Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Road-race engines and ancillaries - general discussion
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Lee67
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Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Lee67 » Wed Dec 28, 2016 7:08 pm

Hi all,
I need some advice regarding cylinder heads that I have and my best overall options.
I currently have a 105TC head as far as i know (casting No 4460623) with 43.5mm inlet valves but with fairly small inlet ports, 41mmX33mm measured at the gasket face.
I also have an 1800 head (casting No 4277590) with standard 41.5mm inlet valves but featuring much larger inlet ports (45.5mmx36.5mm).

My understanding for best results would be to use the 1800 head but with the larger 43.5mm valves fitted - am I correct? Also is it possible to fit the larger valves by having the valve seats re-cut to suit or are more modifications required?

The bottom end is an 1800 currently fitted with standard flat top pistons although I may consider domed pistons assuming there will not be valve to piston clearance issues when using the larger valves, assuming of course that I actually can use these.

The 105TC? head has been mildly ported (photo of combustion chamber area attached for info) - in your opinion has the modifier gone about this the right way and should I look to replicate this with the 1800 head if I use it?

My second question although relevant to this concerns my choice of inlet manifold. I have available a well ported factory waffle manifold with matching 40IDF's and all the necessary distributor parts to swap from block mount to head mount distributor. Also I have a 131 type IDF manifold which is made by a well known aftermarket company and allows the fitment of the standard block mounted distributor. This manifold has longer inlet runners than the standard waffle item which I'm thinking will produce more torque? Has anyone any info regarding these manifolds and how they perform against each other? I deliberately have not named the aftermarket manufacturer but will do if acceptable to GC?

The engine will be used in a full weight 124 saloon purely as a fun road car and will be a pretty mild spec. Basically an 1800 with hopefully a large port/large valve flowed head, 40IDFs, good inlet manifold and a tubular exhaust manifold, possibly fast road cams and higher than standard compression subject to advice of those in the know.
As always any advice or thoughts are most welcome, positive or negative.

Lee.
105tccc.jpg
modified 105TC combustion chamber
105tccc.jpg (40.73 KiB) Viewed 664 times
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1800cc.jpg
standard 1800 combustion chamber
1800cc.jpg (48.51 KiB) Viewed 664 times
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Spider 1969
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Spider 1969 » Wed Dec 28, 2016 11:53 pm

Hi Lee,


I'm not an expert (other readers please feel free to complement or correct, this is what this forum is about) but will share my thoughts on your first question leaving the second on the inlet manifold for others.
As far as I'm aware:
- your 105TC combustion chambers do not seem to be modified. They look like the ones on the 105TC head that I have lying on the shelf for a future project See attached picture for reference.
- The 105TC/130TC/Volumex combustion chamber do not need modification as the valve are not shrouded like in the early type combustion chambers. The short side radius of the inlet port does need correction and the valves/seats can vastly be improved. Also the exhaust ports need little correction. It seems these type of heads need the least effort to improve. There's some good guidance from Guy on this forum under the "Cylinder head preparation-now unlocked" section of this forum (http://guy-croft.com/viewforum.php?f=2). I can also highly recommend Guy's latest work shop manual (and /or the first but this one's hard to find)
- The 105TC head /valves can be used with high dome pistons. I've seen OE Fiat domed pistons being used with it and forged ones are being made to order so will fit (pending the right specification to he manufacturer of course). Dry building the engine will confirm whether valve to piston clearances are within tolerance.

Difficult to assess whether the bigger ports of the 1800 head will be beneficial compared to the 105TC big valves. Bigger ports and or valves are not always better as the optimum depends on the rest of the engine configuration such as cam's, size of the carburetor(s) and compression ratio. Bigger ports need higher CR and more powerful cams (or the other way around?). Bigger valves can be subject to reverse flow on compression stroke. So your desired output and where you want the torque on the rev curve is critical to make these choices.
I'd suggest you take a look under the "Readers cars" section to review specs and outputs of twin cams show cased there. This will give you an idea on what spec is appropriate for your 124 (nice one by the way!)

Kind regards,
Charles
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Guy Croft
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Guy Croft » Fri Dec 30, 2016 12:29 pm

you cannot run the 43.5mm inlet valves with the valve reliefs sized for 42mm valves..

GC
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Lee67
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Lee67 » Fri Dec 30, 2016 6:42 pm

Thanks Charles and GC for the input.

Charles, I think you're right in saying that the combustion chambers in my 105TC head are unmodified, now I've seen the pic of yours it seems that they are standard. My head has definitely had some porting carried out and when comparing the head with my 1800 head and seeing the differences in the combustion chambers I naturally assumed that whoever has done some work on it had modified the combustion chambers as well as the ports. It seems Fiat had their own ideas anyway and did the work for us.

GC - thanks for the info regarding valve sizes and valve reliefs. I'm now having a rethink, given that my 1800 bottom end is very recently rebuilt (before I got hold of it) including new pistons, is there any value in continuing my idea of fitting the larger valves to the 1800 head if I need to either A: have machining carried out to my pistons to allow the 43.5mm valves to be used without clearance problems? B: Source a set of 105TC or 130TC pistons with the correct oversize measurement?
Or should I save myself the cost involved there and rework my 1800 head to your specifications, keep my standard 1800 pistons and concentrate on gaining horsepower via non standard cams along with selecting the right inlet manifold? Does the cost in purchasing another set of pistons or machining my existing pistons outweigh the power increase from doing it when compared to spending money elsewhere is what I'm thinking?

Lee
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Guy Croft » Fri Dec 30, 2016 6:53 pm

Hi Lee

stick with the 42/36 valve combo!!

GC
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Lee67
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Lee67 » Fri Dec 30, 2016 7:10 pm

Thanks Guy, I suspected this, the cost will outweigh the relatively small increase in power I guess.

DO you have any views on the inlet manifold options I mentioned, swap to factory waffle manifold with exhaust cam driven distributor or use aftermarket long runner manifold (from a reputable manufacturer) that's offset to clear the current block mounted distributor?

Lee
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Re: Fiat TC 8V cylinder head & inlet options - Big valves with big ports or small?

Post by Guy Croft » Fri Dec 30, 2016 7:24 pm

Hi Lee

your circumspection re the mfr of that manifold is appreciated, I know the one! I don't like it at all any more than I like anything made by Mangoletsi but it's one of the few still aval! The appalling quality of their sidedraft TC manifold was one reason I designed my own...

Technically and insofar as the length of that manifold is concerned:

The optimum length of the inlet tract from valve to rampipe entry and its impact on torque (and where that torque IS in the powerband) depends on the length of the exhaust manifold primary pipes (among other things). If the exhaust primary pipe length (chord length - axis of pipe) is less than 17" from head face to collector entry then you can't tune the torque curve at all by altering the inlet tract length.

If it's over 17" - you can. FACT.

if your exhaust meets that critical length then with a longer inlet manifold - or longer rampipes (amounts to the same thing) the torque comes in lower in the rev band. Shorten the inlet tract - torque (and thus BHP - which after all is a merely a function of torque vs engine speed).

BTW suggest you go for 44 IDF not 40, the difference on an 1800 unit is like NIGHT AND DAY!!!!!!

GC
Guy Croft, owner

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