Big Blocks & Superchargers
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Joined: Feb 2006
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From: Mississippi
Big Blocks & Superchargers
Well I had a post about a B&M 174 s/c and overheatin',and then 'bout clutch.Well clutch is on the way Mcleods street twin that should solve cltutch problem...now have dual Ron Davis fan setup on Ron Daivis BB alumin. Rad....also installed deraile oil cooler w/ 650cfm fan.....not much boost though.....Weiand tech rep asked why I ever installed 174 on B/B(427)....contacted superchargerusa and they said the small blower was the over heating problem?.....They suggested a 671 w/ 2 750cfm mech double pumpers....so guess I'll throw more MONEY at it (671)......so what is everyones opion that has alot of s/c experience..... .....mtr 427 .30 over pistons 9.5:1 w/forged trw lunati 50249 Roller cam....GM (290cc flow) alumn. Goodwench heads.....Davis DUI Hei dist....MSD 6BTM .....Hooker sidepipes
Melting Slicks
Joined: Nov 2003
Posts: 2,362
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From: San Antonio TX
There are a few here that run a Super charger. And I know of someone here that goes here as well. http://www.chevelles.com/ You will find a bunch more information over there for what you need. 
Drifting
Joined: Jul 2000
Posts: 1,347
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From: Melbourne Australia
Sorry can't help you with your overheating prob, i'm running a 8-71 on a 427 without heating probs....not in a Vette though.
9.5:1 is to much static for the street, don't know if i'd be going any over 8.5:1.
With 9.5:1, you may have to underdrive that blower that much that it may end up sucking
What info are you after?
9.5:1 is to much static for the street, don't know if i'd be going any over 8.5:1.
With 9.5:1, you may have to underdrive that blower that much that it may end up sucking
What info are you after?
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
Not sure who the hell wants my opinion but a couple of concerns are apparent. Run as high of octane you can get, a minimum of 100+. But i`m sure you were going to run that stuff anyway or else why the blower, right! I also presume your not currently 'O' ringed. Run a very good gasket and possibly a thick one to quell some of the 9.5 compression. That high is only good for the pros and not for the street. I also presume that it`s a solid roller cam to be able to spin that thing well past 7K. Put the 18% over drive pulleys on and start out with 36 degrees total and NO vacuum advance please. Oh, and idle under a 1,000. Start out slow and if the chassis can handle it you should be in the buck thirties the first pass. Experience and tweeking helps from here on.
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Joined: Feb 2006
Posts: 50
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From: Mississippi
Sorry can't help you with your overheating prob, i'm running a 8-71 on a 427 without heating probs....not in a Vette though.
9.5:1 is to much static for the street, don't know if i'd be going any over 8.5:1.
With 9.5:1, you may have to underdrive that blower that much that it may end up sucking
What info are you after?
9.5:1 is to much static for the street, don't know if i'd be going any over 8.5:1.
With 9.5:1, you may have to underdrive that blower that much that it may end up sucking
What info are you after?
Thread Starter
Advanced
Joined: Feb 2006
Posts: 50
Likes: 0
From: Mississippi
Not sure who the hell wants my opinion but a couple of concerns are apparent. Run as high of octane you can get, a minimum of 100+. But i`m sure you were going to run that stuff anyway or else why the blower, right! I also presume your not currently 'O' ringed. Run a very good gasket and possibly a thick one to quell some of the 9.5 compression. That high is only good for the pros and not for the street. I also presume that it`s a solid roller cam to be able to spin that thing well past 7K. Put the 18% over drive pulleys on and start out with 36 degrees total and NO vacuum advance please. Oh, and idle under a 1,000. Start out slow and if the chassis can handle it you should be in the buck thirties the first pass. Experience and tweeking helps from here on.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
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From: Butler Pa
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Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
I ran 8-71 on a 454 without a problem and ran it 15% overdrive for 12 pounds of boost.
I would not get the 6-71. I would move up to the 8-71 if the price is almost the same. The 8-71 in 1 inch longer then the 6-71 and can be run about 7% slower and give the same boost.
The slower the blower turns the cooler the intake charge.
I would like to move up to the 10 or 12-71 on my 540
I just reread the other replies and see you have 9.5 compression. I run 8 and if you run 9.5 and 8 or 10 pounds of boost your effective compression exceeds the 12-1 recommended and you are in the 14-15 range.
I do run normal 93 octane and still run 12 pounds of boost but I can get away with it because of the 8-1 compression. I also run a boost retart computer.
And for Dep I do have $20,000 in my motor.
I would not get the 6-71. I would move up to the 8-71 if the price is almost the same. The 8-71 in 1 inch longer then the 6-71 and can be run about 7% slower and give the same boost.
The slower the blower turns the cooler the intake charge.
I would like to move up to the 10 or 12-71 on my 540
I just reread the other replies and see you have 9.5 compression. I run 8 and if you run 9.5 and 8 or 10 pounds of boost your effective compression exceeds the 12-1 recommended and you are in the 14-15 range.
I do run normal 93 octane and still run 12 pounds of boost but I can get away with it because of the 8-1 compression. I also run a boost retart computer.
And for Dep I do have $20,000 in my motor.
Last edited by norvalwilhelm; Mar 5, 2007 at 03:57 PM.
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
A 671 is adequate. I have gone 235 with one. But you have problems that I dont like. As I suspected, no 'O' rings. And a solid lifter camshaft would be better than a hydraulic roller. If you float the valves and bang the blower the rotors will hit the case damaging the expensive blower case. If this is not for go and only show, your missing the advantages that a blower can give you.
Racer
Joined: Oct 2006
Posts: 435
Likes: 18
From: Florida
check out the blower shop, they have "high helix" rotor supercharger line. they are a few hundred more than regular superchargers. they operate more like a screwcharger........... call and run your numbers down to them. 1 more thing, they are listed as race items though!!!!
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
I have a chart in front of me with compression VS boost. With 9.5 compression your maximum boost should not exceed 4psi.
If you start with 9.5 and add 8 psi boost your effective compression is 14.7
I start with 8 and add 12 pounds of boost for an effective compression of 14.5 I do run on regular 93 octane and don't seem to have a problem.
If you start with 9.5 and add 8 psi boost your effective compression is 14.7
I start with 8 and add 12 pounds of boost for an effective compression of 14.5 I do run on regular 93 octane and don't seem to have a problem.
Le Mans Master
Joined: Apr 2000
Posts: 5,202
Likes: 10
From: cincinnati ohio
St. Jude Donor '09
Le Mans Master
Joined: Jan 2006
Posts: 6,506
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From: Butler Pa
Thread Starter
Advanced
Joined: Feb 2006
Posts: 50
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From: Mississippi
Looks like the Engine will be torn down
I have a chart in front of me with compression VS boost. With 9.5 compression your maximum boost should not exceed 4psi.
If you start with 9.5 and add 8 psi boost your effective compression is 14.7
I start with 8 and add 12 pounds of boost for an effective compression of 14.5 I do run on regular 93 octane and don't seem to have a problem.
If you start with 9.5 and add 8 psi boost your effective compression is 14.7
I start with 8 and add 12 pounds of boost for an effective compression of 14.5 I do run on regular 93 octane and don't seem to have a problem.
this is a street car so I also need to remember it's intended use...Mcleods street twins clutch is in...but I will be working 6 12's for the next two -three months....and I'll put it in when I reassemble motor...also will be putting a water/alchol injection on the car that is boost proportional....running an Msd BTM 6 box
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I would try for 8-1 compression. It is better to run this lower compression and more boost then higher compression and low boost. They always recommend the double key. Water injection is not needed. There is alot of room behind the blower. I run a very small Mallory/homebuild distributor so I don't know if the stock one clears but there is alot of room.
Boost is not the problem, rpm is what kills the rods. Keep the rpm down and the rods will live. They should be upgraded with good bolts but the rods are under compression if the rpm is not excessive.
Forged pistons are always recommended and you can give the supplier your head CC's and they can supply the proper dome for the compression you specify. Mine are dished.
With a blower you can keep the rpm down , the boost up for good response and it should hur the motor.
I ran a nitrous bigblock an always turned about 7500. I went blown, turned the boost up to 15% overdrive or 12 psi and found I seldom turned the motor past 5000, it was so responsive.
Which would hurt the motor more???
The 8-71 I feel if the price is close is a better solution then the 6-71. It is all about making the boost and still keeping the rpm of the blower down to run a cooler charge.
I would like to upgrade to a 10 or 12-71
Boost is not the problem, rpm is what kills the rods. Keep the rpm down and the rods will live. They should be upgraded with good bolts but the rods are under compression if the rpm is not excessive.
Forged pistons are always recommended and you can give the supplier your head CC's and they can supply the proper dome for the compression you specify. Mine are dished.
With a blower you can keep the rpm down , the boost up for good response and it should hur the motor.
I ran a nitrous bigblock an always turned about 7500. I went blown, turned the boost up to 15% overdrive or 12 psi and found I seldom turned the motor past 5000, it was so responsive.
Which would hurt the motor more???
The 8-71 I feel if the price is close is a better solution then the 6-71. It is all about making the boost and still keeping the rpm of the blower down to run a cooler charge.
I would like to upgrade to a 10 or 12-71
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
My view on building blower motors is to run as low of a static compression ratio as you can without causing problems with starting. This allows you to run more boost without exceeding the maximum effective compression ratio. After all, the whole purpose of using a blower is to pack as much fuel/air mixture into the engine as possible. If you can safetly run 15 pounds of boost, you have effectively doubled the size of the engine.
That said, the last blower motor I built had a static comprerssion ratio of 5.6-1, and it ran 22 pounds of boost which gave us an effective compression ratio of about 14-1, but we were using 104 octane gas. This motor was used in a boat and never dyno'd but it would blow away a Berckely jet drive that was rated for 1000 hp.
That said, the last blower motor I built had a static comprerssion ratio of 5.6-1, and it ran 22 pounds of boost which gave us an effective compression ratio of about 14-1, but we were using 104 octane gas. This motor was used in a boat and never dyno'd but it would blow away a Berckely jet drive that was rated for 1000 hp.
Le Mans Master
Joined: Apr 2000
Posts: 5,202
Likes: 10
From: cincinnati ohio
St. Jude Donor '09
While on the topic of blown street bigblocks, for your veiwing pleasure...
http://videos.streetfire.net/video/4...1400d402a2.htm
http://videos.streetfire.net/video/4...1400d402a2.htm