Lightweight e30, have platform/engine ideas, leaning 318is/N52… talk me out of it

[Maxhouse97]

Hi,

New to the e30 community, coming from a couple of different automotive experiences (Miata, GTI, 911, Cayman, E46 M3 - last two I still own). Looking to get into a e30 for these reasons:

• I like small, lightweight cars. Drive a slow-ish car fast kind of thing. Go-kart, short gears, a “you make a control input and the car moves immediately” dynamic.
• I’m a NA engine geek, high-reving but decent torque lover (S54 perfect combo). Prioritize engine responsiveness (fast reving, sound, lack of vibration) over outright power.
• I have a European preference, had good experience with BMW (E46, Z3). Also like the 80s nostalgia. Was thinking of going back to aircooled 911s but prices are ridiculous. And so are e30 M3s.
• Looking for a street car, canyon carver, OEM + build/look, no track planned but would want “track in a pinch” options (E46 is my track car). I’m approaching 50 so want a car with full A/C, amenities, etc.
• I can do some of my own mechanical work (have pulled engines/trans and swapped suspensions) but don’t have a ton of time and don’t do well with electronics/computers so in general prefer OEM like kits/simplicity. Willing to spend some money to get there.
• I don’t want another Miata

As I started to research e30s, I quickly gravitated to the 318is for its ultimate lightweight package. Balanced handling due to low weight over the front end, etc. However as I’m also an engine guy, I don’t think the M42 will cut it. I read the 2019 Grassroots Motorsports article where they spent 8k rebuilding the motor and still seemed to get a meh result. Therefore I quickly resolved to look into good engine swaps that would add some power (and torque for the street) yet keep the lightweight feel.

Here are the options as have I gathered them (it’s funny how detailed some of the swap forum threads get when you’re looking for high level thoughts/details):

• K24/20: this is where I started, I have been intrigued by this motor for some time as it’s a model of NA, high/reving power. I spoke to K-tune and they can do a complete swap with labor. Upsides: lightweight with power torque, amazing aftermarket, reliable, everywhere. Downsides: does not keep it BMW, might be a money pit that would not have residual value in the eyes of e30 enthusiasts, second order vibrations from the long stroke 2.4 motor (K-tune kit gets rid of the balance shafts).
• Stroked M42 + ITBs - then went this way, why not stick with what it came with? Upsides: no swap needed, keeps the lightweight part but adds the motorsports feel. Downsides: $$, don’t think the motor was designed with this in mind (S42 notwithstanding), Grassroots article really turned me off. Very little support. Must be a reason very few have done this.
• S50/52/54 motor - came here next. I love ITBs and M engines. Upsides: pedigree, motorsports feel, great power/torque, good support. Downsides: super heavy, violates requirement number 1 and compromises handling. Expensive. Only thing I’ve thought about is putting a S54 in if I have to sell my E46, but that’s not in the cards now. Feel the S54 would make it into a very different car than the 318is, more AC cobra/muscle car.
• M54 - progressed to this motor. Stout, forged crank, tried and true. They are being raced all the time in Spec E46. E46 330 ZHP is a car I like. Upsides: AL block cuts down on weight (according to a post with pictures of scales, 70lbs lighter than an M20), has been done many times, relatively modern motor. Seem to sound good. Downsides: don’t rev very high or fast, not motorsports like? More torque focused than a balanced torque/upper end power motor. Still heavy compared to the M42. Seems to be the 2000/2010s option, but most now going S54 or something else.
• N52 - where I am now. From everything I can ascertain, this gets me the closest to where I want to be. Upsides: lowest weight BMW Six (hard to tell how close to a M42 weight), inline 6 naturally balanced. Great power/torque for NA, pinnacle of BMW NA engines before turbo took over. 7k or higher redline. Seems to be the “in” swap now, which means many of the smart people who know this platform better than me have landed on this. Very cheap motors. Valvetronic provides quasi-ITB like performance (RPD trumpet kit looks very intriguing with even more weight savings). Right amount of power (I don’t need more than 250 hp). Downsides: too new/clinical, lack of character & sound? Lack (or nascent but developing) support. Too hard to integrate electronics into a 1980s car. No plug and play kit. I have to admit some of these are unconfirmed, mostly concerns that could be proven wrong as I do more research.

Now I have one admission to make - I HAVE NEVER DRIVEN AN E30. Up to now I have exclusively spent time with Porsche/E46 people. I have based all of the above on research/discussions with folks at C&C (I had an in depth one with a guy who swapped in a Pontiac Solstice motor). So I could be completely off base. But honestly I think the world is done making small, lightweight cars that are not Miata’s, so I think the e30 will hit the mark. I love my E46 and I know it was derived from the e30 (strut front, independent rear). And yes I plan to drive them once I can find a way to.

What are your thoughts? Is the N52 the right option for me?

And is the 318is the right starting point for a lightweight car? Feel I get can a real nice one for 10-15k, and then collect parts/build it over the next couple of years (I don’t want to start with a project car). Latest built model would help mitigate old car issues (although I really like pop out rear windows). Or would you suggest another e30 model?

Will be posting in different forums to get both platform/swap feedback. Thanks for reading this far.

[OSAH racing]

I also am after a great driving experience and my preference is handling over power. I have had several old cars ( I am a young 62) and agree air cooled Porsches are too much money to play with. I have had a few different e30's and My experience is the 4 cylinder engine placement is optimal. In General cornering speeds are higher. Your right the M42 needs more power, an oil cooler and a lot of custom work to yield 200 HP. I am in the process of building something similar as you in regards to use. Mostly a street canyon car with a few AX and track days for fun. I am sticking with the M20 because I could not find enough reliable information about K - swap E30's. I do believe the best motor/transmission if your up for the cost is the F20 from the S2000.

My M20b25 decision is based on several points. 1: Spec e30 cars are pretty darn fast with a skilled driver
2: Lots of support with from the aftermarket for engines, brakes and suspension parts.
3: Stock oil cooler, LSD with many choices
4: Durable
5: Cost
My conclusion is the e30 will always have a few compromises built into it with my budget to play. I have had an 97 e36M3, 91 slick top 318i S52, 91 318i M42 for the track and currently a 90 325i. I prefer the handling of the 4 cylinder car, the sound of the M20 car and the power of the S52. Good luck and keep us informed these are fun cars to drive.

[amcp]

You need to drive a 24v swapped e30 before you call the handling compromised.

[uturn]

The increase in power you want will require rear fender work to get wider tires to handle it. Money, work and effort will not be worth it imho.

I think what you want is the Z3 clown shoe.

[OSAH racing]

You need to drive a 24v swapped e30 before you call the handling compromised.

I have, I did, I have owned them and a 24 valve is noticeably slower at turn in compared to a 4 cylinder engine in the e30. I am not saying 24 valve motor's suck. I liked my enough. I am saying if handling is what your after the F20-C is a great choice.

[88Sedan]

Just my own opinion here but I like the idea of an aluminum block m54 or m52tub28 from a z3 but those are getting hard to find and I think US tub28 blocks were nikisil bores making rebuilding a non option or harder. IMO the power level is 'just right' especially with a cam change and tune. While most delete AC I have seen at least a few cars make it work. I imagine the weight bias would be pretty close to 50/50.

[hoveringuy]

I posted my N52 thoughts on this question in the N52 engine sub-section. TLDR; DOHC goodness without the fat.

[varg]

K24/20: Best 4 cylinder option. Light, available, make good power NA and great power turbo. Still a 4cyl with 4cyl sound and vibration.
Stroked M42 + ITBs: You'll spend a ton of money just to make K20A eco power and be left with less low end. Price out a set of cams + head work + ITBs.
S50/52/54: They are definitely heavier, M50s are something like 50lb heavier than M20s, M20+transmission is 70lb heavier than M42+transmission. S52s have a heavier crank than an M50 (I wish I had weighed my B30 crank and B25 crank side by side but oh well), S54s are quite heavy indeed and also long. So you'd be gaining over 100lbs and most of it up front. It definitely will change the character of the car. My M20 swap felt different from my M42, but I much prefer the M20 for everything else. I bet a stock S52 weights almost exactly as much as a turbo M20.
M54: Good option. Pretty light, less than an M20, lots of low end torque, you're correct in that they don't rev high and it's not worth trying to make one rev high. 24V cams are expensive, stock falls flat before 6,500rpm, crank harmonics are supposedly an issue with the B30 crank (same part as the S52 crank btw), with plenty of forum lore from people having issues after beating the hell out of M54s and S52s at high rpm. I haven't driven an M54 E30, but M54 cars benefit from the low end torque, it makes them more fun than if they were gutless and had to rev more to get to the torque like a non Vanos M50
N52: Watching the swaps, these are a better option in every way than an M54, just harder to pull off. They're supposedly lighter, more tolerant of revving. Lack of sound and clinical? With some "ITBs" (really just trumpets on the open unthrottled ports using valvetronic) I have heard sonorous induction noise from an N52. Like all BMW I6s, the exhaust sounds like crap without a turbo to calm it or a well designed equal length system to keep it from just being a buzzy mess. Quieter is better. If I were doing an NA I6 swap in an E30 today, I would probably go N52 and try out the velocity stack setup and a quiet exhaust. We're talking more power and torque than an S52 and less weight than an M20, which sounds like fun.

I think it's best to make an E30 an E30 and appreciate it for what it is. They have limitations. Mine is pretty aggressively modified with coilovers, stiff bushings, pretty extreme tires, then I get in my FD and even without pushing it hard I see that with of those mods my E30 is still an E30, not a sports car. It's a flexible chassis, it has disappointing steering stock and has good steering with a Z3 rack like mine, though it tramlines a lot with the tires I have on it.

For objective performance and handling, there's no better option than a K series IMO. A 318is is in the 2600lb range weight wise, with a medium case LSD and a K series you probably gain next to no weight but could make S52 power with a decent NA build. For everything else, like performance on a budget and E30 character, turbo M20 is unmatched. Bolt in swap, lots of torque and power. All of those NA 24V swaps people did over the years seem like a waste when 300whp worth of turbo on an M20 and makes S54 power, more torque, and at less weight, cost, and difficulty fitting everything in. I, for one, having gone from turbo 4 to turbo 6 love how smooth an M20 feels in comparison.

[packratbimmer]

K20 + a six speed

[E30 Wagen]

Call me a snooty purist but I honestly couldn't bring myself to swap a nice "survivor" 318is with anything but a stroked m42. The balance and handling with the m42 up front felt perfect to me, and after seeing so many get swapped it makes me happy to see that engine still getting some love. Concerning actual chassis weight, the only real advantage I see to starting with a 318is is if you can find a slicktop, which along with the 318i sedan was the only e30 offered as such in the US. Since slicktops are rare and if you're leaning toward an engine swap then you might as well include all the 325 models in your search. You get a larger exhaust opening in the rear of 88+ 325 models (just a single cutout on the 318is), which might be convenient depending on what engine you go with. M42 cars also have a big ignition coil mounting bracket that I always thought looks a bit awkward sitting bare after a different engine is swapped in, but that's just me. Sure, other engines might make more power, but I've always really wanted to do a m4x stroker, itbs with a carbon box, maybe even a carbon valve cover, electric fan, no AC, no PS, carbon hood, carbon trunk, lightweight glass, lightweight seats...

If I could find a slicktop e36 then I'd basically want to do the same style of build because i kinda like e36s more now... Or I'd build a 3L out of the Z3 alu block.

Other car to consider would be a e82 128i.

edit: also, the stroker that GRM built only used the m44 crank, not the 88mm m47 crank.

[82eye]

Call me a snooty purist but I honestly couldn't bring myself to swap a nice "survivor" 318is with anything but a stroked m42. .

isn't parts availability the issue with the m42 now? it seems to get cited more and more as the reason for a swap option

[varg]

isn't parts availability the issue with the m42 now? it seems to get cited more and more as the reason for a swap option

Harmonic balancers are NLA according to a turbo M42 guy I sold mine to. Timing sprockets went NLA after I did my M20 swap so years ago now. I'm not sure about other parts but those are both wear items with the newest M42s being almost 30 years old. If NA performance is a goal a stroll through M42club to see the results of their builds is reason enough to swap.

[Maxhouse97]

Thanks for all of the responses, Varg yours especially with all the detail. Great community here. Seems to confirm a lot of my research.

Yes agree Honda power is best, but after considering it more I’m turned off by the vibration and non-BMW lineage. If it were more of a track car this is where I would go.

WRT to the M42, GRM article likened their built 318is to a 1.6L Miata … that was harsh criticism. However agree this is in line with the slow car fast thought, and respect everyone who owns these.

I do like handling over power, but I also like straight 6s for their pedigree, sound, and lack of vibration. I was not willing to pay the weight “price” when it was 70-90 lbs (M20 over 42). But as far as I can tell an N52 cuts into more than half of that, so I think it’s worth it. Hoveringuy’s response on the N52 subforum sums it up perfectly. I think we are at the start of a number of N52 swaps as they catch on.

As far as platforms, another reason I was thinking of getting a 318is (beyond the weight and slick top potential) is it lets me try before I buy. Maybe I’ll find the M42 ok enough. Any other reasons to start with a 325 over 318?

[82eye]

Yes agree Honda power is best, but after considering it more I’m turned off by the vibration and non-BMW lineage. If it were more of a track car this is where I would go.

all things equal i wouldn't turn my nose up at a k swap personally. especially a nice clean one. power potential, parts availability, and cost factor all make it a possibly attainable dream. s5x will always be the purist swap imo, but you pretty much need to be a youtube star to attain it now, or rich enough to buy a few youtube stars ...
don't think i'll ever have the $$ for that. lol.


edit: also the weight factor is decent on the k. it is a tall engine though.

if you get any e30 both the m20 and m42 are good for some cheap fun while you decide on which way to go. i love my iron lung of an m20 lol .. some simple mods really help and change the car.

[adam.nonis]

Just like posted on the other thread:
M20 w/G260: 497lbs



M54 w/G260: 475lbs



N52 w/GS6-17: 458lbs



M42/Manual Trans: 427lbs




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