355hog

Went to the track on friday to try out the new gears& posi and to my surprise it showed little differnce. Ran a 13.4 at 104.5 the same as it did before the upgrade. It did feel quicker on the steet thats why I figured it would drop into the mid 12s at least. I also got the same 60ft 2.00 that I had before. My brother in law installed them for me since he is a mechanic so I now the gears were actually changed out to 3.73. I have no clue what is going on, if any body does please help.
I have A ZZ4 w/ 770 carb, ported heads and lt4 hot cam

slim84maro

that zz4 is a 350ci?
umm where you spinning more then before? im sure you'll get a better time with 3.73's. maybe the weather was different. but no matter what you will get a little bit of a better time with 3.73 posi

355hog

Its a 355, Idont think I was slip more than before because my 60ft times are the same and the weather was actually better.

ShiftyCapone

iTrader: (7)

Did you change your shifting style or points. What happend to you trap speeds?

freestylzz

I think you may wanna check that he "actually" did install the right gears.

FbodTrek

Your MPH should have chnaged quite a bit at least. You should be able to launch higher too, as you won't be as prone to spin. SOmthin sounds fishy.

ShiftyCapone

iTrader: (7)

How did your 8th mile times change? You may be using one more gear which is slowing you down at the end.

355hog

I know the gears were changed out because I was there and when I am going about 70 mph the rpm are higher than they were before like 24k. When I am at the traps the rpms was at 55k and I did not shift into OD. The only thing I noticed was that the 1/8 mile mph were 83mph about 2mph higher than before.
How can I find out if the 3.73 gears are actually in there without removing the cover from the rearend?

xanax

your mph wont change in the 1/4 mile. no horsepower was added, just the gearing of the car is different

Ramair21

iTrader: (3)

i would perfer 4:11 gear ratio. i know you will feel that!!!

rx7speed

no horsepower might be added to the wheels but torque to the wheels DID increase.


though again horsepower is one of those math numbers. while helpfull it doesn't show if you will go faster or not by itself being it is nothing more then just math



as far as why you might be going the same speed as others have said might of spun, weather, traction, car tune who knows


but also with numberical higher gear ratio while you do put moer torque to the wheels you tend to do so for less time before you need to shift.
it might have been that you went too far with the gears and 3.421 might have been better for you instead.
who knows though will let the others chime more in I'm just throwing ideas out there

Gumby

Id make sure that you wernt slipping the tires. These cars are so smooth you can barley tell or feel it slip unless it major slip.

It will slip the tires but not enough to free rev or lose much traction but say for ever tire rotation your only moving 3/4 a turn.

Or look at it this way. Your car was powerful enough to over come the 2:73 gears???

megaracerx

think thats your problem...i cant think of any V-8 thats supposed to run @ 24k!!


lol just messin..

unknown_host

iTrader: (1)

Why would he be less prone to spin with a steeper gear?

unknown_host

iTrader: (1)

Give me a comparison of your 330' times between the two passes as well as your 60' times.

People overlook the 330', a lot of times it makes the difference.

How tall are the tires you are running? How much total timing are you running?

355hog

Time slips:

w/2.73 w/3.73

r/t ...... .596 r/t .637

60'..... 2.036 2.061

330..... 5.795 5.735

1/8....... 8.795 8.722

mph....... 81.52 82.96

1000....... 11.393 11.288

1/4...........13.626 13.444

mph .........98.48 104.71

The reason why the 1/4 is higher on the 2.73 is becuase the car was falling off near the traps because of fuel problems but before that it would run the same 13.4 and mph. I fixed that fuel problem before I ran with the 3.73

TIRES 55 15" DRAGG NITTO @18PSI

I need to check the timing

jimmy_mac

Ok, I'll go ahead and make a fool of myself. Am I reading that with 2.73 gears your 60 ft was 2.03 and with 3.73 gears your 60 ft was 2.61. And then your quarter mile time improved from a 13.626 to a 13.44 with a 6 mph increase. That is a huge improvement with a terrible launch. I'm mis reading somethinng

355hog

I would usually run 13.4 on the 2.73 but that night I had fuel starvation problem so I had to let off on top end so I ran a 13.6 so really I had no inprovment. I lost the time slips that had 13.4 w/ 2.73 so I but the next best thing. The 13.6 should have been a 13.4

rx7speed

60'..... 2.03 2.61

notice that issue right there?
so off the line you where 6 tenths slower
but yet notice by the time you hit the 330 mark you have already
made that up and then a little

by the end of the 1/4 you are a 2 tenths faster
so just think of what you would have done if you didn't pull .6 slow in the 60' mark

and the mph are what 6mph faster.... that isn't easy to get and isn't minor improvement

your gears are there you just need to learn how to launch :-p

rx7speed

just giving you crap now but your slips are not the same for the 60'


that .6 of a tenth in the 60foot range is HUGE

355hog

Correction That 2.6 should be 2.06

unknown_host

iTrader: (1)

If you are running too much total timing for your setup, going steeper in gearing will make the problem even worse. The motor wont want to rpm with too much timing, and since you went up in gearing this might be where you are hurting. You shouldnt be running much more than 36* of total timing. Check it out and let me know.

dimented24x7

iTrader: (2)

Im not that surprised that it didnt make a huge difference. The gears only transmit the power. It seems to me that the gears would only really make a difference if your launching out of your powerband. One place it does help is if you have an auto. Youll be able to cross the line with the engine at the end of its powerband.

EDIT: Changed my post. Didnt see the part about the fuel starvation.

walterrao

1. Jack your car up put it in neutral
2.put a small mark on the inside of the wheel, and on the drive shaft.
3. the driveshaft should turn 3.73 times to one turn of the rear wheels

unknown_host

iTrader: (1)

Gears make a difference down the entire track, not just on the launch.

dimented24x7

iTrader: (2)

The way I see it is that gears allow teh car to launch in its powerband and also allows you to pull through every gear, which maximizes the ammount of power you put down.

dr1

ultimately you want to be in your powerband down the entire length of the track
but your rear end gear isnt deciding how many rpms your going to drop from gear to gear, only how quickly your going to reach the other end of the tach
and unless you can get all the traction you need at the launch.. those numbers are probably right on

i mean if you were racing identical cars but one with 2.73 and one with 3.73, the 3.73 would jump ahead from the beginning and that would give you the win.... but if numbers is what you care about, make more hp.. heh

but thats just my thoughts.. i dont even drag so feel free to ignore me

unknown_host

iTrader: (1)

Assuming the gears are matched to the powerband, the 3.73 geared car will be in its powerband more often than the 2.73 car all the way down the track, not just out of the hole.

dr1

if you did some math and figured out where you were going to be at the end of the track speed and rpm wise.. yeah, then it would help you there too
but after first gear its up to you to decide where to shift at, and now he probably needs 4th gear at the end, which may have a slightly negative effect of its own

obviously its going to help in this case... but not for 1sec off your time

Gumby

If ya run a motor of similar size with a 700r4 through drag 2000, you do see about the same results he had.

with 3:73 your in 3rd at the end of the run and 2:73 your in 4th.

I had to think for a while and have seen several big motor guys do the same thing. Ditch the speed gears for a 2:73 mileage gear and the results were the same. not much of a time lose in the 1/4 with better highway MPG.

The number came out so close to his its not even worth posting a pic of the D2000 results.

big motor cars can get away with mileage gears.

unknown_host

iTrader: (1)

Assuming he is running a 26" tall tire and a 700r4, 104.5 mph equates out to about 5500 rpm assuming 10% slip in 3rd gear with 3.73's.

With 2.73's, that would be 6500 rpm in 2nd (too much) or just over 4000 rpm in 3rd (too little).

The ZZ4 peaks power at 5250 rpm according to GM, and will pull to 6000 rpm. This is not a tuned port motor, 3.73's are PERFECT for this setup. He just needs to nail his timing and make sure there arent any other factors he is missing.

unknown_host

iTrader: (1)

And according to Dragsim which is the updated version of the program you are using, going from a 2.73 to a 3.73 in a 3400 pound car gives 4 tenths and 4 mph on slicks.

Gumby

Yep, thats about right. not much if a difference. 1 tenth is a big difference to searious racers but.........

unknown_host

iTrader: (1)

LOL 4 tenths and 4 mph isnt much of a difference ? That is HUGE!!! You realize would need a 40-50 horsepower gain to obtain results like that?

Gumby

[didn't I say?]
To a serious drag racers that is allot....

to the common street drivers a whole sec is allot........

If your driving a 17sec car, 4tenths isn't much on the street. go from a 17 to a 15, that is a big deal.....

rx7speed

cehck your personal mesages plz

unknown_host

iTrader: (1)

The slower the car is the less hp it takes to pick up ET and MPH. Most people wont even see 4 tenths/4mph from headers and exhaust.

SLP IROC-Z

iTrader: (1)

this is a common misconception with gearing...

assuming u have a stock stall converter u will be hard pressured to get better then a 1.9 with 2.73 gears and a 26" tall tire with the power u are producing.

people assume that when u install gears the car is going magically rocket down the track 4 tenths quicker.

where the gears make the difference is at ur 60ft mark. like i said earlier ud be hard pressed to get better then a 1.9 with a stock stall and 26" tires.

what the 3.73s will do is allow the car to get off the line quicker and reduce ur 60ft time (if the traction is there), to atleast 1.8s which would give u approx 2 tenths off at the end of the track, 1.7s would be almost a 4 tenth difference. see where ur gains in ET are from a gear change?

its mechanical advantage. on the street the car will feel quicker and in essance it is, when u jump on it around town the RPMs are going to be higher up in the rpms and take less time to get there, this will give the car a better "jump" but in the long run its still accelerating the same.

there is a difference between being quick and being fast. u can take off in 2nd gear at the track and do a **** poor 60ft and still trap the same mph as if u cut a 1.6. but the ET is going to be a whole lot different.


this is not to say that every car is going to react to a gear change the same way. power, weight, transmission, tire size, etc are a big part in all this to.

Ziggster

are you sure you had 2.73 to begin with? My TA had the optional 3.42's maybe your had something like that. Just a thought.

unknown_host

iTrader: (1)

An improvement is seen at the 60', yes. However, you have to realize that the car will be trapping in its powerband with an ideal gear change, whereas with the 2.73's you will be shifting into high gear just before the traps.

SLP IROC-Z

iTrader: (1)

he should be shifting into third a ways before the traps even with 2.73s, with the converter unlocked in 2nd gear @ 5500rpms hes only going about 92mph, so he would have been shifting into third shortly after the 1/8m mark. ur trap speed is an average speed between the 1000ft mark and the 1320 mark. actual speed when going through the traps is 3-4mph higher. so if hes getting a 104 on his slips his speed is more like 107-108.

he was in his power band either way, the gear vs rpm splits are the same between the two gears, see for urself...

26" tires, 2.73s, 700R4 unlocked TC
1000 9 17 27 39
1500 13 25 41 58
2000 18 33 54 78
2500 22 42 68 97
3000 27 50 82 117
3500 31 58 95 136
4000 36 67 109 155
4500 40 75 122 175
5000 44 83 136 194
5500 49 92 150 214
6000 53 100 163 233

26" tires, 3.73s, 700R4 unlocked TC
1000 7 12 20 28
1500 10 18 30 43
2000 13 24 40 57
2500 16 31 50 71
3000 20 37 60 85
3500 23 43 70 100
4000 26 49 80 114
4500 29 55 90 128
5000 33 61 100 142
5500 36 67 109 156
6000 39 73 119 171

this goes to show if he keeps his shift point at 5500 hes still ending up at the same rpm the next gear regardless of the rear gear ratio. so with either gear hes using the same rpm range approx 3000-5500.

i agree that the 3.73s are a better gear ratio, definitly not arguing that point at all. my point is at the track all a numerically higher gear ratio will do for ya is get the car into its power band quicker off the line aka quicken ur 60ft times.

rx7speed

as far as mph if you look at the drag strip there are two markers around 10-20 feet from each other at the end
it isn't the avg between the 1000 and the 1320 it is around the 1310-1320 or so avg speed
kinda like the 1/8 mph there are two sensor thigns about 10 feet from each other there as well

unknown_host

iTrader: (1)

We can calculate and theorize all day long, but I have real world experience with this stuff. I have helped numerous people with rear gear swaps, most on radials where you DONT pick up on your 60' between gear changes, and they still ET/MPH better. I went 12.8's on a bone stock 350HO crate engine, he should be able to do much better with a cammed ZZ4 with headwork, which leaves me to believe there is problem we are unaware of with his motor (ignition timing, cam timing, faulty ignition, etc, etc). But what do i know...

SLP IROC-Z

iTrader: (1)

the HP gm rates the zz4 at seems a little on the high side. the 350 HO uses better heads and cam, it should make more power then a stock zz4. many people with zz4 crate engines dont get nearly as much power as GM claims, not very suprising seeing that its basically a carburated corvette l98 with a little bit bigger cam and slightly more compression.

5500rpm is a little on teh shy side for an LT4 hot cam, that engine should be making peak hp a little after 6000rpms. i suggest to this guy to up his shift points a bit.

SLP IROC-Z

iTrader: (1)

actually were both wrong, i did a search and found that the trap speed u get on ur slip is an average of the 1320 mark and 66 feet before that (1254).