Vacuum vs Duration
#1594666
03/18/14 01:11 AM
03/18/14 01:11 AM
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Joined: Jun 2006
Posts: 5,164 CT
GTX MATT
OP
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OP
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What type of vacuum would you expect to get out of a stock stroke 440 with 252/260 @ .050 duration. Cam was degreed in at 104.5 ICL, its a 110 LSA Comp.
32 degrees of timing locked out on the MSD Pro Billet. I'm getting a fluctuating 6-8 inches at idle. I don't really care, I just expected closer to 10, and my desktop dyno is telling me 12 (which seems very optimistic). I have a 6.5 PV in there now so I'm going to swap it out for a 4.5, and I'm thinking that should help stabilize the reading closer to 7/8.
Just looking for some input. Throttle response is good, doesn't appear to have a vacuum leak checking with carb clean. I'm just trying to get this thing squared away before I venture out for some WOT blasts on the street.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594667
03/18/14 01:25 AM
03/18/14 01:25 AM
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Joined: May 2006
Posts: 740 WA
JD Dart
super stock
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super stock
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WA
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Re: Vacuum vs Duration
[Re: Sport440]
#1594670
03/18/14 03:17 AM
03/18/14 03:17 AM
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Joined: Jul 2006
Posts: 4,319 Puyallup, WA
StealthWedge67
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My 3.75 stroke 451 based motor runs a 252* @ .050 cam. IIRC, it pulls about 8-10 in gear at 900rpm. I believe I'm currently running a 4.5 PV in the front of my 830 DP, with a plug in the back. (I'm not at home, so this is just off my somewhat suspect memory)
LemonWedge - Street heavy / Strip ready - 11.07 @ 120
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594674
03/18/14 12:05 PM
03/18/14 12:05 PM
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Joined: Jan 2003
Posts: 12,206 Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
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Benton, IL.
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If the carb is adjusted okay, then changing the power valve won't have any impact on the idle. Your vacuum seems to be in the right range for the combo.
Master, again and still
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Re: Vacuum vs Duration
[Re: DaveRS23]
#1594675
03/18/14 12:15 PM
03/18/14 12:15 PM
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Joined: Jun 2006
Posts: 5,164 CT
GTX MATT
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LSA is 110, advertised duration is 290/298, it is a solid cam, lashed at .014/.016 cold with aluminum heads (Hot lash supposed to be .016/.018).
Intake closing point is 69.5 degrees after bottom dead center @.015 (as given by Comp).
I will mention, the rings are not yet fully seated as I haven't gotten it on the street for a good beating. I'm just trying to quickly get the tune up close before I take it out.
The reason I want to throw in a lower PV is that it is so close to the opening point at idle, and the idle mixture screws are a little un-responsive/lazy feeling.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594676
03/18/14 12:25 PM
03/18/14 12:25 PM
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Joined: Jan 2003
Posts: 12,206 Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
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Posts: 12,206
Benton, IL.
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If the carb is adjusted right; meaning that the the throttle blades are in the correct position for idle, then the power circuit (including the power valve) does not see any vacuum signal at idle.
Now, if the throttle blades are open too far, then the power circuit could be starting to activate. But that situation needs to be fixed first.
Master, again and still
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594677
03/18/14 01:40 PM
03/18/14 01:40 PM
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Joined: Oct 2003
Posts: 7,506 Az
Crizila
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master
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A little low. What altitude do you live at?
Fastest 300
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Re: Vacuum vs Duration
[Re: DaveRS23]
#1594679
03/18/14 03:53 PM
03/18/14 03:53 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
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Quote:
If the carb is adjusted right; meaning that the the throttle blades are in the correct position for idle, then the power circuit (including the power valve) does not see any vacuum signal at idle.
Now, if the throttle blades are open too far, then the power circuit could be starting to activate. But that situation needs to be fixed first.
The power valve always has intake vacum to the backside of it. Sounds like you mean to say if the throttle valves are open to far then the main metering system may start drawing fuel into the venturi if air flow is starting to go thru the venturi. Ron
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594682
03/18/14 05:17 PM
03/18/14 05:17 PM
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Joined: Oct 2007
Posts: 4,209 New York
polyspheric
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master
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New York
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Dropping your initial spark to 20° may help raise the idle vacuum, but it's a PITA.
Boffin Emeritus
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Re: Vacuum vs Duration
[Re: GTX MATT]
#1594684
03/18/14 10:15 PM
03/18/14 10:15 PM
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Joined: Feb 2005
Posts: 4,318 Prospect, PA
BSB67
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master
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Prospect, PA
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So I guess it is an xtreme energy solid. Its specs are similar to the MP .577 solid. Maybe ask if anyone has/had that cam for comparison purposes. I think Ron (383Man) used it in his 440.
If you are just using a pan gasket for the intake, don't rule out a vacuum leak. The aerosol can spray method is not always reliable.
Last edited by BSB67; 03/18/14 10:15 PM.
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Re: Vacuum vs Duration
[Re: BSB67]
#1594685
03/18/14 11:48 PM
03/18/14 11:48 PM
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Joined: Jun 2006
Posts: 5,164 CT
GTX MATT
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Yup this is the extreme solid line.
The engine idles OK with less initial, but idled better and better the more initial I gave it, thus why I locked it. Although I did not verify with a vacuum gauge I will double check this weekend, RPMs came up and I reset curb idle to get them back down. Once warmed up the engine fires right off at the touch of the key, doesn't even get a full revolution in really before it comes to life.
I am running a valley tin with paper gaskets on either side. The gaskets seemed to crush well, but the reason I am worried about a potential vacuum leak is because I had a little trouble getting the intake on. Port alignment was good, and even with no gasket/tin the intake face to head alignment looked flush, but I did have to touch up the bolt holes to get the bolts started easily.
The only other way I can think to more accurately check for a vacuum leak is with propane and a long rubber hose. Someone on here had suggested something good a few months back for checking for vacuum leaks, and now I can't find the thread. I thought I favorited it.
I've had a cold since Monday AM so I haven't gotten out to play with the car after work.
Last edited by GTX MATT; 03/18/14 11:51 PM.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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