Help me with my itb intake!!

[The Dark Side of Will]

As long as the open throttle isn't much of a restriction, it won't create much of a reflection.

I first laid out the TPI math in this thread:

phpBB/viewtopic.php?t=1384

Take the classic intake tuning example of a 350 TPI:
Intake duration: 202 degrees (presumably at 0.050)
Exhaust duration: 206 degrees
Lobe sep: 115
I think we can guesstimate with reasonble accuracy that this cam has approximately 250 degrees of total duration.
This engine makes peak torque approximately 3,000 RPM. At 3,000, each revolution takes 20 milliseconds. Of that, the intake valve is open for ~14ms (250/360*20).

According to my handy pocket reference, the speed of sound in dry air at 100F is 1160 fps. Thus sound travels, in 14 ms, 16 feet. which would be a runner length of 8 feet....

To use the first reflection to create a torque peak at 3000 RPM requires a runner length of 8 feet. Using the second reflection at that RPM would require a runner length of 4 feet. Using the 4th reflection at that RPM would require a runner length of 2 feet, which is suspiciously close to the factory runner length.

So with a runner length of 2 feet, the 4th reflection operates at 3000 RPM, the 3rd reflection operates at 4/3 or that or 4000 RPM.

Gee, the powerband of a stock L98 is about 2500 to 4500 RPM... coincidence?

The 2nd reflection operates at 6000 RPM, but by that speed the stock heads & runner sizes are restricting the engine too much to show any resonant tuning effect. HOWEVER, I have read a magazine build that used decent small runner heads (Edelbrock(?) Sportsmans, I think) with an intake port volume of about 185 cc's with a carefully selected (short or medium duration) cam and hit close to 400 HP at 6000 RPM. I think good results would also be possible with Vortec heads & TPI base, large diameter runners & ported plenum.

Anyway, Shaun, what's the DURATION of the intake lobe on the 3500 cam?

[whipped]

At first I thought this can't be done with turbocharged engines... But looking up the speed of sound vs air pressure, it doesn't change much at all. tenths of a m/s. However, temperature does have a large impact... 20C - 343m/s... 100C - 415m/s... I don't think 100c is unreasonable for a turbo, no?

[Shaun41178(2)]

TAken from www.60degreev6.com

* Cam Lift (Exhaust):.272"
* Cam Lift (Intake):.272"
* Cam Timing at .050" Lobe Lift (Exhaust Close):12 Deg BTC
* Cam Timing at .050" Lobe Lift (Exhaust Open):32 Deg ABC
* Cam Timing at .050" Lobe Lift (Intake Close):29 Deg BBC
* Cam Timing at .050" Lobe Lift (Intake Open):15 Deg ATC
* Degrees Overlap:39 Deg
* Duration at .050" Lobe Lift (Exhaust):197 Deg
* Duration at .050" Lobe Lift (Intake):197 Deg
* Lobe Centerline (Exhaust):111 Deg
* Lobe Centerline (Intake):113 Deg
* Valve Lash (Exhaust):Hyd.
* Valve Lash (Intake):Hyd.
* Valve Lift (Exhaust):.430"
* Valve Lift (Intake):.430"

[The Dark Side of Will]

Sounds like a GREAT turbo cam.

Let's guesstimate 240 degrees overall duration and figure that the effective duration for resonant tuning is about 220 degrees.

So Whipped's number of 415 m/s at 100C (approx 200 F) is ~1360fps in Imperial units.

So with a 7 inch overall runner length, the pulse has to travel 14 inches, which takes 0.85 ms. With 220 degrees of duration, this would be a revolution every 1.40 ms or 42,700 RPM. I don't think your 3500 will be able to take advantage of the first reflection... sorry mang. Maybe if you rebuilt it with a 76mm crank...

Because the 2nd reflection in the TPI would operate at 6,000 RPM, the first would operate at 12,000 RPM. 26/7 = ~3.7 and 12,000 * 3.7 = ~ 42,000. Sanity check.

So the 2nd reflection would work at 21,000, the third at 14,000, the fourth at 10,500, the fifth at 8,400, the sixth at 7,000, the seventh at 6,000. By the time you get way down there, though the reflections are extremely weak and don't do much.

Do not despair. Just look at an LT1's torque curve. Those engines use even shorter runners (~5") and are basically devoid of resonant tuning. They make peak torque almost off idle and carry it over 4000 RPM. The LT4's carry it higher. With head flow & forced induction, you ought to make a basically flat torque curve with this engine.

One thing you might think of is building a great big plenum that would bolt directly to the casting of your manifold. From there you'd bend the runners over and interleave them INSIDE the plenum. I know you don't want to bend the runners, but with mandrel bends it really won't hurt anything and could get you into the realm at which you start being able to take advantage of resonant tuning. If you can get your runner length up to 14 inches, you'll be in LS1 territory.

[Shaun41178(2)]

I am down to about 9 inches wide, by 18 inches long and still going to try with 2.5 inches high for a total volume of about 405 cubic inches.

I mihgt make the runners half inch shorter to try and get the box to 3 inches of height. Won't really know till I can get it mocked up in the car how much room I have which will prob be several months from now at least.

I have also thought of using a mech roller cam that I have here that is more for an NA setup but rips up top according to SAppy as he ran the numbers for me(thanks) . Prob is its horrible down low compared to a stock cam. Powerband would be from abuot 4500-7k rpm or so with it. Worried about the idle though especially staying with a stock computer and efi.

[The Dark Side of Will]

I think you said on the first page that you have 3" between the manifold and the cardboard?

Make the plenum 5.5 inches deep, a bit wider and bend the runners inside it. Run them between one another like interlocking your fingers.
The runner length will increase, runner volume will take away from plenum volume so it doesn't get so big that it adds lag.

Upstream of the throttle, plenum volume does not affect throttle response... only turbo lag.

[Shaun41178(2)]

Some inspiration here. Look at this intake setup. Somewhat my idea. I like the plexiglass look, and might try to add it to my setup.

http://www.youtube.com/watch?v=3ZwM8P-G38I

[Shaun41178(2)]

bumping this back up. Got a bigger cam with around 550 lift and around 280 total duration with I think at .050 around 216 or so. I will have the specs shortly

I have the injector holes drilled in the intake, just have to epoxy in the efi bungs. also have the holes drilled for either my map sensor feed, or for the iac feed, haven't decided on which one I want to make them.

I have been thinking of how I am going to fab up the TPS as well as the other sensors. 3 coolant sensors by the factory thermostat housing to figure out too. I might have the throttle cable figured out but won't know till I have it all in the car. anyone know off hand the diameter of rubber hose that connects to the thermo housing? 1.5 inches maybe?

Discovered that the mounting points on the cradle between an 88 and earlier years is different. This means I can't use the older style front engine bracket with the 3X00. I will probably be stuck modifying the stock 88 front bracket. I have also thought of redrilling the fiero oil pan to match the 3500 oil pan, then the factory bracket could still be used without modification.

Don't have any new pics.

[Blue Shift]

Just like Will said, try to get your runners to ~14" (from back of the valve to end of runner) if you can. That's almost exactly how long my runners are on my intake and you can really hear and see the effect (and feel it) when they come in.

I think more than a few short runner intakes have been made that flow much better than stock overall (again like Will said with the LT1), but miss out on the resonant tuning that you can take advantage of for a torque boost at a RPM of your choosing. I think bending the runners over in a cross firing arrangement to fit the needed length into the plenum box is a great idea.

[Shaun41178(2)]

cam specs

Dur @ 0.050 Int 231 Exh 234, Dur @ 0.006 Int 281 Exh 283, LSA 111, Lobe Center Int 110 Exh 112, Lobe Lift Int 379 Exh 352, Lift at 1.6:1 Int 606 Exh 563

I won't really have the intake figured out untill I get the motor in the car so I can see clearences. Maybe with those cam specs one can compute a good runner length to use.

[Honest Don]

cam specs

Dur @ 0.050 Int 231 Exh 234, Dur @ 0.006 Int 281 Exh 283, LSA 111, Lobe Center Int 110 Exh 112, Lobe Lift Int 379 Exh 352, Lift at 1.6:1 Int 606 Exh 563

I won't really have the intake figured out untill I get the motor in the car so I can see clearences. Maybe with those cam specs one can compute a good runner length to use.

that seems like it would have a lot of overlap for a turbo motor. I'm still working this stuff out though....



For N/A, it should be a mean motherfucker though


Btw, the Mechanical injection guys generally tune their stacks to up weaker parts of the curve, I.e. where you end up after the shift or somewhere on the way up...