Blower over drive

Gday guys I have been wondering how much overdrive a std helix 8/71 could handle before becoming inefficient with non striped rotors. Engine is a big block chev 469cui running to 7600rpm, thanks.

 

On m1, I would expect gains up to 30% for sure and maybe even 40%. Ive seen guys claim they could go higher and some will say anything over 9000 rotor rpm (18 over in your case) is a waste of time, but I’ve never seen any real world data to back that up on alcohol. My very loose 1471 wouldn’t gain et after about 10,500 rotor rpm, but it’s on a teeny tiny motor so more boost therefore less efficient.

 

When we ran 8-71 stripped standard rotor on alcohol on the 496 BBC, we ran 45% over with no issues (tractor pull application). Very seldom went over 8000 RPM. Remember in pulling, our runs last 12-15 seconds WOT.

 

Bob; as you know my standard disclaimer : I'm just a welder !
In the old days when you licked your finger and stuck it in the air tuning program with a 10-71, going from 32% to 38% gained only two PSI, but with a single battery operated temp probe, it gained 40*F in the manifold, explaining to me the reason it slowed down. Old part time detective Bob

 

Thanks for that gives me some good information

 

Thanks Bob good to hear from you, I have only gone up to 20 over and it did go a bit faster so I thought I might try 30 over, if it slows down I’ll assume it’s the manifold temp at attempt to measure it . And yes I’ve been known to lic

 

Talk to the blower manufactures first....find out what they recommend for maximum blower speed and then try some overdrives from where you are now up to max blower speed...to see if boost increases without drastic change in manifold temp....

 

Thanks will do

 

I would not squeeze a roots, without adding fuel to the hat.

 

Most definitely

 

Hi Bob,
I watched an 8-71 blown 565 BBC video on YouTube last night done by Engine Masters.
Some interesting facts about boost, air temps etc, it might give you data to consider/understand.

 

Thanks I’ll look it up tonight

 

Seen the video very information, the gains are quite minimal, it’s stiits worth trying with alcohol the gains could be better.

 

Their combination was a 555" with a wiz-bang 8-71 on E85, your 469" with an unstripped basic 8-71 could be similar boost numbers but higher boost pressure can also be showing up resistance to airflow ....... ie; heads and camshaft inadequacies.
Good luck, keep us informed please.