Merlin Heads

mgbloke · Post by **mgbloke** » Thu Aug 06, 2009 3:53 pm

Hows this?

[
IMG]http://i76.photobucket.com/albums/j30/V ... ads005.jpg[/IMG]

mgbloke · Post by **mgbloke** » Thu Aug 06, 2009 3:55 pm

One more of exhaust port.

CastleMGBV8 · Post by **CastleMGBV8** » Thu Aug 06, 2009 11:28 pm

Mark,

Very nice.

Thanks for posting the pics. some interesting design features, wonder why the inlet port entrance is no longer rectangular and what that little upward facing divider does.

The chambers seem to owe something to a certain Mr Harry Weslake and look remarkably like full race MGB heads, and they can get 100 BHP per litre out of those with only 2 siamesed inlet and three exhaust ports

There also seems like there is scope for further porting if required.

Kevin.

kiwicar · Post by **kiwicar** » Fri Aug 07, 2009 10:57 am

The devider in the inlet port keeps the inlet flow stable as it turns the short radius and directs it to the centre of the chamber as it passes the back of the valve. Mr Vizard did an atricle on 2 valve pushrod head design a while ago in PPC, it explaines the theory in there.
D shaped exhaust ports offer less surface area compared to port sectional ares at the top of the port where the exhaust gasses are traveling rapidly, while reducing flow reversal at the bottom of the port where the flow tends to be very turbulant (if the bottom of the port is round you cant put a step in the exhaust tract where the manifold face is)
Best regards
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Fri Aug 07, 2009 5:50 pm

Mike,

Understand the divider in the inlet but was unclear as to the reason for the shape of the bottom of inlet port not being a full rectangle as in normal Rover or other heads.

Kevin.

Darkspeed · Post by **Darkspeed** » Sat Aug 08, 2009 6:42 am

Are there any published flow figures for these heads?

I would also like to know the theory behind the non rectangular inlet port - and the partial block of any inlet manifold this would involve.

What are the key dimensions of the Inlet port -

Throat diameter

Manifold face port H&W

Andrew

mgbloke · Post by **mgbloke** » Sat Aug 08, 2009 5:00 pm

The shape of the inlet ports is very interesting, having one lower corner filled in. I cant see any reason for this but I would think it is like that for a reason. It could be ground out to make them symetrical but im going to leave as it is.
Inlet overall sizes are 25mm wide x 44mm high and exhhaust 26mm wide x 33mm high
The shape of the runners looks to be very precise.

When I finally get them fitted I will have a rolling road session to see if they are any good. I see RPI managed over 300bhp with one of their 4.6 engines so with my higher compression and a hotter cam maybe I could expect 310bhp? ( currently making 293).

Cheers
Mark

dnb · Post by **dnb** » Sat Aug 08, 2009 9:28 pm

I keep thinking about these... They look very impressive, but I wonder how they compare to TVR 5 litre big valve heads? Are they enough of an improvement to justify the cost?

(I could then use the 5 litre heads on my Range Rover...)

Robrover · Post by **Robrover** » Mon Aug 10, 2009 8:39 am

Do you know what the flow rates are? And how much hp that cfm will potentially support?

Be interested to see how these rates compare with TVR, Stage 4 and full race Buick 300 heads.

mgbloke · Post by **mgbloke** » Mon Aug 10, 2009 9:41 am

Sorry I have no information on flow rates.
Valve sizes are approx 44mm & 36mm how does this compare to stage 4 TVR heads?

minorv8 · Post by **minorv8** » Mon Aug 10, 2009 10:25 am

To my BIG surprise my set of heads are ready to be sent: looks like I´ll be doing some wrenching next winter.

mgbloke, are you going to do something to the intake ports because of the funny corner in the head ?

I asked about the head bolts/studs when I called RS and they list the specific hardware in their cataloque. I currently have the ARP studs and would like to use them with Merlins as well but probably have to source them from somewhere. Maybe SBC / SBF might have ones with correct length ?

spend · Post by **spend** » Mon Aug 10, 2009 12:12 pm

mgbloke wrote:Valve sizes are approx 44mm & 36mm how does this compare to stage 4 TVR heads?

43/38mm

But it may still possible to fit larger, IIRC there were rumours of race engines fitted with 1.75/1.566" valves (5/16" stems)

Many people suggest that the larger exhaust ratio is only useful for forced induction engines, but I suspect it works particularly well in the TVR NA engines - probably very dependent on the porting / manifolds?

kiwicar · Post by **kiwicar** » Mon Aug 10, 2009 1:01 pm

Hi
I would be very carefull about not removing material from the head at that corner, they will have put the material there to ensure there is no stagnsatoin of flow on that side of the port and to make the air flow around the valve in the most efficient way. They probably have a recomended way of flowing the inlet manifold to match (you may be advised to make a similar fillet in epoxy to matac the heads to the manifold.
I am very suprised there seem to be no published flow figures on these heads, bit like selling snake oil without the data to back them up.
Mike

mgbloke · Post by **mgbloke** » Mon Aug 10, 2009 1:02 pm

Minorv8
Not sure what to do with the odd shape inlets, think ill try them as they are for now.
Please can you let me know if you find any studs that fit. Unlike the rover heads you will need 5 long and 5 short per side.

I phoned Real Steel today and was told that sadly John had been taken ill and passed away Thursday night. As a result RS was closed Friday.
My best wishes go to his family.

Cheers
Mark

CastleMGBV8 · Post by **CastleMGBV8** » Mon Aug 10, 2009 5:30 pm

Mark,

That is sad news, John has been most helpful to me over the course of the last 6 years or so.

Kevin.