CCstinger260

Well done OLSKOOL. The thing most of the young guys don't realize is that turbos are parasitic too, both in back pressure created and air charge density from heating. Bottom line is none of boosters are "free", but each style of supercharger, including turbos have applications in which one type will excel over the others for various reasons.

articfriends

Not to get this thread off track but talking about heads I used afr cnc 315's,540 w/8-1 comp,hyd roller around .650 lift/245/250 at .050 and a highly modified 502 mpi manifold/stock plenum top/bored out stock throttle body,procharger m-3sc and I switched to a mefi4 last time,Smitty

10x

The percentage of exhaust to intake flow differs from a N/A application to a S/C application. In other words, a pr of heads that work great on a N/A engine, will more likely be not as effecient on a S/C engine.

joee

Let me give you a actual example based on my personal experience,my blown 540 had merlin heads at first. The intakes flowed just over 300 cfm,the exhaust flowed just over 200 cfm, it made 630 hp/700 ft lbsof tq on the dyno,with more boost and timing it made a little over 700 hp (based on increase of speed of boat). It was a real stone in my opinion. I freshened it and switched to cnc'd afr heads,put in a cam that had the same lift and just a few degrees more duration (thanks bob madera),did some port work on the manifold to complement the heads and picked up 250 hp using the same blower and same pulleys. The afr heads flowed about 20 % better on the intake and 45% better on the exhaust,I am certain the mediocre merlin head exhaust ports were bottle necking the whole package.


Hi Arctic,

what kind of MERLIN heads did you use?

I'm building up an 572 engine (Merlin III tall deck with splayed caps) among others with Merlin cast iron heads PN 3063B.

I 'm expecting 900 HP @ 5600 with moderate boost level either with an 8-71 or 10-71 blower @ 8,5 cr and will try the crane cam (290-295-12R IG) with 672 int & ex lift (252, 257,@.050) which was as far as I remember used in the 900 SC's.

Flow rates given by world at 700 valve lift are 370 for intake and 261 for the exhaust (with 11/32 stem)

Anyhow, I will prefer the Inconel 3/8 " exhaust stem for better durability.

Any problems to be expected rearding the Merlin heads.

Thanks

Joee

Chris Sunkin

I'm sure Smitty will weigh in on your question...

Here's my take on what I've learned-
You still need proper port sizing with supercharging. Flow is just one aspect of the eqation. Velocity is the other. High flow and low velocity makes for a pig at anything but hihgh rpm. You also leave high rpm horsepower on the table. High velocity in a too-small port is just as bad but you'll get stronger midrange and better idle. Flow ratios are important- and most heads are designed for N/A applications. That means that when blown, the exhaust flow of these heads is typically insufficient to keep up with the engine's production of exhaust gases. The blower overcomes some flow inefficiencies on the intake side, the exhaust doesn't know the motor is blown, so the port designed for non-compressed intake isn't keeping up. This is likely why the AFR 315CNC head works so well- a high I/E ratio

I don't believe you'll get close to your 900 HP goal with those iron heads. The aluminum head's ability to migrate chamber heat is going to be responsible for 50 to 100 hp. The head itself doesn't have nearly the flow capabilities of an engine that size. The 315's that Smitty used are probably on the small side but compare flow and velocity between them and your heads on this chart-
http://users.erols.com/srweiss/tablehdc.htm#BBChevy

P.S. You need to be in touch with Bob Madara (rmbuilder on this board). He owns Marine Kinetics and can work with you to spec the right parts for your goals. He does custom cam grinds and can get you something exactly matched to your motor and the heads you choose. He also takes into consideration your hull, weight, etc. Something you won't get from a one-size-fits-all cam manufacturer.

joee

" I don't believe you'll get close to your 900 HP goal with those iron heads. The aluminum head's ability to migrate chamber heat is going to be responsible for 50 to 100 hp. The head itself doesn't have nearly the flow capabilities of an engine that size. The 315's that Smitty used are probably on the small side but compare flow and velocity between them and your heads on this chart-
http://users.erols.com/srweiss/tablehdc.htm#BBChevy "



Iīm quite sure to reach 900 HP with that old combo.

Nevertheless itīs worth to consider the installition of AFR CNC ported heads.

According to AFR it would gain 80 HP just by replacing the Merlin 345cc heads by the CNC Magnum 357 cc. Due to the fact that 900 HP is the max. for the drive train it would last but not least increase engine efficiency.

I doubt that at my specific application one will gain 50 -100 HP only by switching head material from cast iron to aluminium.

Such tremendous gain might be thinkable if you run the cast iron heads with high jacket water temps very hard at the knocking limit.

Quite the contrary I would always prefer cast iron heads if running in sea water at low jacket water temps, with good fuel far away from hazardous knocking conditions.

What I like on the older merlin heads are the 3/8 " exhaust guides. That size is unfortunately only possible on the AFRīs if you hone them up by yourself.

I donīt like to sacrify durability for just a few horses.

Does anybody know what kind of exhaust valve guides Mercruiser is using on their 1075 SCi.

Thanks

Joee