Milwaukee Midget

[fordboy628]

Spring cup drawing - corrected outside diameter as per our conversation.



Fordboy - any corrections?

Midget,

I would add some tolerancing to all the dimensions to give the lathe or CNC operator some leeway.   This is NOT a hyper-critical part, UNLESS, the part is mistakenly toleranced so as not to fit.

I suggest:

Dimension A = 1.225", +.005"/-.000"
Dimension B = 1.165", +.005"/-.000"
Dimension C = 0.475", +.002"/-.002"  (Nominal 12mm)
Dimension D = 0.030", +.002"/-.002"
Dimension E = 0.228", +.008"/-.008"
Nominal chamfer of .008"/.015" on all outside corners, and vibro-deburr all surfaces.
Material spec: Steel Screw machine material suitable suitable for low-temperature carbo-nitriding, such as "Tuff-Tride" (Tm).
Heat Treat spec: low-temperature carbo-nitriding, such as "Tuff-Tride" (Tm), after deburring.

My memory is that "Led-loy" screw machine stock is NOT suitable for low-temperature carbo-nitriding, but I may be mistaken.

I am also digging through some old Cosworth bits I have to see if I have anything workable.

Graham,

We are trying to keep the springs on a "hardened" surface, so as not to chew up the head/valve spring shims, (this is happening already); and, locate the bottoms of the springs better to prevent "spring walk" @ high rpm.   The solution needs to be on the spring OD because the valve seals differ between inlet & exhaust and are different sizes.
 
Dutchboy

[fordboy628]

Midget,

Spec & size for Chevy/BMC adaptor plate to fit Superflow 901:

Nominal 5/8" thickness, Aluminum tooling plate, 6061-T6 or 6061-T651 or similar alloy.  6061 generally available.  Could substitute 2024 or 7075.

17" x 15" MINIMUM size, 18" x 16" would be better.  This is for the plate as originally designed.   The design could be redone as a pair of "wings", at reduced sizes, thereby reducing the material required.............    If the adaptor plate(s) needs to incorporate your starter, this may not be a good idea.  I do not recall if the dyno has an on board starter.  Please clarify.

Today is your lucky day, part deux:

Searching my AutoCad data files netted the following - BMCBOLT.dwg    which I believe is the correct one.  Will need to apply a few watts to the 'Frankenputer' to revive Acad.  Will also need to connect tablet & plotter to print out/plot out.  My memory is that this is a bare bones 2D bolt layout dwg relative to the crankshaft C/L.   Will report back if not electrocuted...........

In general, I like the idea of standing on the shoulders of those who have gone before, but in this instance I'm trying to stand on my own shoulders.  I'm simply way too old (and way too cranky) to be much of a contortionist anymore...............
 
still Dutchboy

[fordboy628]

Re:  Close ratio gearset

Midget,

Frankenputer has a gear ratio charting program I designed & used.  Give me the gearbox ratios, diff ratios, and tire size.  I'll plug-in estimated peak b/torque & peak b/hp and run the numbers with a graph.  Actual dyno torque & Hp graphs would be better than educated guesses.   But, the information about rpm drops between shifts will be useful.

What you want to do is:

1] space the rpm drops (gearbox ratio differences) so that the engine is always in the peak torque/peak power range.  Gear ratio spacings that are too wide either over-rev the engine and/or drop below the peak torque range with the shift. (where the engine won't "pull")

2] select diff ratio/rear tire size for top speed. (subject to aero drag & engine rev limit)


What racers should be aware of is this:

A] Wide ratio gearboxes with only 3/4 speeds REQUIRE engines with a WIDE operating rpm band, between peak torque & peak Hp.

B] Peaky high Hp engines with narrow rpm bands REQUIRE close-ratio gearboxes with 5/6/7 speeds or more.

My own experience is that progressively smaller rpm drops between gears is way to go for fastest acceleration to top speed.
 
still Dutchboy, but gaining on it.........

[Interested Observer]

My own experience is that progressively smaller rpm drops between gears is way to go for fastest acceleration to top speed.

...because that keeps the operating range in the upper reaches of the power curve.  The torque peak is irrelevant.

[fordboy628]

My own experience is that progressively smaller rpm drops between gears is way to go for fastest acceleration to top speed.

...because that keeps the operating range in the upper reaches of the power curve.  The torque peak is irrelevant.

Yes, THE most important component of the gearing equation is the Bhp curve. (ie, shape, size, area underneath, rpm range, etc.)  The best compromise typically keeps the operating rpm somewhere in the best area (typically the highest area) under the horsepower curve.  Flatter, wider horsepower curves make it much easier to choose gears Vs. peakier, narrow curves where gear choices can be critical to performance.

I don't want to split hairs about language with anyone.  I would not consider peak torque to be irrelevant.   I would agree though, that it is less important than some other considerations when gearing.

Computer programs which help select gearing based on the bhp available x overall gear ratio/tire size @ a target mph can be very helpful.  But I am already on the record in my support of technology............   especially beer databases!!!  Nearly out of my favorite "Octoberfest" though.......
 
Fordboy

[Milwaukee Midget]

Part of what brought this up was an opportunity to pick up a set of close ratio straight cut gears for the Midget.  The strength aspect is clearly an advantage.  The problem is we don’t have a power curve to base an educated decision on.

When the engine is done, it will be able to turn 9 grand, which is about 1000 rpm above where I need to be making peak hp to achieve the speed target of 122.  The 3- 4 shift at 9k drops my rpm to ~ 6600.  The 3-4 in the set I’m looking at changes that to ~ 7500.

A 3.92 diff gets me my target speed in 3rd gear at about 8700.  I have one of those diff’s in the garage.

Stuff to ponder.

[manta22]

"...the speed target of 122." ??

Regards, Neil  Tucson, AZ

[Milwaukee Midget]

"...the speed target of 122." ??

Regards, Neil  Tucson, AZ

I/GT - Class record is 121.779.

It's 20 years old, and owned by an Abarth.

I'm hoping to change that . . . it won't be easy.

[Tman]

"...the speed target of 122." ??

Regards, Neil  Tucson, AZ

I/GT - Class record is 121.779.

It's 20 years old, and owned by an Abarth.

I'm hoping to change that . . . it won't be easy.

Get a bigger Hamster! I am looking for a box for that care package, hope I find one soon or I will drink them and have to start over!

[Stan Back]

Is it too late to protest?  Did they make 500 of them A-barths?  Can you put double bumps on yer roofs?  Does that mean a Fiat ran two days in a row (I forgot about the four hours of fix-it time)?

[manta22]

Ah so! I thought you had planned that your car would top out at 122 mph!

Regards, Neil  Tucson, AZ

[Milwaukee Midget]

Is it too late to protest?  Did they make 500 of them A-barths?  Can you put double bumps on yer roofs?  Does that mean a Fiat ran two days in a row (I forgot about the four hours of fix-it time)?

It's water over the dam, but I'd be lying if I said I hadn't thought of that.  Production numbers on Abarth models are tough to come by - I doubt if THEY know how many they made.  I know an Abarth held the J/GT record for a few years.  But the record has stood for 20 years, and I'm certainly not going to play that game at this point.  

No, I intend to make my challenge on the salt.  I'd rather race than argue.

Besides, anybody who can get a Fiat to run two days in a row deserves a prize.

Now that said, if I DO get this record, it's likely that I will become VERY petty and VERY small with respect to any challenges.

 

Ah so! I thought you had planned that your car would top out at 122 mph!

Regards, Neil  Tucson, AZ

That's all it has to do - twice. 

[JustaRacer]

Probably no help:

I took the Wide Ratio (each gear drops to the same RPM) out and put in a close ratio (each new gear drops less).  This is T-56 six speed with 434rwhp in a 3360lb car.

In the quarter mile, there was no change in MPH or ET.  Might not be valid for LSR, but best I can figure is that the steep HP curve kept the average RWTQ the same.

The drop with the WR was always from 7000 to 4700.  4700 was only half the peak HP.  

[Dr Goggles]

Is it too late to protest?  Did they make 500 of them A-barths?  Can you put double bumps on yer roofs?  Does that mean a Fiat ran two days in a row (I forgot about the four hours of fix-it time)?

hahahahahaha........ I was sitting with the Colonel outside a pub one day and he tapped me on the arm and said "did you see THAT!, two Jags just went past and one wasn't towing the other!!!"javascript:void(0);

love yer work Jim.

[scrapiron aka Park Olson]

Do you have a 4.22 and 4.55 diff's.?