Im sure this has been asked. But besides block and engine difference what all would be needed to turn a 740 NA to a turbo? I know the air box is on the opposite side on a turbo, what other sensors would be needed?

thanks

 

anyone, Im kinda new the 740s, I mainly stick with my 850s but am moving into the other lines. I have a couple of 940ts in the local yard which i can get parts for the 740

 

the block is basically the same, but the turbo head has sodium filled valves and a different camshaft. the turbo has a completely different oil filter/cooler arrangement since the conventional B230F oil filter would be right under the turbo.

everything from the airbox to the exhaust downpipe, including the radiator+intercooler in the middle would have to be swapped. the sensors are all on the engine and/or in the air path or radiator. you'll need the turbo's ECU and ICU. If your 740 has a LH2.2 (up to 88?), then you'll probably need the LH2.4 wiring harnesses from the 940 too.

the turbo has a beefier transmission, and different final drive ratios, so you'll want to swap those, too.

you'll probably want the turbo instrument panel as it has the boost gauge (connects to manifold vacuum), but a 940 panel might not fit a pre 1990 740 (a 91/92 740 is virtually identical to a 91/92 940, so this goes away).

Sounds like a lot of work to me.

 

the car is a 1990 740gl

 

And.. don't forget that the turbo has a point or two *lower* compression than the N/A motor...

 

I guess my question would be do you want to take the NA engine and change the components over to make it a turbo or do you want to transplant a turbo engine in this car. I guess the other option is to put in an aftermarket turbo. Either way this would be a significant job but if I were to do it I would go the transplant route.

 

yeah, the lower compression part is _real important_ ... effectively, turbocharge boost is like raising the compression ratio. if your NA engine has 10:1 compression (I forget the actual numbers), then when it sucks in a cylinder of fuel+air at atmospheric pressure (about 14psi), and compresses it, the charge is 140PSI at the top before ignition. if that same cylinder sucks in a load of +9PSI air, thats 23PSI so compressed 10:1 it would be 230PSI, which is like a 16:1 compression ratio, pre-detonation city. so, turbo engines generally have their compression lowered to like 8:1 or something (8*23 == 180psi).

 

To be honest, buy a turbo car.
By the time you scrounge all the small and large parts up, or buy a turbo donor car, with ECU, intake plumbing, different exhaust, intercooler and longer brackets for radiator etc etc, it's just easier to buy a turbo car.
The hours and money involved are significant changing everything over. Don't be fooled by the ghetto turbo swap stories, they all run like crap and blow up (but the owners never mention that stuff).

 

I second that emotion.

 

Yeah figured somebody would say that at some point. Well i got the car for free from the original owner. would love to turn it into a sleeper. or i might just fix it and sell it and buy a turbo 740 or 745. And it is just a 740 there is no badging other then that,

 

So just drive it and enjoy the car, then buy a turbo later on. People say it for a very good reason.

 

how easy would it be to do a manual swap at least?

 

transmission and shift linkage and interior trim, and the clutch + clutch cylinder. final drive ratio might be different, too, and I bet you need a different front drive shaft as the M46/47 + overdrive is probably longer than the AW70.

from what I've read here and elsewhere, the AW70/AW71 are considered 'stronger' transmissions than the manuals used on 740/940s.

 

No offence mate, but it's a free car. Spend a couple hundred on maintenance and servicing and just drive it. Save up for what you want as you drive an incredibly cheap to run and maintain vehicle.
More than likely you'll keep the car, even after you buy something else, due to how reliable these things are.
The AW boxes, if given even basic maintenance, last forever.

 

Oooh, time for my two cents!!!

I agree with the trouble a complications of swapping components. If have money, time (like you don't need the car any time soon) and just a desire to screw around and build it up, you could swap in a custom build, like a stroker redblock, the 5 cyl turbo or my personal dream: and over built twin turbo S60 I6 engine or a V8. But given that it's a free car, it's probably best for a daily driver, unless you have a healthy budget.

As far as a manual swap, I totally support that idea. I can't stand autos. I don't really consider it driving. It's just riding. You wake up a lot more responsiveness in the car when you have a stick compared to these old slush-boxes. For a manual swap, I would check around at junk yards for a whole car that you could get everything that you need. You can get away with the auto rear end, it would probably increase your gas mileage a bit because of the lower ratio. I think that the drive shafts are different.