Author Topic: A few questions about my turbo build (Read 5776 times)

bflan2001 · « **on:** December 03, 2011, 08:50:10 PM »

I'm rebuilding my M42 to stock specs except with M50 pistons (for a comp ratio of 8.5:1), and a few things to reduce valvetrain weight (vw lifters, single row chain & sprockets). I also have an MLS headgasket, raceware hardware, and I'm thinking about VAC coated main & rod bearings. That being said, if I slap on either a t28 or t3 turbo and boost it to about 10psi, will that get me anywhere near 200WHP?

Now onto the more complicated questions...

What turbo would you recommend for a mild build on a budget? I'm looking for power that kicks in low, rather than the rubber band feeling you get from big turbos on small motors. This is my DD so driveability & reliability are important.

Originally I wanted to buy an m47 crank, s50 pistons & custom rods but it seems like that is a lot of investment for a relatively small return (at least when you add a turbo to the equation). I read that you can use the M50 pistons with otherwise stock internals, can someone confirm this?

Again, concerned about $$, I'm hoping I can avoid custom engine management & tuning. Is this a reasonable expectation? To me it doesn't make sense that you can use the stock ECU with a turbocharger, but it looks like it's been done before. I bought a RRFPR hoping it will help avoid custom tuning.

That's all for now, looking forward to your expert opinions and advice. Please feel free to make suggestions/recommendations that I didn't ask about. This is my first complete motor rebuild as well as my first turbo build so I can use all the help I can get. Thanks in advance, M42 gurus!

DesktopDave · « **Reply #1 on:** December 04, 2011, 06:40:53 AM »

I'm looking forward to answers, wish I knew more about FI.

Did you consider a supercharger instead? They seem easier to tune for low-level torque. The M42 DASC is pricey, but with a smaller wheel I'll bet you could get enough PSI out of it. The Mini Cooper is a great example of a point-n-shoot, but they only coaxed 160hp-ish out of it.

Mercedes used a Roots blower on many of their C-class 2.0 and 2.3 M111 Kompressors. I'll bet it's tame & very civilized if the average Merc owner could live with it. The M111 was a profoundly under-stressed motor...but a similar induction setup on an M42...with few tweaks...I'd figure 200rwhp wouldn't be impossible, if the blower & wheel were properly sized.

bflan2001 · « **Reply #2 on:** December 04, 2011, 08:03:39 AM »

i've thought about both, originally i did want a supercharger but they are super rare and i can't afford to buy new. without the DASC kit there is a ton of fabrication and i don't have the skills or the resources to do it. custom turbo seems to be simpler. also the supercharger is maxed out around 200, i'd like something i can continue to upgrade over the years.

rob_e30 · « **Reply #3 on:** December 05, 2011, 08:33:41 AM »

Let's start with the basics... Cheap, reliable, fast: Pick two! You can make it cheap and fast, but it won't be reliable. You can make it cheap and reliable, but it won't be fast, or you can make it reliable and fast, but it won't be cheap.

There is a lot more fabrication in installing a turbo than a supercharger. With an SC, you only need to worry about the instake side of the engine. If you don't want to keep the AC, I think that would be an ideal place to put a super charger.

I would not run any FI system with the stock ECU alone. You cannot get the degree of control or even an acccurate view of the variables necessary to properly control an engine. AFR, boost/vacuum level, and knock are not properly managed and accounted for. It can be done, but go back to the first paragraph.

Finally, read more. There is a lot to learn so get books, scour the web, and collect different opinions.

Good luck!

bflan2001 · « **Reply #4 on:** December 05, 2011, 12:56:28 PM »

Thanks, Rob! I'm going to need it I'm sure.

My top priority is reliability, then power, then price. I'm not looking for outrageous HP so I think I can get the power I want without breaking the bank. I don't need to keep it under X amount of dollars or anything like that, but I definitely can't afford to call up Downing Atlanta to have them send me their kit. Which means if I go with a supercharger, I need to fabricate an entire intake manifold, airbox, supercharger bracket, etc. The turbo manifold I can purchase, and I plan on using the stock intake so to me it seems like there is much less fabrication involved with this route. Correct me if I'm wrong here.

As for the engine management, I guess I'll have to consider an aftermarket system. I'm familiar with megasquirt in the M10 world, I would love to go that route but I'm afraid there's not enough info on megasquirting the M42. M42 guys seem to hate on it from what I've read, but to M10 guys it's one of the best systems out there. Do you have an opinion on megasquirt vs. other systems?

I've been reading the book Maximum Boost, and I've read through every build thread I can find online. Do you have any recommendations for other books? I'd rather read books or articles than threads. I've found the threads are all incomplete and most have bad information mixed in with the useful stuff.

wazzu70 · « **Reply #5 on:** December 05, 2011, 08:00:03 PM »

Forced Induction Performance Tuning

^^ this is a much better book than Corky Bell. Corky is good for the basics, but it leaves a lot to be desired IMO.

Engine Management: Advanced Tuning

^^ This book does a good job explaining basic tuning theory.

Those are just two books I have read and thought they were pretty good. I usually lend them to friends who are interested in the topic.

I fully agree with what Rob said. I would never consider running a forced induction car on the stock ECU. I guess if you absolutely have to, the W.A.R chip might be an option. Megasquirt is only OK for any car

It uses ultra cheap crappy hardware, it makes me sad

If you look here there is a thread I am working on about getting the car up and running on the VEMS system. Most any engine management system is similar, but if your head spins and you feel nauseous looking over that...standalone is not for you, or hire out the tuning/installing.

Without good management/tune your car is about as unreliable as it ever could be.

I agree with Rob that a supercharger setup is a lot less fabrication. You can buy some of the M42 parts, but its going to cost you!

In Garrett sizes a GT28 or GT30 turbo would be quite nice. T28 better for a street car.

DesktopDave · « **Reply #6 on:** December 05, 2011, 09:49:48 PM »

@bflan:
The M42 is a great motor to 'squirt. You'll need to spend some time on conditioning the BMW crank trigger, but many of the sensors are exactly the same as the M10 & M20.

I have an MS 2.2 collecting dust in my basement right now...thinking about putting it in a motorcycle, but it'd be great in the BMW too. If you head that way, we could possibly even add a section to the board specifically for bins...hint hint...

My personal M42 fantasy is a clutched supercharger running where the P/S pump would normally go with a serpentine belt setup. Not too much more weight, predictable HP, easier fabrication. The Merc 'charger fits the bill...and they're fairly cheap with so many made. They're also usually cheaper to rebuild than turbos.

@Wazzu:
Do the VEMS tunes work in any way with MS? I've been told that the codebase is somehow similar, do you know offhand if that's true?

bflan2001 · « **Reply #7 on:** December 05, 2011, 10:20:02 PM »

Thanks, I added those to my amazon wish list, gotta wait til after the Christmas season before I buy myself any more gifts.

Is a supercharger easier to tune than turbo or about the same?

You guys are starting to make me lean towards a supercharger again...Would it still be less fabrication if I were building a custom system? I really can't afford 3-4 grand for a kit and I haven't seen any supercharger manifolds available for a few hundred like there are with turbo manifolds. I'm not using the A/C or P/S pumps so there is plenty of room for the compressor.

DesktopDave · « **Reply #8 on:** December 05, 2011, 10:27:37 PM »

The mount and the belt are the big problems. The intake would be tricky to get right but it'd be comparatively easy...I'm thinking alu tubes, silicone elbows and stainless t-clamps.

rob_e30 · « **Reply #9 on:** December 06, 2011, 08:30:31 AM »

There would be no need to fab a custom intake manifold with a Vortex supercharger. Desktop Dave has a good suggestion about placement as well and I believe Vortex will work with you on providing a dummy unit to allow you to do your fabrication. There would be a core charge, but you don't have to sink $2K into a production unit to have it lay around for 6 months.

At one point, we had a custom tube made up that went from an M20 throttle body (with the M42 TPS attached) to the M42 intake manifold.

Given the two part M42 manifold, it's a lot easier to fab a plenum and use the stock lower half so you already have the runners, fuel injector boss, and fuel rail.

rob_e30 · « **Reply #10 on:** December 07, 2011, 12:59:18 PM »

Check out this link to see how compact an SC install can be:

http://www.eurotuner.com/techarticles/eurp_0705_bmw_m50_m52_engine/photo_09.html

wazzu70 · « **Reply #11 on:** December 07, 2011, 09:13:02 PM »

Quote from: DesktopDave;108663

@Wazzu:
Do the VEMS tunes work in any way with MS? I've been told that the codebase is somehow similar, do you know offhand if that's true?

VEMS used to use Megatune a long time ago. I don't know if VEMStune has anything in common with MS/Tunerstudio now.

The settings I put into VEMS should be the same for MS as far as crank trigger is concerned. Also if you use a MAP sensor your VE map should be similar as well as the ignition map. Same with any other standalone.