This thread is meant to document my attempt to address the lack of an affordable alternative to aftermarket 5.8/351 EFI intake manifolds when one does a performance or “better than stock” build/rebuild, etc, on their OBS 5.8.

The source for the project was UNTAMND who posted images of his work on a 5.8 lower in this thread:

https://www.ford-trucks.com/forums/1...-upgrades.html

...while I was in the process of rebuilding my 351. I had gotten to the point where I was about to purchase Price Motorsports adaptor plates in order to run an Explorer GT40 upper & lower, but was really balking at the cost.
So I purchased a complete upper/lower set off a 94 F-150 for a whopping $52 at my local Pull-A-Part that does flat rate pricing on all their parts.

Manifold porting is a opinionated art. Without the benefits of a flow bench or other measuring tools or apparatus, or repeatable drag strip passes, its all subjective… So, hope you find something you can use

Personally, what I was aiming for is a gradual tapering of a rectangular wedge down to the port of the head, in order to maintain air velocity. I’d really like to build up the sides of the “egg” walls with some aluminum in order to “square” the lower port, & equalize the runner volume, but that will have to wait for the “mark II” version.

The general idea presented here is taking the 5.0 upper plenum face & using it to make a template that can be transferred to the 5.8 lower. I did not attempt to match the lower to the stock 5.0 gasket. In my opinion, that would create a “balloon” area where port speed would slow & possibly create turbulence in a naturally aspirated application such as what I’m doing. I know the ledge created by the 5.0 miss-match is a possible issue, but I decided to go with what I considered the lesser of two evils.

Here’s what I started with:



A lot of material in the 5.8 lower.





First thing to do was come up with a template that would be transferred to the lower.

I used primarily butcher paper & FelPro gasket boxes for pattern making.

I took a small hobby style ball-peen & used it to tap along the edges of the plenum openings to emboss a cut lines for razor blades & X-Acto knives.



After making a few patterns I laid one over the lower prior to inking.



And for a reference, the stock 5.0 gasket on the template.

 

You can never have too much light.

Work space:



Initial grinding:



Grinding to square the vertical to horizontal transition:



Squaring short side radius:



The red by the way, is the area between the 5.0 gasket & the actual upper plenum. The Black ink is the port match target.

...

 

Here is a comparison of lowers, 5.8 top 5.0 truck and 5.0 GT40/Explorer.

Some very interesting port profiles.



The end result of this project is to match GT40 heads. All gaskets used for matching were from Explorer heads & intakes. Always get the gaskets or save what you have.

This is the Explorer intake gasket on the 5.8 manifold



This is the GT40 head aligned with 5.8 manifold



Another head/manifold alignment/comparison:



Inked in:

 

After a lot of grinding, flap-wheel, cup-brush, combo is ready to bead blast ($15)







Returned.










Completely natural. Wish it would stay this way. Although the look of that "Dow" coating used in the early 60s that was used on magnesium would look tough, I think.

 

Final product, VHT cast aluminum high temp, oven baked:




Embossing FelPro bulk gasket material prior to cutting with Xacto knife.
Took an hour, stuff is tuff:



Finished product with stock gaskets & templates:

 

Very nice! Both the work and the write-up. I'm sure many will reference this thread to see what the heck is meant by mating a 5.8L lower to a 5.0L upper. That's what I did as well, though I didn't make a gasket to custom fit the setup or make the intake look nice (cleaned it but no blasting or paint). What was your weapon of choice for the grinding?

 

Thanks, it was an adventure.

Mostly an air powered die grinder. But the Dremel was helpful too. Cutting with a disc beats hell out of grinding some times.

Really would like to have a long shank cutter set next time, particularly a ball. Invest some time on the grinding "station " as well.

 

I for one are going to referencing this for my project. Awesome write up Thank you sir.

 

I have a question about the lower manifold. When you shaped the ports did you go straight down a ways then blend or just blended to the radius. I just blended mine to the radius.

 

There is a transition from "egg/oval" to rectangular seen best in post #2 where I was just beginning to get some major material removed in order to form a "flat-ish" radius on the floor of the runner.

In post # 4 you can see where I decided to stop in order to not increase the volume too much as well as how the short side radius is squared up to make the runner more like the port of the 5.0 lower.

Some where out there automotive performance land is a type of rubber or foam that porters use to model runners. You port, pour, let dry & pull out so you can see a 3D representation of what you actually created. You can also force into a known volume of water & infer by displacement the volume of the runner in order to match each runner. Of course you can seal one end & use a graduated beaker to do the same for volume but that don't tell you the shape.

I still want to do another & build up the sides either with epoxy or weld up aluminum.

Any of that help or just make worse?...

I did find this long after my project (It uses 5.0/cobra/explorer GT40 manifolds for example, but might help)

Hit "no thanks, take me to the article":

Horsepower Secrets: Intake Manifolds ? Muscle Car DIY

 

Thank you for that awesome read so far. You kind of answered my question. I'll take a little more off the radius. Here is what I have so far then.

 

Really enjoyed reading this write up, Ria2005 sent this link as a suggestion for the motor I've got going. This is my first attempt at transplanting a motor in an efi and really didn't know what I was as getting myself into with the speed density management. It looks like now I pretty much need to plan on converting to MAF and larger injections. I'm curious what your time frame was on port matching the he lower to upper. I have a little experience porting and do have long shaft mandrel carbide burrs and wheel sanders ( machinist as occupation ) but I'm not sure I have the patience required for a job of this magnitude . I've been eyeballing Edelbrocks performer truck efi intake.

 

If you want to make any HP you will need the shorter car style, I still have an unused Typhoon set for sale which is an Eddy performer copy.

David.. how many hours did you put into porting that lower?

 

I have less than $150 in parts/gaskets/burrs/bead blast, paint, etc in the intake.

With the exception of purely aesthetic work that i did for my own satisfaction, 10-15 hours for the basic port job.

I find grinding to be relaxing in the same fashion as whittling/carving, so the time spent doesn't bother me.

If I was going to drop $700 or any where close on a 5.8 intake, I think I'd go for a Trick Flow Track heat.

 

Cool.. just curios.