Minimum head thickness

[gttjames]

Got my hands on some verniers today and measured the head, i got 72.64. Also checked a spare head i have here and that was 72.4 so even worse.

From what iv read it seems alot of different oponions, seen posts from the wizard saying dont go under 72.5 and then other posts saying not to go under 73. Thing is this isnt for oe boost or im sure it would be fine, my aim is 20psi area so before i even bother getting this pressure tested is it even worth it or do i need to source a head?

thanks

[Brigsy]

Id personally look for a thicker head. If your stuck you could get some meat took out the squish area to lower the comp but its not the best way to fix it

[olidaviesuk]

Skimming the head/using a overskimmed head raises the cylinder compression, which by itself is no bad thing, however, higher compression increases the tendency for the engine to pink/det at higher boost levels and higher(leaner)afrs. You can retard the ignition timing by modifying the crank sensor bracket which reduces the possibility of the aforementioned happening, whether you gain a power benefit from using higher compression rather than advanced timing on std compression I wouldn't like to say as the aei unit doesn't allow any adjustability on the ignition map to make the most of it.

To sum it up: using a over skimmed head on the 5 is not ideal, however, you should be able to get a thinker gasket (I think cgb were doing some 2.5mm gaskets a while back) which would take your head back to a safe 73.6ish worth a call


Got my hands on some verniers today and measured the head, i got 72.64. Also checked a spare head i have here and that was 72.4 so even worse.

From what iv read it seems alot of different oponions, seen posts from the wizard saying dont go under 72.5 and then other posts saying not to go under 73. Thing is this isnt for oe boost or im sure it would be fine, my aim is 20psi area so before i even bother getting this pressure tested is it even worth it or do i need to source a head?

thanks

[Nottswoody]

Hmmmm interesting mine measures now 72.9 I have a 1.9 hard gasket to go on but I aim to use 18-20psi.. Is that not going to last? :scratch:

[olidaviesuk]

All comes down to the fuelling, ignition timing and also the petrol you use...

Run it on std unleaded, fairly lean and a bit of ignition advance and in all probability no... On the other hand nice and safe afrs in high 11s/low 12s std ignition timing and super unleaded and no reason why it won't go on for ever...

C1Js are bomb proof little motors providing you get all the little details right



Hmmmm interesting mine measures now 72.9 I have a 1.9 hard gasket to go on but I aim to use 18-20psi.. Is that not going to last? :scratch:

[DaveL485]

C1Js are bomb proof little motors providing you get all the little details right

Hallelujah brother :agree:

[gttjames]

so general oponion is its on the thin side, hmm....

yer i have read about modding the squish area but then it changes shape of cylinder area so this could also have a effect i have read. Its all so confussing

interesting to here cgb where doing a 2.5mm hg, i will give them a call and see what they come up with.

So im guessing renault dont supply these heads anymore... So in a few years to come when we have all had a few skims we are all going to be left with thin heads.

[olidaviesuk]

Thicker head gaskets are nothing new mate, rover supplied a head gasket and spacer for years for the k series... A more pikey way of doing things is to use two headgaskets... Although some peeps have done that and had years of trouble free 5 turboing....


so general oponion is its on the thin side, hmm....

yer i have read about modding the squish area but then it changes shape of cylinder area so this could also have a effect i have read. Its all so confussing

interesting to here cgb where doing a 2.5mm hg, i will give them a call and see what they come up with.

So im guessing renault dont supply these heads anymore... So in a few years to come when we have all had a few skims we are all going to be left with thin heads.

[gttjames]

yer im aware of the k series engine just as far as i was aware there was only standard gasket 1.3mm or whatever it was and uprated mellior 1:7mm lr whatever it was. Didnt know there was thicker available

[gttjames]

just spotted this on cgb website - like thought my head is to thin and only really ok for oe/low boost. I really need to source another head then, is the cgb one a fair price if i get the 73mm+ head. By the time iv sourced a head and had it cleaned it could even need new valves etc so this looks ok really?

http://www.cgbmotorsport.net/cylinder-head-refurbished-938-p.asp

[Nottswoody]

One thing Iv learnt the hard way is what's it worth to you not to be sat without the five.. I would pay it.. Seems a fair price like you said by the time you messed around sourcing then sorting it will cost you that anyway.. My new rule do things properly.. If mine blows it's what I'm buyingnext. Plus you get a warranty?

[gttjames]

I agree, just rtying to work out if i can use a head as thin as 72.64 before i pay the money to have it presssure tested

[Nottswoody]

For that answer you will have to wait for better knowledge guys than me as I haven't got a scoobies matey.. Someone will answer mines 72.9 now so I will be watching as I want 18-20psi out of mine.. Not sure about this advancing the timining thing thoe.. But I will do what needs to be done as the 5s here to stay for good :)