AWD Turbo Parts and Performance

Marc S – Racing / Comparison with Eric Lu’s 95 GSX – Second Race

As a refresher, Eric (EricATCA) and I got together a few weeks ago
to see how our cars would fare against each other. We both have 95
Eclipse GSX’s. Eric’s GSX had several more mods (including a downpipe,
cat bypass, and much bigger compressor wheel in his turbo) yet the cars
were at best dead equal; usually I pulled a car length or two on him.
There were no definite answers to the “why”, but one thing that was highly
suspect was Eric’s turbo- it had no modifications to the exhaust side
yet had as big a compressor wheel as could fit in the stock compressor
housing. It definitely had heavy lag.

Since then, Eric has upgraded the turbine wheel plus give it a 10 degree
clip, ported the turbo housings, and had the exhaust manifold/wastegate/O2
sensor housings ported. We hoped the work on the exhaust side of the
turbo would make the difference, and that his car would pick up some
serious power.

We got together again this weekend, on a street outside of town where
people have been meeting for street races for at least a decade
(probably a lot longer). It’s a nice long (well over a 1/4 mile)
deserted street, and I felt comfortable racing out there in the daytime
when there wouldn’t be any other street racers around. Temperatures were
high, between 90-95 degrees. (Definitely no fun racing with windows
closed & A/C off!)

We got in around 12 runs for the day. We paid particular attention to
trying to eliminate as many variables as possible. We both filled up
at the same gas station (Chevron 92). Eric had a full tank, mine was
around 2.5 gallons shy of full to try and make up for driver weight
difference. In addition to runs off the line and rolling runs where
clutch work was involved, we also did several runs from both second
and third gear where the clutch was already fully engaged, to try and
eliminate variance in driving style. For the 2nd gear runs, we both
had the clutch fully engaged and the engines at 3500rpm when we stepped
on it. Same thing for third gear, except we did it from 3800 rpm.
Regarding boost levels, I think the runs were split around 50/50 between
Eric running at 18.5 psi & 15 psi. I have no boost control, but I have
hollowed out the nipple on the wastegate solenoid on the air box, which
allows me to spike up to 15ish psi (after which boost falls down as revs
increase).

Here’s the list of mods on the two cars. (An asterisk * denotes
changes since last time).

Eric’s 95 GSX My 95 GSX
K&N FIPK K&N FIPK
Nology Hotwires Magnecor 8.5mm wires
Trust 2.5″ Exhaust RSR 3″ Exhaust
*Imagine Motors Int pipe upgrade Imagine Motors Intercooler pipe upgrade
(Was an HRC unit last time)
Test pipe Stock catalytic converter
Buschur 2.5″ downpipe Stock downpipe
EVC (15, 18.5psi) Mod’d wastegate solenoid, +2psi over stk
Secondary (inline) fuel pump Stock fuel pump only
T25 w/ Super60 compressor Stock T25
*”T28″ exhaust wheel w/ 10deg
clip, ported housings
*Ported exhaust manifold, O2 & Stock manifold/housings
wastegate housings

As for the results… Unfortunately they are disappointing and create
more questions than they answer. The cars were very equally matched.
A couple times Eric pulled ahead of me by 0 to 1.5 car lengths, a couple
times I pulled perhaps a car length on him. Most of the time we were very
equal, with the person who happened to get their foot on the gas a
millisecond before the other person getting a nose up. I think the times
I got a little ahead were usually due to my turbo spooling up just a hair
faster (not including the other factors I’m about to mention), but
surprisingly there isn’t much more lag on Eric’s turbo than on mine. I’m
sure all else equal there is more lag there, but the downpipe, test pipe,
and ported exhaust manifold seem to offset the additional lag created by
the bigger wheels.

This time around I took Eric’s car for a drive to compare how it felt to
mine, so my comments re: lag are based on driving his car and then driving
my car.

Ok, now to the “other factors”.. We have some unknown variables here that
pretty much make this weekend’s testing moot, other than to say that
currently our cars are still pretty equal, whatever the reasons. The
first variable is a slipping clutch. Eric’s clutch does have a bit of
slip (When I did some harder shifts in his car, it was not as crisp as in
mine.) I never saw any major slippage, but minor slippage may be occurring.
Eric will be putting a Centerforce D/F in soon, so that should eliminate
the clutch variable. Ok, everything that follows is pure (educated?)
guesswork.

“Variable #2” is a complex one. It’s ECU related. It seems like
Eric’s ECU is retarding his timing, big time. In the races that started
in lower gears (1st, 2nd) where he pulled a little on me or kept up with
me, he was set at 15psi. When he was set at 18.5psi, I usually pulled
a car length on him. In the higher gear races (starting in 3rd gear),
using 18.5psi didn’t seem to hurt as much but it certainly didn’t help
much either. This is a definite sign of a problem, 18.5psi should have
given him a lot more power, not hurt him. He has a big compressor
wheel, going to 18.5 psi should show good gains. He hasn’t played with
the timing on the car yet, but is going to try retarding it a little
to see if that makes a difference.

I’m curious, by the way, if anyone knows the effects that the 2nd
O2 sensor behind the cat (in this case, test pipe) might have on the
ECU?.. Could running a test pipe from an ECU point-of-view be hurting
Eric? (I’m unsure if he even has his 2nd O2 sensor installed?…)

Anyways, to me, I don’t think it’s a matter of the performance parts
on Eric’s car slowing him down or not providing good performance. Take
a look down the list of mods on his car & you’ll note that every
part on there has been proven by many DSM’ers to increase performance.
And I have seen a 95 with a turbo nearly identical to Eric’s run some
impressive 1/4 mile times. A better clutch might help things a hair,
but there is something significantly wrong with how things are running.
What worries me is that there aren’t a whole lot of things to play with
to try and correct the problem. Any thoughts on the matter are
appreciated!

That about wraps it up. We plan to get together again in a few weeks
when the CF DF has been broken in, and after making some sort of change
(ignition retard?) that seems to make a power difference.

Thanks again Eric!

-Marc

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