Boost Problem???

no164ford

Registered User
I have a 1990 T-bird SC when I bought it it was getting about 12.5-13 lbs of boost. Then I installed a 10% OD K&N cold air intake and underdrives my boost was 14-14.5 then. A few years later I blew the head gaskets so when I did the heads I did a major port and polish, resurfaced the heads, valve job with 01 mustang MLS head gaskets Arp studs, mid length knooks coated headers no cats no rez and flowmaster mufflers and a dubble I/C. My boost then droped to 9.75 tops and it seemed to loose bottem end power but yet it seemed to be faster. So the next thing I did was get a mass air out of a 94 SC then I cut out the post and installed it, It brang my boost up to 10.25-10.5 lb. Now the last thing I did was ported a 89-93 blower (a diffrent blower not the one in the car) to some what look like the the new MPIII without the wings also custom built plemum (made out of a stock 89-93) and a 3/4 top with 42lb injectors. And now I am lucky if I can get 12lbs of boost. The car does run a s%#! pile better then stock, but why is my boost so low???
 
no164ford said:
I have a 1990 T-bird SC when I bought it it was getting about 12.5-13 lbs of boost. Then I installed a 10% OD K&N cold air intake and underdrives my boost was 14-14.5 then. A few years later I blew the head gaskets so when I did the heads I did a major port and polish, resurfaced the heads, valve job with 01 mustang MLS head gaskets Arp studs, mid length knooks coated headers no cats no rez and flowmaster mufflers and a dubble I/C. My boost then droped to 9.75 tops and it seemed to loose bottem end power but yet it seemed to be faster. So the next thing I did was get a mass air out of a 94 SC then I cut out the post and installed it, It brang my boost up to 10.25-10.5 lb. Now the last thing I did was ported a 89-93 blower (a diffrent blower not the one in the car) to some what look like the the new MPIII without the wings also custom built plemum (made out of a stock 89-93) and a 3/4 top with 42lb injectors. And now I am lucky if I can get 12lbs of boost. The car does run a s%#! pile better then stock, but why is my boost so low???

It might be that the hose going to the boost gauge has a leak in it. Since this all started after doing the HGs I suspect the little rubber connector that attaches the hard plastic gauge hose to the intake manifold adaptor has a crack in it. It's located just behind the air charge temp sensor.

If it is cracked or split open it can easily be repaired by using a short vacuum hose to replace the rubber connector, and secure it with a couple small zip ties. Same thing happened to mine after removing it a time or two.

David
 
I was thinking mabe that maybe the problem I will try that tomarrow. But how much boost should you lose after a P&P, headers & exhuast? should you lose low end power? And any ideas on what cam I should go with?
 
You might lose a pound or two by doing the headers and free flowing exhaust. Doubt you would lose any from doing a port job on the heads, unless you changed the cam at the same time.

If there isn't anything wrong with hose going to the gauge it could be from the ported blower. My early model ported blower felt a little weaker on the bottom end but pulled much harder at high rpms. If that's the case just overdrive it another 5% at the jackshaft pulley.

David
 
David Neibert said:
You might lose a pound or two by doing the headers and free flowing exhaust. Doubt you would lose any from doing a port job on the heads, unless you changed the cam at the same time.

If there isn't anything wrong with hose going to the gauge it could be from the ported blower. My early model ported blower felt a little weaker on the bottom end but pulled much harder at high rpms. If that's the case just overdrive it another 5% at the jackshaft pulley.

David
I was thinking about over driveing it 10% more 20% total What do ya think that will do? And who carries the best deal on jack shaft pulleys? Also my boost problem started after the head job and before the super charger. PS Thanks for all the info.
 
Not too fast

The loss of low end and boost pressure is from the better flowing exhaust.
You may want to be careful not to overdrive the blower too much. The bearings are rated a certain speed (I believe its 14,000 RPM).
If you spin them too fast they could bind up and really cause a mess.
You mentioned that you updated to the late model MAF.
Have you thought about going to an even larger MAF, throttle body and intake tubes (3-1/2" dia)?
You also may want to investigate an updated cam grind for your ported heads.
Lastly you may want to top it off with a dyno test and chip burn that will make sure your getting the most out of all your hard work.
Sorry if this is a hodgepodge of info.
Just throwing things out to ponder.
Bill
 
no164ford said:
The car does run a s%#! pile better then stock, but why is my boost so low???
The answer my friend is blowing in the wind. :D You're making your exhaust leave faster creating less back pressure. That's a good thing! :) Doing the exhaust should have been your first modification and you might have saved yourself a HG job. When I did my exhaust I lost almost 3psi, then I added the 10% pulley and sealed up some major vacuum leaks. All mine came back. I would worry about trying to get all that boost on your gague as long as your sure the intake isn't leaking you should be OK.
 
Dave, what size cam are you thinking? choseing a cam is not my speicalty I am still learning LOL!
Bill, what is the rpm on a stock blowe and do they make better bearings, I seen some on ebay that was suppose to be rated higher but what can you trust on ebay?
Rick, The sad part is I did upgrade my exhuast alot before Hg's failed, BUT the freaken cat broke and cloged the exhuast, now they are history. and for intake leaks, I can't find any and the car runs smooth at idle (smooth for a SC) but I do only have 12-14 in lbs of vaccum at idle, use to have 20
 
My 93 is stock other than a removed air silencer and i am only getting 10psi at the very most is this normal i mean it screams at 10psi but it seems kinda low? Running around 20hg vac at idle.
 
no164ford said:
Dave, what size cam are you thinking? choseing a cam is not my speicalty I am still learning LOL!
Bill, what is the rpm on a stock blowe and do they make better bearings, I seen some on ebay that was suppose to be rated higher but what can you trust on ebay?
Rick, The sad part is I did upgrade my exhuast alot before Hg's failed, BUT the freaken cat broke and cloged the exhuast, now they are history. and for intake leaks, I can't find any and the car runs smooth at idle (smooth for a SC) but I do only have 12-14 in lbs of vaccum at idle, use to have 20

You don't want my advice on a cam...I tend to go towards the radical side and then make it a little more radical. What usually happens is either it runs real good but breaks valve train parts or it runs okay and nothing breaks.

I'm actually getting ready to try cam #4 in my never ending search for the right balance of power and reliability.

Talk to Dave Dalke (XR7Dave) he speced and supplied my most recent cam and I'm sure he can help you select one for your car.

David
 
Pulley table

no164ford said:
Dave, what size cam are you thinking? choseing a cam is not my speicalty I am still learning LOL!
Bill, what is the rpm on a stock blowe and do they make better bearings, I seen some on ebay that was suppose to be rated higher but what can you trust on ebay?

I have attached a pdf file of a supercharger pulley table I downloaded from SCCoA forum.
It shows the blower RPMs based on the model of blower (early vs late) and the engine RPMs.
There is a lower section where the person that generated the table was looking at a custom overdrive system.
From what I have read about the different models of blowers is that the later model (94-95) is coated and has tighter clearances which produce the same amount of boost as the early model but at a slower speed. Thus reducing the air charge temperature.
My apologies, on TexasThunderbirds.com Wynn lists the bearings to have an 18,000 RPM rating not the 14,000 (which I have seen somewhere ???).
If you want to rebuild your blower Wynn offer the service or the components to do the job.
As with increased blower RPS comes increased air charge temperatures.
Most of the big dogs run the Magnum Powers front mounted intercooler to keep these temps down.
The new "goodie" out now is the Snow water/alchohol injection system that also reduces air charge temps. Check with Dave Dalke.
Hope the info helps.
Bill
 

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