mgbloke wrote:I must admit I know nothing about flow dynamics.
Correct me if I am wrong and this might seem stupid but surely the importance is the amount that the valve, seat, port, runner etc etc can flow as a whole. The amount of time that a valve spends at low lift is small.
What matters is how much air can get past the valve through its complete opening and closing sequence.
The Merlin heads seem to perform better than the flow suggests! are there other factors that need to be considered?
Mark
Hi
on anything but a full race flat tappet cam the valve spends the greater part of it's time at mid to low lift it is why for most heads on road cars the .5" and .6" are pretty irrelevant. Only on very fast road roller cams and street strip roller cams do the higher lift figures become relevant. There are very many things that result in better performance from a head other than just crude flow numbers things like mixture quality and where the flow arrives in the cylinder, this is especially the case in a rover where the standard heads have such poor chamber shape. The merlins have a much better fast burn chamber shape that will contribute to the output.
best regards
Mike
The flow should rise very quickly. Lets take a head that flows a maximum of 200CFM like TA. The lower the lift at which that number is reached, the better the port design is. If maximum flow is reached at .500" lift the head will produce a better power curve than if the valve must be opened to say .700" lift or more to get the good flow.
And if the flow continues to increase much above you maximum lift the port volume is too big and the port is maybe poorly designed and will therefore have a lower velocity and poor power output.
mgbloke: Do you remember witch valve lift you measure those 174cfm readings? 0.7"?
Sadly triumph rover spares are deleted those flow figures on their web site..
They made similar flow at .55 and .6 just a few cfm difference if I remember.
One thing that may have had an influence is that the flow bench was set up for Rover heads where the valves are virtually at right angles. The valves were opened by turning a threaded bolt that pushed the valve stem and measured with a vernier. The Merlins and TA heads have the valves at quite an angle which made the adjustment much more difficult. I didn't do the tests myself but was present at the time.
i was thinking of using a 248 cam with 533 thou of lift. If I can get the CR to about 11 it should work well.
There is also a school of thought that suggests the low lift flow is critical to the ultimate flow potential of the port. The gas has a mass and the sooner it can be got moving the more momentum it has at the higher lifts, and the better the cylinder fill. If the initial flow is prevented at the point where maximum vacuum is available in the chamber, the rest of the inlet process is compromised.
Get the gas moving as quickly as possible for full valve duration, when the valve closes the gas mass flow then creates a pressure behind the back of the valve. This pressure is available when the valve opens at the same time as the port is being scavenged giving a large pressure differential.
Some porters are flowing low lifts at larger differentials 60 to100" to simulate the turbulence and test seat shapes to capitalise on this.
Rover head inlet and exhausts respond very well to radius seat shapes.
On the seat development it is good to measure and draw up in a large scale to better understand what is likely to be happening.
It will be interesting to see how these heads actually perform.
Not going to port them at all.
Although the low lift flow was down it was obvious to me that these heads are in a different league to the others.
What is the current seat configuration on the TA heads? On my stage 4 rover heads the throats were blended etc but I re-cut the setas to a proper 3 angle configuration and then gave each of the valves a quick lap. I looked at the contact patch of the valve and just after the inside contact circumference I put a 30 degree back cut on the valves (my mate has a new machine that does this brilliantly!). On my floating pressure bench (no absolute figures available sorry:-() It made a significant difference! On our rover cams which even in all but the most aggressive guise the area under the curve for flow where the seat is the dependant factor on flow (i thnk its up to about 20% of valve diameter - If i am wrong please correct me - I am a learner) is more significant then the higher lift which are port dependant. I think only in the trully agressive roller cams (NASCAR) the importance of seat flow deminishes - and they then employ a steeper seat (30 degrees) to aid in high lift flow at the expenser of low lift.
Its like a well known tuning porting author said - saying you have too much low lift flow is like saying you have too much money!
Hi
for an ideal port that has a pretty much straight shot at the back of the valve (lotus cortina/ Kawasaki 550 8 valve/ mopar hemi as three examples I know of) then the ideal valve lift is 1/4 valve diameter. However that varies on heads with ports that are less than ideal. When you add a push rod pinch and a 90 degree turn in the port then this will reduce the ideal valve diameter to something more like the .2 times conversely valve shrouding by the cylinder wall can increase this back up again, in a head like an SB2 chevy nascar head where the whole port flow is biased to one side of the port and valve then the ideal valve lift is more like .28 to .3. The other thing is that a valve size that works well at low lift does not necessarily work well at high lift, this is strongly related to what Timo and Darkspeed are saying about initial flow and over sized ports and the change in charge velocity as the valve opens.
best regards
Mike
Hi, I have had to do some serious suspension modifications before I fit the new engine and heads which have taken for ever. I have changed from composite leaf springs to a 4 link with coilovers and a mumford linkage.
To cut a long story short The axle tubes have bent when I welded on all the bracketry which has made the diff bearings wear quickly and my quaife now needs a service. Axle tubes are now straight so just waiting for the quaife to come back.
I have done just one trackday and the new rear end is a huge improvement when putting power down while cornering.
My merlin heads have been repaired by real Steel so I will be using the existing power plant until October.
I have a new V8 Developments 5.0L short engine in my garage and am slowly collecting everything.
Spec is.
5.0L 96mm bore, forged pistons H beam rods.
CR 11:1
Mechanical 248 cam (533 lift)
TA heads with really nice quality shaft mounted roller rockers (make the yella terras look rubbish)
45mm throttle bodies on ported JE manifold ( may need 48mm bodies )
Exhaust is bespoke by maniflow with merge collectors and 1 3/4" primaries
Controlled by a Canems ECU.
On paper it should be quite a nice engine, not too peaky I hope.
Pushrods would have been extra. Not sure about length until I do a trial build. Will get pushrods from Smith brothers in usa once I have determined the length. I am using their pushrods in my present engine, nice quality.
Hi
45s will feed a 480 bhp 383 chevy small block very well, look at the one built by Vizard's daughter some years ago, it ran 45s. I wouldn't bother going up over the 45's the engine will not pull enough revs to make them a limiting factor. If you have to spend more money on it add a roller tappet cam set up.
best regards
Mike
