innerrage

im installing a set of stainless steel roller rockers with polylocks on my vortec heads and i wanted to have some maching work done maybe to open them up more on the exchaust side to match my exchaust and match the ports on the intake side any suggestions

Ghostrider

The Vortec heads have D shaped exhaust ports that aid flow by reducing turbulence so I don't think trying to match the ports to your exhaust will help.
Best thing I've ever read that you can do is machine them to install the larger valves to allow them to flow.

The point on the heart shape in the combustion chamber can also lead to detonation apparently if that edge gets too hot so I've been told it's best to take a small bit off there but I haven't confirmed that so I can't say for sure.

I run about 10.2:1 comp in my 468 with a port matched Performer RPM intake and a holley 850HP and haven't had many problems but I'm still sorting bugs out.

Hope some of that helps!
Let me know if you've got any specific questions.

JimV

In most cases matching the exhaust port to the header kills airflow. Those head castings are a good starting point for a 454. The exhaust ports can be improved considerably but most of the work is in the venturi-short turn not so much at the flange. The intake can be improved with a larger valve and some bowl work. Leave the exhaust valve diameter stock, correctly ported it does not need to be changed although some mods to the valve will help airflow. Jim

Andy

What he said is what I did, worked great and make sure that you remove the sharp point (make a more rounded edge)in the combustion chamber

Raylar

If you boat in fresh water in Ct., then invest in a good of reasonable cost set of aluminum heads and bump your compression with these about 1 point or so and the 40-50HP and reduced engine weight you will see from that change will far outweigh the benefit of putting a lot of custom port and machine work in your stock iron heads. While you are at this also do a good cam choice to take advantage of the higher compression and better breathing of a good set of heads.
Remember, reduced power and torque from bad or weak breathing is a condition from heads ,cam, intake and exhaust as a system!
An engine down on power from a weak cam, with great heads, or a weak exhaust coupled with good head and cams is still an engine not producing best power efficiently.

Best Regards,
Ray @ Raylar

Best Regards,
Ray @ Raylar

innerrage

its a 350ho vortec with msd ignition 8.5 wires 8m blue ignition box holley 650 edlebrock performer rpm intake and revolution marine 4inch aluminum wet exchaust with a gaffrig air cleaner the motors only has about 15hours on it and i got a set of ss full roller rockers for it to put on

Rage

Bottom line compare cost to have the heads ported by Jim Valeko versus the Raylar heads. Either will get you where you want to go. It just boils down to the dollars diffrence. Jim Valako got me enough flow from my 496HO heads (425hp)to produce 625cshp along with bigger valves and a cam and timing change on 87 octane. I chose to have the ECU recaled as well.

paul buckner

Hi i am fairly new to the 496ho motor some .where down the line (even though i said to myself i wouldnt) i would prob like to do some upgrades to the motors going from 425 to say 525hp its where you say (i chose to have ecu recaled ) i may be wrong but i thought you had to R/CECAL with any and all motor perfo changes?? allso i have asked a couple of guys on OSO where to get the parts /pis/rods/ crank ? i have not heard anyone mention the crank are they strong enough ?? thanks paul

Rage

Some hp upgrades can be accomodated by just increasing the fuel pressure with the addition of an adjustable fuel pressure regulator. Of course you need an air fuel ratio meter to confirm what fuel pressure to increase to. If you want 525hp out of your 496HO I would recommend the Raylar kit. I took a DIY path copying the GM 496 HP3 race engine and I am sure I ended up spending more than the Raylar kit because of the trial and error learning curve process even with a lot of help from knowledgeable people. Since only Dustin Whipple is liscenced by Mercury to reprogram the PCM555 ECU for the 496HO and since the later upgrades required an ECU recal this became quite a chore/bottle neck because and expensive. Dustin is a very busy fellow during the summer months and less so in the winter. I am told the crank is good up to 600 hp. The pistons are the weak link and always seem to be involved when the 496 has a catestrophic failure. Raylar seems to have all the various 496 upgrade parts. If you add the Dana Flow Torque exhaust to the Raylar kit you get ~560hp. Using forged pistons with the Raylar kit is strongly recommended for the reason I mentioned.

paul buckner

Thankyou for takeing the time to explain regards paul