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Discussion Starter #1
ok, im comparing intakes on my new head, and i noticed its floor is a little higher. in otherwords, the intake port seems a bit smaller. its got a bit of a kink going in a downwards direction toward the valve. the other later model head, has a bigger port, and its straighter. is it better to go a bit smaller with the port, in general, using the same carbs/jets/valves combo...etc.... is this a question that can be answered in general?? i know there is a gas air velocity thats considered. should i be considering this?? i mean, they are both totally stock. would it make a difference since 2 slightly different cams, but everything else is the same?? i dont know what the lift/duration nums are on the 2 different cams. would the factory do this port config becasue of the cam dif?? questions questions. aaron??? jb??

jc
 

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Joe,
Some of the latest thought on ports is smaller is better....as long as it flows enough. In other words if two ports flow the same and one is smaller in cross section then typically the smaller port will produce more power.
Problem is... you have no idea of real flow without putting it on a flow bench. If you really want a proper answer to your question... and it's a good question... then both heads go to a tuner to be put on a flow bench...probably a fairly inexpensive piece of work and would produce some very valuable information for you and anyone else building that engine.
Heads are mucho strange...the guy that did mine puts everything on a computer flow bench...he said some of the things he did to mine were contrary to what one would expect to work.... like in my case actually lowering the floor...normally a no-no. That "normally" word is a killer...every head/cam/valve combo is different and even manufacturers are finding out that there are no hard and fast rules that always apply. I recently read an article about the new Yam 600 heads that actually have smaller intake ports and make more hp.

Unless there are very obvious differences that would clearly indicate a better flow in one head then the only way to find out is hook them up to the bench, valves, cams etc installed and test a various valve openings.

At the very least show them to a head tuner with experience and possibly they could make an educated guess just by looking at them.... I know I couldn't.
JohnnyB

PS. You are correct about the gas velocity thing. Tuners are finding that the increased gas velocity will often over compensate for a smaller port by increasing the overcharge of the cylinder. The higher velocity smooths out pulses and pushes the gas by the valve better.



Edited by - jbranson on Nov 28 2004 05:18:49 AM
 

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Discussion Starter #3
sounds like what i had already guess was true. i figured the port size should be as small as possible to increase velocity, but not affect volume. its all too confusing. i'll have to ask some poel who know these things better. i think there is probably an answer man out there who can tell me abut this specific one. thats interesting though. most peolple talk about pulling out the ceiling, and avoiding the pocket/guide area. not the floor so much. and yeah, i was using general as a general term. not specific to my app.

anyone else?

thanks

me
 

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There was some humorous/sarcastic comment about flow benches on Endyn a while back.
Widmer prepped a pair of heads with small ports for some Nascar team. They "tested" them, and sent them back: "these aren't as good as the ones we have now, you're a jerk".
Widmer cleaned them up, and sold them to another team, who proceeded to beat the pants off team 1.
I wonder, did team 1 fire their engine/dyno guy?
Blair has about the closest engine simulation out there at the moment, and it's too complicated to describe.
How about a professional bench test, you know, "Super-XXX 3 Million" done by geeks in white lab coats? That will tell you how much change occurred in the head's ability to act as an air pump - very useful if you need a bigger air pump.
Will that translate into more power?
They have no idea, but I'll give you a hint: a section of 18" sewer drain showed 50,000 hp on the bench.
Net result: no, you can't tell what it will do.

Need help with your Mikuni VM? Click here:
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quote:
Will that translate into more power?
They have no idea, but I'll give you a hint: a section of 18" sewer drain showed 50,000 hp on the bench.
Net result: no, you can't tell what it will do.
That's why combustion engines are so cool.
Take one part of the following:
Intake shape/size/length
Carb width/length
Valve size/shape
Piston shape/diameter
Exhaust length/diameter/taper
Various other shit

Add 10 parts chaos theory and you'll have your HP figures.
 

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A flow bench measures flow. Combined with intake cross section you can calculate gas velocity.... however this may or may not be valuable to you if you don't know what to do with it.

A good flow bench operator ( like Mike Rich ) for instance, measures flow rate with valves and cam installed and finds the flow at various valve openings. Why...cause you don't want to sacrafice 50% of your flow at a partial opening to gain 10% at full open..etc.

Of course the 18" sewer drain statement is meaningless. As modern flow bench software and engine simulation software base their esitmates on displacement, valve size, compression, intake track cross section, intake tract length, rpm and a myriad of other data.

Flow measurements are totally independent of hp estimates and just give you a quanitative measurement of flow at a particular valve opening on a particular head. What a particular engine does with this flow is a whole nother story.

I've found the solution is to leave a head in the hands of a proven tuner like Mike Rich. The man is incredibly knowledgable and meticulous. And I think his work for me stands by itself in both dyno and track results. As it does with Hirko and Charlie Cole who have had him do their head work the last two years. Can't argue with success.
JohnnyB
 

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Discussion Starter #8
yeah, but keep in mind, im trying to piece together the best "stock" parts i can find. no metal removal. the reason i asked was becasue ive noticed a difference, and wondered if the larger flater botomed port would typically be the one to use. and also why it was changed and does the cam duration and or lift mean the port has to be different. so if i ran the later model head, would it be a waste. "generally" speaking.

but ive been compiling info here there and everywhere, and thinik i need to run the head with smaller ports. its supposed to be a better setup for the motor. so thats what i think im gonna do. see, i can contribute, a little anyway.

jc
 

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I don't know if it's applicable much at all...but Mike Rich mentioned to me that the OEM ports on my 175 appeared to flow about as much as the valves could handle.

I have to tell you I have no freakin idea which type of port would serve you better... all depends on where the weak links is, port size, valve size, carb size, cam profile.

It would be interesting to put a stock bike through the flow bench and dyno paces to see just where they stand. Might give a clues as to what small changes you can make to give your stock engine the edge over another.
JohnnyB
 

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Discussion Starter #10
pete t is the one for that stuff. he did it with rabs bike. thats interesting about the flow on a stock head though.

i wont be able to go that far though with my bike.

jc
 

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Pete and I had an interesting conversation about Rab's bike. Seems Rab and I have one of the same anamolies at high rpm... and he thinks I can fix mine the same way he fixed his....but it's a secret until Aaron beats you.

It would be quite a bit of fun trying to tweak a stock 350. There's a lot you could probably think up to do if you followed the letter of the rules rather than the spirit :)

JohnnyB
 

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Branson,
I think a gain will be made, but I don't think it will as significant. I mean I hope I'm wrong. I was there when Pete found the hidden hp, and its like comparing apples, oranges, and walnuts with bad springs.

Aaron
 

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That's true enough.... I know we would not see the same AMOUNT of gain...but hell a 1/2 hp would make it worth while to me. Pete was under the impression that I'd pick up 1 hp easy. Maybe on my bike... the chart I saw on your bike didn't show quite the same breakup at high rpm as mine. Could be something as simple as the rotor/trigger gap on my bike being wrong. Or a difference in coils, or a weak battery on my bike at the dyno.

JohnnyB
 

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Discussion Starter #14
ive questioned alot of by the letter rules in the book for my bike. ive have ongoing posts and arguments ment it. im just going to build it as close to the letter, and spirit as i can. after all, for me, its mostly about fun. and, i have to live with the wera folk too.

jc
 

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"Combined with intake cross section you can calculate gas velocity.... however this may or may not be valuable to you if you don't know what to do with it."

Were you providing a sample of a meaningless statement?
Or are you actually suggesting that flow in a port has constant velocity, or at least the same frequency/amplitude regardless of engine design?

Calculated gas velocity = garbage.

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Joe,
I wonder about things like can you ADD stuff..like intake manifold spacers. You could smooth flow from intake to head which is often badly mismatched stock. Removing Altenator rotor is a must I'd think. A PVL would be big plus...a programmable PVL even more of a plus. Aluminum clutch plates would be cool, pick and choose till you find a well indexed stock cam, play with cam timing, high flow valve jobs....just a lot of little things to eeek out a bit more power.
JohnnyB
 

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Discussion Starter #18
yep, thought of it all, i have a milk crate full of 350 cams ive collected looking for a good one. you of course can buy new ones for 300 bucks. (i saw one go for next to nothing on ebay once) ive wondered more about frames, if you can cut shit off, and add shit on, at what point does it cease to be stock?? that frame frank was working on was way outta control. my god. the clutch you can mess with, really, the valves have to be spec. so id imagine whatever they did at the factory, and anymore would be illegal, technically speaking. i was told i cant remove my kickstart shaft buy rp. (what a load of crap in my opinion, so i removed everything from the shaft and left the shaft in out of spite) ive seen alum clutch plates, what a cool idea. a pvl is on the list, but i cant afford the 1k its gonna cost. i know, the unit is cheap, but the cases on the 350 have to be milled apparently. ive seen a few of them go in. lessee, i took the rotor out, and am running the dyna iggy. ive had no probs with it yet, and its been maybe 4 seasons now.


it gets a little shakey on the adding and taking stuff, especially when you start to fukc with the "spirit of the rules" but then again, should you ahve to use all honda gaskets when youre building these things?? (i actually do, and the boys down here say im nuts)

anyway....blah blah blah, lean off, blah blah blah, go fast.

tex, what gaskets are you using again??

jc
 

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JC,
Hirko runs a PVL, cost him about $400, Didn't have to do any case miling that I know of. I'm in talks with a guy about building me one right now... 175's have the same crank taper and OEM stator mount as a CB350. Hirko does run a crankcase block off plate but I've heard of others that don't and haven't had any problems.

As for the frame I don't see it anywhere in any rule that you have to use an OEM CB350 frame. Ohhh... you may be talking WERA right? They are a bit pickier right?.

Richard Peterson told you not to remove the kick shaft? Gotta watch him sometimes, he can be a real ball buster, he might have just been yankin your chain.

Like Rob pointed out... look at the 350gp results in the USCRA...they shouldn't be complaining about CB350's :)
JohnnyB
 
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