Question about 871 retro and set back

I have a Blower Shop 871 retro blower.
It has the delta (pie shaped) opening and an extra opening just under the front cover.
I made a plate that covered the forward opening and installed the blower in original bolt location.
Naturally it feeds the front 4 cylinders a lot more than the rear 4. Really hard to tune using the hat, after installing port nozzles allowing me to lean the hat it worked very well.

Question I have is how far back should I set it to sort of equal out the flow more? Second, how much effect will uncovering the front opening have on boost and tune up if any?

Thanks
Dave

 

If it's a nostalgia classed car, back of blower even with rear motorplate is the limit.

 

Thanks Bob.
It's just a bracket car. It did run 4.30's until it broke a rod last month. I'm going to set it back for sure, but was curious as to information on any gains/losses I may get.
For example, I'm thinking I should get more volume by opening the front rectangle under the front case, but how much will it effect the tune by having it discharge closer to the front four cylinders? I know it killed them when I was only using hat nozzles.

Just looking at the openings, it looks as if I could go at least 8 inches just to get it close to the center of the intake. That would really extend the snout out there.

Thanks
Dave

 

Not sure I understand without pictures but if you blocked the front of a retro outlet it has to be killing power pretty good. If I was taking a guess at a tuneup change after you set it back I’d add 20% to the blower flow as a baseline and see what it does. 8” doesn’t sound unreasonable but you probably don’t need to go that far. What kind of intake? Maybe your lacking a little plenum volume and that was adding to the load on the front of the motor?

 

Huh, i think I found a pic of the type of blower you’re talking about. Never seen that. Wonder why they leave the front of the case intact; seems like it would flow a heck of a lot better without that. It doesn’t really look like the front of the rotor is exposed though so not sure if that even counts as a retro.

 

BJ, believe me boost will come out of there. I found that out when I first mounted the blower, not realizing it was open..

 

Mike, Thanks, I was under the impression it came out at a 90*.
When I first installed it I was running on hat nozzles only. At the 4th pass it would kill the front 4 cylinders. I put port nozzles in and leaned the hat down which fixed that issue. I can run all season if I want on the same plugs now.
I'll see what I can get as far as a snout and build a setback plate. Do you think it would be better to leave the front opening open or block it off?

Thanks

 

Email sent

Thanks

 

Picture of blower.

 

I would definitely move the blower back at least far enough to get the retro opening in the manifold! The idea of the retro is since most if not all of the air is discharging of the front tip of the rotors @ a45 degrees angle the more you unshroud the front tip of the rotors it will improve airflow and not just thrash and super heat the air! They claim a retro blower is worth at least 200hp over a non retro because of the efficiency! Almost as much as a High Helix! The blower shop originally modified the bearing plate to accommodate the retro opening before they designed their XR-1 with a completely redesigned case which actually moved the rotors back so the retro opening is in the case and not in the bearing plate! So definitely move the blower back at least enough to get the retro opening in the manifold even if you can't move it back enough to place it over the center of the manifold it will most definitely make more power if tuned correctly! And you're intake temps will be much cooler!

 

Thank You Neil.
Obviously I was not aware of any of that. Much appreciated. I can build a set back plate to get it as close to centered as I can.

Again, Thanks