M5x and S5x over M20.. Why?

nando · 09-12-2018, 06:31 AM

yeah, lots of people will use 20-25% for drivetrain loss so they can imagine an inflated BHP #. No way, especially not on a modern car - maybe back in the 1960s they were that high, but those are low hanging fruits for engineers trying to claw every bit of fuel efficiency they can.

Plus on a 300whp car that would mean 100hp is turned into heat - and drivetrain losses aren't a straight % anyway..

digger · 09-12-2018, 12:07 AM

the twin roller dynos are more inconsistent as they rely much more on the tie down procedure and tyre parameters/setup.
Correction factors get you only so far, if the ECU pulls timing because something is too hot then the correction doesn't account for that.

one of the traps people also fall into is using an engine that has mileage to come up with bogus drivetrain losses. the BMW m20b25 makes about 150-155 whp stock when fresh. its 168hp SAE when stock, so that's only circa 10% "losses" this doesn't mean the factory underrated it because they certainly didn't.

AWDBOB · 09-10-2018, 05:28 PM

Originally posted by varg

It's nothing personal, just my impression based on the fact that most dynos are optimistic and 94hp/l (based on the 265bhp number you posted) from an M52 with cams and an intake manifold seems a little high. I'm highly skeptical of shop dynos, they have an incentive to inflate, as does the dyno manufacturer. When people see dyno numbers of a stock car and go OMG IT'S UNDERRATED FROM THE FACTORY!!! Most of the time I say no, dynos at tuning shops are usually optimistic, and the manufacturer would have no incentive at all to underrate, barring some sort of limit like the infamous 276hp japanese car. When more horsepower is always a good selling point, why underrate your engines? Car companies are trying to make money from a wide audience, not make inside jokes that "real" car guys will get, like "BMW underrates their engines!"

So, when I see that an M52B28 is rated at 190bhp, and I see a dyno which is showing numbers like 178whp for that engine (stock aside from the muffler), my first impression isn't that the driveline is incredibly efficient (~6% loss) or that the engine actually made over 200bhp from the factory instead of 190bhp, I'm thinking the dyno number is a little inflated. It's great for comparison to see the gains of the cars with the tunes, but the actual numbers are of less important than the shape of the curves and the gap between the lines.

That's why when I tune someone's car, I tell them that dyno numbers are more of a ballpark figure, and a dyno is only truly useful for comparisons such as before and after tune.

I agree in that dyno numbers are a ballpark, but I think accurate results can be achieved if you use the tool how it's designed. Mustang Dynos "read low" out of the box but can be heavily modified to suit whatever results are optimistic.

Dynojets are typically accurate from one dyno to another without adding a correction factor, as it's testing exactly what that car is making on that day at that time/temp/etc rather than adjusting for temp, pressure and humidity. SAE is nice for shops to compare (I think Market uses STD) so that way they can't say "oh well it was hot this day so that's why this car made less/more/whatever". Post-correction all cars are being 'tested' under the same calculated conditions, effectively.

Dynojets are nice, though, as there are much less susceptible to inflation due to standardized CFs.

I've seen smoothing inflate numbers as well. You could have a choppy, spikey curve that when "smoothed" excessively takes a couple spikes and magically gives you 10whp when you smash the graph down, when in reality your car isn't making that.

It is funny though- I've seen tuners post up a pre and post graph, and leave the initial run uncorrected on a hot humid day and then the post tune graph corrected to help them sell their services :D

Anyway, back to m20 stuff.

DBShiznit · 09-10-2018, 05:24 PM

Originally posted by SkiFree

I get to drive around in a 6-speed swapped S52 and an ITB'd 3.1L M20 e30. The M20 engine delivers so much more character it's not even close. It loves to r3v and has a much more period feel. Smiles per/mile the M20 is the obvious choice.

As time goes on an M20-engine e30 will have a much higher value than an M52 e30. Yes, the M52 is a "newer" engine (despite the fact it's now nearly thrity years old), but if I wanted something newer and more efficient, I would have bought a newer and more efficient car. If I wanted something cheap, I would have bought a Honda. In short, your factors are less relevant by the day.

Glad I’m not the only one who thinks this way

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e30davie · 09-10-2018, 05:22 PM

I pulled the engine cover off my brothers mazda 3 engine. And it made a huge difference to the injector/valve train noise. Maybe there is a market for engine covers for the m20....

jeenyus · 09-10-2018, 04:08 PM

You're right. The injectors are loud and it's not just the m20 injectors. I replaced min with 4 pintle Bosch injectors and they are still loud.

Originally posted by MrBurgundy

A properly functioning head wont have any valve noise if adjusted within spec.

Everyone seems to forget out loud those injectors are.

My valve trains makes no noise when warmed up, but my injectors are loud as fuck

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MrBurgundy · 09-10-2018, 03:59 PM

Originally posted by jeenyus

And the valves tick twice as loud.

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A properly functioning head wont have any valve noise if adjusted within spec.

Everyone seems to forget out loud those injectors are.

My valve trains makes no noise when warmed up, but my injectors are loud as fuck

jeenyus · 09-10-2018, 03:30 PM

And the valves tick twice as loud.

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digger · 09-10-2018, 03:15 PM

Dyno numbers are relative, a fresh m52 with intake and cams should make about those numbers. A fresh m20 with the same crank, itb and mild cam coincidently makes about the same torque and hp.

SkiFree · 09-10-2018, 12:06 PM

Originally posted by DesertBMW

I got 4 E30s two with M52 swaps and two with M20. Everything is better with M52B28, they are very cheap now, get better gas mileage, better power band, better throttle response, smoother idle, better resale value.

I get to drive around in a 6-speed swapped S52 and an ITB'd 3.1L M20 e30. The M20 engine delivers so much more character it's not even close. It loves to r3v and has a much more period feel. Smiles per/mile the M20 is the obvious choice.

As time goes on an M20-engine e30 will have a much higher value than an M52 e30. Yes, the M52 is a "newer" engine (despite the fact it's now nearly thrity years old), but if I wanted something newer and more efficient, I would have bought a newer and more efficient car. If I wanted something cheap, I would have bought a Honda. In short, your factors are less relevant by the day.

nando · 09-10-2018, 08:29 AM

Dynos can be reasonably accurate if the tuner/operator isn't messing with the correction factors. Using SAE on a dynojet I got ~218whp on my 330i which is pretty reasonable for 255bhp. Of course you can make the number whatever you like by using a different factor (or none at all), but that's why there are standards like SAE (or Shootout-6 on a dyno dynamics).

varg · 09-10-2018, 08:16 AM

Originally posted by 2mAn

Search through this and tell me I’m wrong or that my dyno was optimistic

https://www.r3vlimited.com/board/showthread.php?t=327183

Dave own beater M52 makes 217whp and mine was a freshly rebuilt motor with ~16k I think when I dynod it

It's nothing personal, just my impression based on the fact that most dynos are optimistic and 94hp/l (based on the 265bhp number you posted) from an M52 with cams and an intake manifold seems a little high. I'm highly skeptical of shop dynos, they have an incentive to inflate, as does the dyno manufacturer. When people see dyno numbers of a stock car and go OMG IT'S UNDERRATED FROM THE FACTORY!!! Most of the time I say no, dynos at tuning shops are usually optimistic, and the manufacturer would have no incentive at all to underrate, barring some sort of limit like the infamous 276hp japanese car. When more horsepower is always a good selling point, why underrate your engines? Car companies are trying to make money from a wide audience, not make inside jokes that "real" car guys will get, like "BMW underrates their engines!"

So, when I see that an M52B28 is rated at 190bhp, and I see a dyno which is showing numbers like 178whp for that engine (stock aside from the muffler), my first impression isn't that the driveline is incredibly efficient (~6% loss) or that the engine actually made over 200bhp from the factory instead of 190bhp, I'm thinking the dyno number is a little inflated. It's great for comparison to see the gains of the cars with the tunes, but the actual numbers are of less important than the shape of the curves and the gap between the lines.

That's why when I tune someone's car, I tell them that dyno numbers are more of a ballpark figure, and a dyno is only truly useful for comparisons such as before and after tune.

digger · 09-10-2018, 12:54 AM

it comes down to personal preference but if i was to swap it would have to be a decent jump in both torque and hp over what a decent m20 could do but not enough that its constantly frying tires or needs body work to get enough rubber and it should look like it belongs in the engine bay.

s54 or s50b32 would fit the bill nicely.....S38b38 might be a bit too much as you cant leave it stock. anything non BMW just looks wrong regardless of how much it make sense