I know there are many factors, not the least of which is the inaccuracy of the factory gauge but I'm curious to see what others are seeing with the wide range of atmospheric conditions we all encounter.

Here's my story

Picked up the Lightning up north on a perfect day for an S/C vehicle, 55 degrees, dry and clear. Saw 8 lb. easy from 3000 rpm on up to redline. Drove it down to Central Florida into the 85+, high humidity air and am lucky to see 6.5 lb. She still runs great and I know there's no waste gate so the boost is purely a factor of RPM and air density. I can't wait for the cooler weather.

What are you seeing? Should I have it looked at or just suffer with less than 8 lb. until the weather cools.

Mark W.

 

Mark,

I live in Orlando and my boost gauge pegs the needle under high rpm WOT bursts. Of course, I bought mine here so the only time it has tasted cool, dry, dense air is when they tested the motor at the Ontario Truck Plant. So, maybe after yours gets used to its new diet of our hot, humid air it'll start blowing a little harder.

Mike Philpott

 

mine shows 8 lbs from about 2500 to 5200 with out sals air cleaner kit. with it its a little over 9lbs.air cleaner should be the second modification you do , chip is a definate first.i ,ve never seen temp or humidity cause a blower to lose boost, but im not saying it want but i believe i would have it checked.

 

Great Topic. In fact it has been one I’ve been thinking about for some time. I have made a few observations that I would like to throw out for comments:

1. My boost gage does seem to change based on weather. Here in hot Arizona, where we are finally going below 95F for a high, I have consistently read 8 psig on the factory gage. Sometimes on cool nights or early morings when I've looked, the gage hit 8.5-9.0 psig. The boost doesn’t seem to care about the Superchip setting.

2. Notice that the "zero pressure mark" covers a huge range. With the engine off, my needle points to the vacuum side edge of that mark. In fact the left edge of the needle matches up to the right edge of the "zero" mark. Assuming that the gage swing is linear (the tick mark spacing indicates this is true) and if my "zero" pressure indication on the gage was in the center of that wide mark, I would easily read 10 psig at maximum boost. Likewise, if my "zero" pressure indication on the gage was at the pressure edge (right side) of that wide mark, I would easily peg the needle . I’ve ordered my Power Surge Performance Filter kit, but haven’t received it yet .

3. When I shut off my engine there has always been a hissing sound that lasts several seconds that I’ve assumed to be pressure relieving from the intercooler reservoir or something. I have discovered that it is the vacuum that is being released by the intake (or more correctly it is the ambient pressure filling the intake). Watching the boost gage as I turn the engine off, the gage goes from pegged on the vacuum side and very slowly returns to "zero." It takes anywhere from 10 to 20 seconds to get a zero reading again. This phenomenon appears to confirms that the bypass valve seals well. When I have opened the throttle plates during this bleed down period there has been no change in the time it takes to go back to zero gage pressure.

Survey question 1: Where are your boost needles pointing on the boost gage relative to the large zero mark before you start you truck in the morning? Pressure side (left), middle, or vacuum side (right)?

Survey question 2: Do you experience a hissing sound associated with a slow moving boost gage needle at engine shut-down?


------------------
Joel.......
99.5 White Lightning,
SVT # 0052
Superchip!!!!!

 

Joel,

I was thinking that exact same thing today as I played with the filter/airbox in between rain squals from hurricane Irene!

I did take a baseline of the gauge in Virginia at a higher altitude under different conditions and it was almost exactly on the 0.

Today the gauge reads below the black 0 box, in essense showing a vacuum relative to the previous readings. If I take the baseline and assume a linear gauge I'm making 8 lb. with the dirty air cleaner (13K miles) and 9 lb. without any filter element (only had the nerve to run without a filter for a mile or so, all the rain was holding down the dust).

I found out today about the incorrect part number in the manual. Pep Boys didn't have any cross references for the FA-1682 and the Ford parts department was closed.

I think I'll drop in another paper filter while I decide on whether to install Sal's filter system.

Great post Joel, thanks for making me think.

Mark W.
'99 White Lightning

 

Hey,

Does anybody know where the boost/vacuum hose connects to the manifold? I looked around but it wasn't obvious.

Mark

 

Mark-
My boost in hot weather usually pegs around 9-9.5. Lately in the cooler air (50-60 F), my needle pegs past the 10 and the white background and into the black background. I don't know how accurate this is but I plan on getting another gauge and hooking it in.
I believe the connection is behind the blower on the manifold.

------------------
$$$$$$$$$$$$$$$$$$$$$$$$$
PFA
'99 WHITE LIGHTNIN'
#0873
RHINO, Soft cover
LoJack
Valentine 1
Mobil 1
Superchip
Water Wetter
Best ET to date-13.58
best MPH to date-102.33

 

I have been seeing 10+ on a cold night from around 3000 rpm and up, during the day when its 70+ degrees, its hard to get it past 8.5.


------------------
Jim
96 Black Cobra,
K&N,OffRoad H-Pipe
NitrousExpress 150 shot
Soon to have a stroked 351W
1999.5 Black Lightning
No Mods yet

 

When you turn on the key and energize the gauges(don't start it) mine reads what would be about -3lbs if vacuum was measured in lbs. However, when I was at the track friday and the blower didn't come in at WOT the boost gauge read dead on "0". And I concur the observation of higher boost when air is cooler and denser.

------------------
Red 99.5 Lightning,#0975,Born 5/6/99...Adopted 5/27/99 Chipped w/SuperChip Flipchip chip,Water Wetter, Mobil 1

 

Mine is right in the center of the large 0 mark, goes up to about 9-9.5.

------------------
99 Lightning black, cd,tow package, stock
98 Cobra coupe laser red
best stock et 13.43 @ 103
one run w/ 3.55 gears 13.34 @ 102 no other mods
former Chevy fan still have a few
72 SS454 11.6 @ 116 (slicks open headers)
68 Camaro 12.2 @ 116 (street tires closed exhast)

 

When I had the Beast dynoed last week, the bow-tie boy running the dyno couldn't believe his eyes when the boost gauge pegged at about 2800 rpm, so, he got out a calibrated gauge and proceeded to check it.

On the next 5 pulls, the gauge read from 11.3 to 11.5 psi every time. Here in Houston, at sea level, this is phenominal. I attribute at least part of it to Sal's PowerStack filter setup, as the SC now spools up must faster.

Just my .02 on the subject....

 

there is a single black plastic line above and to the left of the steering column going through the fire wall.underneath the dash you can see it going up into the dash .great place to T in and put another pillar mounted guage.as far as the other end , it goes behind the blower some where but didnt really care to find the exact place.i juct wanted a place to T into.
while we are at it ,is there by any chance a spare place to put a mechcanicle temp guage sending unit on the motor?

 

Ok, I found the boost/vacuum line coming through the firewall. It connects into a 90 deg fitting right by the scanner plug. I poped it off and put a standard vacuum boost guage on the line. The beast is making between 8 and 8.5 lb. of boost from 3000 up. I didn't get to make a long run to spin up the motor under load (ran out of road REAL quick) but it confirms the factory guage is off by 2 lb. The "real" guage reads 0 when the manifold is at ambiant pressure. The dash guage reads -2 lb boost (inches of mercury and psi don't translate directly so I used the boost side of the guage as reference). BTW, the engine makes over 25 in of vacuum! I think the pegging of the guage on the vacuum side screws it up. As for mine, I know to add 2 to what it reads. I may just have to pillar mount an autometer for effect.

I suspect that most of you are seeing guage errors. My race engine builder tells me the boost, unless modified with the computer, will be whatever the design specifies. The only way to change it is to spin it up faster i.e. a smaller pully. He's installed hundreds of 1471's on bigblocks and the 6 lb. pully ALWAYS makes 6 lb regardless of air temperature. There are slight variances based on intake and air cleaners. That probably explains why Sal's filter makes boost quicker and may let you make a little more boost at top rpm.

Thank for all the input

Mark
Makin' 8.5 and lovin' it.

 

HI everybody,
I just thought I would toss my .02 cents into this discusssion. I have a KB supercharged Mustang with an Accel boost/vacuum gauge. In the 4 years I have had it, the boost and vacuum remains constant no matter what the weather, from 100 to -10 degrees. The boost is either 6 or 8 lbs depending on the pully and the vacuum is 21.5 inches at idle. My lightning varies with the weather from 8.5 lbs to pinning the gauge. The colder it is, the higher the reading. Like some others have said even with the engine off the guage reads differently on different days unlike my Mustang. My best guess is that the factory guage is just not that accurate. Later.

 

When I'm driving at a constant speed the needle is pointing just below the "Vac" mark. At WOT this morning I hit 8.5 lbs but a couple of months ago it would peg no problem.

------------------
--Scooter
'99 RED LIGHTNING


[This message has been edited by Scooter (edited 10-20-1999).]