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 6:25 pm

forget the bigger ex valves, you'd have to fit bigger seat inserts for them and why bother?

36mm is plenty big enough for 43.5mm inlet valves, Fiat knew that years ago and they were right (eg Strada 130TC)

Miroslaw's 2 liter 8v has 43.5/36 and develops 185bhp on 44 IDF...

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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 6:32 pm

I'm thinking about it only because I have to fit a new valve seats, it's not a problem to fit bigger for 37.5mm. If I can get a more power why I shouldn't do it ? The only problem which I was afraid was a problems at low RPM and "nasty" work these type of engine with stock 131/132 gearbox in road car. How to do a good big valve conversion because You made a most detailed "how to" about it. If this is a bad idea I will not simply do this conversion.
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 6:35 pm

you will not get more power with 37.5mm ex valves compared with 36mm.

Use the 43.5mm inlets with 36mm ex.

Don't throw the old ex valves away - beadblast, crack test and reface them, polish the stems and grind the tips flat. Too expensive to junk, I rarely do that.

36mm are BIG enough!

G
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installation dwg 43.5mm inlet.GIF
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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 6:38 pm

But in my cylinderhead that I will use I have a IN/EX seats removed already. I will fit a trojan seats for it. I had also a Trevi head, but it had a very, very worn 43.5 conversion so I don't want to use it, the 131 head from last photo is excellent.
I will use 36mm as You suggest.
GC, You don't have to attached here a 43.5 conversion draw, I have both of them on my disc, it is in Your book and I done it last year and was pleased for result.
Guy Croft wrote:you will not get more power with 37.5mm ex valves compared with 36mm.
This is all info that I need from You, thanks a lot for this info.
Last edited by Piotrek125p on Mon Jan 04, 2016 6:42 pm, edited 1 time in total.
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 6:42 pm

no problem Piotr,

the dwg may help someone else..

G
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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 6:48 pm

Ending of topic about exhaust-valve seat I have a two last questions about:
1.could I use a trojan seats on exhausts in road engine ? You wrote in new book that is good choice for exhaust, but also in road engine ?
2.which seat diameter will be better 32.5 or 33 or another ?
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 6:57 pm

Trojan is good in all applications, way superior to other materials because of its embeddability and fantastic heat transfer characteristics.

I don't understand your dimensional question!

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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 7:00 pm

I asked about a exhaust throat diameter, sorry for unclear question.
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 7:08 pm

ah, thought that might so..

I don't have a cad dwg for the 36mm valve, use this and scale it down. Keep a 2mm contact face as shown.

It is vital to do a 70 into parallel throat otherwise you will never be able to recut the seats at a later date.

G
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Installation dwg_KS insert to 40mm ex valve.jpg
Installation dwg_KS insert to 40mm ex valve.jpg (602.03 KiB) Viewed 1133 times
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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 7:19 pm

It looks that I have to use about 32,2mm throat (throat area is about 80% of valve head area). OK, I will use it.
BTW, I thought that You using a 30 top grind on exhaust seat in TC 8V head.
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Re: Fiat TC 2L Stage II head.

Post by Guy Croft » Mon Jan 04, 2016 7:21 pm

30 deg top grind isn't needed on the ex side..


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Re: Fiat TC 2L Stage II head.

Post by Piotrek125p » Mon Jan 04, 2016 7:24 pm

So it's doesn't matter that I will use 15 or 30 degree ? I wanted to use 30 on exhaust according to Your book. It looks that exhaust valve-seat is really insensitive for flow.
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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..

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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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