531 - porting, valve sizes, springs, what have people done?

[Mertz]

I've got a HX35 with a 10cm twinscroll housing I'm looking to support with some better breathing on a 531 head. These will then be going on the rebuilt bottom end with rods, pistons etc... Power goals, I don't really have a figure in mind other than a good fun car that will see fast road and 3 or 4 trackdays a year.

1) Valves I see 46mm Intake and 38mm Exhaust are popular as they can be reground into stock seats. Has anyone opted for anything different? If so, why?

2) Deshrouding the exhaust ports into the head seems wise for better flow, although not much looks like it can come out before you hit the Head gasket ring and the bigger the exhaust valve you go to, the less relative space to deshroud... There is an optimal size exhaust valve vs deshrouding thing to work out...?

3) Porting I understand there isn't much to be gained on the exhaust side other than smoothing out the short side radius a bit? Is it worth doing anymore than removing some casting marks and a light tidy up of the intake if you can't get the exhaust gas out at the same rate as the intake is flowing? I've seen 80% of intake flow as exhaust flow as a figure to shoot for?

4) Springs I'm thinking some stiffer single springs to keep the valve train weight down and I'm unsure if double are really necessary?

5) Parts sourcing Where would people recommend? I'm after good quality, durable parts. Not looking to spend money for the sake of it but equally, buy cheap and buy twice as they say! Don't mind importing from Sweden or wherever etc..

If anyone has any feedback on any of the above, I'd be grateful for your 2p.

[grumpydad]

Hi
try posting hear https://turbobricks.com/index.php

or go 16 valve head iI have ine if you want

[classicswede]

Valve size exhaust 37/38 is about the ideal size. For turbo I would stay with the 46mm intake but with na move upto 48mm.

Deshrouding as much as you can without hitting the edge of the head gasket

Porting the majority of the work is around where the valve stem comes through and the valve seat is where you will see the biggest gains. The rest of the port wants nothing more than a light clean

Valve springs. The choice is going to come down to the cam and rpm limit. Has this been decided yet?

Parts I stock a range of the bits you are likely to need

[Mertz]

Originally Posted by classicswede

Valve size exhaust 37/38 is about the ideal size. For turbo I would stay with the 46mm intake but with na move upto 48mm.

Deshrouding as much as you can without hitting the edge of the head gasket

Porting the majority of the work is around where the valve stem comes through and the valve seat is where you will see the biggest gains. The rest of the port wants nothing more than a light clean

Valve springs. The choice is going to come down to the cam and rpm limit. Has this been decided yet?

Parts I stock a range of the bits you are likely to need

Appreciate the detailed reply. Thanks, Classic Swede! Just had a look over the valves on your site too.

Cam wise and RPM limit, I'm unsure what would really suit the HX35 best. It'll have some lag that's fine. I'm slightly biased towards a "semi streetable" level of power over an all out peaky max HP narrow type powerband whilst appreciating even on a Kangaroo manifold, a HX35 10cm isn't a TD04 for spool speed. Hope that makes sense... What would you recommend?

EDIT: would be on standalone ECU, plenum intake etc... already on 3" exhaust and will have downpipe changed from TD04 to HX35 etc...

[360beast]

Originally Posted by Mertz

Appreciate the detailed reply. Thanks, Classic Swede! Just had a look over the valves on your site too.

Cam wise and RPM limit, I'm unsure what would really suit the HX35 best. It'll have some lag that's fine. I'm slightly biased towards a "semi streetable" level of power over an all out peaky max HP narrow type powerband whilst appreciating even on a Kangaroo manifold, a HX35 10cm isn't a TD04 for spool speed. Hope that makes sense... What would you recommend?

EDIT: would be on standalone ECU, plenum intake etc... already on 3" exhaust and will have downpipe changed from TD04 to HX35 etc...

A mate of mine has a 16V turbo 940 running around 600hp and he has a HX35, he said it is boosting 5psi at 2500rom and builds very quickly after that.

[Mertz]

Originally Posted by 360beast

A mate of mine has a 16V turbo 940 running around 600hp and he has a HX35, he said it is boosting 5psi at 2500rom and builds very quickly after that.

Interesting, thanks. I guess 3.5k rpm for a 8v then.

Be Interesting to see some dyno graphs of other people's setup.

[classicswede]

Originally Posted by Mertz

Appreciate the detailed reply. Thanks, Classic Swede! Just had a look over the valves on your site too.

Cam wise and RPM limit, I'm unsure what would really suit the HX35 best. It'll have some lag that's fine. I'm slightly biased towards a "semi streetable" level of power over an all out peaky max HP narrow type powerband whilst appreciating even on a Kangaroo manifold, a HX35 10cm isn't a TD04 for spool speed. Hope that makes sense... What would you recommend?

EDIT: would be on standalone ECU, plenum intake etc... already on 3" exhaust and will have downpipe changed from TD04 to HX35 etc...

Cam wise something like the T3 would probably suite best. T25 might be a bit on the mild side and T4 could be one to consider. It has a little less low down but with the bigger turbo that might work out ok as the engine flow is better.

[Mertz]

Originally Posted by classicswede

Cam wise something like the T3 would probably suite best. T25 might be a bit on the mild side and T4 could be one to consider. It has a little less low down but with the bigger turbo that might work out ok as the engine flow is better.

Cheers. Appreciate that.

I'll start with a T3 and see how i get on with that. Won't be built until summer realistically.