JBrady

As promised. The results from my air mod as detailed in the following thread: https://www.clublexus.com/forums/sho...threadid=55111

Went to HRP last night. Air was terrible, hot and humid. 85 degrees and 80%.
Car: my 99 LS400

Best ET: 14.93
Best MPH: 94.57

Miles per hour is the true judge of power. Elapsed time has greater variance.

Stock air box average for 3 runs: 94.02 mph
Mod air box average for 3 runs: 94.46 mph

While not an exact science on a 3500lb car running 15.00 ET needs 10 horsepower to gain 1 mph in the 1/4. With a heavier car it takes more power to increase the speed. I will estimate 12hp per mph for my 4000lb estimated race weight (unfortunately the scale was not on).

Using this quasi-science... 0.44 mph faster X 12 = 5.28 rwhp gained.

The LS 400 looses around 70hp from the flywheel to the road giving us a 70 / 290 = 24% drivetrain power loss.

So, 5.28 / 76 * 100 = 6.9 horsepower gained at the engine.

This mod cost me $0 dollars. I feel it was money WELL spent!!!

JBrady

For those interested in the difference between my 99 and my 96 LS400...

I ran the 96 last September. Do not remember the air temperature but I want to say around 80 and less humid. The 96 ran a best pass of 15.484 ET at 91.22 MPH.

Average of 3 runs for the 96: 15.54 @ 90.67mph
Average of 3 runs for the 99: 14.95 @ 94.32mph

Using my above math: 3.65mph * 12hp/mph = 43.8rwhp more... now we must consider the 99s 5 speed transmission is keeping the car in its best power range better than 96s 4 speed. Remember that power gains in the 1/4 are the average power gained for the run and that the peak difference could be more or less. In other words, the 96 is probably making the rated 260hp and the 99 its rated 290hp but the AVERAGE power used through the gears during the run was nearly 44rwhp in favor of the 99

JBrady

Performance is affected by air quality. Cars definitely are stronger in cold, dry air. Hot humid air reduces power. Case in point, there was 2 mid 90s Lincoln Mark VIII that were both slightly modified (air box and mufflers). I spoke with the driver of one, a young lady!!!, and she said her best pass was a 14.67 at 95mph. I asked what the temperature was and she said in the 40s!!! She goes to the track all the time and said she has been running 15.00s at around 94mph during the Houston summer heat.

Last nights air was BAD and the best she could manage was a 15.2 at 93mph so she was off a couple tenths due to the air. If she was telling me accurate information I would guess my car could go a couple tenths quicker in just normal 60% humidity or an estimated 14.75 at 95+mph.

Now, if the above holds true, I should expect to be able to run a 14.4 at 96mph in cold 40 degree air!!!

This track stays open nearly year round so I will try to go again during the cold weather.

Horta

jbrady

This is some really cool information. Thank you so much for taking your time to type it all in.

I saw all of your pictures and it looks fairly simple to recreate. Sence I just got my 98 I do not wish to mess around with it now. But a couple of years down the road when I get board I will pull out your pictures and have some fun.

Thanks and keep us posted.

Jerry

JBrady

What are you waiting for? I just got my 99 last month. I called the Lexus body shop and the manager GAVE me a slightly damaged filter cover! It takes only minutes to change back and forth. Now I am looking into TC options. I would love another 500rpm of stall on the stock lock-up TC. I do need to keep it "visually" stock so as not to attract any unwanted warranty violating attention. I also HATE the stock Y-pipe, that thing looks like a real power killer

LOTC

So what do u suggest for the Y-pipe jbrady? I have a first gen and I already cut off the resonators so how should the pipping be for the best air flow?

JBrady

edogg, I am not sure about the 1st gens but the 95-00 models have a 60mm (apx 2.4") diameter pipe exiting the catalytic convertor, this 60mm is very short (apx 2") and is cut and welded at apx 45`angle and continues another apx 2" and immediately necks down to a 50mm (apx 2") diameter pipe and right at that junction is where the 2nd O2 sensor juts into the exhaust stream. Just looks very restrictive. I think the GS400 Y-pipe may be different, I will try to look at one very soon. If so that could easily explain the 10hp/10tq difference between the 2. If I get a chance I will also look at a 1st gen to see if that is the issue there as well.

If the GS400 is larger diameter I may be able to get one from someone who has taken theirs off or I will fabricate a 2.25-2.5" part myself.

JBrady

As I posted elsewhere, the GS Y pipe is not better. My current plans are to build a system using an X-pipe. Not just any X-pipe but a true high performance part from people that build REAL performance parts...

See here: http://www.burnsstainless.com/Crosso...rossovers.html


The plan calls for new everything from the cats back. Primaries to the X-pipe, dual path resonator, possible second resonators, dynomax superturbos. I will probably build the 1st one out of mild steel to be able to make changes at a reasonable cost and then sell that system and build it again all stainless.

LexJunkie

Saw your cold intake setup and it looks very nice. I have a '90 LS400 and have started messing around with it.

The first thing I did was to remove the air filter housing completely and attach my K&N filter directly to the housing coming off the MAF. This did not make much of difference, so I put it back (most likely because it was getting all the hot air from the engine compartment). I did not think about removing the head light seal and placing a partition to keep the hot air from the radiator fan from getting to the air filter area. I will try that next.

The second thing I wanted to do was install a cat back exhaust. Looked around on the net and could not stamack spending >$2000. So I went to the local muffler shop and had a 2 1/2 in. system installed from the first resonator to the back with a single Magnaflow muffler on each side (for $400).

This made a noticeable difference in pick up from a stop and seems to have affected the torque curve. Just completed a 3500 mile road trip, it averaged 24-25 MPG (with AC on and ~90MPH) and it seemed to handle the hills much easier. Did drink a quart of oil though :-(.

One thing that has become really noticeable is the timing change and loss in power right before the tranny shifts, and it's starting to annoy me (seems like it takes for ever to shift). Does anyone know if it is possible to disable this or if there are any computer upgrades out there that deal with this??

Thanks in advance,

JBrady

L J, yes the reduced power during shifts is part of the way Lexus creates that "refined" feel... BUT, excessively long shifts can indicate possible tranny problems. I would suggest trying to locate another similar year LS400 to compare yours with.

Interesting on the exhaust mods you have done. Lvangundy has done a similar mod and reports a substantial loss of low end torque... opposite of what you report. Could you post some pics of your system. To see Lee's set-up go here: https://www.clublexus.com/forums/sho...threadid=56976

Have you done any acceleration testing?

LexJunkie

JB, next time I get under the car, I'll take some pictures. Basically everything from flange after the first resonator is
replaced. I wasn't sure how things were going to work out, and I wanted to be able to bolt everything back up if I didn't like the new set up.
I supplied an extra flange (from my 87 Supra, that went to charity). They (muffler shop) bolted on the flange, welded ~ 3" inch single pipe to it, then a 3" to 2.5" Y pipe, from there they installed 2.5" pipes all the way to the back where they went into a 2.5" mufflers, and out 3" chrome exhaust tips.

As far as the shiftting goes, I am confident that the tranny is fine (this is my seconds LS400), and I change the T-4 ATF every couple of oil changes (2 qts of it a least). I did a tranny service on my last LS400 where I dropped the pan and replaced the screen. The mesh on the screen was fairly coarse, and frankly I did not see a reason for doing this ever again??
Anyway I think the change in the torque curve is making the hesitation before each shift a little more noticeable, and I would like to eliminate it if possible.

I am probably going to get some flack for trying to make a Lexus louder and make the shifts firmer (defeats the purpose of having Lexus). I am doing this to tie my over until I save up for GS.
Thanks,
LJ

Lvangundy

LexJ -

I think I have basically the same setup as you minus the supra section and the 3" end piping.

Jbrady - To clear the low end performance issue thing up, I've been noticing this happen for quite a while now. At least 4-5 months. There is alot of lag and no chirping of the tires off the line. I recently had t he differetial fluid changed as I thought this was part of the problem.

I am going to have the tranny flushed completely with 3-4 cans of Type 4 fluid soon, and maybe have this new place I found check the torque convertor. I think this is a big cause of my problems which includes that stuttering while holding the car at a certain RPM point.

Good discussions we got going here ;-)

JBrady

I agree, good information swap

As far as torque converters are concerned... I am leaning towards changing mine to get a higher stall BUT still am under warranty and the PI TC from SRT (hows that for shorthand?) is PINK!!! Any service rep will spot it immediately as modified. In fact, if the tranny did need service even an non-painted PI TC would be noticeable and I am quite certain... void the warranty.

Instead, I have contacted Pro-Torque in NY. The will recalibrate a stock unit and machine re-weld it so that it is visually not distinguishable from stock. The net effect is quicker 0-60 and 1/4 mile times with identical highway performance. Now, low speed operation will change slightly but this is what a heavy car needs. Price is $400 exchange and they will send the unit and wait for your core...

JBrady

Lee, are you saying you did not loose any low end torque with your exhaust mods? I was reading your posts to assume that was the case. Please elaborate.

theSSthatcould

Well, well some nice info here. Looks like i may need to start modding my car soon

Azam