[Alex_F]

I am in the process of designing a sheet metal intake for a ohc6 project I am starting to work on. I was wondering what others thought about plenum volume and runner lengths. I have some tubing that is almost the perfect size to match ports. Inside dimensions are 1.875x 1.375 of each runner. Looking at building an intake similar to the below pictures. I have plenty of room to increase plenum size or runner length as needed. Forgot to get pictures of my current design but initially though 1.5 displacement or 375 cubic inches for the 250.

A little project background, I was given a running 6er so I decided to quickly throw it in my 74 which is currently twin turbod, but only going to run one of the s360 turbos on this. Goal is to crank up the boost and see what one of these will do. I considered buying an offy intake for one but cheapest I could find one for was 300 so i decided to make my own. Car will be efi

[Tom Vaught]

I have built a few Intake Manifolds similar to what you are proposing (for my former company). Personally I think the front cylinder is going to starve for air and the rear cylinders are going to be lean (too much air). The Throttle Body is too close to the #1 cylinder and the air molecules just rush past the runner. You can have the same boost pressure anywhere in the intake but the T/B being that close to the runner would tend to suck away fuel presented into that runner. Kind of like a syphon system works.

Blade angle on the throttle body will also affect the first couple of runners.
Need to move the Throttle Body forward a few inches.

Tom V.

[Alex_F]

Thanks for the feedback. I moved the throttle body 3" forward. I wondered how the front cylinders would react. This is what it currently looks like.

[JSPONT]

The 2JZ has a similar intake style, you can steel some design ideas from them. A few guys make intakes for them. You should be able to get a good idea from there photos. I like what you are doing!

[Tom Vaught]

Originally Posted by Alex_F

Thanks for the feedback. I moved the throttle body 3" forward. I wondered how the front cylinders would react. This is what it currently looks like.

Thanks for the new picture.

If you can get a curve on the floor of the intake from the throttle body to the 1st runner, vs the sharp 'kink" that would also help with the air not overshooting that runner.

Maybe you were going to do that but you quickly created the new cad image without it being there.

Tom V.

[RUDOLFSSON]

Cool project ! keep us posted

[Tom Vaught]

I am a moderator for the Advanced Tech Section on the "Turbo Forums". A Boosted Engine Website.

Here is a link to a 28 page thread on Intake Manifold Design ideas with pictures.
https://www.theturboforums.com/threa...design.361799/

Read thru that and you will know a lot more vs what you might know today.

Tom V.

[Alex_F]

This look better? Trying to keep the intake simple to build so I can get it knocked out quick and on the road this spring hopefully!

[Tom Vaught]

That would work just fine and allow the air to make the turn into the first runner.
BUILD THAT SUCKER!!!
Tom V.

[TheSilverBuick]

Neat!

When I get my good engine assembled I plan on updating the headers to have O2 and EGT ports on each cylinder so I can check up on the air/fuel distribution. Certainly curious how #1 looks with the short distance between the throttle blade and runner.

Hello again Alex, curious to see this made!

Few small things to keep in mind, and do not look like an issue with your design, is that the injectors are either layed over enough or far enough from the flange that the fuel rail clears the thermostat housing. Have the runners long enough to accomodate decent header curves. I had to make sharper bends off the flange than I would have liked to clear the intake plenum, which also put the header pipe really close to the alternator. Have a point for the secondary throttle return spring to hang on. I'm going to drill and tap a bolt into mine to hang the spring from when I have it apart for the engine upgrade.

Keep us updated!

[TheSilverBuick]

Wish I were a more skilled fabricator!

[Alex_F]

I was hoping to run all the parts for the intake after work today but our laser was swapped and it did not happen. Probably do it early next week. But I was scoping out injector placement last night. Looks like I will have to lay the injectors down and move then up the runner a little. I am going to get the whole intake fabbed and bolted on before I drill and weld In the injector bungs. Plan as of now is to use the stock exhaust manifold and run from the outlet up to the turbos in probably 2.5". If I use my driver's side turbo I can use my current down pipe for that side as well as most of my cold side.

[TheSilverBuick]

To use the stock exhaust manifold you'll have to make sure your middle runners will clear the heat cross over, as well as the plate you'll use to seal it up. That was an issue I ran into with my "sheet metal" intake and you can see where I cut the cross over out and welded block off plates where needed. You'll need to find a way to locate (dowel?) the exhaust manifold to the ports. I struggled with a #6 exhaust leak because port alignment.

I would use 2" pipe from the exhaust manifold. This is 2.5" pipe and I had to trim a tab off the motor mount to clear. I think it's too large of a primary pipe for the engine. Though you likely have the ability to be more creative with the piping than I! I used two 1.75" pipes on my turbo header.


https://www.youtube.com/watch?v=6_eAOO-iBAA

[Alex_F]

I got it mostly tacked together for mockup. Just need to figure out what I am doing for flanges to the head to get it all aligned perfectly and keep it sealed. Also need to figure out how I am going to try to keep the exhaust on it and sealed. I was really trying to avoid making headers for this but it is tempting. I may look into doing dowel pins to keep manifold aligned.

[Tom Vaught]

The Intake Plenum you are showing in this post looks nothing like your drawing in Post #8.

You still have the 90 degree turn in the plenum (at the bottom right of your picture) in post #14. Air will blow right past the #1 cylinder. Why did you not make the plenum like the drawing in Post #8?????

Tom V.

[Alex_F]

It is exactly like the model shows, cut from the same file . Maybe the picture is deceiving but tb flange is 75 from intake flange. If it doesn't work I can easily make another plenum to try. Only took about 30 min to make this one. It is exactly 1.5xs displacement. here is another view.

["QUICK-SILVER"]

Tilting the TB flange, so it's aimed down the center, towards 3&4 intake runner opening, might help with what Mr. V. is seeing.

Clueless
Clay

[Tom Vaught]

I think Quicksilver is seeing what I am seeing.
If you tilt the top of the throttle body flange backward and point the TB air centerline towards 3 & 4 runner openings the angle would be just fine for feeding 1 & 2 runners as well. 5 & 6 will always get the air.

Thanks Quicksilver.

Tom V.

[Alex_F]

That looks simple to do. I am going to hopefully get the engine mounted in the car this week and will be able to verify that the intake fits and make sure I can make the orientation of the inlet work. Hoping to get all the fab work finished up in the next month and then tear into the engine for a few tweaks to hopefully make it survive all the boost I am going to throw at it.

[Tom Vaught]

Good luck with your project!

Tom V.