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

[WhizzMan]

Not bridges, but ridges. Right now, the edges of the holes in the bottom of your air box look like they are not flush with the bottom of the trumpets, where they meet the top of the carburetors. It could be just the photograph?

From what I know about "fluid dynamics", the more distance you have from your trumpets to the top of the box, the less the top will interfere with "perfect" airflow. Guy's experience says that one inch should be enough, so with your 1.5 inch, it should probably not be really significant anymore. I've seen a 16V Alfa that had about 2" and a 0.8mm sheet aluminium cover that was resonating so much that it tore nex to the welds holding the top on. That is why I asked about dampening.

[LanciaNut69]

Hi Miro,

Great topic by the way - I am reading this with interest. I always preferred the 131 Abarth to escorts of the day, but I'm funny that way. I know this is maybe approaching the problem from another direction and it won't help, but have you considered using a dog or crash box? I used to use one when I was rallying and part of the practicing I did against such an eventuality was learning to change gear without using the clutch. It's not difficult when you are accelarating through the gears - a slight lift off and change, no clutch - but coming back down the gears does take practice to match revs, gear and speed.

I wouldn't recommend prolonged use on a standard gearbox, but a dogbox I think has straight cut gears and no synchro rings. It makes a lot more noise, but is stronger and you don't lose as many revs between changes. I have no idea of the availability of Fiat boxes of this type, but I'm sure there are adapter plates you can use to attach a Getrag or similar type gearbox.

Hope this helps

Darren

[TomLouwrier]

hi guys,

Miro, point taken. Your diagram lacked the 3rd axis for time.

As Darren mentions, bike boxes are indeed sequential, straight cut, dog boxes. That certainly is a different thing from a regular sync'd car box.
On the road (bike) I regularly do shift up without clutch, no ignition cut-out but just a very short twist of the twistgrip. About half-way closed, enough to take the pressure off of the driveline and then full on again. That works well.

In cars you can also do this, in fact army drivers used to be trained to use that technique in order to maintain speed in rough terrain. Lose speed there and you're stuck. It's hard on your synchros though unless you get the revs right all the time. Not likely when you're doing a stage.

Now here's a funny thought: if you wish to maintain engine speed while shifting up and limit engine speed on a missed downshift, wouldn't you be needing a heavy flywheel? Maybe just a 'regular' one, but not extremely light.
There is certainly a relation between rotating mass and the rate of engine speed change. I've often noticed some cars shift like *** (well... 'less than perfect') when driving relaxed and then when you start chasing down the twisties everything suddenly falls into place and the grin comes on your face. Each car has it's own rythm.


Homme, imagine the air inlet being covered by a half sphere. If the diameter of those trumpets is about 50mm, then the distance needed to clear that half sphere is 25mm or more. You posted a very nice article on velocity stacks recently, thank you btw.
That would be 2" and 1" respectively for non-metric guys.

regards,
Tom

[Walezy]

This is how i change gears in my Fiat
1 cluth pressed and gas pedal relased
2. shifting quickly from 3rd to 4th and relasing clutch pedal when finishing to put 4th gear
3. pedal to the metal

here is a short movie with data how i do it
http://www.youtube.com/watch?v=gXLaJYfuGxg

Of course i loose a bit on it but the car definitely does not slow down but it also does not accelerate at this moment and this is a lost time for sure.

[Guy Croft]

Can we move on please?

That latest post is the contemporary and correct way to shift with a synchro gearbox. Attempts to change by other means are likely to end in tears.

There is only one sane substitute for the 131 box and Tomasz' method and that is a close-ratio gearbox eg: Ford 5 speed with adapter to the 131 bellhousing and 1" x 23 clutch plate spline & TranX gearset and there is only one substitute for the 131 gearset and that is an Italian-made one. Though the names of the mfr of the latter, Bacci Romana and Colotti are frequently cited I know of no more than 2 people in my lifetime who have bought sets from them and the mere mention of them invariably just descends into a silly discussion about cost which I will not accept here! If anyone has a problem with the cost they can jolly-well design their own one-off and see how much that costs.

FWIW a CR setup in this case is easily worth 40bhp (or so) in terms of the rapidity it bestows on the car.

G

[Walezy]

This is close ratio type 9 gearbox with tran-X gearkit that i had in my Fiat before i changed the engine and gearbox for Honda f20c unit.
It was a very nice gearbox that i was able to fit to Fiat with not too much hassle but of course some modifications to gearbox tunnel was neccesary.
The only problem with that gearbox was that it does not like too quick gearchanges but this should be possible to overcome the problem by using steel synchro rings that are available for them. I had the gearkit brand new and installed it with a new rebuild kit(bearings, synchrorings, gaskets, seals, layshaft etc.).

Here is how this worked in my 180HP 2.0l 16v TC engine
http://www.youtube.com/watch?v=ASTJuDr7 ... re=related

[miro-1980]

Gents,

As they say "Gents do not talk money - they have them" and those that do not- pretend they do and keep quiet). The gents here talk mechanics, techniques, etc., so talking money would be out of place.

So money aside let me share few bits on my gearbox selection, and more general project philosophy.

My research on 131 gearboxes well preceded my key decision to ask Guy to build me an engine. It grew out of my general interest and quest to know as much about it as I can.

The experience I gathered so far suggests I did not approach the subject in an optimum way, but I was not totally wrong as to sequence.

I started with a body. True, it was not originally prepared to be a full replica of a Corsa , but rather a Stradale lookalike. Nevertheless it seems to be the right place to start.

I recently witnessed an interesting exchange between a novice who wants to build himself a Polonez 2000 rally car and an old hand who has build at least a dozen of such cars. On old hand told the novice : first get a good chassis and prepare it for rally application , than get an engine and than the rest : get a gearbox diff, braked wheels, etc.

I am on the same track, though notably a bit advanced. I have the body, I have the engine, I have the diff and suspension. What is more the car is sports-worthy and I drive it, gaining experience and modifying other systems to match in performance. I am now working on the brakes. Maybe a gearbox will become a live sub-project in the future, but now it is only in the realm if theoretical considerations.

These theoretical considerations are not unimportant as understanding what makes the car perform and why is key to learning to drive it in manner that maximizes performance and minimizes chance for damage as well as wear and tear.

I remember reading (in late 60's) a book written by Sobieslaw Zasada, a Polish rally champion, winner of Monte Carlo rally and European Rally Champion. What was amazing to me at the time - and became a part of my driving philosophy - was what a rally the car should not be pushed without reason and when pushed it should be pushed wisely. Zasada said : "if you brake the car between stages - you will not make it to the finish and this is where the winners are." I do not have bunch of wealthy of sponsors paying for a team of mechanics and unlimited budget for repairs. If the car is totaled I am out - permanently. If the car is damaged in a serious way - it might take a season to fix. If I blow a GC engine, I will be stuck with standard engine 120 bhp, at least for a good while.

So I drive keep developing my car in a manner that matches my driving abilities and experience. Progress is made step by step and technical changes are made as they are needed, so I have a chance to catch up with my driving skills.

So, once I am happy with the current setup of all systems, I will try to muster full use of what I have.

The decision to change a major sub assembly of the car setup at this stage to another gearbox will come only when I decide that what i have now is a significant limiting factor in making the car perform better, and I am ready for it.
This holds true for the gearbox. One technical element limiting car performances at this stage are the brakes and this is what we are working on. Resolving this will also allow for full Abarth front-end suspension installation.

I am not ready for a straight gearbox, yet. A close ratio synchronized box would be useful. But by no means a straight-gear box or a close ratio synchronized box would make my stage times consistently much better. Currently the driver is the key limiting factor, so no matter what gearbox I have it will not make me drive the car any better. Overall utility of putting any such fine box in my car now would be marginal. For the time being I will stick to a standard gearbox. I have three of these boxes spare and with the reputation of being hard to destroy I have some time to play with my current stock.

This is not to say I have not researched the subject. To the contrary. Identifying the "best" gearbox for my car led me all key contemporary makers and in depth analysis of benefits of every solution. It has also led me to Finland in an attempted purchase of original Cima 168. The communication with the seller was rapid, but a bit murky as he clearly intended me to bid on a "pig in a poke". If it went differently I probably would get one and restore it, though I would not install it, just yet.

When I got my first Abarth diff, I had nothing to be able to install it. An opportunity came and I got it. I also collected a number of Abarth C&P sets. Later this proved to be a very wise move giving me now two diffs (3.9 and 6.14), lots of spare C&P sets and the ability to change major characteristics of the drive-train ratios for different events.

Though I am not a mechanic and my formal education background is very far from any physics, mathematics and or engineering it is fascinating to me to use my skills to learn and understand technical dependencies of car performance. This is probably 50% of the fun and the other 50 % is driving it. Also a bit of patience

Miro

PS: I would not be surprised if the final choice would be Ford 5 speed with adapter to the 131 bellhousing and 1" x 23 clutch plate spline & TranX gearset.
This was Guy's original suggestion. So many times I have initially resisted and than ended up flowing Guy's advice that this is likely to happen again, including gearbox selection.

[miro-1980]

Re: Steering wheel hub adaptor.

I have inspected my steering wheel hub adaptor again. The cracks make it junk, totally unfit for safe use.

Here are the pictures:

CRACKS 1 .jpg (91.42 KiB) Viewed 11656 times

CRACKS 3 .jpg (49.47 KiB) Viewed 11656 times

CRACKS 2 .jpg (62.32 KiB) Viewed 11656 times

CRACKS 4 .jpg (70.48 KiB) Viewed 11656 times

And here is a picture of what saved my next event ; thanks to Walezy who shared with me his spare hub.

CRACKS NONE 1 .jpg (89.94 KiB) Viewed 11656 times

Thanks Tomek !

Miro

[miro-1980]

Airbox update :

Here are some pictures from installation :

AIR INLET x1.jpg (72.98 KiB) Viewed 11656 times

AIR INLET x2.jpg (78.8 KiB) Viewed 11656 times

The inlet will by under the front grill, just over oil cooler and left of the radiator. Heat insulation will be placed between the ducting and the two radiators to prevent air heating up due to heat radiation from both .

Miro

[miro-1980]

Tom

...imagine the air inlet being covered by a half sphere. If the diameter of those trumpets is about 50mm, then the distance needed to clear that half sphere is 25mm or more.

Thanks! This is a very simple and elegant of explaining the issue.

Re: ignition cut off switch. I was told today that using motorcycle type cut off switch" is actually used on rally cars here , so somebody did already copy the idea...

Miro

[miro-1980]

Not bridges, but ridges. Right now, the edges of the holes in the bottom of your air box look like they are not flush with the bottom of the trumpets, where they meet the top of the carburetors. It could be just the photograph?

From what I know about "fluid dynamics", the more distance you have from your trumpets to the top of the box, the less the top will interfere with "perfect" airflow. Guy's experience says that one inch should be enough, so with your 1.5 inch, it should probably not be really significant anymore. I've seen a 16V Alfa that had about 2" and a 0.8mm sheet aluminum cover that was resonating so much that it tore next to the welds holding the top on. That is why I asked about dampening.

Re: Ridges . Sorry i get it now . The ridges are still there . They hold the trumpets on place and getting them off would create a problem of how to fix the trumpets . they could be welded to the airbox bottom , but this is something I will consider later. Thanks for the idea , though

Re: Resonance - My box s made from 2 mm stainless steel and top cover is1.5 mm thick. Will see if this is sufficiently stiff to resonance. But it is quite heavy. Vibrations are a problem I need keep in mind. Vibrations will tend to loosen all the bolts. The airbox hangs of six bolts holding the trumpets to the carbs and loosing one of them causes a risk of the nut ending up in a combustion chamber ... I do not even want to think about the consequence. To eliminate it |I will consider use of Locktite thread glue (aside from good spring washers , or the nuts with -plastic inserts which are resistant to loosening due to vibrations. If I am not 200 sure this will hold the m in place I will initially keep the mesh covers.

Vibrations previously caused the mounting arm of the alternator to crack and all the bolts holding the thermostat loosening up seriously. The arm was welded back on , but needs regular inspections. The thermostat holding bolts were glued with medium (blue) thread glue with good (but imperfect) results. This also needs regular inspections.

So, the resonance is a symptom of vibrations. The vibrations are totally invisible as the engine even at low RPM runs is exceedingly even and vibrations are smaller than the previous standard 12 bhp engine. It nevertheless must there at high RPM on a stage with very stiff suspension. So this is something to watch.

As Guy has turned my attention to this before when we changed the clutch. Now every time we take a bolt out, we try to put a new bolt in , but washer is changed every time. No reuse of washers.

Miro

[miro-1980]

This is how i change gears in my Fiat
1 cluth pressed and gas pedal relased
2. shifting quickly from 3rd to 4th and relasing clutch pedal when finishing to put 4th gear
3. pedal to the metal

here is a short movie with data how i do it
http://www.youtube.com/watch?v=gXLaJYfuGxg

Of course I loose a bit on it but the car definitely does not slow down but it also does not accelerate at this moment and this is a lost time for sure.

My shifting process is obviously the same , I just tried to stress the whole process. Sure, some elements are almost simultaneous. Sorry for oversimplification.

Re "slow down" vs "decelerate". If my "feel" for physics is right , saying that the car "does not accelerate" at the time time of gear shifting looks like "deceleration" and this means loss of speed. But even it this is loss of speed is negligible, the real element of loss is likely to be the momentum. Regaining momentum takes time .... and this time is lost. How much of it - is a really good question. If the loss is as little as 0.2 seconds very time you inappropriate the total loss in 10 shifts is 2 seconds and this is not a small time loss at all. My theoretical knowledge suggest this is the "momentum" loss which is a problem.

Miro

What is the proper English term for this - angular momentum '?

M

[WhizzMan]

Re: Ridges . Sorry i get it now . The ridges are still there . They hold the trumpets on place and getting them off would create a problem of how to fix the trumpets . they could be welded to the airbox bottom , but this is something I will consider later. Thanks for the idea , though

I'm not sure we are talking about the same. The edges of the holes in the bottom, where your trumpets are mounted on, appear to be in the air stream. Just making the holes a bit larger would solve this.

[TomLouwrier]

A picture helps.
I think Homme means these, aka 'downstream mismatches'.

Then again, it may just be a gap between the end of the trumpet and the top of the carb because the opening in the airbox floor is in fact bigger instead of smaller.

Tom

[Brit01]

To eliminate it |I will consider use of Locktite thread glue (aside from good spring washers , or the nuts with -plastic inserts which are resistant to loosening due to vibrations. If I am not 200 sure this will hold the m in place I will initially keep the mesh covers.

What about nut retainer clips as an added safety margin if you're concered about the nuts vibrating loose but I don't think you'll have an issue with the nuts with plastic inserts IMHO?

Nice work on the airbox and air intake in front of the radiator.