Race Engine Forum UK

This is picture of my combustion chamber and as you can see there is some strange "scratch". Is it crack or maybe just leftover of casting process(as I hope it is)?

What gap should be between valve and valve guide?

I want to to port this head on my own but there is this problem.
Pay attention to those cutouts which allow injectors to spray fuel at the right point. Is this going to be affected if I enlarge ports?



Now, the goal with this engine is to make 150/160hp(on flywheel) in near future. What is your recommendation for intake and exhaust port sizes(around 29mm)?

I already want to take care of short side radius on intake, are there any other spots by your experience on which I should pay attention?Any "critical' spots in the exhaust ports? Is there anything that should be done in combustion chamber and should I polish it or just finish it like ports? What about valve sizes(stock is in/ex 36/33mm)?

I know that there are lot of questions, but I hope that there are people willing to help. This is my first engine and I want to get it done right despite my poor experience.


Thank you in advance!

To answer your later questions first, the engine in near stock form will quite happily make the figures you are asking for just by blueprinting, increasing the inlet valve size and paying special attention to the valve seats (3-angle cut).

The limiting factor will be the alignment of the crank - the turbo engines have a nasty habit of twisting the block just enough to sap power but without killing the engine (from what I've discovered this problem is actually consistent across all of their engines but the turbo SOHC engines really suffer).

The ports aren't too much of an issue, the cut-outs are for matching the position of the injector and since that isn't going to change you can enlarge the ports without touching the cut-out profile.

Now for the nasty bit - that "scratch" is almost definitely a crack. The heads on these engines are prone to cracking and given that your example is likely to be about 20 years old it is almost definitely in need of repair anyway. It is incredibly hard to find examples that aren't cracked but they are repairable. The other place to pay special attention is between cylinder 2 and 3 as it is the first point of failure when the head gasket blows (in most examples).

The only other thing you need to worry about is fooling the pressure switch in the plenum chamber as it limits the boost to 0.6bar in a standard engine but the design is for 1.0bar which is what the engine will run to naturally. IHI invested a lot of money in developing the engine for Fiat and did a very good job indeed. The original specification did not include that pressure switch, it was only introduced by Fiat as a precaution. It is best to make sure your fuelling is accurate but all of what is discussed is within the scope of the design.

The boost was reduced on British spec road engines to satisfy the insurers who went mental when they realised how fast the car went. It was the only way Fiat could get them to reduce the insurance group [originally going to be grp 17!! ]. The suspension was set higher then none turbo cars also as well, to reduce the tendency to boy race the car. It must be noted that Italian spec cars run with lower suspension and full boost [1 bar].

Yugo.
The head can be "lockstitched". This is a process of drilling the crack all along its length, then welding in new metal. When the job is done, it is an invisable repair and permanent. Ive had a couple of heads done, one being an Uno 1301cc head and one being a 127 1050cc Brazillian head.

Andy.

Firstly,thank you guys for posting in such short time.

To answer your later questions first, the engine in near stock form will quite happily make the figures you are asking for just by blueprinting, increasing the inlet valve size and paying special attention to the valve seats (3-angle cut).

That's great.
What inlet valve size are you recommending?

The limiting factor will be the alignment of the crank - the turbo engines have a nasty habit of twisting the block just enough to sap power but without killing the engine (from what I've discovered this problem is actually consistent across all of their engines but the turbo SOHC engines really suffer).

Yes,I know for that problem.
Acctualy my crank's been aligned few months ago,when I took it out of block it was twisted a bit.
Well,I know only one payable solution for that problem-aligne it again and again as it twists.
But,I think that this is not so much power and that it will hold,anyway-will see.

The ports aren't too much of an issue, the cut-outs are for matching the position of the injector and since that isn't going to change you can enlarge the ports without touching the cut-out profile

By your experience,what is proper port size for this amount of power(150/160hp)?

Now for the nasty bit - that "scratch" is almost definitely a crack. The heads on these engines are prone to cracking and given that your example is likely to be about 20 years old it is almost definitely in need of repair anyway. It is incredibly hard to find examples that aren't cracked but they are repairable. The other place to pay special attention is between cylinder 2 and 3 as it is the first point of failure when the head gasket blows (in most examples).

Thats the thing I was affraid of.
By the way,this "crack" is present in all comb. chambers on exactly same place.
I'll sort it out.

The only other thing you need to worry about is fooling the pressure switch in the plenum chamber as it limits the boost to 0.6bar in a standard engine but the design is for 1.0bar which is what the engine will run to naturally. IHI invested a lot of money in developing the engine for Fiat and did a very good job indeed. The original specification did not include that pressure switch, it was only introduced by Fiat as a precaution. It is best to make sure your fuelling is accurate but all of what is discussed is within the scope of the design.

I've de-attached that switch.
And, the plan is to install Megasquirt injection system this your and new turbo(not sure which,T25 or maybe it will even be some of Mitsubishi TD04 familly) cause I want to achieve power by flow and to minimize the pressure.

@sumplug

Thanks for info about head welding-very interesting method!

Hot pressure-test the head and if doesn't leak water leave the crack alone.

BMW 4 cyl 6 cyl crack routinely between the seats but the crack tends to be quite shallow and doesn't grow right thru, nowhere near. If you weld it up it will just crack again for sure.

Andy - if you have welded a Brazilian 1050 Fiat head you're a better welder than I - those things are made of mazac!

GC

I will have to dig out the sizes for the valves but it isn't a huge increase to get what you want, you could probably get away without changing them but you will see better torque figures across the range if you do.

The T25 is likely to be overkill, the standard IHI is tiny by comparison and well suited to get you to 130bhp, 150bhp is stretching the limits though and I agree a slightly larger turbo would be a good idea. The injectors are also at their absolute limit too and that assumes they are in perfect working order. Using a smaller turbo and as low boost as you can will allow you to use higher compression and that is where you are going to get the real versatility.

You can obtain the performance maps for the candidate turbos and find the one best suited, just adopting one from another car is a huge compromise that often leads to disappointment.

Guy's advice on the crack is spot on but you need to be quite thorough in looking for other cracks elsewhere.

Guy Croft wrote:
Andy - if you have welded a Brazilian 1050 Fiat head you're a better welder than I - those things are made of mazac!

GC

Had it done at Lockstich Ltd in Rochdale. They are the originators of this techneque, and there skills are way beyond me.

Andy.

@Julian

Yes...well,actually there is not much place to fit big valves like those lovely 40mm ones.
Maybe about 38mm intake tops.
What about ports?
Stock intake ports is cca. 30mm reducing to about 27mm,exhaust about 29mm reducing to about 26mm(pretty rough measures).
Is valve unshrouding recommended?

Well,I realise that T25 is a bit bigger then I need,but here in Serbia(or Croatia,same problem) is hard to find turbos.
So,one of my choices is also MHI TD04-13.
What about turbo from Punto GT or Uno 1.4 Turbo?

Injectors,off course,I'll swap for bigger ones as soon as I install Megasquirt injection system.

Talking about cracks, I haven't noticed any more cracks but I assume that some of them can't be seen by eye so the head is going to be sent to pros to chek it.

@Guy
Do you have any pictures of uno turbo heads you've done?
Any advice about comb. chamber and porting?

Hi,

most of what you need to know about SOHC head overhaul and mod is on view at:

http://guy-croft.com/viewtopic.php?t=64

For porting enlarge the port by 1mm on sides and roof by 1mm, smooth the casting all over from manifold to valve. You absolutely don't need bigger valves because even with a standard Uno T cam and 12 psi boost you are going to exceed your target easily.

Then, most important of all read the outstanding article by my client Nathan Corridon at:

http://guy-croft.com/viewtopic.php?t=239&highlight=uno

Once you have read all this, I should be happy to answer any other questions, as I am sure the other experienced members will too.


GC

Ok...I've read all of these and there are some questions.
We talked about 3angle seats and valves.
And I agree but lets be more precise.
How EXACTLY to modify seats and valves?
What angles and how each "region" should be wide?
I'm not going to do them by my own,but I need to know what to tell to men who is going to machine valves and seats.

Now about Nathan Corridon's car.
Where interesting,no doubt about it.
There are some really great ideas.
Have you driven that car Guy?
I'm asking cause I want to know how much responsive is that engine cause of that turbo.

But there are some major differences between his and mine projects.
He wanted race car and I dont.
Also I cannot afford forged pistons.
And at last I dont need those amounts of power-if you ever driven Yugo you know what I meen.

I'm also interested in those modified oil ways.
What's been done on that field(if it's not secret,of course)?

Once again,thanks for all your and others people's help.

Yugo_Turbo wrote: Well,I realise that T25 is a bit bigger then I need,but here in Serbia(or Croatia,same problem) is hard to find turbos.

I think T25 with .48 ar turbine housing will be good for you, it will enaught for about 180HP, it is almost "bolt-on" with uno 1.4 or punto gt manifold

T25 are very popular- for ex. saab turbo, nissan 200sx, peugeot 405

Yugo_Turbo wrote: What about turbo from Punto GT or Uno 1.4 Turbo?

almost the same, I just heard that IHI VL5 from uno racing is little "bigger"

The crack between the seats is no problem. Have all of my turbos :)

150bhp is easy, install a 5th injector in the middle of the plenum, make 1.2 bar pressure and install a good exhaust without cat ==> that are 150bhp.

T25 has pressure at 4.000rpm, a little bit late or?!

The 1301cc valves a good for 200bhp, you don't need bigger.

Look - you need to know that I do my absolute best to help in the forum, and with many articles like:

http://guy-croft.com/viewtopic.php?t=503

So please don't say things like 'And I agree but lets be more precise.
How EXACTLY to modify seats and valves?' I do have a job to do. I can only write so much.

The material on the site is like a book, and if you read enough you learn how things get done. It is often impossible to give specific advice to individual people. I know (because I have re-read the article on the big valve SOHC) that if you look at the text and photos closely ALL the detail is there.

You can be sure that if you combine the article mentioned above with the SOHC feature at http://www.gcroft.com you will have everything you need.

Everyone likes to think his engine is unique. It's not. If I wanted to write an entire article on 'how to tune the SOHC Fiat' I would. I don't. other engines I missed out but that which people know I'm familiar with. One of the main things about this site is that (if people bother to read that which is written - by me and others) it shows just how much commonality there is between apparently very different engines.

You need to read GC V/W from front to back before going anywhere near a machine shop. That way you will understand more about why things are done a certain way, how there are done and what kind of tools can be used. Only in this way are you likely to be competent enough to be a DIY engine tuner. If you cannot do that, leave the engine alone.

GC