Back to back fox versus 94-95 TB dyno results inside!!!

Paul...I could have lent you my 75 before I sold it

Troy...Im converting myself...Main reason is the Accufab is the most gorgeous part in my new setup. It is polished, but that sucker looks like chrome
That, with the black reducer couplers, T-bolt clamps and polished Vortech D/c tube will really look GREAT!!

RC

GTA_V6_Mustang said:

I like the complicated look of the SN t/b over the fox but hey thats just me.

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WHen you see mine in soon Derrick, you will change your mind
RC

I have to chime in on this one. I’ve calibrated a lot of TB air flow models and there are a couple big points being missed here.

Compare the areas of the two TB’s.

65mm: 3.14 * (65/2)^2 = 3316.625 mm^2
74mm: 3.14 * (75/2)^2 = 4415.625 mm^2

The relative difference in area is about 33%! This is like comparing apples to watermelons.

Don’t get me wrong; I still think that this comparison is interesting, but the only conclusion I can draw from the data is that the 65mm TB is somewhat restrictive when compared to the 75mm part. For further study, I would REALLY like to see how an SN95 75mm stacks up against the FOX 75mm since the 65mm hangs in there so well!

Like someone mentioned earlier, a bigger TB will always give a more aggressive throttle response because you are allowing more air to flow into the engine for the same pedal position. The down side is that driveability may suffer since you have a more coarse/rough modulation of the air flow with the pedal. (This is especially noticeable in creeping traffic/parking lot driving/normal launches.)

The comments mentioned above regarding forced induction are correct as well. Since the increased boost argument is vague, I will put forth the two possible conditions:

1) Pressure measured upstream of the throttle, post supercharger – If the boost pressure increased after a TB swap, you just lost air flow into the engine and added a restriction into the system.

2) Pressure measured directly in the intake manifold – If the boost pressure increased after a TB swap, then you just removed a flow restriction and are getting more air flow into the intake manifold.

3) Turbo engines can’t really be evaluated this way since there are too many variables at play - waste gate.

In all of these cases, forced induction and n/a, the air flow measurement from the MAF would be the best criteria for proper evaluation. RWHP is a rough technique due to all of the other parameters involved (i.e. spark, lambda, temps…).

Consider the scenario where a new TB is installed on a car, it increases the air mass flow by as much as 5 to 10% at WOT, but the RWHP went down. The flow increase could have pushed the ECU to move to the next load breakpoint in the spark map, where the spark is not calibrated properly for this load point for any number of reasons. Or on newer cars, the increased air flow could have pushed the ECU into component protection fueling faster than before and the engine is running pig rich during the dyno run.

I’m not trying to beat up on this thread. I think it’s interesting and I wish I had access to a chassis dyno for my own personal research projects! My only criticism is that a more scientific approach needs to be taken before general statements are made from a part comparison like this.

My two cents, Mike

I say that as far as looks the fox looks the best. But as far as performance this leads me to believe that if you already have a 75mm SN95 then for performance purposes you don't need much else. Unless we do a run with a 75 MM SN and we get the same results, then we will have the evidence that size doesn't matter and its the form of the fox setup

I appreciate the comparison but I don't beleive that is a fair one considering the difference in throttle body size.

greenlantern said:

I appreciate the comparison but I don't beleive that is a fair one considering the difference in throttle body size.

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Did your girlfriend tell you that?

greenlantern said:

Did your girlfriend tell you that?

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No...my wife...and she said "it's TRUE"

There is one good way to settle this debate. What do you think the odds are that if we presented this argument to 5.0 Mustang, Modified Mustangs or any other popular Mustang mag that they would do a comparison test. 65MM Fox TB VS 65MM SN95 TB and 75MM VS 75MM?

what we really need is the ability to compare TB to TB in controlled conditions, much of which is done in magazines.

What about the argument that a 75mm TB is too much for a n/a 302....WOuldnt that make the results even MORE in favor of the Fox setup? (assuming the former argument is true).

RC

94GTLaserRC said:

What about the argument that a 75mm TB is too much for a n/a 302....WOuldnt that make the results even MORE in favor of the Fox setup? (assuming the former argument is true).

RC

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Would be nice to see this done on a 302, 331 and 351. I think it would make for a great tech article write up.

MisterCMK said:

I would be interested to see how much air was moving through there with the Fox vs the SN95 TB in addition to the dyno numbers. It is nice to finally see someone put down some actual numbers though.

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This is an excellent question. Did you happen to record the max VE or MAF voltage with each setup (I forget which computer you are running)? If you have the logs I would be happy to go through them.

In regards to the sizing of the induction for N/A, I am also in the camp that you cannot go "too big" on the induction tubing size. Your choke point is going to be the intake and the heads, why size anything down in front of those??? The only thing you lose on a very large TB is some pedal feel, but I am of the opinion that you can learn to drive it no problems, it is not the end of the world.

Wes