Fiat TC 8v head flows

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Testament
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Fiat TC 8v head flows

Post by Testament »

Hello Guy,
Reading the flowbench summray thread in your results section I was wondering how does the old 8 valve TC head compare to 16 valve designs, and also how significant is the flow difference between the 8v heads with 41.8mm intakes and those with 43.5mm valves?

thank you, Tom

p.s The news site is great :D
Guy Croft
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Post by Guy Croft »

Hi Tom!

The flow is in part function of port size and valve size, you can take two early heads, 131 TC type, both with nominally 42mm valves but one with port narrowest section approx 32mm and another with 35mm and get radically higher results from the latter, typically 89cfm and 86 cfm at 10" test pressure. And can you open out the ports to improve the low flow head, sure. The heads with 43.5 valves - same rule applies - depends on port size, but the bigger valve potentially means +10cfm.
The later 16v heads flow about 130cfm standard but can go to 170cfm at 10" even with standard size valves.

Back to back standard flows mean nothing unless you are going to swap heads round, not what I do, I have to say, but I know some like to do this. By modifying what you've got in front of you - by port, seat and combustion chamber mods you can get say - about 100cfm out of a 42mm valve head, 114 out of a 43.5mm head. If you just swap things round you never learn anything or experience the fun of developing the thing to its limit, that's not tuning.

I am talking bare port flow figures here (bpf), no valves. It is essential to start with this because the valve is always a restriction and you need to know what the flow potential of the port is in its own right. If the head flows better with the valve in you have got at battle on your hands to find out why, maybe ports too small for that valve size and air velocity too high. I've only had that happen once.

At some high lift point the flow with valve fitted should intersect the bare port flow - if it doesn't even at very high lift - you've got a shrouding problem or the valve is the wrong shape for that port layout, some heads are super sensitive to valve shape. 8v Peugeot 205 for example, where only the flattest 'penny on a stick' valve works.

The flow under valve lift is very important, particularly in the 3-10mm lift range, and you're always hoping that in raising the bpf figure, you don't mess up the lower lift regime. Provided you leave the short side radius region alone till the end you are pretty safe. The ssr and valve shape/throat region are the most important factors affecting that flow.

The 8V head below, that I have been working on Dave Beale, for his supercharged Lancia MonteCarlo was interesting, it came to me already equipped with bronze guides, 45/40 valves, inlets of a most peculiar shape, squish bands welded in like the 'reversed-port' heads, but not ported at all. To begin with the head would not flow any more than a 131 2 liter head.

GC
Attachments
Flowtests (well, few of them, there were dozens of tests) on Dave's 45/40 valve head. I could have gone further, but only by sacrificing the squish bands.
Flowtests (well, few of them, there were dozens of tests) on Dave's 45/40 valve head. I could have gone further, but only by sacrificing the squish bands.
D Beale 04.065.jpg (87.13 KiB) Viewed 3902 times
Here you can see why, to begin with, even with high BPF after enlarging the ports, the valve-in flows were poor.
Here you can see why, to begin with, even with high BPF after enlarging the ports, the valve-in flows were poor.
DB MC 8v possible shrouding_01.JPG (133.42 KiB) Viewed 3901 times
This is the final chamber shape on the deshrouding got the valve-in flow closer to the BPF, but it was a struggle even then.
This is the final chamber shape on the deshrouding got the valve-in flow closer to the BPF, but it was a struggle even then.
DB MC 04.065 final cc shape.jpg (111.88 KiB) Viewed 3899 times
Dave Beale's 8V Fiat head refaced, I had to do was recess the inlet seats nearly 1mm to get clearance from the head face, and hoped the cutter would then clear the seats. It did.
Dave Beale's 8V Fiat head refaced, I had to do was recess the inlet seats nearly 1mm to get clearance from the head face, and hoped the cutter would then clear the seats. It did.
pic 010.jpg (115.54 KiB) Viewed 3897 times
Flowtests on Alexis Grant's 16v Fiat Coupe turbo head, no horrors with these heads, port them right and they fly..
Flowtests on Alexis Grant's 16v Fiat Coupe turbo head, no horrors with these heads, port them right and they fly..
A Grant 06.106.jpg (78.22 KiB) Viewed 3895 times
Doing a bit of deburring round the waterways after refacing - on the 16v Fiat Coupe Turbo head for Alexis Grant shown below,
Doing a bit of deburring round the waterways after refacing - on the 16v Fiat Coupe Turbo head for Alexis Grant shown below,
A Grant 16v post reface head deburr.JPG (157.2 KiB) Viewed 3892 times
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