[02'TrueBlue]

Hey guys. I know there's debate as to what's better on our GT's..75 or 70MM throttle bodies? But I was looking on the AM website, and if you opt for the edelbrock intake, you can either get an adapter plate, the 6061 plenum, or edelbrock's plenum that allows you to run a 90MM fox throttle body. Now my question is, if you're running a JLT CAI which is pretty much 90MM(slightly more I think) would it be a benefit or a negative to run an intake setup this big? I would think 90MM straight from the intake filter to the intake manifold would be a good thing

[casper gt]

Originally Posted by 02'TrueBlue Hey guys. I know there's debate as to what's better on our GT's..75 or 70MM throttle bodies? But I was looking on the AM website, and if you opt for the edelbrock intake, you can either get an adapter plate, the 6061 plenum, or edelbrock's plenum that allows you to run a 90MM fox throttle body. Now my question is, if you're running a JLT CAI which is pretty much 90MM(slightly more I think) would it be a benefit or a negative to run an intake setup this big? I would think 90MM straight from the intake filter to the intake manifold would be a good thing

it would be a good thing IF you had the motor to support it & the rpm capabilities.

[02'TrueBlue]

That's what I figured, but thought why not spark a debate lol. Thanks Casper. I've just been considering swapping my BBK CAI, Roush 75MM throttle Body, and Trick Flow Plenum for the BBK Throttle Intake and JLT CAI..They're slightly bigger and look a lot nicer together than my setup. Then I saw the 90MM options and wanted to ask

[4.6DreameR]

Sometimes too much of a good thing is a bad thing.
If you are running high boost I think it would be worth it but highly doubt the increase on a NA car.
Accufab TB/Plenum flows the most, I remember seeing a link to the flow charts.

[casper gt]

Originally Posted by 02'TrueBlue That's what I figured, but thought why not spark a debate lol. Thanks Casper. I've just been considering swapping my BBK CAI, Roush 75MM throttle Body, and Trick Flow Plenum for the BBK Throttle Intake and JLT CAI..They're slightly bigger and look a lot nicer together than my setup. Then I saw the 90MM options and wanted to ask

I'd keep what you have.

[casper gt]

Originally Posted by 4.6DreameR Sometimes too much of a good thing is a bad thing. If you are running high boost I think it would be worth it but highly doubt the increase on a NA car. Accufab TB/Plenum flows the most, I remember seeing a link to the flow charts.

heres the chart,

Mustang GT

[02'TrueBlue]

Yeah, I'm definitely keeping what I have, just because I know the extra couple horsepower isn't worth the money I'd have to spend. It's cool to want things though lol. While on the topic, has anyone ever used crinkle coat paint on a throttlebody? What kind of precautions would I have to take when masking and spraying? I want the throttle body to match my trick flow plenum..I feel like that would give me a new appreciation for what I have visually

[cliffyk]

Here's Accufab's flow data, reformatted and annotated by yours truly--the bottom line is that for any n/a 2V application a 70mm TB is as big as is needed.

Also it's the stock upper plenum that is the weak point. Any aftermarket plenum with even the stock 65mm TB, will outflow the stock plenum with a 75mm TB...

[02'TrueBlue]

yeah I see that lol. I already have a 75MM throttle body and a trick flow plenum, I was just considering switching for looks mostly. But if anyone has any tips on how to properly paint a throttle body, that would be awesome! I'm guessing it's pretty much self explanitory but still

[cliffyk]

I got my Pro Products plenum powder coated at a friend's shop...

[02'TrueBlue]

That looks pretty good, but I'm painting the throttle body, not the plenum. Like would I have to take the sensor off and the throttle cable spring and stuff off or could I just mask them? That's what I'm figuring out now

[cliffyk]

If you mask it tightly you should be OK, use a heat resistant paint as it can get pretty hot under the hood...

[Eagle2000GT]

I'm still not sure I unterstand the 5", 20", etc. part of the table. How do you create or change the pressure differential?

[cliffyk]

Originally Posted by Eagle2000GT I'm still not sure I unterstand the 5", 20", etc. part of the table. How do you create or change the pressure differential?

On a flow bench you vary the airflow until a desired pressure drop (differential) across the DUT (Device Under Test) is at the level you wish to use as the standard for comparing the devices you wish to test.

In Accufab's tests they selected 5, 20, 25, and 28 inH2O (inches of water--0.4, 1.5, 1.8, and 2.0 inHg [inches of mercury]) as the "standard" differential pressures for testing the various combinations.

Then, each plenum and TB/plenum was mounted in the flow bench and the airflow in Cubic Feet per Minute (CFM) was adjusted so the the pressure drop was at each of the four standard levels.

The CFM flow at those standard differentials was recorded and listed in the table for each DUT.

[02'TrueBlue]

VHT Wrinkle Plus Coatings i was gunna get my hands on a can of this. Think the engine heat will be able to cook it or would I have to stick it in an oven still since its not really attached directly to the engine?

[cliffyk]

I have a can of that in the garage, it may get a tiny bit soft at higher temps until it cures full--though the heat will help it cure.

Have you used it before? I ask because it takes at least 2 (and as many as 4) pretty heavy coats to get a deep wrinkle, with 30-45 minutes between coats, and then will take 8-12 hours before you can handle the part without upsetting the finish.. Even after 24 hours it will be a bit soft and in my experience it can take 3 to 4 days before it really toughens up--however once it does it's pretty tough stuff.

[Eagle2000GT]

Originally Posted by cliffyk On a flow bench you vary the airflow until a desired pressure drop (differential) across the DUT (Device Under Test) is at the level you wish to use as the standard for comparing the devices you wish to test. In Accufab's tests they selected 5, 20, 25, and 28 inH2O (inches of water--0.4, 1.5, 1.8, and 2.0 inHg [inches of mercury]) as the "standard" differential pressures for testing the various combinations. Then, each plenum and TB/plenum was mounted in the flow bench and the airflow in Cubic Feet per Minute (CFM) was adjusted so the the pressure drop was at each of the four standard levels. The CFM flow at those standard differentials was recorded and listed in the table for each DUT.

OK. I understand how you could vary it on a flow bench. How does that apply when it is mounted on a 2v motor?

[cliffyk]

Originally Posted by Eagle2000GT OK. I understand how you could vary it on a flow bench. How does that apply when it is mounted on a 2v motor?

On an n/a engine it is roughly equivalent to manifold vacuum, except that manifold vacuum is an aggregation of the pressure drops of all components of the intake right back to the outside world (plenum, throttle body, intake tube, MAF air filter, air box, and NVH snout).

Pressure drop across the TB and upper plenum is a function of engine RPM and throttle setting, which dictates intake air CFM. Assuming for a moment WOT operation (which I am sure is where Accufab ran their tests), then

intake CFM = 281in³ / 2 / 1728 * RPM * VE;

where VE = volumetric efficiency, always less that 1.0 for n/a, assume 0.9 at best for the 2V engine;

or combining the constants, 0.813 * RPM * VE;

or 0.0732 * RPM, including VE of 0.9.

So, at 6500 RPM the most a 2V could possibly suck in is 0.732 * 6500 = 475 CFM. This is why too large a TB can affect charge velocity and actually cost power at WOT and high revs. With a 75mm TB this reduction is negligible (but you won't gain anything vs. a 70mm unit)--IMHO the BBK 78mm TB/plenum combo is too big for any 2V n/a application.

[Eagle2000GT]

So, on the vaccuum gauge (no boost if n/a), you really do not want the gauge to go below 1.5 in hg because going to 0.4 in hg reduces the CFM by half?

I'm assuming by the comments on your chart that 20" (or 1.5 in hg) is the correct comparison for our cars.

[cliffyk]

Originally Posted by Eagle2000GT So, on the vaccuum gauge (no boost if n/a), you really do not want the gauge to go below 1.5 in hg because going to 0.4 in hg reduces the CFM by half? I'm assuming by the comments on your chart that 20" (or 1.5 in hg) is the correct comparison for our cars.

You are confusing flow bench comparative testing with empirical performance evaluation--and also ignoring the velocity of the fluid (air in this context). BTW, it is not "my chart", it's Accufab's, I wish I had a flow bench.

Greatly simplified, at WOT, the engine will attempt to draw in a fixed amount of air (Cubic Feet per Minute, CFM) that is directly related to engine RPM--higher RPM = more air--let's call that amount of air "Z". That air flow ill create a pressure differential in the intake tract--it has to, or there would be no flow. For this discussion we are talking about the portion of that path between the TB inlet and the lower plenum.

Using the pressure drop numbers you presented, and again simplified and ignoring other losses, at a 1.5inHg differential the air velocity would be "X" FPM (feet per minute) to move "Z" CFM of air. If the inlet were enlarged so that the pressure drop was only 0.4inHg (the onlly way to reduce the pressure differential at Z CFM flow) then the air velocity would be only have to be a fraction X FPM to move Z CFM of air.

Now, air has mass and like any mass in motion the faster it is moving the more it wants to keep moving (inertia).

So, the inlet valve opens and the air begins being sucked in; and it would get going faster in the 1.5inHg pressure drop path than in the 0.4inHg path.

Near, and at, and a bit after, the bottom of the intake stroke the higher velocity mass rams more air into the cylinder than would a lower velocity mass; and more air to burn equals more power.

There are no hard and fast numbers to all of this, however there is a real point at which a less restrictive intake path leads to lower charge velocities and costs you power/