So you took the BOV totally off and just ran an open tube? I'd be really shocked if you made much more than a pound or two of boost if that's what you did. Air takes the path of least resistance, so it would all escape out of the tube, and not build boost. I have actually done this on a friend's car (run it without the surge valve), and it didn't make any boost, even at redline at WOT. We did it that way to break the engine in before putting it on the dyno to fully tune it.

 

yep thats what i did. my MAF is still placed in the fender so my BOV vents back into the suction tubing for the blower. so when i replaced the valve with the open elbow, the released pressure goes right back into the blower.

the tube is only 1" diameter so not all of the pressure is lost. i think that if i had the tube open to the atmosphere then id lose a little more boost & power.

but believe me, its still pulling hard. ive run the car without the blower and its night and day. with the hollow elbow instead of the BOV, i can barely notice a difference.

like i said before, i know im boosting because i can see the ignition is pulling timing under boost. there is a little red LED light that comes on when its sensing boost and retarding timing. i just dont know how much boost im actually loosing.

after i relocate my MAF to the factory position ill see how it runs. i just thought id experiment a little. my motor is still stock and i have been thinking of ways to reduce the boost so that it will be easier on the motor. and then when this post came up it motivated me to try my idea.

but i will carry the BOV with me incase i ever run up against a worthy opponent, ill have pull over and do a quick swap though.

 

I do have a gage. My bov vents to atmosphere so I don't know if that would make a difference.

It seems I could just keep my bov from fully closing and adjust it to where I want but I may not have to. I dynoed today and saw at max 8.5lbs at 6k. I will shift sooner so I may not even be past 8. I may live with that.

 

so your motor is stock?

im worried about having 5-6 psi on my motor.

good luck.

 

Mike you could rig up what is called a waste gate, not a "pop off valve" or blow off valve. The wastegate can be set to bleed off boost at high rpms.

 

SS, yeah my motor is stock. I wouldn't worry at all with 6lbs if you have a good tune.

Cpt, I know of the things I could buy to manage boost but since I am cheap, I didn't want to resort to that yet. I wish I could get all the buttons.

 

I was told by Doug Mangrum that you can adjust the BOV to adjust the boost level(to bleed some off). I am not sure how it is done, but they do it alot.

 

That is not a good idea on a blower car...when you vent the boost to atmosphere to keep it at a certain level, it drives up the parasitic losses of the blower, and it is also very hard on it.

I don't know if Mangrum has done that on any street cars, but I know for a fact that he doesn't do it on his race car.

 

How would boosting to atmosphere and therefore loosing boost, cause more stress on the unit?

And short of buying another pulley, and restricting the intake, how else could I do it? And not being able to buy anything anyway.

 

I don't see how it can be any harder on a blower unless you are just talking about the difference in how fast the blower is spinning compared to a high boost set up and a low boost set up. When I was talking to him in his shop, I ask the same question. Instead of the swapping pulleys, is there any other way to lower boost. He told me that all I have to do is adjust the BOV to vent some of it and he acted like is was no big deal and no additional wear... Maybe the best thing is to swap pulleys, but it is easier and quicker to adjust the BOV than to swap pulleys. If you plan on doing alot of street driving then i probably would swap pulleys. Mine is going to be mostly race(very little street driving..friday/saturday night and to the track 5 miles away).

Good Luck

 

I don't know that a blowoff valve is going to solve your problems completely. If you think of just plain ATM pressure vs. a hungry 350 CID engine sucking down everything I think you'll find that a 3/4 or 1 inch pipe isn't going to make much of a difference.

I think you totally fine as you are. Just as long as it wasnt' tuned to the edge with timing you should be quite alright.

I ran 10 PSI with a eaton supercharger (one known for its heat) and 10.5psi for a good time without hurting anything. I finally rebuilt it because the 133k engine was leaking oil everywhere.

 

It isn't on the edge timing wise. Wow, 10psi is awesome. Maybe I will have the same luck.

 

Here's why:

When you have a blower that is making 20 psi (x), then it is taking (y) amount of power to make x amount of boost. But then you only want to make 12 psi, so you put a pulley on it to make 12 psi (w). The blower is now only using (z) amount of power to make the 12 psi (which is lower than y).

Now you want to use the 20 psi pulley to only make 12 psi of boost. So you take a boost controller to regulte it down to 12 psi. Well, the blower is still trying to make 20 psi, so it is still taking y amount of power to turn it.

So you are actually asking the blower to work a lot harder than it needs to, which means that it is consuming more power. It's all parasidic losses.

 

I understand that. But I don't have a bigger pulley so I have to use the one I have. Therefore, in my case, regulating boost by the bov won't work the s/c and more than it is working now at full boost. Theoretically, it would be working less although the efficiency would be reduced.

 

maybe someone else who agrees with your theory can explain it better, because what you said doesnt make any sense.

the supercharger doesnt expect to make any boost at all. and it surely doesnt know what YOU expect it to make.

boost pressure is a byproduct of the resistance of the blower's airflow from the motor etc...

if your saying that there will be less stress with a larger pulley because the rpm of the blowers impeller is reduced then you are correct. but i dont think that the blower he owns has any problems at the rpms it is running now. the lowest advertised ATI blower is 8psi. im sure his blower can easily make over 20psi when pullied to do so.

slim doesnt want to fork out a bunch of cash to reduce the boost so we are throwing out ideas for him to relieve excess boost.

releasing boost to the atmosphere will not cause anymore stress on the blower. it will not be working any harder. the blower rpm is directly related to the engine rpm. reguardless of how much boost (resistance) you will see on your boost gauge, with the same pulleys the blower will be "working" the same amount.

its like this, the blower creates a certain amount of air flow at a certain rpm. resistance creates pressure on the discharge side of the blower. bleeding off air doesnt change how much flow the blower is putting out, it just changes where the air is going.....into the motor or into the atmosphere...