Fiat TC 2L Stage II head.

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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 7:30 pm

it's not critical on the ex side,

remember that if you 'top-cut' the valve will naturally go deeper into the head... it also makes the chamber bigger!

The 30 deg top cut on the inlet side definitely gives better low-lift flow, but same rule applies and for those reasons I rarely use it, especially if working with production seat inserts. Mostly I stick with 20 or 15 both sides and nobody complains about the power from GC engines (or throttle response!)

Of course having the valve tip height higher than standard 40.7mm can help with shimming, but it can be very difficult to get it right simply by cutting the seats...

If you don't plan it before you start - - you can end up with no insert left at all for the 70 deg and parallel sections..

If you want to be safe, draw it all on cad first..

G
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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 7:34 pm

Ok, I understand it, this is clear for me.
BTW, if I remember correctly the GC IIB has also reduced by 1mm base circle as IIIA cam so it's look tha 41.5-42,5mm tip height is also optimally on exhaust with GC IIB cam. Am I right ?
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 8:04 pm

you've got some work to do Piotr!

Put them in the cam boxes and compare with standard!!

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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 8:05 pm

OK, thanks GC.
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 8:17 pm

this exchange betw Piotr and me is what GC Q&A is for readers.

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Re: Fiat TC 2L Stage II head.

Post by cormac » Mon Jan 04, 2016 8:51 pm

I love the exchange between GC and Piotr and just had an epiphany...I am now confidant that I can impose on GC and his expertise when I start my engine build, submitting good pics/diagrams and definitive questions - to the end of building a strong performing engine, am very excited (love the new youtube stuff, thanks heaps GC)

Dave (Cormac)

PS just a little note...how I got the Cormac...watched a British movie (a bad spy movie) probably in the late 60's and the hero used the phrase "Cormac Shannon is my name and loving is my game", somehow it has stayed with me all these years (am 62) and I use it as a user name as often as I can...wanted to name my son Cormac but my wife objected and he is named Conor (notice the correct Irish spelling, though we are only a little Irish, the name wasn't as popular twenty years ago UNACCEPTABLE)
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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Tue Jan 05, 2016 7:30 pm

I decided to post here some drawings from another my topic about SSR in 36-35 TC head, I think it is a good idea to put this together in one topic.
Guy Croft wrote:This reply is about how to develop the curve on the central region of the short radius that has such a critical effect on lower lift flow - 0-5mm lift (or so..). This region is important because the inlet flow 'sees' that even twice in the cam cycle.

Captions to follow, sorry data lost last week.

G
inlet SSR 43.5mm valve TC_07.GIF
inlet SSR 43.5mm valve TC_07.GIF (11.63 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_06.GIF
inlet SSR 43.5mm valve TC_06.GIF (9.5 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_05.GIF
inlet SSR 43.5mm valve TC_05.GIF (9.91 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_04.GIF
inlet SSR 43.5mm valve TC_04.GIF (10.03 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_03.GIF
inlet SSR 43.5mm valve TC_03.GIF (10.4 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_02.GIF
inlet SSR 43.5mm valve TC_02.GIF (9.88 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC_01.GIF
inlet SSR 43.5mm valve TC_01.GIF (10.89 KiB) Viewed 841 times
short radius region.JPG
short radius region.JPG (54.73 KiB) Viewed 841 times
inlet SSR 43.5mm valve TC.GIF
inlet SSR 43.5mm valve TC.GIF (10.82 KiB) Viewed 841 times
I also found another GC drawing about 43.5 intake valve conversion
Fiat TC 43.5mm valve insert2.GIF
Fiat TC 43.5mm valve insert2.GIF (17.84 KiB) Viewed 841 times
Also I found GC drawing about 36mm exhaust valve-seat.
Fiat TC 8v ex seat 70deg throat.jpg
Fiat TC 8v ex seat 70deg throat.jpg (51.53 KiB) Viewed 841 times
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Tue Jan 05, 2016 8:29 pm

nice dwgs!

Did I really do those?!

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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Tue Jan 05, 2016 8:53 pm

Yes, this is Yours.
BTW, many of non Fiat engine builders recommended a 20-30 degree top cut on exhaust valves. I notice that You doesn't do this on TC valves. Do You doesn't do this because You want to avoid shimming problems or this is not a good idea on exhausts ? I will be do somee porting job on head from my daily car and I want to know what do You thinking about top cut on the exhaust valves (in Fiat TC and in general).
In the drawing that I attached a contact face is 1.5mm, why do You change it since then ? A wider contact face causes better seal ?
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Tue Jan 05, 2016 11:42 pm

Many of the non Fiat race engine builders? Give me some names!

I guess it depends which forums you read, I only read my own,

On a 36mm ex valve - 1.5mm - 2mm, not critical..

2mm if you can get it, 1.5mm preferred minimum, it make no difference to flow. And the TC unit flows so well frankly the ex port is the least of your problems. Wait till you get to optimising the exhaust system!! Then you will need very deep pockets.

I swear in 20 years you may be a future race engine builder, dear Piotr. You ask good questions. All you need now is £1000s on dyno testing at your own expense and 8 years with a flowbench on the most extreme stuff known to man..! Stuff where the limits of achievement are uber-hard to find and nothing but 1000% attainment is good enough. Check out the new GC Youtube channel, you will see what I mean..

Add twenty years of backache and worrying yourself sick every night..

Add in - every mistake a skilled ex F1 engine man with an honors degree in automotive can make + tens of thousands of hours of getting things right or wrong and hoping the client will be happy with what you did with his money!!

GC

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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Wed Jan 06, 2016 8:14 am

For example David Vizard wrote about 30 degree top cut on exhaust valve in his Ford Pinto engines book. I read an article wrote by Ferrea and they also advise a top cut on exhaust valve (very interesting article, if You want I can put here a link for it).

About dyno testing, yes I will do some tests with my engine, sadly in Poland we haven't many racetracks so engine building is a something like hobby for me, not the way to make money.

Flowbench now is a very, very expensive machine, but I want to make my own, DIY Flowbench. I have some articles about it, some photos, some knowlegle about flow machines (non engines type) and maybe in 2016 I will get my own, partically design by me Flowbench. Heaven knows.
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