for those of you running 12-11 sec

[turbobluestreak]

I'm woundering what kind of gears you are running in you cars I have 3.90's and the 81-83 n/a trany in my turbo car. I'm just woundering if I could have got the 12-11 seconds with out the gears and if I could then what kind of times do you think I could get with these gears and with the mods listed in my signiture??

 

tbs

[spork]

let me ask you this...what times are you running now? how much wheel spin are you seeing? What gear do you finish the 1/4 mile in? I'm only in the low 13's right now...13.44 @105 to be exact, but I'm well into 4th gear at the end of the 1/4 and I'm running the stock 3.54 gears with the BW t-5. I can't imagine that if you were running 3.90 gears even with the regular 5-spd tranny that you wouldn't be switching into 5th on a run with the ET's that you desire...and most guys will consider that a bad thing...maybe some others will have more to comment...cause like I said...I'm not to the 12's or 11's yet..not till I get slicks atleast.

[turbobluestreak]

I'm sorry but I got lost in what you mean by this

 

"I can't imagine that if you were running 3.90 gears even with the regular 5-spd tranny that you wouldn't be switching into 5th on a run with the ET's that you desire...and most guys will consider that a bad thing" are you saying I'm going to run out of gears last time I did a street race, because I haven't had the time to go up to the track I finish our measured 1/4 mile in third gear so I'm a little confused on what you mean I don't get wheel spin at all because the turbo is what makes my torque and I launch at about 2500 so it makes a small chrip and just goes for me to go. I know that my 5-spd has the best gears of all inline zcars. I'm just wanting to know if this was a good thing for me to switch to for time wise or not??

[Mike C]

Street racing is NOT a good way to estimate what it does at the race track. He means that you will be passed redline in 4th gear requiring a shift to 5th, which usually is not optimum for fastest times. Also, racing in 5th is notorious for busted transmissions, regardless of the manufacturer. Turbo cars like less gear (smaller number) to help build boost. I don't know how high you turn your motor, but assuming 5500 rpm, the 3.90 are probably too much for anything above 100mph in the quarter. But that also depends on your tire height. Is the ECC the only mod to your car?

[Scottie-GNZ]

Hard to believe that with your mods and a 3.90 you could finish the 1/4-mile in 3rd gear. The math just does not support it. All 5-spds have a 1.308 3rd gear. Combined with a 3.90 and an assumed tire diameter of 25", you can only get a tad less than 86mph at 6000RPMs in 3rd. So, either the car is EXTREMELY slow in the 1/4-mile or the 1/4-mile marker is way off. Even running a conservative boost level, you should be at or better than 100mph with a hybrid turbo, putting you around 5380RPMs in 4th.

[turbobluestreak]

ok first yes as of now the ecu is the only mod and what your saying is that I should look for smaller gears either go back to 3.54 or get a 300zx lsd 3.70, so that I don't bust my trany racing it. My goal is to get into the low 12's right now and also my car weighs with me in it and a 1/4 tank of gas 2800 even and yes they scales I used where at a brass factory were my dad works and they have the most accuate scales peiod.

 

tbs

[turbobluestreak]

Scottie do you still have your LSD and if so are you willing to part with it?? Baised on what you told me so far this is what I want to go with to have better ET times. Please let me know soon and also could your downpipe's flange be moved forward to miss the cars body to fit a 280zx?? I'm really looking for a down pipe and jeffp sell the whole exhaust but that's too expensive. Thanks

 

tbs

[Bob_H]

Ok, while I admit I suck at spelling, I gotta say, fix the spelling in your sig. I only bring it up because what we are addressing is somewhat a result of your "beter ratios" transmission. I won't even go into what I think of sigs. I piss enough people off about heads!

First, the 81-83 zx 5 speed, while in some peoples opinion offering better ratios, is a much weaker design. The countershaft bearings are small for higher power outputs. The small contact area on the gears themselves lend to pushing the oil out from between the teeth under high loads,(not a good thing). And I really can't stand how it shifts,(that obviously being a personal opinion). I have hard so may people say how they don't like the T-5 shifting. I'll tell you what, I have a 2000 BMW M coupe that shifts better than most cars. And I love the T-5 I recently swapped in. Much more precise, and I have a good stock shifter. The internals of the shifter mechanisim break down,(there are plastic parts), and you lose some of the precision of the original shifter. Mine is still in good shape. A quick easy fix is the B&M ripper shifter or the Hurst, which is the same as all Mustang and Camaro's through the 80's. But I digress.

Using a 6000 rpm shift point, here are some approximations of mph and rpm drops btw the zx and T-5 tranny. All of these assume a 3.9 ratio rear end.

BTW, I referenced this page for the info:

transmission calculator page

 

So, in one corner, weighing in at slightly less than the T-5, we have the weakling 81-83 zx box:

1-2 = 31mph, drops to ~3600 rpm

2-3 = 51mph, drops to ~3850 rpm

3-4 = 80mph, drops to ~4350 rpm

4-5 = 110mph, drops to ~4710 rpm

 

And in the other corner, weighing in just slightly more than the ZX box, the T-5.....

 

1-2 = 35mph, drops to ~3573 rpm

2-3 = 59mph, drops to ~4240 rpm

3-4 = 84mph, drops to ~4614 rpm

4-5 = 110mph, drops to ~4475 rpm

 

Many people go with and suggest the 3.36, 3.54 or 3.7 vs the 3.9 and 4.11 in a turbo motor'd car. In a non-turbo car, absolutely, stick with the lower ratio,(higher number).

But lets look at the real stuff. Both boxes top out at the same speed in 4th with their 1.0:1 ratio in 4th. Which for 6000 rpm is 110 mph. 110 mph will get you into the 12's with a good launch. Otherwise, low 13's. A better choice is to swap your rear end for the 3.54. Now your theoretical top speed in 4th is higher, and better for the turbo,(more gear to pull against).

-Bob

[Bob_H]

I just thought of some more issues. look at the mph change in each gear,(assuming a 6000 rpm shift):

T-5 box:

1-31mph

2-20mph

3-29mph

4-30mph

Now the ZX box:

1-35mph

2-24mph

3-25mph

4-26mph

[Scottie-GNZ]

Bob, great responses.

 

TBS, my LSD is long gone. I also do not make the DP anymore but it did not fit the 280ZX anyway.

 

If your car weighs in at 2800# w/driver, you need about 325rwhp (note I said RWHP) to go 12.30 @ 114. With a better I/C and 3" exhaust (you did not say what you have), you all all the pieces to do it. As you can see from Bob's post, you can only get 110 in 4th with your combo. This assumes a normal diameter tire. Since you are going to need something sticky to run low-12s, then a 235/60-15 DR (26") will do the trick or or a 3.70 LSD with a normal <25" sticky tire. No getting away from the tire upgrade unless you get real good at slipping the clutch off the line to not light up the street tires.

[SHANE]

FWIW i run the 3:54 rear