boost question

in my 526 bbc im running a a Littlefield 8-71 supercharger. 28.6 over I believe it is. top pulley is 28 bottom is 36. for the first time out now that I have my racepak, the boost is telling me I am pulling 16 lbs. of boost. my engine guy said he thought it should be about 25 lbs. does this make sense? I do have about 40 runs on the blower. and I did buy it used which I was told it only had a very small number of runs on it. my car ran a 7.76 at 176 on a very rich tune up. this Saturday im going to lean it out a bit and see where it goes from there. but I am going to have to go faster soon since I was the 16th qualifier in top sportsman with that run. should I change the pulleys? have the blower restriped?

by the way, I was very happy I qualified for my first ever top sportsman race. but I was too anxious and went red in the first round. oops. was a good day anyway

 

25 psi seems high for that od.

 

which end of the manifold is your boost sensor located ?

 

I have the backside of the manifold tapped into a fitting with a steel braided hose going into the boost sensor for the racepak mounted on the fire wall.

 

In my experience with a setup close to what you have I'd say 16 psi is very realistic.

A "Littlefield 8-71" can still be many things, is it 25 yrs old or is it a LB-20? big difference.

Also in my experience cams make a big difference in psi readings.

We make more then 25 psi with our BBCs with our 8's, but that doesn't mean there are troubles with what you have, probably just means your combination makes 16.

Are you happy with its performance, if so, leave it alone.

 

My calculations comes up with 16.75 psi for that motor size.

 

that sure would make sense. I am getting a new pulley to go about 35 over for this Saturday. thank you

 

Isn't boost a resistance to air flow? If so, a poor set of flowing heads will show a higher boost given the same blower and OD than a set of good flowing heads?? JW

 

I always thought boost was an increase in airflow.

The main difference between the psi numbers is the motor size, larger motor has more volume so more air is needed.

 

Boost is a measure of air you're not using.. You can vary your boost numbers by any number of ways.. Cam, compression and even where in the manifold you measure the boost. The higher the number, the more air you're keeping stacked in the manifold and theoretically the greater the pressure and more air you're letting into the cylinder, but it's not always the way leading to the most power at the crank.