1971 sbc400 head casting mark - Chevelle Tech
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post #1 of 25 (permalink) Old Jul 13th, 20, 3:36 PM Thread Starter
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1971 sbc400 head casting mark

i checked for casting marks on my engine but if i google i cannot identify these marks.

Anybody can help me with this?
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post #2 of 25 (permalink) Old Jul 13th, 20, 4:19 PM
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Re: 1971 sbc400 head casting mark

Casting marks like that on the ends of smog era heads are rather unreliable for identification purposes, as a lot of the charts you see are incomplete and many of the so-called pattern configurations were used a several different size engines with different valve sizes in them.

if you want to know what you really have, pull a valve cover off and get the actual casting number.
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post #3 of 25 (permalink) Old Jul 13th, 20, 6:22 PM
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Re: 1971 sbc400 head casting mark

Quote:
Originally Posted by Ericnova72 View Post
Casting marks like that on the ends of smog era heads are rather unreliable for identification purposes, as a lot of the charts you see are incomplete and many of the so-called pattern configurations were used a several different size engines with different valve sizes in them.

if you want to know what you really have, pull a valve cover off and get the actual casting number.

That is EXACTLY the best answer.
These three heads are probably the best of stock SB400 heads. They were used on early 70s 400s (and some 350 usage). On ANY, repeat, ANY Pre-75 SB production heads, they were the better choices. The reason is because Pre-75 heads were the "heaviest". That is, those castings did not have a reduction in metal in the casting. They had only ONE exhaust crossover passage and there was more metal around the lower head bolt bosses 3951598, 3973493, 3998997.

I consider these SB400 heads to be junk. In 75, GM began to cut corners in head castings. They were thinner in some areas (depressions between exhaust ports reducing water jacket volume), there was less metal around the head bolt bosses and they had TWO exhaust crossover passages in the center, which increases heat in the center, thus, increasing the possibility (very likely) of cracks developing in the center of the head 333882, 462624, 468642. These heads were used on SB400s, as well as some other engines, from 75-80.

Of all the SB400s (about 25) I've built since 1972, I've only used one pair of aftermarket Iron heads, DART Sportsman. All other 400s got bone stock GM head castings (70-74 castings) with and I had multiple upgrades done to them. I'm not aware of any issues with the 70-74 400 head castings I've used over the years.


To the best of my knowledge, ALL GM 400 head castings had 76cc chambers, which makes and excellent combination when used with flat top pistons (with valve notches), which works very well with pump gas and produces about 10:1 compression (compression numbers may vary depending on conditions and modifications).
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post #4 of 25 (permalink) Old Jul 14th, 20, 12:27 PM Thread Starter
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Thanks!

I intent to create an seperate topic in a year or so, but maybe i could kick start my question right now.

My 1971 camino is propane only, the previous owner removed the gasoline tank i drive in the netherlands and gas is expensive compared to propane so i like to stick with propane.

It is a sbc400, stock heads i guess stock heads.
I measured compression ratio around 8:1 (deviates among cylinder between 7.5:1and 8:1)

It has headers and edelbrock intake
The propane supply goes via an 300a mixer which according specs delivers max 275hp. The mixer is directly mounted on a 750cfm edelbrock 1407.
In general the engine runs fine from idle to 4000rpm. Above 4000rpm the engine doesnt pull that hard anymore.

I guess it makes 200hp.

What would give me 50hp extra? Only a cam? Only other heads? Or the combo.

Besides propane can handle higher compression but should that be the way to go for me?

If i can chose, i like low rev high torque above high hp at high rpm.
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post #5 of 25 (permalink) Old Jul 21st, 20, 5:02 PM Thread Starter
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Quote:
Originally Posted by DZAUTO View Post
Quote:
Originally Posted by Ericnova72 View Post
Casting marks like that on the ends of smog era heads are rather unreliable for identification purposes, as a lot of the charts you see are incomplete and many of the so-called pattern configurations were used a several different size engines with different valve sizes in them.

if you want to know what you really have, pull a valve cover off and get the actual casting number.

That is EXACTLY the best answer.
These three heads are probably the best of stock SB400 heads. They were used on early 70s 400s (and some 350 usage). On ANY, repeat, ANY Pre-75 SB production heads, they were the better choices. The reason is because Pre-75 heads were the "heaviest". That is, those castings did not have a reduction in metal in the casting. They had only ONE exhaust crossover passage and there was more metal around the lower head bolt bosses 3951598, 3973493, 3998997.

I consider these SB400 heads to be junk. In 75, GM began to cut corners in head castings. They were thinner in some areas (depressions between exhaust ports reducing water jacket volume), there was less metal around the head bolt bosses and they had TWO exhaust crossover passages in the center, which increases heat in the center, thus, increasing the possibility (very likely) of cracks developing in the center of the head 333882, 462624, 468642. These heads were used on SB400s, as well as some other engines, from 75-80.

Of all the SB400s (about 25) I've built since 1972, I've only used one pair of aftermarket Iron heads, DART Sportsman. All other 400s got bone stock GM head castings (70-74 castings) with and I had multiple upgrades done to them. I'm not aware of any issues with the 70-74 400 head castings I've used over the years.


To the best of my knowledge, ALL GM 400 head castings had 76cc chambers, which makes and excellent combination when used with flat top pistons (with valve notches), which works very well with pump gas and produces about 10:1 compression (compression numbers may vary depending on conditions and modifications).
Are the valve cover seals re-usable?

I did a lot of research to heads now, and i find that CR can be rised by smaller heads chambers like 64cc OR go for flat top pistons.

Why is the majority in favor for the flat pistons ?

I am looking for around 300hp. I if would replace my dished pistons for flat top onces, the CR will rise and boost the power also. Maybe a 3angle work on the heads to get them fresh?
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post #6 of 25 (permalink) Old Jul 21st, 20, 5:38 PM
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Re: 1971 sbc400 head casting mark

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Originally Posted by Bart Fransen View Post
Are the valve cover seals re-usable?

I did a lot of research to heads now, and i find that CR can be rised by smaller heads chambers like 64cc OR go for flat top pistons.

Why is the majority in favor for the flat pistons ?

I am looking for around 300hp. I if would replace my dished pistons for flat top onces, the CR will rise and boost the power also. Maybe a 3angle work on the heads to get them fresh?
If the valvecover gaskets are cork and still soft, or rubber, they can be reused....if cork and they are getting hard it is best to replace them.

Pistons are cheaper than heads would be my guess as to why your search found flat tops to be popular.

My opinion is a better flowing head with a smaller combustion chamber is by far the better way to go.

You can put a flat top piston with open chamber heads...but those open chamber heads are all smog era stuff, not the best flowing heads around. Depending on casting number, some are real crap.

As far as gains compare, increase in compression ratio can't do nearly as much as better head flow can do....pick up 40 cfm of intake port flow will do more than raising compression ratio 3 points will do for you.....and flat tops with open chamber heads won't get you 3 full points of compression gain, only about 1-1/4 points.
Changing to a better flowing small chamber head covers both gains, airflow increase and increased compression.

On a 300 HP engine, 1-1/4 points of compression is going to be about 10-15 HP....40 cfm flow gain on the other hand can be 60+ HP gained.


Now, with that said, running on Propane means you can raise the compression quite a bit to optimize it?? it'll allow a lot more than pump fuel will, correct??

Flat tops and 64 cc chamber heads would get you up to a hair over 11:1 compression with either a decked block or stock block and thin steel shim head gasket for tight qeuch..
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post #7 of 25 (permalink) Old Jul 22nd, 20, 1:41 AM Thread Starter
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Ok maybe i missed a bit in my previous reply. What i meant is that for what i read, the increase in CR allows a bigger cam which also results in higher power output.

Because my propane supply only supports 275hp i can spend money on AFR heads or something (like 1700,-) but that still wont give me the power.

On the otherhand, at this moment a camshaft upgrade (200,- incl timing gain etc) would also not gain alot due to my low CR.

What if i would buy flat top pistons which should bring me at least 9:1 (76cc heads) and then add a camshaft? Maybe i can gain some torque?
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post #8 of 25 (permalink) Old Jul 22nd, 20, 12:24 PM Thread Starter
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Quote:
Originally Posted by Bart Fransen View Post
Ok maybe i missed a bit in my previous reply. What i meant is that for what i read, the increase in CR allows a bigger cam which also results in higher power output.

Because my propane supply only supports 275hp i can spend money on AFR heads or something (like 1700,-) but that still wont give me the power.

On the otherhand, at this moment a camshaft upgrade (200,- incl timing gain etc) would also not gain alot due to my low CR.

What if i would buy flat top pistons which should bring me at least 9:1 (76cc heads) and then add a camshaft? Maybe i can gain some torque?
If i write it down myself like this i wonder...

275 is my max HP.
Hp = torque x RPM

If i can get a lot of torque below lets say 4000-4500rpm the car will pull hard but wont rev very high. I dont like high revs anyway, so maybe the limitation in hp isnt a big problem.

Anybody ideas to create a low rpm high torque engine?
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post #9 of 25 (permalink) Old Jul 22nd, 20, 12:59 PM
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Re: 1971 sbc400 head casting mark

HP = Torque x RPM ÷ 5252

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post #10 of 25 (permalink) Old Jul 22nd, 20, 2:11 PM Thread Starter
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Quote:
Originally Posted by dyno jonn View Post
HP = Torque x RPM ÷ 5252
I know its not exactly that, but in principle it is
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post #11 of 25 (permalink) Old Jul 22nd, 20, 3:17 PM
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Re: 1971 sbc400 head casting mark

Keeping the heads you've got, you could even use a small domed piston to get the compression ratio up over 10:1 to go along with the Propane. That along with adding a small torque style cam would give a pretty good boost to low and mid rpm torque.
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post #12 of 25 (permalink) Old Jul 22nd, 20, 4:19 PM Thread Starter
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What you refer as a "small" cam.
A thight lsa?

I am just gettin in to cams to be honest, there is a lot to read about them:
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post #13 of 25 (permalink) Old Jul 22nd, 20, 4:43 PM
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Re: 1971 sbc400 head casting mark

Back to your first question, I agree with those that say pull the valve cover to determine the actual casting number. However, I have had 4 sets of 493 castings over the last 25 years and all have had that same casting mark. I just pulled apart a 400 to rebuild three months ago and is also had one 493 head on it, with the same casting mark.

If they are 493 castings, they are good stock heads - heavy castings and about the best flowing heads of the early 1970's.
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post #14 of 25 (permalink) Old Jul 22nd, 20, 7:12 PM
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Re: 1971 sbc400 head casting mark

As far as cams are concerned before you pick one you should call or email the cam company of choice for their advice about a propane fueled engine and what would be their recommendation ?
For pistons if you go with flat tops make sure to get pistons with only 2 valve reliefs because of the compression drop with 4 valve relief pistons.That propane engine needs all the compression you can give it.
You can also add a lot more timing than you can a gas fueled engine.With the added timing,a slightly larger camshaft and the new pistons you should be able to get the 50 extra HP that you're looking for.
Butin all reality,you really should be getting advice from a engine builder or tuner who's experienced with propane and LPG fueled engines.

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post #15 of 25 (permalink) Old Jul 22nd, 20, 7:31 PM
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Re: 1971 sbc400 head casting mark

Quote:
Originally Posted by Bart Fransen View Post
What you refer as a "small" cam.
A thight lsa?

I am just gettin in to cams to be honest, there is a lot to read about them:
I would call a small torque cam something about 204° to 210°[email protected] and around .420-.440" valve lift, and maybe a 108° lobe separation.

The stock cam is something like 196° [email protected] and .390" lift on a 116° or 117° lobe separation.

I agree with he other posters, call a couple cam companies like Howards Cams or Erson Cams and see if propane fueled needs any specific duration or lobe separation amounts compared to gasoline engine cams.
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