head cam work to decompress a Fiat Uno Turbo 1372cc

[unomas]

Hi Guy,

nice to talk to you..... I must say your forum has a lot of useful information, you must be proud of your work.

I already sent to you an email to introduce myself, but I will write some info again , just FYI.
My name is Martin Ponce, and I live in Argentina (the southeast country in the American continent).

From this lands, is common to see some cars that you have improved.-
Just in example : Fiat UNO, Fiat 125 (mirafiori), etc.....

Actually I have a Fiat Uno Turbo 1372cc (146A8000 engine), 1990 in a overhauling process.

All the things I did in the car from the beginning, was having in mind to get more "extra" power from this tiny engine. I¢ž¢m been working on it from 2 years up till now.... so as you can see, is like a hobby for my.

My problem now is based in a bad head cam restoration from the rectification process.

I think the rectification guy, leave the head not totally parallel, so I have differences from one combustion chamber to the other. In fact , I have this values on each one :

CC#1 : 31 cm3
CC#2 : 31 cm3
CC#3 : 32 cm3
CC#4 : 33 cm3

I will upload a picture to show you more deeply the head cam in the precise moment when I bought the car :



As you can appreciate, the state of these combustion chambers were really bad.

I restored all the necessary parts : valves, valve guides, I changed the original valves springs, for racing ones, etc‚¦

This are some pictures from the process :





(In this case, my dad is giving me a hand to cut some …œextra‚ material from the CC. He has a very good hand to do that‚¦. and nothing is more comfortable, to me, like spend some weekend sharing with my dad this kind of activities‚¦ :)

After a lot of work in the head cam, and after I read your notes in the …œTuning hints and theory‚‚¦ the CC‚´s looks like this :



I¢ž¢m not a professional like you, but I¢ž¢m feel happy from the results of this work‚¦. But I will feel bad if I make a mistake during this last part of the work, and for that reason I¢ž¢m looking for your advice.

My friends told me I can correct this, doing the rectification process again, but this time I must add some degrades to rebuild the parallelism of the head cam.

But certainly I¢ž¢m really scared about this process, because if this process fails again, I will have a head cam very hard to decompress to the 7.8:1 original compression ratio.

For that reason, please I need to know, if you can explain me, based in your experience with this kind of motors (that I sow is really long), where is the precise places to cut some material, to reach the 33 cm3 on every CC.


Tks in advance, and let me know if you need more information from my car.
Martin



PD : Sorry again for my bad English, but I¢ž¢m working to improve it.

[SirYun]

Have you calculated the CR you have? (including ring lands, piston to deck distance,piston dish, head gasket (compressed!) volume). question being: do you have a problem to begin with

For non hard core racing purposes a 0.5 to 1 cc difference between chambers is not all that bad.

Are scrap heads hard to find ?? I personally use a head i hit water in, to see how thick the casting should be at a certain point .. then be very conservative as castings can vary quite a bit

My guess (based on other heads!! best wait for GC to answer or locate a scrap head) is that finding volume in the chambers is best done by cutting the wall (angle it) on the spark plug side as this tends to be quite thick. That would have the added benefit of deshrouding the valves a bit.

other options would be either dished pistons ($$) or a decompression plate if the head does not allow to get extra volume from it.

[unomas]

Have you calculated the CR you have? (including ring lands, piston to deck distance,piston dish, head gasket (compressed!) volume). question being: do you have a problem to begin with

Yes I have it.
Is near 8.0:1 with a head gasket of 2.4mm of width. I calculated everything to raise the CR from 7,8:1 original to my desired 8.0:1.-

For non hard core racing purposes a 0.5 to 1 cc difference between chambers is not all that bad.

Good to know!, I will keep on mind this. I thought the difference had to be near 0.25 cc between each one.

Are scrap heads hard to find ?? I personally use a head i hit water in, to see how thick the casting should be at a certain point .. then be very conservative as castings can vary quite a bit

Of this car, yes. Keep on mind there was just 29 units imported in the past.

My guess (based on other heads!! best wait for GC to answer or locate a scrap head) is that finding volume in the chambers is best done by cutting the wall (angle it) on the spark plug side as this tends to be quite thick. That would have the added benefit of deshrouding the valves a bit.

Thank you. I really appreciate your answer. I supposed that place should be the target of my dremel....

other options would be either dished pistons ($$) or a decompression plate if the head does not allow to get extra volume from it.

Thanks a lot for your help.

Martin

[SirYun]

just to make it absolutely clear..I don't know this particular head and my comments are purely based on what i have done myself and seen done to various charged heads.

as we say in medicine : IN DUBIO ABSTINE

[Guy Croft]

Hi Martin,

good article, great English, well done.

I assume that 33cc chamber volume gives you 7.8/1? I don't know the piston VR or bowl volume or the setup height of the piston crowns realtive to the block so I will just 'take your word for it'.
I will mail you a CR calculator that you can put your values in, but basically I have just done the calcs based on 31 and 33 cc and gasket 2.4mm thick compressed and it tells me that 33cc will give 8.08/1.

Is that too high? Well, one cc is nothing to worry about on a normally aspirated engine although it's a pity the machine shop did not do the job right, on turbo I would wnat to be sure. Don't know what boost you are using, standard I guess and Integrales imported into the UK ran that CR with 1 bar boost, but then we have 95 and 97 RON octane fuel.

If you don't have our grade fuels go for 7.8/1 or lower. If your boost is higher than standard go down on CR. I think your engine probably has a knock sensor, but I don't know for sure and anyway you don't want it over-working because they retard the ignition and you'll lose power.

Whatever CR you want 7.8/1 - or anything else - make sure you burette the pistons and put that data into my calculator, and also check and enter the relative height of the piston to the block face (deck). Make sure the figure you use for head gasket thickness is the 'compressed' value - get this from an old head gasket. ‚¬A new one is going to squeeze down 0.3mm or more.

Here is a picture showing where to remove metal if you want to get it right. To take off one cc make a 1cc cube from clay and then mould it to give you an idea how much metal removal that means in the head. Removing a wide thin section is better than one deep pocket.

My biggest worry actually will be that if the head has been really badly machined end-to-end the cam belt may run off the cam pulley. Do a dry run with the cam in and the head on the block (don't need pistons and valves, just the belt fitted) and make sure it is safe.

GC

[unomas]

Thanks for your time writing me about this.

Below my responses.-

Hi Martin,

good article, great English, well done.

Really thanks, I am learning a lot of your language (and fighting a lot too with the nouns!!)...

I assume that 33cc chamber volume gives you 7.8/1? I don't know the piston VR or bowl volume or the setup height of the piston crowns realtive to the block so I will just 'take your word for it'.

I will mail you a CR calculator that you can put your values in, but basically I have just done the calcs based on 31 and 33 cc and gasket 2.4mm thick compressed and it tells me that 33cc will give 8.08/1.

Is that too high? Well, one cc is nothing to worry about on a normally aspirated engine although it's a pity the machine shop did not do the job right, on turbo I would wnat to be sure. Don't know what boost you are using, standard I guess and Integrales imported into the UK ran that CR with 1 bar boost, but then we have 95 and 97 RON octane fuel.

If you don't have our grade fuels go for 7.8/1 or lower. If your boost is higher than standard go down on CR. I think your engine probably has a knock sensor, but I don't know for sure and anyway you don't want it over-working because they retard the ignition and you'll lose power.

Is exactly as you are telling... the 7.8/1 is the original ratio, but I am increasing it to 8.0/1. At least that was my dessign objective. And for that reason, I must use a 2.4mm head gasket.

Thanks for the calculator, I will check it as soon as I can.
Thanks too for the aclaration about the differences between the cc in the chambers, but I am running a Garret T25 .38 / .46 (outlet/inlet), and I changed from the original 0.7 bar to 1 bar.
I decided to increase the CR and the turbocharged pressure, because we use RON 100 octanes, and this car was originaly designed for 95 RON fuels (remember the year of production was 1990).

About the knock sensor, the L-Jetronic 3.1 that comes with the car, has one, but as you told me , is my intention to be away from picking. In fact,
I made a knock sensor device to detect picking, and I already tested in other car with 1.2bar of pressure and the 7.8/1 original compression, and tehre was not detectable picking.



Whatever CR you want 7.8/1 - or anything else - make sure you burette the pistons and put that data into my calculator, and also check and enter the relative height of the piston to the block face (deck). Make sure the figure you use for head gasket thickness is the 'compressed' value - get this from an old head gasket. ‚¬A new one is going to squeeze down 0.3mm or more.

OK... good point , I will keep on mind those values.

Here is a picture showing where to remove metal if you want to get it right. To take off one cc make a 1cc cube from clay and then mould it to give you an idea how much metal removal that means in the head. Removing a wide thin section is better than one deep pocket.

Very nice explanations!!!... tks a lot for your response and the time involved.

My biggest worry actually will be that if the head has been really badly machined end-to-end the cam belt may run off the cam pulley. Do a dry run with the cam in and the head on the block (don't need pistons and valves, just the belt fitted) and make sure it is safe.

I already did it, and it worked perfectly, but thanks for the preocupation and advice.

GC

As soon as I get finished my work, I will update about the performance of the engine.

Again many thanks for your time, and patience.
Martin.

[Guy Croft]

Thanks for the acknowledgement and extra info.

GC advice:

If you raise the boost - lower the CR

Never, never raise the boost and the CR in the hope of improving the off-boost performance.

You just don't want to do that with turbo engines. You have to accept that the higher the boost the worse the off-boost is going to be or don't turbocharge.
Raising the CR will give little by way of extra torque off-boost and most likely lead to detonation. Actually in my experience it always leads to a wrecked engine...

OK?!

GC

[unomas]

Thanks for the acknowledgement and extra info.

GC advice:

If you raise the boost - lower the CR

Never, never raise the boost and the CR in the hope of improving the off-boost performance.

You just don't want to do that with turbo engines. You have to accept that the higher the boost the worse the off-boost is going to be or don't turbocharge.
Raising the CR will give little by way of extra torque off-boost and most likely lead to detonation. Actually in my experience it always leads to a wrecked engine...

OK?!

GC

OK... I will keep on mind.

Tks again.


Martin

[Acki]

The head will break on high pressure...

/edit:
Oh I see Guy has marked the problems on the head.

With the T25 you can drive 1.2-1.4 bar on the stock engine without problems.

[Molerpa]

For non hard core racing purposes a 0.5 to 1 cc difference between chambers is not all that bad.

excellent info!

Molerpa, in his first message

[unomas]

Hi Guy!!...

I hope your things are going well!

I am just writing you to let you know about my finished work in the camshaft following your previous recomendations.

In a first place, I must say THANK YOU, for your patience and time spend to give me a solution for my problem (excellent info!)

I was working hard on the combustion chambers, first with my DREMEL, but it was not a good idea (my pulse was not the ideal to do that), and after a while y created an special tool to devastate with more precision.

This is a picture of the "manual" process :



As I told you I created a simple machine, but more precise than the Dremel. Even faster.






After a few hours of work with this machine, and calibrating the paralelism of the camshat, I reached the requested cubic milimeters in the camshaft, and I did some improves in the water and oil internal pipes.

The final work is this :





Is not a professional work like yours, but is a good begining for a enthusiast like me.

As I told you in the beginning of the thread, and as I am telling now, all the things that I learned would be impossible to do without your advices.

You can close the thread if you want it.

Thank you very much, and I hope we can meet us someday.
Martin Ponce
Argentina

PD : Sorry again if my English is not so good.