Thread: need head advice

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I need some head advice for my 496 build. This engine is going into a superstock mud truck and here are the rules i have to follow:
engine must pull 15" of vac at 800 rpm
stock cast heads only
only 3 engine bolt ons ( carb intake and headers)
My plan so far is to build a flat top 496 but i have no gm heads for this engine. ( i do have some 781 cores but they are in rough shape) Since i have to buy heads i was wondering what casting no's, valve size, and combustion chamber volume i should be looking for. I would like to see close to 6000 rpm out of this engine but torque is the priority. Just curious to see what other people here have used on 496's in the past.

781 and 049 and rec port heads in iron all with bowl work with 219 and 188 ex or bigger intake your 781 head could work

I found a set of 781's for sale with 2.25 and 188 manley severe duty valves and 250lb isky tool room springs. they were just built and never installed, seller wants 850 for the pair. would these be a suitable head for my build. I didn't think 850 was to bad for the new parts that are in them.

well isky tool rooms are great springs if new over 400 a set. but the iskyloys are very good to abit less i use them . is the cam your going to run need a spring like that? if you have to set up the heads for other springs it not that geat of a deal

the guy was setting them up for a solid roller cam. since my engine is basically going to be a street engine those springs would be a little big. I suspect that to get my 15" of vac i will have to go conservative on my cam choice. I was tossing around the idea of hydraulic roller with rhoads lifters to get back some of my vac at idle. My tech inspectors barely understand what vacuum is let alone how to manipulate it.

well they are but i run them for the street on my roller stuff . i was just thinking .i have a set of iron gm rect ports .a guy i am building a 489 blower engine for may sell them he using dart heads

Can you use custom grind cam ? The only way to go imo. Put a solid roller,custom grind in 496 and pull 17'' @ 1000 rpms per our street class rules.

Hey Pat,

Correct me if Im incorrect but the orginal post stated "Flat top" 496. I assumed flat top he meant flat top pistons...Now I may be wrong but if you use flat top pistons in a 781 head (119 cc oval) or 049 head (121-122 cc oval) I think he will be lookin gat some low compression. Maybe Im wrong but I think with either of those large cc oval heads he is gonna need a domed piston to get in that 9.5-10 :1 compression range.

Originally Posted by blueblazes

Can you use custom grind cam ? The only way to go imo. Put a solid roller,custom grind in 496 and pull 17'' @ 1000 rpms per our street class rules.

yep and i know a guy thats on here that can do just that if he wants one

Originally Posted by 30-A Rider

Hey Pat,

Correct me if Im incorrect but the orginal post stated "Flat top" 496. I assumed flat top he meant flat top pistons...Now I may be wrong but if you use flat top pistons in a 781 head (119 cc oval) or 049 head (121-122 cc oval) I think he will be lookin gat some low compression. Maybe Im wrong but I think with either of those large cc oval heads he is gonna need a domed piston to get in that 9.5-10 :1 compression range.

not with a 4.250 arm it will be around 9to 1 at 119could get better with a good hair cut

I am not really looking to build a high compression engine. In this sport reliability is important. Mud pits change from town to town, sometimes i clear a pit in 5 seconds, sometimes 30. These engines run hot and we have to box them in to keep out the mud, so it it very difficult to get under the hood to fix problems or make adjustments. I once had a starter failure and had to let my truck run for 30 minutes between heats, so a high compression engine just leads to more problems in my sport. I like the idea of a custom grind making 17" of vac though.

yep i know. i built some engines for guys that run in the mud pits . sand drags . they take a hell of a beating

I have found some very cheap rotating assembly's that come with kb's. Does anyone here have any experience with these pistons. Guys here either love them or hate them, personally I have never owned a set. just wondering what you guys think.

well i have. but the KB hypers are ok but for the price of them i am better then 1/2 way there .i can buy a SRP piston so that what i try to use.but if a low dollar build i use more of the speed pro hypers then the KBs. i have seen KBs brake at the top ring land even with the big ring gaps you have to run with them. with the speedpros you do not have to gap them no more then a std piston but you have to go over them good now there made in inda

Eagle crank, eagle rods and srp flat tops, kit is balanced and comes with flywheel and balancer for 1400.00 usd. Now i just need to decide on a head, the kit's seller claims 8.7 to one with a 118cc head. I am guessing by decking the block and giving the heads a shave i can probably expect and honest 9:1 cr.