All sorted head on its way
Thanks ash. i may just give you a call when this head arrives. strongly considering the larger valves while its off the car. And thanks mark :)
Head arrived safe and sound today. cheers
For what it's worth, I've been doing a bit of research into valve sizing for these heads lately, as I'm part way through doing up two 531 heads at the moment, one for myself and one for another forum member.
I won't go into details or reasoning here/for now as I'd be writing a massive post, but I've decided to go along the following route for my head, which will be for a turbo application:
Intake: Stock valves, smoothing of the sharp edges where the port transitions into the bowl, not much metal needs to be removed here at all.
Exhaust: 38mm valves, new seats with 33.4mm ID, which is 2.4mm bigger than the stock seats. Ports smoothed and matched to the new seats.
Combustion chamber: Edge of chamber around the exhaust valve "deshrouded" as much as possible, in my case only about 1-1.5mm of metal could be removed, as the gasket fire ring sits very close to the edge of the chamber.
A good "rule of thumb" for good two valve per cylinder head design is to make the exhaust port about 75% of the size of the intake port. This is what Volvo have done with the redblock heads, stock they have an exhaust port that's 77.5% of the size of the intake.
There are heaps of factors that come into play, but put simply, if you deviate too far from that sizing, you can reduce efficiency of the design in a number of ways. Particularly, if you go too large on the exhaust port, you may increase flow, but reduce velocity, and both are important for getting the exhaust out of the engine efficiently.
The shape of the exhaust port is also very important, so if you go for too big of an exhaust seat, you end up having to remove a lot of metal to transition the bigger seat into the bowl and port, and you change the shape away from the ideal shape required for flow.
My 33.4mm seats are 83.25% the size of the (stock) intake seats, this is about as far as I'd like to push it on a turbo application, before risking too big of a reduction in velocity.
In a mild NA application, I'd recommend sticking to the stock exhaust seat size, but going to bigger valves can still have advantages, as it allows the seats to be re-cut with different angles, to improve the flow past the seat itself.
I bought some RSI valves in 2008 which turned out to be incorrectly manufactured to an incorrect length, making them unusable without major work. I've more recently ordered some well priced, high quality valves from DVS to use instead.
Thats very comprehensive Angus. i appreciate it. As to the specs of the head itself im not too sure about the de-shrouding of the combustion chamber or the size of the valve seats. the exhaust port does have some obvious signs of being machined to improve the exhaust flow straight out of the valve.
I was planning on speaking to my mechanic friend in regards to what else to get done to this head as i have already dropped off the larger bottom end to get cleaned up for this new head :) How much were larger exhaust valves from DVS?
The valves are about $40 each, but are good quality, postage is much cheaper than from overseas suppliers, and you shouldn't have to wait as long as you would when getting parts from overseas.
When choosing valve size, it istheo important to consider camshaft duration and lift.
Volvo used to have different spec (with different part numbers) valve springs which were used across various models and engine configurations, these have all since been superseded by a single part number with a new design which also requires new upper and lower retainers.
The new spring is very robust and suitable for most applications.
If the engine sees constant high rpm usage, and stronger or double valve spring is likely a better option though.
fair call, i can see the value in that. would you be willing to give me a quote on the double springs and 38mm exhaust valves? also its a VX3 cam if that helps at all?
Why a vx3 cam assuming turbo setup?
most certainly is. which reminds me, i should look at a new manifold and turbo to get the most out of it
Ported 90+ is fine
15G is good to 180+ KW at wheels
new style billet 19t is good for 220KW at wheels
Doubble springs are complete overkill unless you want to take it above 6500 on a daily basis
Also when you start looking at some of the stuff being proposed in this thread... LSx conversion is going to deliver more reliable power for less investment
Just for refrence...
The 531 head sitting on my dinning room table...
I'm at about $800 into it for
Clean + skim + beadblast
38mm EX valves, seats machined to accept (Paid $13 per valve)
intake port work
Exhaust ports polished,
Deshroud of valves
New non VW beetle behive springs (some random ford application iirc) sourced from KG 3 years ago and sitting in a drawer until now
RSI Stage 2 Turbo Cam
I have no idea if I will ever use the head... but it is pretty...
Barwick10;36526 wrotefair call, i can see the value in that. would you be willing to give me a quote on the double springs and 38mm exhaust valves? also its a VX3 cam if that helps at all?
VX and VX3 aren't 'real' performance camshafts, though they are better than some of the other standard volvo options. 38mm exhaust valves will be fine with the VX3 though.