Fiat 125 race car (& others!) in western Australia

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S&B125
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Joined: Mon Nov 27, 2006 6:57 am
Location: Perth, Western Australia
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Re: Fiat 125 race car (& others!) in western Australia

Post by S&B125 » Tue Jul 14, 2015 11:49 am

Another update after a long break. We've had a fair bit going on here, just short of time to sit at the computer and write it down. One of the more interesting projects I have been involved over this time is the development on the engine which powers a historic open wheeler campaigned by a friend.
LCshot1.jpg
Purposeful!
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The lure of getting involved with this engine was the "utopian" way in which classic 60's open wheeled racing cars gave such room for exhaust and induction systems. This car is a Brabham from the late sixties which has quite a competition history and was re powered with a Fiat Twin Cam in the early 70's.
LCengtop1.jpg
Look at that exhaust system - manufactured by the current Driver.
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This engine is quite frankly a testament to Guys products and most assuredly his inspiration to us amateur engine builders through his published works and ongoing support. All aspects of the cylinder head - cams IIID on both inlet & exhaust - valve guides - valve springs - instruction on how create great flowing valve seats, are attributable to GC. The fact that a couple of ordinary blokes between them (I built the head Lance built the engine) have been able to achieve over 100BHP per Litre on carbs in an "analog" engine is very rewarding.
LCback1.jpg
This thing is quick!
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A recent Dyno run on this engine after a full seasons competition in 2 countries gave the the following results
188hp @ 8129RPM
184nm @ 6234RPM
Look carefully at the shape of the power and torque curves in the Dyno printout.
lance0715.pdf
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Here we have a 3000RPM operating range (almost any gearbox can keep you in that) and 2000RPM between max Torque and max power. Not at all peaky and this thing absolutely flies.
Click on the link below and watch an intriguing view of this engine during a "power run" on a chassis dyno (rolling road) from the perspective of looking straight down the carburettor throats. You will see the the throttles as the car is worked gently through the gears and then when in top the throttles are snapped open and it comes "on cam" and pulls through to 9000RPM. TURN IT UP and enjoy a Twin Cam in full flight.

https://www.youtube.com/watch?v=S2HgLlejJYs
GC_35 Fiat 125T

Will01
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Re: Fiat 125 race car (& others!) in western Australia

Post by Will01 » Tue Jul 14, 2015 11:57 am

I haven't listened to the video yet or had a look over the power curve.
But just seeing pictures of these cars has given me a huge smile. What a lovely bunch of vehicles together, i think my jaw would be dragging on the floor.
GC_21

Guy Croft
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Re: Fiat 125 race car (& others!) in western Australia

Post by Guy Croft » Tue Jul 14, 2015 12:46 pm

MODEL POST!

GC
Guy Croft, owner

S&B125
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Location: Perth, Western Australia
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Re: Fiat 125 race car (& others!) in western Australia

Post by S&B125 » Tue Jun 14, 2016 8:57 am

Yet another update after a long absence. It has not been a long period of inactivity or recalcitrance to post, it is just that since I built the engine (detailed earlier in this tread) in late 2011 it has been utterly reliable. Now after 4 seasons of competition it is being retired - not because it's diminished but the new engine is now almost ready. In keeping with "Rules" and in deference to the cars' long history this is also a 1608 but a move from a good club spec engine to, "hopefully" the best 125 engine I can build.
TBIGCAMBLOCK.jpg
Block plateau honed with Flex hone and decked.
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The Specs
Bore 81mm
Stroke 80mm
Capacity 1649cc
C/R 10.9:1
Pistons GC Custom JE - JE Race Rings
Rods Argo I Beam (Australian made)
Crank Race Prepped - Tapped plugged balanced STD journals
Cams GCIIID inlet Timed at 102 deg ATDC Exhaust IIIA Timed at 103 deg ABDC
Springs GC 3VSR and bases
Valves Std 42.4mm inlet, 36mm exhaust
Guides GC Bullet 15mm Flex honed to fit
Head Sorry all prep done my me to GC specs
Induction Offset manifold Dellorto DHLA45 37mm Chokes
Exhaust Existing headers and pipe.
Clutch Ap Racing with lightweight steel flywheel (total weight clutch & fw) 5kg
TBIGCAMHEAD.jpg
Ported, valve seats cut by hand with Neway Cutters, Comb chambers deshrouded
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So if you bother to compare the specs of this engine and the last you will see that all of the effort in this design is centred around the breathing. When you can't just increase the capacity then your only option to make significantly more power is to spin it faster. This will decide which camshafts to use and really,they dictate the piston design. The rest of the build is all about reducing reciprocating and rotating mass.
TBIGCAMCLUTCH.jpg
AP Clutch and superlight flywheel.
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The oil system and cooling system will remain as they are in this car as the capability of those systems have been up to the job so far. I haven't been able to kill it and I certainly don't spare it.
With the outgoing engine producing 146HP @ 6900 and 162nm @5100 we are hoping for about
165hp @ about 8000rpm and hopefully above 180nm at about 6000rpm.
We should know in about a month
I'll keep you potsed,
GC_35 Fiat 125T

Piotrek125p
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Re: Fiat 125 race car (& others!) in western Australia

Post by Piotrek125p » Tue Jun 14, 2016 9:24 am

Very good news that you still work with your 125T

Could you do me a favor and share wit me a details about your intake manifold ? I have to make a manifold for my FSO 125p, who has a simillar engine bay that italian 125, could you tell me which type of manifold you are using in your Fiat ? Do you have a cold air intake system ?
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S&B125
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Joined: Mon Nov 27, 2006 6:57 am
Location: Perth, Western Australia
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Re: Fiat 125 race car (& others!) in western Australia

Post by S&B125 » Tue Jun 14, 2016 11:10 am

Hi Piotrek
I have run various intake manifolds on my 125 over the years and while most of them have not been designed specifically for the 125 they have all functioned well. What is important is that they swing the carbs towards the firewall so as to clear the distributor and are relatively short. All the manifolds I have tried are cast, this would be hard to achieve by fabrication. I'm sure Guy's 131 manifold will work with your 125. If you look at the photos earlier I'm this thread you will see one of the inlet manifolds with carbs and ram tubes in place. Are you running a Twin Cam?
If you need me to photograph and measure one of the manifolds I have here I am happy to do so.
GC_35 Fiat 125T

Piotrek125p
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Re: Fiat 125 race car (& others!) in western Australia

Post by Piotrek125p » Tue Jun 14, 2016 11:40 am

I know that the worst problem with sidedraughst in 125 is a very limited space for carbs and especially for rampipes and intake system. I also want to make a offset manifold, but only for space reason, I will use a exhaust cam driven distributor.

In old GC book I saw a 125p with M131 manifold and it is looks that a space for filters are really limited.

If you can make a photos of your intake system I will be very glad to see it, in Poland everybody use an IDF's, but I want to use a twin DCOE's in my 125p. Of corse power reason is very important for me, but if I can't make a sealed, cold air intake system with 2,75" manifold I will use IDF's.

I wan't to avoid a detonation problems with my Twin Cam as much as I can so hot air in intake is undesirable.
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