Cyl.Head Combustion Chamber Polishing? Engine guys, Racefab?

[Bass]

I'm trying to get the heads ready to go on my new small block once it gets back from machining, and I'm curious what the best way to prep the chambers is?

My combustion chambers as cast look like this:

http://pic3.picturetrail.com/VOL19/1983783/4017955/57800374.jpg

Not too bad, but a couple of the spark plug holes look like this:

http://pic3.picturetrail.com/VOL19/1983783/4017955/57800317.jpg

So do I need to just knock the burring off of the hole where it was tapped, and bolt 'em on? Or should I go ahead and polish the chambers? Will it really make a noticeable difference in a motor that going to be predominately used on the street?

And if I do decide to lightly polish the chambers, do I have to disassemble the heads and have another valve job done afterwards?

If so... a light deburring to get rid of potential "hot spots" seems like the way to go, right?

Thanks in advance for any help.

[Unkl Ian]

Definately knock off the sharp edges.

After that,polishing is just Eye Candy,for a street motor.

[BIG RIC]

I would just knock the burrs off.

[Flat Ernie]

Concur. Not required for street engine at all. But definitely knock off those hanging threads...

http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[Deyomatic]

You may want to run the Shop-Vac with the other hand while grinding that stuff off, just to be sure that little chunks don't end up where you don't want them.

[Bass]

OK, thanks guys. A couple of hand files made quick work of the burs.

Here's a pic of the same chamber that's in the bottom pic above after deburring:

http://pic3.picturetrail.com/VOL19/1983783/4017955/57817165.jpg

Does that look ok? Anything wrong with knocking the big 'bumps' off the rough/ as-cast portion of the chamber with a piece of 180 grit paper? Or would I just be wasting my time?

[Scotch]

Here's a few thoughts to shake you up.

Polishing a chamber to a mirror finish doesn't really do anything. In fact, leaving the surface as you have keeps the air and fuel mixed. A smooth surface could help pull fuel out of supension.

Sharp edges are a funny thing. Flow-wise, they prevent vortices from developing and keep flow headed in the right direction. Detonation-wise, the sharp edges provide a potential "hot spot" for preignition to begin. What to do?

A little of both. I'd clean all the sharp edges anywhere near the exhaust valve. It's the hottest part of the chamber, so it needs to stay cool.

I'd be gentle when rounding off everything around the intake valve, though. Keeping the edges a little sharp may help here.

If you can, once you're finished with your chamber work, send them to Calico to get coated with thermal barrier coating. This will insulate the chamber, keep the heat in, and the energy as well. The coatings are porcelain, and I get the ports, chambers, and valves all coated with the stuff. Pistons should be coated with the thermal barrier on top and anti-friction graphite coatings on the skirts to limit friction.Buy your bottom-end bearings from Calico too- they sell all common sizes pre-coated with anti-friction and that's free power and extended durability.

Just some ideas, but if you want to talk more let me know.

Scotch~!

[Bass]

Good stuff, Scotch...thanks.

I'd never considered coating the combustion chamber, and it's not going to happen on this build...but it is something I'll keep in mind for future reference.

I've read and heard that the intake port should be left with a 'pebbled' surface when porting to keep fuel from puddling, but I'd never heard that the combustion chambers are best left the same way.

I've just finished doing pretty much what you suggested by knocking off the sharp edges and it looks like I'm going to stop there.

The bottom end is out for balancing at the moment...it should be fully assembled by the end of next week or so. I'm using Keith Black hypereutectic pistons...and I've gotten all kinds of different opinions on those. http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif

[Unkl Ian]

Some of the high end engine researchers have experimented with
combustion chanber textures and patterns,Jim McFarlin(sp) being one.
Real cutting edge theory competition stuff.

Just tell everyone it's ported and polished.They will believe you. http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[Bass]

I'm also going to tell everyone that it's a 283.

http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[FWilliams]

all good points, i would however radius that ridge between the spark plug and the intake valve, looks to be quite sharp near the valves in that last picture. maybe just the photo?

what brand heads are those.

[Roothawg]

What kinda heads are they?

[Bass]

They are Trickflow G2 Twisted Wedge heads. There is a ridge there, but I think the shadow in that last picture makes it look sharper than it actually is.

Thanks for all the advice fellas...anything else I should keep in mind as I get them ready to bolt on?

[JOECOOL]

Just another opinion here. Put the head on with an empty block and scribe the bore size on the head. Depending how big the bore is some of the head beside the valve can be slightly enlarged to help unshroud the valve. Not too much tho,as larger combustion chambers have less compression.
Other than that,check all threaded bolt holes with a tap ,clean and radius the drain back holes on the top side. Measure the height of the spring retainers with a dial caliper and write it on the garage wall so when you have it apart again you can check how much the valve or retainer has sunk. I would pick one particular Cyl and have a machine shop check and record spring pressure at seat and open for future reference. Just my opinion.

[Hot Rod To Hell]

Actually JOE, on older heads, I would TOTALLY agree about unshrouding the intake valve;

BUT: On the newer heads they put a ton of time and money into R&D, and those chambers are shaped "perfectly" to get optimum swirl and quench characteristics. I don't think I'd go screwin around with 'em! http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[Scotch]

Welll...if your ASKING for more tips...LOL!!

Seriously..

I assume you're looking for more go outta this deal and that means addressing the port alignment between the intake and the head. The natural urge is going to be to perfectly match the intake port in the heads to the corresponding port in the intake manifold. Here's a tip: Make the intake manifold side about 1 mm (that's one little millimeter) smaller than the port in the head. Leave this 1 mm border all around the circumference of the port. What this does is pull whatever fuel may have puddled or fallen out of suspension on the way to the intake port and get it into the head. It also serves to increase the velocity of the incoming air charge by use of a "step". This is becoming a common move, but few seem to have heard about it. If you doubt to effectiveness of "stepping" the flow path of your air/fuel charge, look at stepped headers.

Much research has been done to develop the stepped header, where larger diameter tubing is used to carefully graduate the diameter of the header pipe to larger and larger diameters as the exhaust flows further back. This has been proven to release the boundary layer of slow-moving air right at teh surface of the material; in this case the internal wall of the header pipe. By stepping up to a larger size, the boundary layer is violated and becomes a faster-moving column in the next-larger pipe in the chain.

Further research has shown a similar effect on the intake tract. Stepping the various stages of intake air charge (from carb-to-intake, which is a natural progression, to the 1 mm mismatch between intake and head, to the choke point around the valve) has shown efficiency gains. Like the exhaust, the intake charge gets lazy and a boundary layer of air/fuel (which is actually much heavier than the exhaust, and much cooler/less willing to expand) lies along the walls of the intake- particularly on the floor (where the heavy fuel falls out of the airstream). By adding successive steps in the system, the air/fuel charge is more apt to stay well-mixed and provide a better shot at the valve. It's still far from "perfect", but if you're in a position to make an improvement (while yo're porting and polishing), it'd be worth the time to carefully "step" the intake/cylinder head mating point. 1 mm is all it takes!!

Scotch~!

[Bass]

I am planning on matching the intake ports to the heads....so I'll give the 'step' a shot. Thanks for the info!

As far as working the heads anymore, I think I'm just going to bolt them on as is, now that I've cleaned up the casting/ burring a bit. They are supposed to be a pretty good head straight out of the box. FWIW, I don't believe this pair of heads has ever been run on a motor (i.e. they are new.)

Thanks again for the advice!

[Scotch]

I'm with you on the "as-is" with regard to working over the insides of the ports. The heads you have are good out-of-the box, and the suggestions I've made can only make them better for ya. If you want to get inside them and smooth out the short-side radius and carefully taper the valve guide bosses, that won't hurt a bit either. These are castings so they're always going to be able to be improved upon with hand-finishing simply because no mfr. will take the time to hand-finish every set. Yours are indeed better than most, but while you're in there...LOL!!

Scotch!~

[Bass]

Any opinion on how a single plane intake will affect these heads?

If I was going for all out streetable horsepower, I think I'd run a Performer RPM Airgap...but I have a really cool medium rise Offenhauser dual-quad that I'm going to give a try. I'm going to run 2 500cfm Edelbrocks on top of that (non-progressive linkage). I'm willing to sacrifice a little for the look.

The best I can figure, I'm going to end up with a motor with decent torque from about 2500 on up, but a strong HP punch at higher RPMs. Should be fun with my 4spd.... http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

Hot Rod magazine built almost an identical motor, with the exception of a single 4bbl on an Airgap, and with a tad less cam and compression back in 2001... and it made 434 ft./lbs. of torque at 4200, and 414 HP at 5700.

I think (well, hope) I'll be somewhere close to that range even with the 2x4s....although I am expecting to lose a little torque.

[Scotch]

How'd this thing end up? You got me all curious...

Scotch!~

[Bass]

Hey Scotch...the bottom end is supposed to be ready to pick up from the machining/ balancing this week. I'm in So-Cal right now so it'll be another week or so before I can pick it up.

I still have to buy pushrods and a good fuel pump, but other than that I think I have everything I need to put it in when I get back.

I'll let ya know how it runs after I get it back together.

http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

[Scotch]

I'm in SoCal too- Wanna stop by for a beer? We can talk motors.
714-305-8926