 /4 head question....modify exhaust side only???, for stock or near stock cams...... |
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| Mueller |
 Nov 22 2004, 09:01 PM
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#1
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914 Freak!  Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None 
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So I was thinking, (oh no Mr. Bill (IMG:style_emoticons/default/ohmy.gif) ) the exhaust side of the /4 heads is supposed to be the main weak link when it comes to getting any decent power gains from the type IV motors.....the ratio of what the intake flows compared to the exhaust is too lopsided (the exhaust should flow 75%-80% of the intake or something like that to be ideal?????)
If one was to keep the stock cam (not really keen on splitting the case) and just install a much larger exhaust valve and re-work the exhaust port only, would it make any appreciable difference?? This is for a 1.8 motor with a European racing header.....otherwise all stock...currently D-jet, but that can be changed (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/smash.gif) |
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| SirAndy |
Nov 22 2004, 10:17 PM
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#2
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Resident German Group: Admin Posts: 41,636 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
QUOTE(Mueller @ Nov 22 2004, 07:01 PM) and just install a much larger exhaust valve and re-work the exhaust port only, would it make any appreciable difference?? This is for a 1.8 motor with a European racing header.....otherwise all stock...currently D-jet, but that can be changed (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/smash.gif) yes, that's the theory ... put it on the dyno before and after so we'll all know for sure ... (IMG:style_emoticons/default/biggrin.gif) Andy |
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| Brad Roberts |
Nov 23 2004, 01:03 AM
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#3
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914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
HUm... (IMG:style_emoticons/default/idea.gif) *somebody* you know has been asking this question for a few years now.
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| Mueller |
Nov 23 2004, 01:07 AM
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#4
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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I'm going to try to get to whats-his-names shop this week to drop off my heads...we'll discuss pricing for such an "experiment"
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| Mueller |
Nov 23 2004, 01:08 AM
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#5
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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QUOTE(SirAndy @ Nov 22 2004, 09:17 PM) QUOTE(Mueller @ Nov 22 2004, 07:01 PM) and just install a much larger exhaust valve and re-work the exhaust port only, would it make any appreciable difference?? This is for a 1.8 motor with a European racing header.....otherwise all stock...currently D-jet, but that can be changed (IMG:style_emoticons/default/smile.gif) :smash: yes, that's the theory ... put it on the dyno before and after so we'll all know for sure ... (IMG:style_emoticons/default/biggrin.gif) Andy wanna help pay for a dyno run??? R&D is expensive (IMG:style_emoticons/default/wacko.gif) |
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| Brad Roberts |
Nov 23 2004, 01:49 AM
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#6
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914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
I'm working a guy in Mountain View for "use" of his engine dyno for "our" testing. He has one identical to Jakes so we should be able to compare some numbers (Mountain View is 10 feet above see level)
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| chunger |
Nov 23 2004, 02:11 AM
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#7
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Member Group: Members Posts: 409 Joined: 11-January 03 From: Albany, CA Member No.: 133 |
What happens to a type IV if you make the exhaust valves really bigger at add NOS?
(IMG:style_emoticons/default/alfred.gif) |
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| Rgreen914 |
Nov 23 2004, 02:46 AM
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#8
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Member Group: Members Posts: 285 Joined: 20-October 03 From: West Covina, Ca. Member No.: 1,266 |
QUOTE(chunger @ Nov 23 2004, 12:11 AM) What happens to a type IV if you make the exhaust valves really bigger at add NOS? (IMG:style_emoticons/default/alfred.gif) chunger Are you referring to Nitrous Oxide (N2O) or the company named "Nitrous Oxide Systems" (NOS)? I think this company is now owned by Holley. Ron |
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| chunger |
Nov 23 2004, 04:40 AM
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#9
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Member Group: Members Posts: 409 Joined: 11-January 03 From: Albany, CA Member No.: 133 |
oops NO2 the stuff that turns into N and O2 and happy fun hp.
didn't know holley bought them. Guess holley buys a lot of companies. |
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| Mark Henry |
Nov 23 2004, 07:32 AM
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#10
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
A big valve doesn't help much if the port is still small.
A 38mm is about as big as you will need. Porting on the exhaust port will help, but don't get too carried away, the exhaust port wall doesn't have a whole lot of meat on it. My 2.7 nickies engine will have (most likely) 44mm intakes and 38mm exhaust and a lot of carefull exhaust port work. |
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