A 3.4 DOHC Build then... F40 Turbo (Page 11/57)
Joseph Upson MAR 20, 07:59 PM

quote
Originally posted by fieroguru:

You can run the VSS wired right to the ecm and enter 60K for the ppm. This will make the ECM see the right speed. Then you can splice into the Yellow VSS wire to drive the Dakota Digital box and use it to run only the Fiero speedo. The best thing about this method is that the common "noise" (where the speedo randomly jumps to 20mph) the Dakota Digital box produces at low vehicle speeds will not be sent to the ECM, which can change idle speeds and cause other drivability issues.



I believe I tried this approach unsuccessfully and I don't have any jumpy needle problems with the SGI unit in place, perhaps the cause is somewhere else.
fieroguru MAR 20, 08:19 PM

quote
Originally posted by Joseph Upson:


I believe I tried this approach unsuccessfully and I don't have any jumpy needle problems with the SGI unit in place, perhaps the cause is somewhere else.



I ran the 92-94 HTOB getrag with a 24K VSS through the 7730 8D for several years using this method. During this time I also verified that the 7730 8D would accept 60K for PPM and all it did was scale the ECM speed by about 1/3.
Joseph Upson MAR 20, 08:52 PM

quote
Originally posted by fieroguru:
I ran the 92-94 HTOB getrag with a 24K VSS through the 7730 8D for several years using this method. During this time I also verified that the 7730 8D would accept 60K for PPM and all it did was scale the ECM speed by about 1/3.



I'm sure it was one of your threads that I was following when I tried it, whatever the case I wasn't able to get it to work with 8F. My odometer is pretty close with the current arrangement and trouble free although I would have preferred the method you've described.
Fierobsessed MAR 28, 02:08 PM
More updates!

Since we love these so much.

Back to the exhaust, We start out with another pile of pricey 304 stainless parts to be welded.
Borla muffler
2, 2.5" mandrel bent 180's
4, 3" mandrel bent 90's
1, long piece 2.5"
2, exhaust tips.


The muffler itself is 5" in diameter, the factory muffler is around 4". So I had to find a little bit of room where a 5" round muffler would fit, I found that spot a little higher up. And of course, this meant loading the cradle back into the car yet again for yet another fit check... Seems like I do this alot.


The reason I chose this borla muffler was because its 304 stainless like every other component of this exhaust system. It has what practically amounts to a lifetime warranty, it is of a straight through design, it is relatively compact for a 3" muffler and only 15" long.


I started adding some pieces to the question mark pipe to extend it towards the rear for the muffler, I decided to add a V-band flange at this point as well, so that the muffler can easily be removed, if needed.


Some more test fits, It's like a game. I used a long level and a pair of clamps to give me a location reference of the trunk firewall, it just so happened to be located where the level was almost even with the back edge of the cradle mount platforms. So it was easy to keep track of.


Prop a few things up, make a few cuts and some welds, and the muffler is in place.


This is what I envisioned for after the muffler, that way I can keep the dual exhaust look. Which if it is a GT, really needs to have. I got smarter about plumming, I ditched the sawsall for the stainless and broke out the abrasive chop saw. I should have done that a lot earlier. It made easy and cheap work of these pipes! The number of sawsall blades I was burning through was costing a bit of money.


Got that in place


Starting to see it all come together, the finish line is close


And with the last couple of welds...


I can finally take a breather. There are a couple of little things to do, but the exhaust is done.



Onward!
My fuel pump arrived yesterday. High Flow Fuel Systems, HFP-343


I suspected that this pump was probably the same one that TRE Performance sells, well... there is little question about that theory now!


I happen to have a Walbro kicking around that I have no intention of using, but to see them side by side is always a welcome comparison
Clearly, they share the same top piece, possibly the same physical motor?


Looking into the inlet of the TRE Performance pump, it clearly has a (at least) two stage design, having a first stage "Fan Like" velocity pump that feeds fuel into the second stage positive displacement pump that pressurizes the fuel. Second stage pump's design I couldn't tell you. I can say that this style of design is very similar to all factory GM pumps, using a velocity pump that feeds a positive displacement pump. 4 cylinder Fieros actually use a two stage velocity pump only, that's why they produce so little pressure, but they actually flow very well.


The Walbro however, has a very obvious design, probably a single stage, Gerotor style positive displacement pump. This partially explains the Walbro's great dislike for low fuel levels, and to some extent the reason for its noise.


Another thing, both of these pumps draw around 13 amps. This is kind of a lot of power. All the fuel that gets pumped actually goes through the core of the motor carrying away the heat produced by this small high performance motor. So if you starve it for fuel, the motor will overheat quickly. So all high performance fuel pumps are subject to damage in the event of any fuel starvation. So having the first stage pump helps ensure a constant supply of fuel to the second stage pump. The walbro doesn't have this type of first stage, so that's why I say it's more sensitive to fuel levels. Not sure if all Walbro's are like this, the one I have is meant for a Grand Prix, so its not exactly apples to apples.

Lastly,
I finally purchased a clutch. I went back to Clutchnet as I did previously since I was so pleased with the quality.
I purchased a 6 puck sprung disc for a 2006 G6 GXP, which is 9-1/2"
#6BS7G61


And, I got a pressure plate for a 1992 Firebird 3.1, which we all know is the 9-3/4" Pressure plate. I went with their "Yellow / Stage2" pressure plate.
#YP3121

Clutchnet called me the next day to ask me about the difference in diameter from the disc to the pressure plate, and graciously offered since they had to make the clutch to order anyway, to fit the disc to the pressure plate. Which of course I agreed to. I have to say, that was a pleasant surprise.

I chose this disc and pressure plate based on Matt Hawkins reccomendations. He has a similar engine setup and he is using a 9-1/8" version of this disc with a stock replacement pressure plate, and has had no issues with it. So I have a larger diameter, and a somewhat stiffer pressure plate, so I'm less worried about slipping. I think I am a very conservative manual driver, and I am great about breaking in clutches anyway. I also have to tune this engine with boost disabled (WG spring removed), so the clutch and engine will have a chance to break in before I start adding boost to the equasion.

That is todays update.
Fierobsessed MAR 28, 02:22 PM
Oh, and if anyone is curious, I am sick of welding stainless. I circled a piece of stainless with my TIG a total of 38 times to create the exhaust, from manifold to tips, and it still isn't quite over, but I think my skill has improved quite a bit.
Joseph Upson MAR 28, 04:27 PM
I'm sure you know this but the pump current is a function of load and voltage so when it fires up it will not likely draw that kind of amperage unless you're running high pressure and at the max voltage it is specd for, it would put a nice load on the motor at that output level also.

I believe you made a very good choice going with a pump other than Walbro for a daily driver. That was one noisy pump and every bit as sensitive even to normal low tank levels that stock pumps see without a problem. The 8100 V8 pump I just replaced it with almost requires that I put my head near the console in order to hear it.
Joseph Upson MAR 28, 04:43 PM

quote
Originally posted by Fierobsessed:

The digital IO extender chip "U10" on ALL 7749/7730/7727 based ECMs are physically wired to output the pulse divisor to digital outputs 5, 6, and 7.

The input byte is configured by the high 3 bits of a byte.

So it looks like this:
Divisor A = Bit 7
Divisor B = Bit 6
Divisor C = Bit 5

76543210
00000000 = 0
00100000 = 32
01000000 = 64
01100000 = 96
10000000 = 128
10100000 = 160
11000000 = 192
11100000 = 224

So the working divisor bits should simply be increments of 32, up to 224.



Just a heads up since I ran into this problem today as the last hanging point before being able to drive the car after completing the new harness. Some two pin plugs are labeled in reverse with A and B terminals on the opposite sides so if you use a plug that didn't come directly from a Vss sensor make sure it has the proper arrangement, or you'll connect the plug up correctly color wise but backwards terminal wise, which may cause you to dig into your harness unnecessarily all of which I did before my Christopher Walken like psychic powers kicked in and prompted me to check after a new pull up circuit didn't resolve the problem.

[This message has been edited by Joseph Upson (edited 03-28-2013).]

Fierobsessed MAR 28, 06:47 PM
Thanks, I'll have to check out that connector thing. I wouldn't think that it's important, as far as I know the output signal is A/C, so it should have no polarity. But I did get that connector from some random harness...

The fuel pump has a "fixed" (sort of) displacement, and voltage is relatively stable, so it's load is only really dependent on pressure for the most part. And according to the chart it will draw between 12-13 amps all the time. The walbro would draw 9-11. So it is a bit of a hefty pump. It contributes to heating the fuel in the tank, which is a bit undesired. But for an engine that should be over 400 hp, I'm willing to make that small sacrifice.

I started machining the flywheel this morning, I have the 92 firebird flywheel, I'm cutting the outer ring off of it.
Fierobsessed MAR 28, 06:55 PM
Double post...

[This message has been edited by Fierobsessed (edited 03-28-2013).]

Joseph Upson MAR 28, 07:01 PM
It shouldn't but believe me it makes a difference and my guess would be that it's because the square wave that is triggered would be negative (upside down) instead of positive. One thing is for sure, the odometer didn't budge and the data log showed no speed with it connected backwards.