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Old 03-14-2008, 11:54 AM
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home porting on BBC heads - deshrouding etc

I am slowly working up the courage to do some home porting on my BBC "049" heads, then plan on having the larger 2.19 / 1.88 valves installed. If anyone can give me any guidance I'd greatly appreciate it. Heads are in great shape,running as is now. -- was planning on porting first, then taking to machine shop to have larger valves machined (correct?). Do I need to worry about nicking the valve seats or will it not matter since I am having larger valves put in ? Also, I have read that you need to do some deshrouding to open up the flow better right next to the chamber wall -- is this necessary? Can I do this myself? How do you keep it consistent between chambers?

Also, what exactly is a "valve job" and would I need this done? I've heard 2 angle, 3 angle, etc...

This will be my first attempt and thus the basic questions. I don't plan on actually doing anything until next winter...figure I'd better start learning now !

Thanks

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Old 03-14-2008, 12:48 PM
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Quote:
Originally Posted by fire_hawk108
I am slowly working up the courage to do some home porting on my BBC "049" heads, then plan on having the larger 2.19 / 1.88 valves installed. If anyone can give me any guidance I'd greatly appreciate it. Heads are in great shape,running as is now. -- was planning on porting first, then taking to machine shop to have larger valves machined (correct?). Do I need to worry about nicking the valve seats or will it not matter since I am having larger valves put in ? Also, I have read that you need to do some deshrouding to open up the flow better right next to the chamber wall -- is this necessary? Can I do this myself? How do you keep it consistent between chambers?

Also, what exactly is a "valve job" and would I need this done? I've heard 2 angle, 3 angle, etc...

This will be my first attempt and thus the basic questions. I don't plan on actually doing anything until next winter...figure I'd better start learning now !

Thanks
Buy this book; How to Build & Modify Chevrolet Small-Block V-8 Cylinder Heads
by David Vizard

Think about what he examples on an SBC as rocket science that can be applied elsewhere as the principles are the same for a wedge or almost a wedge engine.

You want to port first, then do the valve job as yes you'll probably nick a seat or more.

Reading Vizard will confirm this; air doesn't like to turn at angles greater than 15 degrees max. A 3 angle valve job starts the turn from straight with a 60 degree cut in the throat, then -15 to the 45 seat, then -15 to a 30 degree top cut. Race engines apply more cuts between the 30 and the chamber roof and sometimes between the port wall and the 60 degree cut, but this is pretty expensive when you get into 5 and 6 angle cuts so the average guy doesn't usually go there. Besides the gain of these extra cuts is small, if you're not front row competitive it ain't worth the cost.

The 049 head doesn't need the wall opened up. Equalizing chambers is highly over-rated the difference in hundredths of a point of compression isn't measurable at the crankshaft, especially considering that the heads will carbon up quickly and every chamber will have a different static ratio. Once again screwing around with equalizing chamber volumes to a fraction of a cc is only, and probably not even then, strictly the purview of people who get in the front row. An getting there takes way more than a big power numbers, first you've got to finish, then if your nuts are big enough to run with the big boys, you can can start to work on getting speed. But if you don't understand chassis and handling; gears, torque and weight all the power in the world still won't get you there. So money time and effort spent screwing with chamber volume is well better invested in a good balance job.

Bogie
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Old 03-14-2008, 02:46 PM
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Thanks for the info -- I have a 396 with who knows what pistons ( I think they're 10.25 with closed chamber heads) so I think my CR is low. As TBIRD and others stated, I need to take it apart and do a full static CC check before I do anything -- may end up doing some milling (in which case I need to mill the intake ?? --> its an edelbrock performer II, I believe)

-- Would it be worth going to roller rockers ??

THanks !
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Old 03-14-2008, 03:49 PM
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Quote:
Originally Posted by fire_hawk108
Thanks for the info -- I have a 396 with who knows what pistons ( I think they're 10.25 with closed chamber heads) so I think my CR is low. As TBIRD and others stated, I need to take it apart and do a full static CC check before I do anything -- may end up doing some milling (in which case I need to mill the intake ?? --> its an edelbrock performer II, I believe)

-- Would it be worth going to roller rockers ??

THanks !
Roller rockers are a good investment if the cam lift is getting on toward a half inch. The take a lot of side load off the stem so wear at high lifts of the stem and guide is reduced. This in and of itself doesn't do much for power except that with reduced wear and binding moments the clearance stays in limits longer so power doesn't evaporate over time because the guides are sucking air and oil, and allowing the valve to wobble on its seat. This can also let you get away with a little less spring pressure which if your building a high winding engine does take some stress and strain off the valve actuation components.

If you go to a higher ratio rocker, its a good idea to go with a roller, as higher ratio rockers force the pivot, rocker, pushrod, lifter, and lobe to see more load than originally designed for. The roller with the above sighted advantages for cams around .5 inch lift and up as well as these components are being accelerated at a greater rate. So overall wear and tear goes up along with the rocker ratio. The higher ratio tends to increase power, mostly on the top end, by 10-15 hp because it not only adds lift but increases overall intensity of the lobe, which is a way to say the instant events of lift versus duration go up, so the cam looks bigger to the engine.

Bogie
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Old 03-15-2008, 02:09 PM
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if you're working with a 396-325-350hp 10.25:1 cr motor with the stock pistons that used closed chamber oval port heads, why do you want to drop the cr into the toilet by swapping on 118-120cc heads.
Open chamber heads do not need any deshrouding at all.
The most you would want to do to the chamber to allow physically fitting a larger valve is to grind the chamber wall just a bit at the closest point just to restore the stock valve edge to chamber wall clearance that you had with the stock valves.

Yes the open chamber heads are less shrouded and breath a bit better in stock form. But if you want to deshroud a head (that can use that) with bigger valves for a 396 with the stock pistons work with the stock small chambered 396 closed chamber oval port head. Deshroud near the spark plug to improve chamber flow. (don;t get carried away) Deshroud just a bit around the valves just enough to allow clearance for the new large valves. use a drill bit as a gauge with the stock valve in the chamber and compare with the larger valve to see what minimal chamber wall grinding is required. On the early closed chambered oval port heads a 2.19x1.84" valve set works very well with moderate correct chamber deshrouding and home porting.
Since the new larger 2.19"-1.84" valves are .060" larger in radius, thats as much as you need to rework the chamber wall near the valve edge to fit larger valves. A 1.88" valve is not recomended on this head.
Spray water with the garden hose thru the bare cylinder head ports to see the flow pattern into the chamber. You're neighbours may think you've lost it, but you'll get a good idea of what chamber mods will help flow.
Move the hose around, top of port, bottom floor etc and watch the water flowing into the chamber from the port.
Again, BBC open chamber heads do not need deshrouding.

Yes you will need a new valve job and stay off the valve seats with the die grinder. Use old valves to protect the seats while working the chambers. use long stemed carbide burrs while working the bowls.
You'll also want the valve guide bosses shortened for new seals and higher valve lift retainer/ guide seal clearance.
Do not try to hog out a closed chamber head the same as a open chamber head. it is not nessessary to go that far to get improved chamber flow.
Once properly ported and properly deshrouded for improved flow with larger valves, the closed chamber 396 head will flow all the airflow you'll need to make big power on a 396. it will have the right combustion chamber volume for your 396 w/ stock small domed pistons with minor flat milling. CC the heads after moding the chambers and mill as required.
It is critical that you maintain the as designed net quench clearance (.040) on a high compression 396 on pump gas. Measure the deck clearance and pick a suitable head gasket.
If you will not be boreing the 396 cylinder bores +.060" or more you will need to notch the cylinder bores top edge for the larger valves as was done on the factory 375hp L-78 motors with the rectangular port big valve heads.
If you're working with stock bore size 396, and do not want to notch the bores for valve clearance, use stock sized valves. general porting is still very effective even with the stock 2.065"x 1.74" valves on a 396.

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Old 03-15-2008, 03:18 PM
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If you are going to work with 049 heads for a 396 with the stock small domed pistons (325-350hp oval port motors), I would CC the heads first. Some, are quite large in chamber size.
Deshrouding for larger valves will increase the chamber volume from stock.
Excessive head milling to get back to a decent measured cr will reduce the piston to valve clearance on stock GM pistons, limiting the cam duration and overlap you can run without notching pistons for additional clearance.
When running stock 396 cylinder bores + larger than stock valves in the heads, valve edge to cylinder wall clearance may be an issue. It will be close.
Something to check on a stock bore 396 motor before you get all carried away.
All these issues are why I prefer staying with and reworking a closed small chambered head on moderate street oval port 396 motors with the stock pistons. Doesn't take a lot of "deshrouding" in the right spots even with the stock valves, to wake them up.
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Old 03-16-2008, 10:28 AM
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Thanks for all of the input! I believe I was unclear up above -- what I meant to say is that I believe I would have 10.25 cr (thats what pistons are ) if I were to have closed chamber heads...however the motor came with 049 heads thus that is what I am running. After reading the above input though, I am almost thinking I should just find some closed chamber heads so I don't have to do anything trick fancy to get my compression up. Looks like they're pretty cheap. I think I'll eventually upgrade the cam as well, which I don't think I'll be able to do with the 049 heads. My 396 (actually its a 402) is bored 60 over right now. Correct me if I'm wrong, but I believe I'd be able to get more power out of the closed chamber heads when everything is said and done...are the ports on these heads "regular oval" or "large oval", like the 049/781 heads ?

One questing on deshrouding -- to make more room for bigger valves -- do you deshroud all the way from the bottom of the wall (where the valve is ) to the top (where the head gasket is) or just "notch" it ?

Thanks for all the info...have learned a lot !
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Old 03-16-2008, 11:21 AM
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Bowl smoothing is the low hanging fruit of head porting. Pull out the valves and smooth out the transition between the valve seat and the port.

Bigger valves should require a little unshrouding were the valves come closest to the chamber wall. Changing out 2.06's for 2.19's moves the valve 0.065" closer to the wall which cuts off flow.

10.25:1 cr 402 wth 110 cc heads with drop to 9.25:1 with 120cc 049 heads.

820 BBC head's flow really well, especially on the exhaust side due to a very nice shaped combustion chamber. These heads are typically on 402's. What heads do you have?
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Old 03-16-2008, 10:30 PM
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Well I get a whole different result on cr using a stock piston or a same replacement. A oval port 402 will have no compression even using a thin head gasket with a 110cc head. The 110cc heads came on the 1970-1970 454LS5 not the oval port 402. The 10.25:1 402 came with a 101cc closed chamber head and a thin .022" head gasket. I don;t have the TRW catalog but I believe the piston had a +17cc dome and .020"-.022" below deck at TDC.

Do you know the exact piston you have in your motor? You need to check deck clearance and dome volume.
Like I said the actual chamber volume varied even on the same casting # depending on what cid size GM installed the head on. You have to cc your heads.

The ports on the early 396-427 oval port closed chamber heads are just as big as the ports on the open chamber oval ports. the OC head is les shrouded near the plug, but you can fix the CC head for plenty of flow.
The flow pattern is just a little different on a early CC oval head.
the Open cc 049-781 head is definatly prefered on a big bore 427-454 based build up but the small er 396-402 bore is not so critical. the closed chamber with proper reworking, works very well on a 396-402 engine.
Once the cc head is reworked, the trade off of airflow compared to the OC head relative the requiring a larger more intrusive dome (or excessive milling which limits V-P clearance) for cr does not pay off.
Yes you would clearance the chamber wall all the way to the floor same as it is now with a nice radius corner from wall to floor. A lot of this is just common sense. The chamber wall that is right near the bore edge is not a hi flow area. The air does not flow in that direction into the chamber. Use the garden hose as I said to see the airflow pattern from port to chamber. Most every where you think is a shrouding issue, is not. A closed chamber head only needs specific minor deshrouding of the chamber wall near the spark plug area to wake up the flow. Similar to what you would do to a SBC camel back head.
Just restore the orignional valve/chamber wall clearance around the new valve the same as the old valve had. Don't get stupid and hog out all the way around the valve thinking that will make it flow. It won't.
Don;t make the chamber bigger than the cylinder bore. Don't use a head gasket as a guide. It is way bigger than the cylinder bore. Think, measure, check before you grind. Do not over grind. You're not Bill Jenkins.
Get the book on porting cylinder heads by David Vizard. There is a good DV online article available free all about cylinder head shrouding and where you need to grind. Look at other similar BBC cylinder heads Dart Edelbrock GMPP etc L-88 L78 rec port and LS-6 heads. remember evey bit you carve out of the chamber makes it all the bigger, requiring more head milling. thats why I like the early small 96-98cc bathtub chamber 396-325HP oval port heads for this stuff. Lots of room to play with the chamber and still end up with decent cr without excessive milling.

get the real numbers and input them Here to calculate the measured cr. You're going to need a 98 to a 105cc chamber for decent cr depending on your exact dome volume, gasket volume and deck clearance.
How much do you think your going to chop off a 120cc head? Many, many times the actual cc volume is large than listed.
You'd best measure your Valve to piston clearance now (with the cam you'll be using) before you start cutting big meat off the open chamber head for compression on a 402. BBC's with stock type pistons are famous for the lack of V-P clearance with any cam bigger than the L-78-LS-6 factory cam.
Check all roller cams. All hyd and solid flat tappet cams bigger than 244@.050" Every bit you chop off the head deck and or block deck reduces the V-P clearance.
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Old 03-16-2008, 10:42 PM
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The green area is the zone that can use some deshrouding and laying back a bit.
Do not get carried away.
there is a "good port" and a "bad port". the bad port flows in to the chamber wall a bit more.
It will always flow less than the good port. The difference is minor, especily with minor proper deshrouding. The closed chamber oval BBC head gives of a bit of ultimate flow but makes up for it with mixture swirl and "tumble" mixture motion on compression and raw compression ratio. You can make big street power with the CC heads on a 402. The open chamber heads need the big 454+ bore size and very high .600"+ valve lift to show their advantage above 550hp.
The ports are essentually the same. The porting work to the ports required of both the OC and CC heads is essentually the same.

You need a 24cc+++ ("11:1") L-78 396-375HP type big piston dome to use the OC heads on a 396 or 402 for a cr of 9.6 to 10.25:1 and a milled OC head (115ish cc) You don't have that piston in your motor.

If you bolt a 120cc head on a +.060" 402 with the stock 10.25:1 piston and no decking and a felpro .039" gasket your cr will be 8.25:1

If you rework a 96-98cc 396 CC oval head for 101cc with big valves and some minor deshrouding and bolt it on with a LS-6 .022" shim gasket for proper quench, you will have 10:1 even. use a 2.19" intake valve and a 1.84" max exhaust valve. A 1.88" ex valve requires too much chamber removal with no gain. No good on a 396-402 bore.
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Old 03-17-2008, 05:34 PM
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Thanks FBIRD, I think you made my decision a lot easier. I believe it would make sense to find some cheap closed chamber heads to work with. That way, I can upgrade the cam as well, if I want to, and have a good set of heads if I ever decide to build a 454 +! It doesn't sound like open chamber heads were really meant for those motors. I don't know exactly what CC the pistons are -- I'll have to tear the motor apart to find out. I'm sure my compression is way too low.

I think I have a better understanding of what is involved with the cylinder head porting as well (thanks for the illustration!) but definately plan on reading some books and practicing before I touch anything. I'm sure I'll have more Q's when I dig into it !

Thanks
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Old 03-17-2008, 09:46 PM
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All of those closed chamber big block heads will require hardened valve seats and that's going to cost some dollars plus the valve job and porting time and parts... also be carefull installing 2.19/1.88 valves with hardened seat inserts-many heads will hit water when cutting for the inserts. Edelbrock makes a small chamber oval port head that might work if there's enough bore clearance.
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