So the other day at work, I decided on my lunch break that I was going to make myself a dual throttle body intake manifold for my 2.8.
Got home and pulled the car apart to get at the middle intake, brought it to work with me the next day and stayed late building this:
The TB's are Holley units off of an Eagle Vision of an unknown model year. Whatever it was it had the chrysler 3.5 24v v6 with factory dual TB's. Theyre 48mm at the smallest, I think. The plenums are the same volume on each side and are offset to match the offset in the manifold. It all went together fairly smoothly.
Basically, I got the thing on there, got the throttle linkage worked out, got the map sensor remounted, got the PCV's plumbed in, got the EGR and all the related vacuum spaghetti deleted, got the vacuum fittings for the fuel rail and MAP plumbed up, got the Discovery's TPS wired into the fiero harness correctly after a couple tries, and made a little bracket to sync the TB's together. Its not in the picture because I hadnt made it yet.
Anyways, the thing runs, just not well. So next on the agenda is tuning, I think Im going to go with a Microsquirt. Then it'll get the **** -o-matic transmission swapped for an '84 4.10 ratio 4 speed from my parts car. At that point, once its running decent, Ill take it to a dyno day at one of the local performance shops. Im curious to see what it makes over the stock motor. Its got no other mods done to it besides deletion of the EGR.
Once thats done, the long term plans include a 272 cam, shaved heads, ported manifolds, and some other mods to culminate into a stage rally/rallycross car
What do yall think?
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quote
Originally posted by Frank2:
here's the goal: Build a mid engine car 1/2 as good as a Lotus Elise at 1/10 the cost.
I have no idea what Im doing, but Im doing it.
IG: @giveintogravity
[This message has been edited by Boot (edited 06-28-2017).]
Looks interesting. How did you handle the idle air control?
Took care of itself, mostly. It fires up and idles fine, a little lower than it should, but its stable. Its when I step on the gas hard that it leans out and dies. You can hear the air rushing into the TB's I can get it to rev higher if I take my time opening the throttle, and it runs pretty well actually. Doesnt backfire at all, and the exhaust looks normal. The plugs are white, which I imagine is mostly from the lean condition on opening the throttle.
It doesn't really need a balance tube. The idle air passages in the LIM connect all the intake ports to a common location (the idle air port). So pressure can distribute between the intake ports. But if he were using a different LIM (with no idle air passages), then he would need a balance tube.
Not having idle air control is going to drive the ECM crazy. Don't be surprised if the engine surges and stalls a lot. A cheap and easy solution would be to hack up a stock throttle body (if you have a spare), and keep the idle air portion of it. Although, you'd need to make some kind of air filter for it, or it will be letting in unfiltered air.
It doesn't really need a balance tube. The idle air passages in the LIM connect all the intake ports to a common location (the idle air port). So pressure can distribute between the intake ports. But if he were using a different LIM (with no idle air passages), then he would need a balance tube.
Interesting, thanks. I don't recall that ever being pointed put before, but I guess it stands to reason that the IAC air passages connect all six intake ports together.
I do not see any need for a balance tube. Since in my view there is no need for a balance tube, the IAC manifold (connecting all cylinders) contributes nothing.
The engine can work as two separate inline-3 engines on a common crankshaft. If you think that the air pressure between the plenums needs to be equalized by a balance tube, then you might as well go all the way and use a common plenum for all 6 runners...
The only practical need I can see for a balance tube is because of "shared peripherals/accessories", such as the vacuum lines for the brake servo, MAP sensor, fuel pressure reference, etc.
So all of these accessories would hook up into the balance tube, to read an average air pressure from both plenums.
That said, I would not use the IAC manifold as the MAP sensor reference. It seems that MAP sensors are normally placed at the end of a plenum in relatively still air. I think the MAP sensor would have unstable readings (seeing the fluctuations from intake vale opening events) from the IAC manifold.
The IAC manifold would work well for its original purpose though; idle air.
I'm planning to use my IAC manifold for water/alcohol injection.
[This message has been edited by pmbrunelle (edited 06-28-2017).]
Are you sure the Discovery's TPS and Fiero ECM are speaking the same language? Is the TPS supplying the correct values from idle to WOT?
Im fairly certain yeah, the throttle bodies on both the original Fiero manifold and the Vision TB's were actually Holley units, and the TPS's are nearly identical. In fact if it werent for one slight difference in the way they mate to the butterflys I could have bolted the fiero TPS up and just used it. Also, when I first wired it up, I had the ground right, but the +5v and the signal were backwards. So it ran super rich at idle (wouldnt idle actually) and also wouldnt run past about 3k. So I switched them around and then it idled fine and ran all the way through the revs.
As far as Im aware, a TPS takes however many volts is thrown at it and sends a proportional signal back. I could put 3 volts or 10 volts through it and it wouldnt care :P
As far as Im aware, a TPS takes however many volts is thrown at it and sends a proportional signal back. I could put 3 volts or 10 volts through it and it wouldnt care :P
Sure, it's just a voltage divider with a potentiometer on one side of the divider and a fixed value resistor on the other side. When the resistance changes in the potentiometer, so does the voltage sent to the ECM which then extrapolates that voltage into a throttle percentage. An issue would arise if/when the fixed resistor and potentiometer values do not correspond with the factory values such as a with non-GM sensor. In this case, the TPS would be sending throttle percentage voltages outside of the ECM's expected values.
Also, did you mean to make two posts about this? Just curious.
The first post I realized wasnt titled properly to indicate that itd be about this manifold, it was more about tuning. So i made one that would show up if someone searched for dual throttle body intake manifolds
Black Top Racing used to sell a dual throttle body intake manifold. If you can find a picture you can copy what they had.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Main problem with the stock intake is the kink below the TB. Doubling the TB area seems like it might be bit of overkill - you've eliminated the kink/restriction, but the twin TBs will flow far more than the engine can use, I should think. The
One of the other ways to deal with the restriction is to use a later 3.4 intake - no link, but also no room for the distributor, so you need to implement DIS.
Truleos have ceased production, and they're damn near impossible to find :/ I wouldve gotten one but it would have been ten times as much as Ive got into this.
[This message has been edited by Boot (edited 06-29-2017).]
Reviving this thread to ask if anything further was done ... If the dual TBs are too much flow for the given 2.8 features what about trying to insert some flow restriction into the intakes and gradually increase to see where the performance maxs out?
I agree that it could benefit from a balance tube; not just for the sake of equal manifold pressure, but also to help control the intake pulses. The balance tube would also be a good place to install the idle air motor with it's own little filter like an old school valve cover breather filter. It would work and would be a conversation piece. You might be able to control the throttle lean condition by a slight increase in fuel pressure and making a small adjustable bellcrank assembly to turn the input shaft at a slightly higher ratio to account for the increase in off-idle airflow with a stop/spring "bungee" to absorb input past 100%. Out there, I know, but it's fun to do things differently even if it's not popular.
EDIT: I didn't notice the dates in this thread, what's done is probably done. I'd like to see it though.
[This message has been edited by ZCR1 (edited 01-27-2019).]
Shortly after I last updated this thread my daily driver died so I had to put the fiero back to stock so I could get to work. I never got it put back on until I totaled the car in february 2018 at the hands of a tree off the edge of an icy driveway. It still ran okay and drove fine but the core support was crunched and it had so many other little problems that after nobody wanted to buy it for $300 I drove it to the pick n pull. Its a real shame, it has only 92k on it. I ended up actually buying an 1987 MR2 to replace it I still have the manifold and all the pieces, so maybe someday when I own another fiero I'll give it a shot. Sorry for the disappointing closure.
Originally posted by ZCR1: I agree that it could benefit from a balance tube; not just for the sake of equal manifold pressure, but also to help control the intake pulses. The balance tube would also be a good place to install the idle air motor with it's own little filter like an old school valve cover breather filter. It would work and would be a conversation piece.
It's also a good place to tap in for brake booster vacuum and fuel pressure regulator. It may not be so great for MAP sensor input, because the idle air and brake booster may have weird effects on MAP sensor readings.
I had to use a vacuum manifold on my dual plenum build, because the lower intake didn't have idle air passages. The idle air valve sits on top of the vacuum manifold. See below.
Originally posted by Boot: Shortly after I last updated this thread my daily driver died so I had to put the fiero back to stock so I could get to work. I never got it put back on until I totaled the car in february 2018 at the hands of a tree off the edge of an icy driveway. It still ran okay and drove fine but the core support was crunched and it had so many other little problems that after nobody wanted to buy it for $300 I drove it to the pick n pull. Its a real shame, it has only 92k on it. I ended up actually buying an 1987 MR2 to replace it I still have the manifold and all the pieces, so maybe someday when I own another fiero I'll give it a shot. Sorry for the disappointing closure.
An MR2! Well I hope to see you picking up another Fiero soon and continuing the intake investigation.
Very sad news indeed. At least you're okay, and yes, we hope you find another AMERICAN mid-engined car in the near future. I recently acquired an '86 GT and would gladly bolt on a fully developed, fleshed-out version of such a manifold in the quest for more power and greater throttle response. Keep us in the loop!
I had to use a vacuum manifold on my dual plenum build, because the lower intake didn't have idle air passages. The idle air valve sits on top of the vacuum manifold. See below...
Damn, that's a Frankenstein looking build. I love it! Is it currently running? Any video?
Very sad news indeed. At least you're okay, and yes, we hope you find another AMERICAN mid-engined car in the near future. I recently acquired an '86 GT and would gladly bolt on a fully developed, fleshed-out version of such a manifold in the quest for more power and greater throttle response. Keep us in the loop!
Hahaha us mid engine guys have got to stick together, you know... The fiero and the mr2 are both great cars, I can confirm after having owned both. Theyre both good at different things and theyre both really cool in their own ways... And I'll definitely own another fiero in the future. Maybe a duke this time. I gotta admit that manifold I made was kind of sketchy (The aluminum welding was a learn-as-you-go sort of thing) and it probably wouldnt have performed as well all around as the stock manifold on a stock engine. I didnt chamfer the ports in the plenums, I didnt port match it very well, and it was full of odd angles from the square tube. I just didnt know what I was doing. Thats not to say that this wont be the last time I'll attempt such a project
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quote
Originally posted by Frank2:
here's the goal: Build a mid engine car 1/2 as good as a Lotus Elise at 1/10 the cost.
Damn, that's a Frankenstein looking build. I love it! Is it currently running? Any video?
I have some videos of it idling and revving, but no driving videos. For some reason, the camera picks up wind noise more than the engine, even though the engine noise reverberates loudly inside the car.
I still have the manifold and all the pieces, so maybe someday when I own another fiero I'll give it a shot. Sorry for the disappointing closure. 
I love it! Is it currently running? Any video?
