I'm just starting out with this very stock 1988 with ~114,000 miles on the engine. Would enjoy hearing some creative ideas on "removing the limiting factors" at minimal expense. I'd like to evolve a "ranking" and "order" of improvements.

Engine swap is not an option here as the vehicle's fuel economy must be preserved (I have seen these 2.5L/5spds get almost 40mpg on the highway).

[This message has been edited by Art Doyle (edited 10-21-2002).]

You could look into a 91 VIN U duke... The best I can tell it looks to be the same externally but rated around 112 HP to start. (According to NADA and a couple others I'm not 100% sure are correct. I've never been able to find official GM data on them.)

I know there are internal changes vs VIN R but I don't know all of what. The only thing I know of that you'll find them in are 91 Olds Cutlas Calais. I haven't been able to work out all the details on that one yet. I'm fairly sure they even use the same ECM but with some differences in the PROM. The rest of what stuff I have is in my cave.

You should be able to find one of them for a couple hundred. If they fit that's probably the cheapest HP gain short of completely rebuilding the Vin R you've got.

A better exhaust manifold might help. The only thing I know of off the shelf is the hooker header. That will run you as much as the above engine.

GM/Delphi offer the 700 TBI with up to 48mm bore but I've never found one in use on anything. Far as I can tell.. the stock one is 45mm on all the L4 dukes. There's stuff about them in the tbi article... yup... in my cave.

Besides all the maintenance stuff... One thing to check... make sure you are really getting to WOT. They don't seem to rotate the butterfly all the way open. I'm not sure if that is a flaw or by design but it's something to look into. You'll need an ECM scanner for that. (Don't just eye it. You want to make sure the ECM says it's at WOT, which may not be the same as a vertical buterfly.)

That's not really bad on a dyno for these engines. Especially on a manual tranny for torque.

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11-Sept-01, The day the world as we knew it ended.

You might want to find out why it's running so rich.

i think his screenname is mechanix
you have to do a search in the tech section.

But he was able to mod his 2.5l to make somewhere between 160-190hp.

I have almost the exact sam situation an 88 duke with 125,000 miles on it. Purchased it about four months ago. So far my plan has been to first replace all the normal wear items. I replaced the plugs and wires with OEM style units and was suprised that it actually provided small increase in power and greatly smoothed out the engine. Next I am looking at the O2 sensor to change it. Take a good look at the engine if these times of things look old change them out first.
After that I am looking into a low pressure (~5 to 7) turbo set up. I know I will probably catch hell for this but if done properly IMHO it should be relatively reliable and geve 130 to 150 hp.
Jon Steckelberg

I confirmed today that my car (87SC) is only only opening the 700 TBI unit to about 75%. 80% if I really mash the pedal hard. (Not good for it I'm sure) This was checked with my scanner and pyhsically at the TBI. (And yes, WOT to the TBI and ECM is a vertical throttle butterfly.)

There is allot of play at the gas pedal. Nothing seems worn etc with it. (You'd do major damage before bending it...)

There is enough slack to pull back a good 1/2 inch of cable at the TBI. Some of it could be cable streatch or wear. Some could just be the cable is a hair too long. Some could even be intentional to prevent over reving it.

There is no easy way to adjust for it. The simplest way I see is to slot the holes in the idler plate so you could move it toward the valve cover. (I'd be leary of doing anything on the wire that could damage it or make it jump the pulley.)

WARNING! Altering the idler plate or throttle cable in any way will most likely result in required adjustment of the TV cable to the transmission. (Yes I know the Art's car is stick. This is for anyone else...)

plug in a scan tool and see what yours is getting... If it's less than WOT then try another dyno pull after fixing it, at least temporarily. You may be able to use the cruise cable's pully to provide a temporary way to test on the dyno.

Also check the MAT sensor if it's rich... That sensor is used in FA calculations among whatever else.

Can't add much to what Ogre has already mentioned. A good tune up (new plugs and wires, etc.) and inspection of all the sensors is a good start.

If you want more power and fuel economy both, then the Hooker header and free flowing exhaust system is the best route to go.

For more work and expense, pull the head and have a machine shop recondition it with a multiple angle valve job and if you have cash left over, maybe some minor pocket porting.

Milling (resurfacing) the head will not only give you a good head gasket seal by taking out any warpage, but it'll also increase the compression ratio a bit which might give you a couple more ponies. If you pull the heads off, I'd advise buying new head bolts.

www.dynotuner.net for their power tuner.. and pull back all that nasty over fueling!!

I'M SOOOO Glad somone is dynoing a 4cyl! rock on! your old school Pontiac has more torque at the ground then a $40,000 Honda S2000! now if you goud just get it to carry out higher in the rpm range..

[This message has been edited by 1FST2M6 (edited 10-22-2002).]

From Holley, they've done some research on this.
http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSFI/500-1.html

How about some Nitrous Oxide!!!

That will improve that dyno run.

i have just a thought or too.
port, polish, forged pistons(if you can find them) and do all the ignition stuff you always see, wires, msd ignition, etc.
just my thoughts

-Fish

quote Originally posted by RotrexFiero: How about some Nitrous Oxide!!! That will improve that dyno run.

that'll fix his lean condition too! NITROUS FIXES EVERYTHING

i wouldn't recommend throwing parts at it till you've remided your over fueling issue. via, proper management, hardcore cleaning of your fuel system, and making sure your sensors are all reading properly. if somthing is out of wack it'll skew your ECMs readings thus killing your drivability/Performance and Economy.

7-10psi will make 150 at the ground reasonably and inexpensivly with that displacment... with the con rods i don't know anything about.. but i've heard they are frail do some research on that before forcing more air into the works.

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Put the Lime in the Coconut... drink it all up...

Well... (Again... this is for 87-88 L4...)

I'm on vacation today to I decided to finally do something about not reaching WOT...

I slotted all the holes in the idle plate. I notched two and cut the third about a 1/4 inch as shown below.

When mounted the bolts end up centered in the cuts. This should provide more than enough adjustment to reach WOT, especially on a manual tranny car. (You don't want the bolt threads past the edge of the plate or they may not hold well.)

The Automatic will reach WOT but the TV cable's extra load puts some additional streatch on the main throttle cable. W/o the TV connected I can now easily make WOT. With the TV reconnected and readjusted, yes readjustment was required, I can now get to 96%. (This is just sitting stopped... I think the TV cable load is different when driving... I'll scan it again while driving as see what I get. That probably won't be till tomorow at least.)

Remember that I could only get to 75% before... This is a big jump. over 20% more throttle. Once I finish fine tweeking the TV cable I may get more.

When I readjusted the TV cable, the sleeve dropped a few teeth more into the tranny. That will affect shifting but I don't know all just how yet. That always takes a day or three to see how it shifts under all conditions. (I may break this out into another thread later....)

One thing I did notice right away... The Duke spools up allot faster when it can reach WOT vs 75% throttle... You can quickly red line it, especially in lower gears. You'll need to watch out for this or you could fry the motor real quick.

While it was off... I took off the idle pulley and cleaned it all... if you lube it use something like Dry Teflon or a Silicon. DON'T use oil based stuff. I noticed some rust at the base of the pivot, so I cleaned it off and put a very thin aluminum washer on the stem to give the pulley a smooth surface where is rubs the plate. (The washer has to be thin or you'll bind up the pulley.)

[This message has been edited by theogre (edited 10-22-2002).]

Hey ogre, I did the same thing on the Duke-inator a few weeks ago. It really makes a big difference on the cars. If I had to guess I would assume its cable stretch give the quality of the other cables GM used on the Fiero. Only way to know for sure would be to take a new cable and compare once installed. YOU CAN MAKE THE DUKE FIERO run pretty well. Takes some attention to detail though. You also have to have some thick skin as well. Some will sware your wasting your time and money but then it is YOURS. Right?
Since we are talking about dukes...
I have replaced the ign module (GM), coil packs (GM), added MSD 8.5 wires and new plugs. I have replaced the TPS, Fuel filter and cleaned the T/B and added some good fule system treatment and I still get a slight miss. I cant figure it out. Its ususally about 3,500 rpm or so then clears up. Ideas?
Keep up the good work on the dukes. I have changed many opinions of 4cyl fieros at Langley Speedway (www.langleyspeedway.com)every Wensday night (weather permitting). I would love to have some fellow fiero owners come out!

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88 Fiero coupe 2.5 5 speed, Custom IHI RHB6 turbo equipped, gutted and track abused
87 Fiero GT 14.9/ 89mph CSP car
87 Mazda RX-7 SBC v8 5.0L/700R4 ---FOR SALE
84 Fiero 2M4 T-top, Turbocharged and tons of extras!
87 Conquest TSi 406 SBC V8!
93 Lumina Z34 organ donor :)

Cool! So that is what the 2.5 power curve looks like. It takes a nose dive after 3.2k rpm.

I rebuilt one of the U motor Iron dukes from a 91 Pontiac Grand Am. It was rated at 110 horsepower but it seemed like it had more especially after I rebuilt it.

If the only reason why you are not considering an engine swap is because you want good gas mileage than you might want to reconsider. My Formula with the 2.8 would get 30-miles to the gallon on the highway with the five speed transmission. My 87 coupe with a duke, 40,000 miles, and in top notch tune only got 22 mpg with an automatic. The 3800 series engine would probably get about 30 mpg on the highway too. If you want a four cylinder engine than consider one of the new mid nineties GM DOHC 2.4-liter engines with about 150 horsepower. That engine will probably even get better gas mileage than a 2.5 Duke.

Just some possibilities to consider!

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Zack is already scouting for a replacement Oxygen sensor One of those

quote Originally posted by 88formula: Just noticed the air fuel ratio after 1fst2m6 mentioned it. Might be why the torque takes a nose dive.

I *really* wanna take the duke I just built for a guy and toss it on a dyno. I only drove the car for about 10-15 miles after I did it (and we're talking RIGHT after so the thing wasn't seated in at all) and it had pretty good jam to it (well, for a duke). It was raining out unfortunately so it was all over the place through the first 2 gears.

Popped in a custom cam (available through me! Go figure...), shaved the head .030" (ummm, he's now forced to run 94 - might consider less next time!), 180lb valve springs, decent valve job, gasket matched it, and then told the block we'd turbo it someday - I think it liked that.

I've talked to him a few times since then (probably got 1000 miles on it now) and he raves about it! Says it's never had this much power.

Hay BV Motorsport have you posted information on your 88 2.5 turbo setup before? If you have can you direct me to the thread if not I would be very interested in what you did and the results you got. I am defenitely a fan of the Duke and don't care if people call me insane because of it.
Thanks
Jon Steckelberg

New Chrysler Prowler Turbo- 2.5L four cylinder and 215 HP. That's a turbo on a stock 2.8L V6 territory.
I believe that the Chrysler 2.5L is stronger, revs higher and breathes better than the Duke but adding a turbo could get you 150-170 HP. However, the Duke redline will limit you to 4500 RPM.

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87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm

quote Originally posted by cy1clown: Hay BV Motorsport have you posted information on your 88 2.5 turbo setup before? If you have can you direct me to the thread if not I would be very interested in what you did and the results you got. I am defenitely a fan of the Duke and don't care if people call me insane because of it. Thanks Jon Steckelberg

I used to come on alot and talk about different swaps or performance upgrades but I have never had much luck getting my point across without sparking off some kinda of stupid debate. Needless to say, I dont talk about v8 swaps or dukes much. I used to have a nice website up but its off line and I lost tons of information that can not be replaced when the plug was pulled w/o notice. Dennis knows alot about me and my turbo dukes. We have kicked many ideas around about forced induction dukes. I REALLY REALLY need to get the chip out of my old IRM/Hi-Tech turbo duke and send it to him so EVERYONE would be able to purchase it.
I will be installing another IHI RHB6 or Mitsu 12a turbo kit on a fiero soon and plan on doing up a step by step write up about it. If you need more info give Dennis a holler or ask and I could snap some pics of the set up. Oh and as always, its your car, your money...do what makes YOU happy.

Steven

------------------
88 Fiero coupe 2.5 5 speed, Custom IHI RHB6 turbo equipped, gutted and track abused
87 Fiero GT 14.9/ 89mph CSP car
87 Mazda RX-7 SBC v8 5.0L/700R4 ---FOR SALE
84 Fiero 2M4 T-top, Turbocharged and tons of extras!
87 Conquest TSi 406 SBC V8!
93 Lumina Z34 organ donor :)

Someone commented that the cables stink....

actually it's not a problem of the quality of the throttle cable as much as length... The cables are constucted using the same stuff as almost any other used by all of the car makers, not just GM.

The bigger problem is that they aparently forgot something about longer cable/rope... If you make them longer, you need to make them thicker to support the same load. These cables are at least twice and up to 3-4 times the lengh of almost every other throttle cable I've ever seen in a car. These Fiero cables are all about 6-8 feet long depending on which motor. I think the V6 is a little shorter than the L4 one. In mine I get a rough measurement of about 8 feet. That means allot more streatch over the length of even a new cable in Fiero vs the 2-3 foot jobs in many other cars.

Thanks for the reply BV Motorsport I have noticed that duke performance threads either dont last long get flammed out or both on this forum. Do you post on the Iron Duke list on Yahoo? I forget exactly what it is called. They at least wouldnt flame you. IF you get some time I would be interested in info on your turbo work. If it would be easier you can email me directly at cy1clown@yahoo.com
Thanks for the reply and keep the duke flame burning.
Jon Steckelberg

[This message has been edited by cy1clown (edited 10-24-2002).]

If someone is going to sell a direct-bolt-on turbokit for the Duke I think it will be a best seller

The Turbo will increase the HP/Torque and if set up properly it will increase the MPG too

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'85 Fiero 2m4

Nederlands Fiero forum

[This message has been edited by Morninglight (edited 10-25-2002).]

!!!!DUKES RULE!!!!

hehe i wana build an impresive duke my self

Chris

quote Originally posted by 4BanGinFun: !!!!DUKES RULE!!!! hehe i wana build an impresive duke my self Chris

The Duke takes me from here to there... reliably and comfortable but I was used to 5.8KG/HP in my Golf (Fiero=8.47HP/KG)... oh well.. I'll just have to wait for an 3.8SC

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'85 Fiero 2m4

Nederlands Fiero forum

Everyone needs to check the throttle cable out.... If you aren't reaching WOT, you've got issues. I expect all OE fiero engines have various problems with this, not jsut the DIS L4. (Tho the DIS L4 may be the easiest to fix.)

My car has been like a whole different car since fixing the cable setup so I can adjust it. Amazing what more throttle will do for an engine. In my case it was 20-25% more. Your results may vary depending what tranny you've got. (Auto's load the cable more.) Even a brand new throttle cable will have considerable streatch on these cars. If you don't compensate for it you will not reach WOT and you Will Not get full performance from the engine. Any engine... Old/New L4 or V6. Even swaps to other motors need this checked.

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11-Sept-01, The day the world as we knew it ended.

quote Originally posted by theogre: Everyone needs to check the throttle cable out.... If you aren't reaching WOT, you've got issues. I expect all OE fiero engines have various problems with this, not jsut the DIS L4. (Tho the DIS L4 may be the easiest to fix.)

Going to check that tomorrow.. I think it may solve another problem, my 2.5 shifts very early (at leats what I'm used to in european cars with big engines) if the throttle cable is stretched it could result in early shifting (I adjusted the TB-cable to shift just before the limiter kicks in at WOT).. or am I totally wrong?

Let me explain my thinking:

The throttlecable is 25% stretched, the shift rpm is just below the limiter when I push the pedal to the metal.

The tranny will always shift 25% too early (on lower revs)

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'85 Fiero 2m4

[This message has been edited by Morninglight (edited 10-25-2002).]

This sounds very promising! Could you post more instructions on the mods you made? How did the adjustment to the TV go?

Who's mod? mine? Just as shown above for the DIS L4. No Idea for any others. All you need is a Dremel or Die Grinder. (I'll get all this in the cave at some point...)

The test is easy... watch the throttle plate while someone hold the pedal to the floor. Don't mash it. just hold it. If the throttle isn't straight open in the bore then the cable is streached.

The TV cable is adjusted the same way as always... The old L4 and V6 are in all the books...

WARNING!!! DO NOT EVER step on the gas pedal to do this!!!!! Not on any Fiero or any other car. Even all the GM documents I've seen say this. (You'll see way further down.)

For the DIS L4 ONLY.

This is covered in my cave as well...

Once you make sure the TV adjuster isn't stuck etc... Pull the jacket of the TV cable out of the adjuster about 1/4-3/8 inch. (The button MUST NOT be crocked or pop up higher than the shell. If it does then the jacket has been pulled out too far.)

Rotate the idler pulley by hand until the TBI unit reaches WOT. There is a mechanical stop on the 700 TBI at WOT. (This is easier if you turn the idler pulley with one hand and unload the TBI quarter pulley a little with the other. Don't allow any slack in the small bit of cable between the two pulleys.)

As you rotate the idler, the TV cable will ratchet into the tranny. Where ever it stops you are done. (Mine ended up with the fat part of the jacket about even with the adjuster hole.)

In all cases. The TV cable is always synchronized to the Carb/TB/TBI. NEVER the gas pedal position. If it is adjusted correctly, the car will shift correctley even with a severely streached cable between the motor and pedal.

The purpose of the TV cable is to tell the transmission what the actual throttle angle is. The transmission doesn't give a rat's a_s about the gas pedal.

If you try to do the TV cable adjustment by mashing the pedal it will not be right most of the time, especially in Fiero with it's snake of a cable.... You could even snap the cable.