My 131 abarth (never ending) story - 2017 season updates

[miro-1980]

GUY

OK, You are ON !

M

[miro-1980]

That is one really beautiful stopwatch, Miro!!!

regards
Tom

Thanks, It should complement the interior quite well.

Will post some pictures when this is done.

M

[miro-1980]

Rev limiter and full throttle shifting

Guy's suggestion to install rev limiter got me to research the subject .

Benefits of rev limiter became so painfully obvious that really deserve little attention .

What was more interesting and challenging was additional functions some units offer.

1/ Shift up light - benefit is obvious

2/ shift down light - benefits not so obvious , but worth considering.

My (limited) experience indicates that when on a stage I do not keep my eyes on anything but the road and that includes the rev counter. Hence the need for shift up light. The mare engine noise is not enough to know then the RPM are too high. Risk of over revving the engine and or going past optimum engine power to torque combination (loosing time ). The same is respectively true about the shift down timing. The risk is possibly greater as shifting down too high may over-revving the engine more quickly than not shifting up at the tight time. A green bright light at the tine when the engine drops below RPM that give you max torque ( in my case cs 4000) looks like a very good idea.

3/ full throttle shifting - Shifting up means drop in the rpm.

In my case with standard 131 gearbox shifting from 1st to 2nd at 7000 means going down to 4000 (losing 3000 RPM in the process). I have tried a known technique of not releasing the acceleration pedal while pressing the clutch to change the gear. What happens is that once you press the clutch ( keeping full throttle) the engine suddenly revs up significantly without any limit. This can easily lead to over revving the engine( especially if you attention os 100% on the road you do not have the time watch the rev counter. The full throttle option on the ARMTECH Speedshift allows maintains the RPM level at the time you depressed the clutch to change gear. In my case say 7000 RPM. I do not need to take any pressure of my accelerator - the REV speed remains at 7000 until I release the clutch. It will not go up. The affect is that when the higher gear is engaged and clutch released the initial engine speed is 7000 and not 4000 as it would be without this feature. The expected effect is that you can change the gear quicker without fear of over revving the engine and hopefully do not lose so much speed in the process. Hopefully this will push the car a little faster from the beginning of higher gear engagement.

To illustrate this is a graph below:

full throttle shifting.JPG (59.13 KiB) Viewed 11008 times

The angle created between the green arrows and violet arrows represents the benefit of this technique. The actual angle is unknown and the one drawn here is for illustration purposes only. It is probably somewhat exaggerated , but illustrates the concept. The actual benefit is probably not in gaining speed but not loosing speed. This can be measured and when we have the possibility we will in fact attempt to measure acceleration to full speed on a straight using this feature and doing it conventionally.

Obviously the stress on the clutch, gear box, main shaft joints and the differential will be greater, but it is a part of trying to achieve the best speed. In fact this will be safer done with the "full throttle shifting " REV limitation feature than without it.

The ARMTECH Speedshift requires several REV levels to be pre defined:

1/ REV limit ( I will set mine at 8500 )
2/ Shift up light REV ( will set mine initially at 7000)
3/ Sift down light ( will set at 4000)
4/Gear Shift REV level (I will set mine at 6000) This defines minimum RPM to activate "full throttle gear shift feature". Below this level the system assumes you are just starting or shifting down.

There is one additional feature of this system which I am also considering: "launch control switch".

speed shitf.JPG (18.92 KiB) Viewed 11008 times

Here is how it works / You have a button on the shift lever or on your steering wheel. When the system is engaged you press the button to mark the level of initial REVs while starting. Instead of immediately loosing traction ( as is often the case ) you start from a predetermined REV level to limit the wheels spinning idly (and the car still in its not moving). When the car starts trolling (with full traction ) you release the button and the engine revs freely up giving your car maximum from zero acceleration).

I am not sure what initial RPM level will assure full traction at start, but this can be determined by the temperature of the tires as well as kind and state of surface on which you start( i.e. presence of sand gravel or water). As this level is determined by the river before every launch this is likely be a matter of experience.

Will see practical results and application when the unit gets installed later this month.

Miro

PS: to explain planned revs setup here is my engine dyno (again) :

My dyno.JPG (33.45 KiB) Viewed 11008 times

[Guy Croft]

MODEL POST!

You show extraordinary skill at presenting quite complicated tech issues concisely and clearly with excellent illustrations Miro.

I should perhaps emphasise, readers, that Miro's native language is Polish not English which makes his posts all the more remarkable.

G

[Walezy]

There is also an issue with slipping clutch, race clutches do not stand too long when used under slipping conditions. When you are looking at such gains on upshifts and downshifts then you acually need a dog clutch gearbox instead of some electronic box that will control rev limit. Rev limiter will be fine so that you will not overrev the engine but it will not save your engine if you downshift too quickly. The ultimate solution for this will be sequential gearbox with some paddle gearchange that will not allow downshifting until you get to safe revs(just reading about this as i need such gearbox for my Fiat).

[miro-1980]

Tom,

You are quite right. Your remark re use of race clutch under slipping conditions is very well taken.

The idea to install a rev limiter is precisely geared at not over-revving the engine.

Re shifting down : due to characteristics of the gear box I use (standard 131, 5-gear box) setting a maxlimit for downshifting at 4000 looks safe. I can safely downshift from 2nd to 1st at 5000 ; from the 3rd I can safely downshift into 2nd at 5500; from the fourth I can safely downshift into 3rd at 6000 and from the 5th I can safely downshift into 4th at 7500 and each time hit maximum RPM on a lower gear not in excess of 8500.

The problem comes when you make a mistake and by slip of the hand instead of shifting up from 4th to 5th you actually downshift from 4th into 3rd at say 8000 RPM. The RPM just flies off hitting 10 000. With rev limiter installed it will stop at 8500 no matter what downshifting mistake you make.

So while I agree with you in principle that a dog clutch gearbox (with proportional ratios) and or sequential gear box are an ultimate desired solution. I beg to disagree with your statement that (rev limiter) "will not save your engine if you downshift too quickly". it will.

While shifting up you can over rev the engine pushing it too hard into high range RMP. My RMP counter has a waring light set to go on at 7000 , so if I follow the light on up-shifts just I am fine. The greatest likelihood to over rev the engine is on downshifts. This is when you need the rev limiter the most. Now obviously if you put 1st at 100 km/h is is not the engine RPM that will drive the car but the seed on rear wheels. Likely you will damage the clutch and the gearbox , but even under such drastic conditions the engine should survive.

When I set the rev limiter at 8500. (almost no matter what I do) the engine will not rev above 8500 )

Now this is all theoretical, as I have never used a rev limiter and thus have no idea how performs under extreme conditions, but the idea of having one appeals to me quite a lot and I will install it as soon as I get it.

Miro

[Walezy]

Rev limiter works by cutting ignition and in injected engines on fuel but if you downshift or misshift too quickly then the wheels will force the engine to spin at about 10000revs so rev limiter will be no help then, you can kill every engine like this.

[miro-1980]

Ok,

So rev limiter works on up-shift only and on "neutral". It has no application on downshift as the wheels will drive the engine to high RPM. It would make sense though that if the speed difference is drastic the clutch gets hit first - it should slip , if the slippage is not sufficient or too rapid the clutch will be blown (ground) , if it holds the second will be gearbox main shaft, and if this holds , than the engine will rev out of range.

As this typically takes two seconds max, before the driver reacts the chance the engine will be blown is not very high. However , even if this assessment is correct one should remember that small risk to big value is a big risk, so learning to keep your eye on the RPM while downshifting and knowing when not to shift down especially on low gear and into 3rd from 4th or 5th.

There is no insurance against the worse case scenario of mistakenly down shifting from 4th at high RPM into 3rd instead up-shifting to 5th can still. This might force the engine into 9500 RPM level. You do it you lose the engine !

I have looked at the graphs and came up with the following: to keep the engine under 8500 RPM one should not shift down:

a/ into 4th above 7400 RPM
b/ into 3rd above 6250 RPM ( from 4th) and 5450 from 5th)
c/ into 2nd above 5650 RPM
d/ into 1st above 4800 RPM

(the above roughly applies to both 6.14 and 3.9 diffs)

The Armtech Speedshift has a downshift light. Setting it at 4000 RPM should give me a good indication when not to downshift. Shifting down at 4000 every time keeps the engine within the optimum operating range. So , if the green light is off do not dowshift !

The rest is a risk I need to take. Looks like not watching the REV counter is not a good idea , especially that the lower you go on gear the lower the downshift max REV.

Incidentally this subject got me thinking again about the benefit of a close ratio gear box

I considered a standard vs close ration ( Bacci) gearbox) up-shift RPM /speed on two diffs 10/39 ( 3.9) and 7/43 (6.14)

The benefit of close ration with 3.9 are quite clear.

10-39.JPG (82.9 KiB) Viewed 11130 times

The speed gain (acceleration) is clearly much better with the close ratio gearbox (CRG). With standard gearbox (SGB) at 7000 in first gear you get a speed of 50 km/h while with the CRG you get 100km/h at the same RPM. The drops in RPM during up-shift are significantly smaller and almost the same for all gears ( roughly 2500 RPM , while with SGB the lower the gear the bigger RPM loss in up shifting. I.E. first tom second it is the loss is 3000 RPM , from second to third it is 2350 , from 3rd to 4th it is 1850 and from 4th to 5th it is 900 RPM.

This makes the SGB far less elastic in terms of freedom to select a lower or higher gear at a given road speed ( assuming you want to operate between 4000 ( when the torque is close to max) and 7200 (when the power is max).

However when the graph for the 6.14 ( 7/43) diff is studied the benefit of a CRG is less obvious

7-43.JPG (90.12 KiB) Viewed 11130 times

The RPM range in each gear (except the first) is well within optimal operating range (4000 - 7500). In case of 1st gear its is practically on this limit.

[miro-1980]

Re AIRBOX

Guy , you doubted i have an airbox as you have never seen it.

I have experimented and continue to experiment with it ,. but here is the latest ( probably not final) version.

The box is big enough and has sufficient clearance with the trumpets. The air filter takes fresh air from behind the front grill.

airbox 1.jpg (84.35 KiB) Viewed 11129 times

airbox 11.jpg (84.41 KiB) Viewed 11129 times

airbox 2.jpg (75.03 KiB) Viewed 11129 times

airbox 6.jpg (69.72 KiB) Viewed 11129 times

airbox 5.jpg (75.43 KiB) Viewed 11129 times

I am still considering different air hose attachment to airbox. Current design feeds the airbox from the bottom. I think iot would be better to feed it from the top , however due to space constrains it is not possible . I could make a front side feed, but it seems that the box shape should be reduced to oval than , and this would decrease the air volume in the box. So far the airbox works fine , with no negative influence on engine performance. In fact I wouls d say there is a bit of improvement over open trumpets as the air is cooler and the mesh does not hamper air flow at all. The air filter seems to accept easily any airflow required.

I plan to put a simple temperature gauge into the filter housing ( there is a special connection point provided) to give me an idea of the air temperature incoming into the carbs.

When design is final it will be polished to create a nice chrome look , also serving as a reflector to heat.

M

[WhizzMan]

Did you remove the ridges between the bottom of the trumpets/airbox and the carb entrance after these pictures were taken? Can you make the box any higher without hitting the bonnet? The more free the trumpets can breathe, the less hindrance you will have from the lid of the box. You may want to put some reinforcement and dampening on the lid of the airbox to dampen the noise and vibration. I don't know what noise restrictions your race classes have, but in the Netherlands they are very strict and people have to resort to such techniques to meet regulations.

[Guy Croft]

Can you make the box any higher without hitting the bonnet? The more free the trumpets can breathe, the less hindrance you will have from the lid of the box.


Homme the critical minimum distance betw rampipe and anything else is 1". Miro has loads more than that.

G

[miro-1980]

Did you remove the ridges between the bottom of the trumpets/airbox and the carb entrance after these pictures were taken? Can you make the box any higher without hitting the bonnet? The more free the trumpets can breathe, the less hindrance you will have from the lid of the box. You may want to put some reinforcement and dampening on the lid of the airbox to dampen the noise and vibration. I don't know what noise restrictions your race classes have, but in the Netherlands they are very strict and people have to resort to such techniques to meet regulations.

The bridges were not removed. Did you mean I should take the bridges off and weld the trumpets to the box? Why ?

The clearance between the lid and the top of the trumpets is 1,5 inches. The box is almost as high as it can be. We will see if there is any more space after final fitting and (if possible) make the box as high as will fit. There may be 5 mm clearance left, but this we will see it inserting a scope under the bonnet through the Abarth air scoop and this will give us final reading of any space left. Making the box higher is not a problem. 5 mm can be raised bu using a thicker rubber seal. If there is more space ( say 1 cm ) additional strip of stainless steel can be easily welded on top of the edge of the box all around to raise it. We could make the box a little bigger from the front , but not the rear side , so I have decided to make it proportional so that access to air on the first and the fourth is the same.

The lid sits on an elastic rubber seal placed on the edge of the box and it should not resonate. Actually it should make the engine a bit quieter.
The car has to meet general rule (a 100 db limit) As the car has a vintage vehicle registration it also has a permanent technical inspection (MOT), so it will not be formally tested on noise , but I have had it tested at an inspection station and the car meets the 100 db rule. Typically it is the muffler which makes a car fail. Incidentally my 124 spider with the loud muffler is closer to the limit than the 131 abarth.

The box is 9,5 mm high , and has a capacity of almost 3,8 litre. The duct is 2 x 20 cm long with 7 cm in diameter (plus 20 cm of air filter). Assuming the air filter capacity is as large as the air duct we have a total capacity of ducting equal to 2,3 litre. The proportion of air box to air duct capacity of 1,65 should be OK.

Miro

[miro-1980]

Friends ,

Maybe some one has a spare 131 steering wheel hub.

This is what I need :

capture #401x.jpg (50.64 KiB) Viewed 10933 times

My steering rod has 21 teath and the steering wheel has ca 55 mm opening , uses 6 bolts spread ca. 35 mm apart (center to center). Opposing bolts are spread ca 70 mm apart.

Miro

PS: mine is cracked and too lose to be fit for use.

M

[TomLouwrier]

hi Miro,

I do understand you want to shift up quicker, but I don't get the purple lines. You can't accelerate while shifting, so the drop in revs is fixed as result of your gear ratios.
About maintaining engine speed while shifting: racing bikes take a different strategy on that. When reaching the point to shift up, the rider cuts the ignition (push button under the left hand thumb) taking the force off the drive line. He can then kick it in the next gear, without using the clutch at all. Release the button and the engine picks up immediately. There are varieties that have the ignition switch in the gear lever, so it cuts out whenever you even push it down.
There are even kits that do it all, including the shifting by means of a pneumatic cylinder, so all you need to do is the 'up' button.
This is extremely fast and much less hard on clutch and gearbox.

As for over-revving the engine on a down shift: do that on a bike and you'll not just kill the engine but likely have a fall when the rear wheel blocks and slides. For that there are mechanisms in the clutch that release it at a certain torque when driven by the wheel. This works very much like the plates in a limited slip diff, with slip governed by preload and ramp angle. They are known as Anti-hop or Slipper clutches.
As far as I know there are no such clutches readily available for cars, alas. Maybe someone should.

regards
Tom

[miro-1980]

Tom

Thanks for your comments. Very well put.

RE:

I do understand you want to shift up quicker, but I don't get the purple lines. You can't accelerate while shifting, so the drop in revs is fixed as result of your gear ratios.

You are quite right. This war really an oversimplification on my part. This dotted line drawn at an angle was to represent gain in time you shift and go from full engagement and acceleration in lower gear into full engagement and acceleration in lower gear.

I tried to indicate this by saying:

The angle created between the green arrows and violet arrows represents the benefit of this technique. The actual angle is unknown and the one drawn here is for illustration purposes only. It is probably somewhat exaggerated , but illustrates the concept. The actual benefit is probably not in gaining speed but not loosing speed.

There are two interconnected issues speed and time. While shifting gears you may actually loose little or no speed but still lose time! I meant to say that this angle was a ""dramatization" representing less time loss from 'full engagement and acceleration in lower gear into full engagement and acceleration in higher gear." If you can imagine this graph in 3D ( third axis being "time") this angle would represent "less time"

Let me put it this way. Normal sequence while shifting say from 3th to 4th is this :

1. take foot of gas
2. press the clutch
3. take the gear from 3rd gear position to neutral
4. put it in neutral put 4th gear position
5. release clutch
6. put foot on gas again

No matter how quick you are this still takes time. While you do this the RPM drops from say 7000 to 3000 and while you press the gas pedal again you need to get the engine speed to over 4500 for the car to maintain speed , and push it hard to continue accelerating.

This means additional time as you need to bring up the the engine speed under full load load

If on the other hand you eliminate taking foot of gas and putting it back again as well as maintain 7000 RPM until you release the clutch again the engine speed will be brought down to the equilibrium point when the car starts accelerating again. This takes less time than if you do it the standard way ( and you take no risk of over revving the engine in the process).

At first glance the loss of time while shifting the standard way seems to bring little delay effect but ...

When the whole stage takes 2-3 minutes and differences of 1 second do count , shifting up 10 times - every time gaining 0.2 sec - gives you 2 second advantage. This means often a jump of 4 places up or down.

Same goes for non-spinning start, late hard braking, proper path on curves, etc , etc.... in total proper driving technique can bring you up 6-8 place up without the risk of over-pushing the car and loosing control in a spin.

Look on the graph below. This is still a rough graph ( based on unrefined data - just road speed on different gears) but it illustrates the idea.

slow shiftb delay.JPG (28.4 KiB) Viewed 10912 times

The continuous line represents "perfect shifting" as if there was no delay in any gear shifts. Different colors represent different gears. The fuzzy lines of same colors represent slow shifting.

Note that the delay in shifting accumulates until the clock is stopped and you are on a finish line. This loss of time is permanent - it cannot be regained.

The idea is to be as close to perfect shifting as possible. This full throttle shifting is an attempt to get the shift time and speed /momentum loss to a minimum.

I have tried to do this few times without "quick shift" electronics and it DOES WORK ! I hope that with it I will be able to do it at a more controlled environment and no risk of over revving the engine.

Re: "push button ignition cut off switch". This is a fascinating idea. I wonder how it would work in a car. My immediate intuition is that the car being much heavier and this having a greater momentum would not allow for shifting gears without the clutch at all. Also restarting the engine at full speed may not be as painless for the car engine as it is for a bike's. But let me chew on it for a while . I can't believe someone has not thought of it before. I will not experiment with just yet though it seems technically very simple and would like to hear other opinions of possible application in a car ...

M