Looking for more 3900 performance

[Fieroghini]

I currently have a fiero running a 3900 with a 9396 ECM and a 4t65e-hd. I recently picked it up from the dyno tuner and am fairly disappointed. The cam phaser works but doesn't seem to add power. At least not at the fully retarded position. I am getting a fairly radical cam from the store with .610/.602 lift and 224 duration. Or somewhere around there, can't remember exactly. Ben says 309hp minimum. After looking at superdaves 3500 I think I may still be missing out on some power. I already have some shorty headers I built and northstar throttle body. I'm Currious what the opinions were for other upgrades. I'm thinking about building better headers with a 180 design. Similar to a tri-y, but a four Y. I'll be swapping to 3.69 gears while I'm at it. Any ideas? Oh, right now it dyno'd at 207hp but I have reason to believe the dyno is optimistic.

[robertisaar]

didn't know the 16149396 could run a 4t65e-hd... thought there would be issues with the fact that the 9396 can't modify line pressure...

and i wouldn't complain about 207whp from a 3900, especially if the cam phaser isn't doing anything.

[Fieroghini]

I don't believe it's accuracy. I'm running the trans on a ratchet shifter. But the vss is accurate so I think the 9396 could run the trans. I may get to that or use a smart relay for button shifting. That's another topic though.

[robertisaar]

I don't believe it's accuracy. I'm running the trans on a ratchet shifter. But the vss is accurate so I think the 9396 could run the trans. I may get to that or use a smart relay for button shifting. That's another topic though.

i'm sure it will shift right, the two-solenoid setup would be the same as the 4t60e the PCM is expecting, but how is line pressure controlled? did someone retrofit a vacuum modulator onto it or what? i think all 65e trannys used the PCM to control the line pressure, so if thats not being addressed, you may be looking at worn tranny parts in the near future.

[ForcedFirebird]

207whp isn't too bad for a stock 3900. Weren't they rated at 225 or something? Don't forget in the Fiero, you have limited options on the exhaust routing and usually end up loosing some power with a poor header design.

You can't compare a stock 3900 to Dave's car He is cam'd, ported and has long tubes. Get your cam in, and build yourself some nice headers, should wake her right up.

[robertisaar]

207whp isn't too bad for a stock 3900. Weren't they rated at 225 or something? Don't forget in the Fiero, you have limited options on the exhaust routing and usually end up loosing some power with a poor header design.

You can't compare a stock 3900 to Dave's car He is cam'd, ported and has long tubes. Get your cam in, and build yourself some nice headers, should wake her right up.

depending on the year and E85 capability, up to 240/240...

X2 on the cam/headers

[rsisbetter]

a stock 3500 should be able to put out 210 with headers and misc bolt ons...

[Superdave]

we put down 205 ish with a stock 3500, 2.8 log manifolds, cone filter and rough tune... it was a 5 speed car though.

that 3900 should do a little better, work on the tune some more. Spark advance is a huge thing for them, i've lost 10 HP by adding 2 degrees on the dyno.. lol

If you can find the room to do longtubes, get all the primaries as long as possible and equal length. It'll like that. I wouldn't mess with any Y design, more trouble than it's worth in my opnion.

[Fieroghini]

What do you think about building a tuned runner intake? The stock variable intake manifold is useless to me. I could make one without too much trouble.

[robertisaar]

What do you think about building a tuned runner intake? The stock variable intake manifold is useless to me. I could make one without too much trouble.

you can make it functional...

[Fieroghini]

I considered it when I made thebcam phaser operational but the connector was $80 or something rediculous that and the fact that it's a four wire I decided not to mess with it and just took the door out. If you k ow how to wire it I'll give it a shot though.

[SappySE107]

Use the 3500 VVT upper intake.

[robertisaar]

I considered it when I made thebcam phaser operational but the connector was $80 or something rediculous that and the fact that it's a four wire I decided not to mess with it and just took the door out. If you k ow how to wire it I'll give it a shot though.

its unfortunate i don't have the alldata disk that covers it, but you do realize being stuck full open kills the bottom-rpm ranges (compared to stock), but it does leave all the power up top alive

it seems like ben's suggestion will have to work unless anybody else can dig up the schematic...

[Fieroghini]

I have the diagrams. I haven't looked at them In a while but I don't remember it being that easy. While it's true I don't have good bottom end, which is magnified by my gearing, I also have poor top end. Right now peak hp is at 5500 and peak torque is 4900. It drops quickly and is not worth reving out. I'm not trying to be hard headed. If I had to do it over I would have saved the headache and kept the stock computer, which would have just been different headaches. So here I am making the best of the choices I made. I'm trying to find a picture of the 3500 intake, I think I read it was goofy looking. And obviously I'm making the jump to a real cam. I just figured if I'm dropping the engine I should take advantage. For a little perspective, my old 3400 5speed dyno'd about one horse power less and about the same power curve. It was completely stock. That is the reason for the disappointment.

[ForcedFirebird]

Joseph Upson has a 3900 in his Fiero and made the cam timing functional. In fact he has a video floating around of him connecting/disconnecting the timer and you could hear the idle change. You could easily hook it to an RPM switch and take full advantage of it.