Anyone here ever converted a 671 GMC blower over to gas to run on a street driven car?
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. thanks for the help.383 6-71 over 456 ci go with 8-71
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.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?