Thread: 8-71 blown 390

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Hi everybody, new to forums. Thought I'd start off with getting some opinions. First off my project is going blown with my 390. Going to do forged rods and pistons, 8v71 converted for gas with dual predators on top. Its in my 75 f250 4x4, 4 speed, currently with 38's. Planning on running 15% under drive for about 7 lbs. boost with swapped pulleys to 15% over drive for around 19 lbs. Nice cam, don't have the specs on hand but I'm going to have Isky grind that for me. And of course, the rest of the valve train, ARP's where needed, etc. the whole ball game.

So the question ... looking at intakes. The blue thunder blower intake is very nice and I would need a 3'' blower spacer too, that would run around $1000 total, plus $200 for the adaptor for the blower. Or .. I can get an adaptor to run the blower on a 2x4 intake, and for spacers I found some nice 4'' carb spacers. Intake, adaptor and spacers would run around $750 tops. I would make some support brackets to help support the blower since it wouldn't have as big of a mounting area plus be raised up on a theoretically less sturdy foundation .

Now I love to be different and to do my own thing, plus this would save me money and I could easily swap back to N/A if I wanted to, but I want to make sure this would work. Blower manifolds have bigger plenums then carb manifolds and I don't want this to restrict the flow (I know its pressurized but its still possible) and I'm also worried about the blower being unsteady on top the spacers. Even with the support brackets, its still only aluminum and it does strip easily.

Just curious to get some opinions. Thanks to all in advance, I really appreciate it!

If you want to run a blower, run a blower manifold---------

In my opinion, what you're suggesting would look like your sister designed it. I side with Jerry.

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Motox_19, welcome to the forum! Once you get a few posts I'd like to see pictures of your '75 4x4, it sounds like it should be a neat truck lifted and running 38's! Hope you find what you're looking for here and that you enjoy a long, active stay.

While I'm all for saving money I can't see your 2x4/spacer manifold being the right choice. You're going to restrict your flow, and like Tech says it just sounds like it's gonna look a bit too "backyard". Spring for the blower manifold and do this part right, and I'd say you'll be a lot happier down the road. If you ever decide to swap back to NA swapping the blower manifold for a regular intake won't be a big deal.

there were a couple places that used to make blower manifolds out of carb type manifolds--it entailed cutting away every thing except the area around the ports and weld a structure together that was very much like the true blower manifolds and it let many people put 6-71 type blowers on some ngines that Cragar,etc didn't make manifolds for-----I don't remember for sure but it might of been Gary Dyer near Chicago-----yeh---he makes rods now

A guy in AZ that's on another forum has a turbo kit that he ordered for his FE and now is selling the un-used kit to fund another project. Sounded like this would be in your budget too, as he gave another guy a price of 900.


http://www.garagejournal.com/forum/s...postcount=2318

Originally Posted by jerry clayton

there were a couple places that used to make blower manifolds out of carb type manifolds--it entailed cutting away every thing except the area around the ports and weld a structure together that was very much like the true blower manifolds and it let many people put 6-71 type blowers on some ngines that Cragar,etc didn't make manifolds for-----I don't remember for sure but it might of been Gary Dyer near Chicago-----yeh---he makes rods now

Jerry, there were people running 671's and 871's on a 1" thick aluminum plate bolted to a single or dual 4 barrel intake right where the carbs would bolt on. They usually have 4 thick pieces of aluminum welded to the corners of the manifold to bolt the plate to for support. Is it optimal? No, but it will work. There is a guy in Wahoo Nebraska that builds 871s and 671s and he is very familiar with these. I had him make me a plate to bolt on to a 7.3 IDI diesel. I stuck a 671 on it. It worked pretty slick. I also had one of these setups for a SBC but sold it.

But I agree with these guys, if you can buy an actual blower intake, do it. The blower will flow more air and will just be better over all. If you want to go back from a blower to NA, you'll have to swap cams too more than likely as well.

The opportunity of building up a manifold to mount a blower was simplified when Edelbrock and others came out with the single plane type units----------


The biggest issue is having the blower set flat and alignd perfectly with the crankshaft--if crooked it will not only eat belts but will pumm the thrust main bearings out on the crankshaft in very short order and you will have wrecked a complete engine just for some eye candy????????


Ryan, I am completely aware of every aspect of a 6 or 8 71 blower on about any v 8 out there--------

Other than the alignment issues the thing that makes me cringe is thinking about the flow path and the flow velocities of the open plenum area of the blower compressed and then constrained to the ports of a NA manifold which would be like four (or eight for 2x4's) little sharp edge orifices, then expanding back into the open plane area of the NA intake into the runners. It just seems very, very inefficient to me, and I'd think that an open plenum blower manifold would be the only way to go here if you're planning to drive the truck and not trailer it everywhere.

Thats what i was worried about was the 2x4 manifold being flat. Was hoping.someone made one but the closest i found was 3* off. So blower manifold it is. And about the backyard thing, i'm sorry but i think thats stupid. Innovation got.us where we are today. I'm not saying duct tape everything but i mean being different to me is way cooler then doing it "right" as most people say. As long as it works right and isnt like a rust pile then there shouldn't be a problem. But i am doing the manifold.
Also about the pictures, ill see if i can figure out how to post some. I guess on my profile, not sure how all this works yet. But it isnt lifted yet, will be hopefully by next summer.
Right now just slowly gathering all the pieces for the blower. Then gotta pull the heads, see what size pistons i need, (not sure if its been bored) and hopefully get those and the rods as a package deal.

Its all time and money .....

motox_19,
I'm a lot more concerned with the efficiency than the "look", and I think you're making the right choice. As for pictures, I believe that you'll have to get around ten posts before your pictures post without a moderator approval which is a spammer defense issue. Here's a link to some methods of posting, and for me posting in a thread is the only thing that I do. I never post to the gallery as it's all but impossible to reference back to a specific picture later. Here's the link - http://www.clubhotrod.com/shop-talk/...es-thread.html

does the 8 71 your talking about have a stock housing case or an aftermarket one?????If its an original stock 8 71 housing you won't find a manifold for it---------

Originally Posted by jerry clayton

does the 8 71 your talking about have a stock housing case or an aftermarket one?????If its an original stock 8 71 housing you won't find a manifold for it---------

Nope, but there is a place that used to sell an adapter plate on ebay to bolt a V style case to an inline type mount intake. I believe this is the guy who had them. He doesn't have one listed for the 8-71, but I purchased one about a year and a half ago.

6V 71 6V71 Blower supercharger Adapter Plate for 671 6 71 Intake Manifold | eBay

Flow was my main concern too. But no worries now. It just bothers me when people say its not done right because its not how everybody else does it or it looks different. I think its more fun.
Yes i found a guy on ebay who makes adaptors. There is actually a couple people who do. I should probably just ask a machine shop here as it could be cheaper for me but i'm figuring it would be easier this way since this guy already has all the specs and has done it before.
So i guess as an update. The conversion kit and triple pin kit should be here today or tomorrow. The front cover i bought yesterday. Other then that. I'm kind of putting it off until after Christmas because I'm taking leave and plan on going home for the holidays. But next up will be the intake adaptor plate and carb adaptor plate. Then the second predator because I already have one. Then the actual intake and spacer. Which the guy I'm getting the spacer from is pricing a spacer for me as well. Hopefully its cheaper.

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