One & Two: Totally agree w/you. Three: I don't believe a 400WHp bimmer is any more reliable for the same reasons you mentioned for the VQ. I assure you it can be broken if driven hard enough. Maybe the Bimmer drivers don't beat on their cars as much?

Reliability is obviously greatly dependent on how heavy one's right foot is. Just because Christian's car is tuned to 600+ WHp doesn't make it any less reliable. His motor should last quite a while if his boost controller is set to WG spring pressure and he doesn't drive like a maniac.

In the end, people will pick the car that suits them but I'd say the Nissan camp wins the battle of absolute Power/Price ratio.

 

A reflashed 335i (with the oil cooler) should be plenty reliable assuming you're not going for some retarded boost. If I got one of these cars, I'd do the standard reflash which would put the car at around 330whp/370wtq, if I remember correctly. That's LS3 territory and would put the car solidly in the upper 12s and mid 12s on drag radials. Do some exhaust work and you can add another 15whp/wtq.

Motors designed for boost are generally much stronger as are the drivetrain components. When you're only increasing power by 20%, you're still within the realm of safety......except for the clutch, especially on DRs or slicks Adding boost to an NA motor introduces all sorts of possible problems including:

1) Detonation on throttle tip-in/initial boost. Essentially the ECU isn't smart enough or quick to adjust A/F when a turbo initially ramps up. This is where many a boosted NA motor has been lost.

2) Horrendous MPGs. Most tuners go super rich on the A/F to keep the combustion chambers cool under boost. This results in lower mpgs, clogged cats, and a somewhat laggy feel.

3) Sound and clearance. OEM turbo cars are designed to reduce the odd noises of turbos. NA cars are not therefore you get lots of whistles, piping clanks, additional NVH, etc because so much junk is crammed under a hood not designed for said junk.

4) Drivetrain. These trannies and differentials are not designed for the torque loads of a turbo.

5) General driveability. No matter how good a tuner you get, your always going to have odd driveability quirks that pop up under certain load conditions, weather conditions, high engine temps, and for no real reason at all.

6) General reliability. NO aftermarket turbo setup is remotely as well designed as OEM. Millions are spent ensuring that these OEM turbos can handle sub zero and triple digit temps, have no leaky seals or pipes, cooling systems are adequate, and clearances/tolerances are acceptable. These cars are designed to go 200K+ miles. Nissan never had intentions of the VQ35/VQ37 lasting any set time under boost.


I will never own a boosted NA car. Never. I don't know of a single owner of one of these cars that hasn't had issues and as had to make really good friends with one of the local tuner shops so as to keep these cars running correctly. I want my cars reliable and a boosted NA car will never be truely reliable.

If Nissan really thought the VQ35/VQ37 was capable of handling boost reliably, it would have used a slight revised verison in the GTR. Instead, the GTR's VR38DETT motor shares nothing with the VQ other than V degree, number of cylinders, throttle bodies, cams, and valves.

 

A boosted NA engine is almost never going to be as reliable as a boosted factory motor.

The only na motor that was boost ready (over built bottom end) was the old SR20 engine.

 

While I see your point...I will say your reliability is only as good as your tune. A fully built motor can be blown on a crappy tune.

 

So by this reasoning, wouldn’t an FI’d G be just as reliable as a 335 if the G’s power were only boosted up to 330 WHp?

IMO, motors and drive train components are designed according to the specified output of the motor. The engineers are not going to spend the extra cost to “over-design” a motor for more strength just because they know it is forced induction. In other words, the 335 is designed to 300 Hp with some margin of safety. Anything more than that chews into the safety margin. Same is true for the G. All I’m saying is if the power output of both cars is raised by 20% by whatever method, both of them are potentially less reliable. As a matter of fact, I would speculate that a 20% flashed 335 is maybe even less reliable because of the steeper torque curve up front whereas the torque curve on a 20% boosted G is more level across the entire RPM range.

Not sure if one can say the ECU on the bimmer is any smarter than the one on the G. If the G’s ECU were reflashed using OSIRIS, it is essentially using the stock MAF so no corrections are needed as if using a piggyback or stand alone.

Yes, but TT cars are not always in boost so they are not always running rich. Again, this is directly related to the drivers right foot. If not on boost, a TT car is running 14.7 A/F like any other N/A car. Obviously, the mileage will suck if the motor is on boost all the time. But the same is true for the 335, right? Cats don’t get clogged because most aftermarket TT cars use test pipes. One can therefore even argue that under vacuum, the car without cats will even get better mileage because of no exhaust restrictions. BTW … I’ve been getting 18 mpg in my car combined city/hwy. The laggy feel does not exist when using properly sized turbos. Remember, the G already has 306 Hp without boost.

That’s all in design of the kit and the installation workmanship. Those that have rode in or driven my HR-TT actually say it runs quieter than a comparable N/A car with HFC and catback.

Again, the drive trains of BOTH the 335 and the G are both susceptible to added stress, whether reflashed or mildly boosted to a comparable amount.

I would think this depends on the type of engine management and the tune. If both are cars are using reflashed ECU’s, the driveability should not change because they are using the factory tables when not in boost (most of the time). The tune is obviously more critical while under boost.

Well, maybe the millions are spent because of higher overheads? I honestly don’t I know if the materials used on a N/A bimmer is any different than on a TT bimmer. Maybe all BMW did was “slap on” twin turbos. After all, the first 335’s did have cooling problems. Shouldn’t that have been caught during testing? In any case, we must compare apples to apples. In the end, the bimmer is also compromised when it is reflashed to make more power than designed. Again, I submit that if both cars have equivalent added power, both cars are potentially less reliable to a similar degree.

Well, technology has come a long way which should lead to better reliability. I suppose the community will learn whether or not this holds true as more HR/VHR motors are boosted. But I have always learned that there is ALWAYS room for improvement on anything.

I never believed the HR/VHR was designed for boost. But it has been shown that substantial design improvements have been made over the previous DE design making it more boost friendly. The DETT motor is hand built by a single technician which obviously does not make sense for the G’s selling price. And we all know even the great GT-R is not bullet proof. There are various threads from GT-R owners that broke their transmissions when launch control is used.

I think in short, we can agree that any car can be broken if driven hard enough and that both the 335 and the G are equally compromised when comparable power is added. However, if one were to build both cars to make 600+ WHp with similar reliability, it will be less expensive to build up the G. But the Bimmer is less expensive to build up to the limits of it's turbos.

 

Both na and boosted engines are probably designed to be x% stronger than they need for various reasons. But consider this. The VQ/HR motors are probably close to it's design limits. BMW's TT is putting out crap loads of power, it's only 3.0 liters and it's in it's infancy for it's production run. I'm sure BMW put a ton of design considerations for strength and reliabilty because this basic configuration is probably going to power many of the models in the future.

Turbo engines have different design considerations than na engines do. Mainly heat and stress. You won't build a NA engine to turbo spec stresses if it will never see oem turbo duty. But if you have a boosted oem motor and if you want to use it in upped boosted form for possible M or racing use, you will build the bottom end well from the get go.

 

The VHR is only in its second production year as well, so both designs are relatively new. Without doing the analysis ourselves, we don't know what the design margin of safety is for each motor which is why I assumed they are the same for the sake of arguement. I also wouldn't say I know the VQ is close to it's design limits. We know for sure the crank journals are completely redesigned from the DE and the rods are significantly thicker making for a much stronger and more rigid bottom end. I would actually be a little more concerned about pulling equivalent power from a comparable configuration (V), lower displacement motor.

I agree about different design features, all I'm saying is both motors are designed to run about 300Hp using different induction methods. Both motors are potentially compromised if we up the power output.

We can only compare reliability of both motors running comparable power since they have roughly the same baseline output, e.g. stock to stock, 400WHp to 400WHp, 600WHp to 600WHp. It is certainly possible that BMW designed their motor to handle 330WHp from the get go, but I seriously doubt it otherwise they would have done it and would have slapped Infiniti in the face with that fact.

We just shouldn't compare the reliabilty of the stock TT in the 335 to an aftermarket boosted G because the G is adding power that is outside it's design spec and the bimmer is not. Again, both motors are compromised if they are adding equivalent output. The bimmer is no more reliable than the G if they are both pushed to 330WHp, 400WHp, etc.

 

Last time I attended a track event last year, I had to chance to meet up with two 335i owners who were tuned, one of them with drag radials (great guys btw). The one with the drag radials was running high 12's all day. The other was running low 13's on wider street tires. This is the same SoCal track where stock G37's would be running low 14's at most, mid 14's for G35 6MT's. Stock 335i's and E46 M3's were running high 13's (13.9-13.7).

Both of them ended up with broken cars (engine & ECU problems). Yes, they both had oil coolers.

I'm skeptical as to how you can claim that a tuned 335i making low 400 whp is any more reliable than a turbo'd VQ37VHR making the same power. The HR and VHR is a whole different game than a DE.

 

Mike,

Kudos for this thread. I like the mathematical approach you are using rather than the "this is just the way it is" approach.

Considering how different their powerbands are, this is definately not a simple yes or no answer when it comes down to which car is faster; that would be too general of an answer. Too bad the G37 is heavier than the 335i. If it wasn't, it would make up for a real interesting head to head battle without the additional and very important variable [weight].

 

Great thread. Civil view points on both sides without dumb bickering.

 

The BMW motor is probably designed to be upped to well over 3.5 liters (Probably up to 4 liters) in it's development lifetime. IMHO, it's built to hold well over it's oem ratings. As this basic motor will power diff models and probably power the M version? Look at the hp diff BMW got in it's NA M and non-M versions.

The HR series are new but how large go you think it can go before reaching it's physical limit vs it's intended design? A V6 can go only so big before becoming a truck motor

 

You have to remember, the 1st gen G35 FI was tuned by a fuel regulator and a split sec box. I believe these modded BMW turbo motors will get much more reliable as the tuning on them matures (as it did with the VQ35)

 

We all know that both the 335 and the G are both rated to around 300Hp. But again, the point I’m trying to make is we do not know how much margin of safety each manufacturer designed into their respective motors. The only thing we can say for certain is the motors as configured are designed to around 300Hp.

Adding power to the stock block of both cars potentially compromises their reliability.

As for upping the displacement, sure, it can probably be done to both motors by boring, stroking, adding sleeves or a combination of each, but they will no longer be a stock block and more variables to calculated reliability will be introduced.

My personal opinion about the 335 TT motor being introduced into the M is that it won’t happen. This is because people pay a large premium for the increased performance with corresponding reliability. If this were indeed the case, people would buy a 335 and go order all the M components to get the M performance and reliability.

Even now, BMW fans argue that the M3 is not worth it because a re-flashed 335 can match the power of the 400 Hp M3. But they fail to see that they comparing a modified car to a stock car. It would not make sense that a reflashed 400Hp 335 will be as reliable as the stock 400Hp M3. And in this case, a modified M3 will always make more power than a comparably modified 335 – but again, they will both suffer from potential loss of reliability when doing so.

So, back to the core of this discussion … the 335 motor and the G motor are both great motors in stock trim. We can’t speculate that the 335 motor is any more reliable than a N/A G motor simply because it has OEM turbos. IMHO, a 335 motor that has been upped to 600WHp like Christian’s VHR-TT coupe is just as likely to blow up. But of course this hypothesis will never be tested because the 335 will never make that kind of power using its stock turbos!

 

i know that my 335 drinks gas like a fat kid drinks milk early in the morning when u step on it. One canyon run will average less than 10 mpg on the bimmer. On the other hand you will go through less gas with the 335 on normal highway driving than the G with HR. My 04 6MT was more economical than any of them and also was as fast.

 

I've been debating which weight to use.

I'll be using the "official" figures for a 7AT sport vs a 6AT with sport package.

If someone could find me figures for the cars actually being weighed, I would much appreciate it.

If the weights of the BMW stock rims and brakes could be found, then I will factor in unsprung mass as well.


Additional data I need before I continue:

Swept area for both cars.

I will assume for Cd that neither car has factory aero.