2.0 vs 1800 question

[RRoller123]

Great discussion, I have learned a lot from you guys and appreciate all the time it must take for you to construct and edit these technical posts. Ok, so for my 80FI first get a better flowing air filter, then lighter unsprung weight, lighten the flywheel, then what next (on a limited budget) to get the best bang for the buck? (and keep it driveable!) Cam change? higher CR pistons, NO2?

Pete

[MrJD]

why do you want a light flywheel? You planning to race it? Otherwise, there is a distinct chance you could lose some drivability under normal conditions.

With a FI car, you're going to have a hell of a time tuning the system to match any mods you use.I don't even know what type of FI system these cars use... or how tunable it actually is. Kinda like my previous post... if you do a radical set of mods (new pistons, cams, some porting) you will need a method of measuring your A/F ratio through the RPM range (wideband O2 meter... go do some reading) and a method of perfectly metering out the fuel required to meet your preferred A/F ratio (IE a "piggyback" system to alter the signals from your ECU... or a stand alone ECU like a megasquirt.) Either way, that is $500-$2000 worth of equipment... to manage the engine.... in a $3000 car..... to get an extra 15-25whp. Overkill.



My advice? Get a nice exhaust system to make it sound great and then make it pretty. :p

[Tobi]

I have a done the flywheel, high compression, cams and removed the cat on a 2.0l block and head.
My tires are of a smaller diameter and that is similar to having a short rear end.
The motor sounds awesome, it has much more torque and it goes well up to 6000rpm.
I can feel that the original exhaust and air filter are holding it back a little in the higher rpm's and I am going to change that next.
I am not an expert but there was no tuning of the Fi needed. That is the beauty of it, it's a Fi, it tunes itself.
20 years with Bosch L and LE Jetronics and they never let me down.

[narfire]

Kinda loosing the original post but the FI can be tweeked to provide a nice bump in power without loosing drivability or reliability.
The "bolt-on" mods help a bit and comparatively inexpensive...headers, lightened flywheel, 1800 head...
Where it gets expensive in my opinion is the purchase of oversized HC pistons, the re-boring to fit, then HAVE to balance the rotating mass (I noticed a smoother engine), the massaging of the head, aftermarket cams, then the adjustable cam wheels and of course degreeing in the engine..
I have done all of the above to my FI and although perhaps a bit of loot for the few extra HP, I do enjoy the car with the suspension upgrades I did as well..
Chris

[MrJD]

if you are changing your compression, cams, etc and not touching the FI system, you are not fully taking advantage of your modifications. In essence, the car -thinks- you have done no mods, and is metering out fuel like its a stock engine.

Do fiat FI systems run off of an AFM or MAP system or?

Any time you mess with the short block you are spending big money. When you changed your flywheel, did the car get boggy when changing gears at low rpm/speed?

[timinator]

But up to the magic 5252 RPM point, the more torque you make, the more HP you will achieve.
HP and Torque curves intersect at 5252 RPM.

Sorry,but there is no magic about 5252. It is just a constant derived to equate the work done by a living, breathing horse and an engine. Many engines do not have the ability to achieve 5252 rpm, and the two curves don't cross.

I would submit that most Fiat Spiders are run at 5252 RPM or lower most of the time, and therefore; if you concentrate on making more torque, HP will come naturally per the engineering equation stated above.

Agreed that most Fiats operate below 5252rpm, and are limited in the torque they can produce because of their size. A stock B18B1 Honda makes 142hp@6300 and 127lb-ft@5200 and is very driveable. If you notice the torque is not that high. The horsepower is pretty respectable. It is only possible by extending the rpm capability of the N.A. engine. The same engine with v-tec makes 197hp@8000 and 134lb-ft@7500. It does not make much more torque than non-v-tec, notice the 50 more hp. Horsepower is what you are looking for if you want spirited driving.

If you just like driving your Fiat then concentrate on reliability. If you want to flog it you need horsepower. Nitrous is the best bang for the buck, but it has it's drawbacks.

[Kevin1]

timinator, narfire, MrJD,
Relative to your conversation above, I admit I am confused. If the mechanical improvements (pistons, cams, porting…) work to improve air flow through the engine doesn't the airflow meter measure the increase and admit fuel for that amount of flow? Up to the point of the injectors being "topped out" how wouldn't this compensate for those changes

[timinator]

doesn't the airflow meter measure the increase and admit fuel for that amount of flow?

The air flow meter function is to tell the ecu how much air is entering the intake manifold. The ecu has set maps to deliver fuel and timing at a specific rpm. More air through out the rpm range would mean the set maps would not neccesarily be sending the correct amount of fuel or desired timing to run the engine properly. At some point the amount of air entering the intake manifold would exceed the maximum value the ecu has maps for and fuel cut will occur and shut off all fuel to the engine. The stock ecu can be fooled to run acceptably by piggy back systems, however only to a certain point.

On my turbo engine the stock ecu, with a piggy back to correct fuel, will reach fuel cut at 4200rpm. When run on my AEM programable ecu it reaches the fuel cut I set at 7500rpm.

[BEEK]

thats not exactly how the bosch ecu works. it can be fooled to add more fuel, see how they did it with the legend industries turbo. im not getting into how it all works, but it can be fooled to support 150hp. it also doesnt control the timing at all.

[bradartigue]

thats not exactly how the bosch ecu works. it can be fooled to add more fuel, see how they did it with the legend industries turbo. im not getting into how it all works, but it can be fooled to support 150hp. it also doesnt control the timing at all.

It can be fooled at the sacrifice of other areas; in other words, if you monkey with the spring that controls the sweep of the FI rheostat, you can get more fuel earlier (or later), but you're going to get flat later (or earlier). It's a primate of a system compared to anything today. You can add injectors with more flow and impede the O2 loop and do all sorts of things, but in the end I find most people increase performance on a Spider by modifying the hard parts in the motor, increasing/improving air flow, adding bigger pistons, optimizing the exhaust, etc.

One of the fun things with these cars is you can swap stock parts around to make it run better, and it's cheap and easy. Removing and replacing a head really isn't all that hard on the cars, it's messy and possibly tedious, but it isn't hard to do in your garage. So certainly you can take an 1800 head and put it on a carbed 2000 motor and get a little more compression, a little less emissions stuff, and have some power. Highly recommended in fact!

The target though should always be a balance of good driveability (which depends on you) and maintainability (within your limits).

[timinator]

thats not exactly how the bosch ecu works. it can be fooled to add more fuel, see how they did it with the legend industries turbo. im not getting into how it all works, but it can be fooled to support 150hp. it also doesnt control the timing at all.

Yes Beek you are 100% correct. Sorry for being inaccurate. I was thinking of a modern ecu not the Bosch system. Since I wanted to control 350hp there were very few ways to fool the ecu. Also my ignition has a crank sensor so apples and oranges. It is much more of a problem to control the Fiat distributor output. Under boost, with nitrous, or at higher rpm with it's mechanical and vacuum advance, spark timing and spark strenght can be a problem. Luckily Mark's distributor can deal with the rpm and spark requirement.

[vandor]

Just a few comments. My Spider has an aluminum flywheel that weighs ~9 lbs vs the stock ~17 lbs for a 2L one. Maybe I'm used to it, but I do not notice having to rev the engine more for taking off. It drives fine.

My previous Spider also had a 2L and was converted to the stock Bosch FI. The only mod was a free flow airbox. This engine had mild cams and compression, and the car was quite quick. I dynoed it and we calculated ~130 HP at the crank. So the stock FI can support about that much without mods. This car also had the stock FI exhaust manifold, which was likely a restricting factor.

Regarding the airflow meter: at around 3500 rpm at full throttle its flap is fully open. From this rpm up, at full throttle, the injectors inject the same amount of fuel regardless of rpm. The reason the engine does not run lean is that after the torque peak (which occurs where the best cylinder filling occurs, in a stock 2L ~3000rpm) the engine takes in less air per stroke, so actually would need a little less fuel per stroke than at the torque peak. It still makes more power as the rpm rises because there are more power strokes per unit time. Then at a certain point cylinder filling gets so poor that increasing the power strokes per unit time (rpm) does not help, and this is where peak power occurs.

So when people loosen the AFM spring, it only really richens the mixture at part throttle, or at lower rpm at full throttle.

[BEEK]

actually i use a jap air flow meter, that has a larger flap area, the calibration of it leaving the spring alone works fine, to add fuel, i add a variable resistor to the coolant temp sensor, fooling the ecu about temp, which will make the ecu run rich. then you can add fuel pressure or larger injectors to also help compensate. a wide band 02 sensor is needed for tuning. but hey thats just me, i dont know everything, just what works for me.

[MrJD]

One of the fun things with these cars is you can swap stock parts around to make it run better, and it's cheap and easy.

Which is the overall point of this post... what IS the best block head combo. I am of the opinion that for the average driving condition, a 2.0 block is the way to go (internals, thats up to you). But what head? People have said that the 2.0 head is actually a better performance piece than the 1.8. Is the 1.6 any different? I've heard there is some extra work needed to get the 1.6 to work correctly.

Beek:
Man that's a load of extra. I'd have built a megasquirt and called it a day, lol. Cudos for figuring all that out and getting it to work though.

[BEEK]

im cheap and not a programmer. it was easier to use parts i had on the shelf and work with those, i had access to a chassis dyno so everything was easily provable. i would love to work with one of the digital fuel injection systems, but setting up all those tables is more than i want to try and learn how to do i think. maybe if someone with knowledge can explain how to do that and simplify it where i can understand how to come up with the values i might try it on a itb build