Blower sizing

Hi I am running an BBC 481 ci altered 125" weighs 2100lbs car had run 6.90@196mph with a BDS 871 basic blower running 35% oh and 29psi boost, the car has run since with a kobelco k8 1471 but fuel system all wrong so 8.0 but the blower which i had rebuilt when i bought the car has broke so my question is with so many choices hi helix , retro etc would a new hi helix 871 be much different to an older 1471 not looking to push hard but to run a 6 would be good, from what im told its better to run a 1471 slow than to spin a 871 hard but surely with the new hi helix it would be so much more effecient. either way i need another blower but cant go new unless its an 871
thanks guys

 

Rotors and case unfixable ?

 

Beyond economical repair

 

I would look for a good used 14 71. You didn't say how the other one was damaged, but it seems pretty rare to hurt one (although I have destroyed one myself).

There are 1 or 2 good threads on here in the last couple years, but in general these 14 71s would be the best bang for the buck:

SSI F series (1, 2, or 3. A 4 is probably pricey still). Even a high helix d rotor is probably better than a new 871.

Littlefield lb20 or 21 or they made a few with k series rotors.

Kobelco k11

Really any delta retro1471 is probably better than an 871 unless the 871 is tricked out. I stayed away from k8 and k9 rotors when buying mine because I thought they wouldn't be repairable in the event of minor damage (Plus I could t figure out how to identify the scary lightening hole thing in pictures), but I think Andy came on here recently and said that he could replace or repair bad rotors in those older blowers.

 

A good used K11 Superman with some mods and fresh service should be less than 6000.00 . There are several for sale. Remember to put fuel in rhe rear of the case.

 

My kobelco sheered the shaft, most of the blowers ive seen are the retro bottoms which need a set back plate whats the benifit of a retro against a normal delta by the way mine was an open bottom

 

I had a shaft break recently too, I messaged Andy Wilfong from Littlerfield on here and he reckons they can be fixed, depends how much damage has been done to the body of the rotor I suppose.

 

Retro just means more airflow with everything else being the same because there is less front bearing plate obstructing the blower outflow. From what I've read it seems the transition to the retro design happened pretty quickly after the deltas became popular around the late 90s. A delta, even if it happens to be non-retro, is better off with a setback plate to even out the fuel distribution. I suspect you can run either with no setback (pretty sure I've seen it done) but you're probably going to be putting a lot more stress on the front cylinders.