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Would anyone know if a 313248 (219015) head would be a straight replacement for a 312388 (218225) head? I’m looking at getting the latter unleaded whilst continuing to run my USA carb car (CC781xxL) and then just replacing one with the other to keep the car on the road for the rest of the summer.

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Dear jake-a

The port spacing of carb heads changed at a specific engine no.  The wide spaced inlet ports of the later carb heads are the same as all PI cars. This happens from engine no CC75001 The no is stamped on the block upper face lh rear - I think you have quoted the vehicle commission no. in your post.  You will need to know the engine number to get the correct head gasket set. (flat or recessed block)

Read this from Chris Witor.  I put the same info in the Moss TR250/5/6 printed parts catalogue - get yourself a copy free from Moss Europe and read the wealth of info we gave.

https://www.chriswitor.com/cw_technical/head_applications_chart.pdf

The part number heads you have given, for my money, are interchangeable except for diameter of exhaust valves. - It is said the smaller exhaust valve diameter from later heads is more reliable - Discuss.

Cheers

Peter W

PS You could always try the inlet exhaust gasket you intend to use on both heads.  Given a photo of your inlet manifold fitted to the head we may be able id from that.

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Hi Peter,

The engine is CC783xxUE.

I’ve checked with a couple of the specialists in the last hour too and they say they are interchangeable, and have said the same as you about valves.

Very helpful Peter, thanks.

Jake

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On 7/31/2019 at 11:04 AM, BlueTR3A-5EKT said:

Dear jake-a

The port spacing of carb heads changed at a specific engine no.  The wide spaced inlet ports of the later carb heads are the same as all PI cars. This happens from engine no CC75001 The no is stamped on the block upper face lh rear - I think you have quoted the vehicle commission no. in your post.  You will need to know the engine number to get the correct head gasket set. (flat or recessed block)

Read this from Chris Witor.  I put the same info in the Moss TR250/5/6 printed parts catalogue - get yourself a copy free from Moss Europe and read the wealth of info we gave.

https://www.chriswitor.com/cw_technical/head_applications_chart.pdf

The part number heads you have given, for my money, are interchangeable except for diameter of exhaust valves. - It is said the smaller exhaust valve diameter from later heads is more reliable - Discuss.

Cheers

Peter W

PS You could always try the inlet exhaust gasket you intend to use on both heads.  Given a photo of your inlet manifold fitted to the head we may be able id from that.

The smaller exhaust valves was an attempt to cut down cracking of the cast iron between valves? But the later heads were also more meaty in construction to try to stop warping and blown head gaskets by using modified fire rings and counter boring the block. I would speak to Chris Whitor, he is an expert on this sort of thing, he has a web site. You will probably have to change your manifolds?

Bruce.

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