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Old 02-14-2011, 03:45 PM   #76
Rob Farmer OP
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There's something quite beautiful about well executed engineering work.



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Old 02-14-2011, 04:35 PM   #77
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Red x's not so much.

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Old 02-14-2011, 06:10 PM   #78
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I probably should have just made a new post instead of editing the one I messed up but oh well.
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Old 02-14-2011, 07:01 PM   #79
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I think raised port floors have their roots in oval intake ports. Back in the early 30's Art Sparks and a Aerodynamicist professor from Stanford came up with oval ports for Spark's Offenhausers. I think Stanford had THE first flow bench and that guy made it. Offenhauser himself made them standard from then on. Then in the early 60's I think Smokey Yunick started raising them as we know it today with great results. MANY a production engine or even production aftermarket heads come stock with raised port floors now. It works! The problem with raising the floors in our heads is that it is a LOT of work!

By "raised port floors" are you referring to raising the the inner radius of the intake and exhaust tracts? Oval'd or "D sectioned" ports can be used in radius-ed intake tracts to reduce losses in charge velocity and inertia.

Modern high output engines try to utilise straight shot intake ports (to minimise the losses in a curved or radius-ed port), but our old airheads were never designed for maximum efficiencies.

The story behind the Thunderstorm motor at Buell (which has a similar intake tract radius as an airhead) was that Erik was poking through some HD racing dept heads with highly specialized port shapes and asked "Any reason we can't cast our heads to utilise these port shapes?" The gains from those ports in combination with combustion chamber and piston profile are impressive, taking the cammed Lightning motor from 85 to an honest 100hp.

Basically, when the charge is moving through the curved port, just like a river flowing around a bend, the majority of the charge is forced to the outside of the radius leaving the inside of the radius in a low pressure state. This low pressure area causes drag and reduces the inertia of the incoming charge where it meets the low pressure portions of the charge.

Solution? Fill the inner radius with a "speed bump" to prevent the development of a low pressure area. Also works in a fashion to create a venturi effect as the charge accelerates past the raised portion of the port floor.

Ride a Thunderstorm equipped Buell back to back with an identically cammed pre-T-Storm Lightning and the difference is night and day. In comparison the ported engine feels like it's mildly turbo boosted as the revs build.

Not meaning to sidetrack the conversation to Buells, only referencing something I'm familiar with to illustrate the concept/idea. Am curious to know if this is the effect being referred to as "raised port floors".

Incidentally, a friend who operates a successful motorcycle performance tuning business (dyno, flow bench, many years experience and lots of costly equipment and serious customers) was hard pressed to improve on the flow characteristics of the Buell head when used at 1200cc's. Only when increasing engine capacity to 88 inches did he find it necessary to fiddle much with the stock port shapes.
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Old 02-14-2011, 08:02 PM   #80
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Lornce, thanks for asking that question more eloquently than I could have. I appreciate the background that you added. This stuff is generally a mystery to me but your river analogy helped a lot (having done some kayaking and rafting that really helped me visualize the gasses heading 'round the bend leaving behind eddies just swirling in place).
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Old 02-15-2011, 05:15 AM   #81
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Just got back from another dyno run. I wasn't really interested in the figures but just wanted a snapshot of where things are in preparation for the upgrade.

The BHP figures recorded without any problems but the air/fuel readings kept cutting out and the dyno's whitenoise light kept flashing - seems my bikes throwing out so much white noise it's interfering with the electronics. I've fitted a dyna coil since my last dyno run, this may be the culprit.

The bad news is I've lost 8 BHP since my last run if you find them drop me a PM. the good news is we ran the LM2 side by side with the dyno's sniffer and they read virtually identical figures. They both use Bosch wideband sensors so it should only be expected.

The loss of BHP is mostly down to filthy air filter, worn plugs. I haven't set the tappets in months and I didn't balance the carbs so a loss of HP was only to be expected. The verdict on the jetting was I need to fit a smaller needle jet. I'm running a 2.66 and need a 2.64 (at least) This falls in with Richie Moore's comments. At full throttle the AF is around 14.2 so the 158 main jet is slightly too small.

Not the sort of bike they're used to on a dyno


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Old 02-15-2011, 10:25 AM   #82
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If I remember right, "raised port floors" is what Yunick, Axtell, and most others that I have read, talked and/or worked with call raised port floors. I have always borrowed AND returned Yunick's books so I can't look it up to be sure. If I have remembered wrong, I will stick with whatever Yunick called it since he pretty much is the one that first started doing it as far as I know.

It is all about the inside radius. It's really about the entire port bowl area. So many people think of flowing the port. In actuality you are flowing the valve. It's ALL got to get around the valve!

Same dyno Rob? A lot of HP can disappear on a different dyno! Same jets? Airbox?

I am not very familiar jetting 40mm Bings but didn't you say that bike came stock with a 150? If so, I can't figure how it even ran at all if it is getting 14.2 with 158's AND a filthy filter. Surely all that isn't from the airbox?

I guess everybody remembers those are CV carbs. Slide position is disconnected from throttle position to a certain extent.
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Old 02-15-2011, 10:28 AM   #83
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Same Dyno SS

Today's run was a spur of the moment thing just to get a snap shot ready for the work coming up over the next few weeks. I'll be putting the bike back as close to standard as I can get it, take a dyno run and then fit Richie's kit before taking another dyno run.

This is the state it was in when I first bought the bike. 37 BHP. All standard apart from a Keihin Y piece and one tooth out on the cam sprocket - A new cam chain had been fitted just before I bought it and had been fitted one tooth out, lucky it didn't bend a valve.


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Old 02-15-2011, 11:10 AM   #84
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One tooth out could surely be the cause of the low HP. IMO, they barely run like that. Why do you think you now need a new cam? I couldn't figure that one out.

So you obviously got the cam timed right to see 50hp. What have you changed since then?

BTW, I noticed on the chart that Moore agrees with just about everyone else I know about a/f ratios. 12.5 to 13.5. There is perhaps some HP to be gained within that zone. I saw it with my bike. I felt it with the seat of my pants before I saw it but I wanted to be safe about melting stuff. The sniffer said I had the room so I went to above 13. The difference between 135's and 130's on my bike for some more HP. That's with a slightly modified airbox, 38mm Dellorto's with the fuel pumps disconnected, sport cam, port shape changed, titanium valve spring retainers, and Staintune Sport mufflers.

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Old 02-15-2011, 11:15 AM   #85
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The cams an unknown quantity, it's unmarked and nobody seems to know what it is, if I fit a 308 at least I'll know what I'm dealing with. To get the bike to run as it does now I've had to change the jetting a long way from standard. If I put the bike as close to standard as I can and get it running as well as it can with that configuration I'll then have a starting point to look at fitting the Morespeed pistons and airbox. Changing too much at once gives too many variables.

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Old 02-15-2011, 11:48 AM   #86
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I don't understand what you mean by "unknown quality"? It's at least a 308 if you are seeing 50hp. I suspect that happened after you got the cam timed right? I would suggest timing the cam if it is an issue. That would be a whole lot easier AND cheaper than replacing the cam with a 308 when I suspect that is exactly what is in there now.

When I first read your chart I though that oh maybe it does have a 296 but then I read you reporting that the cam was timed a whole tooth off. That will do it!

I still can't figure out how you are getting 14.2 with 158's and a filthy air filter when it came stock with 150's? Oh well, it's usually a guessing game here on the net.

I saw where Moore was claiming that gear box only looks like a BMW box. I can't figure that either. I guess I need more clues!

BTW, I have worked on bikes a bit that were making a substantial bit more power than that and they had a completely BMW box on them. RS close ratio gears but they are the same design. They suffered no issues out of the ordinary.

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Old 02-15-2011, 01:10 PM   #87
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I was just thinking about that 14.2 reading with richer than stock jetting and a filthy filter. 135's to 130's got my bike from mid/high 12's to low/mid 13's. It won't even pull above about 5k in top gear with 125's in it. It flat out just quits like you bumped the kill switch.

And about that 37hp. Why did the run stop at 5500rpm? That has got to be at least part of the low hp rating one would think?!?

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Old 02-15-2011, 02:10 PM   #88
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Originally Posted by supershaft View Post
And about that 37hp. Why did the run stop at 5500rpm? That has got to be at least part of the low hp rating one would think?!?
The AF ratio had dropped through the floor and was never going to achieve anything meaningful. The jetting at the time was completely standard (150 Mains) and had the standard airbox fitted. Later dyno runs with the early RS clam shell airbox and starter motor cover flowed more air than the standard airbox so I stuck with that. With the 160 main jets it was just about right at the top end.

Chopping and changing airboxes and jetting probably seems an odd way of doing things but it's a "suck it and see" way of finding out what does what. The clamshell airbox does flow more air than the later type, The Keihin Y piece screws things up completely unless you have the original headers with a balance pipe. How else do you find out what works?
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Old 02-15-2011, 02:21 PM   #89
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Originally Posted by supershaft View Post
I don't understand what you mean by "unknown quality"? It's at least a 308 if you are seeing 50hp. I suspect that happened after you got the cam timed right? I would suggest timing the cam if it is an issue. That would be a whole lot easier AND cheaper than replacing the cam with a 308 when I suspect that is exactly what is in there now.
308 Cams are cheap enough and at least if it's stamped on I know what it is. It's easy enough to swap a cam over so makes sense to have one to hand when I pull the unknown one.


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I saw where Moore was claiming that gear box only looks like a BMW box. I can't figure that either. I guess I need more clues!
Richie uses different internals on the gearboxes for the high output engines. He did tell me the name the other night but I cannot remember now.


Just for you SS. That's my LM2 Wideband sensor being checked against the Dyno for accuracy. Works a treat


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Old 02-15-2011, 02:26 PM   #90
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. . . That and the cam timed correctly? I can't figure how the rest of the story pieces together. It seems to me that you are for the most part comparing a cam timed a whole tooth off to one timed correctly?

Some do think the claim shell breaths better but I don't see it making that much difference. Dr. Curve stuck with it, for instance. On the other hand, Wrecking Ball had most of a square airbox on it when I was around it and I suspect it was pulling a few more ponies than White Dog. You can have even longer velocity stacks with the square box and historically speaking surely you have noticed all the super long velocity stacks on many a racing beemer through the years.

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