Are my heads holding me back????
 

I have a set of oval port World Casting Merlin steel heads on my blown 489. I am Running a B&M 420 w/ 8 Pds boost and dual 750's Here are the head specs.

[ MERLIN OVAL PORT ]
Cast Iron Big Block Chevy Heads

Merlin 269cc Oval Port heads are excellent for most street-driven big blocks up to 468 c.i.d. They'll out-perform larger heads in many applications because the intake runners have a very high velocity, and the stock 2.190" diameter sized valves have been replaced with 2.300" diameter valves to also improve flow. It's the best of both worlds. True D-shaped exhaust ports help expedite the flow of spent gasses, which also contributes to improved performance. We used these heads on World's own “Daily Driver and Cruiser ”engines because of their excellent low and mid-range torque output. Merlin Oval Port heads are great for towing applications, and have a strong following in the marine market.
030040-2 Solid/Hydraulic Roller Iron Head Oval 269cc Manley Race Master 1.550"Dual150#Seat .650" 119cc


Here is my Hydraulic roller cam


Advertised Duration IN/EX: 304/309
Duration @.050 IN/EX: 245/250
Gross Valve Lift IN/EX: .612"/.612"
Lobe Sep Angle / Intake Ctr Line: 112/110
Valve Lash IN/EX: Hyd/Hyd
RPM Range: 3500-6500


Are my heads holding me back or can I still achieve more power with a few more pounds of boost? Say 10-12? How much more if any? Thanks....
Thanks.....

At 280 cfm intake at .600/203cfm exhaust at .600 they are killing your power. You can pour all the boost you want to it but the exhaust is never going to let it out,Smitty

That cam is way too large for a 468.

It will blow with any more boost

Yeah, I was impressed with the Merlin oval port heads too. I don't know anything about what you're asking when it comes to a blower and Merlin oval port heads with your app, but I can tell you I once had some Merlin oval port heads (2.30" intk valves, a lot of bowl/pocket/short side radius port work) on a pair of naturally aspirated 468cid engines that came in my boat when I bought it 7 years ago with 9.5cr, Dart single plane intakes, solid roller cams, 850cfm Holleys. Don't know if it is true, but the dyno sheets said 599-604hp @5700rpm with dyno headers. I was very impressed with how the boat ran with those engines and heads! Anyway, I hope it all works out for you.

Explain please.

Did you port match the head to the manifold? I don't think B/M made an oval port intake. At 203 CFM on the exhaust side your just under 100 CFM down from a fully ported exhaust port. How much overdrive?

No, I did not port match on the intake side as it is soooooo far off it's futile.. The exhaust, yes it is matched. The heads were lightly pocket ported and valve reliefed. As far as overdrive, not much, I can get a lot more if needed. Will I get much with this Cast Iron Big Block Chevy Head?


When larger displacement engines (468 and up) require additional flow, choose Merlin Rectangular Port cylinder heads. With RightCast® 320cc and 345cc intake runners, you can expect solid gains in air/fuel mixture combustion charges. These heads will really respond to higher compression ratios, and are ideally suited for hot street/strip cars. The larger heads with 345cc intake ports are used successfully on Merlin crate motors with up to 632 cubic inches displacement and can support 760 HP in box stock mode! I'm sort of split here...

You need to establish what the flow on the exhaust port is,203 stock is very restrictive,your blower is going to force the intake port to flow somewhat but the exhaust will bottle neck it for sure. Even if you spring for a new set of merlin rectangle ports keep in mind they use the same exhaust port. The mismatch on the intake isn't helping you build any power here either,I would use the heads on something else or have everything professionally ported,Smitty
also-245/250 at .050 is pretty big for a 468

Do you need iron heads? There are a lot of good alum. heads out there that will do better. Canfield and AFR both make an excellent small rectangular port head. Either would be good for a hundred hp or so. They would also lower boost and heat in the intake possibly allowing you to spin the blower faster. The Dart Iron Eagle is a better iron head than the Merlin. The Merlin has a crappy exhaust port. Maybe Jim V can help it. Your cam is about the right size for your present combination. The long duration is probably helping the poor intake and exhaust flow. If you get better heads, you may want to use a smaller cam.

I've had most success porting the intake to a height of 2.1" by 1.750. With a 2.25 intake valve they will flow low/mid 360 cfm. With the small port opening, I dont think the 2.300 is being utilized. I'm a little consern when you say the ex ports have been port matched. Exhaust ports are sensitive in the bowls and the port floors out to the flange. You can hurt airfow if not ported correctly. Overall the heads will work good with some porting.