JesasaurusRex

iTrader: (3)

Ok well now that i have your attention heres the thing. Currently useing a T-5 tranny and trapping 130 in the 1/4, car is roughly 3000lbs at race weight. Now looking at either a power glide or a th400 as my next tranny. However both trannys ending in a 1:1 ratio isnt going to make the freeway driving any fun. So a friend suggest to me useing the Th400 as a glide with od. So basically crossing the traps in second gear (1.48:1) instead of 3rd (1:1) Now on paper this thing seems to make sence.

Wanting to cross the traps at 6500rpm useing the power glide id need a 4.30 final drive gear and a 28" tall tire, top speed would be 125.9mph now im guessing that makes sence since going from a standard tranny to an auto id be loseing some mph so that would be fine and dandy. Except ofcourse still no overdrive.

So useing the th400 and wanting to cross the traps at 6500rpm and in 2nd gear, so i could use 3rd as an OD, id need a 3.0 final drive gear and a 29" tall tire and it should put me across the traps at 126.3mph and leave me 3rd gear to cruise back on the highway with. Now i know i didnt take into account converter slippage and I know the Th400 is gonna take more power to turn than the glide and what not but I just want to know why i should or should not do this. Im certain im not the first person to think about this, actually i know im not cuz a friend suggested it to me. Id like to know other peoples takes on this. Should I do it? Or just do 40 on the highway now on with a 1:1 final tranny gear thanks yawll.

AlkyIROC

Powerglide first gear is normally 1.76. That would be like starting off in second gear with a TH400 or TH350. The weaker PG gear set is a 1.82 first gear. Aftermarket straight cut gears are available in 1.80 ratio.

All the transmission gears are for is to multiply torque to get a heavy vehicle moving up to speed. Once you're in high gear, it's all HP. If you have enough HP, you don't even need low gears. There are some racers who have a PG modified with about 10 direct clutchs and only use one gear.

What you're trying to do isn't practical, cost effective or even possible inside a TH400. If you feel you need an OD gear you can either use a 200-4R tranny which has roughly the same gear ratios as a TH350 but also has an OD or get a TH400 and have a Gear Vender OD attached to the end of it.

OD gears are small and weak and are not designed for high HP or torque appilcations. They're designed to bring engine rpms down at highway cruising speeds to improve fuel economy.

Changing gear ratios inside an automatic tranny is not as easy as inside a manual transmission. Sun and planetary gear sets have very few if any ratio options and you can't make a non OD tranny into an OD by changing internal parts.

You've only got 3.73 gears. Highway driving without an OD isn't such a big thing yet. Before the mid 80's when OD trannys started becoming popular, hundreds of thousands of muscle cars did it all the time.

84z28350

Its not nice on the bank account running 1:1 with tall gears but you also dont need to be doing 100mph!

Ive got a TH350C (1:1 third..) and 4.11s in the rear, the lockup is not wired so i always have some slippage on the highway which really makes this car just that much more expensive to run on the highway. This thing screams bloody murder above 100km/h (60mph) and without the use of an aftermarket tach to see how close i actually am to putting a rod through the block, im not going to be going much faster.

If i were you i would opt for the gear vendor OD unit, neat little piece but pretty pricey. But depending how many highway miles you put on it can easily pay for itself in fuel and maintenance costs!

JesasaurusRex

iTrader: (3)

ok you didnt read anything i wrote ... or i completely wrote everything wrong

i dont want to change the gears in any transmission. Its like this, if i use a power glide with 4.30s and a 29" tire id go through the traps at almost the same speed (in its final gear of 1:1) as I would with a th400 with a 3.00 rear end gear and a 28" tall tire in 2nd gear (1.43:1) and then id still have the 1:1 final 3rd gear in the th400 and a really low 3.00 rear end gear to keep the engine rpms way down
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Thats just the thing, with the glide it would be utterly useless, but id be useing the th400 down the drag strip like a power glide because id only be useing 2 gears. Then the 3rd gear yes would be 1:1 but id only have a 3.0 rear end gear and thatll keep the rpms way down over say 4.30s that id be using with the power glide.

86interceptor

definately use the 400 turbo trans. you will be much happier with your wallet

JesasaurusRex

iTrader: (3)

lol, ya it looks nice on paper but i know im not taking something into account like some weird physics cr*p

TraviZ

iTrader: (2)

i agree, go TH 400

JesasaurusRex

iTrader: (3)

But why bish, here ill do the math for you guys that i had to do for everybody else on a different forum

a power glide with 4.30s in the rear and a 29" tall tire [1st gear(1.82x4.30=7.826)] [2nd gear(1.00x4.30=4.30)]is almost exactly the same as a th400 with 3.00s in the rear with a 28" tall tire[1st gear(2.46x3.0 =7.38)] [2nd gear (1.46x3.00=4.38)]

So 1st will be a lil slower and ill make up a little of that in 2nd, spin the same RPMS and have a 1:1 with a 3.00 final drive gear to save gas

TraviZ

iTrader: (2)

i say th 400 because you have sticky enough launch to use that first gear to get you going real good. and with the 3.00 gears, you still have that 1:1 for the highway which you wont be using on the track.

kg4chm

Whats the weight of the car? Usually wont see any increase in performance by going to a PG in a car thats over 3200 pounds..........I say USUALLY.....some people may have seen an increase in performance.
In other words PG's are better for light cars (under 3200#) and anything over would be better off with a TH350 or 400.......TH350 is lighter of course. I would go with the 400 over the 350 though. A friend of mine actually ran over half a second faster by going to a TH400 from a PG. Then he decided to switch to a TH350 to save weight and the car ran the same as it did with the TH400.

JesasaurusRex

iTrader: (3)

As of now about 3000lbs race...i only see it getting heavier before lighter tho, still need to put a cage in and ive put some beefier suspension parts on. So id say 3100-3200 when its all said n done. Why would it go faster with a th400 if the gearing comes out close to even? If anything itll be slower just because its got a great parasetic loss plus the weight...not really the point tho i would like somebody to give me a negative reason (other than the weighing more more parasetic loss) for why not to do the th400 set up and only use the first 2 gears in the 1/4 and throw a 3.00 gear in the rear

84z28350

Just a little FYI, no matter what you do you dont have overdrive, just higher gearing!

JesasaurusRex

iTrader: (3)

FYI you're not helping

84z28350

Go with the Th400, its going to be a bit more street friendly than the PG. Theirs just something about only having 2 gears that sounds like it would be just plain brutal to drive around town!

JesasaurusRex

iTrader: (3)

itll be just a brutal on the street tho ... just more friendly on the highway

Apeiron

Why not run a 1.75 or so gear on the rear with the TH400 and only use 1st gear? It'll be like having two overdrives.

You'll probably go fastest using the TH400 with whatever gears you need in the rear to put you across the line at redline in third. That way you'll have the benefit of the extra torque multiplication of the lower first two gears.

JesasaurusRex

iTrader: (3)

I realize that, ok lets just say i do the 4.30 thing with the th400. Now 1st gear is a little less agressive than it is now

T-5 (2.96x3.73 = 11.04)
TH400 (2.48x4.30 = 10.664)

How much gear is too much tho? I know theres plenty of 10 second cars running a glide so why cant I be just another? Especially with a 9-10" wide tire it doesnt take much to over power them. So yes the 400 as of this moment with the correct gearing to cross the traps at the end of 3rd would most likely be the fastest way down the track. Then again, a glide might be, i honestly donno. Only thing im worried about is if i get the th400 how do I know first gear wont be as useless as it is on my T-5?

AlkyIROC

That's all a T56 is. It's a 4 speed tranny (compare the gear ratios to an old 4 speed) with 2 overdrives. You just happen to have 6 gears. My 4L80E tranny in my truck is only a 4 speed but an aftermarket kit can allow it to add OD to every gear making it into a 6 speed. 1-1OD-2-2OD-3-3OD <-3OD is what fourth gear really is. Technically a Gear Vendor OD on the back of a TH400 can do the same thing.

18 speed Eaton Roadrangers transmissions in highway trucks do not have 18 gears. You can drive them around with only 9 or 10 gears. The other gears are from using a splitter which is like giving each gear an OD.

I like the reply above. It's not so much that you want to change transmission gears but you want to change tire size and diff gearing to get the same results. Going from 26" tires to 28" isn't an overdrive gear because it decreases the effective ratio of all the gears. Without changing the diff gears, the taller tire will increase your top mph but will also decrease the mechanical advantage off the line for a slower 60' time.

Properly set up for 1/4 mile racing, your tire height, gear ratio, engine rpm should have you crossing the finish line at or just before your shift point. If it's a lot sooner then you're run out of rpm before the end of the track. If it's later, then you've run out of track before the engine peaks out.

You could put 30" tall tires on the car with 2.77 gears. It would be a snail off the line, probably cruise down the highway in high gear at 1500 rpm and have a top speed of 150+ mph but that's not the same as having an OD.

Best case situation. GM produced the 700R4 tranny. It has a deep 3.06 first gear to get you off the line quickly. Why? Because common diff gearing is 3.42 or worse. Now with those 3.42 gears, you add in the 700R4's OD gear and you now have a respectable gear ratio for highway driving. Complicate the matters by installing some 4.10 or 4.56 gears. You now have too much torque off the line with the low first gear. The OD will still help slightly for highway driving but not as much as having a second OD gear.

JesasaurusRex

iTrader: (3)

Ok so lets say i toss that idea, and just gear it to cross the traps at the top of 1:1 in any tranny i get. Which tranny would be for me? Th400 or glide? Id like to throw a 200 shot at it in the future if that changes anything. Which and why. Thanks fellas

AlkyIROC

The reason 10 second cars can run a glide is because of torque. My first gear is 1.76 and I have 4.56 gears in the diff

1.76 x 4.56 = 8.02

My engine puts out approximately 765 pounds of torque at my launch rpm.

8.02 x 765 = 6135 pounds of force to the wheels at launch a 3000 pound car.

Now using a more modest car putting out 500 foot pounds of torque using a TH400 and 4.30 gears

2.48 x 4.30 x 500 = 5332 pounds of force to the rear wheels. To get that same amount of force as mine to launch the car, this car would need more gear in the diff, lower first gear in the tranny or a lot more torque. Bump this car up to 4.56 gears 2.48 x 4.56 x 500 = 5654. Just over 300 pounds more force to get the car moving.

JesasaurusRex

iTrader: (3)

I understand the #s (thats what i was doing all the math for) but why shouldnt i do the glide approach? Currently on motor i ran a 11.1@129 with a gay *** 1.74 60.

Apeiron

If you have enough torque that you're going to burn the tires off and go nowhere when you launch in 1st gear in the TH400, then use the powerglide.

AlkyIROC

The gear ratio choice is always the last thing to calculate. You know what the engine's peak rpm is. You've stated it crosses or will cross at 6500 rpm so that's now a fixed number. If you can bump that to 6800 or even 7000 then it will change other things but we'll use 6500.

Tire size. Width is just a size that fits between the fenders. There are low 10 second cars running on a 9" slick. Height is the inportant thing. A tall tire gives a longer footprint on the ground so the tallest tire you can squeeze under the fenders is best. Width will just be whatever will fit with the selected tire height. Lets say you squeeze a 30" tall tire in there because 28" although it will fit, it will still leave lots of room.

Now we have a max rpm of 6500 and a 30" tall tire. Using some easily available calculators on the web, 4.30 gears will give you a top speed of 135 mph. 4.56 gears will give you a top speed of 127 mph although I'm not sure if these are 1/4 mile or just plain top speeds.

AlkyIROC

As a comparrison, when I had a 383 under the hood, I ran a TH350, 27.3" tall tires and 3.27 gears in the diff. The car ran high 11's at 117 mph. Trouble was, the gearing was all wrong. I was shifting at 6800 rpm but crossed the finish line at around 5500. The engine was just starting to pull hard as I crossed the finish. Changing the tires to 28" tall and going to 4.10 gears allowed me to use more rpm and it dropped the ET into the low to mid 11's and the MPH had a slight increase

JesasaurusRex

iTrader: (3)

Thats what im asking...from experience(which im lacking, first 10 second car, never used an auto) as of now 1st is pretty useless for me. T-5 tranny so 2.96 x 3.73 (only using that gear cuz its what i have and i dont wanna drop a load on a gear change for a 7.5" 10 bolt when it could snap any pass) now with the 26" tall tire its the closest size thatll put me through at 6500rpm. Second gear is 1.96...and the th400 is right in between those. So from personal experience i donno what to get. All i know is that with a standard tranny its trapping damn near 130 and the reason im scared to get the 400 is because i only plan on going faster (its never fast enough) and i dont wanna be stuck with a tranny where 1st will be useless again.

AlkyIROC

Watch a SuperGas car run 9.90's. Many of them use a TH400 because it allows the engine to stay in it's powerband longer. The amount of torque they produce is even more than I do however they also normally use a 33" tall x 16" wide slick to handle all that torque.

I like my PG because with only one shift, there's less to go wrong. I've considered installing a device to do the 1-2 shift for me but have it set to shift by time instead of rpm. Instead of shifting at 7000 rpm around the 1/8 mile mark, have it shift 2 or 3 seconds off the start line. I get into high gear quicker then it's just a high hp pull to the finish. ET will slow down but consistancy will increase and that wins bracket races not speed.

There's also a weight and power consumption factor. A PG is about 97 pounds. A TH400 is about 130 pounds. The PG only uses up about 18 hp while the TH400 uses around 44.
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From many racers standpoint, any car that runs quicker than 11.0 will like a PG. It's just that a PG won't be a friendly street tranny. It'll work, but it just won't be as friendly as a 3 speed tranny.

JesasaurusRex

iTrader: (3)

ok...so if you were in my shoes which would you do? The glide is looking like a nicer and nicer option...especially with the future nitrous

AlkyIROC

Depends on your budget. TH400 is a harder swap but still common for a street car. The TH400 is still easy to find since GM stopped production in 1990.

The PG is harder to find, it's very cheap to build, it can take a lot of abuse with some simple aftermarket parts. It will fit anywhere a TH350 will normally fit. Like the TH400, there's more than just one variation so you don't want just any PG.

For a full race car, I'd recommend the PG. If it's street/strip, put in a TH400. There's a lot more to it than just which is better. Vehicle weight, traction, suspension setup all will determine which tranny works best.

JesasaurusRex

iTrader: (3)

ill be ordering either one from mikes transmissions

either the ultimate glide or the competition th400 (i think it was the competition, which ever one was the highest one)