10% overdrive making 10lbs

Csirny

Registered User
my 1990 is only producing 10lbs of boost. I've read that stock boost is 10-12
my current mods are:
10% sc pulley
raised top
cold air intake
mustang headers
2.5 exhaust into a dual in dual out resinator and summit Race mufflers (no cats)

its my understanding that the early model m90 pulley is smaller then the later model ones. so is the 10% pulley still 10% overdrive on the earlier models?

also for future pulley combinations i would like to get a 10% js pulley. when I do this should i change my sc pulley to a 5% to keep the supercharger operating efficiently? I think I would like to use the 10% js pulley to allow for 20% overdrive in the future when I am able to upgrade my supercharger.
 
10% is probably the max OD you should run on an early model blower, especially with a stock intercooler. One mod you have that may drop your boost level is your exhaust. Less restriction in the exhaust means less pressure building up in the intake, but still more power. Also stock boost gauges are not very accurate. Check the car thoroughly for any vacuum leaks, but if nothing is leaking, and the car is running good and making good power, don't worry about what the boost reading is.
 
thanks for the advice the car is running really good but i wanted to make sure this was normal.
 
Are you sure you used the right belt(s) and that the tensioners are working properly and you don't have belt slip?
 
I used stock size belts with a larger wheel on the tensioner. doesn't seem to be slipping as far as i can tell.
 
My 90 was seeing 12lbs on the stock gauge with stock pulley, cai/throttle body/SCP down tubes with cats and a flowmaster resonator/cat back. Stock gauges of any Ford vehicle of this vintage are not know for their accuracy. That being said it is best to remember that boost is a measure of restriction as much as how much pressure is being forced into the engine. I would be more apt at seeing an increase or decrease on the gauge when changes are made instead of it being an accurate number. Do you recall what it was before you changed the pulley?
 
I bought the car with the 10% pulley. I added the exhaust and did the tensioner pulleys when I did head gaskets. If I remember right I was getting about the same amount of boost before the hg. The car did have some belt slip when I first bought it. It would squeel at about 6-7 psi. I changed all the belts and it event away. I am considering getting the better springs when I have some extra cash
 
Changing exhaust and getting the same boost is a good thing = more power mp springs are a cheap upgrade well worth the money spinningwheels-sc.com have them cheaper than anyone else and Victor is a genuine good guy my .02 cents
 
Is it just the sc tensioner or do I do all of them? I took all of the tensioners apart once already to powder coat them. Wish I would have changed them then. Didn't know they had these.
 
As others have mentioned, any muffler changes will affect your boost reading. On my SC, I was getting about 10.5 psi of boost, but had realized I had put a K&N air filter in, and also that the guy that had the car before me, had taken the cats off.
 
I used stock size belts with a larger wheel on the tensioner. doesn't seem to be slipping as far as i can tell.

I would bet money that you have belt slip with a stock belt. Increasing the tensioner pulley doesn't do anything for belt slip. Get the springs and the correct belt. Also you likely are seeing great low end power from the 10% pulley but the experience of many is, the massive heat you generate on the top end makes the computer pull a lot of timing causing you to lose HP there. You have to balance mods with correct supporting mods or you are wasting your money

Ken
 
Ken
What would you suggest to lower the temp? I also have an intercooler fan. Does this make a significant difference? I would like to do a double intercooler eventually. Hopefully by spring. I will upgrade the springs and belt soon also.
 
I also have an intercooler fan. Does this make a significant difference? I would like to do a double intercooler eventually. Hopefully by spring. I will upgrade the springs and belt soon also.

I run 10% on my '90 Anny, auto trans, stock intercooler, 7" 1100 cfm puller fan, narrow condenser and hi-flow down pipes /cats. I also run temp senders on the intercooler inlet and outlet, and can vouch for the fan being a good money/effort spent mod.

The idea with the fan is to run it all the time in hot weather, as it can take approx. 10+ minutes to bring it down otherwise, so pre-need air flow seems best to avoid/delay heat soaking the IC (soaks well when parked hot, of course). 90º weather just cruising around stop/go I see a max of 105º in with 90º out. That is a typically minimum offset that is of course wider with a cooler outlet temp, in cooler weather.

Cruising on the freeway, I see around 105º in & 80º out or lower depending on speed, hills, etc. The max outlet temps in all examples are well below the 150º intake air temp where the computer will start pulling timing. The highest IC outlet temp I've seen during a WOT 14# pull to 3-digit speed was 125º while the outside air temp was 85º. Inlet temp hit 205º in that example.

Depending on conditions, the 7" fan on my car makes a difference that ranges from 15 to 35°, on average, where the higher the temp coming in the higher the drop in temp going out.

A common sense tip when running the factory intercooler is to remove it and clean it out so that it's efficiency returns to like new levels. Gasoline worked for me, with multiple flushes and sufficient dry time.
 
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Thanks for the info. My fans hooked up to key on power so it runs all the time well the cars running. I flushed out the intercooler in the parts washer at work when I did my head gaskets. I like the idea to run air temp gauges.
 
Thanks. That seems like a cool set up. My tax return money is going to get spent before I get to see it.
 
Ken
What would you suggest to lower the temp? I also have an intercooler fan. Does this make a significant difference? I would like to do a double intercooler eventually. Hopefully by spring. I will upgrade the springs and belt soon also.

KMT covered it pretty well. The biggest problem is the early blower is very inefficient compared to the 94-95 blower. So running a 10% pulley likely will feel great off the line but the heat you generate at higher RPMs will have your timing pulled costing you a lot of HP. I would back the 10% down to 5%. pick up a later blower and the 10% pulley will make a noticeable difference at that point. The shorter belt will help as well as the tensioner springs. The best thing after that is to address the entire intake side. Blowers need as unrestrictive flow of air as possible to perform the best

Ken
 
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