How many BHP is a three angle valve job worth?
Discussion
Surprisingly it’s only £75 per head to have done, my case of while it’s apartitus is getting worse 
Are there any differences between the 4.2 & 4.5 heads, just I noticed mine had 4.5 stamped into them. I guess it’s maybe just to identify the engine rather than the heads with the block saying 42.... GT
What I did notice was the combustion chambers are clearly the same as the 4.2’s as their cut outs in the head are the same size as the 4.2 cylinders (the 4.2 head gasket matches). That means there is spare metal there to cut away to de-shroud the inlet valve. BUT seeing as the pistons domed tops are nicely matched to the heads shape, I guess it could have some rather detrimental effects on the squish area, so I think I’ll leave that one.
But back to my actual question, is it worth £150 for a three angle job? Or more to the point any reason not to
Are there any differences between the 4.2 & 4.5 heads, just I noticed mine had 4.5 stamped into them. I guess it’s maybe just to identify the engine rather than the heads with the block saying 42.... GT
What I did notice was the combustion chambers are clearly the same as the 4.2’s as their cut outs in the head are the same size as the 4.2 cylinders (the 4.2 head gasket matches). That means there is spare metal there to cut away to de-shroud the inlet valve. BUT seeing as the pistons domed tops are nicely matched to the heads shape, I guess it could have some rather detrimental effects on the squish area, so I think I’ll leave that one.
But back to my actual question, is it worth £150 for a three angle job? Or more to the point any reason not to
Edited by Luckyone on Friday 21st June 17:17
I had my heads flowed ported and de-shrouded by a specialist and 3 angle valve seats cut. It was checked on a flow bench before and after the work. There was a 7% increase in flow on the inlet port and a 28% increase in flow on the exhaust port.
On a high power V8 engine the guy recons 3angle valve seats can be worth up to 20bhp. A few of the more specialist companies offering this service have an even more complex machine and valve profile that can be worth even more power. best place is google it.
On a high power V8 engine the guy recons 3angle valve seats can be worth up to 20bhp. A few of the more specialist companies offering this service have an even more complex machine and valve profile that can be worth even more power. best place is google it.
a1rak said:
I had my heads flowed ported and de-shrouded by a specialist and 3 angle valve seats cut. It was checked on a flow bench before and after the work. There was a 7% increase in flow on the inlet port and a 28% increase in flow on the exhaust port.
On a high power V8 engine the guy recons 3angle valve seats can be worth up to 20bhp. A few of the more specialist companies offering this service have an even more complex machine and valve profile that can be worth even more power. best place is google it.
Ah thanks, that’s very interesting. Did you have that done before you fitted the ‘charger? Or was it part of the same job? Or to put it another way did do it in a way you could feel / measure the power difference?On a high power V8 engine the guy recons 3angle valve seats can be worth up to 20bhp. A few of the more specialist companies offering this service have an even more complex machine and valve profile that can be worth even more power. best place is google it.
Did your specialist say anything about de-shrouding with domed type pistons? I’m by no means any kind of authority but going by what I’ve read it’s better with flat tops.
My heads are with Powers Performance right now so £150 for a possible 20BHP? Seems rude not to really
ukkid35 said:
How much is this going to affect intake valve shim clearances?
That’s a good question, it shouldn’t have any effect as it’s not the sealing surface they cut away, but I’ll check with Dom. I’ve gone for a new set of inlet valves, so I should be starting again with the big shims I hope! (The heads are away as the exhaust guides were badly burned & needed replacing)Luckyone said:
Ah thanks, that’s very interesting. Did you have that done before you fitted the ‘charger? Or was it part of the same job? Or to put it another way did do it in a way you could feel / measure the power difference?
Did your specialist say anything about de-shrouding with domed type pistons? I’m by no means any kind of authority but going by what I’ve read it’s better with flat tops.
My heads are with Powers Performance right now so £150 for a possible 20BHP? Seems rude not to really
You say you are going for domed pistons, now i'm no expert but I would have thought the piston crown needed to match the combustion chamber shape, that's what the original pistons did. How does a domed piston work with the AJP combustion chamber?Did your specialist say anything about de-shrouding with domed type pistons? I’m by no means any kind of authority but going by what I’ve read it’s better with flat tops.
My heads are with Powers Performance right now so £150 for a possible 20BHP? Seems rude not to really
anyone enlighten me.
a1rak said:
You say you are going for domed pistons, now i'm no expert but I would have thought the piston crown needed to match the combustion chamber shape, that's what the original pistons did. How does a domed piston work with the AJP combustion chamber?
anyone enlighten me.
No sorry I wasn’t very clear there, I’m not changing the pistons, I just said ‘domed type’ to save going over what I’d put at the top again which was anyone enlighten me.
Luckyone said:
seeing as the pistons domed tops are nicely matched to the heads shape, I guess it could have some rather detrimental effects on the squish area, so I think I’ll leave that one.
Calling the AJP pistons domed is wrong, but I just couldn’t think of a better way!
As we both said the pistons are matched to the combustion chamber shape, looking like this:
Only reading the tuning books it seems the best kind of piston for the canted bath tub type combustion chamber is a flat top, as that concentrates the mixture up towards the spark plug as it’s compressed, using shaped / domed pistons apparently negates this advantage. The problem with the canted bath tub type combustion chamber is that you can’t get a high CR with out using domed pistons. Those are the only facts I have, going from them I assume (& could well be wrong) that TVR had to make the cut outs in the in the heads for the valves, so had to raise as much of what was left possible to bring the CR back up, that I don’t think is too much of an assumption!
But this really is guess work on my part – I assume that nice little cut out at the bottom of the spark plug not only makes room for the spark plug but also creates a pocket for the mixture / squish to concentrate right under the spark plug. By going & cutting away the side of the cylinder heads combustion chamber next to the inlet valve to de-shrouded it you are creating a different pocket away from the spark plug, that may well end up having adverse effects on the flame front as it progresses.
The only way to tell for sure is to do back to back testing, but I’m not sure there are that many AJP heads about to go cutting up! So you may well have an advantage there with your de-shrouded inlets, I’ve no doubt they flow more, but I think I’ll leave it to be on the safe (& lazy!) side.
Gray_101 said:
I ll watch this thread with interest ... As I'm pulling my engine in October for some more head work .
Keep an eye on my rebuild thread the other inlet mods are there & I’ll more likely put updates there too. 
Just in case anyone was interested I didn't go for three a angled job in the end.
When I spoke to Dom (Powers Performance / TVR Power) again he said he really wouldn't recommend it for road cars, much better to have a good big seal on the 45deg face. Also the standard seats are too soft to cut for three angles so they'd all need changing too. He also added as the standard valves are so big there is much less to be gained on the AJP from it (unless your going for an all out race engine). If your looking for power gains you'd be much better with a head skim.
Mine didn't need a skim, I'll save that for the next rebuild!
When I spoke to Dom (Powers Performance / TVR Power) again he said he really wouldn't recommend it for road cars, much better to have a good big seal on the 45deg face. Also the standard seats are too soft to cut for three angles so they'd all need changing too. He also added as the standard valves are so big there is much less to be gained on the AJP from it (unless your going for an all out race engine). If your looking for power gains you'd be much better with a head skim.
Mine didn't need a skim, I'll save that for the next rebuild!
I wonder whether a slightly smaller inlet valve would actually increase power on the AJP. The 4.7 conversion increases capacity by less than 5% but yields ~15% more power. This is mostly attributed to de-shrouding of the valves afaik. I'm only thinking of a slight reduction, eg 2mm in diameter.
I would say that balancing all the reciprocating parts is probably the easiest way to find power in the AJP, it's not very good as standard. There is lost power waiting to be had whilst reducing stress on the engine so a win win. Make sure the combustion chambers are balanced as again this is a problem area.
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