M20 B3x Naturally Aspirated Stroker build past, present and future

[vehicular]

Readings of dynos are always under debate.

That's precisely the point. Why would you intentionally muddy the waters by introducing intentional inaccuracy to your dyno reading?

[luckybk]

I would only imagine that you would reverse calculate bhp because the total number is higher and that makes the guy who just paid for all the labor on his upgrades and knows nothing about how it's attained happier.

[digger]

look its fairly logical to be able to want to be able to compare an engine against what it was from the factory or against other engines which are rated in bhp which is fine, but just got to compare apples to apples.

e.g. with dynodynamics in shootout mode you can ask for either roller hp (rwhp) or estimated losses (bhp) and there is a set correction factor for number of cylinders and whther its NA or FI but this is clearly evident usually on the sheet if you know what to look for.

As long as the dyno sheet clearly says what it is i'm ok with either as even chassis numbers are sketchy at times and there is no one number that is correct. you should not be cross comparing different brands anyway even though if you define test procedure all eddy currents should read the same they simply don't.

Some systems e.g. Maha use coastdown loss estimations which are good at estimating some of losses accurately and the unknown losses are modelled so it probably works out fairly close. They certainly are not exact.

[hasa]

Exactly.... if car manufacturers would announce the power as whp, there would be less interest about the engine power.

But I don't see where the inaccuracy is if the dyno measures both WHP and the losses. The dyno sheet contains exactly the same whp information + losses and the calculated engine power as extra.

The dyno numbers are any way muddy waters. They are sometimes used for marketing, look for example the numbers given by VAC. Plenty of unbelievable examples are found where basic race cars are "measured" to have volumetric efficiency of best Nascar or F1 engines. Bullshit sells.

[digger]

Exactly.... if car manufacturers would announce the power as whp, there would be less interest about the engine power.

But I don't see where the inaccuracy is if the dyno measures both WHP and the losses. The dyno sheet contains exactly the same whp information + losses and the calculated engine power as extra.

The dyno numbers are any way muddy waters. They are sometimes used for marketing, look for example the numbers given by VAC. Plenty of unbelievable examples are found where basic race cars are "measured" to have volumetric efficiency of best Nascar or F1 engines. Bullshit sells.

the inaccuracy is that different brand dynos measure whp differently and the measured losses are done under coast down not under load so the losses measure are not the same as during the run.

[digger]

Some hopefully interesting Mass/Inertia data

So first eveyone knows what mass is, its linear or translational inertia. Mass moment of inertia (MMOI) is the rotational equivalent. it tells you the resistance to angular accelearation.

the simplistic formula for a point mass is MMOI = Mr^2

so 1kg at 150mm distance is 1 x 0.15 x 0.15 = 0.0225 kg.m^4

Here are some formulas for simple shapes like cyclinders etc



Here some data for flywheels, essentially the mass is meangless its the MMOI that dictates what the resistance to spinning up.

Stock M20B25 228mm Flywheel (FW) and Pressure plate (PP)
Metric Mechanic 240mm lightweight FW (based on M30 with M20 starter gear) and M5 PP

Mass were weighed data and inertia values were from some CAD approximations. The density were tuned in the CAD to match the weighed values as steel and Cast iron density varies. The bits that are steel are steel so the inertia is fairly accurate.

What it shows is what i suspected the pressure plate has as much MMOI as the flywheel and even though the 240mm FW is lightened the net effect is mostly diminished as the M5 PP is fairly hefty. The point wasnt to have the lighest though as relatively comfortable pedal effort with nice modulaton like OE but a bnuch more torque capacity is what i wanted. This is what i have used since 2007.

Also for interest i showed the crank and rod MMOI as a point of reference. The rod MMOI is based on the big end mass at the centre of the crank pin.

Stock M20


MM 240mm


Results


Anyone that has a 3D CAD of the RHD one i can work out the numbers.....

[vehicular]

I have an RHD flywheel on the floor of my shop now. I'll try to make time this weekend to model it.

I have some other parts I need to model anyway.

[zwill23]

How's the car digger? Make any progress on the engine build?

[digger]

How's the car digger? Make any progress on the engine build?

Been working on a side project for an ATI vibration damper for the M20 that's essentially plug and play, it is fairly well developed from a design point.

Also got some other non engine things to work on with the car with rear axles, diff etc, plus interior dash, carpet etc so will be on hold for a while longer yet.

Also still a bit to do before i swap engine in as want to get a more modern standalone and new carbon airbox (requires the install of the Massive dual MC booster delete which is ready to trial).

[zwill23]

Been working on a side project for an ATI vibration damper for the M20 that's essentially plug and play, it is fairly well developed from a design point.

Also got some other non engine things to work on with the car with rear axles, diff etc, plus interior dash, carpet etc so will be on hold for a while longer yet.

Also still a bit to do before i swap engine in as want to get a more modern standalone and new carbon airbox (requires the install of the Massive dual MC booster delete which is ready to trial).

Very cool, I assume the damper is going to facilitate higher rpms?

Sounds like big things are on the horizon

[digger]

Very cool, I assume the damper is going to facilitate higher rpms?

Sounds like big things are on the horizon

yes, the stock damper wouldn't be best for the longer stroke engines as its tuned for different frequency(s) plus they will start to be NLA soon if not already. The catch it is a very tight envelope so some light trimming to the lower timing cover is required but that should be about it.

[zwill23]

I've been hearing of more of the stock units exploding with age and they have gone NLA as far as I'm aware, nice to see we have some options in the works.

[digger]

I've been hearing of more of the stock units exploding with age and they have gone NLA as far as I'm aware, nice to see we have some options in the works.

yeah but it might be spendy enough to keep people away though, like other ATI vibration dampers for BMW's....though when i bought a new OE one it was still a few hundred

[beemaestro]

You have to compare apples to apples. Is that a real wheel power number, or that weird calculation of brake power calculated from wheel power?

Hi, they use a SuperFlow AutoDyn 30 AWD dyno if that clarifies things for you!?

Short vid of the car on the track:

https://youtu.be/YFAlrWJ0lEk

I'm looking to get a new head, 44-45mm intake valves, cam 292 or up, 12.4 or higher CR pistons and ITB's (tapered 45>42mm) for this year and maybe get another 20-30HP out of it... but posting my wants here is off-topic I guess :D

[beemaestro]

stock manifold is good for around 220-230 whp +/- which is around 250-260 bhp+/- so yeah 235 SAE hp at flywheel is achievable.

years ago a guy build a 2.7 whith good CR stock manifold and huge dbilas cam 312 degrees or something crazy and it still fell with this ball park.

It does come down to your definition of proper power

It think with fairly basic components like 81mm crank, 272> cam, headers, anything over 210-215hp is bonus