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671 Blower Conversion

11K views 12 replies 3 participants last post by  camaroman7d 
#1 ·
Anyone here ever converted a 671 GMC blower over to gas to run on a street driven car?
 
#2 ·
While I have never done it personally. I looked into it before buying a blower kit and it is not something you do in your garage and bolt it on. If you do the research you will see that by the time you buy all the needed parts and have the required machine work done, there will be no money saved. With that said all the old time blower shops (any still many today) start off with a diesel core. Over the last few years more and more shops are using or casting/machining their own new cases.
 
#3 ·
I was thinking maybe I could save a few bucks buy converting a gmc, but it sounds like its not a money saver. I guess I'll just spring for a new kit. Who's kit would you recommend. I plan to do some weekend racing once occasionally.
 
#4 ·
Buy one that if anything you need restripped and it will cost you half them trying to convert. Unless you have access to a machine shop and have a full understanding of Root blower dont mess with them. They are hard enough to deal with to begin .
 
#5 ·
Richey,
I bought a Hampton Blower (Don Hampton) www.hamptonblowers.com He's a great guy to deal with and was the first to open a blower shop. My next blower will probably be a one from The Blower Shop www.theblowershop.com they make the nicest looking blower out there the cases are not cast they are machined billet aluminum, they are a work of art. All of the custom blower shops can set you up, shop around and see what you like and who you feel comfortable with. I called around and a few of them didn't give me a warm fuzzy feeling so, when I talked to Don Hampton he took the time to explain exactly what I would get and he asked what I was looking for. Some of the places just wanted to sell me a kit and didn't want to be bothered with questions. I have done some business with The Blower Shop as well and they are great guys to deal with. You can't go wrong with Hampton, The Blower Shop, Littlefield, Mike Kuhl, Mooneyham.

As far as a teflon stripped blower for street use, I personally don;t like the idea. It is great for race applications but, for the street it is not needed because you will not be able to make enough boost on pump gas to take advantage of the teflon strips. The other factor is that they wear, so you they will only be useful for a little while. When I talked to Hampton, he explained that he would set up the clearances tighter and not use teflon, he did not suggest using it for a street blower.
 
#6 ·
camaroman7d has good advise I dealt with Little field and it was great I spoke to Mert Littlefield for about an hour her was telling me all about hi blowers and the racing he did over the years . The piece I got from them was sweet. The ones you get from Summit or Jegs is a line built blower and they don't look half as good or run like the ones camaroman7d mentioned
 
#7 ·
hey guys thanks for the info. I'm going to back away from converting and order one from the people camaroman7d recommended. I'm building another 383sbc to go in my camaro for blown application. does anyone have a combination that will work well as far as motor build up? Which size blower would yall recommend 671 or 871?
 
#9 ·
383 6-71 over 456 ci go with 8-71
I was considering the 871. Its good to have people like those on team camaro to go to with techical questions and to be able to get good solid responses. :D thanks for the help.

Richey
 
#10 ·
Richey,
I have a lot of detailed pictures of me building my 388 with an 8-71. Just click on the "pictures" link in my signature. While a 6-71 will be fine and was my original plan, after talking to Mr Hampton we decided an 8-71 was a better choice for what I was doing. You will be happy either way. You haven't mentioned your goals for the engine/car so it's hard to make a recommendation. I'll tell you why I went with an 8-71. My goal was to make as much power as possible with my engine on pump gas, with an 8-71 I can make the same or more boost while spinning it slower than a 6-71, by spinning it slower I keep my intake charge cooler, this allows me to run a little more boost. My compression is 8.42:1 and I am running 12lbs of boost on 91 octane. Some said it couldn't be done with a roots blower on pump gas and 8.42:1 compression. When you start your build feel free to ask lots of questions. When I built my engine I couldn't find good information and did a LOT of research to learn as much as I could about roots blowers. I am not saying one is better than the other just trying to offer info so, you can decide what's best for you.

A couple of things you need to know, you can ask 5 different blower guys the exact same question and get 5 different answers. You have to use your judgement and also not mix and match the info you get. Stick to one plan that will keep you out of trouble. You will need to run a short water pump, sure there are long water pump applications but, the blower puts quite a bit of stress on the crank snout and the more weight and distance you stick on there the more stress the snout will experience. Some people will tell you that you need a double keyed crank, this will work but, I personally (at the recommendation of Mr Hampton) went with a single keyway just made it the full length of the snout (instead of woodruff keys, I used key stock). I also do not run a balancer/damper, I use a crank snout and let the 3" wide rubber bel take care of the harmonics. This is done to keep stress off the crank snout. If you haven't bought a crank yet and you need one, you can order it with a big block snout and that will eliminate the worry of breaking the snout. I already had my crank regular SBC snout and it has worked fine. As a matter of fact I already have the crank for my next blown engine and I went with a regular SBC snout. If you are going to run a balancer/damper then I would suggest the larger snout for insurance.

Make sure to keep your quench tight as well this will help prevent detonation. Meaning do not lower your compression using a thick head gasket, get your compression down using the correct chamber and dish size. As far as head gaskets go, there is not need to "O" ring the heads or block anymore, just use Cometic MLS head gaskets, there are guys running over 20 lbs of boost on them with no issues. They will cost you about $150 for a set, you can get them in any bore size and thickness, keep that in mind when figuring out your piston and chamber sizes, you are not stuck with 1 or 2 gasket thickness choices.

There is so much info to throw at you I don't want to overwhelm you and much of it you may already know. Just ask if you have questions. We still haven't even talked about timing, cams, and carbs.

Hope this helps?
 
#12 ·
Richey,
I have a lot of detailed pictures of me building my 388 with an 8-71. Just click on the "pictures" link in my signature. While a 6-71 will be fine and was my original plan, after talking to Mr Hampton we decided an 8-71 was a better choice for what I was doing. You will be happy either way. You haven't mentioned your goals for the engine/car so it's hard to make a recommendation. I'll tell you why I went with an 8-71. My goal was to make as much power as possible with my engine on pump gas, with an 8-71 I can make the same or more boost while spinning it slower than a 6-71, by spinning it slower I keep my intake charge cooler, this allows me to run a little more boost. My compression is 8.42:1 and I am running 12lbs of boost on 91 octane. Some said it couldn't be done with a roots blower on pump gas and 8.42:1 compression. When you start your build feel free to ask lots of questions. When I built my engine I couldn't find good information and did a LOT of research to learn as much as I could about roots blowers. I am not saying one is better than the other just trying to offer info so, you can decide what's best for you.

A couple of things you need to know, you can ask 5 different blower guys the exact same question and get 5 different answers. You have to use your judgement and also not mix and match the info you get. Stick to one plan that will keep you out of trouble. You will need to run a short water pump, sure there are long water pump applications but, the blower puts quite a bit of stress on the crank snout and the more weight and distance you stick on there the more stress the snout will experience. Some people will tell you that you need a double keyed crank, this will work but, I personally (at the recommendation of Mr Hampton) went with a single keyway just made it the full length of the snout (instead of woodruff keys, I used key stock). I also do not run a balancer/damper, I use a crank snout and let the 3" wide rubber bel take care of the harmonics. This is done to keep stress off the crank snout. If you haven't bought a crank yet and you need one, you can order it with a big block snout and that will eliminate the worry of breaking the snout. I already had my crank regular SBC snout and it has worked fine. As a matter of fact I already have the crank for my next blown engine and I went with a regular SBC snout. If you are going to run a balancer/damper then I would suggest the larger snout for insurance.

Make sure to keep your quench tight as well this will help prevent detonation. Meaning do not lower your compression using a thick head gasket, get your compression down using the correct chamber and dish size. As far as head gaskets go, there is not need to "O" ring the heads or block anymore, just use Cometic MLS head gaskets, there are guys running over 20 lbs of boost on them with no issues. They will cost you about $150 for a set, you can get them in any bore size and thickness, keep that in mind when figuring out your piston and chamber sizes, you are not stuck with 1 or 2 gasket thickness choices.

There is so much info to throw at you I don't want to overwhelm you and much of it you may already know. Just ask if you have questions. We still haven't even talked about timing, cams, and carbs.

Hope this helps?
I've read the book street supercharging a few times and that is about the extent of my knowlege. My current motor has under two hundred miles on it and was built by Speed O Motive out of California. They built it to produce 538hp. I have all the specs on it that I will post so you can take a look at them. Its possible it might be built good enough to handle a blower. I've emailed them several times asking if it would handle it but have had no response. Your post have been really helpful. Thank you for taking the time to answer my questions. i'll get those specs up for you later this evening.
 
#11 ·
#13 ·
Softail,
Like I said you can ask 5 different people the same question and get 5 different opinions, neither may be right or wrong, it just depends. I did not suggest and 8-71 I only put the info out there.

Take the "final compression" thing with a grain of salt, it is a guideline to keep people safe but, as you can see it is not 100% accurate or true. According to that chart my engine and many others couldn't run on pump gas. There are FAR too many variables that will effect what you can and can't get away with. Perfect example of 6-71 vs 8-71 the chart doesn't take that into account. An underdriven 8-71 will make a cooler 12lbs of boost compared to an over driven 6-71, cooler boost is less detonation prone. Again the goals in mind will determine what is best for each application. This is why I don't like those charts. Also boost is not all that great of a measurment to use. Boost only shows the pressure in the manifold, so if you have poor flowing heads you can show more boost and actually make less power, you need boost and flow. Flow makes power. Not arguing with you just giving a different view point that is often not discussed.

Richey,
That is a great book to build your knowledge around and is where I started. Your short block just needs to have a forged crank, good rods, and forged pistons. Since you will be changing the pistons, you only need to worry about the crank and rods. A 538HP 383 should have a forged crank and good rods. Which ever company you decide to deal with make sure they are willing to spend time on the phone with you. One of my first calls were to BDS and they didn't want to answer any questions, just wanted to take my order so, I called a few other places. All were much more friendly than BDS. I chose Hampton for a couple reasons, he took time on the phone to discuss my goals and asked me questions about my car/engine. He was close enough for me to drive down and pick it up. I was lucky enough to get to spend quite a bit of time with him in his shop. He showed me around and let me watch as he set up my blower. In the Street Supercharging book he was called the "Godfather" of blowers and after talking to him I see why. All of the blower guys know each other, I found that out as well. You really can't go wrong. Mike Kuhl, Littlefield, Moonyham, and The Blower Shop were all great to talk to and deal with. I don't know who is closest to you or if you have a more local blower shop.
 
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