So I was thinking about the iron duke siting in my fire which I had planned to throw away when I thought to myself, "2.5l is a lot of potential, can't something be done with it?" So I looked around and saw that back in the day pontiac had a 272HP version, but that it takes serious $$ to do it. But what can the average joe do? Well there's always a new cam, port matching, intake and exhaust, but what really drags the duke down is that lack luster single port injection system. After doing some research I come up with a design for a Sequencial Multiport system and I'm interested in anyone's thoughts on it.
The system works like this: split the fuel line into 4 separate lines and run them to injectors at the end of the manifold like they do in an L31. Then to time the injectors hook them in parallel into the normal injector circuit, but between the two insert a set of 4 MOSFETs (basically super high speed relays) and wire the MOSFET trigger into the spark wires with a voltage reducer. This way when the #4 cylinder fires it turns on the injector for the first cylinder during its intake stroke and when the #2 fires it shuts off the #1 injector at the bottom of its intake stroke and the same system works for all the cylinders.
First, the problems with the Duke aren't really fuel related.
Second, you have no way to control fuel quantity (injector pulse) other than based on engine speed and it's going to get less fuel as RPM increases... if I am reading it correctly. Being tied to the stock injector may help with pulse width, but your event timing is going all over the place based on spark timing. There is a reason why ECMs don't use the same table for spark timing as fuel injection.
But hey, we needed a There's Got To Be A Way To Make The Duke Awesome™ thread for the summer...
I figured there had to be about a billion problems with the idea. So the duke doesn't use the throttle to increase fuel flow? Cause in theory the faster the engine goes the more fuel you'll need so it has to increase fuel flow somehow. And if the timing doesn't work would even non sequential MPFI be an improvement over SPFI? It's what GM used before they figured put sequential.
P.S. I'm pretty much throwing every idea I have at the wall to see if any stick.
I really don't think throttle body injection is an issue or will give you more power to change that. If you got it to work, it would probably be more fuel efficient and maybe it would atomize the fuel better giving a little power.
There are ways to get up to around 130ish hp from a duke, after that it can't support it for long for a few reasons
Super thin cylinder walls
Weak weak crank
Stock head flows bad and has teeny valves
The super duty Duke has beefy everything and can support the horsepower.
I figured there had to be about a billion problems with the idea. So the duke doesn't use the throttle to increase fuel flow? Cause in theory the faster the engine goes the more fuel you'll need so it has to increase fuel flow somehow. And if the timing doesn't work would even non sequential MPFI be an improvement over SPFI? It's what GM used before they figured put sequential.
P.S. I'm pretty much throwing every idea I have at the wall to see if any stick.
The Fiero uses a Speed/Density fuel injection system. Feel free to Google that. The ECM uses the MAP sensor, intake air temperature and RPM to determine engine load versus just reading a tach signal... you need less gas to cruise at 2500RPM than you do taking off from a stoplight and accelerating. The Alpha-N method uses the throttle position sensor (alpha), intake air temp and RPM (N) to calculate the amount of fuel to inject in place of using the manifold absolute pressure (MAP) and RPM to calculate the amount of fuel to inject.
So what does the TPS do in a Speed/Density system? It is used for acceleration enrichment and decel fuel cut calculations as changes in TPS position will lead changes in MAP pressure readings. So basically, the Fiero is primarily Speed/Density, but it blends aspects of Alpha/N to get the best of both worlds. Hence the reason the car will still run with the MAP unplugged, or the TPS unplugged, it just won't run well under changing loads.
But your method of controlling fuel based on spark is going to give you problems. The RPM measurement in any fuel injection system comes from the distributor pickup coil/ignition control module, not the final timing delivered to the plugs after EST has been applied.
Ignition and fueling are truly separate but similar entities.
[This message has been edited by carbon (edited 07-17-2013).]
Not on a stock Duke you haven't... there is a 3.0L Duke-based Mercruiser boat engine crank with a longer stroke that people have investigated using in our stock Fiero Duke. Even in the Super Duty series, the engine displacement was usually determined with a crank selection, not increasing the bore.
[This message has been edited by carbon (edited 07-17-2013).]
Back in the day you could get parts from pontiac to get the higher (2.7 or 3.2) dispacement and push horsepower as high as 330HP using the stock block with the heavy duty parts.
Actually, the original 230 HP "duke" in the original Indy Pace Car used throttle body injection. It had to, because it had to be fueled the same way as a stock Fiero to be used as the official pace car. One thing I have been thinking of doing, to increase power in my duke (which already has an Accelerated Motion camshaft and big block Chevy roller rockers in it) is to use a 7730 ECM and a knock sensor. That should give me a little more power without hurting the engine.
Ill take a picture of my old duke block for you it has very thin cylinder walls. I think the SD4 is awesome and love every SD4 build thread and would like to own one myself one day, but to put enough money into a duke to get it past 130ish horsepower is not worth it because you are looking at custom crank and then an SD head and intake and exhaust and by then you need the SD4 block anyways. If you had the cylinders sleeved with a hard material then maybe you could do it, but you would have to improve the oiling of the engine and the crank journals I believe are not very reinforced so something would have to be done about that. But once again you are looking at SD4 costs.
And I am not talking about buying a new SD4 I am talking about the ones that show up on ebay once in a while, new SD4s from Kansas Racing are crazy expensive.
The Chevy 2.2L 4cylinder saw a significant power increase when they updated it to MPFI. It leapfrogged the iron-duke at that point. There's also notable differences between TBI and MPFI versions of the 305 V8 during the 80s. I'm just assuming MPFI was a major reason for those increases, but other improvements could have been involved at the same time. It always seemed to me that the 2.5L was left behind with TBI because GM had already decided the 2.2L would replace it. Of course, the need for structural improvements to the 2.5L may have been a big part of that decision. They didn't need both engines so they let the 2.5L fade away without updating it much. It's kind of weird that Pontiac had a racing program based around that engine, but never built the production version to perform. It makes me wonder what they were thinking. Maybe Pontiac and GM were thinking different things.
As far as sequential - I've read that at least on later generation 60V6 engines, they are only sequential at low RPM. When they're actually running hard enough to matter, they switch to batch mode. I guess the reason for being sequential at low RPM was for smoother idling and maybe mileage. It leaves me wondering how much performance difference it would actually make if they stayed sequential under a real load. Maybe it's not very much.
Maybe you could get MPFI (not sequential) on a duke by using the factory TBI signal, but I'm not sure how good the results would be. I'm guessing you couldn't drive them directly due to the load of 4 injectors vs 1. Sequential wouldn't work the way you described because the input pulse from the ECM isn't going to be in phase with the timing of the ignition for every cylinder.
If you were going to adapt port or sequential injection to an iron duke, I think really you'd need to adapt an ECM that was designed to support this, and do a custom tune to get it to run right. Something like a 7730 could work for MPFI, I don't know what it would take to get sequential. It would be a complicated project, but if something like this isn't done well then the results might be worse than the factory TBI. If you're interested in the details of how an ECM calculates fueling, check out the thirdgen.org site. They have a bunch of tutorials about ECM tuning on there which I found helpful. There's probably similar articles on gearhead-efi also.
[This message has been edited by armos (edited 07-18-2013).]
Ive seen a duke with a injection rail off a H23 2.3 honda motor running a stand alone unit on it. there was no distributor , they were running a flying magnet (crank trigger) The Intake had been milled down and had a holley throttle body on it, just glanced at the motor while out at the dunes in western okla. the rail they had it on was turning some serious rpm's and was tearing up the scat motors out there. so i know it can be done. its been done.
I suppose when your talking about increased displacement your talking about this part of the Wiki you linked?
quote
Though not a production engine, the Super Duty 4 racing engine was notable and widely publicized at the time. It was the basis for NASCAR's Touring Car series. The Super Duty 4 (usually called the "SD4") is still in use today for ARCA Racing.
A 2.7L 232 hp (173 kW) SD4 engine powered the 1984 Fiero Indy Pace Car to over 138 mph during the race. The SD4 was never available in production vehicles, however Pontiac's Performance Parts counter had all the SD4 parts available and one could garner a 2.7L 272 hp (203 kW) version and a 3.2L 330 hp (250 kW) version. All 2000 Indy Fiero replicas came with the 2.5L 92 hp (69 kW) Iron Duke engine.
The SD4 was the last in a line of high performance Pontiac "Super Duty" engines. Kansas Racing Products still makes the engines after buying the rights to make them from GM.
Cosworth also produced a 16-valve head (Cosworth Project DBA, 1987) for the Iron Duke.
The thing is you need to pay attention to this part of that section.
quote
Though not a production engine, the Super Duty 4 racing engine
The Iron Duke and the Super Duty 4 are 2 entirely different animals. The SD4 was never used in production so it never came in any car from the factory that was sold to the general public for use on public roads. It was an engine strictly made and sold for racing. The block and all internals were a heck of a lot beefier than those from the Iron Duke. Do some searches on here about the SD4 as some members have swapped them into their Fieros. It is not a cheap swap as you usually have to collect parts to do it. Blocks and heads can go for thousands each.
The Iron Duke was made to be fuel efficient not a power house. Some have swapped the S10 head over as it flows better. Some have done a new crank or cam, polished ports, better exhaust and such. However trying to get real power out of a duke is costly as so much of the engine is weak and needs to be upgraded.
quote
Originally posted by Treep78:
Back in the day you could get parts from pontiac to get the higher (2.7 or 3.2) dispacement and push horsepower as high as 330HP using the stock block with the heavy duty parts.
Just to note, the SD4 Block and the Iron Duke block are not the same. You couldn't buy the parts from Pontiac and throw them into a Iron Duke block and get 330 hp, and even if you theoretically "could" the stock Iron Duke block wouldn't handle it for long.
[This message has been edited by Khw (edited 07-18-2013).]
I have had several Iron Dukes over the years....and I have fond memories of them. An Iron Duke is like an old friend to me. I certainly understand one's desire to build one up. However...after refreshing the Duke in the convertible, I swear I am done with them. Never again will I spend any notable amount of money on repairing/refreshing/upgrading an engine that will never satisfy my right foot. It is simply not a performance engine. By the time you spend all the money, time, and research to build an Iron Duke to pull 150 hp....you would have been further ahead doing a swap.
Just my opinion, it is worth about what you paid for it.
Is this accurate information? Back in the early 90's I belonged to the Michigan Fiero Club and I knew a handful of people who had built SD engines and installed them in their cars. I had always heard the same story about the SD4 engines - that they were available in 2.7L, 2.9L or 3.0L depending on the rotating assembly that was installed in the block. I did not know anyone who had a 2.9, all of the people I knew had either a 2.7 or 3.0.
Is this accurate information? Back in the early 90's I belonged to the Michigan Fiero Club and I knew a handful of people who had built SD engines and installed them in their cars. I had always heard the same story about the SD4 engines - that they were available in 2.7L, 2.9L or 3.0L depending on the rotating assembly that was installed in the block. I did not know anyone who had a 2.9, all of the people I knew had either a 2.7 or 3.0.
There were different cranks available to create different displacements for different racing classes. Using the same 4.00" bore, the different strokes gave you several engine sizes. My SD4 engine is bored over to 4.020" and has the 3.9375" stroke crank.
I'm pretty much throwing every idea I have at the wall to see if any stick.
While there's nothing wrong with blue-sky speculation, it really helps to take some time to understand how the existing system works before proposing new "designs" to improve it.
Sometimes it does and sometimes it doesn't, that's why I edited this post earlier... I reposted thinking you did it wrong and I ended up with the same results... As I type this I can see the pic, last night I couldn't... I blame tripod...
[This message has been edited by carbon (edited 07-19-2013).]
The easy, cheap way to "FIX" a 2.5 is to use the 2.2 ohv engine that replaced it. I have one in my cavi. Gm just fixed all the weak stuff and improved it for fwd use all in one shot. I hear about guys with turbos, making a lot of power, with out the engine puking it's guts out every week. It has sfi, roller rockers, aluminum head all stock. And it is cheap. I get 35 mpg on a 170k drive line.
Apparently the reason it is so weak is because GM knew that the block could not support the HP and to make it a nice little commuting engine they gave it a light crank so it revs quickly. But it is super weak.
My friend's dad has a performance built duke in his 84. It makes around 135 hp. He has cracked a block, and he has broken a crank. Now it has a custom crank and a humongous custom cam, professionally ported heads, Holley TB and fuel pump, Hooker header, and machined crank damper from a corvette. It sounds awesome, almost like a dirt bike but in car form. My modified 2.8 is faster though, and he put a lot of time and effort into it. He did most of the work in the late 80s. Unfortunately the car has been in storage the past few years.
So if he cracked the block and broke the crank autocrossing it with around 130 hp, I do not think it can support much more than that.
There is a reason they are called the 'Iron Puke' - that's what they do with their innards if you try tuning them to the level of a stock 2.8 V6.
The SD4 was quite a nice engine; the Iron Puke is not. Stop being a masochist and learn from all the mistakes others have made and all the money it cost them, trying to get these engines to do what they were not designed to do.
I blame tripod...
