Big V8 Builds - Why always autos?

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bankz5152

bankz5152

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Just wondering really, almost everytime ive seen someone do a big V8 conversion or the ones from Kahn etc... are always autos?

Why so? If it where me it would be a manual all day long.

I would like to, one day in the distant future, build a V8 90 soft top with either a chevvy V8 or ideally an LS3 but it would have a manual box for sure.
 
I think the autos are easier to install and obviously no clutch to worry about, also you can use an auto like a manual if you want to so why not have both.
 
Think it's because the dog style gears in an auto are stronger weight for weight than a manual, so you need a bigger heavier manual box for same power....
 
The V8 man said:
I think the autos are easier to install and obviously no clutch to worry about, also you can use an auto like a manual if you want to so why not have both.
Click to expand...

Only if it has paddle shift. Alot of the ones I saw at LRO where just normal autos. I'd be happy with a paddle shift!

Never knew auto boxes where stronger, interesting. Not sure why but Ive always wanted a big V8 Defender, just think it would be hilarious fun.
 
With big engines and heavy cars, especially in the US, manufacturers tended to prefer some sort of fluid coupling between engine and gearbox to help dissipate shock loads. Whether it's a fluid flywheel or some sort of hydrodynamic drive, it's the fluid that transmits the drive. Given that many V8 engines are US derived, and many standard US transmissions were designed to mate with these it's not surprising that you find a greater variety of auto boxes that can be fitted to US engines, and the boxes themselves have been developed to cope with the forces from v8 engines and the rigours of propelling a 2 ton plus car. So when people are retrofitting V8s it's often just easier to fit a matching transmission, rather than mess about with trying to find a tough enough manual gearbox (because most UK car-derived ones will be over-stressed), then getting one-off adaptors made up that will allow things to fit together, and so on.
 
bankz5152 said:
Only if it has paddle shift. Alot of the ones I saw at LRO where just normal autos. I'd be happy with a paddle shift!

Never knew auto boxes where stronger, interesting. Not sure why but Ive always wanted a big V8 Defender, just think it would be hilarious fun.
Click to expand...
hell auto boxes are in 1000hp vehicles from semi truck to off road construction/mineing equipment. them things are tought. it is nothing to get 300k miles out of a auto transmission, with nothing more than fluid and filter changes, over heat your engine and you are cooking your trans fluid
 
The mg zt 260 uses a 4.6 ford v8 and getrag 5 speed manual. 260 bhp and 310 lbft torque produced but a good few road cars have been supercharged to around 420 bhp and dreadnought racing compete with one. The gearbox seems to be up to it.
4wd is another matter unless you want to do donuts in a defender :)
 
A good auto coupled to a big engine is great to drive :D

Most of the autos have a shifter in a PRND321 pattern, which allows you to lock out higher gears. What this means in practice is that you can force a downshift- you're following a truck and want to overtake: move the shifter from 'D' to '3' which will lock out fourth gear and cause the transmission to drop a gear ready to go when the road is clear. Similarly you can use it to hold a lower gear during acceleration, then use the shifter to allow the transmission to upshift. Not quite full manual control, but it does what you need. On the P38, presing the sport button while in low range gives you full manual control- the gear number on the shift gate is the gear you're in.
 
Hmmm thats cool as well. Learning quite a bit from this thread! Explains what the 1 2 3 buttons where for!

That is the big problem it seems, finding a transfer box that can take the power. That said according to Jim at Gigglepin the TX box thats in the TD5s (forgive me I cant remember the name) can safely tame 300bhp and can handle 400bhp.

Still though im not 100% id be happy with an auto in a car thats meant to be fun. Great in an RR because its meant to be simple, easy and comfortable.
 
bankz5152 said:
Hmmm thats cool as well. Learning quite a bit from this thread! Explains what the 1 2 3 buttons where for!

That is the big problem it seems, finding a transfer box that can take the power. That said according to Jim at Gigglepin the TX box thats in the TD5s (forgive me I cant remember the name) can safely tame 300bhp and can handle 400bhp.

Still though im not 100% id be happy with an auto in a car thats meant to be fun. Great in an RR because its meant to be simple, easy and comfortable.
Click to expand...
Hell dragster doing a 1/4 mile in 4 seconds with 3000k hp or more use autos2 or 3 speeds and shift them Manuel less shock to the drive train
 
bankz5152 said:
Just wondering really, almost everytime ive seen someone do a big V8 conversion or the ones from Kahn etc... are always autos?

Why so? If it where me it would be a manual all day long.

I would like to, one day in the distant future, build a V8 90 soft top with either a chevvy V8 or ideally an LS3 but it would have a manual box for sure.
Click to expand...

Right box will be OK, land rover box can't take big torque
 
Manual gearboxes on a large engine inevitably need a fairly hefty clutch to take the torque, which can literally be a pain in traffic. Auto is good for off road driving too as the torque converter takes up the shock loads without overstressing anything. You can use the manual downshift to control the gears depending on the terrain.

A few years back I'd never driven an auto, but having driven a couple of different vehicles with various auto boxes I'd probably choose one if I was to buy a new car now. A good automatic can be both convenient and fun to drive. Badly set up automatics really are terrible though. You need the right torque converter to suit the engine (too small and the engine will rev like mad without going anywhere, too large and it will bog down at low revs) the gear ratios need to be right, and the kickdown cable or ECU need to be set up properly to shift at the right speeds.
 
Ahhh yes, clutch. Totally missed that...

So basically the reason why its done is because its just 100x times easier and more convenient, without much downside.

Anyone ever done a paddle shift Defender? Or is that just a whole new pandoras box?
 
bankz5152 said:
Anyone ever done a paddle shift Defender? Or is that just a whole new pandoras box?
Click to expand...

With those you'd be looking at a much more modern transmission, which would be ECU-connected to the engine rather than a standalone unit. Without the right signal inputs from the engine it won't work well if at all. I don't doubt it can be done, but wouldn't be easy.

I'd like to try fitting a column shifter to a defender- seems like it would be the best place to put it, particularly if you had 3 seats in front or a large cubby box.
 
Other consideration is the higher gearing, especially in first gear you get with an zf4hp22 auto box normally bolted up to the rover v8. Means going slow off road is more difficult.
 
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