Merlin Heads

ged · Post by **ged** » Thu Dec 10, 2009 10:16 pm

kiwicar wrote:"So What are RPI charging an additional 50% for, over Real Steels price!!!!! "
Because they are RPI and that is what they do
Mike

Recommended Price Increase!

Post by **katanaman** » Fri Dec 11, 2009 6:15 pm

thev8kid wrote:wonder what RS would say about that advert

Pretty sure they will have seen it.

bigaldart · Post by **bigaldart** » Sat Dec 12, 2009 12:21 pm

RPI are including rocker shaft assemblies, Real Steel dont! £600 for rocker shafts is a bit steep.

Alan

mgbloke · Post by **mgbloke** » Wed Jan 13, 2010 8:21 pm

Bodywork finished so finally started on the engine.
Armed with a new burette I have measured my existing cylinder heads and they came out at 27.2cc. piston dish is 13.5cc. Bore is standard 94mm and 4.6 stroke is 82mm. head gasket is 0.048 and deck height 0.038
So by my reconing my static CR was 11.18:1
I have re checked all measurments.
This is a higher figure than I was expecting as the car seemed to run fine on normal unleaded.
Hear engine in this clip,
http://www.youtube.com/watch?v=TiajCKtQSeQ
Now Im not sure what CR to aim for with the merlins, I was planning to keep it somewhere near the same or maybe aim for 10.8:1 which would mean having the merlin heads skimmed down to 29cc ( havent measured them yet, waiting for spark plugs). Real Steel have quoted 32cc for the merlins.
Just wondering how much I would need to take off to drop 3cc bearing in mind that the merlin combustion chamber covers a smaller area than the standard heads.
One small problem is the pushrods seem to be a tad short although skimming heads will help.
Mark

kiwicar · Post by **kiwicar** » Wed Jan 13, 2010 9:46 pm

Hi
you would gain more by raising the compression by decking the block, the squish band is .086, in an ideal world you would bave a squish band between .035 and .045. The chamber shape of the merlins is different to that of the rover, so you can't skim it as if it were a rover head you will have to skim a bit, measure, skim a bit more. . . if you cant skim the block, you could just use tin gaskets.
Best regards
Mike

mgbloke · Post by **mgbloke** » Wed Jan 13, 2010 10:12 pm

Mike
Hadn't thought about having the block skimmed.
I dont really want to go back to using tin gaskets after a bad experience where one failed ( 4.0L engine ) and the hot gasses carved a channel in the block/head.
Looks like skimming the block is the way to go to start with.

minorv8 · Post by **minorv8** » Thu Jan 14, 2010 6:39 am

I had my block skimmed a couple of years ago and it was not exactly cheap...

kiwicar · Post by **kiwicar** » Thu Jan 14, 2010 7:05 am

Decking my chevy was about £80, it was part of having the bloch rebored, but if you are having it rebored at the same time just supply them with a piston and rod and get it decked to 0 down the bore, or even .005- .01 pop up.
Best regards
Mike

mgbloke · Post by **mgbloke** » Fri Jan 15, 2010 8:32 am

After more re measuring deck height is 0.035 and not 0.038
Been reading up on compression ratios and im not sure what to do. If I just assemble the engine as it is the CR will be 10.54:1 which is a drop of 0.5 but still quite healthy.
Im thinking if i start with 10.54:1 then I have got somewhere to go.

My exhaust manifolds are the RV8 type from Beehive and were a very poor fit on the standard heads and will need some tweaking to fit the merlins.

What to do?

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jan 15, 2010 10:10 am

Mark,

After a quick calc I make it 10.74/1 with the Merlins so with a skim of 20 - 30 thou. should get you in the right area.

If you speak to someone at RS who knows what there talking about you should be able to get a figure for the skim to get you into the 11/1 area.

Kevin.

kiwicar · Post by **kiwicar** » Fri Jan 15, 2010 10:14 am

10.5 is a pretty good place to start cor CR, the better design chamber should give you a good margin against detonation, if you tighten the squish band by decking the block that should help further. What is the timing and duration of the cam you are using? that has a big influance on the CR you can use.
Best regards
Mike

minorv8 · Post by **minorv8** » Fri Jan 15, 2010 12:18 pm

I had to do some grinding of the manifold flanges, especially at the top of the bore. I had them laser cut over 10 years ago with a Rover gasket as a template. I also had to removes some material from the gaskets to match the heads. I had big bore gaskets but they did not fit the heads.

mgbloke · Post by **mgbloke** » Fri Jan 15, 2010 10:12 pm

camshaft is a RS 238 mechanical listed as a race/rally spec from real steel. 0.512 lift
Kevin
How did you get 10.74?
Pricing up a new exhaust system and manifolds. its not gonna be cheap!

CastleMGBV8 · Post by **CastleMGBV8** » Sat Jan 16, 2010 10:00 am

Mark,

Just redid figures on basis of swept volume = 569cc deck vol. = 6cc. 4.0 piston vol. stated as 13.2cc comp gasket compressed = 8cc. Merlin chamber your figure of 32cc.

So 6 + 13.2 + 8 + 32 = 59.2cc. + 569 = 628.2cc. divided by 59.2 = 10.611/1 so a bit more accurate having checked all the volumes.

Comp gasket volume is Real Steels figure.

A reduction in chamber size to 29cc would get you back to approx 11.16/1 and guessing the chamber may only be 70% of bore area you would probably need to machine heads by 30 thou. but real steel shoud know what figure is required as previously mentioned.

You would need to get the full cam specs from RS to calculate the dynamic compression ratio as they do not publish the figures.

Kevin.

bigaldart · Post by **bigaldart** » Sat Jan 16, 2010 3:28 pm

RS 238 cam is an old Crane profile, may be easier to get information from their site.

Alan