From knowing nothing to having a Thunderbird supercharger on an m20b27i

[Ether-D]

EDIT: This turned into a build a few weeks in, the good stuff starts around post #40 or so….


TLDR: Click for the Cliff's notes on this ordeal and phase 2, twin charging

First start video:

https://www.facebook.com/photo.php?v=749426495070352&set=vb.100000090243381&type=2&theater

0-80mph non-intercooled, big pulley:

https://www.facebook.com/photo.php?v=758488297497505&set=vb.100000090243381&type=2&theater

Walk-around:
http://https://m.youtube.com/watch?v=1RHeG2W_4Ok


M20b25 1992 325i cabby

There seems to be precious little about it. I've been thinking a lot about it recently. What I've read is mostly people who want 3-400 hp. I can't afford (and frankly, have no business with) that many horses.

I'm decent at fabricating, not at making it pretty, but making it work. I don't care if it's not pretty.

This is what I want: About 200whp, motronic 1.3, as cheap as possible (I have three kids), and above all, completely dd-able.

There's a t-bird turbocoupe s/c and intercooler on cl for $150. I could grab it as a starting point. I was thinking I'd just under-drive it maybe?

I really just want something to tinker on. Something new and fun and not too spendy to dick around with.

Advice?

Oh yeah, I know "turbo, turbo, turbo". I don't want to do what's been done so much already. Thanks for that though.

[TheTacoMan]

Bottom line is if you are going to DD it you NEED an aftermarket way of managing the boost and timing. From what I understand the eaton m90 supercharger has a few versions only one or a combination of one work. Im not so sure.

Also, quality parts are a must. Cheap ebay parts break, ask me how I know.

[Ether-D]

^Ok. I'll give that some thought.

After looking at pics of various OEM superchargers on ebay all evening, it looks to me like there are a few potentially good (looking at least) ones. One of the mercedes ones looks good (it has a clutch, which could be helpful), the t-bird one looks pretty good, and there's a toyota previa one that looks interesting as well (also with clutch).

I should revise my first set of goals a bit. I don't really care about 200whp so much, as what I really want is some more torque. I mean I'll take more HP, but my m20 is pretty fun up over 3500RPM as is. Maybe just a more balanced feeling.

That being said, there is a very small supercharger available on ebay that came on a Subaru "Pleo". It's a tiny little JDM car, 600 or so cc I think. How crazy is the idea of over-driving that little charger so that it is blowing hard at low RPM and then free wheels up around 3500 RPM using a clutch? The idea feels totally bonkers, but WTF? Right?

Educated opinions welcomed.

[Ether-D]

http://www.autospeed.com/cms/article.html?&A=110294

Quick fun read. Good to know...

[Ether-D]

I'm almost sold on the previa one. Smallish, made for a 2.4l, rectangular inlet and outlet for easy adaptation, and a clutch. Also around $200+/-.

[TheTacoMan]

You absolutely have to research what supercharger would work, and check efficiency maps(if thats the right word).
Having too small of a supercharger will literally get no boost and also blow really hot air.

A friend of mine tired a eaton m62 I believe off a 4 banger Mercedes. Didnt work at all, inefficient.


Also a turbo setup can be just as potent on the low end with the right setup.

[Ether-D]

Thanks Taco man. Anybody else wanna chime in?

[wazzu70]

Well running the factory Motronic is pretty much a non-starter for anything FI. You have to figure out how you intend to tune the car first.

You cant just overdrive the supercharger without consequence. The air heats up and decreases the efficiency. The supercharger you are talking about is probably an early (89-93) supercharger which would work, but its the least desireable supercoupe supercharger.

Anything you slap together is just going to cause you a lot of headache and cost to repair. Plan out what you want to do and do it right.

[Ether-D]

I'm not being clear enough I think. Plus I've changed direction a time or two in this thread (sort of thinking out loud).

To be clearer, I was talking about overdriving a small supercharger just during the low rpm range (for added torque) and then using an electric clutch
(like an a/c clutch) to disengage it for higher rpm. Thus, not actually running it any faster than it would normally run, eliminating the inefficiency/hot air aspect. My thinking was that it could be helping a little for torque and be freewheeling at higher rpm where the power of an m20 is already fine (for me). I'm past that part of the brain storm now. But thanks.

I now am thinking about a toyota previa S/C. The previa motor was a 2.4l. My motor is a 2.5l. It (the previa motor) also has a 6500RPM red line. So, very similar air volume across the board. I get the feeling this could work.

And again, I'm not reaching for 500 HP (or 400 or 300 or really even 250). This seems to be hard to contemplate. My goal is to play around with some parts and see if I can get something to work. I really don't mind failing. Worst case is it does nothing and I put it back to stock. Or I cook my motor. I'll just toss another one in if that happens.

[Cletonius]

In the OP you stated you were budget conscious because you have a family. Now you're stating that you're willing to break parts and throw money away. Which is it?

It's exhilarating to buy parts and build stuff, sure. This however does not go hand in hand with reliability which you've said is a must have result. Slow down.

You need to read compressor maps and pick a S/C that does what you want. You also need to learn about engine management and how to properly size your injectors.

Spend a few months reading up on this stuff, buy/build your management, buy all the other parts you think you might need, and then get started. Build it on a stand and swap it in complete.

[Ether-D]

I am budget conscious, in that I won't be buying a $4000 kit. If I have to give up and put a $200 junkyard motor all the while learning something, that's not throwing money away, it's paying for an education. I need to do to learn. It's my favorite way anyway.

[Ether-D]

Also, in the op I should said "This is what would be ideal:" instead of "This is what I want:". What I want is to build stuff.

[UpstateMike]

Sounds fun but scary at the same time. Aren't there any other threads on this topic that could help you??

[TheTacoMan]

The entire electric clutch disengaging the supercharger sounds plausible but expensive.

I mean Im gettting boost by 2300 rpms with a gt28 sized turbo. If you were to go smaller who knows. I dont mean to drive you away from a supercharger, turbos are just cheaper and more efficient.

[Ether-D]

I agree that the turbo option is cheaper and well documented. I just need to be a special snowflake.