Milwaukee Midget

[manta22]

One advantage a mid-engine layout has is no driveshaft to worry about.....

[Peter Jack]

Actually you have two, and they can be problematic! 

Pete

[Milwaukee Midget]

One advantage a mid-engine layout has is no driveshaft to worry about.....

Actually you have two, and they can be problematic! 

I think in my case, it's a combination of what Bill ran into and, to some degree, concern about the range of motion the combination might encounter.
 
Assuming a 30 inch tire height, at 125 mph, Neil's half-shafts are only turning at 1,400 rpm.

The record has me at almost 6x that, provided the combination can pull 4:22s. If I need 4:55s, we're approaching 9,000 driveshaft RPM.

[Peter Jack]

Basically I was being a smart ass!

Actually with halfshafts usually the problems are joint related.

With your shaft being as short as it is I think you'll find that you're okay. A thicker wall or larger diameter shaft is a pretty simple operation for any driveline shop.

Good luck with it Chris! It's great to have you back regularly on the site. 

Pete

[Stan Back]

My "guess" is that it would be beneficial to stiffen the rear springs  and/or limit their travel.  I'd "guess" that the sudden changes in angles can lead to driveshaft failure.

Many moons ago, when the salt was flat and hard, running solid was not a problem.  But we don't know now what we're gonna get until we show up.  And the association tends to grade it better than the actuality.

In 2005(?) we were the fifth car out and the first one to navigate 1 all the way.  We were sprung then, but it was a parts breaker for a lot of cars.  So, what's the answer?  I'm showing you I don't know.  Maybe a compromise.

[manta22]

Chris pointed out that a transaxle ring & pinion gear reduces the RPM to the axles and they are only about 18" long but the CV joints can be a problem.

[fordboy628]

The $64 questions on everyone's mind a page or two ago . . . .
Can the K provide the power to propel the MM beyond its' current best run ever?

Well, since I'm basically a "data guy", here is my 2 cents worth:

What is important here is that speed is basically a function of power available Vs drag, IN ALL FORMS . . .   My experience dictates that when you graph out power available at the drive wheels Vs power consumed by the aforementioned "drag in all forms", at some speed, those 2 function lines cross.   That's it, game over.    Regardless of gear ratios.   Gear ratio splits of 2% or 3% or even 4% merely change the engine RPM.   Any "gain" or even LOSS, is a fraction of a mile per hour.

UNLESS YOU HAVE MORE POWER AVAILABLE . . .

I'll point out a few things here - at least as I understand them. I'm certain Mark will join in when his ears stop ringing.

Note the torque curve - it hovers between 63 and 67 ft lbs from 6,300 to 9,500 rpm, and was showing no indications of rolling off any time soon.

Horsepower, of course, is a function of torque and revs - and as long as the torque remains constant or doesn't fall off, as the revs climb, so does the hp.

So what does this mean for our attempt this year?  Well, let's look at what's worked in the past. Mark superimposed the Grenade graph onto the K graph -

GrenadevsKseries by Chris Conrad, on Flickr

We tested in a much narrower range with the old A-Series, and it gave a LOT more torque below 7,000 AND better power numbers - UNTIL 7,800 RPM. That's where air flow and electronic fuel injection start to really show their mettle.

We set the rev limiter at 10,000. It appears that the way we'll need to drive this thing is to just simply wring it out in the lower gears and hope 4th doesn't drop us below what the A-series gave us - the 3-4 is right there in that pocket where the two engines power curves cross.

Kindly take note of the power comparison graph above.   Pay close attention to the blue power line of the "Tractor" in 2014 Vs the red power line of the K in 2021.   Nota bene: THOSE LINES CROSS @ 8000 RPM.

The salient points are:

A/  The Tractor bhp peaked @ 8000 rpm
2/  The MM fastest run peaked @ 126.xxx mph, approximately 8200 rpm, WHERE THE TRACTOR POWER WAS FALLING, to 97.5 or so bhp
d/  At 8200 rpm the K is making approximately 102 bhp during run #24, 4.5 bhp more.   About 4% more.

The questions that need to be answered are:

B/  Is 4% more enough to push the MM to new levels of incompetence?
3/  Is the rate of increasing power of the K enough to push beyond the 130 mph barrier?
e/  Are there any aero improvements for MGT in the "bag of tricks", before September?
z/  Just how much "stupidy" is there being held in reserve?

In the past, we have proven that our level of stupidy is superlative.   Without a doubt. 

Personally, I think the current car with the K engine is capable of a 132/133 mph run.   Adding an air dam or front splitter?  Perhaps adds 1 or 2 mph.   Can any "record run" be backed up?    Will everything stay glued together?    That's why they have the races.   I guess we are going to find out the answers to all of the above.

 

[Koncretekid]

Here is my prediction using the best run from the tractor motor and the rule of cubes.  That is the increase in speed will be proportional to the percentage increase cubed times the known speed with the same aero characteristics.  So the known speed was 126 mph with 97.5 horsepower, the new speeds will be determined using that formula.  Therefore, the new speed, if the gearing is correct will be 133 mph at 114.7 hp.  So gear accordingly to get that speed at peak horsepower rpm as indicated by the dyno results.  Which is why I suggested using the 4.55 rear axle with the same tires/wheels as before.  If you overgear it using the 4.22 rear axle, and the shift to 4th gear drops you down to less than 97 hp, you may not be able to go any faster because you have hit the aero wall as you did with the previous motor.  If you look at your horsepower curve, it is increasing proportionally to the the torque curve which is flat.  But the increase in horsepower to speed increases exponentially.

In your post 7681, using Sumner's spreadsheet, you suggest using third gear to get you to 131.xx mph, but remember that the shift from 2nd to 3rd drops your rpm by 35%, whereas the shift from 3rd to 4th is only 26%.
So even if you wring it out to 9500 in 2nd gear, you'll drop down to 6175 rpm in 3rd at about 85 mph which may put you too far down on the hp curve to recover.  I've been there and done that.



Tom

[Milwaukee Midget]

Tom - Thank you for those calculations. God help Volkswagon's diesel engineering division if you ever decide to become an investigative reporter!

I dug up a historical reference from Wheels magazine, December, 1970 on an MG Midget they tested.

The quoted data gives us a maximum of 65 HP@6,000 RPM. How accurate the factory numbers are will remain conjecture, but the magazines observed data indicates a top speed of 86mph in 4th, which, with a 22.5 inch 145R-13 tire, put things at about 4,950 rpm.

Assuming a linear slope of horsepower on a stock 1971 Midget (certainly not a given), peak advertised torque of 72 lb/ft occuring at 3,000 rpm (41 hp), 4,950 RPM should equate to ~57 hp - which is what the magazine claims propelled the car to a top speed of 86 mph.

Provided we're making more than 57 hp at 85mph, I think we'll be good on that shift.

It's the 3-4 that's on the borderline.

[4-barrel Mike]

Long ago, you considered a Ford T9??

First           3.36   
Second   1.81
Third           1.26   
Fourth   1.00   
Fifth           0.83

Mike

[Rex Schimmer]

Chris,
I was at the WOS meet that you set your record at. I made a real effort to make sure that I watched your qualifying run and as I remember it was late after noon and the "Gods of speed" had gifted us a 8-10 mph tail wind that was blowing directly down the race track. You took full advantage of this and ran some where around 128 then followed up the next morning with a 123 mph run which gave you your 126 average. So what  I am saying is that the Midget (with the tractor motor) in still air is probably really a 123 mph car. If you use this number for the power to go 133 you will need 25% more hp. This all comes down to going with the short tires and the deeper gear and twisting the tail on your new piece!

Regarding your drive shaft speed, back in the "dark ages" when I was working on an IMSA GTU RX7 Mazda we were typically turning that engine 10 to 11K and the
Mazda competition tranny had a 15 or 20% over drive top gear, so we would see drive shaft speeds in the 11 to 12,000 rpm range. We ran the car several times at Daytona and did have some drive shaft vibration problems when you got on the high bank and really turned it hard. We went to a 3.5 inch dia, .083 or .071 wall 4130 shaft and that pretty much ended any problems and we probably had 3-4 inches of rear end travel.   

Looking forward to seeing you and the new "killer" at the WOS!!!

Rex

 

[Koncretekid]

Chris,

Thanks for the compliments, but I use these spreadsheets all the time for my bikes.  It was no problem to just change the parameters to match your previous speed and hp.

I hope to see you (and Rex and the others) at World of Speed in September, if the creek don't rise and I can get there!  Unfortunately for me, both my bikes are sitting in my barn in Colorado where they have been since W of S 2019 and I can't go there yet.  I'll have about a week to resurrect them for duty, but with no real changes.

Tom

[Interested Observer]

Thinking that a picture is easier to contemplate than a page of numbers, I re-worked a previously generated spreadsheet for use on the "K" that shows power available and required vs. speed in the various gears and other driveline components.  Three resulting examples are on the accompanying attachment.  Pertinent assumptions are noted.  It is easy to change any of the factors if someone has an issue with what was done.
The upshot is clear that this effort is in need of shorter overall "gearing" to likely exceed the existing record.  Or, as was previously suggested--just wring it out in 3rd!
At some point in the discussion I believe someone said an overdrive ratio was available in the trans--can this be an underdrive?  A 4th gear ratio of 1.18 rather than 1.0 would produce about the same situation as the speculated 5.0:1 rear end ratio.

[fordboy628]

IO,

Thanks for the analysis effort.    You make my case.

FB

[fordboy628]

midget,

Does a 4.55 rear gear and your smaller diameter tire get close to the 5.0 rear gear/22" tire permutation?

I would think that it is "close enough".

FB