Just dynoed my rebuilt 558's BBC tall decks and not getting the hp I was looking for. I'm thinking heads and or other factors. Here are my specs. TRQ 682 HP 545@4200 TRQ584HP 623@5600
Looking for 750-800 hp. Any Ideas?
Thanks

Merlin iron heads 2.190,1.880 310 cfm @700 lift
Crane Mechanical Roller 680 int 708 exh 252,258 - 108
9.8 compression
4.500 bore 6.375 stroke
Weiand Team G with Holley 1050 Dom
All forged rotating Assembly

Heads are way, way to small for 558". Merlin iron heads are not much better than stock. I'd put some 335 Pro 1 CNC heads on to start with and then run a cam with about 10 degrees more duration on a 112-114. 750hp is dooable at 6000, 800 is a stretch unless spun pretty hard (high 6's)

What volume Merlin heads do you have? The intake valves should be 2.300 dia. which should flow around 390 cfm @ .7 lift. The exhaust should be the stock 1.880 diameter, ported the can flow 300 cfm. Stay away from the nail head design ex valve. Also the heads will benifet with some chamber work. 108 is a little tight which is probably why the motor is sighning of at 5600.

Call RMbuilder/Bob Madara of Marine Kinetics to set you up on an accurate cam selection for your application. He can really help you a lot....he's got many years of experience and he's a gentleman and JimV is an excellent choice/source for head porting. I had Jim and Bob work together on my two 565cid engine projects with excellent results and they have for other customers as well. They can definately help you find the KICK in your engines that you're lookin' for!

The Merlins Are The Small 2.190 Int And 1.880 Ext.
Do You Have A Cam And P/n ?
Also Thought Of Adding Tunnel Rams With 2 Holley 750's, Or A Procharger, Or Blower???

8-71 with 6# of boost and a Crane 651 cam will get you close to 800hp quick. Is your existing cam ground on 108, or is it a 112 +4? Do you want to stay solid roller? If its a 112+4 then its a good blower cam and is why I'm asking.

jdnca1, Not sure here is the grind# TR-252/400-2s-6Ig