Milwaukee Midget

[fordboy628]

I agree with you on the density altitude and thought the car would be faster in the cool of the morning.    However, it's undeniably faster in the heat of the afternoon, (approx. 3 mph!) so we are missing something important here.    Could be any one of a number of things.

In theory engine power should change at about 1/(the square root of the absolute inlet air temperature change)
Air drag drops with the air density

Power required goes up at the cube of the speed change. This implies that in hot temps you are likely making more power along with the lower aero drag from air density as power required to go faster increases faster than power drops due to inlet temp changes.


Intake tuning will change with intake air temp change, the tuning will move toward higher rpms as air temp increases. Perhaps your intake is moving the torque peak up the rpm range slightly in the heat giving higher average power.

Fuel density will change slightly with ambient temp if the fuel has time to stabilize at the new temp (and is not some how controlled for temp like running through an ice bath).

Rolling resistance on the tires and wheel bearings should also drop with increasing temps.

If you have the data, see if your shift points change (time in each gear) between the cold and warm runs, you might be getting into better gears earlier on the hot runs or something so you have more time to pull the long gears.

Interesting puzzle will be fun to see what the key variable turns out to be.

Seems like the only way to know for sure is to go the data logging route.    Midget would need to log some vital and some esoteric info.    Looking more and more like some Brewery is going to have to pony up for sponsorship dollars . . . . . . . .

Hope this doesn't mean I have to drink American Pale Lager . . . . . . . whatever . . . . . .
 
Fordboy

[Milwaukee Midget]

is there anything prohibiting you from running another head? something crossflow and japanese or korean from one of their small .8-1.3L engines? sohc or dohc? or are you limited by class rules on using the BMC piece?

It's a production class, and I have to use a BMC "production" head or aftermarket equivalent.

That said, the jury is still out on some very esoteric 7 port cross-flow heads complete with BMC casting numbers.  The problem with those pieces is that they are rare, expensive, and not very dependable.

Last year, the Kiwis brought up a Mini Cooper with a BMW DOHC 4 valve fitted to it.  That immediately throws it into modified.

The best alternative that is obviously legal would be to destroke a 1.1 dohc Rover K-series engine - an option I'm considering, but for 2-3 years down the road.

The rules for GT, which allow for swaps, are clearly ambiguous and ambiguously clear.

[fordboy628]

If you don't have EGT's on every cylinder do you know if it is the one that will run the leanest?  What reading is acceptable for your engine?  How far should it be from the head?  What reading is comparable to what air/fuel ratio.  I find air/fuel to give us lots better data to tune with as we can see what it is under any condition at any time of the run.  Data logging isn't cheap but it is way cheaper than replacing a blown motor.  Most modern tuners that now have good air/fuel reading capabilities use that more than the EGT readings which is pretty much all they had to use before reliable/accurate wide band O2 reading was possible.

Sum

I'm pretty sure EGT is in the mix for the next outing.

Not to say you still can't blow one up but taking a cautions approach (very rich) approach with air/fuel and looking at the data kept our old motor alive for a lot of runs/years and it set 2 records.  Without data logging I'll bet we would of blown it up at least once.

Sum

Given all the previous engine issues, the main goal this time around was to have a stone reliable, reasonably powerful engine for the donk.   Nobody was certain the body shape would allow competitive speeds for the class, given that the fastest stock bodied BMC up till now, was only 108+ mph.    Top speed potential was going to make or break the project, and everyone is happy that the car ran 118+ mph.    Woulda been happier with a record, but all things considered . . . . . . .

If you are running faster in the hot air then something else is going on and I don't think it is aero,

Sum

I'm not sure what is going on and data logging is probably the only way to be sure . . . . . .
 
Fordboy

[lsrjunkie]

No matter how things shake out, I think some sort of data logging will take a lot of the mystery out of things.

A friend of mine had a very good point concerning small engines. Simply put, the fact that you are getting that much power out of an engine that displaces enough air to roughly fill three beer cans is absolutely amazing!

That being said I need to get out and slop the hogs. Good luck MM! I'll be following this intently, and can't wait to see the mystery solved!

Sincerely, The Kolorado Kaiser

[fordboy628]

I originally added the 2V to make an early AFR sensor work, there weren't enough volts without an alternator for the heater to work correctly.  However, the electrical power jump from 11.5V to 13.5V is massive (power = V^2/R) so the extra volts give me the power that I need for my fuel pump, and the faster injector switching times that my engine needs (I'm turbo and injection).

Andy

The electrical power requirements for this donk keep going up & up & up . . . . . . . . . .      Chris, when are the dual video cams going to be enabled?

I'm also devoted to KISS, and won't have anything on my race car that doesn't have to be there

Andy

IMHO, anything extra on/in your car is merely poorly placed ballast, that negatively affects your vehicle's center of gravity.    And that's the best case scenario . . . . . .
 
Fordboy

[Milwaukee Midget]

Chris, when are the dual video cams going to be enabled?

I turned my studio into an engine build room.

I will not be turning my cockpit into a studio.

[fordboy628]

Chris, when are the dual video cams going to be enabled?

I turned my studio into an engine build room.

I will not be turning my cockpit into a studio.

Why not?   The masses DEMAND: LSR with Midgets from Milwaukee.   This is such a great idea for reality TV!!!!!   You could franchise it to other cities!!!!!!    Just think of the possibilities . . . . . . . .    midgets everywhere would want in on it!!!!     AND . . . . . . .  Think of the possibilities for Brewery sponsorship . . . . . . . .   EVERY "SMALL" Brewery would want to participate . . . . . . . . .

CALL THE TRADEMARK OFFICE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 
Fordboy

[manta22]

Chris, when are the dual video cams going to be enabled?

I turned my studio into an engine build room.

I will not be turning my cockpit into a studio.

Why not?   The masses DEMAND: LSR with Midgets from Milwaukee.   This is such a great idea for reality TV!!!!!   You could franchise it to other cities!!!!!!    Just think of the possibilities . . . . . . . .    midgets everywhere would want in on it!!!!     AND . . . . . . .  Think of the possibilities for Brewery sponsorship . . . . . . . .   EVERY "SMALL" Brewery would want to participate . . . . . . . . .

CALL THE TRADEMARK OFFICE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 
Fordboy

Not "Bigger is better" but "Small is all".

Regards, Neil  Tucson, AZ

[Interested Observer]

Ref. Hotrod’s reply #3148  and C.F. Taylor Chp. 6

As a point of information:
Doing the calculations, and assuming T1 = 75F, T2 = 90F, Baseline Bonneville Hp = 85, and a baseline speed of 115 mph, the resulting speed as a result of a temperature change from T1 to T2 would be 116.6 mph.

Since this is considerably less than the spread that Midget achieved, it is reasonably apparent that some other effect is also contributing to the “hotter-is-faster” results observed.  (Although, there were some “slow” runs at 90F also.)

[Sumner]

....Doing the calculations, and assuming T1 = 75F, T2 = 90F, Baseline Bonneville Hp = 85, and a baseline speed of 115 mph, the resulting speed as a result of a temperature change from T1 to T2 would be 116.6 mph.....

I still don't understand how the hotter air will result in higher speeds.  Goes against everything I've ever heard about intake temps and what is desired.  Maybe it will start a new trend though and we will be all alone in the morning running  .

Did you try plugging in the numbers using the link I posted that helps pilots figure out what their HP will be for takeoffs at higher altitude density numbers (warmer air at the same altitude)?

Sum

[Interested Observer]

Looked at in the simple, overall sense, it is rather intuitive, and correct, that the drag is proportional to air density, which is inversely proportional to the temperature.  And, power would be considered proportional to air density, which is inversely proportional to temperature.  So, a change in temperature would affect both, proportionally. 

However, to produce power, what is really important is the mass flow rate, not just the air density.  Mass flow rate is the product of the density and the volumetric efficiency.  It turns out that the volumetric efficiency has been shown to vary approximately as the square root of the temperature which, when multiplied by the air density (being inversely proportional to temperature), results in a mass flow rate that is inversely proportional to the square root of the temperature, as Hotrod stated.  This, in effect, says the volumetric efficiency increases slightly with temperature and makes the power loss due to increased temperature less severe than the directly proportional loss of the simpler concept using air density alone.  It is, however, a small effect--the calculated loss of horsepower in the Midget example is only 1.17 hp.  This also assumes that the cooling due to fuel evaporation is the same in both cases.

Conversely, the gain in horsepower in going from 75F to 60F of 1.22 would result in a speed of 114.45 as the drag overcomes the power gain.

Again, this is an academic treatment concerning temperature alone, and as is the case with the Midget, obviously there are other, larger effects taking place somewhere/somehow.  The point of the exercise was to estimate how significant the temperature change alone might be.

NOTE:  Due to a misplaced parenthesis in the worksheet where the calculations were made, the 116.6 mph figure in my previous reply should be 115.5 mph.

[fordboy628]

I agree with you on the density altitude and thought the car would be faster in the cool of the morning.    However, it's undeniably faster in the heat of the afternoon, (approx. 3 mph!) so we are missing something important here.    Could be any one of a number of things.

In theory engine power should change at about 1/(the square root of the absolute inlet air temperature change)
Air drag drops with the air density

Power required goes up at the cube of the speed change. This implies that in hot temps you are likely making more power along with the lower aero drag from air density as power required to go faster increases faster than power drops due to inlet temp changes.


Intake tuning will change with intake air temp change, the tuning will move toward higher rpms as air temp increases. Perhaps your intake is moving the torque peak up the rpm range slightly in the heat giving higher average power.

Fuel density will change slightly with ambient temp if the fuel has time to stabilize at the new temp (and is not some how controlled for temp like running through an ice bath).

Rolling resistance on the tires and wheel bearings should also drop with increasing temps.

If you have the data, see if your shift points change (time in each gear) between the cold and warm runs, you might be getting into better gears earlier on the hot runs or something so you have more time to pull the long gears.

Interesting puzzle will be fun to see what the key variable turns out to be.

Ref. Hotrod’s reply #3148  and C.F. Taylor Chp. 6

As a point of information:
Doing the calculations, and assuming T1 = 75F, T2 = 90F, Baseline Bonneville Hp = 85, and a baseline speed of 115 mph, the resulting speed as a result of a temperature change from T1 to T2 would be 116.6 mph.

Since this is considerably less than the spread that Midget achieved, it is reasonably apparent that some other effect is also contributing to the “hotter-is-faster” results observed.  (Although, there were some “slow” runs at 90F also.)

Looked at in the simple, overall sense, it is rather intuitive, and correct, that the drag is proportional to air density, which is inversely proportional to the temperature.  And, power would be considered proportional to air density, which is inversely proportional to temperature.  So, a change in temperature would affect both, proportionally. 

However, to produce power, what is really important is the mass flow rate, not just the air density.  Mass flow rate is the product of the density and the volumetric efficiency.  It turns out that the volumetric efficiency has been shown to vary approximately as the square root of the temperature which, when multiplied by the air density (being inversely proportional to temperature), results in a mass flow rate that is inversely proportional to the square root of the temperature, as Hotrod stated.  This, in effect, says the volumetric efficiency increases slightly with temperature and makes the power loss due to increased temperature less severe than the directly proportional loss of the simpler concept using air density alone.  It is, however, a small effect--the calculated loss of horsepower in the Midget example is only 1.17 hp.  This also assumes that the cooling due to fuel evaporation is the same in both cases.

Conversely, the gain in horsepower in going from 75F to 60F of 1.22 would result in a speed of 114.45 as the drag overcomes the power gain.

Again, this is an academic treatment concerning temperature alone, and as is the case with the Midget, obviously there are other, larger effects taking place somewhere/somehow.  The point of the exercise was to estimate how significant the temperature change alone might be.

NOTE:  Due to a misplaced parenthesis in the worksheet where the calculations were made, the 116.6 mph figure in my previous reply should be 115.5 mph.

Interested Observer, Sumner and Hotrod,

Thank you for your interest in helping us sort out the "big picture".

Your help with the explanations and formulas filled a hole in my knowledge base and I just don't have the skill to provide as cogent an overall explanation as Interested Observer.

Like I keep telling guys:   "It's Complicated".

Will post up any details of plans for data logging and the information to be collected.    Anybody with any experience data logging this type of situation, feel free to post up.
 
Fordboy

[Milwaukee Midget]

Okay, let's go back to the run data -
Track orientation sw to ne

Date   Time   Temp   Humidity   BP   D A   Wind    Wind Speed   Mile 2   2 1/4   Mile 3   Note   Air jet   Timing
12-Aug   8:37   70.6   15   25.73   5863   ssw   1   102.464         Rookie   180   37
12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886      180   37
12-Aug   17:08   89.8   7   25.66   7106   ese   9   111.12   115.185   116.698      180   37
12-Aug   18:42   90   9   25.65   7145   sse   10   112.234   117.155   118.069      180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878      180   37
13-Aug   11:41   77.8   20   25.78   6279   ne   5   110.386   114.275   115.028   push start   180   37
13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293      175   37
13-Aug   17.57   91.5   6   25.68   7177   sse   11   113.586   117.161   118.257      175   37
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816      170   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693      165   37

Let's toss the highlighted rookie run and the push start as outliers, then separate by jet size -

On the 180 “rich” jets, my best speed was with a bit of help from a 9-10 mph sse wind, and we'll toss those –

12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886      180   37
12-Aug   17:08   89.8   7   25.66   7106   ese   9   111.12   115.185   116.698      180   37
12-Aug   18:42   90   9   25.65   7145   sse   10   112.234   117.155   118.069      180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878      180   37

We leaned out the mixture - we'll dump the wind enhanced outlier -

13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293      175   37
13-Aug   17.57   91.5   6   25.68   7177   sse   11   113.586   117.161   118.257      175   37

Switch to 170 jets
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816      170   37

Switch to 165 jets
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693      165   37

Final dataset -


date       time      temp  rh  bp      adj        wind   1mile    2mile        3mile              jet     timing
12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886           180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878     180   37
13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293       175   37
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816        170   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693        165   37

I'm going to take some credit here - most of the actual "driving" of the car is in the first mile - the one mile numbers are consistent enough for a rookie.

Compare the two best 1-mile times - and note the adjusted altitude, and wind direction and speed -

13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293       175   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693        165   37

I think we were getting pretty close on optimal jetting.  I never did anything with the timing other than to take out the rev limiter after the rookie run.

I know this does not lead to a conclusion, but I think it leads to a direction.

[fordboy628]

Okay, let's go back to the run data -
Track orientation sw to ne

Date   Time   Temp   Humidity   BP   D A   Wind    Wind Speed   Mile 2   2 1/4   Mile 3   Note   Air jet   Timing
12-Aug   8:37   70.6   15   25.73   5863   ssw   1   102.464         Rookie   180   37
12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886      180   37
12-Aug   17:08   89.8   7   25.66   7106   ese   9   111.12   115.185   116.698      180   37
12-Aug   18:42   90   9   25.65   7145   sse   10   112.234   117.155   118.069      180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878      180   37
13-Aug   11:41   77.8   20   25.78   6279   ne   5   110.386   114.275   115.028   push start   180   37
13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293      175   37
13-Aug   17.57   91.5   6   25.68   7177   sse   11   113.586   117.161   118.257      175   37
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816      170   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693      165   37

Let's toss the highlighted rookie run and the push start as outliers, then separate by jet size -

On the 180 “rich” jets, my best speed was with a bit of help from a 9-10 mph sse wind, and we'll toss those –

12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886      180   37
12-Aug   17:08   89.8   7   25.66   7106   ese   9   111.12   115.185   116.698      180   37
12-Aug   18:42   90   9   25.65   7145   sse   10   112.234   117.155   118.069      180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878      180   37

We leaned out the mixture - we'll dump the wind enhanced outlier -

13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293      175   37
13-Aug   17.57   91.5   6   25.68   7177   sse   11   113.586   117.161   118.257      175   37

Switch to 170 jets
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816      170   37

Switch to 165 jets
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693      165   37

Final dataset -


date       time      temp  rh  bp      adj        wind   1mile    2mile        3mile              jet     timing
12-Aug   14:28   88.9   8   25.7   7008   s   4   109.781   114.844   115.886           180   37
13-Aug   9:25   71.9   31   25.78   5943   nnw   1   111.944   115.336   115.878     180   37
13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293       175   37
14-Aug   11:07   79.2   22   25.77   6391   n   0   113.241   117.077   117.816        170   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693        165   37

I'm going to take some credit here - most of the actual "driving" of the car is in the first mile - the one mile numbers are consistent enough for a rookie.

Compare the two best 1-mile times - and note the adjusted altitude, and wind direction and speed -

13-Aug   15.29   88.4   9   25.73   6946   sse   5   113.319   116.444   117.293       175   37
14-Aug   13.56   88.5   11   25.73   6965   n   3   114.456   118.141   118.693        165   37

I think we were getting pretty close on optimal jetting.  I never did anything with the timing other than to take out the rev limiter after the rookie run.

I know this does not lead to a conclusion, but I think it leads to a direction.

Midget,

I agree that there is consistency and I think there is also more than just a direction.    With the outliers tossed, leaner is conclusively faster, what I would expect, given that jetting was optimized just below the "cheddar curtain", with a D/A of 1600/1700.   Given the higher D/A at B'ville, it stands to reason a carbureted engine would need to be leaned out to maximize "localized" bhp output.    This does not account for any "mass airflow effects" at higher altitudes & higher inlet temperatures.

BUT, given that the goal was to prove the concept:

A/   that the "MM" COULD be competitive,
2/   have a reliable powerplant, to allow as many runs as possible for data gathering,
d/   prevent you from going nuts repairing/modifying/flogging the donk,
z/   AND, gather some basic information that can be used to chart the way forward,
$/   Not send the contestant to Debtors Prison.    (Is that still Australia?)

I, for one, am very pleased with how things have worked out.

As a lot of forum members have pointed out, there are a batch of effective things that can be done to improve the aerodynamic performance of the donk, at minimal cost.    I'm hoping that you will decide to run it once again in this refined specification, just to fly the Union Jack & the MG flag for the glory of the Queen & the Empire.    Eh, what say you?
 
English Fordboy,
vowing to consume only Ale until you possess the RECORD!!   Why, I think I'll have a Speckled Hen right now!!
 

[Milwaukee Midget]

For those who were wondering how loud the Midget is . . .