[Jamesons Viggen]

I see no reason for one car to out slalom the other. This is not the 335 vs 328 where we have different engines, balance, noticeable weight and weight placement.

Same engine and trans, same suspension, 100lbs at most variance, and as little as 50lbs when you option a 320 up a bit more than BASE-and that weight is not exclusively over the nose like a 335 in comparison to a 328.

One will out shine the other only with the variable of drivers, tires, conditions etc. All it would take is a 320 with a better tire than a similar 328 or vice versa.

[300hp]

Originally Posted by Cyberdemon

What does the IS350 have to do with anything?

A figure 8 is nothing more than a glorified skid pad. It's great as a magazine metric, but it's a number that's easily modified.

1: Not all run-flats are created equal. It's well known BMW configures their cars with different tires even in the same class. I'm willing to bet one set of those tires provides marginally better grip. Even if it's the exact same tire, different tires will perform differently based on their wear, temperature, and PSI.

I could make the exact same car, on the exact same tires perform differently in the skidpad/figure 8 just by adjusting a few PSI in or out of the tires.

Also, the weight difference posted in the second set of posts shows a much narrower weight gap. The weight of the car has a lot more to do with how it is configured. You can bet that just adding a navigation system and some seat heaters and window washers will tweak the weight of the car.

This isn't rocket science, and skidpad scores that are .1 second different on different cars on different days, don't mean the car will lap a race track faster, out corner you in a turn, etc.

Skidpads are no different than dyno tests.

I can take my car to 5 different dynos, and do 5 runs on 5 different days, and every one will give me a different number - you have to take that information for what it is, and not for what it isn't.

All I am saying is the 320i is a great car, see the comparison done by Car magazine. It's beating an IS350 on the figure 8 too.

[tuned2ride]

Originally Posted by Anodite10

Here is the comparison data between the 320i and 328i that is referred to in the article I posted above. They are scans from the magazine itself. Sorry about the quality.

Odd that the 320i has an higher compression ratio / delivers less HP.

[Jamesons Viggen]

Originally Posted by tuned2ride

Odd that the 320i has an higher compression ratio / delivers less HP.

It runs like 8psi compared to 18psi for the 328, typically the higher the compression the lower the boost that can safely be run.

But tuned 320's can be tuned 90% as aggressively as the 328's, so the gap is small.

[Vervain]

Originally Posted by Jamesons Viggen

It runs like 8psi compared to 18psi for the 328, typically the higher the compression the lower the boost that can safely be run.

But tuned 320's can be tuned 90% as aggressively as the 328's, so the gap is small.

I always seem to be learning things from your posts. Very informative. Thanks.

[bavarianride]

Originally Posted by Jamesons Viggen

Same engine and trans, same suspension, 100lbs at most variance, and as little as 50lbs when you option a 320 up a bit more than BASE-and that weight is not exclusively over the nose like a 335 in comparison to a 328.

I read the drive and half shafts on 328i are beefer than 320i, that probably will be a factor on how aggressive the 320i can be tuned.

[Jamesons Viggen]

Originally Posted by Anodite10

I always seem to be learning things from your posts. Very informative. Thanks.

Thanks!

Originally Posted by f30fanboy

I read the drive and half shafts on 328i are beefer than 320i, that probably will be a factor on how aggressive the 320i can be tuned.

Where did you see that, sure it applied to US cars? In some countries, the 320 has smaller brakes, not here. It would surprise me that they kept the bigger brakes for the 320 in the US, but downsized the other running gear components.

[Cyberdemon]

Originally Posted by 300hp

All I am saying is the 320i is a great car, see the comparison done by Car magazine. It's beating an IS350 on the figure 8 too.

That's all well and fine, but when the topic is called "why is the 320i faster than the 328i" the answer is "because random variables", not because it's actually faster.

I'm not saying it's an inferior car - but by every almost measure the 328i will be faster on the road and on the track.

[tuned2ride]

Originally Posted by Jamesons Viggen

It runs like 8psi compared to 18psi for the 328, typically the higher the compression the lower the boost that can safely be run.

But tuned 320's can be tuned 90% as aggressively as the 328's, so the gap is small.

Why no 100% of the boost and benefiting from the higher compression ratio, getting more?

[trey100]

The torque curves look odd. It seems the 320 has more torque than the 328 at the higher rpms.

[Jamesons Viggen]

Originally Posted by tuned2ride

Why no 100% of the boost and benefiting from the higher compression ratio, getting more?

Because boom lol.

You reach a point where the pistons want to see daylight. Low compression means high boost, increasing compression and boost typically not a good combo when going for more power.

[bavarianride]

Originally Posted by Jamesons Viggen

Where did you see that, sure it applied to US cars? In some countries, the 320 has smaller brakes, not here. It would surprise me that they kept the bigger brakes for the 320 in the US, but downsized the other running gear components.

It was mentioned in other enthusiast forums, realoem also has data:

6/2013 production N26 for USA(earlier months have same numbers)
rear axle output shafts -- 320i: 28mm; 328i: 31mm; 335i: 35mm
drive shafts for AT -- 320i: 1563mm; 328i: 1539mm; 335i:1508.5mm

The output shafts are beefer for higher HP engines. On the drive shafts, I assume shorter ones may have better power transfer? Not sure.

Another interesting observation is, for N20, the MT drive shafts are longer than AT ones(same trend for all 3 engines).

EDIT: On the brakes, I recall US spec 328i has smaller brakes than European ones, I wonder if that is the same for 320i too, maybe it is really 328i gets degraded rather than 320i is kept the same as 328i.

[Jamesons Viggen]

Originally Posted by f30fanboy

It was mentioned in other enthusiast forums, realoem also has data:

6/2013 production N26 for USA(earlier months have same numbers)
rear axle output shafts -- 320i: 28mm; 328i: 31mm; 335i: 35mm
drive shafts for AT -- 320i: 1563mm; 328i: 1539mm; 335i:1508.5mm

The output shafts are beefer for higher HP engines. On the drive shafts, I assume shorter ones may have better power transfer? Not sure.

Another interesting observation is, for N20, the MT drive shafts are longer than AT ones(same trend for all 3 engines).

EDIT: On the brakes, I recall US spec 328i has smaller brakes than European ones, I wonder if that is the same for 320i too, maybe it is really 328i gets degraded rather than 320i is kept the same as 328i.

For axles and driveshafts, diameter is a bigger variable related to strength than length-though a short driveshaft with an increased diameter and made of the best materials-that is the combination for power. The material is the other big variable, we are starting to see more and more carbon fiber ones for example.

Looking at all of those numbers, about a 10 percent variation in diameter, we are talking about weight differences here and maybe 1lb lol. In terms of ability to handle power...should be another non issue. In my experience BMWs start shredding driveline parts like driveshafts and axles at silly TORQUE amounts like 600+ ft lbs to the wheels is when my cars are known to do that.

[bavarianride]

Originally Posted by Jamesons Viggen

For axles and driveshafts, diameter is a bigger variable related to strength than length-though a short driveshaft with an increased diameter and made of the best materials-that is the combination for power. The material is the other big variable, we are starting to see more and more carbon fiber ones for example.

Looking at all of those numbers, about a 10 percent variation in diameter, we are talking about weight differences here and maybe 1lb lol. In terms of ability to handle power...should be another non issue. In my experience BMWs start shredding driveline parts like driveshafts and axles at silly TORQUE amounts like 600+ ft lbs to the wheels is when my cars are known to do that.

The final drive units do have different part numbers between 320i and 328i. If the 320i one is not spec'ed to take the extra HP/torque, it can be problematic in the long run while outside warranty periods of the tuners.

[Jamesons Viggen]

Originally Posted by f30fanboy

The final drive units do have different part numbers between 320i and 328i. If the 320i one is not spec'ed to take the extra HP/torque, it can be problematic in the long run while outside warranty periods of the tuners.

Anything is possible, but I do find BMW drivetrain components to be robust and overbuilt in most instances.

Would you believe my E36/7 hit 81k miles this week and its on the ORIGINAL and STOCK brakes and clutch. The clutch is holding twice the power of stock and has yet to slip. I only replaced the headgasket just now, not because it failed from 13+psi, but to ensure future reliability and hold more boost.

So even if the 320 has a bit daintier components, I do not see it being a failure point until power levels reached that would not happen until big turbos and or internals are beefed up.

[bavarianride]

Originally Posted by Jamesons Viggen

Anything is possible, but I do find BMW drivetrain components to be robust and overbuilt in most instances.

Would you believe my E36/7 hit 81k miles this week and its on the ORIGINAL and STOCK brakes and clutch. The clutch is holding twice the power of stock and has yet to slip. I only replaced the headgasket just now, not because it failed from 13+psi, but to ensure future reliability and hold more boost.

So even if the 320 has a bit daintier components, I do not see it being a failure point until power levels reached that would not happen until big turbos and or internals are beefed up.

Brakes and clutch have a lot to do with the driver and driving style than the boost IMHO. Your points are valid, as long as people don't get greedy swapping in big turbos, 320i probably does have head rooms(more so than 328i) for tunes.

[Jamesons Viggen]

Originally Posted by f30fanboy

Brakes and clutch have a lot to do with the driver and driving style than the boost IMHO. Your points are valid, as long as people don't get greedy swapping in big turbos, 320i probably does have head rooms(more so than 328i) for tunes.

Very true...but


Everyone who hears my clutch and brake specs assume I must granny shift and drive it like a little old lady. They take that back when they get a ride in the car. However, I never launch the car from a dig. If you throttle it in 1st enough to build boost, it's a smoky fishtailing show.

To me, BMW drivetrains sell me on the mark. They are always faster than they should be given the specs.

[bavarianride]

Originally Posted by Jamesons Viggen

Very true...but


Everyone who hears my clutch and brake specs assume I must granny shift and drive it like a little old lady. They take that back when they get a ride in the car. However, I never launch the car from a dig. If you throttle it in 1st enough to build boost, it's a smoky fishtailing show.

To me, BMW drivetrains sell me on the mark. They are always faster than they should be given the specs.

BMW gets you at drivetrain. Yes, with care and respect, BMW brakes and clutch are quite durable, my old ride was stock E39, the original brakes lasted 90k and 95k(front and rear), and still original clutch when sold at 100k. I mainly aims to not upset the chassis and be smooth, and the rest(i.e. speed) follows.