you're working on alot of modifications to your car all at once already, from my experience, I would try to narrow your focus to the engine/transmission swap, then work on other things once the car runs and drives again, the snowball can very quickly derail your build and then you end up with a 10 year old build that's barely been driven (like mine).
Good luck
-Eric
Yeah, that's for later spring/early summer, I've always worked best when I have clear paths planned out for basically everything, so yeah, I'm not getting wheels until it is a running, driving vehicle (and needs better tires), I just plan ahead so it doesn't take me time to decide when I do actually want them.
Well I finally got to the point where I could start the engine today, I had already been playing with the tune for the last few months out of the car, to get it as close as possible to useable before having to actually try and start the car, turns out that paid off, it started the first time I turned the key!
Oh and for now I'm using the 3400 VR crank sensor, directly wired to the megasquirt, the 3400 hall effect Cam position sensor, wired to the megasquirt on digital frequency in 2, and I'm using the original Fiero ICM to connect to the coil, with gm 7x settings in the megasquirt, which does not include the bypass signal, so under the on/off outputs, I have a spare spark out wire set to turn on when rpm is > 400 or something like that, just as the original ECM did. Turning the distributor will adjust the non bypassed (cranking) spark advance (running off the ICM), but not the megasquirt commanded spark advance.
More progress, I'm finishing the exhaust and the routing of the intake, seems like it will all work just fine.
From the turbo to the water/air intercooler, it runs down between the transmission and the frame rail, then goes into the bottom of the Intercooler, from there it goes from the top to the throttle body.
More wiring today (yesterday now I guess), got the reverse switch wired, got the speedometer working (f23 speedo in to ECM on the cam in wires, 4000 ppm speedo out on digital frequency 1, through a 1.2μf capacitor from the tweeter of an old bookshelf speaker to the yellow speedometer high wire going to the dash. Hooking it up directly did not work, speedo is expecting the AC signal from a VR style sensor, not the switched DC of the ECM output, and apparently a simple capacitor in line fixes that).
Also removed the reverse lockout from my 4 speed shifter, and the "centering spring" (holds the shifter in the far right position as default)
Megasquirt has an option to fully open the IAC valve during WOT, I'm using a Porsche/Bosch/PWM 3/4" hose IAC valve, sitting where the EGR tube would be, running into the lower intake IAC passage, then will be going into a port on the intake tubing before the throttle body (the blue tube in pictures). Would this be beneficial? In theory it would allow a decent bit of air to bypass the restrictive upper intake (3/4"all the way to the lower intake, then reduced to the 1/2" barb there, then the IAC passages), unless airflow is so unevenly distributed to cause issues, or it adds turbulence to the main stream that slows everything down. Thoughts on this? I would assume it would be somewhat well balanced, especially with the cold start injector in there (from factory, I'm not using it any more), you'd think that would be designed to be distributed fairly evenly, but who knows.
Originally posted by 1985 Fiero GT: Megasquirt has an option to fully open the IAC valve during WOT, I'm using a Porsche/Bosch/PWM 3/4" hose IAC valve, sitting where the EGR tube would be, running into the lower intake IAC passage, then will be going into a port on the intake tubing before the throttle body (the blue tube in pictures). Would this be beneficial? In theory it would allow a decent bit of air to bypass the restrictive upper intake (3/4"all the way to the lower intake, then reduced to the 1/2" barb there, then the IAC passages), unless airflow is so unevenly distributed to cause issues, or it adds turbulence to the main stream that slows everything down. Thoughts on this? I would assume it would be somewhat well balanced, especially with the cold start injector in there (from factory, I'm not using it any more), you'd think that would be designed to be distributed fairly evenly, but who knows.
I guess it would partially depend on how quickly the IAC goes from full open to full close. When you do WOT upshifts you will likely not want a 3/4" opening to stay open or you could likely hit the rev limiter.
With boost, the neck of the plenum will be less of an issue (just add more boost) or do the Dawg neck modification. I would do the Dawg mod simply to help remove the restriction. While you can add more boost, it would come at a penalty of more heat, which would need to be addressed. For my build, it I focused on making everything up stream of the cylinders as free flowing as possible to maximize hp with the least amount of boost/heat.
Creating and using a large air path from the the air intake track around the throttle body and into the runners, will skew the readings from the MAP sensor in the plenum. It will shift the readings higher (higher kPa) because the plenum will see less vacuum than what is present in the runners between the cylinders and the cold start ports. Having the IAC wide open will magnify the issue.
Loudias did a modification to the lower intake where he created a slot between the runner walls at the lower to middle intake gasket surface to allow some airflow equalization between runners. This showed something like a 20 hp improvement on the dyno. I would consider this modification vs. the IAC mod.
I guess it would partially depend on how quickly the IAC goes from full open to full close. When you do WOT upshifts you will likely not want a 3/4" opening to stay open or you could likely hit the rev limiter.
With boost, the neck of the plenum will be less of an issue (just add more boost) or do the Dawg neck modification. I would do the Dawg mod simply to help remove the restriction. While you can add more boost, it would come at a penalty of more heat, which would need to be addressed. For my build, it I focused on making everything up stream of the cylinders as free flowing as possible to maximize hp with the least amount of boost/heat.
Creating and using a large air path from the the air intake track around the throttle body and into the runners, will skew the readings from the MAP sensor in the plenum. It will shift the readings higher (higher kPa) because the plenum will see less vacuum than what is present in the runners between the cylinders and the cold start ports. Having the IAC wide open will magnify the issue.
Loudias did a modification to the lower intake where he created a slot between the runner walls at the lower to middle intake gasket surface to allow some airflow equalization between runners. This showed something like a 20 hp improvement on the dyno. I would consider this modification vs. the IAC mod.
It's a PWM solenoid, so I would assume pretty fast, I would also think megasquirt would release it as soon as TPS gets under x percent, where my foot would still be releasing the throttle, and that is not an instantaneous event either.
Yes that's one reason why I'm doing all this, 3.4 and a turbo, I don't want an engine that falls on its face due to a choked air supply (non turbo 3.4), and I will not give up the Fiero intake, so a turbo just blows right through the restriction and as a benefit makes even more power everywhere else. I was hesitant to do that on the 2.8 and 3.4 firebird engines because of reliability concerns, but the 3400 is stronger so seems a perfect match. I will not be doing the dawg mod, I can't weld aluminum (still learning to do exhaust haha), and anywhere near me would charge an arm, a leg, and take a kidney for spite, small towns in the middle of nowhere where services charge a premium, last year I got an exhaust manifold crack welded, 2" weld cost nearly $200, and I had the part cleaned and prepped already. I've sent my intake off to Quebec, Quebec to be powder coated, still expensive, but I'm tired of dealing with bad paint adhesion (failed paint twice already).
I didn't think of the map sensor, but being only at wide open throttle, how will it act with boost, I mean theoretically with an open throttle, x amount of boost, it's just going to be pretty much equalised through the intake, I don't know how sensitive this is though.
Would it even be a problem? If the map reads higher, but that is because more air is getting into the engine, wouldn't that make sense? When you open your throttle more, the map reads higher, more air is getting into the engine, IAC opens, more air goes to the heads, less vacuum to the plenum, which reads as higher map, that's expected, what would this do that it isn't supposed to. More air=less vacuum, would this setup amplify that? (10 units sucked in by throttle, 1 by IAC, would it read as 10% higher on the map, because that would be true, or more than that?)
I won't be doing that mod at the moment, maybe after more research, but the middle intake is already on, and I'm trying to get finished haha.
Originally posted by 1985 Fiero GT: More wiring today (yesterday now I guess), got the reverse switch wired, got the speedometer working (f23 speedo in to ECM on the cam in wires, 4000 ppm speedo out on digital frequency 1, through a 1.2μf capacitor from the tweeter of an old bookshelf speaker to the yellow speedometer high wire going to the dash. Hooking it up directly did not work, speedo is expecting the AC signal from a VR style sensor, not the switched DC of the ECM output, and apparently a simple capacitor in line fixes that).
Direct Current, or DC, is a misnomer; in French it is called Courant Continu, or CC. Continous current you could say.
DC means unchanging over time.
If the DC is switched, then it is no longer purely DC; it is DC with an alternating (AC) component added on top.
Capacitors block DC current, as there is no electrical connection between both electrodes. However, AC current can pass through capacitors, as electrical charges on one electrode can attract/repel charges on the other electrode for short durations.
quote
Originally posted by 1985 Fiero GT: Also removed the reverse lockout from my 4 speed shifter, and the "centering spring" (holds the shifter in the far right position as default)
I'm planning on keeping my centering spring in the shifter (but messing with the springs in the F23 to make everything work); I think that it will help enhance shifter feel and mask the feeling of backlash in the mechanism.
quote
Originally posted by 1985 Fiero GT: Megasquirt has an option to fully open the IAC valve during WOT, I'm using a Porsche/Bosch/PWM 3/4" hose IAC valve, sitting where the EGR tube would be, running into the lower intake IAC passage, then will be going into a port on the intake tubing before the throttle body (the blue tube in pictures). Would this be beneficial? In theory it would allow a decent bit of air to bypass the restrictive upper intake (3/4"all the way to the lower intake, then reduced to the 1/2" barb there, then the IAC passages), unless airflow is so unevenly distributed to cause issues, or it adds turbulence to the main stream that slows everything down. Thoughts on this? I would assume it would be somewhat well balanced, especially with the cold start injector in there (from factory, I'm not using it any more), you'd think that would be designed to be distributed fairly evenly, but who knows.
I think that you can work this out later when testing/tuning the car on the road.
If you are running in open-loop, and during a pull the measured AFR is leaner than before the change, then whatever you did increased airflow.
quote
Originally posted by 1985 Fiero GT: Yes that's one reason why I'm doing all this, 3.4 and a turbo, I don't want an engine that falls on its face due to a choked air supply (non turbo 3.4), and I will not give up the Fiero intake, so a turbo just blows right through the restriction and as a benefit makes even more power everywhere else.
I haven't done this yet, but I'm planning on having a boost target that rises with RPM to help mask the restrictive nature of the stock intake. The car drives ok with constant boost pressure, but I think that rising boost with RPM could help make things feel a bit more linear.
[This message has been edited by pmbrunelle (edited 03-05-2025).]
Direct Current, or DC, is a misnomer; in French it is called Courant Continu, or CC. Continous current you could say.
DC means unchanging over time.
If the DC is switched, then it is no longer purely DC; it is DC with an alternating (AC) component added on top.
Capacitors block DC current, as there is no electrical connection between both electrodes. However, AC current can pass through capacitors, as electrical charges on one electrode can attract/repel charges on the other electrode for short durations.
I'm planning on keeping my centering spring in the shifter (but messing with the springs in the F23 to make everything work); I think that it will help enhance shifter feel and mask the feeling of backlash in the mechanism.
I think that you can work this out later when testing/tuning the car on the road.
If you are running in open-loop, and during a pull the measured AFR is leaner than before the change, then whatever you did increased airflow.
I haven't done this yet, but I'm planning on having a boost target that rises with RPM to help mask the restrictive nature of the stock intake. The car drives ok with constant boost pressure, but I think that rising boost with RPM could help make things feel a bit more linear.
Yeah, makes sense, it took an afternoon to wrap my head around how the capacitor can generate a negative voltage when the 5v is turned off, it seemed to easy of a solution haha, another note, I never realized how loud the speedometer/odometers are, they click and whir, which you don't hear when the engine is running and you're driving, but stationary with the megasquirt outputting a test signal, it was alarming the first time I did it haha.
Yeah I saw that, I'm not going to fiddle with that until after I can feel what it feels like with nothing additional.
