ptuomov

Ok, the car is coming apart for a little while again. I need to change the primary jet of the carburetor.

dprantl

You broke it didn't you

Dan
'91 928GT S/C 475hp/460lb.ft

VehiGAZ

Carburetor?!? I think I have one of those on my lawn mower...

ptuomov

No, I didn't have that much fun yet! ;-)

The primary jet of my carburetor = the in-tank fuel pickup and the hose to the fuel pump. At least it seems to function like the primary jet! :-)

The fuel pressure gets inconsistent when tank is not full, which means that the fuel pump is cavitating. I have an undersized in-tank fuel pickup, which needs to go. A better 5/8" ID part is in the mail. At the same time, I'll be changing the fuel pump fittings that currently touch the tank, to get rid of the fuel pump noise. Couple more signal wires will be drawn as well.

blown 87

Go up two sizes on your drill instead of one on them thar jets man.

IcemanG17

Tuomo
Your 928 is an 87 right? I didn't think those had intank pumps?

The intank pump is problematic at best in 928's.....on my ex 89 racer it would fuel starve out in corners below 1/3 tank..which is VERY annoying..... The Lemons racer with only 1 pump (external) will go all the way past the warning light with no starvation.....my 88 S4 was the same way with 1 pump

ptuomov

My current primary jet:



I don't have an in tank pump. Instead, I have the above piece that works well for most people. For me, not so much -- the hole in this thing is too small for my current needs. The new piece will have a nice 5/8" hole in it.

ptuomov

Back up and running.

The new bigger pickup is installed, and the fuel pump is working less hard sucking vapors. The TechEdge wideband controller with the usual Bosch sensor is hooked up. ST2 and Sharkplotter up and running. The car is in a non-cat mode for some AFR experiments. Car runs well and AFRs are in the ball park, but there's always more work to do.

Next up: More and more sensors and WinLog install.

Gregg K

I hope this isn't a silly question, but... Where can one see the exhaust manifold? This is one of the more interesting things, to me at least.

ptuomov

It's also probably the single most expensive component in the system, right up there with the gt3071r turbos.

Here some photos:

Gregg K

I've been waiting a long time to see these.

I can't tell if it's a modified cast iron manifold or not. I admit that I am not familiar enough with my own car to know. Shame on me!

I'm assuming these are steel tubing and not cast iron.

ptuomov

I have these waiting to get in, but the stock engine and transmission are refusing to give up:





I've been running it with 12 psi boost in the mid range ramping up to 18 psi boost above 6000 rpm, and the stock motor is just shrugging it off. No split cylinder towers, no burned head gaskets, no chronic overheating. It does throw off oil from the cam cover breather ports into the catch can, but I guess that comes with the 928 territory.

In other words, the stock '87 motor is taunting me!

We'll see who'll have the last laugh, though, I've gotten in touch with a guy seven miles from here in Framingham who's got Dynapack dyno. Let's see if we can help the 24-year-old motor to achieve an attitude adjustment strapped on for, say, six hours.

In the meanwhile, I decided to do something about the fuel pump noise. The fuel pump is loud.

***LOUD***

If my exhaust sounds like four Hells Angels speeding away, the fuel pump sounds like the siren on the police car chasing them! Who needs radio? ...I have to do something about the noise because I need to be able to hear whether an actual police car is chasing me with the siren on. ;-)

The pump is loud for a couple of reasons, but the most significant of those reasons is that I've installed it in an f'ed up way. The pump fittings are touching the tank, conveying the entire vibration into the echo chamber aka fuel tank.

Here's why the fittings are making contact. First, the fuelab pump is much longer than the stock pump:



Second, the fittings that I am using are first -10AN ORB to -10AN male, and the 90 -10AN hose end. Together, this adds a mile of length to the already long pump. See on the left:



Right of the previous fittings are the new fittings that I think will help significantly. Those are the lowest profile 90-degree ORB to AN 90 degree swivel coupler connected to a straight hose end. As you can see, this arrangement will save a ton of space. The low profile XRP fitting is very expensive though, so expensive that I am tempted to give up money management! (Actually, not.)

In addition, I am creating room on the pressure side of the pump by using a shrink-wrap sleeve (instead of rubber hose) around the stainless hose. This looks like a winner solution for anyone looking to run stainless lines that might otherwise rub against and destroy something. Mail ordered from Canada, cheap.



Since there's some room around the pump, I am wrapping the pump inside a mass loaded vinyl sheet. This will both protect the pump surface and maybe also absorb/block/whatnot some noise and vibration.



I also built a hose from the pump to the hard line in the fenderwell that has some vibration dampening / insulation built into it:



Finally, to put it all together I "made" -10AN wrench that is small enough to tighten the hose to the pickup with the tank straps in place:

ptuomov

Only a small help with the fuel pump noise. It's still way too loud, especially at idle. I was able to cut off some high-freqnecy noise but the lower frequency noise is still there.

Any ideas what to do?

My next planned step is to use a stethoscope to listen to all the parts around the fuel tank and try to find out the path of sound transmission. Beyond that, I am out of ideas.

Mike Simard

Do you have one of the counterfeit Chinese "Bosch 044" pumps? That would be any "Bosch 044" pump from Ebay or anywhere else that's not an actual Bosch reseller.

AO

He has a "Fuellabs" fuel pump. It's pictured above.