SlinkyCinqi said:

ahh i see, and 2 bar boost HAHAHA madness! So, whats the reasoning for all the others being so unreliable and yours not? not being ars*y about it, just wondering, cos HB is starting to tempt me :slayer:

Lenny

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Various things I would say, don't think the other owners would get too upset about me pointing out that they have all pretty much seen what a melted piston looks like for a start...

Not saying mine was perfect and never broke but all that went was the manifold cracked which isn't unheard off either...

Just before I bought it it also went for a full tune by VA before they stopped doing that where they turned the boost down as well
But I raised the boost back after buying it and was still fine...

I think they key to getting it reliable is the obvious stuff really make sure the fuelling is setup up properly, regualar servicing, fix don't bodge parts etc... and and prob the most important remember it's not going to ever be able to cruise at silly speeds for 100miles without doing some damage...


P.s Mine also did a trackday with no adverse effects to the engine other than me and Aaron getting a bit nervous approaching Tower at Combe with no brakes

In response to your first question, of what should you change, I would say as much as possible.
Are you doing the work yourself?
If the engine is out anyway the relatively low cost and low trouble on changing the mains and big end bearings (or at least checking clearances) is worth it for the possible reliability extra.

And to add something into the high boost mix:

Run 2 head gaskets to lower the compression then you can crank the boost a bit more.

The problem with the above is that the FIREs eat headgaskets anyway, but If you get some ARP studs it should hold together for a bit longer. Its a technique that tuners in parts of the world where parts are scarce (south africa etc) use on the Toyota 4age engines (MR2 mk1's, corrollas, etc).

cartledge_uk said:

And to add something into the high boost mix:

Run 2 head gaskets to lower the compression then you can crank the boost a bit more.

The problem with the above is that the FIREs eat headgaskets anyway, but If you get some ARP studs it should hold together for a bit longer. Its a technique that tuners in parts of the world where parts are scarce (south africa etc) use on the Toyota 4age engines (MR2 mk1's, corrollas, etc).

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Fair point but like i've added in previous posts I would much rather let the H/G go before any of the internals making a bid for freedom so for this reason I would say stick with a standard H/G....

But hey two or three dif versions of getting the same end result

The absolute key to turbo charged cars is fuelling, something that wasn't done correctly from VAD, so no matter what direction you go in, get the fuelling right and it will prove to be the safety margin these engine need. the reason for melted pistons is detonation, normally caused by under fuelling on these cars as standard set up is not up to the job as for a fuel injected car the fuel pressure is low, anywhere from 0.8-1.2bar from factory. So even low boost of 0.3bar can have a big effect on a car running only 0.8bar of fuel pressure.

Emma's car has been faultless and has covered more than 10K now since it was built, we bought it as a running but sick hi-boost turbo. It does runs Mahle pistons now though that have been machined with a dish in them to give a better squelch which means better fuel burn. the compression is about 8.7:1 so a little higher than VAD set them up at, mine was 8.1:1. It also has vernier to set up cam timing correctly as I think it is retarded 10degrees, though can't remember exactly, it was all worked out by her Dad.

I have heard that decomp plates can affect the squelch, but have never really looked into this to find out why and what effects this has.

I think the owner of Jamie's old car has said that now it has new fuel pump and 2nd regulator it is running even better than before.

As Jamie said though, we did track day at Castle Combe and it was the brakes that went first, though engine temps were high nothing let go.

As Aaron touched on above, proper piston with a dished chamber give squelch or squish. Simplistically it is about the piston getting close to the head. This clearly doesn't happen when using 2 head gaskets or a decompression plate. One of the side effects of decreasing cmpression by physically moving the head away from the top face of the block, and consequently away from the top of the piston, is that it increases knock. Knock or pre ignition eats pistons. And the set ups I've seen on turbo Cinquecentos don't have a knock sensor to back off the boost when they start knocking.

Fivehundred said:

One of the side effects of decreasing compression by physically moving the head away from the top face of the block, and consequently away from the top of the piston, is that it increases knock. Knock or pre ignition eats pistons.

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Not quite, its INCREASED compression that induces knock as its a characteristic of the fuel (which is why higher RON reduces pre-detonation).

But if running a high boost with timing out these can both lead to knocking.

And as for the squish, unless you are a pro engine builder whos career is based on race engines, then i doubt just using a decomp plate will affect the squish by any noticable amount.

I can only repeat what Jamie said above, using a de-comp plate is often looked on as a bodge, but its NOT. Its a well known solution to a problem.

balidey said:

And as for the squish, unless you are a pro engine builder whos career is based on race engines, then i doubt just using a decomp plate will affect the squish by any noticable amount.

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Funny you should say that, cos that's what Emma's Dad has done, he now develops modern car engines the likes of which are found in many cars on our roads today, some of which are very high performance from well respected German manufacturers

Though as you say, the differance is probably not that noticeable on cars at this level of performance, but when he built Emma's car he had the knowledge, experience and contacts to do it, hence the dished pistons he designed for the job as he doesn't like decomp plates.

As i said before, the absolute key to these cars is fuelling, get decent pump, 2nd reg all plumbed in series and MF2 set up and everything is good.

J333EVO said:

The absolute key to turbo charged cars is fuelling,

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Couldn't agree more

Just to say if I was to turbo one from scratch in all honesty I would go with a De-comp plate and save the extra cash from the pistons for an electronic boost controller.. plus any other parts you dont have already eg: Punto Gt brakes all round, new brake hoses, decent fluid, oil cooler, fuel regulator, uprated pump.... the list is endless... pretty much find a spare 3k :yum:



and maybe a spare head skimmed ready to go for when it goes pop LOL

J333EVO said:

As Jamie said though, we did track day at Castle Combe and it was the brakes that went first, though engine temps were high nothing let go.

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balidey said:

I can only repeat what Jamie said above, using a de-comp plate is often looked on as a bodge, but its NOT. Its a well known solution to a problem.

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Well that's someone agreeing with me done for this year!

balidey said:

I can only repeat what Jamie said above, using a de-comp plate is often looked on as a bodge, but its NOT. Its a well known solution to a problem.

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2 head gaskets are a bodge. You dont know exactly what the clearance volume will be (its affected by how much the HG compresses). A properly bonded deco plate and single HG will work much better.

bonding one side and HG the other seems silly to me.

If you can rely...on say...the block being flat and using a sealant, surely with a flat head, you can do the same? and remove the gasket altogether...or is it to do with the additional flex of the alu head?

Kristian

kritip said:

bonding one side and HG the other seems silly to me.

If you can rely...on say...the block being flat and using a sealant, surely with a flat head, you can do the same? and remove the gasket altogether...or is it to do with the additional flex of the alu head?

Kristian

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Block face might not be perfectly true (who skims a block face when the HG goes?) So HG goes on block face. The decomp plate goes on a newly skimmed head because it should be flat. Mine was flow and pressure tested the other day with no apparent problems.

If you were building a turbo from scratch you wouldn't design the engine to run with a decomp plate you would fix the internals first, but as an after market mod it is as good a fix as any, but most have realised you really need a vernier pully to get it running as well as it can (and to pass mot emmisons)

I have screwed as much out of my NA 1108 SPI as i feel comfortable as an everday reliable user and i must admit if it were me (and TBH i have been looking at forced induction) i would be looking at low boost.

On a good set up on an 1108 you would be looking at least 90bhp so on a 1242 i would have thought at least 99

allanhelen said:

On a good set up on an 1108 you would be looking at least 90bhp so on a 1242 i would have thought at least 99

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90bhp you can get more than that N/A'd

Avanti used to do a 98bhp kit for the 1108.

But it all depends on how far you go on things.

If it was me doing the conversion,i'd get those pistons,get the block bored out,crank+rods lightened and balanced.

Also on a 1242 + decomp plate does that mean you have to make an even bigger exhaust spacer??

P.S im very temped to get those pistons:yum: :yum: ....but he says there high comp but there dished,surly they'd be low comp

this thread is going great ! very very helpful stuff! i'm tired right now (late night last night)! But tomorrow I intend to compression test my car again, properly this time and get the results posted up on my other thread. Then i'll add some pictures to this thread and use it as a 'build thread'. Picked up a brand new garrett gt15 today (yes the right style of one, with the actuator near the exhaust side!) for £100 so things are moving along steadily, yea i have already copied and pasted information about injectors and plumbing in of the 2nd reg (originally posted by aaron) and kept them in my documents, I an intending to do everything properly and take my time

Many thanks for all your help, and please follow my thread and check back for updates

Thanks again guys

Lenny

spacer will make no differnce to the exhaust manifold tbh. theres more than enough clearance.

Haynes maximum rebore for the block is way less than 72mm, and I don't know who have rebored that much. You pistons may hold out, but will the cylinder wall?! (why is he selling)

Kristian

kritip said:

spacer will make no differnce to the exhaust manifold tbh. theres more than enough clearance.

Haynes maximum rebore for the block is way less than 72mm, and I don't know who have rebored that much. You pistons may hold out, but will the cylinder wall?! (why is he selling)

Kristian

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Good point,what is the standard bore of a 1242 block.
And surely if the guy cracked/holed his block then 1 of the pistons would be scored/damaged.

ahwell

The standard 1242 bore is 70.8 ... you can take it out just under 1mm further as far as i remember...those few . mm may not sound much but there is not much meat between the cylinders as it is.

Kristian

balidey said:

Not quite, its INCREASED compression that induces knock as its a characteristic of the fuel (which is why higher RON reduces pre-detonation).

But if running a high boost with timing out these can both lead to knocking.

And as for the squish, unless you are a pro engine builder whos career is based on race engines, then i doubt just using a decomp plate will affect the squish by any noticable amount.

I can only repeat what Jamie said above, using a de-comp plate is often looked on as a bodge, but its NOT. Its a well known solution to a problem.

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Turbo charging an engine and knock isn't just about compression, it is about how the piston compresses the air fuel mixture and into which space. With a dished piston which gets close to the head the mixture is forced into the open space in the centre of the piston, and that increases turbulence. Which in turn increases the burn rate. Given that normal squish is generally reckoned to be 40 thou or so and tight squish is obviously below that head/piston clearance, then introducing a compression plate will certainly make a difference to squish.

I'm not saying an engine with a decompression plate won't work, clearly it will and it does, but properly designed dished pistons and decompression plates do fundamentally different things, outside of the simple fact that they lower the compression ratio for well understood reasons.

Decompression plates are simply not a solution which is as good as doing the job fundamentally well.

Someone on the MK2 forum recently turboed a 1.2. iirc he got 118bhp. Worth a look?

Brooky said:

90bhp you can get more than that N/A'd

Avanti used to do a 98bhp kit for the 1108.

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TBH I've never seen any 1108 car making that, not saying it couldn't be done but considering the single injector is running close to 100% duty cycle at about 80bhp IIRC I would be curious to know how these figures are achieved without changing to say an MPi set up which is no biggy really considering the latter models are Mpi, or even simpler running more fuel pressure which would then mean a complete remap to control fuelling as it could run very rich low down by just turning up the pressure which has a limit of about 1.8bar IIRC when I experimented with the standard regulator found inside throttle body.

If I was doing another turbo Cento, I would look to use a MPi engine/head from latter cars and go after market ECU like the Emerald we used on the 1368cc 16V Seicento to control fuelling & boost much better and ensure higher levels of safety as the later cars have knock sensor as well which the likes of Emerald can use. Though you may be able to add the knock sensor to earlier blocks, I honesty can't remember if the take off is in place or not.

Of course you can still run the VAD type set up and achieve good results, I got 120bhp 140lb ft and Emma's car is running 115bhp 125lb ft both from 1108cc cars, a N/A will never achieve those figures.