Help me with my itb intake!!

[Shaun41178(2)]

Ok so I have been trouble shooting how to get this into my car for about 2 weeks now thinking about it a few times everyday.

I measured the stock intake and I came up with a measurement of 9-1/4 inches from the base of the lifter valley of the block, to the top of the upper intake manifold. I then measured from the top of the upper intake to the botoom of the decklid and I got around 3 inches or so.

This means from the block to the decklid is about 12 inches or so. Now I want to play it safe for engine movement or anything else I might mismeasure which brings me down to about 11 inches for a total height of the intake I can run and still fit under a stock decklid.

I would like to turbocharge this itb intake which would mean I would have to build a plenum box. Now I could probably build 2 of them one for each bank, but I think a single large one would be easier and have more consistent flow between the banks of cylinders as well.

This is what I am working with so far.









Thats 2 inches of runner right there under my mocked up cardboard peice. That leaves me 2.5 inches above that point to allow for the fead from the turbo and still clear the decklid. Where that carboard peice is is about as high as I can go with it if I was to have the plenum be 2.5 inches high. Basically I don't want the air to have to take a hard 90 degree turn to find its way into the runner, which is why I want some height to my plenum.

With the intake, the runner and the 2.5 inches height for the plenum, this would put me at a total of 11 inches from the base of the lifter valley.

This would give me abuot a total of 3 inches from the plenum, to the throttle body blade inside the runner. Talk about a short ass runner

Questions I have.

1. Someone please help me choosing the volume for this plenum. its to feed 3.5 liters with a camshaft around .430 lift and a 114 lsa or so. Basically its a stock 3400/3500 cam. Also with a runner length from the plenum to the blade about 3 inches and to the valve about another 3 inches.

2. How screwed am I with this runner length with the cam I am running? I am pretty sure this is a low to midrange cam from GM and this is a short runner intake. Not designed to work well with each other from the reading I have done.

I can take more pics if need be.

Thanks

[whipped]

Your ports are like perfectly spaced for some crossover runners....

http://www.globaltecheng.com/ProductCar ... oduct=4457

3" radius is probably plenty tight.

http://viper.dragtimes.com/viper/engine.jpg

Just a thought...

Runner length is defined as opening in plenum to back of valve. You'll need to measure that total distance on your heads and intake to get a better picture. I think a turbo engine is going to want a smaller plenum because it acts like a spring, storing pressurized (or atmospheric) air. So you'd get more lag and give your bov a workout

[Shaun41178(2)]

well from teh back of the tb blade to the valve is about 4 inches so I would have a 7 inch runner or abouts.

Crossing the runners would probably work but like I said before it would probably require 2 plenums. Also adding a bend to the runner will hurt flow and I am wanting to keep it as straight as possible.

adding a second bov wouldn't be a problem, and having a little bit larger plenum is going to delay spool by maybe .01 second as it already has to presurize a ton of intercooler piping, and even the intercooler itself.

Perhaps looking at BMW's E46 or similar setups as far as runner length and plenum volume will probably give me a good idea as to how big to make mine since it uses itb's with a large plenum as well.

I guess finding cam specs on the E46 engine will prob help me out. Maybe S8n has that info available?

[Series8217]

What ever happened to doing another dual-throttle body intake?

[Kohburn]

I say stick some 3" tubes with velocity trumpets ont he ends on each runner. mount the box about 2" amove the LIM

place your fuel rail inside the box with each injector point straight down into the trumpet from about 1/2" above it. The volume of the box after the runners should have a very minimal effect on throttle responce but will assist with the top end. So i say make it just big enough to have the perimeter of the box be spaced away from the runners by the diameter of the runner, and just tall enough to fit the injectors. taper the shape slightly from front (the end you put the TB on) to rear to help maintane even air distribution inside the box.

should be pretty easy to make since it can be square.

[AkursedX]

It's funny because every time I see "itb" I think of "In the butt" And then I'm like "why does Shaun need help with his 'in the butt' intake??"


Anyways, on a more serious note, is this actually going to be an individual throttle-bodied intake or is there going to be one throttle body in front of the box and then 6 individual runners? Personally I like the idea that Whipped had of using 90* runners. I think this is your best bet to getting some longer runner length without adding too much height.

This is quite an interesting project and with proper turbo sizing and a good tune, some serious power could be made. I forget who it is here who has that turbo-3400, and he puts out some good power. This would probably even have more potential.

[Series8217]

a more serious note, is this actually going to be an individual throttle-bodied intake or is there going to be one throttle body in front of the box and then 6 individual runners?

The manifold you can't see very well in the pictures has 6 throttle bodies built into it.

[AkursedX]

The manifold you can't see very well in the pictures has 6 throttle bodies built into it.

Oh, I remember seeing pics of it now.....

So, how does having a butterfly in the middle of a runner effect airflow? I would imagine the runner length after the butterfly is more important than what is in front of the butterfly. And the runner length after the butterfly cannot be adjusted.

I'm not good with airflow dynamics. All I know is short runners for top end hp, long runners for low end torque. So I'm curious as to how this works.

[Kohburn]

a more serious note, is this actually going to be an individual throttle-bodied intake or is there going to be one throttle body in front of the box and then 6 individual runners?

The manifold you can't see very well in the pictures has 6 throttle bodies built into it.

oh yeah - in that case the volume of the box makes almost no difference except what volume is imediately available and low vacuum when you first crack the throttles (ie larger box = improved throttle response)

and longer runners would be pretty useless.

what about the injectors? are there bungs bellow the throttle flaps?

if so then to size the air box basicly imagine a ball the same diameter as the runner and make sure you can fit it between the intake throat and the walls and top of the intake box.

so if the runner is 2" tall then has a 1" velocity stack inside the box and 2" up to the lid ont he shallow end (farther from the intake tube) then the shallow end would be a total of 5" tall. and the front end probably 7" tall.

you could easily make it our of fiberlgass unless you plan to boost it.

[Series8217]

People with ITBs often tune with velocity stacks.. so the runner length before the throttle blade DOES count. When at WOT the blade is hardly a restriction, and certainly doesnt look like a plenum opening to the airflow..

[Kohburn]

this is shaun we are talking about - if we make it too complicated he'll just stick a shoe box over it with a nylon stocking inplace of the lid.

[whipped]

1. Someone please help me choosing the volume for this plenum. its to feed 3.5 liters with a camshaft around .430 lift and a 114 lsa or so. Basically its a stock 3400/3500 cam. Also with a runner length from the plenum to the blade about 3 inches and to the valve about another 3 inches.

2. How screwed am I with this runner length with the cam I am running? I am pretty sure this is a low to midrange cam from GM and this is a short runner intake. Not designed to work well with each other from the reading I have done.

heh, I forgot you want a turbo. Kohburn's right, tuning runner length is almost impossible with a turbo because the pressure keeps changing, which changes the speed of sound. So no intake resonance for you.

Volume for plenum... If you want max power and don't care about lag, use >1x engine displacement.

And using ITB's will probably help a lot with engine response, so maybe go even 2x engine displacement.

[Shaun41178(2)]

what about the injectors? are there bungs bellow the throttle flaps?

.

You can see where the injectors will screw in right here. Those brass peices are the old mechanical style injectors but I am converting to efi. These are below the throttle blades.

this is shaun we are talking about - if we make it too complicated he'll just stick a shoe box over it with a nylon stocking inplace of the lid.

HAHAHAHAHAH could be somewhat true. :thumbleft:

Actually there will be no length of runner inside the box. I do have velocity stacks, and they will be right at the bottom of the box, not protruding into the box at all.

So 2 inches before the throttle blade isn't a big deal then huh? I guess it won't matter too much then with my small cam? I could go with a larger cam but I don't want to ditch the roller cam that comes stock to put in a flat tappet.

Ok so if I was to make an intake box the same displacemnt as a 3.5 I would need it to be about 210 cubic inches or abouts. Its been a while since I took geometry but it would be L*W*H to get volume. What dimensions woudl I need to get 210 CI box?

I know I have a 2.5 inch height to work with, and probably around a 12.5 inch width. Which leaves length.

I plan to have a box welded out of sheet aluminum.

[Shaun41178(2)]

Ok so I guessed at the length I will need to fit all of the velocity stacks in plus to leave some extra room around the opening of the box, and I will probably have around a 18 inch length. Which puts me around 540 cubic inches of plenum.

[p8ntman442]

your length and height are determined by the decklid and the length of the ITB setup, so all you have to do is calculate the depth of the box, from the fron to the back of the car. Thats the only measurement you have to play with.

[Kohburn]

you might want to consider cutting some tubing in half for the sides of the plenum rather than straight flat sides. it would look a lot nicer and air doesn't flow around corners well.

I say make it 2" tall since your velocity stacks end at the bottom of the box.

square corners would make a 2x12x18 box 430cu in - take off the corners for using split tubing and it should sit right under 420 making it about 2x engine displacement.

you can then run a 3" pipe down the center and out the end. I'll draw what i mean up real quick.

[p8ntman442]

go from the enterprise to the woopie cushion intake.

[The Dark Side of Will]

You can still set up runner length for your cam with forced induction... or calculate what your available runner length will give you with your cam.

I thought there were starting to be aftermarket cams for these engines... or at least regrinds? Just don't feel like changing?

I'll put up the math later. It's 2130 and I'm just about to leave work.

[The Dark Side of Will]

Sorry it took so long.

The way intake tuning works is this:

When the intake valve opens, a low pressure wave leaves the cylinder and travels up the intake runner. This wave bounces off the open end of the runner as a high pressure wave and heads back down into the cylinder. At the tuning RPM, this wave, or an integral reflection thereof, aids in packing the last little bit of air into the cylinder right before the valve closes.

For N/A engines, the strength of the initial low pressure wave is enhanced by good scavenging on the exhaust side. Turbos benefit less from it because the greater lobe separation angles don't allow as much exhaust/intake interaction.

Anyway, here's an example of how to do the math associated with intake runner length:

Engine: L98 (TPI 350)
Intake lobe duration (1990-92): 202 @ 0.050, 250 total (estimated)
Intake runner length: 26 inches
Intake air temp (estimated) 100 degrees F

More to come...

[Kohburn]

and how does that corespond when the throttle valve is in the middle of the runner