Sheet metal intake, questions about runner lengths

In reply to frenchyd :

The firing order is 1-4-2-5-3-6

kitsune1324 said:

A couple things that came up, since this car is dual runners per cylinder, am I able to take runner length 1 and add it to runner length 2 to get the total runner length? 

Can you post a picture of the ports you are working with, I am having a hard time picturing what you are working with.

Sure thing, here's a pic with and without the gasket on, not sure which way is easier to see. Keep in mind, these are stock heads, the ones on the care are ported to match the gasket.

Each of those ports feeds its own intake valve? Valves the same size? Chamber a normal 4v pent roof?

It's a ford 3.8/4.2, 2 valve per cylinder.  Here's a slightly better pic. It's two intake ports leading to the same valve. One is smaller CSA and takes a longer, lower route and one is larger CSA and takes a higher, more direct route to the valve. It does add some interesting questions to pulse tuning! 

I've honestly always really liked the 4.2. I have nothing against the 3.8 but just find the truck intake manifolds a lot more interesting to think about. When you look at a 4.2 truck engine it seems like a much more optimized design for a 'base model engine' compared to the manifolds and heads you see on a chevy 4.3 or dodge 3.9. Go figure then why i own a 4.3 and 3.9 vehicle and have still NEVER owned a 4.2.

In reply to Paul_VR6 (Forum Supporter) :

It's just as Vigo said, it's two intake ports to one intake valve (2v heads). It's really weird. 

In reply to Vigo (Forum Supporter) :

Definitely a better pic. I was wondering if the runner length is effectively doubled due to there being two runners per single intake valve per cylinder. Any ideas?
It's funny, the mods to stroke my motor I ended up using the F150 crank. I was reading why the F150 had better numbers than the same year mustangs with the same engine, and it's thought to be baecause the 3.8's were already getting close to the 4.6's horsepower, and if they had the f150's performance it would be even less incentive to get a v8. 

kitsune1324 said:

In reply to frenchyd :

The firing order is 1-4-2-5-3-6

Sorry I've been busy, It's more complex since you have two paths. A short direct for high speed and a longer more winding for slow speed.  
     Anything I conceive that might take advantage of inertia becomes extremely complex and maybe it could be 3 D printed  but I sure wouldn't know how to convey it 

What is the port csa of each runner compared to the valve size? Gotta say its an odd one!

In reply to frenchyd :

No worries, any and all help is greatly appreciated. If you want to 3d print something, you're more than welcome to do so, I just want it to be worth your time if you do it. 

In reply to Paul_VR6 (Forum Supporter) :

That's going to be a hard one to calculate due to the complexity of the "long runner" port. The easy one has a radius of .75, the hard one is 1.5" by 1.31" inches. I can send you a 3d file of where the intake meets the head if you'd like. It has the port traced out and extruded.

Quick question, I'm trying to design the plenum, how close is too close from the runners to any wall? I'm looking at around .735", but the closer I can get the better. I'd basically have trumpets in the plenum to maintain the size of the plenum and barely increase the full runner length to 12", which puts the harmonics in the very tip of the rpm range (limited on runner length due to intake height restrictions).
 

An update to what I'm looking at with the runners in the plenum, let me know if the spacing/area looks fine. The shape is due to height requirements.

The runners are about .9" apart and have a .75" radius. I found that's about the actual size of both the "short" and "long" runner, the long runner is basically just squished on two sides.

I would put the end of the stacks no less than 1/3 diameter off the plenum floor. 

I'm sorry..I'm not quite sure I understand. Could you be more specific?

While I'm at it, I finished the intake and here's what I came up with. Changes are simple enough to perform

Example: if your stack is 2" diameter, put the throat of the stack min .66" off the port floor

For the csa you only need the diameter of both at the manifold flange, and add the area of both up and compare to the area of the valve. Assuming it's a huge valve compared to one port, but this is an odd duck for sure.

I am asking out of curiosity.

Do your intake runners draw with the same velocity given their different shape? ( the length could be changed in plenum by varying the intake trumpet) Would it improve flow to round the sharp angles within the plenum? Why isn't there an intake on each side of the plenum? (Thinking crossram) And are you putting a rectangular filter over the plenum For the velocity stacks to draw through?

For further research purposes. Thanks.

Can I get your guys hive mind to help me determine runner length on my next wankel build? This was a great read. 

Paul_VR6 (Forum Supporter) said:

Example: if your stack is 2" diameter, put the throat of the stack min .66" off the port floor

For the csa you only need the diameter of both at the manifold flange, and add the area of both up and compare to the area of the valve. Assuming it's a huge valve compared to one port, but this is an odd duck for sure.

I think I understand you now. I should be good as I'm planning to raise the stack as high as possible off the floor without blocking the air passage.

In reply to BarryNorman :

I don't believe they'll pull the same velocity since their shape is different, however, in my case I'll be using the same 1.5" pipe for all runnners, but will either shape the bottom of the pipes to match the more oval runner, or I will smooth out the plate they'll be welded to to match the pipe (on the mating surface.
It most likely would help improve flow, but the metal I'll be using (6061) doesnt' like to be bent.
There was with the stock intake, but the way the stock one was one bank typically saw more airflow than the other.
I'm not sure where you're going with the rectangular filter, can you explain? This isn't a carb setup.

In reply to fidelity101 (Forum Supporter) :

I used this site they told me about in some of the early posts. http://www.bgsoflex.com/intakeln.html
All I did was decide where I wanted the RPM range to be and changed the length in the calculator until the RPM range matched mine.

For the end of the runners don't use an unfinished tube. Even just a little flare helps a lot, you can usually make a mandrel out of scraps or other things sitting around (I have used a giant socket before) just to flare them out. A full 90 or 180deg radius at the end is preferred but those are $$

In reply to Paul_VR6 (Forum Supporter) :

I'll definitely be flaring the tube, it was just difficult to do in Solidworks so I settled for a quick filltet. Any recommendations on how to flare it without cracking the aluminum?

kitsune1324 said:

In reply to Paul_VR6 (Forum Supporter) :

I'll definitely be flaring the tube, it was just difficult to do in Solidworks so I settled for a quick filltet. Any recommendations on how to flare it without cracking the aluminum?

Would it make more sense to buy flares of the proper diameter and have them welded or bonded on the ends of the tubes?

Or design it so that there is a flange to bolt/rivet/bond somewhat standard velocity stacks to the bottom of the plenum?

In reply to Stefan (Forum Supporter) :

Definitely would make more sense, I had a hard time finding any though. Maybe I'm using the wrong search terms..