raised port heads
Turbo Mini Forums

would like to have an idea of how much can I raise the inlets on 12g940 cyl head.
If you have pics of a raised one, datas (flow) or sectionned a 12g940 I'm much interested.

Fabrice

I will head to the work shop In 10mins FAB and Ill get you pic of a section 12G940

Id say a maximium or 3mm ,ive done this and ended up with a porous head.

the top of the inlet port is about 5mm thick if my sectioned head is anyhting to go by

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3mm.. that's not a lot!
what about upper port thickness at the middle of the port , just where the port is at his minimum width, is there is enough meat to push an 'o ringed sleeve tube?

Sorry Fab just realised I cut it trough the Ehxaust port If you tell me where you want me to cut one of the inlets Ill do it monday for you :)

right in the middle of the port should be perfect.
Thanks
Fabrice

Own the day

not I'll raise the port by more than 10mm ideally 20, then where I'll sleeve it I need more metal support to keep it all together...

Fab, are you looking to fit a sleeve in the same plane as the origional port or invert in slightly [downdraught] they are a pig to seal because where the boring meets the port abopve the valve you cannot get one flat surface because the port starts to open out for the valves at this point,


carl

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that's it!
didnt' think about the reopening of the port.....
ideas to counter this???????

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do you have a brand to recommand?

i uaed some generic epoxy type, either way it will seal for a time , then leak, as the constant expansion/contraction/fuel contamination/ water pressure from behind will lift the edge allowing water in ,
ive got my camera on charge later today i will get some pics of the one i did years ago,

carl

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Edited by fastcarl on 21st Jun, 2009.

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thanks, exactly what I had in my head!
I'm obliged to ask if the gains are worthing the efforts and unreliable side?

this wa asthe head i used when my car could run 11.7 sec 1/4 miles,

i had to reseal it once at the begining of the season and once half way through.

i got fed up of the work involved in sealing up time after time so set about cutting myself a more conventional head for nitrous,i never had the same results as previously for one reason or another,

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so FIRE!!

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From the looks of the cross section if you have the right tool you should be able to bore a new inlet port angle and shrink fit a phosphor bronze sleeve with some sealant. Once normalised it should be air tight.

Own the day

mean I'm conviced and should go on

Ive seen better flow figures from a convenbtionally ported head, but it had much larger inlet valves, and was distroyed by Nitrous withing 3 meetings,
shrinking a sleeve is not that easy IIRC as there is little or no support at the bottom of the port as its not touched when dored out, only the top and sides are machined,

also to but a sleeve in that is this enough to stay pressed in and not collapse you obviously need to make the wall thickness substantial , all this extra thickness meens a bigger port bore which encroached even more into the pushrod holes,

I think i could make a much better one if i were to nowadays now that iv'e done one already and know where to improve.

it still not for the fainhearted , these jobs usually end up as unfinished projects,


carl

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I sat looking at a head last night and was wondering if it was ever considered to raise the ports to the extent that they were semi in the rocker cover?

Own the day

Yes, that's been done. I started a thread a while ago about it. Search for "downdraught head".

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obviously the steeper the incline the greater need for a tulip valve.

i kept mine below the top of the head as it makes things less complex.


carl

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is that a crack through the spark plug hole?

"Cars are a lifetime of pain"