other , does it? maybe i screwed up when i set them or re-measured ??
Once i get the head back and figure out what squish I’m going for, i will reset the LC anyways.
i had trouble going to smaller lobe centers due to the valve to valve clearance. Larry has sunk the exht valve a bit more now. so i will check the v to valve at 105 lc up to 111 and at varying LC settings. This will give me the data i need down the road, so i can change the LC to what ever i need, without checking the v to v again.
As for squish, i learn some thing every time i take this motor apart. I measured the base and head gasket and the base had squished from .020" to .012". The last one had only swished to .018"
The had gasket went down to .038" - .040" from about .050" new.
My previous hd gasket only squeezed down to about .044”
The hd gasket I just bought measures .045 but says .043” on the package??
So I thought I had a squish of .048” when in fact I ended up with .036”.
I measured the squish after assembly and toque and got about .050” using solder. But after running and re-torqueing it squeezed a lot more than expected and when I rechecked the squish with solder I got only .036”
So what I have learned is that the gaskets don’t always end up the same thickness. I will have to account for this and be more generous with my squish clearance.