Discussion
Cams currently give 13.5mm lift.. Which is where it starts to plateau for flow.. 13-15mm only gives an extra 2cfm @10" head. If you take the valve out you gain 20cfm.
I have been told the back of the valve is too flat and a poor design for higher lift.. So trying to see if it would be worth finding some new valves with a better shape or back cutting the current ones..
I have been told the back of the valve is too flat and a poor design for higher lift.. So trying to see if it would be worth finding some new valves with a better shape or back cutting the current ones..
Edited by Jhonno on Saturday 14th July 11:44
Mignon said:
I bet that flow specialist guy Pumaracing would have known the answers but some knob end banned him.
Yeah big shame he isn't still about... I've really enjoyed reading many of the threads he has been involved in! Massively informative and interesting. It is probably his fault I am being so anal about this though..
Edited by Jhonno on Saturday 14th July 11:45
So, it was originally quite a generic question, as I thought there might be a fairly generic answer, but as always with engines, it isn't necessarily so..
The engine is a high revving flat plane V8, 4474cc, 2v heads, making ~90-100bhp/L.. I've done the maths (based on one of Pumaracing's old threads) and IMO the ports and the valves are fairly well matched in size, the ports have been flowed not enlarged. Ports are 39mm, valves are 45mm. A good factory engine is 400-420bhp.
Here are the flow figures before and after @10"
The engine is a high revving flat plane V8, 4474cc, 2v heads, making ~90-100bhp/L.. I've done the maths (based on one of Pumaracing's old threads) and IMO the ports and the valves are fairly well matched in size, the ports have been flowed not enlarged. Ports are 39mm, valves are 45mm. A good factory engine is 400-420bhp.
Here are the flow figures before and after @10"
stevieturbo said:
A very open ended question...and the only answer is for you to test on your setup, with whatever valve diameter and head setup you have, at the lifts you intend to use.
As for the back of the valve being too flat ?
Have you looked at many competition style inlet valves ? They're almost all quite flat on the back.
I was intending to used 13.5-14mm lift, with some extra duration.. As for the back of the valve being too flat ?
Have you looked at many competition style inlet valves ? They're almost all quite flat on the back.
I can only go by what the head shop says, and I am paying him for his knowledge. He looked at the heads and one of his first comments was the poor shape of the back of the valve for higher lift.
227bhp said:
As you infer you can then go on to spec your cam from this. I see a lot of ex cams which lift to 12mm or so when the port stopped flowing at 9 - 10mm, it isn't just a waste, it's often a power loss and for more than one reason.
Going back to this, looking at my flow figures.. I take it that even adding 0.5mm of lift won't benefit the engine? Maybe just some extra duration instead?Kccv23highliftcam said:
How did the engine run before though, was it tractable and driveable?? Adding bits of cam timing here and there could end up being more trouble that it's worth in the long run...
It was OK.. These engines often seem to run out of puff a bit at the top end, would be good to get it to hold on another 500rpm or so. Same as most OEM spec'd engines tbh. I don't think adding a bit of duration would ruin it. I'd rather do it now when the engine is in bits. Going by what I have seen, something around 280 duration would make a decent "fast road" spec.. 
Mignon said:
That's about as shrouded as you can get. Hardly surprising it flows better without a valve in the hole.
To be slightly fair to him, I may have misunderstood and he hadn't even looked at the chambers at that point.. It was conversation as I dropped the heads off. So not much can be done about it, without major (£££) surgery..
Mignon said:
If you put a tulip valve in there it would direct more air sideways to the shrouded bit and make flow even worse. In this situation you want the air to skip across the shortside into the open part of the chamber. It's pretty clear whoever you are paying knows sod all about port flow, chamber shapes and valve shapes. Now I've explained it to you I guess it seems pretty obvious but that's the thing about knowledge. It always looks easy after the event. But it takes many years to get it in the first place.
Yes it all makes sense.. So in conclusion. I've got to live with it.. The valve suits the setup, but is badly shrouded.
stevieturbo said:
Flow is barely increasing after 13mm...almost begs the question if it is worth pushing lift further.
Presumably this will be a custom camshaft or something or are people already using this ? And your springs etc can accommodate the lift you intend to use ?
Is there any room/bore diameter to reduce shrouding ?
This is what I mean.. Is it worth it?! Doesn't seem so really. It would be a custom profile cam, I am speaking to the cam people tomorrow.. I've put higher rate springs in to allow me to run a "bigger" cam.. Presumably this will be a custom camshaft or something or are people already using this ? And your springs etc can accommodate the lift you intend to use ?
Is there any room/bore diameter to reduce shrouding ?
I've gone up to 91mm bore from 88mm so there is 1.5mm available
Maybe a bit more, I'd need to offer the new HG up.. There won't be loads though.Max_Torque said:
Looking at the graph on P1, something happens at 8mm of lift and significantly reduces flow until 13mm of lift. Suggests a seperation that squashes flow. If you could trim that out i reckon there's 10% more flow at the same lift.......
Would it be something obvious..? Stupid question? 
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