Hi guys, I'm looking for some input on the ISF. I currently drive a tuned 335i with a manual transmission. I do all of my own maintenance/repairs/mods. I love the 335i, but am tiring of the frequency of repairs, and I know that as it ages (95k miles), it's not going to get any better. So I'm in the market for a reliable, powerful sports sedan. On paper, the ISF makes perfect sense - power, reliability, luxury, etc.

So I test drove my first ISF last night, and the difference in power delivery between the 335 and ISF around town seemed like night and day. The ISF has great power, but it seems to be accessible largely in the higher rpms (4k+), whereas the 335 has so much torque down low, that it's power is there from 2k+. Now, my test drive may not have been a good indicator because the owner did not currently have the car registered (supposedly bought another car and didn't want to pay the registration for the ISF, I guess). So no license plate, and the seller was really nervous about me taking it on major roads or freeways for fear of being ticketed. So the test drive was on empty industrial park roads. Still was able to poke it pretty good, but on the short roads probably never got over 70mph.

I know that driving both cars at the limit, the ISF would hang pretty close to the 335, so I'm not looking for more comparisons about driving these 2 cars at the limit. So here's the twist: ISF drivers, what is your impression of driving the car around town and accessing power down low when needed? Especially if you are a former 335i driver. Was it much of a transition learning to access power down lower in the rpm range for quick squirts when driving on the street? I really like the ISF, but worry that I would not be happy with it if the power is weak under 4k rpm, where I do 95% of my driving.

Here's an example of the 2 cars for those who have not driven a 335. In the Bimmer, if I am tooling along at 1,500 - 2,000 rpms and want to pass someone, all it takes is a gentle tip into the throttle (not WOT, and no downshift needed) and boost/power comes on almost instantly and I've gained 20-30 mph in no time, and without going over 4k rpm. In my (abbreviated) test drive of the ISF, if I dipped into the throttle, even with a downshift, it seemed like I had to wait a few seconds for the car to get over 4,500 rpm before it really came alive. Maybe I should have downshifted further? And yes, it was in sport mode. Give me some insight. There's another one about 100 miles away that I'll drive in the next week, but want some feedback before I do. Thanks.

 

You're asking if the IS-F drives like a torque-y turbo car. It does not. It drives like naturally aspirated car; power builds gradually and torque is mostly flat.

 

^ Yeah, this car is not a powerhouse on the low end.. However, there are a few things that can help improve the feel & responsiveness at lower RPMs:

1. Apexi Throttle Controller (I don't have one, but others on this forum seem to like it)

2. Drive in manual mode.. Unless I'm in heavy stop & go traffic, I'm always in manual mode. Otherwise, the transmission tries to shift up too soon & too high.. In manual mode, I can keep the RPMs where I want them for spirited driving. Like most vehicles, after awhile you adjust & learn how to get the most out of it.

3. The RR Racing ECU tune provides a small, but noticeable increase in low to mid-range power.

-Mike

 

Right on the money here. I cannot speak for #3, but #1-2 are necessary.

 

Yea, sounds like you will still yearn for the feeling of Boost down low with smaller turbo(s) that spool in the lower RPM range like the 335 does providing instant torque.

Like SubOrbital said above the ISF is naturally aspirated so obviously it's going to behave like one with a flat torque curve and the majority of the power will come when the secondary flap opens up on the intake which allows more air into the intake. Actually Lexus spent millions on development of the 2 stage intake system on the ISF with Yamaha to acoustically develop the sound and power above 3600 rpm, it's one of the things that most ISF owners like about the car.

But like you said in your description, if you want a powerful N/A motor and the reliability that comes with Toyota/Lexus products then the ISF fits your description perfect!

Also there were only about 5,100 ISF's sold in the U.S. so the aftermarket is pretty small compared to BMW so something to keep in mind.

 

Great input - especially the suggestions for Apexi TC, manual mode, and RR tune. This is what what I am looking for. I also need to do more research on freeing up the exhaust - are there certain headers (equal length perhaps)/exhausts that focus on low-end gains over high rpm gains? Or any mods to stay away from if I don't want to hurt low-end torque? BTW, the ISF I test drove had a K&N intake tube with open cone element, so I didn't get to experience the 2 stage intake, and with heat gain, I could see how the cone wasn't helping performance. And it had an ISS forged cat-back exhaust - wow - what a beautiful sound that made...

I understand that there is no way to get the ISF's NA motor to low-end torque levels achieved by the BMW N54 engine - that thing is a torque monster. And I am willing to give up some of that low-end torque to gain more reliability. I guess I just need to determine if I can get the ISF to an "acceptable" level of lower end grunt, through driving style modification and/or mods. Keep the commentary coming. Would love to hear from some ISF drivers who are former 335i drivers...

 

Just curious, is it really that bad to keep the 335i maintained? What year is it? I had toyed with the idea of getting a BMW before the ISF, but the maintenance issues always turned me off.

 

xellos, it's not horrible to maintain the 335i, but at times it does seem constant. BTW, it's a 2007. I had the original turbos replaced at about 65K (right before warranty ran out - woo hoo), so I figure that will have to be done again at +/- 130k. HPFP replaced (warranty), walnut blasted at ~70k, and it needs it again (95k now), if you are tuned, plugs every 20k, coils last about +/-50k. Then at some point you'll get the dreaded 30FF (boost lower than target) code. I fixed that once a while ago due to a leak at my intercooler connection, and then got it again - turned out to be weak boost solenoids this time, but they are not monitored for function by the ecu, so there was a LOT of troubleshooting to find the issue. Oh, and then there is the electric water pump that dies at about 70-80k and leaves you (or better yet, your wife - yeah that was fun) stranded by the side of the road. I've replaced 3 window regulators and 1 lock solenoid/latch - that was awesome because the door was stuck shut/locked until I could take off the door panel (with the door closed) to pick the latch and open the door. Based on other people's experience, I should have had to replace my injectors by now, and the clutch is probably thinking about a permanent vacation before too long. I'm at the point where I either get out now, or commit to keep it for 50k more miles and just keep grinding through some of the larger impending issues. And of course, you add to that the brakes/tires/fluids/etc that you do to maintain any car. The sport suspension has mucho negative camber built into the rear, so rear tires are about an every 16 month expense.

It's got 95k miles, so some repairs/maintenance is expected, and for the most part it's been worth it so far. Honestly, if my wife didn't drive it 60% of the time, it would not be that much of an issue, but she's coming from Honda/Toyota reliability, and to her the BMW seems unreliable and like a money pit. And at times I feel the same way.

I'll say this, though, if I didn't DIY all my own repairs, I would have gotten rid of it a lot sooner - parts are expensive enough, no way I'd want to add labor to all that...

 

Why are BMW's like this?? Do they engineer them like this to go out prematurely? Or in Germany do they have a different mindset or something to justify the performance they put into their vehicles? I'm sure if they wanted to engineer longevity into their designs they are more than qualified to do so, just never made any sense to me why the German builds (Audi/Mercedes/BMW) are so costly to upkeep?

 

Smaller turbos make more low end torque and less top end power -- very similar to how NA motors behave. If you look at dyno charts of the 335 and the IS F, they have quite similar curves.

The difference you are feeling in your test drive might be a bit in your head, and maybe a little bit of engine noise/exhaust note difference...maybe a little bit of the transmission too.

 

I was in the same exact boat as u. 2007 n54 same damn problems. I got rid of it at 88k miles. So many annoying issues I got tired. Did my research and everything pointed to the ISF. 4 door, reliable af, 400hp+, luxury, looks nice...etc. yeah it doesn't nearly have the very low end torque like 335i (cuz no turbos) but now that I'm FBO it is comparable to a stage 2 335i. Just not the 420lbft at less than 3k rpm my stage 2 n54 had haha.

 

I had a 2009 335i and did Dinan stage 2. The car was a blast but never knew when something else was gonna go like the HPFP. I had 5 replaced in 25,000 miles. I had the auto trans. In the ISF I liked the following much more than the 335: trans is night and day better, sound (PPE and Borla), rarer car, and I prefer top end power of a NA engine. The one thing that I preferred in the bimmer was the steering. I usually get bored of cars quite quickly but I am almost 3 years in with the ISF and I still love it. Now with all the goodies from Rafi at RR racing I have fallen in love with the car all over again. You will not be disappointed leaving the 335 b

 

I currently have both cars at the moment. ISF with catback exhaust & intake. '07 335i with Cobb Stage 2+ tune, downpipes, 7" intercooler, CP, DCI & catback exhaust, with 67k miles & stick shift. It has been my DD after selling my tuned C63 (which was a huge money pit) while I was shopping for the right ISF. My car had the turbos replaced, high pressure fuel pump, LPFP sensor replaced, walnut blasted, waterpump & thermostat done, all plugs & coils are were replaced. Basically all the common N54 issues were already taken care of, yet the car loves misfiring & throwing codes every so often. Boost leaks & random sensors going out has been pretty common on my car. Its a great fun car when it is properly running, has tons of torque & gets great gas mileage. You are correct that the power of the ISF lays in the upper RPM's, the E92 M3 that I drove had even less torque down low than the ISF. I guess it depends on what you like more, the ISF has way more creature comforts & luxury amenities than my fully loaded 335i has. Also seems to get more respect from fellow AMG, M3 & M5 owners in my experience where in the 335i they didn't really pay me no mind. If you do plan on getting the ISF, headers, intake, exhaust & the RR racing tune is a must, members have been getting pretty impressive results from those.

 

I would not buy the throttle controller or the Tune if you get the car. Waste of $$$$. The tune isn't perfected yet either, and tunes on naturally aspirated ECU's.....well, enough said there.

Off the line the car seems quite a beast to me, but I've owned it for 3.5 years now.

The headers you want are PPE, that will be a big jump in power.

 

Not sure why, but it is a shame. If you buy/lease them new, you've got a warranty and they give you free maintenance for 4 years or something like that. I guess that keeps the cars moving off the lot. There are a lot of loyal BMW owners that would never own one out of warranty - that ensures that those buyers trade in and buy/lease again every few years...

Interesting (surprising) dyno charts, Sedition. Some of it may have been in my head - the 335 is relatively quiet as it makes power. The ISF with exhaust that I drove made a lot of noise (beautiful noise), but made that noise before the power surge. Big noise without immediate response could have colored my perception.

Good to know that even though the aftermarket is not as big as BMW aftermarket there are good bolt-on solutions for more power. Sounds like PPE headers would be mod #1 and then go from there.

Thanks for the "335 to ISF" feedback jspec, jmt, and sleepy - great insight from your experience. I'm going to try to test drive the second ISF this weekend, with a bit different perspective this time...