Just bought a '71 455 as a future spare for my '71. My original 350 is working as new currently & will leave it at that. Should I be forced into the swap in the future I have a few options to choose from. I have not been there with one of these cars & don't know all the details. I have time on my side to gather/restore whatever I may need. Car currently has 2.56 open rear. Car is used only for street driving, cruising on sunny days. No tire smoking, no street racing. Occasional quick leave at a stop light but very seldom. I love getting on the on-ramp & seeing an import spot this big 'ole banana yellow Buick gaining speed. They usually floor it to make sure I'm in the rear. Hasn't happened yet, all they see are taillights. They usually don't have their 4 cams set just right.....or the NOS bottle wasn't open all the way...or the turbo didn't kick-in right....the new tail fin wasn't adjusted yet.uzzled: Option #1. Leave the freshly rebuilt original TH350 in the car. 2500 miles on it. Option #2. Get a TH400 ready. I can get the kickdown mechanism reproduced from a member here when needed. Cross member & driveshaft work to do but minor? Option #3. Local yard has a 4L60E, universal GM bolt pattern.No idea what's involved here. Thanks for your input.
There are no universal bell pattern 4L60E's. The 4L60e would require an electronic controller. I would just use the TH350. Possibly build a spare if you are worried about it failing. A properly built TH350 is very reliable to the 650-700 HP level.
or have a 4l80E built.. can be built with full-manual valve body (no electronic controller) and still be had with lockup (will need a controller for that)
Stick with your 350 the way you describe your driving habits it should last forever ( OK a long time ). You will need an adapter to run a 4L60 and you would need to change your rear gear ratio, right now its geared to high for an overdrive. The 4L80 would be overkill for your set up they are a huge tranny and use up a lot of horsepower. Goodluck Bob H.
How much bigger/heavier is the 4L80E than a 4L60, TH400, Th350? How does it "use up a lot of horsepower"?
The electronic transmissions are more efficient (both in parasitic drag & gear number and ratio) than your turbo 400 or turbo 350 for that matter- but you aren't bolting one to your 455 without an adapter, and the electronics, and retaining your mechanical speedo...I can go on and on. BTW- I burned up 3 'built' 4L60s with a measly 450 hp chevy motor. I wouldn't take one if you gave it to me. Stick with the 350, and build the 400 and keep it off to the side.. my .02.
How would a 4L80E be more efficient in parasitic drag and gear ratio than a TH400? Same components in the rear, same gear ratios in 1, 2, and 3, with an additional few bushings, thrust washers, and a couple of extra clutch packs to drive through...
The 4L60E would be overkill of overdrive. You have a 2.56 gear already so unless you're planning on go to the salt flats I'd forego the headache involved with changing to it. Having worked at Hydra-matic division on the 400 THM I can tell you for sure it was built to take just about anything you can throw at it. That is why a ton of non-GM logos choose to purchase and run it (i.e. Jaguar, Rolls Royce etc.) in their high dollar products. It is the trans others are compared to. That being said the 350 is a very good trans especially when freshed up and a little (repeat, little) harder shift kit installed to reduce slippage between clutches at shift points. If it were mine I would surely run the 350 till it fell over. Anything less than 450 hp is a walk in the park for the tranny you already have.
Use up a lot of horsepower is probably an over statement on my part but they do require more horse power to turn than a 350 and they are definately a lot heavier which would take up a little more horse power just to haul around. When we are trying to squeeze all we can out of these street type cars the 4L80 just doesn't make sense. And they are expensive to buy and repair. Bob H.
You're probably right. GM Transmission technology hasn't advanced much in 40 years. Or- Say you have a car with a th400 in it, and you do 3 seperate 3rd gear pulls on a dyno....and you're putting a consistent 380hp to the wheels....then you roll the car back 30 feet, put it on the lift, swap in a 4l60, don't touch anything else, and roll it forward back onto the dyno 2 hours later, do 3 seperate 3rd gear pulls, and your putting a consistent 395hp to the wheels...all I can suffice is that real world, maybe the 4l60 transmission was more efficient- thats all I'm saying- This actually happened. I had to settle an argument between myself and my buddy. His car, my dyno, my tools, his transmissions. I lost the bet, but learned something in the process. Just my experience.o No:
How do they require more HP to turn than a 350? I can turn the input shaft on either one by hand... If they are "a lot" heavier, how much heavier are they? I see that statement often about a 4L80E. Most of the parts in a 4L80 interchange with a TH400, so what makes them expensive to repair? Core costs are higher, but they aren't all that expensive compared to breaking everything else. A "street type" car isn't worried about gaining a few pounds, or very slight parasitic HP loss. We aren't trying to cut hundredths off our ET at the drag strip like a stock class racer would be. Think about one of the basic laws of physics, an object in motion tends to stay in motion. There is always some parasitic drag from fluid shear, bushings, thrust washers, etc, however if you have 10 lbs more rotating mass and the parasitic drag is the same, it takes the SAME amount of power to keep that mass rotating (the same speed), no matter what the weight. It does take more power to accelerate the greater weight, but this isn't even a factor until a car gets well into the 10's in the 1/4 mile. Then it is in hundredths of a second. This has been proven many times in back to back trans swaps from TH350-TH400 (almost exactly 10 lbs difference in the rotating mass). Sometimes there is no ET loss even on a low 10 second car. Sounds like "a lot" of HP consumed to me...
The 4L60 is a bit different, and should be a bit more efficient on a dyno for several reasons. Less weight, and the input drum that contains almost all the clutches is all contained, not in seperate drums like a TH400. However MOST of the power for your swap wouldn't be due to the transmission, there is one other major item that had to change when you did that swap, the torque converter. Very likely most of your power came there, and if ti was locked up, almost definitely the power came form that.
Look the guy ask a question and I gave my opinion. If you have access to a 350 and a 4L80 that you can " turn by hand " wiegh them and you tell us the weight difference. No one wants too waste their money, at least I don't and thats the standpoint I give my answers from. You give me a logical reason for putting a 4L80 behind a 350 in a street car. They are expensive as I said if you don't believe me go price them. Why spend money on something you don't need. Besides he didn't even ask about a 4L80. Bob H.
Bob, The 4L80 was brought up in the thread. I know exactly what they weigh, I also know the differences in the weight of the rotating mass. I build performance transmissions. I know exactly what they cost me to build, cores, and what I sell them for. The 4L80E isn't nearly as huge or heavy as they are believed to be by those who probably couldn't even identify one if they saw it.
Then you should also know that when you turn these transmissions by hand all you would be turning is the front pump which wouldn't tell you much. I also know that I can pick up a 350 and put it in the back of my pickup without the converter in and there is no way I would do that with a 4L60. I can buy a good 350 for under $600.00 rebuilt off the shelf. Will you sell me a rebuilt 4L60 for that price? I might be interested. Bob H.
Once again you show your lack of knowledge about transmissions... When I turn the input shaft, I would be turning the forward drum in a TH350, TH400, the input drum on a 4L60, or the overdrive assembly on a 4L80E. If you can lift a TH350 from the ground to your truck (125 lbs, short shaft, dry, without converter) you should also be able to lift a 4L60E, unless 15 extra lbs is too much additonal for you. A 4L80E weighs more but not so much that I can't also pick it up. Any OD trans weighs 140 lbs, 700-R4, 4L60E, 200-4R, they all come in around 140 lbs. The 4L80 is 30 lbs heavier than that. I can take a 30 lb hit for a trans that can live at 800+ HP in almost stock form. Yes, A Th350 is cheap and reliable, but there is no OD. I build them often, but in a street car that wants to be able to run a decent rear diff ratio, you need OD.
You are right the notches on the neck of the converter turn the pump. I'm not a transmission builder myself and I wasn't sure you were because of the statement you made about turning the tranny by hand. You can't tell if one transmission takes more power than another by turning by hand I don't care how good you think you are. And I don't really care what you run in your car. And if I have to get into an argument with someone with a different opinion I guess there is no need for someone with my lack of knowledge to reply or try to help someone. I will leave it up to the mental giants such as yourself. Have a good day. Bob Harris
You are correct, you cannot determine the HP used by turning the input shaft by hand. However a transmission doesn't necessarily "use up a lot of horsepower". I see these types of statements often by the internet experts who have never rebuilt a transmission in their life, usually wouldn't even be able to identify the different transmissions they are talking of, much less the internal components, and obviously don't understand the very basic physics involved, nor do they have any real world factual information to back up their statements. They are just repeating what they read somewhere else on the internet or in a magazine. A transmission consumes power, there is a pump to operate, clutches and/or bands that must be driven through, friction within the planetary gears, and when accelerating, the rotating mass would consume power. The amount of power consumed would depend on the weight of the rotating mass AND the rate of acceleration. A grandma car wouldn't notice a significant power loss if the trans internals weighed 50 lbs more because it wouldn't accelerate it fast enough to cause a huge power loss. An 8 second drag car would see a power loss. If you are going to make a statement, you should be able to back it up with facts, or not get upset when you are called out. My statement about turning the input shaft by hand is intentional. The common phrase I hear is "it takes more power to turn". I want to know what takes more power to turn?
Local yard has a '73 Grand Prix with a TH400. Local means 2 hour drive from here. Looks like this is the direction I will go with the car. George's site gives pretty good detail on what parts I need. I'll get the engine/trans. combo restored over the next couple years & have it ready to bolt in should I ever need it. I have time on my side. Thanks everyone for your input. Steve Craig
It took you a while Bob... I got out of it a few replies before when it was pointed out I don't know sh!t either!! :TU: I guess we know who the tranny guy is now.
