Road engine rebuild - what will be better?

Road-race engines and ancillaries - general discussion
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Honza
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Joined: June 22nd, 2006, 8:04 pm
Location: Lomnice nad Popelkou (60 north from Prague), Czech Republic
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Road engine rebuild - what will be better?

Post by Honza »

Hello,
I have one evening dilemma.
I´m planning rebuild of engine in my Fiat Stilo 1.8 16V.. reason is simple -excessive oil consumption.
But I want to also little improve its performance to the territory of Stilo Abarth or even better.
It will be used as daily driver as it was till these days.
I would like to know your opinion what will be better in case of performance increase. All parts wich will be used will be new/used from various Fiat/Alfa engines.

I have three options - all will be based on new block because the mine is badly worn.
Block/bottom end is exactly the same as many AR 156 1.8 Twin sparks, Barchetta, Punto HGT or Coupe 1.8 16v engines. Head is simmilar to 20VT coupe but with bigger valves (34mm/29mm)

Few info about current engine:
Power: 98kW/6300rpm
Torque: 164Nm/3800rpm
Swept volume: 1747ccm
Bore: 82
Stroke: 82,7
CR: 10,3:1
CH of the pistons 36,15. (ring thickness 1,2/1,2/2mm)

Camshafts:
Intake:
237° (206° -1mm),FL 9.00 mm, LaTDC 0.20
Exhaust:
235° (202° -1mm),FL 8.50mm, LaTDC 0.90mm

Engine is equipped with Variable length intake system and Cam phase variator which retartd inlet cams by 25° in certain conditions to improve low-down torque.
The engine has Two catalysators bolted directly on the downpipe (~30cm from the exhaust valve seat) to improve emissons.
I will build brand new exhaust - replace the header by item from Fiat Barchetta, fit one 200cps catalysator instead of middle silencer and go to oversize 54mm straight through exhaust system - like some exhaust companies creates performance exhaust for AR 1,6-2LTS or Stilo 1.8 16V engines.

What I want to use are the cams from Alfa romeo 1.8/2l TS cams:
Intake:
247° (215° -1mm),FL 9.50 mm, LaTDC 0.30
Exhaust:
251° (218° -1mm),FL 9.50 mm, LaTDC 0.75mm
I have already modified head - modified Valve seats/valves and slighty modified ports(removed imperfections)-so the work is here done.

the option no. 1:
Keep the volume of the engine, built the bottom end from new parts (I plan to use "old type" pistons with 1,2/1,5/3mm piston rings - these old types didn´t have problems with oil consumption) and use only cams + exhaust+ modified ECU.
Estimated power will be 108kW+ /164Nm+ - at least same parametres like similar engine in Alfa 145-6/156 1.8 TS... This will be probably the cheapest way, but I prefer it by 20% due to the lovest power increase.

The option no. 2:
Rebore the block to 83mm, use 2l TS crank and create "copy" of AR 2l TS engine+ mentioned cams + exhaust+ modified ECU.
Rods are in the case of 1.8L vs. 2L same, what differs is compression height of the pistons & stroke.
The parameters of the 2l TS engine:
Power: 114kW
Torque: 186Nm
-curent values of my build could be maybe higher
Swept volume: 1970ccm
Bore: 83
Stroke: 91
CR: 10,0:1
CH of the pistons 32.

I would 100% preffer this variant (standart solution in Alfa, would be "Almost standart" in my Fiat), but due availability of the parts, I only preffer it by 40%

In these two variants there is possibility to use modern "All steel" two layer head gasked with thickness 0,49mm.
The avalability of good, used parts is not so good -there are too many damaged engines around...

The option no. 3:
Keep the block to 82mm bore, use 1,9 JTD crank, AR 1,6 TS(=Bravo HGT) domed pistons and create "hybrid" + mentioned cams & exhaust..
So I will get 1910ccm engine with 11,2 compression ratio.
Power and torque figures will be probably simmilar to 1970ccm.
The only thing I affraid of is that High CR and possible engine damage in the case of bad work of tuning company, however such high CR could bring higher gains of BHP/Nm... like on Alfa 2l JTS (=direct injection) engine with 121kW/206Nm & 11,3CR.

The JTD crank has 90,4mm stroke and 1,6 TS pistons has CH 32,9mm -> usage of thicker head gasket from pre-1999 engines (1,65mm thick) will necesarry due to by 0,6mm greater overrun of the pistons in TDC.
The availability of the parts - nice JTD crank I have in garage, pistons from HGT aren´t such problem (I had bravo HGT few years ago, and I also have spare engine) .. so availability is very Good.
Also there is higher chance to get undamaged JTD/HGT engine/components for reasonable price in comparison to 2L TS...
I preffer this option also by 40% because there are few vorries:
Will the tuning company do its job correcly and will not detonate my engine to inappropriate?
Will the thicker/conventionel head gasket last? (of course not in comarison to "All steel")
What will brings more - Higher CR/lower volume (11,2/1910) or lower CR/higher Volume (10,0/1970)?

Nice is that the JTD crank comes from the same casting mold as 1970ccm crank and is grinded to lower lift...for all variants block is the same, bearigns are the same, so the engine is like "Lego".

As I mentioned I would like to get perforance like mentioned JTS engine. ~121kW/206Nm are very nice numbers, with shorter gearbox (final drive 3,866)&lighter car in comparison to Stilo Abarth (125kW/225Nm, final drive 3,56) it should be little rocket.

What do you think which "way" will be better?
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