I'm doing a 235 project and its time to do the head. Need a bit of advice now. Lower end is pretty normal - cam, bored, balanced, etc. Top end is going to have 3 carbs, dual exhaust, hei, etc. I'm just looking for a nice street engine. We have offset ground the crank and stroked it, so the compression is at 9.3 or so. So, I have been having trouble getting the machine shops to do anything other than a stocker head. So, I need a bit of advice on what to specifically ask for on this head. I know that for a little porting and polishing at home, they can inprove flow quite a bit without going to an expensive racing application. I know that a good valve job is important but thats about it. So, give me some advice to ask for to get a good street head. Guides? Seats? Mill? Port? any specifics to watch for? cost estimates? maybe its better to just buy the thing from clifford for $1000 and be done with it? What do you think?
here's one plan...which may or may not be what you want to do.... first get the head cleaned, inspected for cracks, guides replaced as needed, and seat inserts in the exhausts. Then take it home and do some mild porting, don't bother with the polish, but spend time on the area just below the valves, blend the ports into the seats with a nice gentle curve. Don't hog it out, just smooth it out. Then take it back to the machine shop, maybe get the exhaust valves back ground at 30 degrees (leave the seat angle at 45), and have the valve job done, and the head milled just enough to clean up the surface so it's flat. Put the springs in that are recommended by the cam company.
Since the intake ports are round, they can be reamed oversize with a shell reamer. I've done this to a couple of heads, and it results in a uniform port diameter and does increase breathing, but eliminates the stepped area in the port where the steel rings locate the intake manifold, so it will have to be lined up and drilled on each end for a pair of roll pins to keep it in alignment. Shell reamers can be used to open up the port underneath the valve seats as well. As far as milling goes, the intake valves will have to be recessed into the head the same amount that is milled from the surface to avoid having them collide with the pistons, especially with an aftermarket high lift camshaft. Once they are sunk into the head, a like amount will need to be ground off of the valve tips, and the tips will then need to be rehardened. A spring shim pack equalling the amount of the mill will need to be placed under each intake valve spring to maintain proper pressure. Shell reamers and mandrels are available from any industrial supply catalog. I bought mine from Grainger's. The cost of them will make you want to do two or three heads for others to help offset the cost. So, how much of a head does a grand get you from Clifford?
The major design flaw in a 235/ 261 is the cylinder head. The best improvements will come from cleaning up the ports, and improving the bowl on the exhaust side.
Thanks a bunch for the info. Its more help than I thought I would get. A sincere thanks for the time and advice. Clifford head goes like this: standard clean, magnaflux etc. Milled .100, oversixed valves, hard exhaust seats, ports relieved, new springs, retainers, locks. Can I save some $$ by doing this myself as described above, and still not screw it up?
Oh yeah, I forgot.....for some reason, the '50-'52 235s had 1.94 inch intake valves, as opposed to the 1.875 intakes that the '53-'62 heads used, so the early intake valves are an easy upgrade in later heads.
Have you seen the converstion to weld two V8 heads together and make your own 12 port. Cut off one cyl. from each and weld them together, sounds simple enough, drill and tap a couple mounting holes and Voila.
That split head conversion works on the 230 250 292 motors.It's a lot more involved then a weekends thrash.Are you a machinest?Better get to know one well. Although it's a way to run a twelve port head.
the V8 head thing is shown in the Santucci 6 cyl chevy book, which deals only with the "late" 230-250-292 engines
Do a query on lump port and you should get some good porting information, haven't done it myself yet.
Something else I learned years ago by studying the size and spec chart in the back of the TRW engine parts catalog---Buick 455 valve springs make for an inexpensive high tension spring for a 235.
Unless you are planning on racing keeping the valve spring pressure under 100# is fine. I've turned my GMC's 5800 @ 90#. If you have the time and patience the exhaust ports can give you a lot. The smoother the better. A HEI ignition is the best and easiest. They are available on line already coverted for the earlier engines. Good luck keep the 6's on the road
First, start with a '848' casting, as these heads have the smallest chambers at around 75cc. Get the head spotless, then mag for cracks. Most cracks I've seen are in the chamber, can be cold-pinned. I have one head cracked on the top, above a water jacket - the material seems too thin to cold-pin, so I'll find a shop that can weld it some day. Easier to ream out worn valve guides and install bronze guide liners than trying to locate new guides and a grayberd to install them. Knurling is a short-term fix at best, if wear is UNDER .004". Intake valves can be upgraded from stock 1.88" to 1.94" pre-1955 POWERGLIDE valves. Stellite exhaust valves and hard seats are a good idea for a daily-driver, but OVERRATED for a hobby car IMO. IF the valves and seats are worn, ya, go do it. Valves are the same as an early V-8, so they aren't expensive. BEST bang for the buck is 'pocket porting' the last 1/2" of the intake port below the valve seat, lots of material there to remove. Don't go bigger than 80% of valve size. Use an old exhaust valve as a checking tool, maybe cut down the head a little ( 1.60", cut down .010-.020"). Best to do this BEFORE grinding the seats. My shop did this for $150 back in '07. A DIY job IF your air compressor can support a die grinder - they are air hogs! IMO, porting is a TON of work, for little gain - the ports on both sides are just too small, walls are thin. Maybe just smooth them up, but don't try to go bigger! Ask around to local racers - WHO do they trust for their valve and head work? Look for a shop that builds performance and race engines, ask around for their reputation. I LIKE squirrel's idea of back-cutting the exhaust valves, cheap and easy to do during the valve job. Use a COMPOSITION head gasket over the copper-jacket gasket, as they are thinner AND cheaper! I like to dab a thin coat of Permatex #2 sealer around the water and pushrod openings for GP. I got burned once with an oil leak at a pushrod opening BEFORE the engine ran! MOLLY rings are available from SPEED-PRO, but I want to look into gapless rings from TOTAL SEAL in Phoenix for my next build. Test ***emble the engine, see how far the pistons sit down in the bores at TDC. Anything more that .020", I would deck the block close to '0-deck' to help compression and reduce quench. HOW much did you stroke the crank to gain 9.3 compression? I NEVER thought of doing that! We both know these engines are HARD to gain compression without custom forged pistons. Egge Machine has NO intrest in making hi-compression pistons... THEY are missing the boat!!! Hope my tidbits helps... MUCHO luck with your build! If you dyno your mill, come back with some numbers for HP and torque. WHAT cam are you using, have any specs for duration @ .050" lift and total lift? -Tim
I'd like to know what rod and piston combo you used, how much stroke increase? Watch your intake valve to piston clearance. 6-bangertim - What you said sounds right on. I don't see there is much to be gained from excessive work to these heads unless you are trying to squeeze every last bit out of your engine. Better to get the compression up and keep the head simple.
Thanks, Gofannon, just want to see the OP get the BEST bang for the buck! Great question about rod and piston combo - GMC rods are .300" longer at 7". Egge Machine once posted a build series about a 235 stroker, used 292-six rods, custom cast pistons with a dog-turd dome. For reasons unknown, the build was never compleated and dynoed, and the series delieted from their website. I SO AGREE about compression! Money spent for a full porting job would be better spent on forged pistons to get 9:1 or better. With stock pistons, deck the block close to '0', and keep cam duration SHORT on the intake side - closing the intake early will LENGTHEN the compression stroke! IMO, its all about building for mid-range power and TORQUE... party is over past 4500, unless you are racing with cubic bucks! My 2-cents... Tim
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