DIY Intake Spinoff Thread for Sheet Metal Design

[Hotrodtractor]

OK so off the top off my head.

CI. =365
RPM =5000
VE = 85%

5000(365)=1,825,000
1,825,000/3,456=528.07
528.07(.85)=448CFM.

Sound about right?

OK so VE for our engines is actually 1.6. So that would get us to 844 cfm

For the most part - I'm going to let you work through this - but I have three comments.

1) You do not have a VE of 1.6 - your first guess is probably a whole lot closer. Charles would have a hay day with you on VE if he ever reads that you think its actually 1.6.

2)The engine displaces 365 cubic inches every two revolutions.

3) List out the equations and include units with them - it helps everyone follow along and critique.

Beyond that - I'm going to let you figure it out.

 

[gjoski515]

opcorn:

 

[amarillo250]

opcorn:

 

[6leakertweeker]

For the most part - I'm going to let you work through this - but I have three comments.

1) You do not have a VE of 1.6 - your first guess is probably a whole lot closer. Charles would have a hay day with you on VE if he ever reads that you think its actually 1.6.

Learning is one of my favorites things to do. Nothing better than soaking up information in my past times. Constructive criticism is welcome as long as flaming is left out. No need for that. I thought. 85 was for a naturally aspirated engine. Doesn't the VE increase with forced air applications?

2)The engine displaces 365 cubic inches every two revolutions.

3) List out the equations and include units with them - it helps everyone follow along and critique.

So far I think I have and will continue to do so.

Beyond that - I'm going to let you figure it out. [/QUOTE]

 

[steedspeed]

All the math and calculations mean nothing if you don't have the room to fit the "perfect" manifold. Every design is always a compromise unless you have unlimited space to work. All you can do is make it the best you can in the space available.

 

[6leakertweeker]

I'm working on all of the calculations. As soon as i get them complete I will post them.
Intake runner length
Intake runner diameter
Plenum diameter
Plenum design

Stay tuned.

 

[6leakertweeker]

OK here's what I have come up with so far.
The goal we are trying to reach:
Intake Runner Diameter
Intake Runner Length
Plenum Size (length and diameter)
I'm going to do one at a time due to the length of the post.

Intake runner diameter.
Formula. sqrt(RPM @ which peak torque is desired x engine displacement x VE)/3330

I wasn't sure what RPM would be best so I chose 5000 just for the purposes of this post.
We know our displacement is 6.0 liters and we estimate VE of 85% even though its probably higher due to this being a turbo charged application. So lets plug it in.

IRD = sqrt(5,000x6x.85)/3330
sqrt(25,500)/3330
sqrt 7.65
2.7"
I theorize that we would divide our calculated diameter by 2 due to the fact that we have 2 runners per cylinder which would leave us with a runner diameter of 1.35" for our design.

 

[6leakertweeker]

Intake Runner Length

Again I went with 5000rpm on this one. I'm not real confident on this one as the value I have calculated would leave us with and intake sticking out of the hood. So if somebody could fill me in here that would be great. I believe this calculation is to achieve optimum intake runner resonance so maybe that's why its so large. Keep in mind this length is measure from the back face of the valve.

Formula:
(((10,000-desired RPM)/1000)4.3)+17.8cm
(((10,000-5,000)/1000)4.3)+17.8
(((5,000)/1000)4.3)+17.8
((5)4.3)+17.8
21.5+17.8
39.3cm
Converting cm to inches
(39.3)(.3937008) =15.472441 or 15.5" rounded up.

 

[6leakertweeker]

Plenum Size

Through my research I've concluded that for a turbocharged engine 150% of engine displacement works best for total Plenum volume. As you may know if we know volume we can work backwards through equations to determine Plenum length and diameter.

We know our engine is 6.0 liters so if we multiply that 150% we end up with a volume of 9.0 liters or 549.2 cubic inches.

I also theorize in this part that since we have 2 sides to our Plenum will need to divide our plenum volume by two to accurately calculate the size of the tubing necessary to construct the manifold. That would get us to a volume of 274.6 per side.

Again through research I've found that with the type of plenum design we are using roughly and inch should be added to the rear of each plenum tube to improve flow for the rear cylinders.

OK so to calculate the proper diameter of tubing for the plenum we would have to know the total length of the plenum which could be found by measuring but its cold out and I'm sick so I'm not going outside.

But anyways the equation for volume of a cylinder would work for this.
V=(π)(R squared)(height or length in our case)
274.6=(3.14) r2(length)
R would be the value we are trying to find and if we had a length we could do that. I'm going to just say 15" for sh*TS and giggles.

So if we plug in 15 we would need to divide volume by that to get us closer to a radius.
274.6/15=18.30
18.30=(3.14)r2
Now we divide the pi
18.30/3.14=5.83
Now we need the square root of 5.83
Which would be 2.41"

So we now know that at a 15" length our intake plenum is going to have a radius of 2.41" and a diameter of 4.82".

As was said above a mathematically sized intake would not fit on a stock based engine and would be tough to fit in a full out performance engine. With more accurate measurements I'm sure that number would drop but probably not much.

I also want to note the fact of the coefficient of friction against the air inside the plenum. To make the plenum most efficient we would have to increase the diameter of the plenum to 100% overcome this effect. When air flows inside a tube like that 80% of the is flowing at 100% velocity and 20% would be moving slower than optimal speed. With that being said you would want all runners 20% of the plenum diameter away from the floor, sides, front, and rear of the plenum.


Okay now have at it.

 

[windrunner408]

I have a question, maybe a dumb one and i am sorry if it is, but why dont you model the shape of the manifold after that of the stock one?? I mean let's face it, aside from the known blockages that originally come in the manifold (and we know that by removing them air flow increases), that design is proven to flow air fairly well. So why wouldnt you try to imitate that design? I realized it is cast but it seems that if the shapes were very similar and the ports werent rough, then a design based on that should still flow fairly well right?

I guess, I just see a lot of calculations based on a lot of assumptions and have to ask if all this spinning is going to be worth a damn. Just trying to wrap my head around it is all.

 

[6leakertweeker]

Well I was trying my best too. I just couldnt come up with something I liked. Also, I haven't been too impressed with the way the stock or modified stock manifolds bolt down or the fact of welding on a cast aluminium part. With this design I believe you would have less chance of leakage at the head and zero worries of intake bolts leaking.

 

[windrunner408]

I got ya. Makes sense.

 

[Mwilbur516]

I like your design. I just keep going back to the thought that an intake that wrapped around in the back (kinda like the regulated return resolves the dead head issue with the fuel system in the heads) would flow better to the rear cylinders. I am by no means an expert, this is just a thought. I also don't know how or if you could fit some sort of crossover in the back of the intake.

 

[6leakertweeker]

I like your design. I just keep going back to the thought that an intake that wrapped around in the back (kinda like the regulated return resolves the dead head issue with the fuel system in the heads) would flow better to the rear cylinders. I am by no means an expert, this is just a thought. I also don't know how or if you could fit some sort of crossover in the back of the intake.

There's one in there from the factory. A 1" tube or some large stainless braided hose would work as well. Just not sure if its necessary.

 

[Mwilbur516]

There's one in there from the factory. A 1" tube or some large stainless braided hose would work as well. Just not sure if its necessary.

Yeah, I'm not sure that it's necessary either, just a thought.

 

[6leakertweeker]

It wouldn't be too bad I don't think.

 

[JoeDaddy]

I'm not sure if you got it but as Jason pointed out 5000 revolutions... is 2500 of EACH cycle... accounting for 2 revolutions to complete. Also VE is most commonly figured in N/A because one can have a more complete evacuation without boost in the exhaust. Charles pointed out once that a turbo motor is likely to never reach even close to a theoretical 100% VE.

 

[Dieselcraft]

I'm not sure if you got it but as Jason pointed out 5000 revolutions... is 2500 of EACH cycle... accounting for 2 revolutions to complete. Also VE is most commonly figured in N/A because one can have a more complete evacuation without boost in the exhaust. Charles pointed out once that a turbo motor is likely to never reach even close to a theoretical 100% VE.

did this get out of hand?:gethim:
ill just read and int:

wheres the results of this MOD???

 

[6leakertweeker]

any news on this

I'm having an intake shop look into my design. I should know more soon.

 

[TyCorr]

I'm having an intake shop look into my design. I should know more soon.

Im in belief that you should have that intake be a closed loop. Marry the ends you.have terminations at currently. The air needs to move. The marrying of the ends wont necessarily allow through-flow but rather allow full volume to reach the rear cylinders and.create a buffer. Id probably have each plenum feed cylinders on opposing banks to keep.pressure kosher. A little piping analysis could make obvious some weak points. Forced induction will cover some weak spots.and make.some.unbearable in this.design. Its.a good start though.