entropy
Moderator
Posts: 8671
|
posted January 04, 2002 05:23 AM
D Meyer - pls read
Doug,
I don't know if you have seen it but on another thread:
http://www.bikeland.org/board/viewthread.php?TID=1107&FID=1 there is a clik to a site which has some very interesting thoughts on porting. The G rated pix of swimsuited chix are an added benefit, but real performance discussions are in there
I think many of us would be interested in any comments you might have.
____________
This moderator uses moderation in moderation
  
|
RAC4IT
Needs a job
Bergie
Posts: 3009
|
posted January 04, 2002 02:23 PM
correction
Actually the correct URL is http://www.mototuneusa.com/think_fast.htm
Athough I understand the port velocity theory he describes I don't buy into his conclusions. That might work on a stock motor 600cc R1 but everyone knows there is more power to be had in a ported head.
My '95 Z28 LT1 makes 419 rwhp on motor. It made 245rwhp stock. Tell me you can do that on stock LT1 castings that are not ported? 
|
dougmeyer
Needs a job
moderated
Posts: 2713
|
posted January 04, 2002 03:35 PM
I think the problem is with the definition of the word "porting". Most people, (especially car guys) think it means "hog 'em out and make 'em bigger". To me, and those like "motoman" I suppose, it means "reshape to increase flow without losing velocity, increasing it if possible". Too often people don't feel like they've gotten their money's worth unless everything has been hogged out and polished like a mirror (another thing that is counter productive).
RAC4, Remember, your chev heads are two valve. The valve to bore area ratio is significantly different than with a 4V.
4V engines can very easily have too much port area if the ports are enlarged. It is harder to do on a 2V. Same goes for camshafts. A 4V engine needs much less "cam" than a 2V.
I can't tell you how many car guys call me wanting to know why their ZX-12 has such wimpy cams (and small valves) and why nobody makes a "good" one.
____________
It's not that I think you're dumb, it's just that so much of what you know isn't true....
|
RAC4IT
Needs a job
Bergie
Posts: 3009
|
posted January 04, 2002 11:24 PM
4 valve vs. 2 valve
Good point. I guess that's also why there isn't much to choose from as far as aftermarket cams is concerned.
|
magzx12r
Expert Class
Posts: 252
|
posted January 26, 2002 09:36 PM
Talked to a mechanic who does a lot of headwork for big bore motorcycles. He mentioned that when "flowing" the heads, he does a blend grind on the valve seats, increases the intake valve port size and Decreases the exhaust valve port size. He said that a lot of bikes come from the factory with exhaust ports that are too big.
____________
Mark
'03 ZX-12R
'12 1199S
|
dougmeyer
Needs a job
moderated
Posts: 2713
|
posted January 28, 2002 01:32 PM
Well sort of. You can't generalize that much. Many motorcycle exhasut ports are not optimized. But to "fix" an exhaust port sometimes requires welding up and re -shaping.
____________
It's not that I think you're dumb, it's just that so much of what you know isn't true....
|
|
|
HOME
NEW TOPIC