Mark IV head reccomendations.....

[gcarter]

I'm kickin' around ideas.
Currently, I have a built Mark IV w/GM Hi-Perf iron heads w/rectangular ports.
For a good all around engine, are these the optimum? For N/A use, are there better?
What I'm lookin' for is 450 HP and being able to use switchable exhaust.
Can I get some good solid answers from some folks that really know?
Also, cost and availability.......

[mrfixxall]

I'm kickin' around ideas.
Currently, I have a built Mark IV w/GM Hi-Perf iron heads w/rectangular ports.
For a good all around engine, are these the optimum? For N/A use, are there better?
What I'm lookin' for is 450 HP and being able to use switchable exhaust.
Can I get some good solid answers from some folks that really know?
Also, cost and availability.......


George,no problem getting 450 hp with those heads. what pistons do you have in the block now? Flat tops,mild dome?swichable exhaust depends on the cam you use,make sure its a 112deg lob center and you wont have any problems. If your running a flat tappet hyd look into a comp xm 270 or if you want a little more rough idle then lok into the xm278..

[BigGrizzly]

George I have rectangular ports on my engine. I like them.

[f_inscreenname]

George I have rectangular ports on my engine. I like them.

Ditto

[gcarter]

It'll be bored .030" over. New forged pistons. Currently it has the slightly raised flat top pistons and with those heads, I think it's 9.8:1 CR.
I have bought a Comp flat tappet cam (CB XM 278H-12) but I may end up using a roller.

[Barry Eller]

Mine are rectangular. My 502 is a GEN VI. Yellow is the best color too!:cool!:

The heads are VERY heavy. Aluminum heads save a lot of weight, but are expensive.
I'm using a Comp Roller XR271HR-12

[BUIZILLA]

a 278 cam won't feed big rect ports at low rpm, you need smaller oval ports for velocity and air quality for that cam and under 5200 rpm.. did I know about this XM278 previously? i'm a BIG fan of the Edelbrock oval alloys,..

[handfulz28]

However, the dyno pulls and track results indicated that the oval-port heads simply made more power (http://www.chevyhiperformance.com/techarticles/148_0308_track_testing_oval_port_rat_heads/index.html#)

http://www.chevyhiperformance.com/techarticles/148_0308_track_testing_oval_port_rat_heads/index.html

Probably a bit more oval port head info in this article:
http://www.chevyhiperformance.com/techarticles/148_0305_oval_port_heads/index.html

454ci, under 6000rpm, "moderate" cam, is going to like oval ports more than rectangle.

http://www.jegs.com/i/Edelbrock/350/61459/10002/-1

[MOP]

IMO from what I have read and heard big port heads don't do as well as smaller port heads in boats due to the RPM ranges we run, most of what our engine do relies on torque more then HP. With 460 cubes and a moderate cam you will make your 450, I think you can be real close at 9.1-9.2 and run regular gas. IMO George the first time you get that thing over 70 you will do a lot of thinking before you do it again. 385 will get you 70 and a tad!

[gcarter]

e
a 278 cam won't feed big rect ports at low rpm, you need smaller oval ports for velocity and air quality for that cam and under 5200 rpm.. did I know about this XM278 previously? i'm a BIG fan of the Edelbrock oval alloys,..
Jim, I found this Edelbrock document........
Would you make your reccomendation from it?
Please?

http://www.edelbrock.com/automotive_new/misc/company/09pdf/146-151.pdf

[BUIZILLA]

what pistons?

[gcarter]

Bear with me Jim....
What are my choices?

[mrfixxall]

George the 454-0 i believe is what you want to use(61459) they have inconel valves which is for severe marine applications..


MARINE-DUTY PERFORMER RPM 454-O AND 454-R

Heavy-duty, 1.89" Inconel exhaust valves provide added durability for marine applications
Hard anodized to protect the aluminum in the harsh marine environment
Sold with valves only to allow for valve spring choices
Match with an Edelbrock Performer RPM manifold, Performer Series 750 cfm marine carb and Performer RPM cam for proven performance
Smaller-than-stock 11/32" valve stems promote excellent flow and lighter valve weight


PERFORMER RPM 454-O MARINE OVAL PORT
Chamber Size Intake Port Size Valve Sizes (in/ex) Bare (single) Complete (single)
110cc 290cc 2.25"/1.89" N/A #61459*

PERFORMER RPM 454-R MARINE RECTANGULAR PORT
118cc 315/300cc (long/short) 2.25"/1.89" N/A #61559*

[BUIZILLA]

Bear with me Jim....
What are my choices? hundreds... :lookaroun: this requires a telly call, or we'll be here until next year..

[gcarter]

Ok, lets assume stock type raised flat top pistons....

[BUIZILLA]

raised flat top?

call me later in the week..

[LKSD]

I am deliberating the same thing for my TR. DO, I mess with the upper end, Rebuild it all & punch/stroke to a 496 & 500hp, or completely just swap out the engine... Ahhhh :nilly:.. My head is hurting.. lol :boggled:.... J

[BigGrizzly]

Now for the intake manifold. I am going to get beat up on this but the performer RPM works well with the rectangular ports to give back the idle ande has no effect on the higher RPMs that you will run. Done this a lot.

[Barry Eller]

Now for the intake manifold. I am going to get beat up on this but the performer RPM works well with the rectangular ports to give back the idle ande has no effect on the higher RPMs that you will run. Done this a lot.
Is the Performer a single plane intake? When I originally built my 502, I chose the dual plane Weiand Stealth.

[MOP]

I also went with dual plane not to sacrifice low and mid range performance, single plane from all I have read will give some top end at the sacrifice of the bottom.

[BigGrizzly]

Barry it is a dual plane type.