You're supposed to reverse the rotors and use high-speed bearings and double-lip seals at the very least. DON'T try to do it yourself. It's not as simple to time the rotors as you might think. Also you need to know how to set the clearances. Best left to a qualified supercharger shop. I can get you a 5% discount on service work with Supercharger USA (superchargerusa.com), and I highly recommend Tim's work there-- he is METICULOUS! E-mail me direct at blown394olds@yahoo.com if you wish to use SUSA.
Not to hijack the thread but I was curious. How are you planning on adding oil? Does the cool valley cover have a provision for a filler?
I have run a 6-71 with a 3" gilmer belt drive on two different 327 chevys,with stock dampers,not bolted on just pressed,a lot of those older small blocks werent drilled and tapped at the crank snout. I have never modified any of my dampers,and havent had any problems.
I am going to try mine that way. I did drill and tap the crank for a bolt and got a steel damper rather than a cast one. Its good to hear it works.
It never hurts to put the little extra effort it takes to tap the crank snout and add a bolt to hold the dampner on. If you've ever seen what happens when a dampner comes off at 5000+ RPM - you'll be glad you did! It is like a 5 pound sledge hammer bouncing around the inside of your engine compartment. Didn't happen to me . . . but I saw what it did to somebody else's car . . . not good. Like anything else . . . when you have insurance, you typically will never need it -- but holy crap if you don't . . . when shit happens, it can get ugly.
Tudor. On the flip side of that coin, 8th Grade Genius' Chevvie in his Willys ran about 15 minutes before fuckin' up the stock single key. But...I think he runs a pretty good dose of boost. PS. Bitchn Hemis, Kerry and Krooser. REJ. I GOTTA see a pic of your blown "leaning tower of power." I love slant 6s. -Abone.
Yeah - I would do the double key in a heart beat had I been educated when I was putting the motor together. I didn't know I was doing ablower back then. I do have another crank to go in the engine if anything goes bad so I'll get it keyed and put it on the shelf. I just have it all together and decided to roll the dice and get some field experience. I'll keep an eye on it. Krooser - you need about 4 more carbs - I have been told 4 of those 2's will hardly feed a blown sbc with a 471. I am going to do some field experimenting in that department too.
Well, after the holidays were going to get started. I will keep everyone posted and if anyone has anything to add that would be great. If it works...I'll be the guy in the thirty one w/ no tread left to get home from Viva Las Vegas!!
on the keyway thing, on my big block I just run the one original key, no problems. the crank snout on a big block is a LOT bigger than on a small block, plust it goes all the way thru the damper, not just half way. On a small block, I'd want to bolt it on for sure, and double key it if running more than maybe 8 psi boost.
I also rebuilt a diesel blower myself. My buddy was using the 6-71 blower case as a door stop and gave it to me for nothing. He also had some rotors he threw in too. Got the rebuild kit from Deans blowers on evilbay and also scored a slightly used drive kit "cheap". Cleaned and deburred the rotors and case and assembled it myself. The motor is only 280 cid so I run it 20% underdriven. It will spin up to 12 psi at around 4000 RPM with a stock bottom end (no problm so far after 5,000 miles). Mine runs dry and it as it's mutiport EFI. (Not exactly old school, I know) I used wrinkle black powder coat on the case and the finned rear cover which I really like. The drive kit was $600 and the rebuild kit was about $60. There are some articles here that have good info on "converting" a diesel blower http://project33.com/category.cfm?Category=Engine
Hi guys I'm new to the HAMB and thought I would share my GMC 671 experience as it might somehow be useful to someone. About 2 months ago I read this thread trying to educate myself on the old 6-71's because I had run across one for cheap. The thread was a lot of help, so I decided to jump right in on the conversion. First I did the machining of the bottom of the case easily with a riciprocating saw and a grinder. It took about 2 hours but turned out really nice. Secondly I did have to swap sides with the rotors. I left the original shims and gears with each rotor, and upon reassembly ended up with a near perfect .007" drive side rotor clearance. And ended up with .006 rotor to front plate clearance. I'm not sure if this would work on every blower but it certainly did on mine. As mentioned above I bought a seal, bearing, and gasket kit off ebay from dale wilch. Think it was about $80. I also got my pulleys, idler parts, and so forth off ebay from various sellers. Finally about 3 weeks ago I got it installed and fired up. Blower sounded and was working great. At 4% underdrive it was making around 7psi. However, I had been making 7psi with a weiand 144, so of coarse I was dissapointed. So I swapped the pulleys and made 9psi at 5% overdrive. Still not satisfied I decided that my problem was lack of induction (single 750 cfm dp). Added another 750 (1500 cfm total) and made 14 psi. Now we're getting somewhere!! The second time I drove it in this configuration it sheared the woodruff key (yea just one) and broke the stock cast iron balancer. I found out the hard way that to make real power this area has to be addressed.
yeah, running over 8psi or so on a small block with a stock balancer and single keyway is asking for trouble
Anybody know of a way to maybe pin the balancer rather than pulling the crank to have another keyway cut in it?
YOu might discover that the crank snout is screwed up now. And you might want to run a steel crank if you're going to run a lot of boost. Or get one of these https://www.competitionproducts.com/prodinfo.asp?number=353557-4
I imagine you get to buy a custom timing cover also. But that's peanuts after spending 1300 on a crankshaft
Thanks for the link, thats a really nice piece. I have started a new 377 that will definatly have a better crank but it will probably be spring before its ready to go. I guess until then I could turn the boost back down and just limp around with a steel sfi balancer for a while. I got lucky on my crank it somehow lived.
What I meant was, the crank might have some damage to the snout that you can't see, so that it's a bit undersize now, and just putting a new damper on it won't last long. I've seen someone go thru that, he lost a few more dampers before he figured it out.
Ok, I didn't think of that. Now that you mention it, I have put another stock balancer on it just so I could move it around. And it did go on alot easier than I thought it should. but I didn;t think much of it. I will check that out.
I didn't see anyone talk about the old style 671 that have the 6 bolt pattern.Have any of you ever used one like that.This one came off a gmc bus and the mounting bolts are long, two on each side with one on each end of the case. Let me know if any of you guys have ever used any thing like this.
I think so, my hesitation is it belongs to a friend and he is asking me these questions.That looks like what he is describing. Has anyone used one in a stret car application? I wondered if anyone makes a manifold that would mount on or do you need to fab one?
As far as I know only Dyers used the v series blowers-6v71/92 (2 bolts per side). You may still be able to get the manifold top casting from them to weld on a dual 4 intake if you're feeling really ambitious.
This is all defined by "What are you going to do with it?" which is quickly followed by "How much boost are you planning to run?" There are plenty of bolt on blower kits that demand no changes to the shortblock but produce noticable power gains. Wieand / Holley make the 177 and 142 street blower that turns out 6 pounds of boost and are pretty much a direct bolt on. I ran one on my v8 Vega with a cast crank / piston set up for years. Even drag raced it for 2 seasons running high 11's. Pulled the motor apart and it was perfect. Compression and detonation are you big concerns. Compression over 9 to 1 and you are playing with fire. Detonation KILLS... Mallory makes a great boost controlled MSD that can be controlled from inside the cab which defends against detonation extremely well. A secondary concern is your crank snout. Much of that depends on the size of your belt. The big wide ones don't slip much but put a terrible load on the crank snout. This is where you break cranks and tear up bearings. Don't try to do too much with your stock set up make sure the rebuild is solid and uses quality parts and your cast bottom end will be just fine. If you are planning to build boost and leaning on it more than a few times then you are entering the danger zone for cranks, rings, head gaskets etc etc etc. Blowers for performance (8 - 10+ boost) put a lot of strain on the bottom end. Steel cranks, good rods, forged pistons (Blower pistons prefered) start becoming a demand. ARP bolts and studs all around and good bearings. Unlerss you're running alchohol or alchohol injection then your compression should be around 7 or 8 to 1. Don't over think it in the cam department. Blowers compensate for mild cams very nicely. However, if you want to make power then you are looking for a cam with a lot of duration. Off the shelf nitrous cams work very well thank you. Once you've done all that you now have to seal it up with the right rings and good head gaskets. (O-ringed if possible) and a set of ARP head bolts. ARP head studs prefered. When it comes to the heads them selves, again... don't over think it. Blowers create their own flow. A decent performance head (2.02 / 1.60) works great. Make sure the valves are seated well and you have a good set of valve guides. What you have to match up are your valve springs. They have to be stiff enough to keep all that boost in the cylinders but not lean on your valvetrain to hard and bend pushrods or break rockers. High RPM is not only not necessary for a blower motor but it is actually very hard on the blower. That's a lot of rotating mass you're trying to spin. Once boost starts to build you need to retard the ignition. The Mallory MSD boost sensitve unit (or similar) is a must. You also cannot use an off the shelf carb / carbs. Talk to a blower shop and get purpose built carbs. You'll be glad you did.
DOUBLE KEY THE CRANK! RUN A STEEL BALANCER OR CRANK HUB! AND ABSOLUTELY TAP THE CRANK SNOUT IF IT IS NOT ALREADY DONE FROM THE FACTORY!!! It will save you a lot of grief in the long run.
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