sfi

I agree w/ Injected. I bet all 3 w/ the combo are within 1-3 hp. Accufab is overpriced based on the actual gains compared to the others. Jbauer, get the combo, most of the time you can buy them at a discount bought together and definately go with the 75mm. I have the BK 75mm and the C&L plenum. Woke the car up when it was NA. I doubt you will notice much of a difference just buying the TB.

techsent

Here's some comparisons of different TB's and the C&L plenum

http://www.cnlperformance.com/plenum11.html

PowerPonyPatrol

I would like to see how you figure you're spending an additional $200 for the Accufab combo
-Accufab Combo $399 (American Muscle)

-C&L Plenum= $139 (CNLPerformance)
-BBK 75mm TB = $209 (American Muscle)
Total = $348

Price difference = $51

I also have a book with dyno charts using different TB+Plenum combos.
C&L Plenum + Accufab 75mm TB = +14hp gain
Accufab Plenum + Accufab 75mm TB = +17hp gain

Not a huge difference, but the Accufab combo is +3hp for only $35 more (C&L Plenum $139 + Accufab 75mm TB $225 = $364)

JayDs Ibanez

75 mm

H0SS302

i got the 70 mm and i would do it again!

75 is OVERKILL on a n/a engine... every manufac. says it, and nobody ever bothers to read it.

ya you may get 1 or 2 extra horses... but i think there is a reson behind their recomendations. iv been in a car with 75mm tb/plenum combo and at 1500~rpms when you hear it suck in air, it does not sound as strong or last as long as it does in my car. when i get up to 1500~ it sounds like a damn vacuum sucking that air up.

just my .02 on the whoe tb thing. ppl can say what they want, but engineers work very hard to produce products and make recomendations for when, and how they should be used.

PowerPonyPatrol

75mm might be overkill on a pure stock N/A engine, but if you have upgraded your CAI or other fuel induction components, it's definitely worth it. Also, you're going to notice a bigger difference as you increase in engine speed (aka 4500+ RPM). Andactually I haveseen dynos on supercharged engines where the 70mm posts bigger gains than the 75mm, but the same does not go for an N/A engine.

STANG0446

75 mm especially if you r doing exhaust later or already have it you will feel the power in upper rpm's. love the accufab looks and performance a+++++++++++

sstang

The plenums are not rectangular on the inside, they are shaped just like the C&L. If you look at your stock plenum, which is rectangular on the outside, you will see it is circular on the inside. Same goes for other companies like Accufab.

techsent

Hey sstang,

You're right. I just looked inside the stock one and see what you mean.

Thanks for setting the record straight!

5spd GT

You guys are funny

You are not going to see any difference between a 70 or a 75mm unless you have some fairly serious engine modifications N/A.

Read this from the very company being talked about, Accufab Racing. I think they would know.

Increased throttle response is the same thing as a touchy throttle. Do not think they are different. WOT stays the same.
THE AIR PUMP UNDER YOUR HOOD
By George Klass
What size throttle body or carburetor do I need?
Good question but the real question should be “how many cubic feet per minute (CFM) of air will my engine require?”
An engine is an air pump. Based on the size of the engine (displacement) and how fast it will be spinning (RPM), it will pump out a certain amount of air. Works just like an air compressor. Of course, there are many variables to CFM requirements, such as cylinder head flow capabilities, intake and exhaust manifold flow capabilities, etc., but the basic engine block will pump a certain amount of air over a specified period of time, measured in cubic feet of air per minute.
If the engine is to be carbureted, it should be a relatively easy decision to pick out the correct sized carburetor. Carburetors are defined by CFM. If your engine calls for (or pumps out) about 664 CFM, the correct choice is probably a 650 CFM carburetor. Unfortunately, throttle bodies are rarely defined by CFM ratings. Instead, most throttle body manufacturers define their throttle bodies by the inside diameter of the unit, measured at or around the throttle blade, and usually in Millimeters (MM). Unless you have a direct correlation between the measurement in MM and the related CFM of that particular unit, the selection is going to be based on “best guess”.
And to further complicate the “guessing” process, all throttle bodies of the same dimension, do not have the same CFM rating. You might think that Brand A’s 75 MM throttle body would flow the same as Brand B’s 75 MM throttle body. Such is not the case, because all throttle bodies have a “major obstruction” in the middle of the air path, namely a throttle blade and shaft. How well the air flows over and under this obstruction will define the CFM a specific throttle body will flow. A big fat shaft with the attachment screws for the blade sticking up into the air stream will impact the CFM of that throttle body.
While most enthusiasts with EFI engines continue to purchase throttle bodies based on Millimeter size, caring little about the actual CFM ratings, the carb guys purchase carburetors based on CFM ratings, caring little about the size of the throttle plates. Score one for the carb guys.
But, back to the original question, “how much CFM do I need”?
Below is a chart with the CFM requirements, based on displacement (in cubic inches) and RPM. This chart will work for any piston engine with any number of cylinders. After you have determined the CFM for your specific engine combination, you can then choose the corresponding throttle body or carburetor size to best fit that combination.
DISPLACEMENT………….6000 RPM……….6500 RPM……….7000 RPM
280………..…………………486………… ……..527………………..567
290……..……………………503………… ……..545………………..587
300………..…………………521………… ……..564………………..608
310……..……………………538………… ……..583………………..628
320……..……………………556………… ……..602………………..648
330………..…………………573………… ……..621………………..668
340……………..……………590………… ……..639………………..689
350……..……………………608………… .…….658………………..709
360………………..…………625………… ……..677………………..729
370………………..…………642………… ……..696………………..749
380………………..…………660………… ……..715………………..770
390………………..…………677………… ……..734………………..790
400………………..…………694………… ……..752………………..810
410………………..…………712………… ……..771………………..830
420………………..…………729………… ……..771………………..830
430………………..…………747………… ……..809………………..871
This chart should give you a general idea of the amount of air your combination will pump. Engines will pump less air because of the restrictions in the cylinder head or intake manifold design or valve lift, or all three. But, the chart still gives you a ball park starting point.
One other thing to know. A carburetor requires air speeding over the venturi to draw the gasoline into the mixture. Using too large a carburetor (high CFM rating) will usually cause derogatory performance in the lower or midrange. This is because the lower air velocity is inefficient in mixing the gasoline with the air. In general, and particularly for street use, a slightly smaller carb (less CFM) will give better overall performance.
With an EFI system, this is usually not a problem. The throttle body only controls air flow. A computer monitors the gasoline supply and the mixing of gasoline and air takes place inside the intake port, and not inside the carburetor. Using an oversize throttle body is not nearly as detrimental to low and midrange performance as is using an oversize carburetor.
So, to find the CFM ratings of a carburetor, all you need to do is to look in any catalog from Holley, Edelbrock, Barry Grant, etc. That’s how the carburetors are listed. To find the CFM ratings for a throttle body is going to be more difficult, unless you happen to choose an Accufab throttle body.
Below are the various throttle body sizes and corresponding CFM ratings for the Accufab throttle bodies. Because the Accufab throttle bodies are designed to “race engine specs”, the flow ratings are going to be greater than most of the other aftermarket throttle body designs, so don’t automatically expect a “75 MM Brand B” throttle body to flow as much as an Accufab 75 MM unit.
65 MM - 664 CFM
70 MM - 787 CFM
70 MM - 896 CFM (Race version)
75 MM - 924 CFM
75 MM - 1045 CFM (Race version)
80 MM - 1142 CFM
85 MM - 1322 CFM
90 MM - 1369 CFM
105 MM - 1550 CFM
Cobra (’96-’98) - 1284 CFM
Cobra (’03-’04) - 1696 CFM
Lightning Pick-up (’99-’04) - 1696 CFM

So, there you have it.