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Old 04-18-2012, 03:21 AM   #16
rambozo
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hp loss

don't mean to hijack the thread but how does the starter cover cover take away 2hp?

i only ask because i was going to put either my 78 clam shell and cover on ebay or my 79 setup, just cant decide which one i like best, cast in scoop or rubber scoop

a hp loss would make my mind up pretty quick
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Old 04-18-2012, 10:05 AM   #17
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warm vs. cool air?
benefits of the later, rubber "velocity stacks"?

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Old 04-18-2012, 10:56 AM   #18
Hedge36 OP
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It makes sense if you look at the airflow... The later intake and filter doesn't force the air to change directions as often.
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Old 04-18-2012, 01:06 PM   #19
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Quote:
Originally Posted by rambozo View Post
don't mean to hijack the thread but how does the starter cover cover take away 2hp?

i only ask because i was going to put either my 78 clam shell and cover on ebay or my 79 setup, just cant decide which one i like best, cast in scoop or rubber scoop

a hp loss would make my mind up pretty quick
It's the air box that takes away HP not the starter cover. The 79 is the cooler looking starter cover.
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Old 04-18-2012, 01:18 PM   #20
Kai Ju
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Originally Posted by bmweuro View Post
It's the air box that takes away HP not the starter cover. The 79 is the cooler looking starter cover.

The '79 also has the larger opening, compared to the rubber ones.
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Old 04-18-2012, 02:43 PM   #21
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I could see the clam shells giving 2hp on top and a bit less real close to peak hp rpm. I could also see the square airbox adding a bit more hp than 2hp at say 4500 rpm with that advantage being spread over a wider rpm range than the clam shell's advantage. The by far strongest running airhead on top end and just about everywhere else that I have ever been around had most of a square airbox on it. That was Hodgson's Wrecking Ball at just about the end and most developed stage of its road racing career. It was running damn strong on top when I helped him some with it. Airbox setup is so dependent on so many other factors it's pretty much a waist of time saying one is better than the other. My point is that what is better is more complicated than peak hp. Square airboxes can be the answer. It depends on the question.

An engine sucks the most air PER pop at peak torque, not peak hp. Unless peak hp IS peak torque which is always the case under 5252rpm.

I had my airboxes backwards and edited it to what I really meant.

supershaft screwed with this post 04-18-2012 at 05:22 PM
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Old 04-18-2012, 03:30 PM   #22
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2hp is quite a lot between two very similar looking clamshells

i'll keep the 79 one then, cheeers
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Old 04-18-2012, 05:21 PM   #23
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Originally Posted by rambozo View Post
2hp is quite a lot between two very similar looking clamshells

i'll keep the 79 one then, cheeers
Oops! Was euro comparing clam shell/clam shell? I thought it was clam shell/square box?
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Old 04-18-2012, 06:07 PM   #24
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re: clamshell (79 RT) vs box.
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Old 04-19-2012, 05:44 AM   #25
rambozo
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maybe i'v confused the situation

my 79 is an early one, if they changed to the box in 79 mine could of been made before the changeover

it makes a lot more sense for the box to be better for hp than a clamshell
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Old 04-19-2012, 11:30 AM   #26
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Box vs clamshell. Most have come to the conclusion that the clamshell gets a little more power on top where the box gets you more power in the middle. I think overall the box works better but that's just me with my setup. I also think the box is easier to service and set up a clean crank vent to atmosphere. But I don't think the clamshell looks any better over the box either.

I don't care for the very early sand cast looking boxes and lids. They often don't fit right and according to BMW the lid horns don't flow air right. I was working on a bike a few years ago and figured out the the cast box was too thick and butting against the starter cover which didn't allow the top of the tranny to be drawn down against the case. It had been like that since new I think. It was chewing up input shafts too!
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