Stock 1UZ rev limits?

[GSMnow]

How high can we safely rev a stock 1993 LS400 motor? With the stock ECU or a programmable??

Now that my 1UZ Celica is up and running, I am thinking about "improvements". My main use for the car is autocross racing. The events are run on very tight courses made up of traffic cones in a large parking lot of airport surface. Only one car runs at a time and the quickest through the course wins. An average course has a top speed close to 70 mph for streetable cars and about 30 turns in 50 seconds. If a car is set up right, you usually will launch in first gear and shift to second fairly quick, but then the rest of the run is just second gear. Here is my little problem. My car has a 3.727 rear end (stock Lexus is a 3.62) and I run 22.8 inch tall tires (alot shorter than the 26 inch high tires the Lexus LS 400 ran). Add up these two factors, and I think I will be running out of second gear. If I manage to either get the Lexus ECU re-programmed, or set up a stand alone box, then how high can I rev a completely stock LS 400 V8 in such a light car. I am getting mixed reports. Some say the early 1UZ's rev limit at about 6300 RPM. Another post claims it is more like 6800 rpm. I know I will be losing power if I just rev it high, but I just want to be able to avoid shifting into third. From some caculations, it look like the rev limiter will hit at about 68 miles per hour. I really want to stretch that over 6700 rpm. So, my motor is all stock original, what do you think I need to change for safe revving to 7000? I may set up a programmable ECU for just when I am racing. It will also have to hold the trans in second, if I don't make the stock ECU keep running it.

Gary M.

 

[Zuffen]

These engines will rev to 7,500 safely.

No point though as they are well past making good power at that point.

Either shift into 3rd or change the diff ratio so it can hang on in 2nd.

 

[deankdx]

i would think it would do 80mph in second as is, it would be reving near 6000 at that,
when i first got the Falcon i have with auto and 2.92 diff it used to do 60mph in first, took off fairly slow though.
with 3.45 diff it did 50mph in first, 85 mph in second at 6000rpm in each,
i think you may want to work out a way to LOCK it in second if you are say above 40mph in the course. maybe a switch on a solenoid?

 

[WDoherty]

stock rev limit on the ecu is 6500rpm. you should be fine with your set-up. My sc400 pulls to 80mph in 2nd with a 3.92 rear and stock height tire so with the 3.727 and a little bit smaller tire you should actually be about perfect!

 

[GSMnow]

Maybe the ratio chart I have for the trans is wrong then. I got it off of the Lextreme site, but I can't find it now. My current Hoosier race tires (225 50 14) have to turn at 1045.5 rpm at 70 mph. That comes out to 3896.75 rpm at the drive shaft with my 3.727 ratio. The ratio chart for the A341E Lexus trans. showed a 1.8 to 1 ratio for second gear. SO... even with no torque converter slip the input shaft of the trans has to turn at 7015 rpm. Which is whay I wanted about 7100 for the rev limit.

Gary M.

 

[WDoherty]

maybe so, if you can tell me the revolutions per mile of your tire or the 70mph rpm of 25.8" tires then i could try some calculations based off what i have observed from my sc400.

 

[WDoherty]

ok, according to this calculator with your set-up you'd achieve 65.75mph with your set-up at the 6500rpm redline. So, what about wheel size, are you allowed to upsize to 15's or 16's?
http://www.wallaceracing.com/calcmph.php

 

[GSMnow]

Here are the tires I race on
http://www.tirerack.com/tires/Spec.jsp?make=Hoosier&model=A6&tirePageLocQty=
I currently have just 14 x 7 inch rims. If I go to a different tire package, I would like to go wider, and as you can see from the listing, the 225 50 14 is very wide for its UTQG sizing. The measurements actually reflect a tire size of 244 46 14. This particulare tire size is an anomoly in the Hoosier line up. Most of the other tires fall very close to the real UTQG dimensions. Even other 225's are narrower. Hoosier started bending their measurement when the SCCA rules stated tire size limits of +20 from the stock factory tire size in stock classes. That rulke has been thrown out, but the odd sizes remain. Many cars ran 205's back then, so their 225's are all wide. Looking at the chart, I want a slightly taller tire that is a bit wider, I have to go all the way to a 245 45 16. These come out to 1.6 inches taller, or raising my ride height 0.8 inches. I can lower the car a tic k more, but I am close to the practical limit due to bump travel and geometry for cornering. Add to that, the custom 16 x 8.5 rims to fit an 83 Celica will set me back about $2,000 and the tires go from $185 each to $208 each and last less than a season of racing. All to get just 0.4 inches of tread width. Tire sidewall height is just 0.2 inches less with the 16 inch rim. If I can find a way to get rid of more negative camber in the back (LEGALLY in SCCA) I could run a larger rear tire and stay with my current fronts. As I lower the rear though, negative camber climbs fast. The National Class winner last year runs the 295 35 17's on his BMW 3 series. That gives him 2 inches more tread width. My only hope is that I weigh in 400 pounds lighter. He also has 350 hp to my stock 250 hp 1UZ

Gary M.

 

[WDoherty]

i don't think you need an 8.5" rims to fit a 225 and you can certainly find some 16x8 or so wheels for much less than two grand, actually what about stock sc400 rims they go a few hundred a set and are light and wide enough for 225 width?

 

[GSMnow]

My stock wheels are 7 inches wide with an 8 mm positive offset and a 4 on 4.5 inch bolt pattern. The only sorta off the shelf wheel that might fit is a Kosie K1, custom drilled and center bored. They have a 16 inch rims in 7.5 inch or 8.5 inch width and a 12 mm offset. I have to do careful measuring to see if it will go. I did run a 15 x 8 zero offset wheel a while back, but the car is lower now. I didn't have coilovers back then, the rear may be a tighter fit. There is no stock wheel that fits my car wider than the 14 x 7 I run now. These are stock 82-85 Supra rims. Yes I could run a 225 on a 7 inch, and some even run them on narrower rims, but I want to improve the handling, as cornering is more important in autocross racing. If I am staying at a 225, I will stick with my current 14 inch setup. Rev the motor to 7250 and I hit my 70 mph in second gear goal. Now if I can jam the 245 45 16's under the car, it could be a win/win, except for the increase in ride height at 24.4 inches tall vs my 22.8 inch tall current setup. Still lower than the 24.7 inch tall stock 225 60 14's though.

 

[GSMnow]

I did some searching and I found that my A341E trans ratios are wrong. And this does make a huge difference in my calculations.

Here ios what seems to be the correct ratios.
1st 2.531
2nd 1.531
3rd 1.000
4th 0.705

SO.......

My trans input shaft rpm at 70 mph is now 5966 rpm. Now the numbers others quoted for engine rpm at speed make sense. Where did I get the 1.8 ratio 2nd???? So if the rev limiter in the 1UZ ECU is around 6500 rpm, it should just hit 70 with some torque converter slippage.

Thanks for your patience in my error.

Gary M.

 

[WDoherty]

glad it worked out i should have picked up that 2nd gear ratio being of but i didn't look, i just knew that 2nd in my sc400 is long as hell.