First, I wanted to give a little background. I have been a bmw fan since I bought my first 3 series out of college and owned 03 330i zhp, 05 330ci zhp and my current 08 335i coupe.

I have never taken one of my cars to a track or a drag strip. I just enjoy having a car that can handle any turn on the road, stop on a dime and push me back into the seat with some fun. BMWs fit the bill for 8 years, but I have been itching to move up to a porche.

I loved my two 330s, but with their NA engines, there was limited bang for your buck for performance upgrades. This of course is not the case for 335i. The n54 twin turbo engine is incredibly detuned from the factory. For a meager $800 tune, you can bump the whp/wtq from 270/275 to 350/370. There are few engines that have the turbos, airflow, tuning, and fueling to take such a huge jump in power without flinching. After another $2,000 on airflow mods, I am just about 385/400 on my 08 with 37,000 miles and a warranty expiring next summer.

Originally, I wanted to keep the 335i long term (5-7 years). However, now I am getting a little leery of having a car outside of warranty.)
With the current options for the 335i, I can take my car up to around 500/500 whp/wtq for another $5 – 6k, but would need to spend another $5-6k to be able to put that power down effectively. At this point, I thought, instead of pumping this much power into a car that wasn’t designed for it, buy a car that has all this and more. Hence I am here.

I have been looking at a used cpo 911 turbo, preferably an 09. If I picked up an 09 in early 2012, I would hopefully have one year left on the original 4 year warranty and an additional 2 years on the CPO warranty pushing me to 2015. This would ease my concern about owning a German car outside of warranty.

Now, being I have been bitten by the modding bug, I know I won’t be able to just say I am fine with a stock turbo. So I have been reading through a lot of the threads here to educate myself on what are generally the best modding routes and preferred brands. I would prefer to just go tune ($2-3k) for the easiest power bump without messing physically with the car.

(Now, for those that might suggest susp, brakes or other performance mods, I am coming from a 335i with a stock susp and brakes, and I never track my car. Therefore, the 911 turbo on a whole will be more than enough of an upgrade compared to my 335i for now. So the only real performance mods I am considering right now are those that make the car go faster).

So, my questions.

I noticed that unlike the 335i, a tune is generally not the first mod. On a whole, I have seen an exhaust or an exhaust + tune is. I was wondering why that is?

And I apologize if I incorrectly apply the modding characteristics of the n54 to the 911.

Would I be correct to conclude that most of the exhausts for the 911 are as much for freeing up back pressure on the turbos (to decrease spool up time and back pressure to extend the turbos life) as for exhaust note?

From what I have seen, a base tune for the 911 is good for 40-60 whp/wtq or 8-13% gains. Is the stock exhaust that restrictive to really start being bottle necked at such a small bump? I would think if a small power bump as 8% could cause damage from back pressure, that risk would be present even at stock. Am I missing something?

In addition, I have noticed posts commenting on slipping clutches with only a tune/exhaust mod? Similar to my questions above, is the stock clutch that close to its limits that such a small bump would shorten the life of the clutch?

Next, can someone provide a basic explanation on how the 911 ecu controls the three key tuning variables (boost, timing and AFR)? The n54 is a load based ecu that strives to hit a constant power band independent of air temp, air density, fuel quality or other variables by changing timing, boost and afr. Is the 911’s approach the same or does it hit a constant boost with adjusted timing and afrs.

The tuning approach used by the tune I selected (Cobb), is to hit max safe boost pressure for the turbos with safe timing (no timing drops) and safe AFR ratios. Ideally, as long as air temps are not too high and you don’t have bad fuel, the tune will run just below the max power limit and not require the ecu to pull timing, drop boost or adjust afr to keep the engine safe.

From what I have read, I have noticed that certain tunes “adjust” to physical modifications without requiring a new map. To me, for an ecu to do this, it would need to push boost, timing and afr’s to possible dangerous levels to know it should back down (pretty much what a custom tuner does but only while tuning the car and not every day).

Do I understand this correctly? If so, is this something the ecu does stock and proven very good at or something the tuners have added? Ideally, I want a tune that either runs similar to stock logic or runs a set safe level of power without pushing boost, timing, or AFRs to eek out the last couple hp or tq.

I know the n54 ecu is very powerful at protecting the engine and wouldn’t be surprised if the 911’s ecu is similar, I was just hoping for an explanation.

Thanks for reading and please look for my soon to be posted noobie threads like “which tune is best” and “**** the porsche tax”

 

Easy - exhaust is one of the few mods you have near universal alignment between hardcore performance purists, "lite" modders, cosmetic modders, and first time beginners all rolled into one.

No matter how beast the stock TT is, some ppl just want to get every bit of power they can, others don't give two hoots and just want their ride to look/sound great, etc. Exhaust seems to be the catch-all for everybody.

For whatever reason, Porsche stock exhausts on any 911 type and especially turbos, always come with the double whammy of:

1) pathetic sound (as compared to most other performance cars, including far less expensive and "common" ones)

2) restrictive exhaust - you can debate which aftermarket one is "better", but haven't heard anyone ever debate stock being significantly worse than pretty much any aftermarket one

Exhaust also sets you up for a tune if you want to go that route at same time or later. So I'd say it's why it's at or near the top thing most ppl do - because it combines performance + cosmetic modders all in one.

 

>>>>I noticed that unlike the 335i, a tune is generally not the first mod. On a whole, I have seen an exhaust or an exhaust + tune is. I was wondering why that is?

Because most tuners don't recommend just adding a tune by itself (although it's certainly doable) without relieving the very high back pressure of stock 997 Turbo exhaust, from the 600 cell density.
Also, as Jacob has mentioned, the sound of stock 997.1 Turbo is so horrible - a stressful whinny sound like that of a hair dryer -that a lot of people actually change the exhaust before the tune.

>>>>Would I be correct to conclude that most of the exhausts for the 911 are as much for freeing up back pressure on the turbos (to decrease spool up time and back pressure to extend the turbos life) as for exhaust note?

Correct. And golden-eared audiophiles would even venture the exhaust sound alone is good reason to upgrade. As mentioned we have the distinction of having one of the worst sounding world class sport cars of all times. Incidentally, 997.2 exhaust note is a mild improvement over 997.1 because it is warmer and a little louder, but that one needs a change too.

>>>>From what I have seen, a base tune for the 911 is good for 40-60 whp/wtq or 8-13% gains. Is the stock exhaust that restrictive to really start being bottle necked at such a small bump? I would think if a small power bump as 8% could cause damage from back pressure, that risk would be present even at stock. Am I missing something?

You've done your homework well; 10% is the usual claim - but do note that the bottom line on these very well informed Porsche forums is not as much dyno numbers anymore since these numbers have been so manipulated, but proof by Vbox timing. https://www.6speedonline.com/forums/...le-thread.html
Anyway, tune without exhaust is doable and it won't cause damage, it's just that Turbo owners tend to be compulsive and loaded with both $$$ and a class A type personality, so once the tuners recommend (rightly) that it's better to have exhaust, everyone does it.

>>>>In addition, I have noticed posts commenting on slipping clutches with only a tune/exhaust mod? Similar to my questions above, is the stock clutch that close to its limits that such a small bump would shorten the life of the clutch?

Very rarely and only with more sporty/abusive driving. My car does, but only when it's cold, and only when my tuner test drives my car when he tunes the suspension, etc. The stock clutch in general could handle tune+exhaust ok. It's only when you go to next stage, adding an intercooler, that you are very likely to need to change the clutch.

BTW, my own recommendation for the order of changes:
1. Suspension
2. Exhaust
3. Tune (the "big" names are: EVOMS, GIAC, Protomotive, Softronic, Switzer)
Part of the reason is that the stock Turbo suspension is very soft and as a result the car has excessive weight transfer - body roll, squat, dive. An increase in power would only make this weight transfer worse, IMHO therefore it is a good idea to firm up the suspension before bringing in even more power. Lastly, a firm car *feels* faster, so that is an additional advantage.

 

First, thanks a ton for the helpful reply.

This makes a ton of sense. After testing driving one, I thought my car's exhausted sounded better than the 911s. Which on the face doesnt make sense at first.

So an exhaust isnt required for safety, its going to help free up some backpressure and it just works best when mated with a tune.

How are dealers on warranty work with an exhaust? I know for my car, bmw couldnt give a hoot about a modified exhaust, but if you messed with the downpipes right after the turbos, they are unhappy.

 

Thanks for the helpful reply.

Ok, it looks like I will need an exhaust and tune.

Yea, dynos are the marketing tool for many of the bmw tuners, where actual road results truly matter. That being said, a dyno can give a feel for gains. As I dont track my car or run 60-130 runs via vbox (i can do rough calcs from the logs I pull from my ecu), I am sure that I will feel the bump in power from a tune and at lease appreciate it.


Good to hear. I think if I find a 09 that doesnt look like its been beat on and combined with my driving habits (no track time, no 1/4 miles, no clutch drops) I should be good on a stock clutch . . . unless I go stage 2+

After test driving the 911, the susp was more than firm enough for me, and jaring when on sports mode, so i feel like it will suffice for me.

For tunes, I have been leaning towards Softronic. I like the flash at home approach similar to my cobb. However, I really would like to understand how the methods of how the stock and tuned ecu works. Any good threads on there that go into detail on this?

 

Ha, i am literally on you tube watching this video over and over.

http://www.youtube.com/watch?v=D22xta9mjuM

 

Yea, from what I have read here, its the most popular. I live in the chicago burbs.

 

Im not sure if you could call the europipe the most popular. The most expensive, if not by a great deal, yes. And the fact it is more expensive makes it not so popular amongst the wider masses that aren't able to get their heads around why the system costs more than the others. Is EP the best system? Absolutely no question in my mind and, my EP isn't the first AM system I've had on my car. Spending bloody good money on something that fails to deliver in both performance and sound without interior resonance is something you really need to be careful on. Yes I've still got a spare AM system for sale if money is an issue. The EP on the other hand definitely delivers performance you can feel and, the awesome sound is a bonus (especially as it doesn't drone you out of the car) as is the fact it's actually saleable and worth something if you ever want to remove and sell it when you sell your car.

The other thing i agree with is cannga saying how many put exhausts on with tunes because of the well worn story that an exhaust is necessary to release unwanted back pressure. Well, the need to relieve back pressure with a tune has truth in it yes but if you actually need a tune to be able to feel any gain from an AM exhaust then the exhaust in my mind can't be much chop to begin with if without the tune the thing pulls power out and tubi isn't on its own with that. That is what i found for e.g. with the tubi first hand so this problem is real. Without a tune that damn thing took the sting out of the midrange i.e. the stock system delivered more power and the car felt zippier/better. So if an exhaust doesn't deliver power you can feel without a tune then that says a lot to me. Buyer beware. Very aware.

Now on to the clutch. I can't agree with anyone who says a stock clutch is up to handling a tune (sorry....maybe i should say "decent tune"JK). Sorry Can but if you say your tuner can get it to slip, what it says is you don't know what you're missing out on and you aren't likely to ever know until you change it out (sorry mate), as i did. Frankly even with the stock tune it feels better everywhere and my car was sub 8k KMs when i changed mine....so it was hardly worn out. The car with the Sachs 764 pulls cleaner at wot at any time, temperature, rpm etc. If a clutch slips at wot under any circumstance or condition it simply isn't up to the task...end of story. And lets face it, why would you really want to put up with not being able to give your tuned car full noise at any stage in the rev cycle if there was any degree or chance of slippage regardless of how little it was. I find the real strain on the clutch is when it's brisk weather (mornings/evenings) and you stand on the gas wot in second and/or 3rd @ the 2800 rpm range through to 4,000rpms (when the boost really hits the drivetrain). Can, do yourself a big favour this xmas (ask santa) and change your clutch, it'll be the best $ you have spent in a long time (you can thank me later ok).

The suspension is another story. I personally don't find my stock suspension is any issue at all for street driving nor does the tune affect it but to each his own on that.

So, all that said, i would do the mods in the following sequence:

1) EP. It'll give you a genuine seat of the pants difference and a good sound to boot whilst not droning you out of the cabin like pretty well every other system will do in this car, least of all gut power without the addition of a tune.
2) Sachs 2.5 clutch. Even if your car remains stock you'll know what I'm talking about after the changeout. It's just better everywhere. There are them's that knows.
3) Tune. But be careful. There is a lot on the market to choose from and I'm not saying any more on that subject, but adding a set of .2tt ics is a good (and cheap) move if you can do that as well. Lowering the IATs on a boosted car has its longevity benefits. I certainly wouldn't be tracking the car with a tune without them. Best to flash back to stock for those occasions.
4) Body enhancements. Change the front lip and have the body colour matched around the car (unless its black). GT2 sills, rear lights are another worthwhile consideration.
5) Suspension. This one is too subjective for me to buy into. Personally if the car is a DD then you'd want to be very careful changing anything imho. The car in stock trim is more than most would ever be able to advantage, with or without tune.

Finally GL choosing the right car. You need a car first and foremost or all this talk and advice is meaningless. Yes, getting the car is the real starting point but i can assure you after stepping out of a 335 bimmer you won't know yourself. The 997tt is in a totally different league.

 

Great info speed. Thanks for the help.

 

Found some more information. After reaching out to Rob Irish at Cobb (he hasn't reverse engineered the 991, but has done some limited research), he believes the 991 ecu is similar to the n54 and is load based.

In addition, I think I found more informaiton on how certain tunes can be somewhat adaptive.

More info from Giac
On the 91 pump program you won't see a difference from say 96 octane, (mixing gas) to 108 octane. On a 93 pump program that range becomes more like 98 octane to 108 octane. Our race gas options do have minimum octane requirements such as 98 or 100 octane, but they will make gains on octane levels all the way up to C16 leaded gas.