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.

Definitely something to think about....

If you choose to raise the boost, you are sacrificing reliability.
The cam IMO is way too fat in its centerline and you are blowing off your pressure through the duration. Nice cam.. wrong application.
Like JimV said , basically you are needing to open the exhaust ports, now to compensate.... and that compensation is for the cam. IMO
If you want to hear a similiar application , email me at this name on AOL. Would be glad to talk.

JimV, they have only been port matched to a Stainless Marine manifold opening..... Very little as it was almost dead on to begin with...We are talking about the oval port heads that I have when you are opening them up to 2.1x1.75 ??? correct???

Your heads are holding you back a ton!!! With a Supercharged application, a rect. port design is the way to go. I would use a Dart Pro 1 or Brodix BB 2 - plus CNC head on your application with a runner volume of 320. I built a 468 with a B&M 420 with a superchiller same 2 X 750 Holley double pumper with mech. roller camshaft. With 8-9 lbs of boost engine made 875 HP at 6000 RPM. Your camshaft is not "TOO BIG" either. I ran a .672/.672 lift 252/257 @ .050 on a 112 lobe seperation.Degreed cam on a 108 intake centerline.8.75:1 compression ratio, 93 octane fuel . Engine still had power left with timing very conservative. The engine went into a 25' Baja from Michigan. Wild Ride!

Yes, grind the material off the roof of the port. This will help but to make it right it needs a good ex port and some chamber work.

I thought the Merlins were a good, raised exhaust port and that's why I decided on them for my normally aspirated motor. Is that not the case???

Yeah that's what people in the know are telling me abot my cam. Who's cam did you run? What's the part #?

Crane Mech.Roller CHB 290009 Grind # 290-295-12 R IG

Their better than the stock GM heads by far, but out of the box even with a bowl port they don't flow to their potential.

You have the best input I've seen on heads with some real experts.

The cam is too big, big is not better, a 232/[email protected] on 112 would be max if I was doing it, Maybe a little smaller, but let these guys offer suggestiond with there heads.

LH

I'm not a head porter BUT I also had a set of merlin vr rectangle ports (previously to my afr's) and they used the same exact exaust port as the oval ports,my motor had a hard time breaking the 700hp mark no matter how much boost I put to it and it was a 540. The exhaust ports are raised but flow virtually the same as most STOCK gm heads until they have a grinder put to them by a professional head porter,203 cfm at .600 lift is what the stan weiss chevy head flow dat base shows,most good flowing bbc head exhaust ports are more like 260-320cfm,a 25-30% difference. They are restrictive,if it was just the exhaust ports I would say have them ported but you also have mismatched intake ports that would be ok on a N/A 454 but again don't flow enough for a blown application,Smitty

Oh yeah.....I forgot to mention the 468 made that power with full port GM rect. port heads we ported in house. The camshaft works fine. 232/240 is what I run in my lawn mower.:D :drink:

The exhausts on my AFR's after being worked by Jim V flow 290 at .6 lift. Your Merlins are probably flowing around 200 at the same lift. That's about 45% more. With the mismatch the intakes are somewhere around 250. Out of the box, most small rect. alum heads are 350 or more at .6 lift. There is a lot of hp to be gained with a head swap.

If you want to stay with cast iron, talk to JimV about porting a set of the Dart IE 308's. These heads supported 820+ HP in 505 ci NA with a 323 cc intake runner; the acceleration is absolutely awesome. JimV had the flow on both the intake and exhaust at industry leading levels that were as good as any similar sized CNC aluminum heads.
Cast iron has numerous benefits vs. aluminum in a marine application.

THANKS EVERYBODY HERE!!!!
Any input on the AFR steel heads?
Should I look at a 360 or a 320 runner on this application? Power is the # 1 goal, and being me, I would choose the 360's however I need to live with it cruising 85% of the time....And, I also want to be able to expand from here and not end up with a dead end head like this again....

Small runners for a small engine. If you were drag racing, 360's would be good for 8000 rpm's on a 489.
Arcticfriends is getting 950 hp out of a supercharged 540 with AFR 315 heads.

Ben Perfected, How fast you going now? Can you post some pictures of the boat / engines? thanks

Jim,
I will post some pics in early June on my next trip to OH. Last weekend I got the boat out for the first 2007 ride. We briefly ran to 100 MPH and backed off as everything is is at zero hrs...couldn't wait! Between your newest heads and the Wilson Manifolds prepared Merlin X marine intakes, this is the most responsive package I have have ever had...only took 20 years! It did take $1100 of work to fix each intake. :eek: My initial impression of the Peterson wet-sump oil pumps is also positive...still dialing in the initial pressure settings.
MRE's Spinton tested valve train includes a 55 mm cam, Crowler .937 lifters and 7/16" tapered .180 wall push rods. This stabilized combination should set a new base line for high performance BBC marine valve train longevity, except maybe for Mercury Racing.
The 820+ HP is not "in the boat" real as we used 2.25" ID dyno headers. Real world in the boat with my current CMI Sport Tubes is about 780-785 HP.
I am thrilled with the performance of your heads and your ongoing contribution to my project. If the A & B classes still existed, we would be hard to beat in 2007!
Your intake runner size is proof that size does matter...
Thanks,
Sprague

A 360 is too big. Like I have mentioned prior.....that everyone seems to forget here is, you have a BLOWER on top this engine. Give me a call if you need some advice before you get confused. I will be more than happy to help you in any way I can. We do our own cylinder head developement in house for over 50 years. You made a great point...." I want to be able to expand from here". PM me for more info.

Thanks,

Dean Gellner
Gellner Engineering Marine Power

Sprague, That's awesome!

Thank you.....

A 360 is too big. Like I have mentioned prior.....that everyone seems to forget here is, you have a BLOWER on top this engine. Give me a call if you need some advice before you get confused. I will be more than happy to help you in any way I can. We do our own cylinder head developement in house for over 50 years. You made a great point...." I want to be able to expand from here". PM me for more info.

Thanks,

Dean Gellner
Gellner Engineering Marine Power
__________________
Gellner Engineering Marine Power
"Powering The Leaders" TM

Dean, can you enlighten us on what we are forgetting and explain port volume/airflow vs having a blower on top this engine?

Jimmy,
As you know it's all relavent to many things....not just engine cubic inch size. With Supercharged applications you can , in most cases run a larger runner volume "slower moving" cylinder head and make a ton more power. With the blower the fill volume of the cylinder head is your restrictor plate you may say. Of course camshaft design plays a major part as in any engine. The end all be all to this post is....yes the GM heads are holding the engine back. Everyone starting relating to a N/A combination instead of a SC. I will have to post some pics of stuff I have done, I am certain you will like them. Your work looks nice Jim! I can appreciate that since my old man started me hand porting heads at 13! What size flow bench do you have Jim? I have 2, a Superflow 600 and the "Big Boy". Speaking of induction systems, this weekend we just re-set our world's quickest and fastest single 4 barrel drag car @ 6.65 @ 208 MPH with heads and intake we designed and built. 1 CARB!