Innovation Marine was able to get 560 hp from the stock intakes (extrude honed) with 87 octane for their HP3 race engine. Then 575 hp with additional tricks and 93 octane but still the stock (extrude honed) intake manifolds. The intakes were a bottle neck but good power could still be achieved with them with pump gas.

I tested the Dart heads with 3 different camshafts and several rocker arm ratios and different valve sizes to get the best results with the stock intake manifold. I took a stock 375 HP and put forged pistons in it because all of the dyno testing I was going to do but I kept the compression the same at 9.1 I installed the Dart heads right out of the box No Porting just a valve job and put a camshaft and roller rocker arms on and we made 575 HP and well over 600FT of torque. The ex ports flow so well we found out that we did not need the extra lift on the ex side. Dart took the stock head and cut it all into pieces so they could beef up all the weak areas like in the exhaust port where they get thin and leak coolant into the cylinder.

Extrude hone wont do these intakes anymore. They loose too much material and wont do it. Besides, it cost $800 plus shipping, you may as well buy an intake at those prices because you arent going to gain much. I tried numerous times thru Extrude Hone and Bonehead Performance... You can port the runners and port match them and maybe do a little in the plenum otherwise that is it. If Tyler is getting 575 with stock than why bother.

Hello Tyler: Happy New Year to You!

Glad to hear you did a lot of testing.
To make the 575HP number, what intake manifold did you have to use to get to that number. I thought you could give the fellow OSO'ers here the full specs on this 575HP version so they really know if they can take for example a stock 496Mag or 496MagHO bolt on the heads and cam and get these exact results on their stock engines. I assume also you got these numbers with headers?
Thought the information of this exact detail would help 496 users know exactly what they have to spend and how much equipment and work will be needed to get to these numbers.

No doubt the stock iron head can be improved, that's why we came out with an aluminum head 8 years ago. but we found that when a good flowing head was bolted on the engine with a good camshaft profile, the factory stock intake could not deliver the air the engine needed to get up to good horsepower numbers.
Curious what you found in your testing?

Best Regards,
Ray @ Raylar

I was only reporting the facts about the HP3 engine configuration that produced the hp numbers noted and in no way recommending the very expensive extrude hone that only provided ~10 hp improvement to the stock intake.

Will the heads CFM flow numbers versus valve lift increments be available to the public?

I am starting to think the block is more attractive than the heads. If you get the block with 4.5 in bore (you can I already checked) then you end up with a N/A 557 cu in engine. Nice!

Happy New Year to you too Ray.

I used a bone stock intake manifold on this 496 engine with a Mefi 4B ecu so I could program it myself. I believe the max HP thru this manifold is 575HP so why port the heads to get more power. When Dart looked at making these heads he looked at your heads and the stock heads that we had ported and made 575 HP with and fixed all the problems and all the weak points and casted a head that would make power without any porting. Dart made the new block and corrected all the oiling issues and the cooling issues that were a problem with the stock block. They also have availible 4.375, 4.500, and a 4.750 Stroke cranks that can make youe 496 inch motor over 638 CI. They also made a sheetmetal manifold so we could run a single carburator on and we made more power but lost a lot of torque so we went back to the stock manifold to have the torque. Dart is casting a single plane and a duel plane manifold for these engines that you can use a carb or put a throttlebody on and run the fuel injection. we ran the CMI Sport tube headers for all the testing on the dyno. I am working on a package right now with Heads, camshaft, Roller rocker arms and studs, and exhaust with a exchange computer program to 575 HP. Sure the heads are 100 pounds heavier and we are keeping the compression at 9.1 but with 575 HP as our target we are there. If they want to get crazy Richard built a 638 ci with a duel plane manifold and 650 carb and made over 830 foot pounds of torque at 2800 RPM's.

I am really glad all this comes to light as I am putting the last bolts in my 496 build project... Really I am.

What octane does the 575hp version require?