Blower overdrive.

Gday guys, what are your thoughts on the amount of blower overdrive on a 1471 hi helix standard opening blower on a 509 cui alcohol race boat Chevy. Max RPM is 7500. We have just fitted a temp probe in the manifold for the racepak for future reference. We are running 23 over at the moment at are getting 23 LB boost at 7000RPM . Would like to rev to 7500 and increase the boost to 30 LBs , how much overdrive do you think we could put into it before it becomes inefficient and what manifold temp should we look for , thanks guys.

 

I run a 14 HH with a delta at 42% OD and I see 38 PSI on a 526 alky hemi with big chamber fuel heads. Does not seem to be too hot on the air temp. I would suggest a pulley change to at least 35%OD and run it.

 

Our blower has a standard opening not a delta, but thanks for your info I appreciate it.

 

I don't believe that they made any HiHelix (120 degree rotors) blowers with standard openings. I thought they all had deltas because the 120 rotor twist would open a path from the bottom to top on the standard opening. Are you sure you're not running a standard helix blower?

 

That makes a lot of sense, I must be wrong . It’s probably not a hi helix . Thanks for that.

 

Hi Bob,
We ran a 6.006 sec (6.000 QE index) at 21.0 psi @ 25% over at 7300 rpm with a Littlefield HH with delta opening in our Cheyenne Jet boat.
I hope this helps. Joe

 

I am making 24-28lbs depending on air with a TBS 14/71 XR1 at 14% on a 540 BBC. XR1 is a very efficient blower

 

I also have an XR1, 30#@17% with 45 1/8th mile passes since stripped. 540 12° BBC

 

Thanks for that, that’s about the same blower numbers as ours.

 

Sounds good mike but I just wanted some info on efficiency by spinning our blower higher to 31 percent, if at all possible.

 

We actually raced on the weekend mike and the 31 over gave us a 3lb boost to 26lb, so our expectations of 30lbs is probably too optimistic as you have suggested and yes I did richer it up. Thank you very much for your input you have been a big help.

 

Don't forget, if you want to spin the blower faster with what you got you have to add timing and fuel. With good air we can get 7300 rpm at 29 deg, using a Grid/crank trigger and a 44 mag. With a BBC you could go to 34 deg easily, with the correct air to fuel ratio. As Mike has said "a good rule-of-thumb is 100hp/1 deg."

 

Yes mike we gained 2 mph with the 3 lb extra boost , manifold temp unit didn’t work so we have no data on that. Do you know what manifold temp to look for on this type of combo? Remembering it’s a circuit racing boat at continuous high speed for 3 laps.

 

Whats the reason for adding timing? I assume you mean advancing it more? I would have said the opposite but I'm open to learning

 

SoDak,
I have found with my bbc if I advance my timing closer to optimum, I can increase the rpm required for the blower to make more boast to burn the added fuel. For example, if I am near my index (6.000 sec) and need to get a little closer I can advance my timing by 0.1 deg with the Grid and get right on.
Joe