Blower question for all the huffer gurus

[Roothawg]

Got a buddy that is trying to get ready for the Day of the drags. He has a Blown 454 in his 48 Chevy pickup.

Here's the question:
If you drive the blower 1:1, what other things should be taken into consideration?
This is a street truck but, he wants to change pulleys for the track.

What about timing etc?

[Roothawg]

Oh yeah, btw, it is a 8-71 BDS blower.

[Roothawg]

Anyone? BlownOlds?

[Roadsters.com]

There are too many unexplained variables to make this simple to answer.

You would reach more blown rat gurus at the Chevy Talk Performance forum.
http://www.chevytalk.org/threads/postlist.php?Cat=&Board=UBB64

Dave
http://www.roadsters.com/

[av8]

I'd call Scott Railsback at BDS.

[Roothawg]

Thanks.. Mike.

We just wanna make sure we don't blow it up.

[38Chevy454]

Root, one thing to keep in mind is that when you spin a GMC blower faster it heats up the air more, so even though it has more pressure, it may not actually have much more total air. That old hot air expands thing you know? Besides, it takes more hp to turn the blower faster. It is lind of a diminishing return.

I agree that there are a lot of variables and there is not a simple answer. I would estimate an 8-71 should make 6-8 psi boost at 1:1 or slightly underdriven. That should be enough? Or does he want a full on drag race engine?

[Roothawg]

It's set up for 7-8 lbs and it's underdriven. He's gonna try and go direct but no more. 1:1 should be plenty.

[Blownolds]

WAY to many variables with not enough details given, like:

--what's your static CR (and do you know it for certain from careful measuring, cc'ing, and calculating?)

--what is the blower being spun at now (actual ratio, not boost)?

--what fuel, and if gasoline, what ocatne/brand?

--what exactly is the blower? Standard case, retro case? Standard rotors, hi-helix rotors? Teflon lining between rotors, or no lining? Clearanced properly for the type fuel you are using (alky blowers will lock up with gas use according to Littlefield)?

--capabilities of the cooling system?

--any electronic timing adjusters like MSD boost retard?

--what do the heads flow (will the engine be able to freely move the air you are trying to stuff in, and at what point will it get constipated)?

And many other factors.

I will not be able to tell you what you what you can safely do, each application is different. I have seen 1:1 on a few different street machines, and it seems to be a fairly stout amount of drive ratio on the street. Your best bet is to either invest in a bunch of pulleys and start stepping up and doing your tuning changes as you go, or give your best tuneup (and engine analysis) with the ratio you have now, then get a pulley or two to step up the ratio a little bit, and re-tune and analyze. If it isn't pinging yet, try another pulley or two for the next drive ratio up. Take small steps.

That is my best advice, just common sense. I have not yet personally gotten to this point on my project yet. I am supposed to be picking up my blower at the HRR this weekend http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif