Swapping Heads Question - Team Camaro Tech
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post #1 of 26 (permalink) Old Sep 19th, 16, 10:43 AM Thread Starter
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Dave
 
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Swapping Heads Question

I have my 402 down to the short block right now to put a new cam in it. I'm going with a Comp Cams Xtreme Energy CL11-250-3 and full Roller Rockers 1.7.
I was planning on installing a set of Brodix heads when I put it back together, but there was a problem and I can't do that right now. The guy I was getting them from had them checked and they had a crack between the cylinders...
My question is: What would result from me swapping my born with 396/402 L34 heads on to my block? I'd be going from 3993820 oval Port, Open Chamber 113cc heads @ 9:1 to 3964290 Oval Port, Closed Chamber 101cc heads that are ~10.5:1 from the factory.
I'm hoping to bump up the power. Would this work or would there be problems/interference/too much compression? I don't have the flow numbers, so I can't estimate what the compression would be.
Here's the pistons my 402 currently has:


'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

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post #2 of 26 (permalink) Old Sep 19th, 16, 11:45 AM
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Re: Swapping Heads Question

Dave, its been a long time since I messed with BBC but I have a flow table on both of these heads. I always ran open chamber piston with a matching head. To give me more compression, I milled the EXHAUST SIDE of the head .100 and 0 on the intake. I ran Brooks pistons and had some 13.1 comp, but all of this was race stuff.

Below is what I found,

I show the 290 oval with 105cc and the 820 with 113 cc.
I show the 820 flowing better than the 290. I believe the piston dome has a lot to do with this.

Just by looking , you going to a closed chamber , with an open chamber, tells me you have more compression. Remember the piston plays a part of this.

I got this info from a Stan Weiss flow table , it doesn't say anything about pistons.
So, I would place one of those heads you want, on the motor and turn it over , with the cam in place , to check for clearances. Maybe some playdoo to get an impression of your clearances without the cam. Good luck.

This flow table list is long, you have scroll down to your head and it reads head manufactor by cfm flow @ cam lift.

Stan Weiss' - Cylinder Head Flow Data at 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software

Don
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post #3 of 26 (permalink) Old Sep 19th, 16, 01:32 PM
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Dave
 
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Re: Swapping Heads Question

You are going to bump up your compression considerably: assuming the domes don't actually hit the head; which is a distinct possibility.

I have seen a lot of big blocks but those pistons are a first. Never seen a mirror image piston dome on a BBC. That is a SBC thing incorporated because of pistons having an off set to keep them quitter on start up and they have to go on a pressed pin (nothing wrong with a pressed pin, full floaters are only of value if you take your motor apart frequently to inspect it for damage).

I would see if they, the domes, hit first (don't spin it over hard with a starter motor, but turning it over by hand easily, expecting contact, and the damage it will cause at any moment). If they do clear find out by how much, with some modeling clay. Even offset pistons rock in their bores so if it is paper thin expect contact unless the domes are cut down. Third check piston dome volume and cc the head to calculate your static compression ratio.

Also mock up your cam with a solid lifter body to check piston to valve clearance, especially on the exhaust side, six to sight degrees after TDC.

Finally have you checked the foot notes to see if those Brodix heads will clear your small bore big block? Frequently with a big valve head and a small bore motor the valve either hits the cylinder wall while opening or is so close as to be heavily shrouded. (that is why a 396 has those eye brows cut in the top of the bore. It is to clear a 2.19 inch valve not a 2.30 inch valve).

Big Dave
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post #4 of 26 (permalink) Old Sep 19th, 16, 01:52 PM Thread Starter
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Re: Swapping Heads Question

Quote:
Originally Posted by zdld17 View Post
Dave, its been a long time since I messed with BBC but I have a flow table on both of these heads. I always ran open chamber piston with a matching head. To give me more compression, I milled the EXHAUST SIDE of the head .100 and 0 on the intake. I ran Brooks pistons and had some 13.1 comp, but all of this was race stuff.

Below is what I found,

I show the 290 oval with 105cc and the 820 with 113 cc.
I show the 820 flowing better than the 290. I believe the piston dome has a lot to do with this.

Just by looking , you going to a closed chamber , with an open chamber, tells me you have more compression. Remember the piston plays a part of this.

I got this info from a Stan Weiss flow table , it doesn't say anything about pistons.
So, I would place one of those heads you want, on the motor and turn it over , with the cam in place , to check for clearances. Maybe some playdoo to get an impression of your clearances without the cam. Good luck.

This flow table list is long, you have scroll down to your head and it reads head manufactor by cfm flow @ cam lift.

Stan Weiss' - Cylinder Head Flow Data at 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software

Quote:
Originally Posted by Larger Dave View Post
You are going to bump up your compression considerably: assuming the domes don't actually hit the head; which is a distinct possibility.

I have seen a lot of big blocks but those pistons are a first. Never seen a mirror image piston dome on a BBC. That is a SBC thing incorporated because of pistons having an off set to keep them quitter on start up and they have to go on a pressed pin (nothing wrong with a pressed pin, full floaters are only of value if you take your motor apart frequently to inspect it for damage).

I would see if they, the domes, hit first (don't spin it over hard with a starter motor, but turning it over by hand easily, expecting contact, and the damage it will cause at any moment). If they do clear find out by how much, with some modeling clay. Even offset pistons rock in their bores so if it is paper thin expect contact unless the domes are cut down. Third check piston dome volume and cc the head to calculate your static compression ratio.

Also mock up your cam with a solid lifter body to check piston to valve clearance, especially on the exhaust side, six to sight degrees after TDC.

Finally have you checked the foot notes to see if those Brodix heads will clear your small bore big block? Frequently with a big valve head and a small bore motor the valve either hits the cylinder wall while opening or is so close as to be heavily shrouded. (that is why a 396 has those eye brows cut in the top of the bore. It is to clear a 2.19 inch valve not a 2.30 inch valve).

Big Dave
Thank you both for the info. I was thinking about doing the Playdough trick, but I think there might be too much of a chance for a problem running these heads for minimal or no gain. I've seen what Don mentioned about the 820s flowing better. I guess unless you're running a race motor, open chamber is better than closed. These are my born with heads off my 396/402 that I was thinking about running on my spare 402. I'd be sick if I hurt them. They'll stay on the 396 now...

The piston I posted I thought looked just like a factory open chamber 402 piston. I guess not. I had the same pistons in this motor as well as a 71 SS396Chevelle motor I sold.
I'd be happy bumping up the compression a point to a point and a half.
The Brodix heads wouldn't be a problem. They claim they'll bolt right on with no modifications. 2.25/1.88 valves. I have seen those brows. I've heard some guys knock the edges off them to smooth them out.
Either way, I suspect I'm looking for something I'm not going to get with this head swap. "The juice isn't worth the squeeze..."

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

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post #5 of 26 (permalink) Old Sep 20th, 16, 04:41 AM
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Re: Swapping Heads Question

Keep in mind what the operating range of this engine will be and tune/build accordingly.
If a street driver, build for torque. Torque is what pegs the Seat-O-Pants meter.
Torque needs velocity of the in filling the chambers - small ports are better.
If building for 5k rpm and above, then yes, larger ports needed for more flow.

Also, buy a new honing stone and a can of WD40, and 'hone' the block deck and head for a smoother surface for better sealing.
if you can remove the dowels for the heads in the block, better yet.

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post #6 of 26 (permalink) Old Sep 20th, 16, 06:02 AM Thread Starter
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Re: Swapping Heads Question

Quote:
Originally Posted by Everett#2390 View Post
Keep in mind what the operating range of this engine will be and tune/build accordingly.
If a street driver, build for torque. Torque is what pegs the Seat-O-Pants meter.
Torque needs velocity of the in filling the chambers - small ports are better.
If building for 5k rpm and above, then yes, larger ports needed for more flow.

Also, buy a new honing stone and a can of WD40, and 'hone' the block deck and head for a smoother surface for better sealing.
if you can remove the dowels for the heads in the block, better yet.
Thanks Everett. I want heads that are around 250cc for the intake runners for that reason. All the inexpensive ones on places like ebay are 310 and above. I think they'd be worth trying if they had some that were around 250cc.

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

"The galleries are full of critics. They play no ball, they fight no fights. They make no mistakes because they attempt nothing."
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post #7 of 26 (permalink) Old Sep 20th, 16, 06:21 AM
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Re: Swapping Heads Question

Stock heads are 320 cc for rectangular port high performance heads and 250 cc for the PASS round port heads. The smaller 1975 and newer "peanut port" heads started out at 230 cc and continually shrank smaller every few years as the engine got older, down to 190 cc (which is the size of a camel hump SBC head) before the engine went out of production in 2001.

Smaller ports build torque down low where you need it for towing (which is why the Chevy engineers constantly reduced the port size as the big block was competing with diesel engines in the light truck market) or on the street, but they compromise the engine's ability to make peak power; which is what you want for racing.

Big Dave
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post #8 of 26 (permalink) Old Sep 20th, 16, 06:28 AM Thread Starter
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Re: Swapping Heads Question

Quote:
Originally Posted by Larger Dave View Post
Stock heads are 320 cc for rectangular port high performance heads and 250 cc for the PASS round port heads. The smaller 1975 and newer "peanut port" heads started out at 230 cc and continually shrank smaller every few years as the engine got older, down to 190 cc (which is the size of a camel hump SBC head) before the engine went out of production in 2001.

Smaller ports build torque down low where you need it for towing (which is why the Chevy engineers constantly reduced the port size as the big block was competing with diesel engines in the light truck market) or on the street, but they compromise the engine's ability to make peak power; which is what you want for racing.

Big Dave
Thank you Dave! I've been looking for that info, but I haven't been able to find it. So L78 heads would have had 320cc stock. That's good to know. The heads it looks like I'm putting back on are '69 truck heads with 2.06/1.72 valves unfortunately.
I know it's not ideal, but what do you think about a set of aluminum heads that were c&c'd in GA. Completely done in the USA. $900+- for a pair assembled... 310cc runners, 2.25/1.88 valves. Up to .700 lift. These are the ones I posted a link to in my other thread last night. Looks like nobody had an opinion they wanted to share on them. I just don't have the $2k for the heads I want.

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

"The galleries are full of critics. They play no ball, they fight no fights. They make no mistakes because they attempt nothing."
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post #9 of 26 (permalink) Old Sep 20th, 16, 06:51 AM
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Re: Swapping Heads Question

Aluminum heads will shave nearly a second and a half off of your E.T. just in weight savings; not to mention save your back.

The heads are cast in China from copies of GM heads and assembled after machining the raw castings in the US. I don't know as to their quality as I have never bought them in the past preferring newer head designs that are entirely made in the US such as Edelbrock, Brodix, AFR, or TrickFlow.

Heads determine the engine's ultimate power level. Designs have changed tremendously over the decades since the BBC was first designed back in 1961. A copy in aluminum of that 1961 design only buys you weight savings; not a power gain due to changed port size, shape, and location, with much more efficient and smaller combustion chamber shapes found on modern heads.

Big Dave
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post #10 of 26 (permalink) Old Sep 20th, 16, 07:05 AM
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Re: Swapping Heads Question

From my experience the pistons you have in the block will work with the 3964290 oval port heads...The pistons you have are not factory pistons they are considered rebuild pistons...One of the 402 BBC I used to run I had those same pistons with closed chambered heads (063) and had no problems with valve clearance because the dome is so small like around 5 CC...With the 820 heads and those same pistons I calculated my compression around 8.5:1...I swapped the 820's for 063 heads which are closed chamber oval port heads (101cc) and bumped my compression up to around 9.5:1...

Hope this helps...

Mike
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post #11 of 26 (permalink) Old Sep 20th, 16, 07:31 AM Thread Starter
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Re: Swapping Heads Question

Quote:
Originally Posted by knuggles68RS/SS View Post
From my experience the pistons you have in the block will work with the 3964290 oval port heads...The pistons you have are not factory pistons they are considered rebuild pistons...One of the 402 BBC I used to run I had those same pistons with closed chambered heads (063) and had no problems with valve clearance because the dome is so small like around 5 CC...With the 820 heads and those same pistons I calculated my compression around 8.5:1...I swapped the 820's for 063 heads which are closed chamber oval port heads (101cc) and bumped my compression up to around 9.5:1...

Hope this helps...

Mike
Definitely gives me something to think about Mike. I appreciate the feedback.

Quote:
Originally Posted by Larger Dave View Post
Aluminum heads will shave nearly a second and a half off of your E.T. just in weight savings; not to mention save your back.

The heads are cast in China from copies of GM heads and assembled after machining the raw castings in the US. I don't know as to their quality as I have never bought them in the past preferring newer head designs that are entirely made in the US such as Edelbrock, Brodix, AFR, or TrickFlow.

Heads determine the engine's ultimate power level. Designs have changed tremendously over the decades since the BBC was first designed back in 1961. A copy in aluminum of that 1961 design only buys you weight savings; not a power gain due to changed port size, shape, and location, with much more efficient and smaller combustion chamber shapes found on modern heads.

Big Dave
That explains their low price. Makes sense. I thought I saw where the ones from GA were all USA made including the castings. Maybe not. I really wish I could go with the Brodix I wanted, but that's going to have to wait a little while. I'll look a little closer at the design etc and go from there. They'll definitely be back savers at least if I go with them... I appreciate the info.

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

"The galleries are full of critics. They play no ball, they fight no fights. They make no mistakes because they attempt nothing."
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post #12 of 26 (permalink) Old Sep 20th, 16, 06:23 PM
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Re: Swapping Heads Question

Put the 2.19/1.88 valves in the closed chamber oval port heads. My Vette cam with the same set up. Those heads are way better on the street than the rectangle ports. Headers I assume?

Cam, what are the numbers? Solid?

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post #13 of 26 (permalink) Old Sep 21st, 16, 06:10 AM Thread Starter
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Re: Swapping Heads Question

Quote:
Originally Posted by 1971ls6 View Post
Put the 2.19/1.88 valves in the closed chamber oval port heads. My Vette cam with the same set up. Those heads are way better on the street than the rectangle ports. Headers I assume?

Cam, what are the numbers? Solid?
My closed chamber heads are the born with virgin heads off my 69. I was going to pull them off the motor and run them, but I don't want to screw with them by putting bigger valves etc. I'm going to do something else.
I'm not planning on running rectangle ports. Oval ports, open chamber in whatever I end up with.
I have Doug's headers w/ 2" tubes. I know, a little too big... She'll grow into them someday.
My cam will be a Comp Cams XE284H. Hydraulic flat tappet.

110 LSA
Duration @.050": 240/246
Valve Lift: 574/578

I'm still deciding whether I should buy the full kit at $430 or go with the cam and lifters for $208. The full kit ads a non-double roller timing chain, springs, valve seals, locks and keepers. I have a good double roller timing chain in there right now. The only thing I'm unsure of is the springs. Mine are stock.

I talked to Competition Racing Supply last night about their heads. They sound pretty decent and I'm leaning in that direction. I'm thinking I should get the second set of springs listed.

Specifications :

•Brand
ProComp
•Manufacturer’s Part #
PC3021-396
•Cylinder Head Style
Assembled
•Cylinder Head Material
Aluminum
•Combustion Chamber
115cc
•Intake Runner Style
Oval
•Intake Runner Volume
300cc
•Exhaust Runner Volume
110cc
•Intake Port size
1.800W x 1.990H
•Exhaust Port size
1.900W x 1.680H
•Spark Plug Style
Standard Angle
•Intake Valve Diameter
2.250 in.
•Exhaust Valve Diameter
1.880 in.
•Rocker Stud Thread Size
7/16 - 20 in.
•Accessory Bolt Holes
Yes
•Valve Guide Material
Bronze - 11/32”
•Valve Seats Machined
Yes
•Valve Seat Style
Multi Angle
•Valve Seat Material
Hardened Ductile Iron
•Intake Bolt Pattern
Oval port; 65-90
•Valve Cover Mounting
Perimeter (OEM)
•Quantity
Sold as a pair



Build Specifications :

•Valves
Stainless Steel
•Valve Length
IN. 0.250 L / EX. 0.100 L
•Intake Valve Diameter
2.250 in.
•Exhaust Valve Diameter
1.880 in.
•Valve Seals
Viton Seals
•Retainers
Chrome Moly Steel
•Locks
10 degree Forged Steel
•Rocker Studs
7/16
•Guide Plates
Moly Steel
•Locator Cups
Chrome Moly Steel
•Valve Springs
See Options Below:
3021-396..300cc Oval.........1.485............110 lbs...........300 lbs..........0.590

3021-396..300cc Oval.........1.550............135 lbs...........350 lbs..........0.670

3021-396..300cc Oval.........1.550............200 lbs...........600 lbs..........0.740

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

"The galleries are full of critics. They play no ball, they fight no fights. They make no mistakes because they attempt nothing."
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post #14 of 26 (permalink) Old Sep 21st, 16, 06:44 AM
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Re: Swapping Heads Question

Dave, my $.02 cents on this...You are going to need different pistons to achieve the 9.5 compression that the cam (XE284H) recommends. The ProComp heads you are looking at have 115 cc combustion chambers and with the pistons you are running will make less than 8.5 compression. Just my opinion...To achieve a compression of 9.5 you will need a piston with at least a -17cc dome...

Mike
U.S Air Force Retired
68 RS/SS, 396 BBC .060 over, M-20, 373 12 Bolt, factory color Island Teal blue, redline bias ply tires.

Last edited by knuggles68RS/SS; Sep 21st, 16 at 07:03 AM.
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post #15 of 26 (permalink) Old Sep 21st, 16, 06:46 AM
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Re: Swapping Heads Question

Quote:
Originally Posted by HawkX66 View Post
Definitely gives me something to think about Mike. I appreciate the feedback.


That explains their low price. Makes sense. I thought I saw where the ones from GA were all USA made including the castings. Maybe not. I really wish I could go with the Brodix I wanted, but that's going to have to wait a little while. I'll look a little closer at the design etc and go from there. They'll definitely be back savers at least if I go with them... I appreciate the info.
Go to racingjunk.com. Click on the classifieds. Go to engine parts or cylinder heads. Lots of dealers offering great deals on premium U.S. made heads as well as good used heads.
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