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Old 03-14-2008, 12:54 PM
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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, 01:48 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, 03:46 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, 04:49 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 03-16-2008, 11:28 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, 12:21 PM
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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 03-17-2008, 06:34 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, 10:46 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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