Milwaukee Midget

[Moxnix]

Well done, Chris.

[Captthundarr]

Nice read Chris.

Frank.

[Milwaukee Midget]

Just caught this Vizard quote on "Pistonhead" -  Regarding the A-Series engine -

"The intake situation with the robbing of one cylinder by another 180 degrees later is far more complex.  Indeed it is more complex than a F1 intake system by far. . . . If we can reveal what is really going on in an 'A' Series intake port feeding two cylinders we will be able to handle F1 stuff with ease."

Hmmm . . ., I hadn't thought that far ahead.

I hear Monaco is beautiful this time of year. 

[Graham in Aus]

I hear Monaco is beautiful this time of year.  

Mark Weber certainly thinks so!  


Sorry, appalling thread hijack.....

He's Australian you know!  

[fordboy628]

Midget,

Posting up a copy of my cam calculations "chicken scratch" page, for your reference.   All calculations are based on the procedure Vizard outlines in the 3rd printing of the "Yellow" book.    FYI: I admit I used a calculator, not my sliderule.



These calculations, however, DO NOT guarantee that a particular lobe displacement profile will "fit" inside the current build spec, or fit inside the proposed revisions to the build spec.   (ie: raise static compression ratio by milling the cylinder head to reduce the combustion chamber volume.)   The NET RESULT of milling is: the positive of raising C/R to race engine spec.; the negative is the loss of valuable valve to piston clearance.   The trick is to strike a reasonable balance for both while suppling the engine's need for airflow.  You MUST meet, or better yet exceed, cylinder demand for the engine to perform as predicted.

Like I keep saying: "It's complicated."

Based on the Cam Pro printout of the SPVP5 cam you were using, the SPVP5 WILL NOT FIT, if the C/R is raised by milling the cylinder head.

The next step is to determine what actual "net valve displacement" (valve lift @ crank position) will fit.   If your choice of cam grinder can not (or will not) provide you with "net valve displacement", the cam "lobe displacement" would be a more math intensive second choice.   The formula for your little jewel is:  cam lobe displacement * effective rocker ratio - valve lash = net valve displacement @ a certain crank position.   Repeat for other crank positions as required, to calculate minimum valve to piston clearance for both valves.

The minimum information required is:   inlet lobe lift @ 10/12/14 degrees ATDC at the specified LCA for cyl's 1/4, and....
                                                          inlet lobe lift @ 10/12/14 degrees ATDC at the scattered LCA for cyl's 2/3, and....
                                                          ex.   lobe lift @ 10/12/14 degrees BTDC at the specified LCA.

Some of the above can be calculated, IF, the cam mfg. shares info about whether it is a single pattern cam.  If it is a dual or multi pattern cam, then all of the above is required to check fitment.

If your choice of cam manufacturer can not (or will not) provide this information to you, the engine builder, you need a different cam grinder who will work with you.

 
still Captain Nemo

[Milwaukee Midget]

Fordboy, again, I am in your debt.

Give me a call when you need that hot tub moved, but I will insist upon draining it first.

Oh, wait a minute - this is the self-draining hot tub, isn't it? 

If your choice of cam manufacturer can not (or will not) provide this information to you, the engine builder, you need a different cam grinder who will work with you.

And therein lies the rub.

[Dr Goggles]

Fordboy, again, I am in your debt.
Give me a call when you need that hot tub moved, but I will insist upon draining it first.
Oh, wait a minute - this is the self-draining hot tub, isn't it? 

Hmm, that's what happens sometimes when you receive assistance from someone who has everything that you are capable of offering........ except labor......

Man , when his revisitation of the engine buid started I was sitting up all alert, now my eyes are glazing a little and I'm starting to fidget.........and the end result is a kind of anxiety, specifically option anxiety.

You are in great hands there, but I can see the wear and tear that it can all have......

when you break the record It will all be worth it. And you will.

[fordboy628]

Man , when his revisitation of the engine buid started I was sitting up all alert, now my eyes are glazing a little and I'm starting to fidget.........and the end result is a kind of anxiety, specifically option anxiety.

You are in great hands there, but I can see the wear and tear that it can all have......

when you break the record It will all be worth it. And you will.

Hi Doc,

Thank you for voicing your anxiety, your honesty is appreciated.

Making the right choice about racing engine components is often an easy, no brainer activity.   When engines are well designed (most japanese motorcycles for instance) there usually isn't much to do.  If you are flogging a popular marque (Chevy & Ford small block for example) there is a huge amount of bits to sort through, BUT, that is mitigated by the fact that most choices are pretty good.   If however, your choice is to race an engine designed in the 1930's and "improved" by Westlake designed airflow, the choices become more difficult and more critical.   I know only too well that "glazed look" & the "fidgeting" prior to making component choices.   The typically huge amounts of data and the complexity of the choices have a tendency to overwhelm anybody who wants to remain sane.

And this is about the point that most racers succumb to information overload, (Mrs. Fordboy calls it: analysis paralysis) and just give up and throw a dart at the board to have the choice be made and behind them.   The racer who can hang in there & wade through the reams of data can improve their engine's performance, significantly & predictably, after all, it is physics.   My experience is: chickens who can use a sliderule/calculator and recognize graphs with more area under the curve always fly faster.

Chris is really close here, (as are probably many who are following along) in making significant choices AND learning how to make the transition from "engine assembler" to "engine builder."   It is a HUGE difference.   The former just bolts bits together and hopes for the best.   The latter chooses engine parts that complement the functions of the other parts of the whole assembly.   Perserverance (with some aptitude for engineering) is usually the difference.

And everybody who has the patience to follow this process/saga along is going to learn something from it.   Or need a psychiatrist.   But I promise the results will be worth it.

Hoping to meet you in person at some point, I'll buy you a beer or 3.
 
Fordboy

[fordboy628]

Midget,

This is a posting to your build diary so you have a record of our conversations & emails regarding cam selection/fitment.

The next step is to determine what actual "net valve displacement" (valve lift @ crank position) will fit.   If your choice of cam grinder can not (or will not) provide you with "net valve displacement", the cam "lobe displacement" would be a more math intensive second choice.   The formula for your little jewel is:  cam lobe displacement * effective rocker ratio - valve lash = net valve displacement @ a certain crank position.   Repeat for other crank positions as required, to calculate minimum valve to piston clearance for both valves.

The minimum information required is:   inlet lobe lift @ 10/12/14 degrees ATDC at the specified LCA for cyl's 1/4, and....
                                                          inlet lobe lift @ 10/12/14 degrees ATDC at the scattered LCA for cyl's 2/3, and....
                                                          ex.   lobe lift @ 10/12/14 degrees BTDC at the specified LCA.

Some of the above can be calculated, IF, the cam mfg. shares info about whether it is a single pattern cam.  If it is a dual or multi pattern cam, then all of the above is required to check fitment.

PROPOSED CHANGES TO CURRENT BUILD SPEC:
In valve depth/height:    .205" net    (After milling .065" from face of head to raise C/R)
Ex. valve depth/height:  .195" net    (See above)
Head gasket thk: .025" net              (After milling .012" from block, changes piston height from -.004" to +.008"  Actual gasket .033")
 
DIMENSIONS FROM BUILD GEOMETRY:
Piston depth @10 degrees B/ATDC:  -.022"   (+.022" piston depth gained.  Note that this is not the actual piston dimension.)
Piston depth @11 degrees B/ATDC:  -.027"
Piston depth @12 degrees B/ATDC:  -.032"
Piston depth @13 degrees B/ATDC:  -.038"
Piston depth @14 degrees B/ATDC:  -.044"   (I can supply a piston movement chart, if required.)

RESULTANT SPACE AVAILABLE FOR VALVE DISPLACEMENT:
Max In valve lift @ 10 ATDC:   .202"  @ .050"   Valve to Piston clr.   (can notch piston if req'd)
Max Ex valve lift @ 10BTDC:   .172"  @ .070"   Valve to Piston clr.   (can notch piston if req'd)

ALSO REQUIRED FOR CALCULATION OF VALVE TO PISTON CLEARANCE:
Rocker Ratios:        Int: 1.53/1 measured            Ex: 1.52/1 measured               (1.50/1 nominal  Harlan Sharp roller rockers)
Valve Clearance:     Int: .016"/.018"                    Ex: .018"/.020"       

INFORMATION PROVIDED BY CAM GRINDER FOR THE PROPOSED CAM:
Cam ground on 110 degree LCA's.    1/4 Inlet lobes & all exhaust lobes.    2/3 Inlet lobes 3 or 4 (?) degrees (cam/crank?) advanced.

1/4 cyl Inlet Cam lobe lift:                Net valve lift:                                     Resulting valve to piston clearance:
      @ TDC:       .10161655"                  .139"                                                          .091"
      @ 10ATDC:  .1353"                         .191"                                                          .061"
      @ 12ATDC:  .1420"                         .201                                                           .061"
      @ 14ATDC:  .14879"                       .212"                                                          .062"
These all exceed the .050" minimum dimension for inlet valve to piston clearance, so that's good.  With a calculated valve displacement increase of .010" per 2 crank degrees the cam could be advanced to 108 degrees and still have .051" V/P clr.

Presuming that this is a single pattern cam, then the exhaust numbers would be reversed from the intake, thus:

All Exhaust Cam lobe lift:                Net valve lift:                                     Resulting valve to piston clearance:
      @ TDC:       .10161655"                  .136"                                                          .084"
      @ 10BTDC:  .1353"                         .188"                                                          .054"
      @ 12BTDC:  .1420"                         .198"                                                          .054"
      @ 14BTDC:  .14879"                       .208"                                                          .056"
This is a bit on the tight side for me, BUT, advancing the cam 2 degrees (as above), would net an additional .010" clearance for a minimum of .064".   Also, the head milling could be held @ .060" rather than the .065" I suggested.  This would add .005" clr to both intake & exhaust.    The new net Ex. clr of .069" is a number I could live with, IF, valve train motion is well controlled. (as in timing chain tenshioner.....)    The resulting additional .005" inlet V/P clr also would allow the cam to be advanced another .005" of lift = 1 crank degree, which MIGHT be useful.  That 1 degree would give .051" inlet net & .074" exhaust net.

Right about now is what I mean when I say you'll have to slice the cheese mighty thin....   (have I mentioned that "It's complicated"?)

NOW THE BAD NEWS:
The clearance for the "Scattered" 2/3 inlet lobes is going to be less, a lot less perhaps.  If the lobe centers are 3 (crank) degrees advanced, then the valve to piston clearance will be .015" less than the 1/4 inlets.   If the lobe centers are 6 (crank) degrees advanced, (as in the cam you had profiled), then the valve to piston clearance will be .030" less than the 1/4 inlets.   While not an acceptable number, it is close enough for some compromise for fitment.   Notch the pistons for V/P clearance, OR retard the cam back to ~109 degrees intake, OR, widen the LCA to 111/112, OR, std, unscattered cam, OR, an alternate cam with less flank lift @ 10/12 BTDC/ATDC, etc.

What should be obvious is that you are near to the point of "Maximum Cram".

WHAT I THINK YOU NEED TO DO NOW:
1  You need to have a dialog with your cam grinder(s) to CONFIRM all the figures being used to calculate these numbers, OR, research 
    alternate cam choices.
2  You need to make some hard choices about suggested changes to the build.   (I suggest maximum C/R be preserved.)
3  You need to take the c-clamp off your head & grab a cold suds, and relax a little while contemplating the choices.
4  Call/email me if you want to converse off line.
 
Fordboy

[Milwaukee Midget]

Taking this all in over a pint of Ole Speckled Hen.

One quick thought - and this comes back to the old "it's all about compromises" quote.

You and I both know there have been very strong BMC engines that never had a scatter pattern cam, and dozens of very competitive grinds are available.  I've been poking through Dema's catalog and I'm seeing a couple of grinds that could be put on an appropriate LCA and look likely to work.

As you pointed out, the 3 degree spread is what APT and Kent have used on the 2&3 (or at least ADVERTISED as such).  Given the tight tolerances we're chasing, might it be to our advantage to adjust the center lobes 1 1/2 degrees to maintain a better bit of clearance and still take a lesser advantage of the lower cylinder robbing characteristics that the SP cam provides?

Yeah, I know, now we're talking the black art of cam design, but at this point, in for a dime, in for a dollar.

[38flattie]

I gotta give you props for riding this out Chris!

My head hurts just reading it!

[Milwaukee Midget]

I gotta give you props for riding this out Chris!

My head hurts just reading it!

Thanks, Buddy.  It's been a week of Tylenol and Rye for me.

I told a friend of mine yesterday that just when I think I'm ahead of the curve, the apex changes.

The talking is all done.  The work proceeds.  The faxes have been sent.  The calls are in.  The information will be forthcoming.  Calculations will continue, both north and south of the cheddar curtain.  The decisions will be made.

But above everything else, here is what is going to happen.  I will build the fastest damned stock bodied, naturally aspirated, five-port, one liter Midget ever to hit the salt.

Period.

And that's not the beer talking.

[Peter Jack]

I like the attitude Chris! 

You'll get there with that approach. 

Pete

[Geo]

Chris and Fordboy,

Now it's getting to the nitty gritty!   
Chris, you know all of us are 1/2 step behind you and wishing we were as close as next door to help with the work. However, we will uspport via the forum.  I would jump in more but you are in good good hands with far more knowledge on BMC than I.  I will put my 2 pence in when I see a space. 

Geo

[salt27]

Chris,
When you set that record I,ll buy you a brew.
Fordboy has sure put a new twist to this thread.

     Don