N62 Z3 Swap Supplement - Why N62

Every time I mention I am doing a V8 swap into a Z3, I get the same responses... "LS? Cool, I love those!" or "M62/S62? Cool, I love those" then I say no, N62... and am met with this face

But you know what - I love the N62. It's a phenomenal engine, so I want to write a short article explaining why it's so good and why it's bad reputation has been unfairly earned

1. Valvetronic gives it phenomenal throttle response, in theory better than ITB's

2. Only production engine to feature a continuously variable length intake manifold

3. Good power stock and have a very robust torque curve, great bang for the buck

4. Once their core reliability issues are sorted they are pretty darn reliable too!

Before I move on lets talk about that last point. Reliability. I own a 2006 X5 4.8is with the N62 4.8, I bought it with 194,000 miles and it now has 209,000 miles. Previous owner took care of the critical repairs so I've just been enjoying it and changing the oil (knock on wood). That's the thing with the N62 - they get a bad rap because sure a lot of them smoke due to valve steam seal issues. Others leak coolant from the coolant transfer pipe or leak oil from the alternator gasket. It's a mere $300 in parts to fix all these issues (okay, its more than that because you wouldn't do valve stem seals without doing a lot of the main gaskets too... but, still). And then you have a pretty solid engine which doesn't have a "kiss of death" like many other BMW V8's, between rod bearings and timing chain guides.

The great thing too is that there are upgraded components for all of it's failure points. Elring-Klinger makes Viton valve stem seals, which won't deform and fail like the original seals. Uro makes a collapsible coolant pipe that allows for easier installation and includes an EPDM seal which can withstand the presence of coolant long-term, unlike the original seal which deteriorates and causes leaking. Uro also makes Viton alternator bracket gaskets in an improved profile design for better sealing, again being Viton it should be able to seal against the oil long-term without failing.

Lets make some general comparisons to some other similar engines:

S62 - 394 hp | 500 n-m | 487 lbs*

N62 - 367 hp | 490 n-m | 470 lbs° (4.8)

S65 - 414 hp | 400 n-m | 445 lbs°

N62 - 333 hp | 450 n-m | 470 lbs (4.4)

S54 - 315 hp | 341 n-m | 478 lbs°

M62 - 282 hp | 440 n-m | 487 lbs

S52 - 240 hp | 320 n-m | 436 lbs

N52 - 255 hp | 300 n-m | 355 lbs

M54 - 228 hp | 300 n-m | 377 lbs (3.0)

M52 - 168 hp | 245 n-m | 377 lbs (TU 2.5)

* No published info but it would weigh a little more than an M62

° These engines also require oil coolers which the weight is not accounted for

I calculated the below figures with the S62's weight at 500lbs

N-m torque per pound of engine weight

S62: 1

N62: 1.04

S65: .90

N62: .96

S54: .71

M62: .90

S52: .73

N52: .86

M54: .80

M52: .65

Horsepower per pound of engine weight

S62: .79

N62: .78

S65: .93

N62: .71

S54: .66

M62: .58

S52: .55

N52: .72

M54: .60

M52: .45

If we also factor cost into this equation the N62 becomes a no-brainer, given that you can buy an entire N62-powered car for just the cost of an S65 or S62 engine.

Now lets talk about what makes the N62 so special, Valvetronic and the DIVA continuously variable length intake manifold.

Power-wise, one of the most common comparisons of the N62 is to the M62. Both came in 4.4L displacements. However the N62 had improved throttle response and efficiency thanks to the Valvetronic and Dual VANOS. In addition to that, the N62 DIVA intake gave it more torque over the entire rev range - as well as more peak HP. BMW included the below graph in the N62 technical release which illustrates the power differences:

The solid lines are the N62, the dashed lines are the M62

That torque curve being that much better is all thanks to the DIVA intake. By the way, if anyone is curious why I love the N62's "DIVA" intake manifold so much (or you are just wondering what the hell a DIVA is because you thought that was a term for a famous female singer) I wrote about it more in-depth a bit here although I will explain it's basic operational principles below.

Historically, intake manifolds were a compromised design - they could be designed to boost low-end torque with longer runner lengths, or help horsepower at the expense of low-end torque with shorter runner lengths.

In the below image we see a dyno, on which three dyno graphs are overlaid. The green dyno line indicates an intake with long intake runners, the red line one with short runners and the gray an in-between. Normally long intake runner lengths suffer in the high rpm, as you can see from the green dyno line trending downwards steeply in the higher revs. Conversely, short runners perform poorly at low rpm, which is why the red dyno comes from such a low torque rating at low revs. A three-stage DISA system allows the engine to follow the "peaks" of each dyno, to get the gains of each type of intake length without the associated drawbacks, as it varies the length between two or three different runner lengths depending on the rpm.

The above image is from an Autozine article about, you guessed it, Variable Length Intake Manifolds. It is great further reading if you are interested in this topic, link here

But the N62's is continuously variable. It is not two stages, or three stages. If we look at that above graph it has three dynos on it and the three stage intake allowed it to follow the peak of each of those. A continuously variable intake length would be as if you plotted an infinite amount of dynos and followed each of their peaks in order to fully maximize the performance of the engine over the entire rev range. This intake was one of this engine's biggest performance benefits over the previous generation M62 and is one of the main reasons for the N62's broader torque curve and higher peak horsepower compared to the M62 in the comparison dyno up above.

So lets talk about Valvetronic, which increased throttle response as well as efficiency but in itself did not do a lot for performance gains

Valvetronic is a brilliant design, which varies the valve lift from .3 to 9.85mm and allows the engine to run with the throttle body wide open in normal operation.

In order to understand what Valvetronic does and how it benefits the engine lets first lets take a step back and imagine a "normal" engine and intake system, with a single throttle body and no Valvetronic. When cruising, the throttle body is barely open, allowing in the bare minimum amount of air to maintain the engine load, the engine is aspirating normally and intaking air which causes the intake manifold to be under vacuum. If you give it throttle from this partial load state, it takes a moment for the intake manifold to fill with air since it was under partial vacuum, this delay results in a moment in which the throttle is open but the cylinders do not have an adequate supply of air - this is perceived as throttle lag.

M engines use individual throttle bodies in large part to quell this throttle lag and make the engine more responsive. As described above - when cruising, a partial vacuum is formed between the throttle body and the cylinder. By moving the throttle body to just in front of the cylinder the amount of vacuum is drastically decreased to make the throttle lag almost imperceptible.

This is a diagram for Valvetronic II which offers a lower minimum lift and a slightly increased maximum lift, compared to the N62's Valvetronic I (.3/9.85)

What Valvetronic does though is it eliminates the throttle body altogether. Valvetronic in conjunction with VANOS can determine how much the intake valve opens, how long it opens and where in the intake stroke it opens. This allows it to control the amount of air entering the engine directly at the intake valve in order to decrease pumping losses and allow for a very responsive throttle. In layman's terms, Valvetronic turns the intake valves into the throttle bodies - meaning there is no partial vacuum and the engine can respond instantaneously.

Since the N62 does not normally run it's intake manifold under vacuum, auxiliary functions that run on vacuum - notably the brake booster - are supplied by a vacuum pump mounted on the cylinder head.

So the engine can be made reliable by addressing it's key leak points, it is cheap to obtain and powerful (and lighter than an S54!) and BMW threw all the tech they had at the time at this engine, it is packed to the gills with some of the coolest technology in the world.

As BMW themselves say in the N62's technical release:

The N62 is the best engine in it's class. At this time there is no other engine on the market which uses comparable technology.

That was true in 2001 and is still true today, as thanks to the move to turbocharged engines, technology like the DIVA intake is not likely to exist again. Not to mention that all modern BMW engines, including M engines, still feature Valvetronic.

Okay, lets get to the swap!