Why is the TH125 so much slower in the 1/4 than a stick?

product1620 · Post by **product1620** » Fri Apr 28, 2006 7:56 pm

Is it because of higher power loss through the auto, or because the smooth, drawn out granny shifts? Whats the deal?

crzyone · Post by **crzyone** » Fri Apr 28, 2006 8:04 pm

Yes and yes. Auto transmissions have more loss (20%+) than a manual transmission (around 15%)

A shift kit and a higher stall on an auto will improve track times as well.

When you get into the big power, autos are generally faster because they are easier to launch off the line, and there is no way you can outshift an auto with a shift kit.

product1620 · Post by **product1620** » Fri Apr 28, 2006 8:12 pm

So it wouldn't be pointless to kit the th125?

whipped · Post by **whipped** » Fri Apr 28, 2006 8:28 pm

more loss, and the low stall converter. Who launches their manual at 1800 rpm? :la:

product1620 · Post by **product1620** » Fri Apr 28, 2006 8:31 pm

What converter would yall sugget? It still has to be streetable.

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Apr 28, 2006 9:31 pm

I doubt you will want to pay for a higher stall performance converter. Protorque makes one. Its around $300 though. Not too many fiero owners feel the need to swing that sort of cash but it will make a bigger improvement then a power pulley for sure.

Another problem with the auto tranny is its only 3 spds. That third gear is an overdrive gear. So its a total dog up top.

When I had my 85 GT auto on the spray it was pretty quick the first two gears. 60 came in the low to mid 5's 1/8th mile would trap 75, qtr mile I would only trap 90 mphish. To me thats horrible. It would start really falling off near the top of second as seen in the 18th mile trap speed and by the time I hit the qtr mile everyone was going by me. I would always get raped the last half of the track. The competition would run the same Et's as me, but would go by me up top because they would trap around 100 or so.

I didnt' have any work done to it though. With a higher stall converter and a shift kit, you can see around 2-3 more mph in the qtr and prob knock off .2 -.4 in the qtr. I prob could have cracked into the 13's with a shift kit. My best was a 14.1

product1620 · Post by **product1620** » Fri Apr 28, 2006 9:42 pm

14.1 is very impresive, how large of a shot were you running?

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Apr 28, 2006 10:46 pm

The Dark Side of Will · Fri Apr 28, 2006 11:38 pm

Shaun41178(2) wrote:Another problem with the auto tranny is its only 3 spds. That third gear is an overdrive gear. So its a total dog up top.

That depends on a number of things.

The actual 3rd "gear" is direct. However, it has the chain ratio upstream of it and the final drive downstream. There are 3 final drives and 4 or more chain ratios for the 125, so there are quite a few gearing options from which to choose. http://home.comcast.net/~fierocave/ratio.htm

Changing chain ratios has the same effect as changing final drive ratios, EXCEPT that the chain ratio is upstream of the shifted gears. This means that going to a shorter chain ratio puts more torque through the guts of the transmission. This can have adverse consequences, especially if you are significantly increasing your engine's output with a power adder. When I turbo my 6000 AWD, you can bet I'll have the tallest chain ratio available in it to minimize torque through the transmission. This will enable me to crank the boost up more and make more power without destroying the trans. I'll also end up coming out of 1st upwards of 50 mph and out of 2nd upwards of 85 mph.

Torque convertor will help, but only so much. The Fiero engine makes most of its torque at low RPM, so it doesn't need a lot of stall to get going quickly.
No matter what you do to the auto, you'll always be down on WHP compared to the stick guys because the auto will always chew up more power. If you're going to upgrade the auto, do HP increasing mods as you do to make the most of the combination.

Pyrthian · Post by **Pyrthian** » Mon May 01, 2006 9:40 am

and, among the crap above, theres also the added weight of the unit itself. and the stupid long 2nd gear....ug

z.MacK · Post by **z.MacK** » Thu Jun 29, 2006 9:57 pm

If I remember right, it shifts into second around 45, hits third at about 65-70.... thats if your shifting at 6000R's.

That would be why it sucks.

Shaun41178(2) · Post by **Shaun41178(2)** » Thu Jun 29, 2006 10:38 pm

my auto shifted out of first at like 35 if I remember right, and went to third at 75 then at 78 at WOT cut to that OD or whatever it was. I think the TQ converter locking up is the precise way to say it. I actually ran faster by disconnecting that switch so the tranny didn't lock up the converter

z.MacK · Post by **z.MacK** » Fri Jun 30, 2006 9:34 pm

ya it is 35mph into second.

Either way, I lost a race to my friends pontiac6000 that had a 4 speed auto and a 2.8

The thc125 is shit.
Only thing its got going is its really strong, I beat the shit out of mine and it still runs fine. It is just so fucking slow!

The Dark Side of Will · Fri Jun 30, 2006 9:45 pm

The 1-2 shift mph depends on the chain ratio. As was previously mentioned, there are three or four available.

Is your car a V6? Was the 6000 modded? A-bodies are light, but I would have expected a Fiero to be lighter and the 125 to have less loss than the 4 speed.

They ARE very reliable. The one in my 6000 AWD is still going strong with 220K on the clock. My WOT upshifts are 41 and 74 mph indicated. I bet it handles better than some of the Fieros on this forum.

wheelman · Post by **wheelman** » Mon Jul 03, 2006 1:58 pm

Shaun41178(2) you said you disconected the switch so that they torque converter didn't lock up in the tranny and you ran faster. What dose they torque converter lock up do(dose it just make the car go into overdrive so you get better gas mileage). Will this hurt my tranny at all? Where is the switch located at if you remember?

wheelman · Post by **wheelman** » Mon Jul 03, 2006 2:09 pm

Shaun41178(2) you said you disconected the switch so that they torque converter didn't lock up in the tranny and you ran faster. What dose they torque converter lock up do(dose it just make the car go into overdrive so you get better gas mileage). Will this hurt my tranny at all? Where is the switch located at if you remember?

The Dark Side of Will · Mon Jul 03, 2006 8:46 pm

Shaun41178(2) wrote:my auto shifted out of first at like 35 if I remember right, and went to third at 75 then at 78 at WOT cut to that OD or whatever it was. I think the TQ converter locking up is the precise way to say it. I actually ran faster by disconnecting that switch so the tranny didn't lock up the converter

That's really strange. My 6000 shifts at 41 and 74, but stays unlock WELL above 80... takes a million years to get there, too.

Shaun41178(2) · Post by **Shaun41178(2)** » Mon Jul 03, 2006 11:20 pm

the switch is on the side of the tranny under the intake tube. Its in the valve body pan on the side. Its a little blue connector. Its just an electrical connector so it pulls out like a normal connector. Unplugging that keeps the TC from locking up, and I picked up about a tenth or so in the qtr.

wheelman · Post by **wheelman** » Tue Jul 04, 2006 9:15 pm

dose the torque lockup make you get better mileage?

Shaun41178(2) · Post by **Shaun41178(2)** » Tue Jul 04, 2006 9:26 pm

yes leave it plugged in when driving around town. I only unplugged it when racing.