Team Chevelle banner

290 vs. 820 Heads

32K views 18 replies 9 participants last post by  Sams454SS 
#1 ·
I am thinking about buying a 1970 454 LS-5 engine. I am waiting on the block ID numbes and date codes. He says it has 820 heads. I thought a 1970 LS-5 had 290 heads. Did they make any 1970 820 heads? What is the difference between 290 heads and 820 heads?
 
#2 ·
According to the source I have 820 heads are 1971 402/454 oval port open chambered heads. The 290 heads are 1969-70 396/402/427/454 oval port closed chambered heads.

A 1970 LS5 would be 3963512 casting with two bolt mains. I'm sure you already knew that. There are a couple different engine suffixes used.
 
#3 ·
the rated CR of an 1970 LS-5 is 10.25:1 with small domed piston, 101cc chamber.
for 1971, the 820 head has 112 cc nominal (114 more common)
figure factory was .023 deck height
dome at -13.8

see what you come up with
http://www.kb-silvolite.com/calc.php
 
#10 · (Edited)
IMHO 290 is the true correct head for an LS5 .

Here's what Mortec one of the chevy motor/blocks/heads/casting id info websites states:

3964290....69-70...oval..CLOSED..396, 402, 427, 454, 101cc chamber
Large or small hex spark
plugs used


3993820....71......oval...OPEN...402, 113cc chamber, 255/114 ports

=============================================================Now ack
OK,now back to my take on this.

In 1970 bbc's l34 396 & ls5 454's came with 290 small chamber lrg oval port heads & approx 10.25.1 compression.

The larger chambered 820 lrg oval port heads were used on 71 bbc's due to emmissions laws for 71 which dropped compression from 10.25.1 to approx 9.0 comp.

The only big difference bewteen the the 290 & 820 heads is mainly the combustion chamber size being larger and that its now also an open design that may breathe a bit better. But both the 290 & 820 heads are roughly comprable/= perf wise given same compression & all else like cam/intake/carb etc being = too. So if you use the proper larger domed pistons to get the compression back up in a 71 bbc motor the 820 heads will perf just as well as the 290s do on a 1970 or older bbc l34 or ls5 motor with stock pistons.

Or if in your case you 70 ls5 moor still has stock pistons with stock dome design/size you can simply remove the 820's and install a set of 290's and your good to go.

The reverse of that would be for example if you had a 71 bbc that came with 820 heads you can simply install the smaller chambered 290 or 063 or 215 heads all being small comb chamber lrg oval port head designs with closed chambers to get the compression back up to the factory rated 10.25.1. Thats because those 71 motors still had the same dome size & design pistons that were used in the 1970 l34 & ls5 bbc motors . It was just the larger chambered open chamber design of the 820 heads that lowered the comp & helped the 71 bbc's meet the newer emmissions regs for those motors in that timeframe.

Now onto the supposed 820 head 2/70 casting date,maybe the prior owner could have mistaken a 3 or an 8 for a 2 because 2-Feb 70 seems kinda early for the larger 820 heads that were not supposed to neever be on any 1970 l34 or ls5 pass car motor to be going onto them.

I have been working on thses motors for just shy of 40 yrs and have never seen 820 heads on a known/verified 70 bbc. But i have obviously not seen every bbc motor built in 1970 either so i guess you never know what may have happend at the factory esp with respct to a very late built 1970 bbc pass car motor.

But possibly if the date on your 820's is correct maybe gm was already mfg the 820 heads in 2/70 to meet truck emmissions regs that can be stricter/comming in a yr ealier then for the pass cars and thats why you have 820 heads dated 2/70. Or who knows,maybe GM was simply casting the 820 bbc heads months ahead in 1970 to get a jump on the 1971 builds which could be possible,crazier things have happend over the yrs.

But normally the earliest you should be seeing 820 heads on the chevelles/pass cars would be for the new 1971 pass car's bbc motors for early production of new 1971 cars built in mie-late july or early august 1970 for early built 71 pass cars to hit the sales floor.

You really need to pull the valve covers and very that head casting id & date code for yourself and if its truely 2/70 cast date look into if either trucks got those heads in 70 or if gm was casting the heads months earlier then normal to get a jump on things which i have never heard of happening but again,you never know.

Scott
 
#19 ·
IMHO 290 is the true correct head for an LS5 .

Here's what Mortec one of the chevy motor/blocks/heads/casting id info websites states:

3964290....69-70...oval..CLOSED..396, 402, 427, 454, 101cc chamber
Large or small hex spark
plugs used


3993820....71......oval...OPEN...402, 113cc chamber, 255/114 ports

=============================================================Now ack
OK,now back to my take on this.

In 1970 bbc's l34 396 & ls5 454's came with 290 small chamber lrg oval port heads & approx 10.25.1 compression.

The larger chambered 820 lrg oval port heads were used on 71 bbc's due to emmissions laws for 71 which dropped compression from 10.25.1 to approx 9.0 comp.

The only big difference bewteen the the 290 & 820 heads is mainly the combustion chamber size being larger and that its now also an open design that may breathe a bit better. But both the 290 & 820 heads are roughly comprable/= perf wise given same compression & all else like cam/intake/carb etc being = too. So if you use the proper larger domed pistons to get the compression back up in a 71 bbc motor the 820 heads will perf just as well as the 290s do on a 1970 or older bbc l34 or ls5 motor with stock pistons.

Or if in your case you 70 ls5 moor still has stock pistons with stock dome design/size you can simply remove the 820's and install a set of 290's and your good to go.

The reverse of that would be for example if you had a 71 bbc that came with 820 heads you can simply install the smaller chambered 290 or 063 or 215 heads all being small comb chamber lrg oval port head designs with closed chambers to get the compression back up to the factory rated 10.25.1. Thats because those 71 motors still had the same dome size & design pistons that were used in the 1970 l34 & ls5 bbc motors . It was just the larger chambered open chamber design of the 820 heads that lowered the comp & helped the 71 bbc's meet the newer emmissions regs for those motors in that timeframe.

Now onto the supposed 820 head 2/70 casting date,maybe the prior owner could have mistaken a 3 or an 8 for a 2 because 2-Feb 70 seems kinda early for the larger 820 heads that were not supposed to neever be on any 1970 l34 or ls5 pass car motor to be going onto them.

I have been working on thses motors for just shy of 40 yrs and have never seen 820 heads on a known/verified 70 bbc. But i have obviously not seen every bbc motor built in 1970 either so i guess you never know what may have happend at the factory esp with respct to a very late built 1970 bbc pass car motor.

But possibly if the date on your 820's is correct maybe gm was already mfg the 820 heads in 2/70 to meet truck emmissions regs that can be stricter/comming in a yr ealier then for the pass cars and thats why you have 820 heads dated 2/70. Or who knows,maybe GM was simply casting the 820 bbc heads months ahead in 1970 to get a jump on the 1971 builds which could be possible,crazier things have happend over the yrs.

But normally the earliest you should be seeing 820 heads on the chevelles/pass cars would be for the new 1971 pass car's bbc motors for early production of new 1971 cars built in mie-late july or early august 1970 for early built 71 pass cars to hit the sales floor.

You really need to pull the valve covers and very that head casting id & date code for yourself and if its truely 2/70 cast date look into if either trucks got those heads in 70 or if gm was casting the heads months earlier then normal to get a jump on things which i have never heard of happening but again,you never know.

Scott
This is interesting to read in that I have a set of 820's on my LS-6 until I can replace them with possibly a new set of AFR's. Good reading.
 

Attachments

#11 ·
Thanks for the input. It sounds like the heads are more than likely 71 heads. The owner is suppose to be sending photos of the date stamp for my review. My car is a true 70 SS LS-5 with a build sheet. It was a frame off restoration it is in great condition except it currently has a 71 402 in it. I am looking to try to find a true LS-5 date correct 454 engine and I hope it will increase the value significantly over having the 71 402 in the car. Any Thoughts? I am not looking for a race car just a solid driver. Any suggestions of were to look?
 
#12 ·
If you're planning on driving it, I don't think "value" should be quite so much of a concern.

OTOH, alot of those earlier motors cannot be used to any great extent on modern pump gas. The valve seats need lead to lube them. They didn't start induction-hardening them until ... about 71. Plus, the earlier design heads are more prone to detonation. IOW, at the same compression, the 820 heads are better for a DD, regardless of which casting will ulitimately make more HP in a go-for-broke HP situation. "More HP" isn't necessarily the right criterion for evaluating heads in all cases.

That said, unless it's a totally all-original, numbers-matching, unmolested, flawlessly perfect specimen, having the wrong head castings shouldn't affect the "value" very much; especially if the "correct" heads would render the car unseable and the "wrong" heads would let the owner enjoy the car in some way beyond merely admiring it sitting in the garage.
 
#13 ·
I am diffinitely going to drive the car. I just want to make a good decision on which head would be the best. It sounds like you would prefer the 820 head over the 290 head unless it was a matching numbers original car which mine is definitely not. Is that right?My current 402 is a mild low to mid 300's HP engine. I am not looking for a race car just a fun driver with a little attitude. I considered a "crate motor" but thought the original block would be more appealing if I decided to trade or sell the car at some point in the future.
 
#14 ·
Right, I think that's about it.

BBC heads have such a HUGE variety with all sorts of things different about them. There aren't a whole lot of "bad" ones, and just about any of them are "good" in some combo or other. The toughest things to watch out for, like the hardened seats, don't really show up in flow or HP numbers; and some of the ones that make the best racers are no good on the street, and vice-versa. 820 is one of the street-freindliest ones IMO. Maybe not the "max HP" type of choice although not too far off either, but a good all-around driver.
 
#16 ·
Just curious,why you say to watch out hardened exhaust valve seats?

No you have me worried because i know your good with BBC perf motors and know what you talking about & my machinest talked me into installing hardened ex valve seats in the 063's with stock valve size on my 396 when i rblt it 9 yrs /approx 6k miles ago & no issues thus far thank god!!!

Have you found there has been more issues with hardened ex valve seats then there should be like for example comming loose ,is it that cutting the casting to install them gets a bit too close to coolant chamber for comfort & leaking,(would think installing larger valves would more of an issue vs stock valve size with my 063's),or do they drastically impead airflow/etc?

Thanks...Scott
 
#17 ·
The factory hardens seats by induction; i.e. they stick a probe that creates a powerful electromagnetic field into the area, which causes a large current to flow in the casting right around it, which heats it up red-hot and hardens it. This is different from "inserts" such as a machine shop would use. They started induction-hardening the seats at about the time that catalytic converters, and therefore unleaded gas, were becoming legal requirements, starting in California.

Well-installed seat inserts work perfectly fine. In fact essentially ALL aluminum heads have them, for obvious reasons. Your machinist did the right thing, IMO; assuming of course that the cut for the insert is neat and all that sort of stuff. That's the common tactic for updating pre-hardening heads to use modern gas. But, it costs money; and unless there's some kind of inherent value in a set of some old stock heads, they're not usually a cost-effective mod. Especially not in a case like the OP seems to be in.

I am telling the OP to watch out for the seats, because you can buy those old heads like 702 and such, all day long; but if you run them any significant mileage on the street, the valves may erode the head rapidly. It's possible for them to get so far chewed through that they can't be repaired. Once the erosion starts, it can be quite rapid. So regardless of which head casting "makes the most power", there's a cost vs reliability issue that must be settled satisfactorily.

Another feature of newer heads including 820 but AFAIK not 290 is the "squish" area under the spark plug. This make a HUGE difference to detonation resistance. Again, it was introduced when fuel octane ratings fell due to the reduction and eventual elimination of the lead additive, so typical 60s heads don't have it. It appeared gradually starting in about 69 or so. But from 73 or so up, the chambers are HUGE, like 781 for example. Great heads as everybody knows, but TOTALLY WRONG for some combos. Just jamming a set of 781s on a stock 402 short block is a dreadful mistake, in spite of the flow and the hardened seats and the "squish", because the compression will be so low. Yet another example of why the "max HP" approach to head selection, with blinders on to all else, can lead one astray if it leads to a bad combo. There's alot of variables to consider.
 
#18 ·
Thanks a lot for your informed explination.

Scott
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top