Iron Duke Intake / Bore Size ... (Page 1/1)
82-T/A [At Work] MAR 10, 01:45 PM
Would someone very much mind measuring the intake opening below the throttle body, of the 1984-1986 Iron Duke intake?

My daughter has an Iron Duke, so obviously I can get at one, but I'd rather not take the air cleaner and remove the throttle body unless I absolutely need to. Just hoping maybe someone has an 84-86 laying around, and they don't mind measuring with a caliper (in MM) the opening on the intake from where the throttle body connects.


Thank you!!!
IMSA GT MAR 10, 04:21 PM
I don't have the answer for you and I don't know if you're looking for a replacement but see this web page. It's just FYI.
https://www.fierofocus.com/...ls/ThrottleBody.html
Stingray92 MAR 10, 05:27 PM
Here ya go,





[This message has been edited by Stingray92 (edited 03-10-2025).]

82-T/A [At Work] MAR 10, 06:42 PM

quote
Originally posted by IMSA GT:

I don't have the answer for you and I don't know if you're looking for a replacement but see this web page. It's just FYI.
https://www.fierofocus.com/...ls/ThrottleBody.html




Thank you! That page is interesting... particularly because of what it says about the TBI units. I actually have a bunch of them that I've (for some reason) collected over the years, and when my daughter rebuilt hers, we did so with the best of the ones I had. I'm not really sure that page is entirely correct though. The Fiero TBI unit from 1984-1986 is identical... it's called the TBI 300 and is interchangeable between all three years. The one from 1987-1988 is the TBI 700 (both are from Rochester). But that brings me to the next point...



quote
Originally posted by Stingray92:

Here ya go,






... thank you! This really helps.

I wanted to know this because the opening on the TBI unit is exactly the same as the opening on the stock intake.

I recently bought a 1984 Corvette with Cross Fire Injection, and I also have some old parts left over from when I had a 1982 Pontiac TransAm with Cross Fire Injection. On a whim, when my daughter was rebuilding her throttle body, I discovered that the ones on the Cross Fire Injection engine are identical in every way to the ones on our Fiero. The one on the CFI are known as the TBI-400, while the one on the Fiero is known as the TBI-300. There's even a smaller version whith is called the 7-103... which is basically a shitty version of what we have (meant for the 1.8 and 2.0 liter).

But here's the cool thing. Everyone that has a Duke wants that Holley 3730 TBI unit... but they're basically impossible to find. The bore measures at 50mm, while the stock Fiero's bore measures at 43mm (just like the stock intake). Well, the factory TBI 400, which is every bit identical to the Fiero's TBI-300 has a bore of 46mm. All you really need to do is remove the dual-linkage bracket, and replace the throttle shaft with the one from the TBI-300, and everything else bolts up.

Of course, as I see now... the factory intake would need to be bored out 3mm for it to even make a difference... but there are options if someone wants a little bit more horsepower and they're feeling cheap.


Thank you!
82-T/A [At Work] MAR 10, 06:47 PM
She's going to post her next video (which is a "How To w/ Upgrades" for the Fiero throttle body) next Thursday, and I'm helping her do a little bit of follow-up on this.


Thanks again!