blower intake question

Hi, I have a tunnel ram thats been modified for a blower with an aluminum plate welded to the top (trick flow). This a Ford motor with A460 heads so there's no production blower intakes. I bought this as a package, the question is that the plate has the small opening, matches a 6-71 gasket which is what was on it when I bought it. I now have an SSI 14-71 and am wondering if its worth the trouble to have the intake machined larger for the 14-71 opening or will it work fine as is? Wondering if it would make more boost with the small opening since it will have to squeeze more air into a smaller opening. Thanks in advance! Chris

 

Remember that it is air volume that you want. It is always better to eliminate any restrictions that you might have.

 

You would think so but have you seen the base of the DMPE M5
the hole in the bottom is realy small

 

Actually, I haven't seen the bottom of Darren's blower design, only the top side. My statement was based on the fact that he said that he had a manifold for a 6-71 blower. That is the smallest that GM designed. A Rootes type blower is not a "compressor" like the screw type.
I was just cautioning him that air volume is truly important to his performance.

 

I was told buy several blower shops that you can make or have one made it is a 3/16 to a 1/4 in. thick plate with a pie shape opening in it to go on the manifold of the large opening on the blowers with the big opening they say you will gain performance...Dave
www.myspace.com/daveloweswr

 

I vagly remember when the big openings started to shrink and owners of big opening blowers were making pie shaped plates. They claimed they worked but I wonder how.

My understanding is that the smaller openings work because the rotors are sealed longer/more. This wouldn't be true when using an "adaptor plate" with a smaller pie shaped hole. Maybe more heat is generated and therefore more fuel is used thus making them think they are making more HP

I would make your plate to the size of the blower outlet then if you want to experiment make a pie shaped one and see if it makes more power.

 

I was wondering about this also, I know that the small opening allows for a greater contact period.

My thoughts are that this also means that the spinning rotors are subjected to the manifold boost for less time. If you can picture the front edge of the rotors and figure its surface area then the amount of boost pressing against it then you can imagine that with say 40 sq inchs of area and 40 lbs you have 1600 lbs of pressure, the rotor tip top rotational center average it say 2 inchs so divide that by 6 and you wind up needing 266 ft pounds of torque during this period to overcome the load. And since the rotor is rotating fast the actual pressure at the face of the rotor is probably at least twice that number, so it seems anything you could do to minmize this the better.

Now for thought number two,

That is that you can decrease the blower opening size to the point of the combined port cross section of the motor at any given moment...(IE all of the cylinders are not breathing at once) without loosing any substantial flow.

As I say these are just my thoughts on the subject, anyone with any knowlege from a blower dyno or has talked to one of the blower manufacturers about this please feel free educate me.

 

blower flow

Bottle fed, You are going in the same direction as what I have seen. A smaller bottom opening reduces reversion into the blower from the manifold boost and makes it more efficient. Regarding the opening size in comparison to the combined port size, a major contributor to engine efficiency is reduction of intake pumping losses. Pumping losses occur from any change in direction, change in cross sectional area, as well as change in speed. A Formula one engine has the intake port biggest at the inlet and gradually getting smaller to the valve seat. And as straight as possible. In contrast, the blown stuff we play with is a real mess from that standpoint. Add to that the fuel flinging from the rotors and it becomes a massive trial and error task. We have some discussion of the pumping issue and intake design in our publications and plan to do more. Pumping loss discussions and info are one of the biggest shortcomings in all of the information resources we have seen and I believe one of the areas for greatest gain. That is why we provide some of that info in our books. It is more often the key to why one engine combo makes more power than another.
Bob szabo, author Fuel Injection Racing Secrets and 5000 Horsepower on Methanol
www.racecarbook.com