Race Engine Forum UK

Hi Guy,

I'm about to flow a head for a 2ltr Fiat TC.

Compression is 9:1
Bottom End is standard
2 X 40 IDF on a Waffle top

The dilemma is the head.

I have two heads. One out of a 124 CC and the one that came off the block. (a late 132 2ltr I think)
The 124 head has 1.5 mm bigger inlet ports and 42.5 mm valve, But a 15 mm valve guide. The 132 has smaller inlet ports BUT has 14 mm valve guide. The size around the throat of the valve is fairly close.

The question is is it better to use the one with the SMALLER Valve Guides and spend the extra time getting the ports out to the bigger size. Because I can throat the seats to suit the slightly lager valve.

Actually now that I've asked the question I think I have my answer... But I'll wait to see what you think.
Thanks Guy

Mack, OK, understood.

To give a reasoned answer (allowing for the foregoing info on guide sizes and ports, which is relevant) I need to see the combustion chambers. Publish a photo of each please, thanks.

GC

Hi Guy,
Thanks for the quick response.
Here are some photos as requested.

On further investigation I thought that the valve guides were of an uneven length on the 1756 head, but it has turned out that the little "Bump" on either side of the guide is almost non-existent on cylinders 1 & 2. So a bit of very fine work will have to be done to even that up, IF this is the head I use. I've added some photos of the inlet ports also.

The exhaust side seems to be fairly equal from head to head.

Thanks for your imput
Gill

Great! Well done Mack.

In fact both have the late roomy combustion chamber, not at all shrouded, so which to use?

The bigger ports on the 124 head are more suitable, but those bigger guides are a significant intrusion, I would not shave them being cast iron but radiusing the top of them helps a bit.

Maybe I'd use the other - 2 liter head - and open out the ports. That way you get the bes tof everything. The smaller guides and the big ports. That porting is no big job.
But - first check to see which head has more metal to reface around the inlet valve insert, the best m8 and m6 threads, the best coolant gallery condition, best plug threads - some simple practical considerations.

If the 2 liter needs a lot of attention and you're not 'up for it', use the 1800 head, OK? In standard trim the bigger port will probably outweigh the negative effect of the big guide.

I hope this helps,

GC