Got a burning question or simply need
some advice with problems you’ve encountered while wrenching on your
current/future projects? Ask our automotive guru Eric Hsu anything literally,
he’s going to answer every single question, as long as it’s automotive related.
Problem
My car is a longtime project '99 Nissan
Maxima with a fully built 3.5L '05 short-block (CP pistons, Carrillo rods, and
balance), Cosworth heads, and ZK2 cams. The engine is controlled by the factory
ECU with MAF and has 440cc DW injectors for the E85, a Walbro 418 (450-lph)
ethanol pump with 6AN lines for supply and return, an Aeromotive FPR, OBX
rails, and a ’08 Nissan Altima intake manifold. The OBX headers and custom
3-inch collector go to a straight-through exhaust to a Flowmaster D-50 SUV
muffler. Other stuff includes a built automatic from IPT in New Jersey, cryo
axles, and traction bars. The car runs M&H 24.5x8x15 slicks on AR wheels or
M/T ET Street radials 26x10.5x15 on Summit wheels.
'99
Nissan Maxima
The direct-port system is built with
extended tip Nitrous Outlet nozzles fed from two six-port blocks from NX 500HP
Lightening solenoids controlled by an NX Maximizer 3 controller, set for
throttle control. For a 150-shot, I jet nitrous for .026 in each and have been
searching for a fuel jet (tried .019-.023) that gives me a Lambda of around .80
at WOT. I have also tested a single NX Shark nozzle ahead of the 75mm TB and
find that (75-shot) a nitrous jet of .041 and fuel jet of .033 gives a Lambda
of .083 on the PLX.
Regardless of what I do with fuel jets I
cannot get the Lambda below .94 and it should be around .80 with E85 (VP Racing
C85). I raised the FP; the engine bogged when spraying. I kept going to fuel
jets larger than .023 and the car felt slower on the highway but no change in
the Lambda reading. Something is very strange; the single-nozzle tunes fine,
but the six-nozzle setup will not drop the Lambda. Is there something weird
about spraying with E85 and the Bosch LSU4.2 sensor? I’m stumped here. The car
pulls very hard, but I don’t want to go to a track and melt down the engine by
running too lean for a quarter-mile (I’ve done that before).
How to fix
The very first thing that comes to mind is
the Bosch sensor itself. How old is the sensor and have you tried a new sensor?
When Lambda sensors fail, they typically do what you are describing by not
reading any richer than a specific amount (in this case .94). It’s almost as if
the Lambda is clipped at .94. Bosch sensors have no issues reading proper
Lambdas on E85. The fact that your experiment of running larger fuel jets
caused misfire and loss of power also tells me that your sensor is probably
dead or dying.
NX
Shark nozzle
Bosch LSU sensors do not last very long on
leaded race fuels. While you didn’t mention what kind of fuel you ran previous
to E85, I would assume you ran some kind of leaded race fuel like most drag
racers. Bosch LSUs are rated at 50 hours of life span with leaded fuels, but
there are a lot of variables that can affect their actual life spans such as
temperatures, moisture, and amplifier drive method, and more. Personally, I’ve
had Bosch LSU sensors fail with leaded race fuel in less than four hours and
some in 20, but I’ve never had one last the full-rated 50 hours. On the flip
side, the NTK LIHx UEGO sensors are also rated at 50 hours, but, in my
experience, last much, much longer with leaded race fuels than Bosch LSU
sensors. I have had a few NTK sensors last for years on leaded race fuel.
The good news is the switch to E85 will
allow your Bosch LSU sensors to live a long, fulllife.
Problem
I just turbocharged my ’91 1.6L Mazda
Miata. The new power is great, but I can tell the car needs a larger exhaust.
My plan was to cut the downpipe (2.5-inch ID) 12 inches or so upstream from the
cat, then go 3 inches all the way to the tailpipe (cat included). My other
option is to get a 2.5-inch cat back and just bolt it
on. Is jumping up to a 3-inch going to make that much more of a difference than
going with 2.5-inch piping? Cost is not a factor if the 3-inch pipes aren’t
mandrel-bent. The current setup has a Magna Flow cat and 2.25-inch cat back.
’91
Mazda Miata
How to fix
The larger-diameter tubing makes the most
difference right after the turbo. The exhaust gases exiting a turbine housing
travel at the perimeter of the downpipe, so the larger the tubing, the lower
the backpressure is going to be on a turbo engine.
MagnaFlow
cat
You didn't mention how much power your
Miata engine is making or the size of your turbo. These will be the main
factors determining how large your exhaust should be. But since it’s a smaller
1.6L engine of an older design (i.e. the heads and cams don’t flow as well as
modern engines), I don’t think you’ll have any issues with a 2.5-inch exhaust.
I do, however, recommend using mandrel bends. Never cheap out on a press- bent
exhaust if you can help it.
