Iron Duke Intake / Bore Size ... (Page 2/3)
82-T/A [At Work] OCT 14, 07:51 PM
Ok, updated picture, and I also discovered that I had the air cleaner stantions installed upside down... which makes sense because they didn't fit well, so I fixed that (nut side up).






I also went a little nuts... I discovered one of my spare TBI 300s actually came with a little sticker that said 6063 on it... so... I replicated it in MS Paint and made a set of 30 stickers from Sticker Mule and stuck it on the TBI. I know, overkill. It's a shame this isn't a Concourse De Elegans... I think I missed my calling.




Anyway... I'm excited to see how this works with the bored intake when I finally get it. This throttle body (as I mentioned above) is 45.5mm (up from the basically 42mm), has a Corvette CFI (front) injector, and the factory Corvette adjustable fuel pressure regulator installed... with all new seals and everything.

When my daughter gets the intake installed, we'll tune it with Romske's ALDL scanner and I'll be able to see my AFR and adjust it.
pmbrunelle OCT 15, 12:18 AM
This Seymour Alumi-Blast finish looks cool, so I did some online searches.

It seems like it's not gasoline resistant. That may be problematic for a TBI unit

I guess on outside surfaces it might be OK if there are no fuel spills when installing/removing fuel lines.
82-T/A [At Work] OCT 15, 07:48 AM

quote
Originally posted by pmbrunelle:

This Seymour Alumi-Blast finish looks cool, so I did some online searches.

It seems like it's not gasoline resistant. That may be problematic for a TBI unit

I guess on outside surfaces it might be OK if there are no fuel spills when installing/removing fuel lines.




So, I sent pictures to the guy who did the machining, he told me they don't use any paint at all on the base. The base and fuel neck are separate (as shown in the pictures below). He tells me that the machine shop that does the work for his business bead-blasts the base and that it isn't painted. I'm just not sure... because the Alumni-Blast (which I used on the fuel neck) looks 100% identical to the base. You can also see on the vacuum ports that it looks like they may have been taped off. So, I'm convinced that it's the same paint... but maybe it isn't? I know the fuel neck is because I painted it... but it has actual aluminum in the can so it could be why it looks similar.

Either way, I recognize that after several thousand miles, it'll look like all the others anyway. But we're hoping to get the Fiero completely finished in a way that... at least in the beginning, when you get in, turn the key, the Fiero feels about as close as someone can get to having a brand new Fiero in 2025. I don't think she'll want to take it with her to college, and I have my own Fiero to work on, but I'll probably hold it for her until she has a place to actually keep it. She's a junior in high school now, so she still has her senior year and the summer, and she wants to start going to more car shows and Fiero meet-ups.
82-T/A [At Work] OCT 15, 08:06 AM
What I'm interested to know, is what kind of horsepower this will make. Realistically, I'm giving it more air and fuel.

It's going from what is essentially 41.4mm (when you consider the fuel atomizer installed in the intake port), and compare it to this bored TBI with a 46mm ported intake... I went larger so that I could still install the fuel atomizer (which I'll modify slight) so the bore size remains at least 45.5 installed. So, that's a 4mm increase in bore size (since the TBI is 45.52mm).

If I do my math correctly, that's a 9.1% increase in size, though not sure what that amounts to in flow?

If the horsepower is directly proportional to the size of the bore of the throttle body (which it totally isn't, but probably a fair estimation), then she'll likely see an ~8.3hp increase. The engine is built up with all new parts, and a totally OEM specification cam, new pushrods and rocker arms, etc., so I'm pretty confident about at least getting the stock 92hp.

We also have a newer catalytic converter, lower resistance and more modern accessories, and a shorty ceramic-coated header... I'd have to say it's pretty reasonable to assume ~110hp. I think it's probably going to be doing a bit better than that .. probably more like 115hp. We also have better gearing from the 5-Speed after the rebuild, etc., but it'll at least be a pretty fun car for her to drive around in.

Not sure if I want to take it to a dyno... (just to see), but maybe we'll do it after she's put a lot of miles on it.

She's going to do a "basic high performance Iron Duke" video, which will include a few things:

- Installing the shorty header
- Installing the bored intake
- Installing the bored TBI unit
- K&N Air Filter & Fuel Filter (OEM replacements)
- Talk about the newer catalytic converter
- Summit Racing Hi-Output Ignition Coil (30k volts, so not crazy, but better than stock)


At some point though, we also have an MSD 6EFI ignition box and also a heated O2 sensor kit that we'll install. The O2 sensor will provide slightly better (and sooner) readings, and the MSD ignition box, I assume will improve around-town driving. I will say though, I don't know what it'll really do... when the engine was together, it ran so amazing. Idle was smooth as glass, and there was absolutely no hesitation, bogging, or anything at all in the performance of the engine. It ran so well.

[This message has been edited by 82-T/A [At Work] (edited 10-15-2025).]

edfiero OCT 28, 12:39 PM
I don't think you are going to gain any fuel flow using the corvette injector.

The 5.7 engine had 2 different sized injectors depending on the car. some flow 55lb/hour while others had 65lb/hour injector.
In fact the corvette had 2 different sized injectors (so maybe one each)

I don't remember the exact number, but the Duke injector is already sixty something. I wanna say 62 but I'm not sure.

Only way I think to get more fuel is turn up your fuel pressure with that adjustable regulator.
82-T/A [At Work] OCT 28, 12:58 PM

quote
Originally posted by edfiero:

I don't think you are going to gain any fuel flow using the corvette injector.

The 5.7 engine had 2 different sized injectors depending on the car. some flow 55lb/hour while others had 65lb/hour injector.
In fact the corvette had 2 different sized injectors (so maybe one each)

I don't remember the exact number, but the Duke injector is already sixty something. I wanna say 62 but I'm not sure.

Only way I think to get more fuel is turn up your fuel pressure with that adjustable regulator.




I would love to know the exact number (lb/hour) of the stock Fiero injector, if you happen to know where I can find it. I didn't see it in the service manual.

Yeah, we are using the front injector from the Corvette, which is the larger one. The front injector is 68 lbs/hour, while the rear injector is 64 lbs/hour. We get the intake manifold back on Friday, and my goal is, once we get it all back together and running... I'll use Romsk's ALDL scanner / reader, and I'll be able to see a real-time AFR... my hope is that then I can adjust the fuel pressure regulator to give a bit more fuel (or take it away if there's too much). I don't know if I mentioned it, but the Corvette's FPR is adjustable, so I swapped out the FPR from the Corvette TBI and installed it in my modified Fiero TBI (but kept the Fiero TBI FPR spring). There's a tool that allows you to reach up and under the FPR and turn the screw to give more or less fuel while the car is running... we'll see how that works.
fieroguru OCT 28, 07:27 PM

quote
Originally posted by 82-T/A [At Work]:
I'll use Romsk's ALDL scanner / reader, and I'll be able to see a real-time AFR... my hope is that then I can adjust the fuel pressure regulator to give a bit more fuel (or take it away if there's too much).



You will not get AFR from the scanner.
You will see the BLM (early version of fuel trims) which will let you know if the closed loop fueling is adding or subtracting fuel.
You will see O2 sensor voltage, but the narrow band O2 sensors are only accurate at 14.7, so it can't be used for WOT fueling.

Adding larger throttlebody and larger injectors without actually being able to tune the ecm is asking for drivability issues and poor performance.

You can adjust the fuel pressure regulator to get BLMs close to 128, but doing that will not add any fuel at WOT vs. stock.

If you dial in WOT performance, then you will be relyng on older, slower ecm with limited range of BLM compensation and only around 9 to 12 BLM zones over the entire MAP x RPM table to keep part throttle fueling in check. This will only happen during closed loop, so the car will run pig rich for cold start until the car goes into closed loop.

I would focus on learning to tune and having the ability to tune before haphazardly throwing parts at the car in the name of performance. You will be much, much happier with the results.

82-T/A [At Work] OCT 29, 07:08 AM

quote
Originally posted by fieroguru:

You will not get AFR from the scanner.
You will see the BLM (early version of fuel trims) which will let you know if the closed loop fueling is adding or subtracting fuel.
You will see O2 sensor voltage, but the narrow band O2 sensors are only accurate at 14.7, so it can't be used for WOT fueling.

Adding larger throttlebody and larger injectors without actually being able to tune the ecm is asking for drivability issues and poor performance.

You can adjust the fuel pressure regulator to get BLMs close to 128, but doing that will not add any fuel at WOT vs. stock.

If you dial in WOT performance, then you will be relyng on older, slower ecm with limited range of BLM compensation and only around 9 to 12 BLM zones over the entire MAP x RPM table to keep part throttle fueling in check. This will only happen during closed loop, so the car will run pig rich for cold start until the car goes into closed loop.

I would focus on learning to tune and having the ability to tune before haphazardly throwing parts at the car in the name of performance. You will be much, much happier with the results.



I appreciate the response, but I think the term "haphazardly" is a bit strong here.

I've bored the stock throttle body larger by 4mm, and matched it with a slightly larger fuel injector 68#s, that mathematically should match the increase in TBI bore size. I also installed a shorty header. I think that's pretty mild... if not exceptionally minimal. I haven't changed the cam profile or anything like that... so as long as the fuel and air increase are proportional, the engine should respond proportionally.

I have changed the O2 sensor to a wide-band. I used this kit from Casper Electronics: https://www.casperselectron...oduct&product_id=101

What I'm doing, I don't think is radical enough that I need to change tuning... my thought is that I should be able to correct any difference by using the adjustable fuel pressure regulator. If it ends up being total crap of course, I can always put back the original TBI unit. I had an issue with a cracked cyl head, but other than some coolant pressure issues, the car ran absolutely AMAZING. The best running Duke I've ever driven in my entire life.

But, to be clear, part of the goal in all of this, is to identify simple bolt on upgrades for the Duke that don't require any modifications to the motor, ECM, or anything other than literally bolting on parts.
edfiero OCT 29, 07:24 AM

quote
Originally posted by 82-T/A [At Work]:
I have changed the O2 sensor to a wide-band. I used this kit from Casper Electronics: https://www.casperselectron...oduct&product_id=101



The kit you reference is for a heated 02 sensor, not a wideband. Maybe there are other details of what you changed that weren't included here.
For example, I always understood that you can't just substitute a wideband for a narrowband sensor. I thought some kind of 'black box' was needed to convert the signal into something the ECM could understand unless you are using a different ECM designed for a wideband. (Not sure on this, never tried it myself).
82-T/A [At Work] OCT 29, 07:28 AM

quote
Originally posted by edfiero:

The kit you reference is for a heated 02 sensor, not a wideband. Maybe there are other details of what you changed that weren't included here.
For example, I always understood that you can't just substitute a wideband for a narrowband sensor. I thought some kind of 'black box' was needed to convert the signal into something the ECM could understand unless you are using a different ECM designed for a wideband. (Not sure on this, never tried it myself).




You might be right... but no... the ECM is totally stock. Remember, this is my daughter's car... and her goal is to keep it as stock as possible, but improve the efficiency. She rebuilt the engine herself, with all new parts, but wanted to keep the engine stock. Anything that requires modification of the motor, or changing to different pistons (other than she went to .040 overbore), she wants to avoid. She's got a Corvette that she's going to be modifying with an aftermarket ECM. She's also going to be building my 3.4 pushrod Firebird motor with DOHC pistons and an H272 cam, and an aftermarket ECM. But for this Iron Duke... she wants literally just bolt-ons that anyone can do. So that's part of the goal, reprogramming the ECM is out of the question.