Merlin Heads

[kiwicar]

What is being said (and certainly what I keep saying) is that you need to consider a combination of parts, nothing in an engine works in isolation. if you put on heads that give you more flow above .45" valve lift but to do so sacrifices flow below .25" lift and fit a short period cam that maxes out at .4" lift it will probably make less power than non ported heads, if on the otherhand you fit a long period roller cam that maxes out at .5" lift then it will be of benifit.
No one component makes an engine a race engine or a docile shopping car, it is a combination of parts working together, that is why it is called tuning an engine, you are getting the components to work together as one.
Best regards
Mike

[kokkolanpoika]

I always say that head flow figures dont tell you anythink..

My friend Ford 2.0 OHC with home ported head flow somethink like 150hp, and engine capacity is 2.2litre, it will produse 248hp at flywheel..
When he but heads whits are ported in flow benc, they will flow lot of better, say 200hp. But with same parts, and he also change cam + etc it will produse allways approx 20hp less. We always wonder how this is bossible, Our 2 flow benc guru is also amazing.. They cant explain how this is possible..

[CastleMGBV8]

What is being said (and certainly what I keep saying) is that you need to consider a combination of parts, nothing in an engine works in isolation. if you put on heads that give you more flow above .45" valve lift but to do so sacrifices flow below .25" lift and fit a short period cam that maxes out at .4" lift it will probably make less power than non ported heads, if on the otherhand you fit a long period roller cam that maxes out at .5" lift then it will be of benifit.
No one component makes an engine a race engine or a docile shopping car, it is a combination of parts working together, that is why it is called tuning an engine, you are getting the components to work together as one.
Best regards
Mike

Mike,

I completely agree with you, throwing a load of mismatched performance parts into and onto an engine is a recipe for disaster in performance terms.

What iimpresses me re the Merlin heads is that even with a pretty wild cam the engine has a very strong and almost flat torque curve over a wide rev range and for a road car this would provide very good performance and drivability.

Real Steel do not suggest that Merlins are race heads and as road performance heads they would appear to do a very good job at a very fair price.

It is very easy to get transfixed by flow numbers which would reflect potential peak power, but says nothing for the flow characteristics across a much broader rev range and the usability of an engine in general.

Timo's latest post above about an engine with increased head flow producing less power would appear to further prove the point.

I am not in any way critizising adams (Darkspeed) work with his flow bench which I think is commendable and very informative, even more so now that Peter Burgess, renowned head guru has joined the discussion.

Kevin.

[kiwicar]

all hail Kevin
everything you said mate! I was beginning to think every one was missing the point
Best regards
Mike

[HairbearTE]

The TVR 500 heads have full size guides, and there are other significant areas that can be improved. Dom, V8D and Jamie all do it slightly differently as well from what I've seen. By your definition then would you class all those modified heads as stage 5! or is it just UBV must be stage 4 - back to my original point.

With the advent of better efi and ignition control many of us have started to use race cams and I suppose what you would call race heads - TB's allow even more radical things to be done. We've not even started to consider the 1.75/1.55" valved variants..

As I said above I don't like to describe any heads as "stage" anything. There are a series of popular mods that are included on rover heads that people associate with a certain "stage". Can you imagine seeing a pair of "stage 3" SBC heads on ebay? It'll never happen. Likewise a head that could be used on one race engine could equally be used on another street engine. In the rover Market I guess you could legitimately refer to a fully ported Wildcat as a race head but that's about it. I'm building Buick300 heads with Ti valves (1.73/1.55) and I'm welding up the chambers to get some good CR with my large overlap cam. Do I consider them race heads? No.

so what you are saying is that some heads that work well on a race engines will have no posotives on a fast road street engine?

No i'm not. As the words:
"Likewise a head that could be used on one race engine could equally be used on another street engine." from my post that you have quoted would appear to bear out.

[Darkspeed]

Here's a thought for flow figures and the conversations that for road engines flow isn't everything

5 port heads on average saloon cars. - 2.0L mundano towing cars that have heads capable of over 100BHP/Litre performance with a cam change and re-map. 16 valve Diesels... they only rev to 5K!!

The heads ability to flow air is everything, it is all important (Slightly tongue in cheek but not much). Without the ability to flow air your combustion chambers superb ability to burn the charge effectively and make the power is waisted. A great cam is just a lumpy stick if the head wont flow. That 8 port induction equipment is just bling unless the head can make use of it.

If designed as a ROAD engine today our V8 would have 16 valves rev to 8000RPM and produce 100BHP/litre -and thats all about flow.......

The Merlin head is good but its not great and its certainly not better than is already widely available and thats the real problem here. Our expectations were not really satisfied after having to wait such a long time for them to arrive.

On the positive side if people take off good heads and replace them with Merlins there are some good s/h bargains to be had

And the head fettlers are happy because those with the £'s will have the Merlins worked to get full payback for all the effort and hassle to fit them.

Andrew - Not Dave Nat Adam Not Adrian Not Chris ....... ANDREW

[mgbloke]

Trying to get these Merlin heads sorted.
Short engine all built up with fresh pistons with reliefs in the right place.
Trial fitted the heads and it apears that the standard pushrods are now too short by approx 0.250
Im using solid lifters which I think are Chevy (Real Steel) with Yella terra roller rockers.
Where is the best place to get some custom pushrods?
Real Steel have no stock of their cut to size ones.

Thanks
Mark

Ill get there in the end.

[kiwicar]

Try comp cams website, find the part number for push rods of the right length, having said that if they are chevy lifters what size ball end are the yella terra rockers? chevy aswell? You may well be able to use chevy push rods not buick, in which case you will have a wider choice. Then when you have the right part number find someone like summit who sell them (or buy off ebay), the comp cams sales people are from a part of the US where they don't understand a UK accent, it is very frustrating trying to get them to understand you !
Mike

[CastleMGBV8]

Mark,

I may have something to suit, what length do you need? and did you mean .250mm. or 250thou.

Also are RS saying they don't have and push rod kits that you can cut to length.

Kevin.

[mgbloke]

Kevin I need approx 8.25 inches thats 0.250thou longer than standard.
I dont really want adjustables as I have adjustment with the rockers.
Rocker end needs to be 3/16 and lifter end 5/32

Been in contact with Smith brothers in the USA and they can do a custom pushrod 5/16 shaft x0.049 tube walls with the right ends and heat treated for $9.05 each plus

[mgbloke]

Just made a checking pushrod by cutting one in half then using a sleeve.
Actual length I need is 8.150

[CastleMGBV8]

Mark,

Couple of points, have you reduced the height of the rocker pillars to correct the geometry and how did you ascertain the length required.

The recommended reduction to correct geometry is 60thou which equates to 96thou. at the valve taking into account the standard rocker ratio of 1.6/1

This is with rover heads so you would need to check with RS if the same applies but if so then you would only need a set that were 50thou. longer than standard.

Cost me 30 of the small coins at a local precision engineering co. 60. off leaves the bottom of the pillars almost flat so you will need to machine a new path for the oil feeds in at least the 4 end pillars.

Just checked the RS catalogue and they state standard length is 8.250" ??

Kevin.

[mgbloke]

Kevin
Been fiddling with the rocker geometry. Best so far is with standard height pedestals in fact if anything they could be raised slightly. All based on the contact path of the roller to valve stem. Roller starts its path on inboard side and rolls outwards.
I cut a pushrod in half and joined again with a tight fitting sleeve.
Assembled the rocker gear with now adjustable length pushrod. Set adjusters approx midway then took apart and measured length.

I did try fitting Lash caps and would think that was similar to shortening pedestals. I like the adea of lashcaps but it would mean raising pedestal by a considerable ammount which seems pointless.

Ordered pushrods from Smith Brothers USA

RS pushrods are cut to length ones and start at 8.250 standard is close to 8 inches. They have no stock and will be some time until they get more.

Now I need to think about raising Rocker covers to clear.
It might be better to have an adpter plate made then use an Edelbrock/Chevy cover, then at least I could use gaskets to seal them.

New exhaust is ready and a work of art. Very pleased with Maniflow in Salisbury.

Mark

[CastleMGBV8]

Mark,

Possibly RS set the rocker pillar support height a little lower to correct the rocker geometry.

Sounds like your sorted with the Smiths p/rods.

Maniflow have a good reputation acquired over many years of manifold design and production so should be a good product, what was the price?

Look forward to hearing the result of the upgrades in due course.

Regards,

Kevin.

[mgbloke]

Kevin
Manifolds with 1 3/4" primarys and merge collectors and 2.5" system was a bit of a cough roughly same price as heads.

Pushrods though are reasonable @ £108