Topic: Is 34mm the largest intake valve for K head?

[PeWe]

Benchmarking.... CB750 vs Kawasaki 900/1000 from the 70's
Is it the 66mm stroke (+3mm compared with CB750) that make it possible for a Kawasaki Z1 900 to get such raw nice power when tuning them?
 A certain timing making the dual cam to work at best must be possible with a SOHC too, but a fixed setting though. Twin cams with more tuning possibilities adjusting the overlap for the needs, compression....

Or, is it the valve sizes as this thread is about?
Z1 900 std IN valves 36 mm, oz 37.5 mm, Dynoman has even 42mm!!
When comparing, I understand why this thread was created....

[gschuld]

Pewe, 

For reference, here are the OEM valve sizes for other 70s period model 2 valve heads on 900-1000cc factory bikes.  These are dead stock heads for dead stock mild street bikes off the showroom floor, not for heavily modified ported head, light pistons, Carrillo rods, big cam, 1100+cc performance engines.

Kz900-1000. 36/30
Kz1000j.       38/32
Gs1000.        38/32

Cb750 K        32/28
Cb750 f2.      34/31

Clearly, in relation, the valves on our sohc4s are tiny by comparison, especially as the displacement increases.

George

[gschuld]

From the Terry Branch article.  I know, this is dark ages data...  But still interesting

60.3 cfm with round top carb, no intake valve, stock port
71.7 cfm with 32 Mikuni carb, no intake valve, stock port
77.3 cfm with v stack entry, no carb, no intake valve, stock port
58.7 cfm with round top carb, factory stock intake port/valve
73.4 cfm @.450 with round top carb, modified port and stock 32mm valve 
81.5 cfm @.450 with 32 Mikuni carb, modified port and stock 32mm valve
105.6 cfm with v stack entry, no carb, no intake valve after port porting

So, if the ported bare intake port (still only for a stock 32mm valve) of an early k head minus the intake valve itself yields 105.6cfm, that certainly supports the notion that a well ported intake port, even the smaller k intake port, flows far more air than the can get past the intake valve, leaving the intake valve/seat being the main restriction.  Naturally the carb, even a larger carb, is only going to flow so much so that is also likely to be far more restrictive than a well ported intake port in total cfm capability.

Which brings me back to enlarging the intake further than 34mm as a possiblity.

George

[gschuld]

The original Terry Branch article, 1971

George

[TurboD]

I would like to comment that I have seen this old article as well, I have always suspected the results. First they say they are at 12" which is not any common standard and secondly 105 cfm, I don't think so. It takes a pretty decent KZ head with a fair amount of work for those numbers.

[gschuld]

The 105cfm, to be clear, is WITHOUT the intake valve installed.  Just bare open port with a velocity stack smoothing the intake flow at the spigot.

George

[TurboD]

Yes understood. Also understand that in many cases with some ports once the valve is open to roughly .450 or so opening it more and even removing it results in little increase.


George what kind of power (number) wise did "Bear's" engine make?

[gschuld]

He said he was pushing 135 RWHP.  That sure seems like a lot, but he was running high compression on methanol, so I couldn’t even pretend to compare that to regular race gas engines here.

Not sure if the smaller diameter rear tire of his side car racer would have any effect on calculated dyno numbers either.

The 1985 Byron Hines built Gary Pena engine had a straight port modified 410 head.  Reportedly 36mm intakes, not sure on exhaust.  The bike was built around nitrous use so I’m thinking Byron sacrificed  a bit of intake flow for xtra exhaust flow as nitrous needs more exhaust flow.

Still, his very light bar/slick bike ran 9.00 N/A during a brief testing period.  1162cc I think, 9.0 suggests a RWHP level in the 130s.

George

[MRieck]

I would like to comment that I have seen this old article as well, I have always suspected the results. First they say they are at 12" which is not any common standard and secondly 105 cfm, I don't think so. It takes a pretty decent KZ head with a fair amount of work for those numbers.

Yes...I agree....where did he get 12" from. The best I have seen @ .450 is 84 CFM with a heavy port/epoxy floor and 34mm valve. That head pulled 36 CFM @ .100 lift (10") which is great if I say so myself. I call BS too on 105....total BS.
 I could talk about Branch Harley heads too...I have some stories from other fellas I know.

[MRieck]

 And I don't care about bare port flow #'s....you have to put a valve in there and carbs on it.

[gschuld]

I think the point behind the bare port number is to get a feel for how restrictive the port itself is independent of both the valve/seat and the carb and being able to measure the post porting intake tract improvement independently.  Just a data point.

I’ve read previously that the Branch article was flawed.  Thanks for pinning down the reasons why for me.

Mike have you ever flow tested a 410 head like Mark Mcgrew or Bear racer with, with a valve combination of 35/30 for Mark.(says he peaked at 100 RWHP at 762) or (+/-) 36/30 that Bear ran?

I’m just selfishly trying to stimulate a discussion so I can learn from you smart fellas.😉

George

[TurboD]

Ok pushing 135 means to me anything over 130, which I guess is possible on alcohol, certainly not gas, those numbers are approaching all out max effort DOHC Honda numbers.


I agree with Mike, no valve number are useless (again I "suspect" the 105 stuff) Lol. Mike if you are asking me about the 12 inches, it is stated on the one chart. Again agreeing with Mike 85+ cfm @10 would be a killer SOHC head.

[scottly]

And I don't care about bare port flow #'s....you have to put a valve in there and carbs on it.

I wonder how many CFM the open valve guide flows @12"? It would be easy for someone with a bench to measure.

[bear]

Ok pushing 135 means to me anything over 130, which I guess is possible on alcohol, certainly not gas, those numbers are approaching all out max effort DOHC Honda numbers.

I suspect Brent (Captain) might take issue re your opinion on "all out max effort DOHC numbers".

http://forums.sohc4.net/index.php/topic,151860.msg1735291.html#msg1735291

As for our motors I don't give a toss what you think is possible or not.
George asked me what HP our last motor would have put down and I told him.

George,
I have your email, I will answer shortly.

Cheers,
Brian

[TurboD]

I don't remember quoting any DOHC numbers... Those numbers would certainly be the highest I've seen or heard of. Don't really care

As for your numbers. I said it was possible, might want to reread my comment. Either way I don't give a toss, still won't go around the Low buck Turbo. Lol

Cheers Turbo D

[slikwilli420]

How do you decide valve size to balance the suction created by different bore sizes and compression ratios. Obviously a larger bore can swallow more air, but do you get to a point where velocity drops and give cam lift/duration, could you see a loss in CFM?

For instance, Im running a stage 4 head with 12:1 62mm pistons. How does that systems needs for intake size/velocity capability stack up to something that runs the same head but is 70mm? The larger bore requires more air to fill completely, but is there a loss of velocity given the larger bore?

The real question is given the cam, carbs and piston specs, how does one properly size the intake valve for maximum efficiency for the target use?

[TurboD]

How do you decide valve size to balance the suction created by different bore sizes and compression ratios. Obviously a larger bore can swallow more air, but do you get to a point where velocity drops and give cam lift/duration, could you see a loss in CFM?

For instance, Im running a stage 4 head with 12:1 62mm pistons. How does that systems needs for intake size/velocity capability stack up to something that runs the same head but is 70mm? The larger bore requires more air to fill completely, but is there a loss of velocity given the larger bore?

The real question is given the cam, carbs and piston specs, how does one properly size the intake valve for maximum efficiency for the target use?

I am a little unclear as to the meaning of your questions, I will give an opinion to help with answering them.

A larger bore and or stroke (larger engine) will have more velocity in the ports not less. As for your last question, in a NA SOHC racing application one might size up the intake valve and porting work by what the budget allows. The low cylinder head flow is the number one single thing that limits the SOHC. In a racing application I don't think you can over do anything when it comes to the cylinder head.

[gschuld]

How do you decide valve size to balance the suction created by different bore sizes and compression ratios. Obviously a larger bore can swallow more air, but do you get to a point where velocity drops and give cam lift/duration, could you see a loss in CFM?

For instance, Im running a stage 4 head with 12:1 62mm pistons. How does that systems needs for intake size/velocity capability stack up to something that runs the same head but is 70mm? The larger bore requires more air to fill completely, but is there a loss of velocity given the larger bore?

The real question is given the cam, carbs and piston specs, how does one properly size the intake valve for maximum efficiency for the target use?

Matt, the different requirements of head flow from a 762 to an 1162 is significant I would suspect.

It’s one reason I offered the stock valve sizes for 1000cc factory 2 valve heads for a general comparison and reality check.

Both the KZ1000j and the GS1000 had 38/32 valves from the factory.  And when these heads are ported for racing, they use BIGGER valves.

It takes MAJOR surgery to get 38/32 valves in Sohc Honda Head.  And even then, it only matches what stock bikes were running.  So logically, the bigger the cc increase on our sohc4 engine, the more proportionately undervalued they are.  The RWHP per cc potential naturally decreases as displacement goes up with these engines. 

As far as the ideal balancing and sizing of valves and port flow, there are so many parts to that equation that it can’t really be addressed beyond broad general terms I’d suspect.  But regardless, it’s pretty inescapable that these heads are WAY undervalued for big bore engines.

George

[gschuld]

35 will fit but I'd go down to a 27 exhaust to get valve to valve clearance without sinking the valves a lot. You have to change the exhaust seat to  fit the 27 valve.

Mike,

Out of curiosity here, assuming the 28mm exhaust can remain and a 35mm intake can be installed on the factory intake seat IF the intake in sunk down further into the chamber, how would that work out?

To do this:

-You must blend the chamber around the sunken intake valve seat (similar result to the 410 head to a degree?)
-this results in an increased total chamber volume(2-3cc at most I’d think)

But if this is done, will there be any expected detrimental effects on intake flow past the seat as a result of sinking the intake valve/seat down a bit? 

George

[PeWe]

Seats will sink at each refurbish cut, right?  Shim on other side to ensure valve spring preload/ height.
So 34/28 in a K head means close valve to valve?  35mm is "only" 0.5mm less valve to valve clearance. I never checked valve to valve, only valve - piston.
34mm IN valve means 1 mm closer to piston and the other valve compared to stock 32mm.
I guess my engine would love 36/28! Head does not support that....