Good luck on finding a reasonably priced 351w GT-40 lower. People want stupid prices for them.

Depending on the engine build you might look at Edelbrock or TFS, or if you're feeling fancy the Holley High Ram.

This is what I did:

Daze wrote:

I have been messing with EFI and a 351W.  I wanted to use an OEM intake and got to looking at the differences between the truck lower that came on my engine and a 5.0 car upper and realized an aluminum adapter could be made to combine the two.  I ordered the aluminum and began drawing it up but then I found a Bronco company that makes the exact adapter I was going to make. I ordered one and while it will do the job it is a cast piece and very "one size fits all" so I decided to make my own anyway so I could have a precise fit.

I started with a 3/4" thick piece of 4"x16"aluminum


I then took the 5.0 gasket and the 5.8 gasket and traced them on to the aluminum


From there drilled the mounting holes and then filled in the area that both sets of ports share 


To open up that area I began drilling holes


With the truck gasket traced on the bottom I was able to see that all my holes were in the correct place

I need to cut out the chunks outlined by the holes and grind the ports to shap.

I did make one mistake and started drilling in the wrong spot but I didn't go very deep and all that material will be removed when I blend the port.  I had to mark it in red to make sure I didn't keep drilling it.

Daze wrote:

TKOPerformance wrote:

On the cheap try dipping your burrs in ATF.  It keeps aluminum from sticking to the burs.  Also using single cut burs keeps them from loading up as much.  Double cut work good for steel and iron, but not for aluminum; they are too prone to loading up. 

The burrs I have are double cut.  I tried dipping them in ATF as you suggested and it made all the difference in the world, no gulling at all.  Thanks for the tip.

I cut out the openings and roughed them in with a carbide burr.  This is the first time I had used a die grinder on aluminum so there was a little bit of a learning curve for me.  I made sure to keep it well inside the lines.


Once I had the openings roughed in I traced each gaskets ports on its appropriate side and began doing the port matching and smoothing.  The more work I did the more comfortable I became with the way the burr removed the aluminum.  With this test fit it's starting to really take shape.


I then traced both gasket outside shapes on to it so that I could cut it. I cut it with a bandsaw then used the carbide burr to clean up the outside.


This is what the finished adapter looks like bolted to the upper intake.


and here it is on the lower intake.


As I mentioned when I started this thread, I designed my adaptor and then discovered an aftermarket made one.  Mine is on the top theirs is on the bottom.


They are almost identical.  The only major difference is mine is 3/8" thinner.  The advantage is it will git me a little more hood clearance but the dis advantage is the transition from the 5.0 upper to the 5.8 lower is slightly sharper. Other slight differences, the shape of their ports are a little rounder where mine are obviously hand cut. Also there threaded holes are poorly cut and mine are much cleaner.



This is what it looks like all bolted up.



Here is a comparison between the stock 5.0 upper and lower (on the left) and my 5.0/5.8 setup on the right.  If I had used the aftermarket piece they would be the same height, but with my thinner adapter is slightly lower.


Had a lot of fun on this project and learned a TON.  The piece of aluminum I started with cost me $65.00 even with my commercial discount.  I had about 16 hours fabrication time into this project.  The aftermarket piece cost me $143.44 shipped so When I compare my time and expenses compared to the ready made uint I was a little less than $5.00 an hour   Not sure what I am going to do with the aftermarket unit.  Might keep it or eBay it... we will see.

There is more info on the original thread, linked at the beginning.

Truck lowers are cheap and easy to find. They make adapters to put a 5.0 lower on a 351 but they are $400 or more.

Daze wrote:

Truck lowers are cheap and easy to find. They make adapters to put a 5.0 lower on a 351 but they are $400 or more.

Standard truck lowers are cheap and easy to find.  GT40 truck lowers are like hen's teeth and priced like gold. 
 

I know explorer has staggered ports.

Could an adapter be made to work with a stock 351w lower?

I’m thinking out of the box of normal.

I’ve seen the box uppers too...pricey as well.

lowercasesteve wrote:

One thing about FI & 351w in a Gen 1 Mustang.  Hood clearance.  I have a Performer manifold on mine because a Performer RPM makes the air cleaner hit the hood  Forget about an Air Gap.  Truck FI's are way too tall for our early cars.  With Dazes amazing FI,  the same situation must be addressed.  You don't want a manifold shaped dent in you hood the first time you shut it!

The Mustang 5.0 upper doesn't sit any higher than a carb and air cleaner.  I took all kinds of measurements before I started this project.  The lower on a truck 351W is almost 1" shorter than the lower on a 5.0 lower but you now have 2 gasket thicknesses. Then by making my adapter out of 3/4" I lowered total height by 3/16".  Due to the increased 351W deck height I still may have hood clearance issues but it should be something I can mitigate with a custom engine mount.  Of course mine is going in the Galaxie where I have a little more engine bay room.

Nos681 wrote:

I know explorer has staggered ports.  Could an adapter be made to work with a stock 351w lower?

I don't think one could be made to adapt a truck lower to the explorer upper, at least not while maintaining stock height.  The ports are too different.  What is wrong with using a Mustang 5.0 upper?

If your after fuel injection on a 351, how about one of these. It's has the bosses for the injectors. 

https://www.summitracing.com/parts/edl-2981
 

I thought of this Mike.




And I thought of this John.


I like the Mustang like yours Daze.
I was comparing explorer gasket to the stock Mustang gasket.
Size difference is quite noticeable.

Raymond... nothing at this point.
This will be street/highway driven.
Figured start with base similar to Daze.

Of course in a 65.
Just thinking about ideas.

Last edited by Nos681 (11/12/2020 1:05 PM)

Eight stack, and call it a day.

Explorer upper, custom open box adapter (explorer upper-stock 351w lower), stock 351w lower (possible porting).

Could get a good vacuum off explorer upper for brakes and fuel pressure regulator.
May have to bell the lower portion to smooth out air turbulence going into lower manifold.
Don’t think there is enough room under a stock hood for all of it.

Next idea is use a blower intake and like Daze, an adapter to explorer upper intake.
Probably the simplest.

All using factory EFI as well.
Not a radical engine by any means.

Just have to wonder how the open plenum would affect operation.
Haven’t seen this combo before anywhere.

There's an NOS 351W GT40 intake on eBay right now.  It too can be yours for the princely sum of $1,500!

The advantage of the GT40 is a better port layout, and the ability to have larger ports, especially when ported via Extrudehone, etc.  IMO if its a stock build the factory intake will be fine.  Adapt a car upper if needed as Daze did.  If you're looking to make power then get something aftermarket.  I used an Edelbrock Performer RPM II on my 331 because I found the Cobra intake I originally wanted to use was no longer produced and now stupid expensive.  They used to be $390.  I wish I'd bought 40 of them...