Improvements on my 320/6

[dlguadiz]

I am currently plotting/planning what improvements I can do on my 320/6 -- found myself reading a lot about chassis strengthening, brake upgrades, engine swaps, the max torque/hp our differentials can hold, etc.

Bottomline, I know that I cant just increase hp without thinking of all the different aspects of the car. So I am willing to compromise, but I have my goals.

Objective: My purpose is to be able to have a fun/exciting car to drive around town and the countryside -- maybe do track days once in a quarter of a year. I read somewhere that the 'sweet spot' would be to aim for around 200-250 hp.

Now I would like to do this without changing the geometry of the car so much - I dont want to mess up the handling and maybe aim for better - so no significant changes for the suspension and no messing with the differential. No slamming the car. No drifting.

Fortunately, my car is a 320/6 so my front subframe is already as strong as it could be - it is currently holding the m20b20 engine (122 hp) and my differential ratio is about 3.64.

Some basic changes done or currently in the works:

1. Chassis strengthening
1.1 Front strut brace installed
1.2 Alpina bar to be installed
1.3 Rear strut brace to be installed
1.4 Install B-pillar bar for further strengthening and to be able to install racing harness/seatbelts.

2. Weight reduction/redistribution, load reduction
2.1 Removed the mechanical fan and replaced it with temp-controlled/switched puller electric fan
2.2 Removed heater, aircon, blower
2.3 Relocated battery to rear
2.4 Remove standard seats, replace with racing seats

3. Suspension/Brakes/Tires
3.1 Currently running 205/50/15s wheels.
3.2 Install Wilwood front massive brakes with 4-piston calipers (from IE)
3.3 Thinking of replacing the rear drum brakes with disc brakes but if its enough for 200-250 hp, I wouldnt.
3.4 Currently running stock suspension - what simple bolt-on springs and shocks should I buy?

4. Engine/Transmission

Now this is the part I am struggling with -- should I just turbo the m20b20/4-barrel carburetor and swap the 4-speed (Getrag 242) to a 5-speed overdrive (Getrag 245)? Or swap it?

If swap, I only have a handful of options in this country - its going to be either an m42 (138 hp) or m52 (168 hp), turbo'ed of course to reach that 200+ hp goal. I don't think I can find any of the Sx and m20b25 engines here.


5. Others/Aero
5.1 Add a kamei airdam with splitter
5.2 Improve airflow underneath car -- dont know what to do yet. My e21's bottom rear is not stock so I dont have any second thoughts on fabing it some more if it could improve the aerodynamics of the car...



Basically, needing answers/thoughts to 3.3, 3.4 and #4 above.

[Somjuan]

Just worth noting that a five speed swap on your car will be a getrag 260 or 265. If yours is a four speed it should be a getrag 262. 240, 242, and 245 were for the four cylinder m10.

Next, only upgrading half the brakes means changing the brake bias (front brake % vs rear brake %). Better to upgrade all around and add brake bias adjustment. Otherwise the front or rear locks up first and you'll have a bad time.

Chassis strengthening is great, no problems there. Just one suggestion, a limited slip differential and around an inch of drop on bilstein sports/H&R springs combined with a rear sway bar will drastically improve handling.

And lastly, if you engine swap for that specific range of power you can do the poor man's s50(sp?) an m50 non-vanos with the m54 internals. There's a writeup somewhere on revlimited about that which goes much more deeply in depth. There's also a camp here that would say just to go with the m42 and supercharge it. If you're tracking the car, that's a great move. Massive handling improvements can be had by moving that engine as far back as possible that simply aren't easy or cheap to do with six cylinders. If you do six cylinders there are also several options of m20 engine that would more or less bolt on. The rest of the drivetrain behind the engine has to be considered for reliability reasons though.

[WantingAfunE21]

Just worth noting that a five speed swap on your car will be a getrag 260 or 265. If yours is a four speed it should be a getrag 262. 240, 242, and 245 were for the four cylinder m10.

Next, only upgrading half the brakes means changing the brake bias (front brake % vs rear brake %). Better to upgrade all around and add brake bias adjustment. Otherwise the front or rear locks up first and you'll have a bad time.

Chassis strengthening is great, no problems there. Just one suggestion, a limited slip differential and around an inch of drop on bilstein sports/H&R springs combined with a rear sway bar will drastically improve handling.

And lastly, if you engine swap for that specific range of power you can do the poor man's s50(sp?) an m50 non-vanos with the m54 internals. There's a writeup somewhere on revlimited about that which goes much more deeply in depth. There's also a camp here that would say just to go with the m42 and supercharge it. If you're tracking the car, that's a great move. Massive handling improvements can be had by moving that engine as far back as possible that simply aren't easy or cheap to do with six cylinders. If you do six cylinders there are also several options of m20 engine that would more or less bolt on. The rest of the drivetrain behind the engine has to be considered for reliability reasons though.

There were Getrag 242's set up for the 6 cylinder cars. In the US they were on low spec 5 series, and are a decent low buck option when putting in a M42 on a track/autocross car.

[dlguadiz]

Thank you John. Learned a thing or two with your reply. I realized my e21 is an '81 model and does not have the rear sway bars. Question: how do you determine if you have the LSD or not?

There's also a camp here that would say just to go with the m42 and supercharge it. If you're tracking the car, that's a great move. Massive handling improvements can be had by moving that engine as far back as possible that simply aren't easy or cheap to do with six cylinders.

I am actually leaning on the m42 swap. The m20b20 engine has a rubber timing belt and would rather have the chain. But did I hear you right? Supercharge, not turbocharge. Any reason behind this?

[dlguadiz]

Just found an m54 3.0 liter that produces 228 hp -- right on the sweet spot I'm looking for -- and cheaper than a turbo m52... or even a turbo'ed m42... but the torque is 100 lb. ft. more than the m20b20... weight-wise, its only 9kg heavier...

Correct me if I'm wrong but I read somewhere that an e21 with 300hp broke its differential easily... while OLD MAN's has an m20b25 with 180hp with no problems on the differential... if I change my differential to be absolutely sure, which LSD should I look for (which can handle 220+ lb. ft. of torque? And would I need to strengthen the front sub-frame?

EDIT: Aarrgghhh... m54 is drive-by-wire... no way I'm going to use this engine as is... nothing beats cable throttle in responsiveness... and I am a software development engineer by profession!!! (now giving a lot of thought on that poor man's s50).

[SoCalE21]

Using your list, this is how I'm set up, it's great.

1. Chassis strengthening
1.1 Front strut brace
1.2 Alpina bar
1.3 Rear strut brace


2. Weight reduction/redistribution, load reduction
2.1 Removed the mechanical fan and replaced it with temp-controlled/switched puller electric fan
2.2 No AC car from the factory
2.3 Relocated battery to rear
2.4 Stock 320is sports Recaros

3. Suspension/Brakes/Tires
3.1 Currently running 205/50/15s wheels.
3.2 Volvo front calipers with '77 vented discs
3.3 Rear discs
3.4 H&R springs/Bilsteins

Also, LSD and rear swaybar.

200hp
2440 lbs. with full tank of gas

So much fun!

[dlguadiz]

200hp
2440 lbs. with full tank of gas

So much fun!

Looking forward to joining you in that club! What setup (engine/trans/turbo) did you install for the 200 bhp? So standard LSD for e21 can handle 200bhp?... thats what I worry about the most...

[OLD MAN]

How fast can you drive on the roads in the Philippines? The reason I ask is that changing the diff to an 3.91 LSD will make a huge difference in the cars quickness without changing anything on the engine. As will swapping out the four speed for a five speed, the lower first gear with the lower diff gear will get the car moving much faster.

The key to more power in any BMW engine is compression, cam, fuel delivery and ignition system. The easiest swap for you is to build a M20B25 with good parts, it will bolt right in - 882 head and go form there. I stayed with the modified M20B20 intake to stay away from all the fuel delivery upgrades required that going to injection would have taken. Probably saved $500.00 dollars or more and did not have to wire in a computer for the newer engine.

[SoCalE21]

Looking forward to joining you in that club! What setup (engine/trans/turbo) did you install for the 200 bhp? So standard LSD for e21 can handle 200bhp?... thats what I worry about the most...

$14

[dlguadiz]

How fast can you drive on the roads in the Philippines?

Officially, its 100 kph highway/freeway driving (62 mph). But after several seconds on the freeway, you'd realize you can go twice as that without anybody really caring at all. Personally, the fastest I did with my 320/6 was 180 kph (112 mph) but was limited* only by the quality of the road 20 years ago. Nowadays, I reckon I can go faster than that (given of course that I upgrade my brakes, etc.)

*Note: Now looking at the 320/6 official specs, I think I maxed out on the speed at 180 kph... the only reason I did not think I did was that my speedometer max is at 220 kph.

Once, I was driving my daily driver Toyota at the official max speed when a new Mustang with racing stripes buzzed by me, I first gave a chase but the 103 hp limit showed itself at around 150/160 kph. I end up thinking, "if only I had my BMW updated to its absolute limit..."

I stayed with the modified M20B20 intake to stay away from all the fuel delivery upgrades required that going to injection would have taken. Probably saved $500.00 dollars or more and did not have to wire in a computer for the newer engine.

You know, for a software engineer that specializes in microcodes/firmware (software programs controlling machines), you'd think I'll be bias towards drive-by-wire technology. No. Like you, I like my fuel delivery to be analog, if given the choice. That's why if I have a choice on what supercar I'd rather own and drive, I'd choose the DeTomaso Pantera.

If only I can find an m20b25 here... then low-boost it... btw, the m20b25 timing is chain-linked? I hate having to think about the timing belt all the time...

The reason I ask is that changing the diff to an 3.91 LSD will make a huge difference in the cars quickness without changing anything on the engine. As will swapping out the four speed for a five speed, the lower first gear with the lower diff gear will get the car moving much faster.

Thank you for this info. Now, I know which changes I would be making first. The engine will be the last change. I suppose any five speed gearbox, driveshaft and LSD differential that works with the m20b20 will work with the m20b25, no? How about if I go with the poor man's s50 above. Or the turbo'ed/supercharged m42?

[dlguadiz]

Correct me if I'm wrong but I read somewhere that an e21 with 300hp broke its differential easily... while OLD MAN's has an m20b25 with 180hp with no problems on the differential... if I change my differential to be absolutely sure, which LSD should I look for (which can handle 220+ lb. ft. of torque?

I found this discussion on bimmerforums... https://www.bimmerforums.com/forum/s...n-e21-subframe

It answers the question(s) I posted. jrcook320 posted it and we just need to google metric-mechanic-differential-booklet.pdf to get the torque rate per differential. My 3.64 diff can take 260 ft pounds. The m54b30 is rated at 220 ft lb at 3300 rpm. Factoring in metal fatigue/degradation over time its going to be a bit risky...

[dlguadiz]

Just one suggestion, a limited slip differential and around an inch of drop on bilstein sports/H&R springs combined with a rear sway bar will drastically improve handling.

Just had time to properly check the car and found out I have both front (23.5mm) and rear (16mm) sway bars. Yaayy!

[OLD MAN]

I found this discussion on bimmerforums... https://www.bimmerforums.com/forum/s...n-e21-subframe

It answers the question(s) I posted. jrcook320 posted it and we just need to google metric-mechanic-differential-booklet.pdf to get the torque rate per differential. My 3.64 diff can take 260 ft pounds. The m54b30 is rated at 220 ft lb at 3300 rpm. Factoring in metal fatigue/degradation over time its going to be a bit risky...

Not sure you will have metal fatigue issues - bmw used some pretty high quality materials plus your tires have been a torque shock relieving factory over the years. Was your car raced/driven really drive for most of it's life?

[dlguadiz]

Was your car raced/driven really drive for most of it's life?

Its manufacture date is 1981. We got the car around 1988. No knowledge of how it was driven then but we knew from inspection later on that it had an accident on the passenger side. Certainly from 1988 to 2007 (almost 20 years) it was not driven that hard. From 2007 to 2014 it was not driven at all. I resurrected it and has only driven it sparsely since. So I guess I should not be too worried about fatigue...

Stamped on the differential is GGG-40 which is a type of ductile iron, which means it has 80% of the tensile strength of steel. That's as far as I could go... any metallurgist here? And Im quite sure thats the composition of the cast body, not the gears themselves.

Besides, im going to use the m20b25 instead with 164 ft lb at 4,300 rpm.