modified merlin heads

[morerevsm3]

Hi from down under,
Thought some here may be interested in this engine build, a friend of mine runs a meteor/merlin (bits of both) 27l engine in a tractor pull tractor, he made the double overhead cam setup himself, running motec management, fuel injected and twin turbo running 29psi on avgas...then I introduced him to an engine guru who is now modifying the heads, and when complete, will then be switched to methanol...

thread and pics for the head work-
http://www.performanceforums.com/for...arged-insanity!

anyone willing to share what engine mods the reno racers do, other than drive the blowers harder? be interesting to compare
hope you enjoy

[FENCELINER]

Re: modified merlin heads

Interesting thread, thanks for posting.

[gp70442]

Re: modified merlin heads

With 29 psi boost, why bother with porting? The fuel/air mix is going to go in there no matter what. Same reasoning with the DOHC. I'm no engine guy but would like to hear the reasoning behind this.

GP

[morerevsm3]

Re: modified merlin heads

the double overhead cam conversion allows more lift at the valve, and stopped the rocker failures, the head port work will mean that the turbos will spool earlier, and it will make more power at the same boost.

[AirDOGGe]

Re: modified merlin heads

Love the work.

Are Merlins known for breaking rockers? I'm trying to think what's the most common failures with V-1650s racing at Stead, and it seems all sorts of things can and have gone ka-putt.

I don't recall broken rocker arms being one of the P-51 nightmares, but that doesn't mean much. I'm not a Rolls-Royce mech., so I wouldn't know what breaks the most and the least often in the V-12 air racing universe. Connecting rods and burnt/sucked valves come to mind from a spectator's perspective.



By the way, I found a couple more photos for your friend's rig. These are dated 2007.

LOVE that monster air filter!:

[ignomini]

Re: modified merlin heads

With 29 psi boost, why bother with porting? The fuel/air mix is going to go in there no matter what. Same reasoning with the DOHC. I'm no engine guy but would like to hear the reasoning behind this.

GP

It's like a restrictor on a racing engine. It doesn't matter how hard you push the air, when the flow hits supersonic speeds (I think it's supersonic but don't quote me) no more air will go down the hole. One common misconception of running boost is you no longer need to care about air flow. Not true. All the boost in the world will be wasted on a poor flowing port design. No idea what is required to fix it, but having seen a chopped Merlin head, the ports looked fair to middling at best.

[morerevsm3]

Re: modified merlin heads

It's like a restrictor on a racing engine. It doesn't matter how hard you push the air, when the flow hits supersonic speeds (I think it's supersonic but don't quote me) no more air will go down the hole. One common misconception of running boost is you no longer need to care about air flow. Not true. All the boost in the world will be wasted on a poor flowing port design. No idea what is required to fix it, but having seen a chopped Merlin head, the ports looked fair to middling at best.

an engine is just an air pump, so the easier it is to get air in and out, the more power it makes, 29psi manifold pressure does not necessarily mean 29psi is getting into the cylinders either, the big open areas in merlin heads cause severe reversion, hence the need for backfire screens etc, the motor will now spool the turbo earlier, and make more power

[ArmyMP]

Re: modified merlin heads

I remember as a kid going to the pulls at the La Plata, MD fairgrounds in the 80's. There was a gentleman that had two Merlins on his tractor and what a sight!!! Not to mention the ear-splitting sound that it created.

He did take the whole contest only having to open the throttle at the line and then cutting it halfway down the track as the speed and weight behind him pushed him across for "full pull" everytime.

Great memories.

[morerevsm3]

Re: modified merlin heads

[440_Magnum]

Re: modified merlin heads

Love the work.

Are Merlins known for breaking rockers? I'm trying to think what's the most common failures with V-1650s racing at Stead, and it seems all sorts of things can and have gone ka-putt.

I don't recall broken rocker arms being one of the P-51 nightmares, but that doesn't mean much. [/IMG]

You know, I haven't read about it much in recent years, but it seems like ~10 years ago or more you'd often hear about a team breaking a few "Merlin Fingers" (the Merlin's approximation of a rocker arm) fairly often. I ASSumed that aftermarket finger followers had pretty much solved the problem since then. Sparrow or Smee could answer that one when they check in again.

[ignomini]

Re: modified merlin heads

an engine is just an air pump, so the easier it is to get air in and out, the more power it makes, 29psi manifold pressure does not necessarily mean 29psi is getting into the cylinders

Would you please contact all my customers. We've been trying to tell them that for years.

[morerevsm3]

Re: modified merlin heads

there are apparently fixes for the rockers now involving hardened inserts, but Joe was not aware of them when he set out to make the double overhead cam conversion, there are other benifits to it though, he can now alter timing of inlet or exhaust valves independantly of each other, it is now shim on bucket, so less inertia than rocker, and now with Ferrera Chev inlet, and Chrysler exhaust valves that are half the weight of originals allows lower spring pressure, the individual inlet runners stop reversion and improve velocity for better cylinder filling by inertia, the larger inlet valves allow much better seat and bowl profile, so these modifications reduce pumping losses, and remove the need for backfire screens.

the Motec is what really transformed it from a temperamental cranky unreliable at times thing, into a smooth running, start immediately, idle lower and smoother, and the ability to alter ignition timing at different rpm and load settings also helps, timing is pulled out over 3600rpm and rev limiter at 4000rpm, fuel is metered to each individual cylinder at rates that are not equal, due to massive variations in how much air has been delivered to each cylinder due to small plenum volume, that is being rectified as part of this program, hope that gives a bit of an explanation of the why

** timing is pulled at high revs to stop boost running away as the old waste gates were a little small, in a racing application, you would increase timing after peak cylinder pressure rpm to hold onto the torque longer

[morerevsm3]

Re: modified merlin heads

ready for the flow bench

[morerevsm3]

Re: modified merlin heads

flow bench results (at 28")-

Lift is .540", I'll let the numbers tell the story, hp figures are V12 aspirated:

Lift - stock - ported - stock hp - ported hp
.1 -111.5 - 110.2
.2 - 206.1 - 224.6
.3 - 295.0 - 325.0 - 910 - 1002
.4 - 344.2 - 400.4 - 1062 - 1235
.5 - 365.2 - 443.7 - 1126 - 1368
.55 - 373.6 - 460.6 - 1152 - 1420
.6 - 380.0 - 469.1 - 1172 - 1447
.65 - 388.1 - 479.6 - 1197 - 1479
.7 - 388.8 - 480.1 - 1199 - 1481

So, at the lift to be used it's up 87cfm & goes from 1152hp potential (NA) to 1420hp potential, so with 29psi boost, plus reduced pumping losses, the power increase will be quite large...

[ignomini]

Re: modified merlin heads

Love the photos. Those heads are ginormous Looks as if it's tough to unshroud the valves.

Thanks for posting.