2.5 Iron Duke / Tech-4 - Rebuild Kit or Long Block? (Page 1/4)
82-T/A [At Work] APR 17, 02:48 PM
Hey guys, I'm looking at possibly rebuilding the 2.5 Iron Duke in my daughter's Pontiac Fiero. The motor is pretty solid right now, and runs fairly well, at least as much as I can tell. I haven't done a compression test or anything, but if I can get a rebuild kit, I may consider just rebuilding it. Does anyone know if there is a company that sells a "kit" or do I need to source all the parts separately?

Basically looking for a complete bearing kit, and if the sidewall has any perceivable wear, I might have it machined to take an overbore piston, etc. Also, is there a decent cam that provides just a little bit more snappiness that still works totally fine with the existing ECM? I'm not trying to build a race car, I just want something that has a little bit more get up and go. I think stock is 92hp, I don't know what motor my 85 has (whether it has the roller lifters or not), but if it does not, I'll probably try to buy an 86 car and swap that in. Would like to get it to run a little bit more smoothly, and perhaps about ~100-110hp without a loud exhaust or any crazy stuff.

I used to have one of those Holley TBI upgrade units, but for the life of me I cannot find it anymore (must have given it away... they are like gold now for the LU5 V8 guys).

Anyway, just looking for someone who did a mild upgrade when they rebuilt their relatively stock 2.5. Again, not looking to build an SD-4... just want something that looks stock but just feels a little bit smoother and snappier.


Thanks!


EDIT: I guess a lot has changed. I used to be able to find rebuilt Fiero or crate engines at all the major suppliers... can't seem to find a single company that has a crate motor anymore?

[This message has been edited by 82-T/A [At Work] (edited 04-17-2023).]

sleek fiero APR 17, 03:04 PM
AMS Racing has kits. looks quite reasonable. sleek
theogre APR 18, 01:01 AM
Is likely doesn't need a rebuild but will need Timing Gears.
Duke Fiber Timing Gear Does wears out. Way faster if has problems w/ Distributor and/or oil pump that runs off the cam.

85 Should be Roller Cam. https://web.archive.org/web...cast.net/~fierocave/ duke quick ref

Very Likely You're Not going to find a Roller Cam in OE or aftermarket grind off the shelf. Maybe hard to find a total custom unless paying $$$$$.

No-one stocks motors for most 25-30+ year old cars. Only "Popular" units like maybe Ford 302 V8 used by Millions of cars.

Can Find Rebuild Kits but many don't have the best parts in them like Felpro Valve Cover Gasket Kit w/ Silicone gasket and extra hardware to stop leak there. Or Felpro Intake Casket prevent leak that #4 cylinder sucking coolant.
armos APR 18, 07:53 AM
There was a "Sealed Power" cam and lifter kit for the 2.5L but it was flat tappet. I had one on my 84 but 85+ are supposed to be rollers. I don't know if an aftermarket cam was ever made for the roller engines.
I don't know if GM switched engines precisely at the model year boundary - seems to me there could be some overlap, so especially if this is an early 85 then try to figure out what you really have.
My timing gear failed at 122K, no idea how common and predictable that is though. That's when the cam got replaced (from the side, engine stayed in the car).

A long time ago there were some long threads on here about upgrades for the 2.5L (once you get past all the "boat anchor"/swapit comments). I don't have the links anymore, but it generally amounted to integrating improvements from later generations of the engine (which extended into the early 90s). The 1987 TBI is supposed to be better, and I think maybe it's possible to use a further improved TBI from ~1990 or whatever. It's all vague to me now, you'd have to find the old threads.

Back when I drove my 84 I always wanted that Holley TBI, but I didn't have the money for it and then it disappeared from Fiero Store. Then right after I gave up on the car, eBay started teasing me with cheap auctions for both the Holley TBI and the Holley intake manifold that's supposed to work with it. If the frame had not been rotted by salt, I always wished I'd been able to rebuild the engine and add those upgrades. I never had that engine at it's best, it was a tired old thing with blowby and a performance cam slapped in without the engine ever getting the overhaul that it needed.

I remember seeing a comment somewhere that claimed an old carburetor intake performed better on the 2.5L than the factory TBI. I have no idea if that's true. In any case for an 85+ roller engine it probably makes more sense to upgrade to later-gen parts instead of old "hotrod" parts that got made for late 70s/early 80s engines.
82-T/A [At Work] APR 18, 08:23 AM

quote
Originally posted by sleek fiero:

AMS Racing has kits. looks quite reasonable. sleek



Thanks Sleek, they have some good stuff there, but their kit seems to have parts that are for non-Fiero specific engines... but I can definitely buy some of the parts separately.



quote
Originally posted by theogre:

Is likely doesn't need a rebuild but will need Timing Gears.
Duke Fiber Timing Gear Does wears out. Way faster if has problems w/ Distributor and/or oil pump that runs off the cam.

85 Should be Roller Cam. https://web.archive.org/web...cast.net/~fierocave/ duke quick ref

Very Likely You're Not going to find a Roller Cam in OE or aftermarket grind off the shelf. Maybe hard to find a total custom unless paying $$$$$.

No-one stocks motors for most 25-30+ year old cars. Only "Popular" units like maybe Ford 302 V8 used by Millions of cars.

Can Find Rebuild Kits but many don't have the best parts in them like Felpro Valve Cover Gasket Kit w/ Silicone gasket and extra hardware to stop leak there. Or Felpro Intake Casket prevent leak that #4 cylinder sucking coolant.



Thanks Ogre, your page actually states that 1986 2.5s had the rollers. I've had a few Fieros, but the other 1985 that I owned many years ago, also had flat-tappets. Ideally, the roller-cam does make a perceivable difference... so I do hope that that's what I have. I guess my question though is, what exactly, if anything, is different about the non-roller lifter block, and the roller lifter block? I don't think the casing is different, it just means that if I wanted the roller lifters, that I would simply need to replace the pushrods and the cam as well. The lifters should still fit and everything, correct? I suppose that other than the distributor gear on the cam, the cam generally doesn't take any wear... and if I wanted to upgrade that cam (so to speak), I could really just replace the rocker arms with slightly higher ratio ones, right?

If I remember correctly, the plate that allows me to see what type of lifters I have is directly under the intake manifold... like, held in place by 3 bolts or something. So I'll try to figure that out this weekend. Here's hoping...



quote
Originally posted by armos:

There was a "Sealed Power" cam and lifter kit for the 2.5L but it was flat tappet. I had one on my 84 but 85+ are supposed to be rollers. I don't know if an aftermarket cam was ever made for the roller engines.
I don't know if GM switched engines precisely at the model year boundary - seems to me there could be some overlap, so especially if this is an early 85 then try to figure out what you really have.
My timing gear failed at 122K, no idea how common and predictable that is though. That's when the cam got replaced (from the side, engine stayed in the car).

A long time ago there were some long threads on here about upgrades for the 2.5L (once you get past all the "boat anchor"/swapit comments). I don't have the links anymore, but it generally amounted to integrating improvements from later generations of the engine (which extended into the early 90s). The 1987 TBI is supposed to be better, and I think maybe it's possible to use a further improved TBI from ~1990 or whatever. It's all vague to me now, you'd have to find the old threads.

Back when I drove my 84 I always wanted that Holley TBI, but I didn't have the money for it and then it disappeared from Fiero Store. Then right after I gave up on the car, eBay started teasing me with cheap auctions for both the Holley TBI and the Holley intake manifold that's supposed to work with it. If the frame had not been rotted by salt, I always wished I'd been able to rebuild the engine and add those upgrades. I never had that engine at it's best, it was a tired old thing with blowby and a performance cam slapped in without the engine ever getting the overhaul that it needed.

I remember seeing a comment somewhere that claimed an old carburetor intake performed better on the 2.5L than the factory TBI. I have no idea if that's true. In any case for an 85+ roller engine it probably makes more sense to upgrade to later-gen parts instead of old "hotrod" parts that got made for late 70s/early 80s engines.




Yeah, I remember that TBI unit. I bought one way back in the day. Unfortunately, they were super popular for Corvette and TransAm/Camaro owners that had the LU5 305 V8 with the "Cross-Fire Injection" engine. It uses the exact same TBI unit as the Fiero, except that it uses two of them. So the Corvette / F-body owners were snapping them up. I did get one, but after I sold my 84 Fiero, I ended up just giving it away to someone else. Really wish I still had it because it was a fantastic TBI unit. The stock intake was already made to support a larger TBI unit if I remember correctly, and it came with the larger mounting gasket/plate. But yeah, I remember seeing that intake manifold as well, and never was able to find it.

There are actually quite a few Holley TBI units that have similar bolt patterns and will fit, but finding them is the problem.

I mean, I realize the 2.5 is half a Pontiac 302, but I should be able to get it to the point where it's running somewhat smooth. I like the originality and simplicity of that motor for my daughter's car... so that anything that might go wrong with it, is super-simple to fix. So that's why I'm sticking with it for her car.

Yeah, I'll have to check compression and everything, but I think that's probably the next thing I'm going to do... pull the engine. All the other things are so much easier to do when the engine and transmission are out of the car.
theogre APR 18, 10:17 AM
I've been told OE lifters and oil holes in the block are different and can't switch flat to roller or other way around. I'm not sure what else is different because Rollers are a lot Taller and connects to anti-twist parts to keep the roller straight.

84 and 85 you need to check cam/lifter type just because many are rollers because engine swap under warranty recall etc. If "DIY" or 3rd parties did a swap, may use whatever available and switch roller to flat cam that includes 86 car w/ older engine bought used or from "Jasper" type companies.

Some "swaps" are likely Trim Level for them too. Example: All 84 Indy may had roller cam. SE 4cyl may had same but 85 SE may had V6 option so maybe that had flat cam L4.
While Base and other Trim Levels had Flat cam setup until most or all 86 and later had rollers.

If engine is still in car...
Many say 4cyl and even V6 "sucks" never check the gas pedal and cable actually open the TBI/TB to WOT.
Just Have someone "floor" the pedal w/o doing anything special and look at TBI butterfly.
Or use ECM scanner and read % throttle etc.

Many GM and other cars have this problem but Fiero is worse because of pedal arm design and Very Long cable. See cave Throttle Cable
82-T/A [At Work] APR 18, 10:24 AM

quote
Originally posted by theogre:

I've been told OE lifters and oil holes in the block are different and can't switch flat to roller or other way around. I'm not sure what else is different because Rollers are a lot Taller and connects to anti-twist parts to keep the roller straight.

84 and 85 you need to check cam/lifter type just because many are rollers because engine swap under warranty recall etc. If "DIY" or 3rd parties did a swap, may use whatever available and switch roller to flat cam that includes 86 car w/ older engine bought used or from "Jasper" type companies.

Some "swaps" are likely Trim Level for them too. Example: All 84 Indy may had roller cam. SE 4cyl may had same but 85 SE may had V6 option so maybe that had flat cam L4.
While Base and other Trim Levels had Flat cam setup until most or all 86 and later had rollers.

If engine is still in car...
Many say 4cyl and even V6 "sucks" never check the gas pedal and cable actually open the TBI/TB to WOT.
Just Have someone "floor" the pedal w/o doing anything special and look at TBI butterfly.
Or use ECM scanner and read % throttle etc.

Many GM and other cars have this problem but Fiero is worse because of pedal arm design and Very Long cable. See cave Throttle Cable




Thanks Ogre, we're going through the entire car to make sure everything is in top shape. My daughter just finished installing the new fuel pump, stainless pickup assembly, and pressure-washing, sanding, priming, and painting the fuel tank. We replaced all the rubber lines, including the fuel fill connectors, and will replace the hard lines next. But this is kind of what got me to this post. I realized... if I pull the engine, doing all of these things will be infinitely easier with the motor out. We also need to replace the battery tray, and it's easier when you're literally standing in the engine bay.


My daughter showing that the tank is ready to go!




But yeah, that's a really good point. I really do hope I have rollers... that would be a big plus for me. I'll check this weekend.
armos APR 19, 01:17 AM

quote
Originally posted by 82-T/A [At Work]:
Yeah, I remember that TBI unit. I bought one way back in the day. Unfortunately, they were super popular for Corvette and TransAm/Camaro owners that had the LU5 305 V8 with the "Cross-Fire Injection" engine. It uses the exact same TBI unit as the Fiero, except that it uses two of them. So the Corvette / F-body owners were snapping them up.


Interesting. I never knew those "crossfire" TBIs were the same as the 2.5L, but it makes sense.
I guess that's the real reason the aftermarket version got made.
theogre APR 19, 03:14 AM
"crossfire" TBI? Whatever BS marketing...
GM 220 series TBI is basically EFI to replace any 2 barrel carb for V8. 84-86 Fiero etc 4cyl has 300 series TBI a 1 barrel carb replacement.
Can even use on many carb intakes w/ adapter plates.

While shares same design and manufacturing, almost no parts interchange. Maybe the injector(s) and some small parts depending on exact numbers on the 220 and 300. Neither shares anything w/ 700 Series TBI in 87 & later.
82-T/A [At Work] APR 19, 08:17 AM

quote
Originally posted by theogre:

"crossfire" TBI? Whatever BS marketing...
GM 220 series TBI is basically EFI to replace any 2 barrel carb for V8. 84-86 Fiero etc 4cyl has 300 series TBI a 1 barrel carb replacement.
Can even use on many carb intakes w/ adapter plates.

While shares same design and manufacturing, almost no parts interchange. Maybe the injector(s) and some small parts depending on exact numbers on the 220 and 300.




Hi Ogre, GM's Cross-Fire Injection isn't that 2-bbl TBI unit, it's a special intake with alternately placed ECM-controlled TBI units that are designed to create a "whirlwind" effect in the intake. It's actually a really good design, but of course, throttle body injection will never be as good as port-injection. Here is an aftermarket version of the Cross-Fire Injection intake plenum:




It's basically the same as stock, but the aftermarket one is a bit more polished with a bowl opening for the runners. The factory one was less fancy, but basically the same (dirty):




The throttle bodies mount to the two holes on the top of the plenum lid like so:




As you can see, the TBI units are identical to the ones on the 84-86 Fiero (same exact part numbers):




Fully assembled, the CFI looks like this (Corvette):




And on the Camaro/TransAm:




The hole on the top would mate with a rubber isolator on the hood that connected it to fresh-air ducts either at the Cowl (TransAm) or in a center-vent configuration (Camaro).


The Holley TBI units were extremely popular among the CFI crowd because it was a simple plug and play. It required no modification, and the bore opening on the intake mated perfectly with the Holley TBI replacement bore. Kind of unfortunate... because it meant everyone was buying the Holley TBI units for the CFI motors... but I suspect that had the CFI engines not also had these, perhaps Holley never would have bothered making them just for the Fiero (or other Duke cars) anyway.


But yeah, we're not talking about the 2-bbl TBI units that were found in the TBI GM Chevy trucks.