I have a mini blower on a sbc it runs fine needs to be fine tuned its a 350 9.5:1 demon 750 vac 2nd backed by a m21. question is this i dont get any boost til 5k then i get my full 5psi what gives? why dont i get it off idle or at lest under 2500?

Jon

 

That's weird. With the 142 blower on my 383 I get almost full boost the instant the pedal hits the floor and it holds that almost constantly all the way up the rev range. You getting full throttle opening? Maybe the secondary side of your carb isn't opening up until very high RPMs (carb problem)? Is the belt slipping?

 

I would figure the belt would slip up in teh higher rpm not the lower and its tight .5 in on each side as the instructions say. my demon isnt blower referenced but that shouldnt cause it not to get boost. I dont have a throttle stop on the car and it goes wot.

 

Hook a vacuum gauge below the carb and see what happens, I think Damon may be on to something tbh. Other than that, what's up with the motor mods wise and are you using the stock pulley? If you don't have enough pulley on the supercharger compared to your engine flow (big cam, aftermarket heads etc. etc.) that can mess with your boost levels. Also, any hissing like the intake leaking?

 

my vac/boost guage is manifold referenced. I show an amazing 20 in of vac. Mod wise its a mild cam stock heads kb hyper pistons 1.5 rockers. No leaks from the intake even if I did miss it there would/ should bed at least some boost down low and ti having boost up high i would assume that i dont have a leak

 

how many miles are on the blower?

Maybe its just wore out and seals so bad that it cannot move enough air to make boost at the lower rpms...?

 

like 30 miles

 

i have a 144 cu. in blower on my 350 . it"s a 8.5 to 1 comp. 350 iI get boost instantly from a little under 3/4 to wfo on the skinny pedal. i am running a 750 double pumper. i would look at your secondarys as the cause for no low rpm boost. it sounds like they are not opening fast enough!

 

they open up im pretty sure but why would that be the cause of not getting boost at low rpm? vacuum?

 

hard to make boost without any air!

 

This is true. My secondaries are opening up all the way. I tried a different Demon and its the same.

 

sorry i did not respond sooner i have been out of town working do not have a lap top. if u know your secondarys are opening fast i would start looking at your valve train as a posibility. if the lobe seperation is to tight it can cause boost to be blown out the exaust valve as its still open. a good blower cam has 113-114 degrees of lobe seperation. have you called the manufacture?

 

Let me ask a question..... if you're getting no boost until 5000 and then it jumps straight up, can you FEEL a dramatic change in power at that point (like hitting a nitrous button)? If what you're observing on the gague is correct that's what it should feel like.

If not, I'm suspecting maybe your gague isn't reading correctly. Maybe the needle movement is a little sticky on the boost side.

Also, you are hooking it up to the fitting above the #5 intake runner, right?

 

Not a dramatic surge but you can feel it. I am not at home so I am not sure if its ont eh number 5 but I am pretty sure it is.


I havent called demon or weiand yet.