Fiat Punto HGT - Engine Rebuild

Road-race engines and ancillaries - general discussion
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

Hello everybody,

Here I will try to present my engine rebuild project.I bought the car at the middle of 2006, i make some modifications like BMC carbon air box, stainless steel exhaust with Supersprint manifold, Colombo Bariani fast road camshafts and now it is time for a total rebuild.
When i take out the cylinder head i notice the one valve spring was cut in the middle and one valve was stack in the valve guide.
I bought a full set of new valve spring (this head has double spring in each valve) and i replace the old valve guides with new ones.

Cylinder head air flow after port and angle job :
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Cylinder head with camshafts and the new springs and guides :
Attachments
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iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

New Bacci final drive ratio 12/53 instead of 15/58 Fiat one
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New alloy Helix flywheel 3.4kg instead of 8.2kg Fiat one
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I also made a new alloy crank pulley with trigger wheel 36-1 for DTA s40 standalone ecu
New pistons has arrived with 11.8 CR, i order new custom rods little longer in height because the forged pistons has 33mm compression height instead of 36mm that the Fiat ones.

This will change the rod to stroke ratio...I want to ask if this will give me more power ?
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

i forgot to say that the DTA s40 ecu was already installed before the engine rebuild...i hope now with more CR to make more power and the shorter final drive ratio to help the car to move faster...

advantages from the change of rod to stroke ratio ?

145 rod - 82.7 stroke (before)
148 rod - 82.7 stroke (after - with the longer rod)
WhizzMan
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Re: Fiat Punto HGT - Engine Rebuild

Post by WhizzMan »

Why would your new pistons have a different compression height? How did you come up with the 11.8:1 compression ratio? Did you buy turbo pistons and "fix" the compression loss by increasing rod length?

If all things are equal, except rod length, there is relatively more time your piston spends on top during ignition. This may give you a slightly faster burn rate, making the amount of ignition advance required for maximum power slightly less. This may gain you a little power, but it won't be more than a few percent at best. There is also slightly less wear on the bore since the angle at which the pressure from the piston and crank work on each other is less sharp.
Book #348
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

WhizzMan wrote:Why would your new pistons have a different compression height? How did you come up with the 11.8:1 compression ratio? Did you buy turbo pistons and "fix" the compression loss by increasing rod length?

If all things are equal, except rod length, there is relatively more time your piston spends on top during ignition. This may give you a slightly faster burn rate, making the amount of ignition advance required for maximum power slightly less. This may gain you a little power, but it won't be more than a few percent at best. There is also slightly less wear on the bore since the angle at which the pressure from the piston and crank work on each other is less sharp.
no I do not bought turbo pistons...also lets say that I bought turbo pistons the compression height must be the same as the normal Fiat pistons and the only change must be in dome volume to lower the compression ratio and not at compression height because this effects at piston squish gap/clearance

my pistons is from an Alfa Romeo 147 1600cc with dome volume much higher than Fiat ones and this goes the compression ratio at 11.5 and with a little bit skimmed of cylinder head and block I accomplish 11.8 compression ratio.But this Alfa Romeo pistons is shorter in height than HGT pistons so I order new custom forged rods to accomplish the correct squish for the piston.

About the rod to stroke ratio I have read the same things as you told me...but I am curious in reality and not in theory which would be the difference.
Last edited by iceman_n on December 2nd, 2011, 10:27 am, edited 1 time in total.
Guy Croft
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Re: Fiat Punto HGT - Engine Rebuild

Post by Guy Croft »

Iceman

may I respectfully request that you start writing the letter 'i' when referring to yourself as 'I'

in other words in proper 'capital case'. It merely requires use of the 'shift' key from time to time.

Thank you so much!

GC

Members please always read your posts back to yourself after uploading.
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

High compression piston
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Engine block after re-boring - I paint it black after I take the photos
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TomLouwrier
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Re: Fiat Punto HGT - Engine Rebuild

Post by TomLouwrier »

As Whizzman explained correctly a longer con rod will alter piston timing -thus burn rate- and bore wear.
The same decrease of force on the cylinder wall that improves wear also improves losses due to friction. Your pistons/rings are the largest bearings in the engine.
This is also why thinner and low pressure rings improve net power.

BMW used longer con rods in their 4 cylinder turbo F1 engines (1980's); stock petrol engine block with longer stroke, diesel derived, crank. The longer rods alone gained them some 4-5% net power due to lower friction losses. Those engines made a lot of revs and had very high BMEP of course. (info from a book by Gert Hack).
I've been toying with this idea a bit, but I think I'll never see the results in a 'fast road' engine offset the effort to build it (although it would be fun to do).

regards
Tom
GC_29
iceman_n
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Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

I am also curious to see the horsepower that my car will make with new setup...and maybe I will need new fuel injectors...
but I need first to see the duty cycle that works
WhizzMan
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Location: Amsterdam, the Netherlands

Re: Fiat Punto HGT - Engine Rebuild

Post by WhizzMan »

Ah, you used existing pistons of a different engine, that explains why you had to modify your rod length to make it work.

What fuel injectors do you have now? What was the engine power before you modified the pistons and rods? Did you make any other modifications that are not in this topic yet? It helps to make a rough estimation as to where your power may end up and if the injectors will be the proper ones for that sort of setup.
Book #348
Honza
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Re: Fiat Punto HGT - Engine Rebuild

Post by Honza »

the engine had around 130HP and the injectors are IWP 006 by weber (same as in PUG/SAXO 1.6 16v) and they have ~200ccm..

I have a spare set for my stilo...
#100
iceman_n
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Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

WhizzMan wrote:Ah, you used existing pistons of a different engine, that explains why you had to modify your rod length to make it work.

What fuel injectors do you have now? What was the engine power before you modified the pistons and rods? Did you make any other modifications that are not in this topic yet? It helps to make a rough estimation as to where your power may end up and if the injectors will be the proper ones for that sort of setup.
Yes they are from Alfa Romeo 147 1600cc...I bought them because my HGT cylinder head has the same combustion chamber as the Alfa Romeo, same bore size and pin diameter.

As Honza says injectors are IWP 006, 226cc at 3 bar. The power that car makes was around 165hp with Colombo Bariani camshafts (Duration 260/258 - Lift 10.4/9.6), Full exhaust system with Supersprint manifold, head work, BMC carbon air box and DTA s40 ecu.

My opinion is that maybe I will need new injectors but I am afraid that the camshafts are too "small" and the engine will not make more power than 170hp.
Older Fiat Coupe with the same engine has an alloy inlet not plastic like mine when I use it the engine make 5hp less than the plastic one. Maybe the runners is shorter in length and bigger in diameter and it needs more aggressive camshafts to balance the sound wave or maybe the plastic has a better design. At the end to mention that I calculate the proper manifold length in 4th wave tuned an it is around 43cm.
WhizzMan
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Re: Fiat Punto HGT - Engine Rebuild

Post by WhizzMan »

The extra information about the fast cams does change the picture quite substantially. You will need around 250cc/min per injector to get to 180 BHP comfortably. If you increase the max. duty cycle of the injectors, you can get there with a little smaller, but I'd try and keep injector opening times limited myself.

With a 2.0 (Alfa twinspark), I've seen people get up to 185 BHP from the head without modification and "sports" cams. The head is the exact same as the 1.8 that you have, with only a very minute difference in combustion chamber shape to accommodate the second spark plug. You've done some modifications, so if those are done right, you should be able to flow enough air to get to 180, if your cams and rev range allow that.
Book #348
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

WhizzMan wrote:The extra information about the fast cams does change the picture quite substantially. You will need around 250cc/min per injector to get to 180 BHP comfortably. If you increase the max. duty cycle of the injectors, you can get there with a little smaller, but I'd try and keep injector opening times limited myself.

With a 2.0 (Alfa twinspark), I've seen people get up to 185 BHP from the head without modification and "sports" cams. The head is the exact same as the 1.8 that you have, with only a very minute difference in combustion chamber shape to accommodate the second spark plug. You've done some modifications, so if those are done right, you should be able to flow enough air to get to 180, if your cams and rev range allow that.
I have already mention the fast road cams in my first post...When I finish the rebuild and the brake-in of the new engine I will go to my mapper to update the ecu map in DTA and we will see the duty cycle and if we need bigger injectors.

About the horsepower I have to mention that a friend of mine with the same engine but with crankshaft from and Alfa Romeo 156 2000cc (91 stroke, 145 length Fiat rod, rod to stroke ratio 159) and also forged Wossner pistons but from a VW Golf (12.5 CR) not like mine (Alfa Romeo 147 1600cc - 11.8 CR, and I believe totally different design of piston dome to match with VW head not Alfa Romeo head), same cams with me and DTA S60 make exact the same power with me.That's why I am afraid that I will not make more power.
iceman_n
Posts: 21
Joined: November 27th, 2011, 9:18 pm

Re: Fiat Punto HGT - Engine Rebuild

Post by iceman_n »

If my engine does not make more power than 170bhp which do you think that would be the cause and which part do i need to upgrade to make more power ?

More aggressive cams ?
Better cylinder head - more flow ?
New custom inlet manifold ?

Any ideas and suggestions please...
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