3900 Forged Turbo build

[Joseph Upson]

That 174 number would concern me slightly. As would the nearly 20 PSI variance amongst the others.

What exactly happened on the first engine that caused it to fail?

I'm not that concerned about the pressures because the test was performed dry on a fresh build that wasn't broken in and the cylinders were lightly honed by a machine shop. More importantly, I saw variations like that on my 7k 3500 (even after spraying oil in the cylinders), that was untampered with. The additional valve reliefs I added aren't a perfect match across all the pistons either so I expect a few points difference due to that.

The motor runs strong.

The first build was damaged by an extremely lean run.

[robertisaar]

what was the need for replacing the trans?

your build is what had me confident a F40 can stand up to boosted abuse.

[ericjon262]

what was the need for replacing the trans?

your build is what had me confident a F40 can stand up to boosted abuse.

his broke

http://www.fiero.nl/forum/Forum2/HTML/120981.html

[Joseph Upson]

what was the need for replacing the trans?

your build is what had me confident a F40 can stand up to boosted abuse.

Hey, when you get a chance I could use your help straightening out the near 1 point difference in my datalog wideband reading compared to my Zeitronix display reading. It's a dangerous situation since the low reading shows up in the log instead of what the wideband controller shows. I don't want to run AFRs greater than 12 under boost by mistake and risk ruining the motor again.

I put the screws to the tranny but I didn't abuse it. Hopefully some of the result can be attributed to the incorrect fluid and the accident it was involved in, otherwise we would have to assume my engine was producing more power than the 350/LS1 V8s on the Fiero forum that haven't broken one yet.

I have a brand new 0 miles F40 replacement in it now and it's a little noisier sounding like the gears need to be worn in some, then again it may be the result of the proper fluid being installed which appears to be thinner than the syncrhomesh used in the first tranny.

I've been kind on launches and acceleration so far. The fresh motor is limited to 3 psi right now but is frighteningly quick compared to the stock motor that hit as high as 15 psi but with a fully advanced milder cam. The reground cam was degreed in on this motor and I can feel the difference, it pulls through the rpm range and feels faster than the stock motor although on much less boost.

I'm getting the false knock trouble I had when I installed the motor the first time and need to try and tune it out in the code as well as make sure there is no contact between the drivetrain and the body which I'm sure a little is comming from the decklid.

If I scrape a gear slightly the knock sensor picks it up, I've seen it register as knock counts immediately on the datalog dash in TP5. Most of the retard occurs off throttle and so far I don't recall experiencing any under load.

8psi on this motor when it was first installed was brutally fast making the car shake although it might have been a side effect of the extreme lean condition it was experiencing at the time. 3psi has the car pulling off like nobodies business and I suspect with proper fueling it will run even harder than before by the time I reach that boost level again.

I've also noticed city fuel economy as well as after running it a little hard is much better than before. The fuel gauge doesn't drop as fast as before eventhough compression is down by about .5 points and the idle vacuum down about 2 points. I find that odd as usually that suggests a reduction in efficiency and the overall AFR is on the rich side all over the MAP and the car is run in openloop.

[robertisaar]

Joseph, PM with info about how the display is acting. and email me the ADX you're using as well.

mostly, is it off by 1 point at all ratios or is it more of a consistent percentage at any ratio?

[NateD4]

I just looked over the pictures of your transmission. Looks to me like you had a faulty blocker ring, perhaps bad material, perhaps over stressed, hard to say for sure. Too bad you don't know the history of it.

I guess when I get my F40 installed I can see how it handles boosted torque. I'm using a Tilton dual disc, so we'll see how that works out.....

I've heard that there is an LS7 attached to an F40 somewhere that dynode 468 HP.

[ericjon262]

I just looked over the pictures of your transmission. Looks to me like you had a faulty blocker ring, perhaps bad material, perhaps over stressed, hard to say for sure. Too bad you don't know the history of it.

I guess when I get my F40 installed I can see how it handles boosted torque. I'm using a Tilton dual disc, so we'll see how that works out.....

I've heard that there is an LS7 attached to an F40 somewhere that dynode 468 HP.

get your reading glasses on, it's 71 pages...

http://www.fiero.nl/forum/Forum3/HTML/000047.html

[NateD4]

Is that the LS7 build or the 3900 build.

If its the LS7 build I've skimmed it already....


What I meant to say is that it is too bad he doesn't know the history of his F40 gearbox. I bought one with 0 miles on it. We'll see how it holds up.

I suspect the blocker ring shown in the pictures is powdered metal and that the failure was caused by over stress or a material flaw.


Then again....

[ericjon262]

LS7 thread.

[Joseph Upson]

Is that the LS7 build or the 3900 build.

If its the LS7 build I've skimmed it already....


What I meant to say is that it is too bad he doesn't know the history of his F40 gearbox. I bought one with 0 miles on it. We'll see how it holds up.

I suspect the blocker ring shown in the pictures is powdered metal and that the failure was caused by over stress or a material flaw.


Then again....

The blocker ring is the obvious failure but that doesn't mean it wasn't a casualty of something else as it was a series of high loads that caused the transmission to start whining. Whatever the case the builder cited apparent fatigue related failure and went on to implicate solid flywheels and solid clutch discs without being told that's what I had in my car as the culprit. The new transmission sounds noisier to me but maybe a few thousand miles will quiet it down unless it's the result of the fluid which appeared to be thinner than the synchromesh I put in the first one.

[NateD4]

I'm not sold on harmonics being the culprit. I thought there were other people not running the dual mass flywheels.

Perhaps the shift was just to fast.

I'll find out since I'm running a 7.25" flywheel and a brand new F40.


Maybe that issue was part of GMs redesign.

At 15 PSI boost and ~4 liters, I'd think you were pushing 500-600 HP.

Could have just found the trans design limits.

[robertisaar]

hmm.... 15 on an otherwise stock 3900 should make somewhere in the 450-475 HP/TQ range....

modded? 500+ isn't out of the question.

[Joseph Upson]

hmm.... 15 on an otherwise stock 3900 should make somewhere in the 450-475 HP/TQ range....

modded? 500+ isn't out of the question.

Very likely, all it would've taken is one launch for you to see how solid the car was off the line. There was no wheel spin and the car felt like it had lift bars it planted so well. A lot of the power in the stock motor was limited because the cam was fully advanced and that's why the forged motor feels so much faster on 3psi than the stock motor on 15 psi. I didn't take time to check it out but I believe the stock motor may have sustained some damage.

The oil was filthy for about 4k miles and there was an intermittent lockup on startup at least once or twice a week. At first I was thinking it was the gear reduction starter, but it hasn't occured on the new motor so my suspicion is that a near 300 deg overheat that didn't blow a head gasket, instead unseated a valve seat and when the engine shuts down with that valve open the seat comes down and is pushed back into place at the lockup point which often resulted in a hard start on second attempt.

Sounds far fetched but my first 3900 was a burnt motor I got for $100 which had an exhaust valve seat displaced from the pocket by about 3/16", it apparently dropped down on the open valve and tightened back in place after the head cooled.

One thing to take into consideration on all the high output motors in Fieros the F40 is behind, I believe most of them are on stock or stock width tires which spin easily. My tires don't spin, the car goes when you come off the clutch so the tranny takes all of the "heat" thrown at it.

The F40 is harmonic sensitive, you can tell when it's behind a motor without a dualmass flywheel, it chatters away and I'm sure it feels different also as I sometimes hear tranny noise that almost sounds like spark knock but know it can't because the engine load is to light in addition to no counts being logged. On the same token I'm sure the tranny noise is responsible for a lot of the false knock retard because it was non existant when the dualmass was in the car.

[robertisaar]

On the same token I'm sure the tranny noise is responsible for a lot of the false knock retard because it was non existant when the dualmass was in the car.

winnar.

tire spin/hopping can cause knock counts, i'm sure the trans clanking around can cause it as well.

[NateD4]

Based on the look of the part, can you tell if its powdered metal?

Sometimes powdered metal parts have a small edge to them where the mold/forge halves come together. This typically can create a stress raiser.

I noticed this on my main caps for my 3900 block. The old 3400 main caps had chamfered edges, the 3900 were a compacted with a nice bur on them. If I end up using them I'll have to remove the bur and polish the edges to avoid a place for a crack to propagate.

My point, I think, is that the tabs for the cone might have some edges on them that weaken the blocker and the crack could have propagated.

If you post some in-focus close up pictures of the crack area it might be possible to see what type of load initiated the crack.........