Right.
I've got the cento bug again. I miss my old one, especially the way for a 1.1 it used to shock some people.
So, I've decided that now I have a good job and earn a steady wage, I want to build a mad cento project.

I have had an idea, but need opinions on whethe it would work or not, and what i could do to improve the idea?

I am thinking something along the lines of:
1368 16v bottom end
Early 1242 16v head (double valve springs and bigger exhaust outlet)
C&b high lift cam
1108 crank
1368 tjet injectors
Standalone ECU and turn the rev limit right up, maybe close to 10k?
6 speed box

Could this work?
The plan is to have a small capacity screamer that is stupidly fast but doesn't weigh too much and ruin the handling of the car...

NosherCento said:

Right.
I've got the cento bug again. I miss my old one, especially the way for a 1.1 it used to shock some people.
So, I've decided that now I have a good job and earn a steady wage, I want to build a mad cento project.

I have had an idea, but need opinions on whethe it would work or not, and what i could do to improve the idea?

I am thinking something along the lines of:
1368 16v bottom end
Early 1242 16v head (double valve springs and bigger exhaust outlet)
C&b high lift cam
1108 crank
1368 tjet injectors
Standalone ECU and turn the rev limit right up, maybe close to 10k?
6 speed box

Could this work?
The plan is to have a small capacity screamer that is stupidly fast but doesn't weigh too much and ruin the handling of the car...

Click to expand...

May be, but you need to have the block decked down. As the throw of the 1108 crank won't allow the piston to reach to the top. Not sure what the capacity of this engine would be then ....

also if you want a screamer, then is better to stick with the 8v.

also if you are using a different crank, then is no need to use the 1368 block, they are pretty much the same as a 1242 block.

I'dd suggest just put a 1368 16v in there, drive then build another engine for it later. You might find id enough power for your liking.

Ming

Is the only difference between the 1242 and the 1368 the stroke then?
I thought the bores would be different?

NosherCento said:

Is the only difference between the 1242 and the 1368 the stroke then?
I thought the bores would be different?

Click to expand...

Yup the stroke.

Ming

I've read that the nose of the 16v cranks are different to the 8v..... Haven't checked mine yet but just a heads up.

hydraulic lifters will not do 10,000 rpm, why not go for a 999cc fire 8v engine and stick larger pistons in? its alreadys a over square engine iirc

a rather reputable source says they(999cc) are safe at oem upto 9,000rpm
sourced at increasing engine rpm
http://turbofire.no.sapo.pt/engine_tuning.htm

i would also say you would need double valve springs to stop bounce and contact

i thought about this abit but i have too many ideas and not enough time

Ash

Also start thinking about the crank pulley if your revving that high.
What you doing for induction?

Brooky said:

I've read that the nose of the 16v cranks are different to the 8v..... Haven't checked mine yet but just a heads up.

Click to expand...

crank are defo different depending on the cc of the engine ... or you refering to the material the crank is made from ?

1108 crank almost certainly won't fit the block and big end diameter is completely wrong.

1.2 is 70.8 mm bore x 78.9 mm stroke
1.4 is 72 mm bore x 84 m stroke

Stroke of either is probably too long for really high revs, regardless of whether you could convert to solid lifters.

The Poles are said to have got n/a 1.4s up to 140bhp in race trim. GOK if they'd pass emissions!

The SuperFIRE engines are said to throw rods past 140bhp (which is why the T Jet is pretty different internally). They're pretty much optimised, so difficult to significantly improve.

So, financially (although they present other difficulties). the Ford, Vauxhall, Toyota and K Series engines all present more power/tuning potential for your buck.

More radical might be an 1108 converted to 16v. It'd need different pistons, so bore out to 1242 dimensions. It'd like to have full floating gudgeon pins, so get H section rods...........

NosherCento said:

Early 1242 16v head (double valve springs and bigger exhaust outlet)
C&b high lift cam
1108 crank
1368 tjet injectors
Standalone ECU and turn the rev limit right up, maybe close to 10k?
6 speed box

Click to expand...

Early head stil uses hydraulic lifters.

you'll need camS

why on earth would you use a 1108 crank?! The throw of the engine is a lot longer on the 1368cc. If you reduce it, you'll reduce the throw and the CR will be very low as the pistons won't travel up.

any newer bosch injectors will require the plastic bravo(a) fuel rail if you are using a mk1 punto inlet.

you don't turn up the rev limit on standalone, you just set it What are you thinking of running? but 10K....no way on the standard setup.

You're right - its mad

The 8v crank will work in the 16v block but you need an 8v head to match. On top of that the 8v crank pulley assembly tends to fall apart on tuned engines, even Fiat got caught out by this with their junior rally cars so unless you want a custom engineering solution there too it isn't worth it.

A shorter stroke (as pointed out) won't work so you need to attack the weight of the parts instead. Forged, short skirt pistons with custom rods, lightened crank and flywheel - none of this is cheap but if you want high revs that's what you have to do.

The 16v head will allow high revs (10k+ if you're brave and the engine is well assembled) but what you can't do much about is lift as the hydraulics just won't do it. When you look at cams (and you will have to) you need to find some that up the duration and overlap without an excessive increase in lift (any performance cams for the 16v Fire will be like this anyway).

Big exhaust valve is a waste of time, it is the inlet valves that need to be bigger on these engines.

The early 16v block is easier to work with for a bit of tuning but if you are aiming past 130bhp it is worth getting it de-stressed before doing anything radical. The block is good for about 190bhp but it will try to distort resulting in a lot of lost power. The ladder brace on the bottom end goes a long way to preventing this but it needs all the help it can get. By comparison the 8v block tends to give up around 130bhp without serious engineering work.

If you're going for high revs you need to work out what you're going to do about oil pressure too. Past 8000rpm it will start spraying out of every joint on a standard engine as the pressure keeps rising plus the oil gets hot and subsequently very thin.

We did something of an experiment several years back - two engines, one 8v and one 16v, both at similar levels of tune and both produce about the same power. The 16v was quite tractable and was much easier to produce, the 8v was peaky as hell and cost a small fortune. In the end the 8v had to be detuned to make it useable, the 16v just keeps going (ignoring broken engine mounts and snapped water pipes).

Jimbro..... Do you have a decent bottom pulley on your engine?
I'm looking at getting one/some made as I'm making abit of a screamer.

Any specific grade of steel to use? Or is anything better than the original.

I bought mine through Supagara in Italy who were making the rally engine for Fiat - found them by pure chance at the Autosport show about 4 years back. I don't think they have the contract anymore and that particular rally engine isn't being made anyway as it has all been shoved over to the GP and 500.

It was an expensive problem for me. After all the grief we'd been through getting the engine together we finally had it running only to see the crank pulley come apart and a set of valves and pistons trashed...

Steel may be overdoing it. I'd think a 5000 or 6000 series aluminium alloy would be just fine.

But, a swine to machine in T5 or T6 state.

I'd just use dear old EN45 -- you can make cranks out of it, you can make springs out of it. And there will be some lying about at work, somewhere.

EN45, it's the steel your father would recommend!

Mind you, if you have any titanium bar....................

Right this seems better place than any, save starting another similar thread..

So i been thinking for a while i would like to build an engine from scratch (a new turbo one for my sei). So the basic plan is to go for a 1242 with a P75 head to get the mpi with an undecided aftermarket ecu to control everything.

But now i'm confused about compression ratio's. I have a random 1242 16v bottom end kicking about (completely stripped and in pieces requiring some work - i see todger is on this thread right now, yes that one from you ).

1. If i bolted a P75 head to the 1242 16v bottom what would the CR be?
2. What CR is too low?
3. Could the head be skimmed to max to bring it back up to a reasonable figure?
4. Would i better off just leaving this 16v block and getting a complete P75 engine and getting a decomp plate.

There is many more questions but this will keep me going for now.

And please no-one just tell me to stick in a 1368 16v engine, its not happening.

Best cheapskate option is any old MPI head (the only advantage the P75 has is that the inlet mani is aluminium, so relatively easy to faff about with, although Munkul did rework a plastic one), late 1242 16v bottom end. That way you've got a rigid bottom end, an easy to work with top end.

You could deck the block to raise the compression (said to be ass low as 7.2 to 1). You'll need to rework the head a little to take 10mm head bolts and for the head gasket to line up.

Chances of finding a P75 engine that doesn't need a complete rebuild now are very low.

The sane(r) way to do it would just be to buy a T Jet, plop that in, do some work on traction control. A relatively easy (and reliable) 180bhp (in a hedge somewhere near you). But you don't want sanity, do yer?

I'm sure he'd rebuild it anyway. Insane not to on a tubby

Brooky said:

. Insane not to on a tubby

Click to expand...

But insane not to start with a T Jet!

I am not an engine builder, but two small comments that I have to the material I just glanced through:

1. About high oil pressures: there is a pressure relief valve in the oil pump that will always limit it to a sane value. So this should not be an issue. Even more, I was told that Novitec turbo conversion included altering the valve internals to keep the pressure a bit higher at high revs (pointless I guess).

2. Crank pulleys. Jimbro, what do you mean by "fall apart"? The locking pin breaking of is a known problem (gave me nightmares when doing pulls on a dyno), but then later I was told two things:

- it is totally vital to renew the pulley bolt each time you take it off.

- If you tighthen it up in a proper way it is much less likely to give up. By proper I mean that the pulley is locked during the tightening, not the crank. This is done by for example bolting on a spare alternator pulley with a bar welded to it, the bar locks against the engine mount and then you torque it up according the the specs.

woj said:

I am not an engine builder, but two small comments that I have to the material I just glanced through:

1. About high oil pressures: there is a pressure relief valve in the oil pump that will always limit it to a sane value. So this should not be an issue. Even more, I was told that Novitec turbo conversion included altering the valve internals to keep the pressure a bit higher at high revs (pointless I guess).

Click to expand...

The oil pressure will still rise, the relief valve will only resolve some of the rising pressure. The higher pressure is very beneficial, especially in turbo engines as it is essential to keeping all of the parts properly lubricated. Turbos really need it as the turbine shafts have to float on oil to work properly, bearings just can't cope, more so as the oil thins as it gets hotter.

woj said:

2. Crank pulleys. Jimbro, what do you mean by "fall apart"? The locking pin breaking of is a known problem (gave me nightmares when doing pulls on a dyno), but then later I was told two things:

- it is totally vital to renew the pulley bolt each time you take it off.

- If you tighthen it up in a proper way it is much less likely to give up. By proper I mean that the pulley is locked during the tightening, not the crank. This is done by for example bolting on a spare alternator pulley with a bar welded to it, the bar locks against the engine mount and then you torque it up according the the specs.

Click to expand...

The pulley torque specs work just fine on a standard spec engine. When you up the torque the key and pulley start to break up. When it goes the result is a sudden, catastrophic failure, the pulley just spins on the crank. Even on standard engines this can fail but only rarely. From what I've seen it is the pulley itself that fails but as I only have one personal experience to go from I can't generalise too much. The problem has been confirmed too me many times over though.