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| Iron Duke Intake / Bore Size ... (Page 1/1) |
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82-T/A [At Work]
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MAR 10, 01:45 PM
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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!!!
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IMSA GT
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MAR 10, 04:21 PM
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Stingray92
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MAR 10, 05:27 PM
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82-T/A [At Work]
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MAR 10, 06:42 PM
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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,
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... 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!
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82-T/A [At Work]
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MAR 10, 06:47 PM
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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!
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82-T/A [At Work]
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MAY 15, 10:41 AM
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Just a quick update on this... there's a company that bores 400 TBIs for the 81-84 Corvette, and 82-83 F-bodies that have Cross-Fire Injection. For the most part, you can actually use a 400 TBI in a Fiero, but will have to re-route some of the vacuum lines for things like the ThermAC and such. But the guy offered to bore out my 300 TBI (the one the 84-86 Fieros use) to 45.5mm, which is the factory size of the 400 TBI. My goal is to increase the bore size from the stock ~43mm to ~45.5mm, while using a throttle plate from the 400 TBI, which is identical looking to what's in the 300 TBI. So I'll literally have a totally stock looking 300 TBI that's got a much larger bore, and reasonably provide more air to the engine.
He's charging me about $395, but it comes with a bunch of other things too... he bead-blasts the entire throttle body, cleans everything to like new, installs needle bearings for the throttle shaft, and restores everything on it to "like new." He'll also bore a set of factory gaskets for me to the same bore.
I'm also having a local machine shop bore the intake manifold to 46mm, and will re-use the little fuel foil, with the indent. I choose to have the intake bored to 46mm because unfortunately, the way it is now... (as you can see from the pictures above that Stingray92 posted) with the fuel foil in there, it actually blocks some of the intake... so you don't even get the full 43mm of the stock TBI bore.
In the end, I'll have a true 45.5mm throttle body, that looks 100% stock, and will most certainly provide a bit more horsepower. I realize it's not going to give me 100+ horsepower, probably not even 10hp, but if it gives the car a bit more power and drive ability, while looking totally stock, then it'll be a nice improvement.
He's concerned about 2 vacuum ports, the one that goes to the EGR, and the one that goes to the fuel evaporative canister purge valve. Both of these port into the bore (before the throttle plate... you may not even realize it), but he wants to make sure that boring the TBI out by 2.5mm won't destroy these ports. But I'm willing to take the risk. He says that if the porting goes well, he'll offer this service at a lower price to everyone else... which will support both Fiero owners, and everyone from like Citations to whatever.
I'll post when I get everything back and find out.
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