75mm TB too much? What MAF to get?

c.moser said:

I just bought a 98 gt convertible a couple weeks ago. It already has a Trick Flow upper intake plenum, BBK CAI, and a BBK 75mm throttle body. As far as I can tell the MAF is still stock. I have a couple questions. One is the 75mm TB too much? The car is daily driver and I never race it or have any plans to. Is this killing my low end or would switching to a 70mm make a difference?

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Couple of things:

1) The engine spends most if its time throttled to varying degrees, which you control with your foot. You're not losing any low-end torque with that throttle body.

2) It's doubful the car needs that much TB diameter because it's got NPI (non-performance improved) heads and probably doesn't flow enough to take advantage of that TB. Still, it's a decent TB to have on the car if you decide to upgrade other parts later.

The throttle also seems a little sticky at times, is this normal with an aftermarket TB?

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No. Get under the hood and check the linkage manually. Operate it to its full extent (engine off) and look for binding, hanging-up etc. Also check the return springs.

What size/brand MAF should I go with? I plan on upgrading to PI heads/cams eventually if that makes a difference.

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I'd stay stock. You'll get the best driveability out of the stock meter. After you go the PI heads and cams route you might think about upgrading to a 99-04 MAF but you won't need any more than that.

Trinity pretty much has this one taken care of.

TB combined with plenum offers a couple hp and could be a worthwhile mod. With your car I would do the PI swap (at least intake manifold and cams) before I spent any time working on the TB or the plenum.

As far as the TB goes:
I've seen dynos done by C&L that claims that the 75mm is superior to the 70mm in basically stock NA stangs, they claimed something like 1-2 hp gains with the 75mm over the 70mm (both have aftermarket plenum and CAI if I remember). That being said, I have a little scepticism of those numbers and I think you cannot go wrong with either the 70mm or the 75mm TB.

c.moser said:

If I get the P.I. intake, should I still use the Trick Flow upper plenum I already have and use just the lower P.I. intake, or would I be better off using the upper and lower P.I. intake?

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Use the T/F upper on the PI lower.