Fiat TC 1800 single carb swap

Road-race engines and ancillaries - general discussion
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helebah
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Joined: July 19th, 2006, 11:44 pm
Location: Brisbane, Australia
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Fiat TC 1800 single carb swap

Post by helebah »

Am starting the long road to set up my CS1 Spyder for local historic racing. The class (Sc) has various restrictions, one being limited to the same type, number and brand of carbs. So off come the dual side drafts. and on goes a single, downdraft weber. I am after some advice as to what I should bolt on. The engine has been rebuilt to standard Australian specs about 10 years ago so has the 9.8 pistons, cams I seem to recall were similar to the 1608 engine everything else basically standard. I am looking at making it stop and go around corners before pulling the engine apart, so am after advice as to what single carb/ cam combo that may be running out there that gives good perfromance in the 4 - 7K range.

thank you
Guy Croft
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Post by Guy Croft »

Hi,

I am well acquainted with conversions on this engine using the Weber 32/36DGV, + 8% total secondary choke area compared with any Fiat carb and I do have suggested jettings. Others have tried other single twin-choke carburettors but I have no exp at all with them. The carb above is available new from Webcon, formerly Weber UK. (I might add the Directors must be applauded for keeping the the brand alive at all, it nearly disappeared following a very serious labour dispute in Spain two years ago)

If you buy it as a kit you get gaskets, fuel filter, choke cable and other useful bits and pieces, it is actually supplied for the Ford Pinto 2 liter (Capri etc) so don't expect it to be spot-on jetted for your Fiat, however it does match the stud positions, although you need shorter studs and need to modify the throttle linkage lug on the intake cam box or it will foul the cold-start lever (choke),make up the linkage and couple of other little things. Moreover you will need to cope with adaption of the standard filter housing - which I strongly suggest you retain, with maybe a K&N if you can get one.

For those sharing my reply:
Please do me the great courtesy of NOT 'shopping around' for a second-hand one, or at least if you do, please be aware I have no time for that kind of penny-pinching with carbs, everyone does it - I should prefer not to know here

Buy NEW with carbs if you can get new, every time. Why?
1st, you have to a thorough overhaul on old carbs before fitting or you'll damage the engine and by the time you have costed it up you might as well have bought new. I have overhauled more carbs than most and this is not theory, it's fact. Most 2nd hand carbs are a total mess. People will think nothing of selling 'poor' on - my so-total pet hate - an internet auction site, to make a buck or two, please excuse my anger about this.

2nd my advice only makes sense if someone benefits. Hard? That's how the world works. Weber, trust me, we motorsport enthusiasts and professionals owe them a huge debt of gratitude for sustaining the marque under the most difficult circumstances. Weber very nearly vanished completely, but, as I said, for the Directors of the 'Weber UK'. What would we do then? I was not the only one panicking I can tell you, and one of the first to write to them in thanks when they finally sorted out production in Spain. (The dispute went right to Government level).

The gain in torque from the 32/36 carb change alone is very real and measureable, I can vouch for it. As far as further power increase and cams, you need to be aware that the performance of an exhaust cam change is very dependent on the exhaust header/system. You might perhaps like to consider porting and valve seat work first, which, while not raising the speed of max power, will certainly, if done to GC spec, add on 12-16bhp on its own.. The next best thing is to change just the inlet cam, and keep the exhaust cam standard. This will yield a very strong, driveable torque response and make the engine less sensitive to the ex setup.

For this setup I commend my own 300deg 10.4 lift billet GC 3A, e mail me for details. I am a cam designer/manufacturer, so I only recommend cams of my own (or Columbo for 16v) and I don't comment on any others at all. The total package of head, cam and carb, will yield over 130bhp and be fabulously driveable,economical and will easily pull to 7000 although it may peak at nearer 6300.

I hope this is helpful to you and should be happy to continue the discussion as far as time allows me to.

GC
Attachments
1608 TC Fiat - same engine height at 1800, fitted with new Weber 34/36DGV carb at GCRE.
1608 TC Fiat - same engine height at 1800, fitted with new Weber 34/36DGV carb at GCRE.
CM 1608 finished.JPG (29.82 KiB) Viewed 5655 times
Closeup (2) view of carb fitted to Fiat inlet.
Closeup (2) view of carb fitted to Fiat inlet.
DP carb closeup 2.JPG (20.58 KiB) Viewed 5652 times
Closeup (1) view of Weber 32/36DGV carb fitted to Fiat inlet.
Closeup (1) view of Weber 32/36DGV carb fitted to Fiat inlet.
DP carb closeup 1.JPG (21.68 KiB) Viewed 5650 times
helebah
Posts: 25
Joined: July 19th, 2006, 11:44 pm
Location: Brisbane, Australia
Contact:

Post by helebah »

Thanks for reply. You mentioned that you have not used to many other single carbs however someone has mentioned a 38DM(XX also off a FORD) I forget the last two digits, as also being suitable. Is this one you are familar with? From the text I think you are saying choice of exhaust cam depends on header however inlet suited to carb. I thought the cam profile should be the same on normally aspirated? or have I missed the point. (My knowledge is sound but basic). I have a set of headers of questionable pedegree, look OK, seem to go OK but no further knowledge as installed on engine when rebuilt from low compression US spec so nothing to compare. Is there a way of telling/testing re perfromance. Put standard ex manifold on and compare?? Does the cams quoted have exhauste distributer drive? Great forum by the way !!! Appreciate the time spent. Will drop in and out over next few weeks. Wife due with first child any day :shock:
thank you
Guy Croft
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Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
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Post by Guy Croft »

Hi!

Forum - thanks!

You will understand readily that my problem in recommending things is that I cannot say 'I've tried everything', but the minute I recommend one thing someone says 'Oh - you can use this as well..' but usually stops short of providing practical detail about the conversion. I try but - I don't know what to say sometimes.

The Weber 32/36DGV is the only twin choke conversion I have used, and the results were so good that until someone can offer quantifiable back-to-back dyno test results (on the same identical spec engine) of this carb against any other - I won't get involved in any others. The advantages this carb has are that A. it is readily available new, and B. I can advise on jetting, something few other people can or will do (without payment). As far as I'm concerned, and maybe you too - that makes it first choice. If it doesn't produce great results on your motor, going to a bigger one definitely won't either.

GC
helebah
Posts: 25
Joined: July 19th, 2006, 11:44 pm
Location: Brisbane, Australia
Contact:

Post by helebah »

You are correct. I suspect someone used a Weber 38XYZ, said it worked OK, told someone else, then a "legend" was born. Will buy a 32/36DGV(new !!!, but but in Australia rather than UK, a little far to buy new jets :D ), the Formula Ford guys use these so they can not be too bad. What size jets would be recomended to get with it ?.At this stage the engine will remain pretty standard for next 6 months or so while I get some track time. The engine is a standard 9.8 with exhaust headers. Longer term I am looking at inspecting the bottom end first, new rings, pistons if needed, balance maybe lightened flywheel. Then after that head,cams (GC 3A ?) etc. Not looking at a nth degree engine, something strong reliable but with good torque without needing to do 8K everytime. Again appreciate the input, will post a couple of pics of the car.
thank you
graham
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