Fiat 2L TC tuning project

[Piero]

Hi

What would be the largest safe size to bore a Fiat TC 2L for maximum power (allowing for possible rebore etc).

Are valve sizes and flow a limiting factor to this? They may not be capable of flowing enough air/fuel on each stroke.

[SteveNZ]

Rebore it the minimum oversize needed. Valve sizes are not important.

[ACE-GREG]

My opinion is to rebore it to minimum always if you have ofcourse problems with your current cylinder wall. I do not think that a reboring could help you too much to maximum power. Anyway, i have tried also 85mm without any problem at highly turbocharged engines.
What is yours, an atmo engine?

[Piero]

Hi,
My thoughts were, there is NO substute for cc.
I was hoping, to take out the bore to a safe size, as it is a lot cheaper than all the head work etc etc.
I will be buying new pistons for my engine build anyway, so I thought why not go bigger :idea:

[dvv]

Hi,
My thoughts were, there is NO substute for cc.
I was hoping, to take out the bore to a safe size, as it is a lot cheaper than all the head work etc etc.
I will be buying new pistons for my engine build anyway, so I thought why not go bigger :idea:

However, in cars as in people, the power lies in the head. Bore as little as you can, only what you must, but rework the head if you want real power.

thank you,
DVV

[Piero]

Hi Guys, first let me say that I am still learning.
So correct me if I am wrong. But the power, so to speak does NOT lie in the head, the restrictions lie in the head!!!!! the power produced is in the combustion chamber.
As with an undersized carb, it just works harder, up to a certain point.
So If the cylinder pressure drawing the fuel and air in, is increaed, the head, like a carb will just work harder.
Yes or know :?:
I would like to make clear, I wanting to oversize for maximum safe power, and not simply because I have to change my pistons.

[SteveNZ]

If you could get significantly more capacity by increasing the bore, it would be worth it. Everyone would be doing it too, why not?

In reality you don't get enough capacity to make any significant difference. Even an 86mm bore will only gain around 90cc. Increasing the bore size this far means there is nothing left if you wish to rebuild it again. You are also making the block weaker.

[sumplug]

Piero.
If you go for max bore, what happens if one of your pistons picks up and damages the bore wall? You cannot take the bore any further to take out any problems. Always go to the minimum bore so you have"meat" left to bore out if needed.
The combustion chamber is part of the head, and most of the power is produced by deshrouding and altering underneath the valves, the seats and valve shapes. Improving exhaust and induction, and timing to alter duration and lift to help fill and scavenge the cylinders should all be done as a package to increase power and more importantly torque where it is required.

Andy.

[dvv]

Hi Guys, first let me say that I am still learning.
So correct me if I am wrong. But the power, so to speak does NOT lie in the head, the restrictions lie in the head!!!!! the power produced is in the combustion chamber.
As with an undersized carb, it just works harder, up to a certain point.
So If the cylinder pressure drawing the fuel and air in, is increaed, the head, like a carb will just work harder.
Yes or know :?:
I would like to make clear, I wanting to oversize for maximum safe power, and not simply because I have to change my pistons.

Modifications to the head are what enables the engine to have and use more power. To be sure, although one starts from the head, and depending on how much more power you want, you will go on elsewhere as well, such as a better carb or two carbs, better and largen intake manifold, or better fuel injection mapping, sharper camshafts, increased compression ratio, improved exhaust system, etc, etc. High quality real power will come only from a well balanced negine.

There's only so much air you can expect from given valves; but enlarge your valves, and especially the intake valve, and you can count on more power and more torque.

In effect, you would do well to sit down and make a list of excatly what you want the car to be at the end. This will enable you to plan what you do, to decide on the best overall setting of the engine and to minimize losses.

In any and all cases, do consult a professional, specilizing in Fiat engines. He'll know things you and I don't.

Just my 2p's worth ...


thank you,
DVV

[Piero]

Hi and thanks for your repleys.
I think some may have misunderstood me, and for this I say sorry.
I am dyslexic, and find it hard to wright down what I mean, as I am so busy trying not to miss spell my words.
I had writen in my very first post, (allowing for rebore etc).
I do intend to do other things to my engine as well.
My question related to over bore safe size.
please read intier topic.
You can only get the head/carbs/headers etc to flow so much, once you have done all that inc cams etc, were do you go.
As I was buying new pistons for my rebuild, I just wanted to know what was the max save size one could go to.
Piero

[Guy Croft]

Piero

You have now had 4 members (all experienced) telling you to use rebore size! The rebore sizes are 84.4, 84.6, 84.8, 85mm. Take your pick.
If you can get OE spec pistons for any of those you're doing well, my engines for some years have mostly been on forged.

GC

[Piero]

Yes Guy.
Forged pistons for me to.
I was interested to see if any one had ever done some thing like they did with the mini engine, and take the bore out to quite a size over standard.
Then it may have been worth the effort to oversize.
but from what has now been said, 85/86 is about max.
Pity.
With this now sorted, I can chanel my efforts into finding a suitible cam for what I want my engine to do.
As you once told me, to wild a cam will make my car very un tracktable.
which is why I was trying the oversize route.
Piero

[Guy Croft]

There is no commonality between the A Series engine and what you can - or have to do to it - to get high power, and the 2 liter Fiat TC. Look at the bore spacings on your own motor - and then tell me why it's a good idea to go to much bigger bores.

GC

[dvv]

... With this now sorted, I can chanel my efforts into finding a suitible cam for what I want my engine to do.

As you once told me, to wild a cam will make my car very un tracktable.
which is why I was trying the oversize route.

Piero

Well, the question of which cam begs an answer to a previous question - do you have carb or carbs, or EFI (Electronic Fuel Injection)?

The reason is quite simple. Carbs are, by their nature, optimized for a certain engine operating regime, and once inside that envelope, they will in effect be just as good as an EFI system. The trouble is, that envelope is very narrow, so below and above it, carbs are fuel wasters.

Conversly, an EFI system, assuming it's externally programmable, is literally incomparably more flexible, insofar you can actually modify some mechanical parameters with intelligent programming. For example, if a cam is power peaked at say 7,500 rpm, with programming you can lower this somewhat, to say 7,000 rpm or so. The reason is simple - as opposed to carbs, an EFI system is infinitely variable in mixing air and fuel.

The net result is that with an EFI system, you can use sharper cams without paying the usual price, i.e. without having to rev up to 4,000 rpm to observe some engine life, fuel consumption is MUCH reduced in comparison with two twin carbs, etc. But the initial outlay is, as these things go, much greater than with two carbs, if you don't already have an EFI system installed.

Another point you should consider are the nitty-gritty mechanical parameters. For example, my cam is peaked at 7,500 rpm, the angle is nominally 288 degrees, valve lift is 10,58 mm. However, the angle is given at a cam distance of 0.1 mm, whereas in my engine, it will be sitting at 0.25 mm distance, so its nominal angle will actually be smaller. At a guess, I'd say around 275 degrees or so.

This, in conjunction with a totally programmable EFI system, should allow me to have around 150 HP at around 7,000 rpm. Yet, my idling revs are just 1,000 rpm, no need for more, the engine is very calm. As for pulling, well, with small and light cars, you can always get away with a slightly sharper cam than with a big piggy like say a Ford Mondeo or some such.

Before you ask how I expect 150 HP from an 8V SOHC engine, the answer in part is that up to 6,000 rpm, the lambda probe does its job, but at 6,001 rpm, its readings are disregarded and the engine changes its operating mode. It goes into a "damn the fuel" mode, it simply takes as much fuel as it need to deliver high power. You can't do that with carbs.

thank you,
DVV

[Piero]

I was hoping to keep things simple, so with this in mind
and as I already own twin 40s and twin 45s Webers, I intend to go for carbs, opting for the 45s.

I have gathered a few other items, ie a 130 Abarth head, with short inlet manifold, will be porting and flowing the head and valves/seats.
Hoping to buy forged pistons from Guy. I will have crank/flywheel/clutch balanced.
And I had thought about maybe rally type cams but have not decided yet.
could do with some help on this one (cam choice)
I am having a 4-2-1 system made.

Piero