Carburettor jetting etc. Fiat Twincam

Competition engines and 'live' projects only. Good photos to illustrate your post are expected.
Pelle_Racing
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Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Dear Guy,

It has been a while since I joined the forum and promised to ask a lot of questions, but as always with cars, things go a lot slower than anticipated!

What I would like to know is what "jetting" you would recommend as the basis setup for my engine.
Below I have tried to give you a detailed description of the engine:

Fiat 131 2L engine
- Balanced crankshaft, flywheel (unlightened from 124-1800 engine) and clutch
- Balanced (+/-0.5g) and polished (not up to GC standards, I think) con-rods
- 0.4mm oversize HC cast pistons balanced to +/-0.1g (unknown CR, but should be around 9.5 with standard head)
- Fully ported head with new bronce guides (grinded off on inlet side) and machined valve seats. Inlet ports have been taken out quite a bit in diameter. Standard valve sizes.
- Original 124BS twin IDF manifold which has been match ported to head and taken out in diameter to fit brand 44IDFs.
- Brand new 44IDF carburettors
- Camshafts (almost afraid to write it...) re-grinded stock cam shafts to PiperCams "ultimate road" 288 deg cams (full detail can be seen on their homepage). I have some extremely nice forged billet cam shafts, but they are without the ignition drive on the exhaust cam, so my conclusion is that they can't be used in the Spider(?)
- Adjustable Vernier pulleys (piper cams)
- Exhaust: I managed to get a 4-1 IRESA exhasut manifold from Guy Morenhaut, but I found it very crudely made with evidently unequal pipe lengths, so I bought a 4-2-1 manifold home from the US (of all places in the world), which looks ideal.
Stainless steel twin silencer exhaust system from down tube and back.
- Ignition: "standard" magnetti marelli electronic ignition.
- Ritmo abarth head gasket
- "Late" type head bolts.
- 16 row Mocal oil cooler and sandwish plate
- Big wing oil sump (why do they never fit in the car?!?)

I probably forgot some crucial details, but please let me know and I will try to fill you in.
Oh yes, the car is a Fiat 124CS1 "europeanized" Spider built for "fast road"

OK, my questions:

1 - Recommended jetting for the 44IDF carbs?
2 - Spark plugs?
3 - "4-1" or" 4-2-1" exhaust?
4 - Any good advice you might give be based on the above?

I will try to post some pictures of the car and parts.

Best regards

Sune Pelle Borregaard,
Copenhagen, Denmark
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

Nice post - but I won't offer jetting advice for reground cams on that engine, sorry,

GC
Pelle_Racing
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Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

I was afraid you'd give me that answer (no hard feelings).

Any sugestions on what I should do with the cam situation then?
(I actually also have a problem at the moment with shimming up the head with the reground cams, as they need approximately 1mm oversize shims).

As I wrote I have a set of steel forged cams without the ignition drive gear on the exhaust. Can they somehow be used?
(Or should I email you for your current stock of GCRE cams?)

Best regards

Sune
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

Hi,

All TC comp cams with higher lift than standard need some means of taking up the increased base circle clearance, this is not confined to regrinds. It can be achieved by dropping the valves deeper into the head by regrinding them or seats or both (which I do anyway when prepping as described in the GC head prep DVD), or by using silicon instead of the cambox gasket, though as far as that's concerned you need to be very careful not to block up the 3 off oil feed holes and also make sure the silicon (Wurth is my preference) is evenly distributed, because if you get a leak it is an awful job to rectify. You can also use top hat shims, which I always stock, 1 or 2mm thick, or machine the cam carrier - the latter being a practice I do not like at all because it has to be absolutely true in both planes or the cambelt will 'wander'. Moreover since the head and cambox move together you're putting a flat cambox (post machining) on a head that isn't so flat and it's not uncommon for the cam to be tight because of distortion in the bearings.

As far as my cams are concerned yes email me by all means if you like. Thanks for asking. As you may know, in the spirit of keeping the forum non-commercial so that we maintain a 'level playing field' for all I don't do technical sales here. You might like to look closer at your steel cams and see it there are any ID nos I can help with. Photo would help too, I know most maker's cams by sight.

GC
Pelle_Racing
Posts: 13
Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Hi,

I will get some pictures taken when I get to the garage (tomorrow), but do you (or any of our co-members) know if the distrubutor will fit below the BS/BC twin IDF intake ("Waffletop") manifold?? (I know that I could check this myself, but the engine is still apart and so on...)
If not I don't think I can use the the steel cams, unfortunately.

Best regards

Sune
S.P.Borregaard
Pelle_Racing
Posts: 13
Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Pictures of the two sets of camshafts:
180_8075-1.JPG
180_8075-1.JPG (66.48 KiB) Viewed 15288 times
Top two camshafts are the "unknown" steel (at least I think so) camshafs, which I got together with the head and intake manifold.
Bottom two camshafts are the PiperCams reground cams from the original engine (1800 US spec).
180_8071-1.JPG
180_8071-1.JPG (62.39 KiB) Viewed 15294 times
Distributor drive on exhaust cam. Base circle reduction is also clearly visible.
180_8065-1.JPG
180_8065-1.JPG (43.47 KiB) Viewed 15292 times
10.3R Is only writing to be found on the steel cams (same on both).
180_8067-1.JPG
180_8067-1.JPG (57.72 KiB) Viewed 15289 times
Ends of steel cams.
180_8068-1.JPG
180_8068-1.JPG (36.88 KiB) Viewed 15293 times
Nose profile of steel cams.

So, any thoughts on what make they are and what they could be usefull for?

Best regards,

Sune
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

The steel cams - if they are definitely steel - look a bit like an older pair of Italian made Columbo & Bariani ones, they certainly have a healthy-looking nose profile and I would use them. I'm just not sure about the origin though, the number codes for C&B are very different these days (maybe always were -so don't quote me). They are not Abarth, their codes were very different and all their cams were cast-iron, and in fact C&B never drilled multiple timing holes on the cam nose. There are several mfrs of steel cams in Italy and they could be from another source. No matter.
Time them up at 110 deg, clearances 0.016" inlet and 0.018" ex. Use new shims and cam lube on start-up, see GC V/W for info on cam timing and fitting!

For ref: If the cam nose is drilled as shown, the cam wheel must be also, with 1 fewer hole to develop an increment between them to adjust timing. It's not a great way of doing it though, you don't get much adjustment and they are a real 'devil' to both adjust and fit-up.

GC
Pelle_Racing
Posts: 13
Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Hi Guy,

The engine is now to be fitted with a set of GCRE 3A cams and I have found my notes on the current setup of the carbs.

2x Weber (made in Spain) 44 IDF 71 6J.
Venturi 36
Idle jet 90FS
Emulsion tube F11
Main jet 135
Air connector 175

(which should be the factory setup from Weber as they are brand new)

Best regards

Sune
S.P.Borregaard
Pelle_Racing
Posts: 13
Joined: March 30th, 2008, 1:17 pm
Location: Denmark

Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Just thought I'd update your all with a picture of the car and engine.

After months and months of no news...

I still have problems with "crusing performance" at ~3500 RPM (has been long distance trouble shooting it with Guy), but will do a seroious effort to fix it this spring...
(Full throttle performance is AMAZING! Especially after 4000RPM)

Regards

Sune
Attachments
The (White) Chocolate Rocket 000_small.jpg
The (White) Chocolate Rocket 000_small.jpg (382.63 KiB) Viewed 14680 times
"Trumpet socks" have been replaced with full "boxed" pipercross unit
"Trumpet socks" have been replaced with full "boxed" pipercross unit
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miro-1980
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Re: Carburettor jetting etc. Fiat Twincam

Post by miro-1980 »

Gentlemen,

Not trying to pretend to be an expert, but aren't the black ones (on the bottom) from a fuel injectd engine while the others form a carburated engine?

They seem to look like mine from 124 CS0 , 1980.

I also noted that the top ef is block munted distributor, while the "black" one is for a head mounnted distributor.
Miro
www.Fiat-abarth-rally.com
GC_93
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

Sock filters too small for anything over about 35bhp per cylinder!

Get some K&N's..

GC
vcg
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Re: Carburettor jetting etc. Fiat Twincam

Post by vcg »

For a very similar motor of mine jetting is as follows on 44IDFs:

38 chokes
F9 emulsion
150 main
170 air
160 idles

Car produced 160bhp on rolling road and was a bit restricted from the exhaust being 42-45-55mm OD, where it should have been 45-50-60mm OD.

The important thing is that when I removed the servo and fitted 45DHLAs on a short straight manifold, I got 174bhp with 40 chokes!

My personal oppinion is that 44IDFs is a great upgeat to the 40IDFs, but still very limiting to the 2.0LT motor
Vassilis
124 BS1, 124 BC1, 131 Racing, E Type 4.2 SII, XJ-S 3.6
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

Quite right Vassilis and that is an interesting comparison with good data, well done.

The problem with IDF on that engine (whatever side) is the 90 deg turn produced in the inlet - it really robs airflow compared with sidedraft. And when a flowbench says 'loss' - it will be a power/torque loss on-engine for sure. As I indicated in my head prep DVD.

GC
Pelle_Racing
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Joined: March 30th, 2008, 1:17 pm
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Re: Carburettor jetting etc. Fiat Twincam

Post by Pelle_Racing »

Hello Gentlemen,

Filter socks HAS been replaced with a filter "box", still from Pipercross, that should be good for 250+ BHP.
It is difficult to fit KNs under the bonnet with the 2L engine. It is considerably taller.

Cam shafts on the pictures are now on the shelf, and a set of GC cams (can't remember the profile, 3B?) has been fitted to the car.

Hopefully I will find the time and energy to get the few last details sorted and take the car on the rolling road this spring.
Guy indicated to me that my "~3500RPM + light trottle" problems could be an ignition problem, so I have purchased a new ignition unit for the Magnetti Marelli ignition and hope to see some improovements.
Any good suggestions on what to do with the vacuum advance system? Leave it as it is? "Block" it, or all together remove it?

Best regards

Sune
S.P.Borregaard
Guy Croft
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Re: Carburettor jetting etc. Fiat Twincam

Post by Guy Croft »

Leave the vacuum unit on the distr since it fixes the baseplate to give the right 10 deg static advance, but don't connect up to the inlet manifold.

GC
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