5 replies to this topic

[1963MKI]

I have a Austin 1300GT engine. I am thinking of as a project switching it to an 8 port design. Does anyone have any expeirience on this ? Seeing as it is based on the cooper S engine. The block needs reboring and as I cant source +20 original pistons I will have to use the other type which are .020 though taller so I will have to machine the pistons as far as I can gather. Any guides on the other machinging to do on the rockers etc ?

[Dusky]

Regarding pistons, minispares sells suitable +20 pistons, p21253

[Spider]

What sort of 8 port head were you thinking of fitting?

[carbon]

If you use the 21253 pistons as suggested by Dusky they will come further up the block. Unless the block has been skimmed then you should find the tops of the pistons are 5 to 10 thou down the bore, which is good.

 

But using 21253 pistons in 1300GT block will raise the compression ratio. The CR is likely to end up between 10.2 and 10.5 using a standard head with 21cc chambers, which by all accounts is too high for engine using standard or mild road camshaft on normal pump petrol.

 

Also your choice of cam profiles for 8 port heads is much more limited than 5 port.

[Spider]

One other thing you may want to keep in mind is if it's an Alloy Head, you'll want to raise the CR around 0.3 - 0.5 CR 'points' over a similar set up with an Iron Head.

[Alex_B]

Have a look into 7 port heads, I believe they use standard camshaft profiles I believe which gives you more choice and should save you some money and I don't think you actually lose much over an 8 port. 

This is just from info I have gained from this forum, I haven't any experience so it may not be the case but worth some research anyway! 

Edited by Alex_B, 28 November 2015 - 06:39 PM.