Ok, so no idea is stupid, but what about stupid questions..? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

Reply
 
 
 
Thread Tools Search this Thread
Old 12-29-2003, 02:15 AM   #1
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
Join Date: Sep 2003
Location: Minneapolis, MN
Posts: 22
Thanks: 0
Thanked 0 Times in 0 Posts
Mandible is on a distinguished road
Default Ok, so no idea is stupid, but what about stupid questions..?

Stupid question of the day...

Why does the boost guage indicate a *negative* boost? The guage shows -10 to 0 to +10. When I'm at idle it sits at -10. When I'm trying to beat the neighbors grandfather in his grandfather-ish Lincoln, it might jump from -10 to -2.5, or even creep up as high as +1. When I stomp on it from a dead stop it jumps up to +6 and (sometimes) higher. Normal driving puts th needle somewhere between -10 and 0. Does a -6 negative boost indicate that my intake air is being expanded by 6 psi, rather than compressed as it should be through the supercharger? Do I not see benefit from the SC If not +0?, why not just start with a 'zero' on the left and indicate psi from there?
Mandible is offline   Reply With Quote
Old 12-29-2003, 02:16 AM   #2
Senior Member
Posts like a Northstar
 
Join Date: Aug 2003
Location: Buffalo Grove, IL
Posts: 666
Thanks: 0
Thanked 0 Times in 0 Posts
Glasuan is on a distinguished road
Default

First of all what year and class of bonneville???

Then all the smarties can put their heads together.
Glasuan is offline   Reply With Quote
Old 12-29-2003, 02:18 AM   #3
Senior Member
Posts like a Northstar
 
Join Date: Sep 2002
Location: Sedro-Woolley, Washington
Posts: 604
Thanks: 0
Thanked 0 Times in 0 Posts
kennlee is on a distinguished road
Default

Negitive boost......Vacuum ????

ken
kennlee is offline   Reply With Quote
Old 12-29-2003, 02:18 AM   #4
Junior Member
 
Join Date: Aug 2002
Posts: 0
Thanks: 0
Thanked 0 Times in 0 Posts
Custom88 is on a distinguished road
Default

you don't see boost until after +0, under 0 and the intake air is entering as if there was no supercharger I guess. The supercharger doesn't actually give a boost in horsepower until a certain RPM is reached because it'* not spinning fast enough.
Custom88 is offline   Reply With Quote
Old 12-29-2003, 04:05 AM   #5
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

The gauge is reading manifold vacuum below 0. This is what a non-supercharged car would read all the time.
willwren is offline   Reply With Quote
Old 12-29-2003, 11:33 AM   #6
Senior Member
Certified GM nut
 
Join Date: Feb 2003
Location: Georgia
Posts: 2,095
Thanks: 0
Thanked 0 Times in 0 Posts
DrJay is on a distinguished road
Default

Yeah to go a little more in depth, and because I like to beat dead horses...but only on Mondays, they don't expect it on Mondays....Anyway, yeah the negative numbers are how much negative pressure *read suction* the pistons are causing on the manifold. At idle its neither a good idea nor necessary for the supercharger to be pounding air into the manifold, you only need this when you're accelerating. At the inlet of the supercharger you have another valve you can't see that looks like your throttle body valve only smaller. At idle or cruising this valve opens and lets air around the supercharger so it never gets compressed, which is why it stays below 0. This is roughly how much power your car would have if you ripped the supercharger off, sad huh? Right now this gauge is handy in diagnosing engine problems. If it only read 0+ you wouldn't have the benefit of possibly figuring out what is wrong with your car. I'm only recently reading into this but here are a few examples:

Intermittent Fluctuaiton at idle - Ignition miss, sticking valves, lifter bleeding off (hydraulic), or just a BIG camshaft

Gradual Drop and Idle - Clogged exhaust, excessive backpressure (extreme cases engine will die at idle)

Mainly all you can use for diagnostics is at idle, above that and the diagnosis is skewed by the supercharger ramming air into the manifold and smoothing out the needle. Just my thoughts though.
DrJay is offline   Reply With Quote
Old 12-30-2003, 03:41 PM   #7
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
Join Date: Sep 2003
Location: Minneapolis, MN
Posts: 22
Thanks: 0
Thanked 0 Times in 0 Posts
Mandible is on a distinguished road
Default

Thanks for the clarifications.

Mandible
Mandible is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
stupid, stupid, stupid... petraman Lounge 19 01-29-2008 11:51 PM
Let's play: Good Idea, Bad Idea MOS95B Lounge 18 05-30-2006 02:03 PM
L67 EGR Blockoff? good idea? bad idea? Marik_bathory Performance, Brainstorming & Tuning 21 04-29-2006 12:50 AM
AAAAAAAAAHHHHHHHH!!!! Stupid, stupid, stupid!!! BonnieBrougham Lounge 13 04-28-2006 01:00 AM
But But But John Deere Boy Lounge 8 07-09-2005 12:05 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 11:36 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.