Can a 6-71support a 540 ci engine?
Can a 6-71support a 540 ci engine?
(OP)
I was talking to a friend on the West Coast about a new
engine for his drag car.We have most of the geometry worked
out for a 4.50 stroke 540ci engine but his class only allows
a 6-71 blower.The class allows the blower to be overdriven
65% but this engine also has to be able to turn 8000 rpm.
I have been trying to find some info on the 6-71s and what
their flow limits are,but so far I have gotten very little
information.I deal more with naturally asperated engines
so this has me at a stand still.Any info would be great.
Thanks
engine for his drag car.We have most of the geometry worked
out for a 4.50 stroke 540ci engine but his class only allows
a 6-71 blower.The class allows the blower to be overdriven
65% but this engine also has to be able to turn 8000 rpm.
I have been trying to find some info on the 6-71s and what
their flow limits are,but so far I have gotten very little
information.I deal more with naturally asperated engines
so this has me at a stand still.Any info would be great.
Thanks





RE: Can a 6-71support a 540 ci engine?
RE: Can a 6-71support a 540 ci engine?
RE: Can a 6-71support a 540 ci engine?
427 ci BBChevy and runs low 7s at 2400 lbs and is turned
at 9000 to 10,000 rpm.We believe that if that the larger
engine will actually be easier on parts and provide a
major power advantage over the smaller displacment cars
in the class providing that we can get the 6-71 to feed
it.As far as screw compressor,its illegal because this is
a nostalgia class and the screw compressor type blower was
not used in the gasser era.
RE: Can a 6-71support a 540 ci engine?
Blacksmith
RE: Can a 6-71support a 540 ci engine?
I assume you are stopping at 540 because of limitations regarding Vintage looking heads or block?
RE: Can a 6-71support a 540 ci engine?
Patdaly---Doubla A 'GAS' ---no exotic fuels. And the 6-71 WILL work OK even if an 8-71 would probably be better. Rules are rules.
Rod
RE: Can a 6-71support a 540 ci engine?
MicronX, I suggest you either get ahold of Craig Railsback at BDS Blowers in California or Jim Oddy at Oddy/Perfection engines ( I dont remember if he relocated to Fla. or if he is still in NY.) Either of those guys have forgotten more about Superchargers than I will ever know!
RE: Can a 6-71support a 540 ci engine?
I am starting out again in "Vintage" racing in a couple weeks at Buttonwillow and it's not the 'real old days'. What I infered about that 540 inch monster was that there NEVER was an A gasser with ANYTHING like that in the late fifties early sixties. If you ran an authentic nastalgia rig today, the guys wouldnt know how to keep it running !!!
Rod
RE: Can a 6-71support a 540 ci engine?
stay with the smaller engine.In the Nostalgia classes the
engines must appear to be period correct but internally
anything goes.I have a Nostalgia SS engine on one of my
stands right now that is 513ci.Believe it or not,some of
the factory team cars had engines this big in the 60s.They
would use them as "Hit" cars to take out the closest
competitor and then claim they broke to avoid inspection.
This would allow the other Legal team cars to advance
without any real threats from the other teams.
RE: Can a 6-71support a 540 ci engine?
stands right now that is 513ci.Believe it or not,some of
the factory team cars had engines this big in the 60s.They
would use them as "Hit" cars to take out the closest
competitor and then claim they broke to avoid inspection."
Ah, for the good old days again!
RE: Can a 6-71support a 540 ci engine?
you have a high enough static mechanical compression ratio and if you spin the blower fast enough.
Obviously you will be limited, but if you build the engine with around a 9.3:1 comp. ratio and run the boost at under 7 psi it will make plenty of power and not heat up the charge too much. The trick is to keep the boost levels down and the mechanical compression high enough to keep from loosing on the left of the curve.
high octane will be an absolute necessity.
I ran a 392 hemi many, many years ago with a 4-71, overdriven 33% with 9.5 to one pistons (before I learned to measure deck height) and it was very strong and stayed together well. The mooneyham blower needed re-stripping fairly often due to the high speeds.
RE: Can a 6-71support a 540 ci engine?
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Can a 6-71support a 540 ci engine?
I have a 540 CID (4.5 bore - 4.25 stroke)with a BDS 8-71 (440 Cid) on it. At 18% overdrive she made 7Lbs boost and with a 25% overdrive she made 10.5 Lbs of boost. Im not sure and im sure someone will correct me if i'm wrong,but i think the heat is produced by compressing the air. At 65% overdrive or less with a 6-71 the boost levels wont be real high. At 10.5 Lbs the motor made 1024Hp and 820Lb Torque.
Call BDS and get there take on what you want to do. If it's Possible, i'm sure they have tried it!
RE: Can a 6-71support a 540 ci engine?
Roots blowers start to heat the air a lot more than is explained by this as the rotor tips go supersonic.
I have not done the sums yet, but I believe from anecdotal evidence by "Blower Experts" that this happens on a big body 6:71, and 8 through to 14:71s at just below 9000 rpm at the blower.
A roots blower is a positive displacement pump, so to get boost, you need to turn the blower hard enough to displace more volume of air at that rpm than the engine would use at it's rpm when the drive ratio is considered.
A big bore 671 theoretically displaces 411 CI per turn of the blower, and your engine probably uses 210 CI for every turn of the engine. With leakdown from the blower clearance. practical examples indicate a 6:71 on a 540 will only maintain atmospheric pressure in the manifold at 1:1 drive ratio. Normally aspirated raceing engines normaly have a slight depression in the manifold, so it is a slight boost in fact.
My sources say 25% OD should give about 10 lbs boost, which falls in line with Steve Huck.
My main source is of info is http://www.kuhlsuperchargers.com
Regards
pat
RE: Can a 6-71support a 540 ci engine?
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)