346236 & 3993820 Heads, Cam, Springs - Chevelle Tech
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post #1 of 12 (permalink) Old Jan 12th, 20, 8:01 PM Thread Starter
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Tim
 
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346236 & 3993820 Heads, Cam, Springs

I am swapping from 346236 (peanut port) to 3993820 (oval port) heads. From my research, if it is correct, both have 2.06/1.72 valves? I am swapping my cam also to a Comp Magnum Hydraulic flat tappet 11-207-3 cam, int/exh @ 050 lift 224/224, duration @ 050 lift 224/224, advertised duration 270/270, int/exh lift with factory rocker arms .510/.510. I am going to have the 820 heads rebuilt. My question is what springs do I need to get in order to handle this cam and will they be strong enough if I decide to get a cam with a little more lift, say 520/520 or 550/550?
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post #2 of 12 (permalink) Old Jan 12th, 20, 8:09 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by Tim's_2nd_Chevelle View Post
I am swapping from 346236 (peanut port) to 3993820 (oval port) heads. From my research, if it is correct, both have 2.06/1.72 valves? I am swapping my cam also to a Comp Magnum Hydraulic flat tappet 11-207-3 cam, int/exh @ 050 lift 224/224, duration @ 050 lift 224/224, advertised duration 270/270, int/exh lift with factory rocker arms .510/.510. I am going to have the 820 heads rebuilt. My question is what springs do I need to get in order to handle this cam and will they be strong enough if I decide to get a cam with a little more lift, say 520/520 or 550/550?

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post #3 of 12 (permalink) Old Jan 13th, 20, 1:31 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by Tim's_2nd_Chevelle View Post
I am swapping from 346236 (peanut port) to 3993820 (oval port) heads. From my research, if it is correct, both have 2.06/1.72 valves? I am swapping my cam also to a Comp Magnum Hydraulic flat tappet 11-207-3 cam, int/exh @ 050 lift 224/224, duration @ 050 lift 224/224, advertised duration 270/270, int/exh lift with factory rocker arms .510/.510. I am going to have the 820 heads rebuilt. My question is what springs do I need to get in order to handle this cam and will they be strong enough if I decide to get a cam with a little more lift, say 520/520 or 550/550?
Keep us posted on how the combo goes with the 820's over the 236 BBC heads.

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post #4 of 12 (permalink) Old Jan 14th, 20, 12:38 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

Quote:
Originally Posted by Tim's_2nd_Chevelle View Post
I am swapping from 346236 (peanut port) to 3993820 (oval port) heads. From my research, if it is correct, both have 2.06/1.72 valves? I am swapping my cam also to a Comp Magnum Hydraulic flat tappet 11-207-3 cam, int/exh @ 050 lift 224/224, duration @ 050 lift 224/224, advertised duration 270/270, int/exh lift with factory rocker arms .510/.510. I am going to have the 820 heads rebuilt. My question is what springs do I need to get in order to handle this cam and will they be strong enough if I decide to get a cam with a little more lift, say 520/520 or 550/550?
Why wouldn't you order the kit that has matching springs for that cam?
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post #5 of 12 (permalink) Old Jan 14th, 20, 1:43 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by suprdave1 View Post
Why wouldn't you order the kit that has matching springs for that cam?
Most kits include "unnecessary" or "wrong" components! Buy it all separate!

Quote:
Originally Posted by Tim's_2nd_Chevelle View Post
I am swapping from 346236 (peanut port) to 3993820 (oval port) heads. From my research, if it is correct, both have 2.06/1.72 valves? I am swapping my cam also to a Comp Magnum Hydraulic flat tappet 11-207-3 cam, int/exh @ 050 lift 224/224, duration @ 050 lift 224/224, advertised duration 270/270, int/exh lift with factory rocker arms .510/.510. I am going to have the 820 heads rebuilt. My question is what springs do I need to get in order to handle this cam and will they be strong enough if I decide to get a cam with a little more lift, say 520/520 or 550/550?
We are constantly working with those "820" heads for the Vette guys!

They will support 550 HP with no porting on the 489" platform using a hyd-roller!

I would recommend using some SBC intake valves, either 2.125" or 2.150" and some BB Mopar 1.810" exhaust valves, all are with .343" stems!

Thanks, Gary in N.Y.

P.S. Here's a shot of a recently finished set, this particular set made 510+ HP @ 5400 and 550# Torque @ 4500 on the dyno with a 9.5:1 C.R. These are easy 100% stock-appearing builds for us here! Q-jet carbs, low-rise intakes!
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post #6 of 12 (permalink) Old Jan 14th, 20, 7:02 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by GOSFAST View Post
Most kits include "unnecessary" or "wrong" components! Buy it all separate!



We are constantly working with those "820" heads for the Vette guys!

They will support 550 HP with no porting on the 489" platform using a hyd-roller!

I would recommend using some SBC intake valves, either 2.125" or 2.150" and some BB Mopar 1.810" exhaust valves, all are with .343" stems!

Thanks, Gary in N.Y.

P.S. Here's a shot of a recently finished set, this particular set made 510+ HP @ 5400 and 550# Torque @ 4500 on the dyno with a 9.5:1 C.R. These are easy 100% stock-appearing builds for us here! Q-jet carbs, low-rise intakes!
I think the 820 heads are the best closed chamber head. The exhaust is very nicely un-shrowded and the short turn is so high it can be easily fixed for a better turn than most BBC heads. They make a great budget head for BBC's up to 480 cubes.

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post #7 of 12 (permalink) Old Jan 14th, 20, 10:46 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

^^^ 68 Chevele those 820 heads are open chamber cylinder heads.Years 1971 and up, similar to the 781 and 049 cylinder heads most of the low compression Big Block Corvettes from 71-2 and on came with them.
3993820 ---402/454---71---2.06/1.77---113cc Oval port

Chevy Casting Number identification - Block casting numbers
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post #8 of 12 (permalink) Old Jan 15th, 20, 2:18 AM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by 71350SS View Post
^^^ 68 Chevele those 820 heads are open chamber cylinder heads.Years 1971 and up, similar to the 781 and 049 cylinder heads most of the low compression Big Block Corvettes from 71-2 and on came with them.
3993820 ---402/454---71---2.06/1.77---113cc Oval port

Chevy Casting Number identification - Block casting numbers
I guess my thought were that the 820's were a semi-open chambered head as the chamber by the plug side was really not laid back like some of the other chamber heads. The first time I has a set of these were off a 1969 265hp 396 2bbl Caprice. I am not sure if the casting number was the same but the chambers were identical to 820's shown in one of the post above. We thought they were junk back then and tossed them in the trash in favor of the bath tub closed chambers that were the in thing in the late 60's and early 70's. But you are right they were on the 71 and up 454's for a while.

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post #9 of 12 (permalink) Old Jan 15th, 20, 9:48 AM
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Re: 346236 & 3993820 Heads, Cam, Springs

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post #10 of 12 (permalink) Old Jan 15th, 20, 3:15 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by 68Chevele View Post
I guess my thought were that the 820's were a semi-open chambered head as the chamber by the plug side was really not laid back like some of the other chamber heads. The first time I has a set of these were off a 1969 265hp 396 2bbl Caprice. I am not sure if the casting number was the same but the chambers were identical to 820's shown in one of the post above. We thought they were junk back then and tossed them in the trash in favor of the bath tub closed chambers that were the in thing in the late 60's and early 70's. But you are right they were on the 71 and up 454's for a while.
I think more than likely you're mixing up those three last numbers 8-2-0 and 8-0-2- can easily be flip flopped around.And there is an earlier cylinder head with the bathtub chambers that has the same last three numbers but it ends in 802 instead of 820.
Check this out :
3909802---396/427---66-67---2.06/1.77---100cc Oval port --- L-34/L-35/L-36/L-68

That cylinder head is really similar to the 702 L34 L35 cylinder head.The reason I knew about it is because I googled it a while ago when I found someone selling a set of 802's but they were stock and overpriced.
That possible mix-up is the reason I think it's best to use the whole part number at least once during a new thread that is being posted for the first time then after that the last 3 will do.It helps save from any mix ups.
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post #11 of 12 (permalink) Old Jan 15th, 20, 11:56 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by 71350SS View Post
I think more than likely you're mixing up those three last numbers 8-2-0 and 8-0-2- can easily be flip flopped around.And there is an earlier cylinder head with the bathtub chambers that has the same last three numbers but it ends in 802 instead of 820.
Check this out :
3909802---396/427---66-67---2.06/1.77---100cc Oval port --- L-34/L-35/L-36/L-68

That cylinder head is really similar to the 702 L34 L35 cylinder head.The reason I knew about it is because I googled it a while ago when I found someone selling a set of 802's but they were stock and overpriced.
That possible mix-up is the reason I think it's best to use the whole part number at least once during a new thread that is being posted for the first time then after that the last 3 will do.It helps save from any mix ups.
Thanks for clearing that up. The heads I had were 148 heads off the 265hp 396 and I remember the chambers were the same as the 820's which were offered on the '71 402's and 454's. Mine were like 111cc's.
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post #12 of 12 (permalink) Old Today, 12:44 PM
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Re: 346236 & 3993820 Heads, Cam, Springs

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Originally Posted by Busted Knuckles View Post
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