Lvangundy

What's going on with my car??

I got my 16" wheels on.. could this be the problem? I kept getting 9.1- 9.2 times! 2 weeks ago it was low to mid 8's.

The factory 0-60 times didn't change between 1992-1993..and I don't think my wheels weigh so much more they cut my 0-60 times down an entire second!

My 2nd rear O2 sensor failed not too long ago, what about this?


Will post pics soon of wheels..

Anyone ideas?

meZoom!

what kind of tires are on those wheels? I remember getting a totally bad jump off the line for like, half a second when i had different tires a long time ago. (hard rubber that took forever to break in). i think wheels has something to do w/ it but u need that 02 sensor fixed. how's check engine light? on/off?

Richie

I think the wheels may have something to do with it.
Do you still have the old wheels, maybe you can weigh them so you can be sure.

JBrady

Are the tire diameters the SAME between the sets? A larger diameter tire has the same effect as changing gears and will effect performance. Weight is definitely a factor as heaver = slower.

How do you time your runs? If you are doing a stopwatch it is hard to be consistant. I will have my new GTech Pro Competition tomorrow and while it does not = track numbers it does give repeatable times for comparison and mods.

Lvangundy

Jbrady - I'm glad you can add the 'technical expertise' whenever possible.

As far as the wheels yes, they are 3/4" larger in diameter. I need to get 55 series instead of the 60 series which make the diameter that 3/4" larger. Tires that came with rims are worn out anyway. Just can't afford thr $400-500 for new tires.

As I understand it, the rear O2 sensors don't have too much effect on engine performance. If this is untrue, please someone explain.

Jbrady - you previously mentioned you suspect my transmission. I knwo the dyno didn't show any error in the toque convertor but daily driving and acceleration somethign isn't right. the TC frequently engages and disengages on the freeway if the RPM's drop. Maybe it's time for another TPS adjustment. (Why does mine keep getting out of whack?) I'd also like to get to tearing the throttle body off, but last time I tried I removed a bunch of bolts but coudn't get it off. Maybe I'll ask for some help today and try to get it off. Can the throttle cable be out of adjustment too?

I'd really like to get the numbers down the factory specs. My LS's performance is an addiction, I have to get those times down! I might be into my car a little too much now, literally it's what I focus on most of the time.

The way I get the 0-60 numbers is with a stopwatch. I do have access to a g-tech pro, but it's not mine and not really up to asking to borrow it. It's the older model.

There's NO WAY I could have been an entire second off when I was getting the 8.2 and the recent 9.2 numbers. I ran daily at night verifying those low 8 times. Up and down up and down the street then averaging. Its either the wheels or the rear O2 sensor.

I ran 3 runs last night and got 9.1, 9.2, and 9.2 again.

Lvangundy

I think I figured it out.

It's 2 things.

One, the diameter of the tire as Jbrady said turns the differential more times thus making the engine rev more to do less.

Two (I think this is it) - The SPEEDOMETER is off a bit becuase of the 3/4" larger tire size. Any numbers on how many MPH the speedo is affected by certain tire sizes?

meZoom!

you can get an idea by knowing how many rpms your tire does. for example, my 205/55/15s do (if i remember correctly) 812 rotations per mile...compare your old and new tire sizes (i think toyo tires has a scale online) to get an idea. there are several different formulas u can use to readjust your speedo, they can be found online....

JBrady

Ahhh yes...

Larger diameter tires do 2 things. The bigger diameter acts to reduce torque and therefore the car will be SLOWER. Also, the bigger diameter means that your speedometer will be reading SLOWER than you are actually going. This means you are going FASTER than 60 when you see 60 indicated.

So, you are slower measuring to a higher speed. Is it any wonder your times stink?

Get or borrow the GTech, measure with both sets.

Here is a little basic math to give you an idea. I have a good program sent to me by Tom Taucher that allows me to calculate a BUNCH of data relating to gearing.

Let me compare tire sizes 215/60-15 to 225/60-16
15" has 25.2" diameter
16" has 26.6" diameter
Ratio difference is 5.5%

Here is a tire size calculator:
http://www.powerdog.com/tiresize.cgi

Using the transmission ratios from a 95 LS400 (4 speed) and the torque rating (engine not rwtq) I calculate the following:

260tq x 2.8 (1st gear) x 3.62 (diff ratio) - 25% drivetrain loss = 1976 lbs of torque to accelerate your car. If we remove another 5.5% (what happens with the above tire change) and you loose ANOTHER 109 lbs of torque to accelerate with.

Speedometer is effected by the same percentage. 60mph indicated with the 16s is (60 + 5.5%) 63.3mph actual. You would actually only time until an indicated 57mph.

Make sense?

Now, I am changing from 3.27 gears to 3.62 gears. I have ordered a speedo recalibrator so my speedo and odo will be accurate. I will GAIN slightly over 10% torque Of course I have more torque already AND better gearing. 300lbs x 3.36 x 3.27 - 21% = 2604 lbs to accelerate. I am about to change to a 3.62 (from a 95 LS400) and that will give me 2883 lbs in 1st gear...

OH YEAH

Lvangundy

Ok..with the 55 series tires on the rear I cut my 0-60 times back down again.

Oddly it's between my old times and the times I was getting with the 60/R16's.

Ran 2 runs at 8.7.