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Fiat TC 2L Stage II head.

Posted: Sat Jan 02, 2016 8:47 pm
by Piotrek125p
Hi everyone.

I'm building now a Fiat TC 2L cylinder head. It will be used in my FSO 125p, fast road and occasionally track day car. The spec of engine is:

OE 43.5mm intake valve with 30 degree top cut
OE 36 mm exhaust valve from Lancia Turbo (sodium cooled)
30-45-70 valve seats (trojan both intake and exhaust)
3A and 2B GC Cams (timed 106-108) or 3A/3A GC Cams timed 102FL.
4-1 exhaust 33" long
Twin 45 DCOE with 38 chokes with my own manifold.
Mondials cast pistons from 1585 TC, about 10.2CR
Stock gearbox from 131.

My question is about a venturi in a intake port. GC, I want to use 36mm on an input of intake port. In the venturi I'm thinking about:
-34mm round
-35mm round
-34 vertical 34.5mm horizontal
-34 vertical 35mm horizontal

I haven't a Flowbench and Dyno back-to-back data. Can You advise me what a diameter of venturi I should to use ? I will port my head on Rottler f69atc CNC machine, I'm not a skilled porting folk.

Sincerely.

Piotr.

Re: Fiat TC 2L Stage II head.

Posted: Sat Jan 02, 2016 8:49 pm
by Guy Croft
36-35mm diameter.

G

Re: Fiat TC 2L Stage II head.

Posted: Sat Jan 02, 2016 8:51 pm
by Piotrek125p
It's a good news, I have a Trevi head with 35mm round venturi. I'm thinking about 34.5V/34H or 35V/34H venturi, but I trust You and I will use a 35 round venturi.

Re: Fiat TC 2L Stage II head.

Posted: Sat Jan 02, 2016 8:55 pm
by Guy Croft
ROUND IS BETTER FOR FLOW..

G

Re: Fiat TC 2L Stage II head.

Posted: Sat Jan 02, 2016 8:58 pm
by Piotrek125p
Yes but I noticed that you use a venturi with another V diameter and another H diameter, Lotus Lada replica and Miro 131 engine with 34V and 35H and 07.132 head with 34V and 34.5H so I want to ask You what I should to choose. Why You use not round venturis in your TC cylinderheads ?

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 8:09 am
by Guy Croft
well,

I try to get them as round as I can!

+/- 0.5mm is nothing really in flow terms..

G

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 8:20 am
by Piotrek125p
Ok, I thought You doing it because You can get have more space for SSR.

I'm asked You about minimal valve margin. What is the minimal valve margin for intakes, solid exhausts and sodium-cooled exhausts that You use?

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 2:03 pm
by Guy Croft
you need to buy my 2013 book!

I mean you REALLY need to buy it!

G

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 2:54 pm
by Piotrek125p
G, but I have Your 2010 red book. Sadly, I didn't find info about minimal valve margin, maybe I looking wrong.

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 5:24 pm
by Guy Croft
you fit guides with tight fit and hone them till the valves just fall under their own weight...!

GC

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 5:32 pm
by Piotrek125p
G, a margin I mean a valve head thickness, maybe I called it wrong before. About clearance and fit between valve and guide I know everything I want, this is very clearly explained in "red" book.

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 9:20 pm
by Guy Croft
OK.

Use a photo marked up with MS Paint to explain your question for me and other readers!

Photos are expected in GC Q&A, the rules for posting here do say that...

GC

Re: Fiat TC 2L Stage II head.

Posted: Sun Jan 03, 2016 9:42 pm
by Piotrek125p
a053643e03.png
Valve margin
a053643e03.png (2.93 KiB) Viewed 2081 times
Now everything should be clear.

Re: Fiat TC 2L Stage II head.

Posted: Mon Jan 04, 2016 11:09 am
by Guy Croft
you can go down to 0.5mm no problem..

G

Re: Fiat TC 2L Stage II head.

Posted: Mon Jan 04, 2016 5:34 pm
by Piotrek125p
Thanks for this info, it looks that I have plenty of good 43.5 and 36 sodium cooled valves.

In Your new book You wrote a lot about E/I. Based on what I read in a book it looks that best size of exhaust valve for 43.5mm is 37.5mm. I thinking about a conversion for it because I have a cylinder head in excellent condition (crack tested, very good flatness, threads without damage etc.)
P1040270.JPG
My 8V TC head after 1st ultrasonic cleaning, before beadblasting
P1040270.JPG (84.58 KiB) Viewed 2066 times
This head had a valve seat removed, it was a subject of my thesis-CNC porting of Fiat TC 8v cylinderhead (long story, if you are interested I can write about it a few words).
In meanwhile I designed 3 types of 37.5mm exhaust valve for 8v TC based of info in Your books, if the bigger exhaust valve for my head will be good idea I will attached here there drawings and valve seat drawings for 37.5mm valve.
I haven't dyno experience with 43.5/37.5 head in 2L TC, for me, this solution has for me a several advantages and disadvantages.

Advantages:
-more top end power
-more flow at higher lift (maybe 3A exhaust cam will work good with it)
-better scavenging effect

Disadvantage:
-less power at low RPM
-too low CR for 37.5mm exhaust valve (I will have approx 10.2:1)
-neccesity for use a close ratio gearbox.

The goal is to have about 165-170bhp/147lbf.ft and acceptionally driveablity (this will be engine for fast road/occasionally track day car). For 1-2 years it will be using a normal 131/132 gearbox.
GC, please tell me is the 37.5 exhaust valve will be good choice for my engine (I know a very reputable firm who can make for me an excellent quality 21-4n valve by my design).

In sum, is the 37.5mm exhaust valve will be simply a few extra bhp or asking for problems ? The rest of data of my engine You can find on 1st page of this thread.

P.S the cost of one 21-4n exhaust valve according of my design is about 20GBP so this is not a lot of money but the valves had several tests by me (a quality engineer) and by my friends (users of very high perfomance turbo engines) and excellent passed everything of them.