Originally posted by TourDeForce:
Originally posted by warmonger:
Oh, and I'm glad you put in the words potential, because it means nothing more than that.
There will be virtually NO IMPROVEMENT in flow at lower rpm, only when the throttlebody becomes the most restrictive portion (and we don't know if it does) will it possibly be of benefit.
The speed of the pistons, the size of the primary/secondary intake runners, the valve opening cross section, these would all respectively be related to the flow potential. To be honest, none of us can really predict where the best potential increase in flow will be.
We know that Ford determined the LIM as the most restrictive on the stock 2.5L because in 1999 they gave the SVT a modified version of the 3L LIM. The TB was never changed. They also did more agressive extrude hone of the heads on 99+ models.
Seems to me that from the LIM to the head was the biggest problem area based on that info. Also, those of us who spent time carefully porting the LIM and heads on 2.5Lheads on 3L hybrids gained the most power as indicated by the dyno....WITH a 60mm TB.

Look at it from another perspective. I was able to make 217wHP naturally aspirated out of my first 3L on stock non-optimized SVT throttlebody.
Later, I ran a 70mm TB and gained absolutley no measureable power from it....on a 3L.
The 3L swallows as much as 20% more air than a 2.5L at 100%VE, and maybe a bit less in reality. By gaining no discernable gains going from 60mm to 70mm on a NA 3L, it just goes to show you that a 2.5L definitely isn't restricted by the stock 60mm TB.

I've always maintained that optimizing the hell out of a 60mm TB for a 2.5L engine is basically a placebo.
Do it if it makes you feel good but don't fool yourself.
Optimizing a 60mm TB for a 3L engine however does make sense and probably results in SMALL gains.

Just FYI, the 60mm TB is stock on all 3Ls.
For a forced induction engine the game is totally changed. I found an improvement and measurable power increases from going to a 70mm from using a 60mm. Again, the 60mm TB was used in multiple dyno's of mine and I was able to make as much as 330 wHP with it. If it is a restriction, it isn't much of one. For the big power engines like 350+ wHP FI'd cars, I'd say 65mm at a minimum, 70mm=good too.



One of the most informative posts I've ever read in this forum. Just flippin' excellent. Thanks warmonger!



I concur!

In addition, on my old 3L (PnP heads, Max Extrude Honed UIM, SHM long tube headers, etc.) switching to the 65mm Mustang TB made a difference - butt dyno says so!

Keep in mind the TB opening for the Max Etrude Honed UIM was ~70mm.

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