327 Double Hump Markings

[62BillT]

Reading some of Fran's replies on the 348 and 409 Engine forum got me thinking again about the double hump markings on my '65 327/275 and a few others that I have noticed thru the years. One of the humps was grinded to look like a point. When I looked close at it, it looked like someone at the factory took a grinding wheel or it was possibly grinded on a milling machine some how. My question is, why did they do this and what possibly did it indicate. I recently put this over at the Chevytalk Performance forum and a couple of guys who work on heads agreed seeing some go thru their shop now and then, but I never got a good answer. Any info would be appreciated.

[MK IISS]

Reading some of Fran's replies on the 348 and 409 Engine forum got me thinking again about the double hump markings on my '65 327/275 and a few others that I have noticed thru the years. One of the humps was grinded to look like a point. When I looked close at it, it looked like someone at the factory took a grinding wheel or it was possibly grinded on a milling machine some how. My question is, why did they do this and what possibly did it indicate. I recently put this over at the Chevytalk Performance forum and a couple of guys who work on heads agreed seeing some go thru their shop now and then, but I never got a good answer. Any info would be appreciated.

Bill: This is really not an answer to you question but may be helpful. The 275 horsepower 327 didn't come out until '66 however there were a couple changes with the '65 250 horsepower 327 which you probably have if it is the original engine. For '65 the 327/250 got the 300 horsepower "double hump" heads with no factory increase in rated horsepower. Also the dual exhaust system was no longer standard but an option. If your 327 has factory dual exhausts and a Carter AFB carb. it may be a 300 horsepower 327.

Richard

[62BillT]

The 275 horsepower 327 didn't come out until '66


Richard, I realized I goofed a little while after I wrote it. Your right the '65 Standard 327 was listed as 250 horsepower, like the '64 327 was, even tho it came with the double humps heads. Mine was just the 250 engine. Still trying to figure out about the markings tho. I bought the engine back in 1972 and even tho I have been asking on the forums just lately, it still a mystery that I'm trying to figure out.

[fatride]

The casting mark,"double hump" did not mean that the head was anything special! That casting mark and others was used on a variety of heads from low to high performance! It was just that, a casting mark.
;)

[MK IISS]

The casting mark,"double hump" did not mean that the head was anything special! That casting mark and others was used on a variety of heads from low to high performance! It was just that, a casting mark.
;)

faride:

The 62-64 250 horsepower 327 used a cyl. head similar to the '61 283 powerpack engine with 1.72 intake and 1.50 exhaust valves. One of the easy ways to spot this head, other then the casting #, was a casting mark on the front of the head at the head/block parting line which resembled a rectangle with a triangle on top.

The 62-64 300 horsepower 327 used a different head with 1.94 intakes and 1.50 exhaust valves which could be determined, other then the casting number, by the so called double hump casting mark. '64 and later 327s rated higher then 300 horsepower also used the double hump head but with 2.02 intakes and 1.60 exhausts.
The point to all this was the '65 327/250 now used the double hump larger intake valve 300 horse head without an increased factory horsepower rating and therefore it could be more easily confused with the '65 327/300.

The double hump head first appeared on the '61 injected Corvettes.

[fatride]

My information comes from what I have heard over the years and is stated in the Cars and parts cataloge of chevy V8 casting #s. they state that the double hump and other reconizable casting marks did not mean that the head was high performance! Double hump heads also came with 1.94" valves. The only way to confirm that the head was a big valve head was to measure the valve size. Seasoned "head hunters" could tell the diference between the 1.94" valve head and the 2.02 valve head by the distance between the intake and exhaust valves. I would not buy a small block head without checking valve size no matter what the casting marks were! But as with all my observations, it's only my opinion! I could be wrong! But I will still measure the valves!
:cheers

[MK IISS]

My information comes from what I have heard over the years and is stated in the Cars and parts cataloge of chevy V8 casting #s. they state that the double hump and other reconizable casting marks did not mean that the head was high performance! Double hump heads also came with 1.94" valves. The only way to confirm that the head was a big valve head was to measure the valve size. Seasoned "head hunters" could tell the diference between the 1.94" valve head and the 2.02 valve head by the distance between the intake and exhaust valves. I would not buy a small block head without checking valve size no matter what the casting marks were! But as with all my observations, it's only my opinion! I could be wrong! But I will still measure the valves!
:cheers

fatride:

Your point is well taken and I agree with you. A double hump head casting mark does not guarantee it is a high performance head with 2.02/1.60 valves.

However that was not the point of my conversation with Bill.

My points were:

1. the 327/275 didn't come out until the '66 model year

2. the '65 327/250 had the same double hump head as the '65 327/300

3. the 62-64 327/250 did not have the double hump 327/300 head.

4. Because for the first time, in 1965, the 327/250 and the 327/300 have the same head it was easier to confuse the two engines.

[Loafer409]

"other then the casting #, was a casting mark on the front of the head at the head/block parting line which resembled a rectangle with a triangle on top."

===

I have a set of SB heads with this rectangle with double, /\/\ , prymids, anybody have any ideal what these are??? Sorry don't mean to hi-jack your thread...09

[MK IISS]

"other then the casting #, was a casting mark on the front of the head at the head/block parting line which resembled a rectangle with a triangle on top."

===

I have a set of SB heads with this rectangle with double, /\/\ , prymids, anybody have any ideal what these are??? Sorry don't mean to hi-jack your thread...09


I think those were early 70s ( 72 or 73 ) high performance Corvette and Z/28 heads. Similar to the "double hump" 2.02/1.60 head but with a larger combustion chamber for the new crappy low octane gas.

[fatride]

My points were:

1. the 327/275 didn't come out until the '66 model year

2. the '65 327/250 had the same double hump head as the '65 327/300

3. the 62-64 327/250 did not have the double hump 327/300 head.

4. Because for the first time, in 1965, the 327/250 and the 327/300 have the same head it was easier to confuse the two engines.[/QUOTE]


Points well taken! Thank you.
:cheers

[SteveD409]

I have to take exception to the statement that not all double hump heads are performance heads, that some of the camel hump heads only came with 1.94" intakes. This is true, but 1.94 intakes are STILL bigger than the 1.72's found on standard heads.
I must admit that I have never measured the distance between the valve stems on 2.02 and 1.94 double hump heads, but I don't think there is any difference. You can easily take a 1.94 double humper and regrind the valve seats for 2.02 valves. I'll have to check this one out.
The double hump head, as stated was first used on the 61 Vette 283, but was intended to be made of aluminum---would that have been COOOOOOOOOOL! Casting problems forced the change to cast iron.

SteveD

[MK IISS]

SteveD:

I used to have some '60 Corvette sales literature which listed the new 315 horse FI 283 with the aluminum 1.94/1.50 valve head. The new heads all failed so none were supposed to have been released and the "top dog" '60 engine was actually the same as the '59 engine rated at 290 horsepower. Some Corvette guys still argue if any of the '60s with the new head were realeased or not.

[62BillT]

I may have a theory. After reading everyones post and doing a little more studying on the subject, I'm wondering if in 1965, GM decided to start to indicate that the particular head we are talking about is the 1.94 smaller double hump head and not the larger 2.02 head, by grinding on one of the humps. What do y'all think of this being possible?

[dq409]

I may have a theory. After reading everyones post and doing a little more studying on the subject, I'm wondering if in 1965, GM decided to start to indicate that the particular head we are talking about is the 1.94 smaller double hump head and not the larger 2.02 head, by grinding on one of the humps. What do y'all think of this being possible?

I seem to remember that talk coming up from time to time way back when.
I bought a low mile `65 Impala SS in `71 that came with a 283 2V with 1.94 double humpers and a powerslime trans.

Very nice car and got 21 MPG on the highway but was a dog when it came to power off line.

[MK IISS]

Bill:

You heads should be casting # 3782461. If they are not then it adds to the mystery.

[jester]

"other then the casting #, was a casting mark on the front of the head at the head/block parting line which resembled a rectangle with a triangle on top."

===

I have a set of SB heads with this rectangle with double, /\/\ , prymids, anybody have any ideal what these are??? Sorry don't mean to hi-jack your thread...09
I have a set of those heads They came stock on a 283 that was in a 66 Impala I rebuild back in the early 80's
I thought that they were Power Packed Heads, They had the 1.94 valves with 66 cc chamber. They were also the heads that could accept the 2.02 valves. Please don't prove me wrong, I enjoy living in my delusional state. :eek:

[dq409]

Jester, Thats what I called them !!

So,,,, whats the diff between the power packs and the fueler heads ?
Is it the PP`s had 1.94 and the Fueler had the 2.02`s ? ,,,dq

[jester]

Jester, Thats what I called them !!

So,,,, whats the diff between the power packs and the fueler heads ?
Is it the PP`s had 1.94 and the Fueler had the 2.02`s ? ,,,dq

Nope, fuelie heads had 1,94 valves or 2.02 valves. At least in 1966.
'
Narrow triangle over rectangle 520, 896 ‘58 & up 283 PowerPak/’57-’60 Fuel Inj.,9.25:1 CR, 1.72/1.50 valves, 59cc chamber; could be good replacement on late 305 but no accessory bosses

Large “camel humps” 291, 461, 461X, 462 Original hi-perf or “fuelie” heads; chamber sizes are 62-64cc; both 1.94/1.50 & 2.02/1.60 valve versions available; 291 on 327’s thr ‘68; 291 have temp sender hole; 462 don't

Small “camel humps” 186, 492 Later hi-perf or “fuelie” heads, some 186 (‘69 & later) & all 492 have accessory bolt holes; 1.94/1.50 or 2.02/1.60 valves; 64cc chambers; ‘70 LT1/Z28 use 492; avail as PN3987376

[SteveD409]

SteveD:

I used to have some '60 Corvette sales literature which listed the new 315 horse FI 283 with the aluminum 1.94/1.50 valve head. The new heads all failed so none were supposed to have been released and the "top dog" '60 engine was actually the same as the '59 engine rated at 290 horsepower. Some Corvette guys still argue if any of the '60s with the new head were realeased or not.

Yup, you right, '60 not '61. Sorry.

SteveD

[Kirby J]

there were two different double hump heads from 61 to 64 and possibly 65.one head was for the 300hp 327 motors in the impalas and corvettes the other was the 3782461 X head these were used on the corvettes only with the 340hp ,365hp with the fuel injection. the X heads have a X on the bottom side of the end intake runner also under the casting number there is the number 13 always.the X heads have larger intake runners (180cc) and smaller chambers(58cc) thats why they are so popular for drag racing. the plain 461 heads have 160cc intake runners and 64cc chambers.most of the 461 and 461X heads had 1.94 and 1.5 valves, the 2.02 / 1.6 versions are super rare.the best way to tell is to mesure the distance between the valve seats. the small valve heads (1.94) have about an 1/8 inch between them .the 2.02 heads have the valves almost touching each other (1/16 or less). hope this info helps :cool:

[dq409]

Thanks,,, great info, I have of set of unmolested 461`s on my 327. Waiting for a new home (engine compartment that is) !,,,dq

[SteveD409]

Thanks, I just keep learnin"!

SteveD

[Southtowns27]

faride:

The 62-64 250 horsepower 327 used a cyl. head similar to the '61 283 powerpack engine with 1.72 intake and 1.50 exhaust valves. One of the easy ways to spot this head, other then the casting #, was a casting mark on the front of the head at the head/block parting line which resembled a rectangle with a triangle on top.




I have these on my '64 283, but they have 1.94 valves :confused: Maybe someone put these in it at some point in the past

[jester]

I have these on my '64 283, but they have 1.94 valves :confused: Maybe someone put these in it at some point in the past
If they were added later, why would you stop at the 1.94? why not go right to the 2.02's?

[Southtowns27]

If they were added later, why would you stop at the 1.94? why not go right to the 2.02's?

Beats me... Why stop at 2.02, go right to 2.08! :D

[Bungy]

I don't think a 2.02 1.60 combo will clear the stock bore of a 283. Maybe that's why only a 1.94 valve was put in. But I'm not 100% sure on this. Anyone ever try (or did) put 2.02s on a stock 283?

[59elcooldsuv]

Here's info on how to read the casting marks. This was published by Car Craft years ago and I copied it and made the drawings of the heads more legible.


http://www.angelfire.com/tx5/randysresume/Headguide.html

[SteveD409]

Nice info, Randy; only the double hump head symbol (E and F) on all the ones I've seen are rounded on top.

SteveD

[Kirby J]

Here's info on how to read the casting marks. This was published by Car Craft years ago and I copied it and made the drawings of the heads more legible.


http://www.angelfire.com/tx5/randysresume/Headguide.html

i have this same magazine and have used it for years it has saved me on several occasions.. there is an easy way to tell if you have 461X heads with out having to pull them off the motor here it is (UNDER THE DATE CASTING THERE IS A NUMBER 13) this is always the case with the 461X heads.. i think it is the factory number or line number , somthing like that.. the number 13 directly under the date is a dead give away if your heads do not have this number they are just 461 heads with 64cc chambers and remember that the X heads have 58cc chambers. and all the markings are the same for either head(rounded humps).. :brow

[Kirby J]

I don't think a 2.02 1.60 combo will clear the stock bore of a 283. Maybe that's why only a 1.94 valve was put in. But I'm not 100% sure on this. Anyone ever try (or did) put 2.02s on a stock 283?


yes they will clear with no problem

[Snegrah]

Hey, I was just browsing and I know this is an old topic but it made me look at the heads on my abandoned 283 on an engine stand in my shop. They are the camel hump "E" with the casting # 3782461. Near the date code on one A122 and the other A52 is the # 13. So, I guess these are the "top O' the line ones"????? :brow

Now I gotta' rebuild them for something?!?!?!?!? :dunno Right next to that engine is a complete 327 I pulled out of my 62 Bubbletop. Am I right in assuming that the date code on the heads are 1962's? Would match up nicely with the 1962 motor?

Or, should I build up a 301 from the 283?????? These 301's ran like a bastar@#@# back in my day.

HELP...lots'a choices!!!!! :?

[jester]

Snegrah, have you been in my garage?
I'm faced with almost the same problem. I have a 1966 283 that has been bored 30 over. it has power pack heads that have but cut .025 . I have a 66 327 that can't have 300 miles since the rebuild. When the pro. rebuilder put the engine together they installed a set of low comp. Mexican head from the mid- 70's. Do I pull the slug 327 out and install the 292 or put the hot heads on the 327? Maybe I should just switch the 327 with the bored 283. Ant suggestion? :dunno

[Firepower354]

Re: 2.02 intake valves- When GM put 2.02's in production heads they used a cutter that unshrouded the chamber around the valve and also cut material from the port bowl. The chamber wall will restrict airflow and you WILL LOSE performance without the cutting. Without the bowl hogging, the valve face to bowl diameter ratio goes bad and again you lose airflow. The 283 bores are a little close for 2.02's as well. I'd clean up the ports, blend the bowls, and smooth the short turn sticking with the 1.94's. Put the good heads on the 327 and get rubber. The extra 1/4" of stroke makes the 327 hard to beat.

[dq409]

Heck ,,,, I`d take that 327 crank and stuff it in a 400 block with a good set of heads it would make a NASTY high revving SBC !!!! :eek: ,,,dq

[jester]

Heck ,,,, I`d take that 327 crank and stuff it in a 400 block with a good set of heads it would make a NASTY high revving SBC !!!! :eek: ,,,dq
Calm down Dq. :rofl I don't have a 400 block in the garage at this time, but thanks for the info.

[SteveD409]

I was just wondering. If a set of 461 had been hogged out for 2.02's, is there anyway they can be returned to 1.94's? New seats or whatever?

SteveD

[dq409]

Firepower, Are you saying the 461 with 1.94`s is a better power head? Or is it if you put the 2.02`s in them without the bowl blend you loose power?

I have a 327 with the 461`s and 1.94`s.

Should I leave them as they are and make better power?
Thanks, dq

[Firepower354]

dq: Short version-Yep, leave em alone and get rubber! Longer answer-If the bowl throat isn't opened and more importaintly the chamber isn't unshrouded, 2.02's will cost flow and thus power. You don't have to use the GM chamber cutter, just put the head on an empty block and scribe the bore outline on the head. Lay into the area of the chamber that's almost hitting the valve with the carbide burr. The port bowl really should be opened with a bowlhog, but a patient man can open them up by hand too. That said, I drop mine off at Burton Auto for the hogging. Unless you plan a port job, leave them alone. The 15-20 peak hp diff correctly installed 2.02's without additional porting will make isn't worth the effort(IMHO). It's still a 60's designed 170cc runner, that even with several hours of porting will only move 240 or so cfm. Unless it's a #8 crayon mark resto, save the coin for something with some port volume that can make use of the big valves. Even off the rack Vortec's will go 235, have hard seats, and a better chamber. My "improved" ones go 255-ish. I put them on 2 different 450hp pump gas 383's last winter. Not for the blower motor though, decks are a bit thin for that, and the exhaust ports need more work. There's also the screw-in stud, pc seal, and retainer to guide clearance issues with GM heads.

Steve: I wouldn't. If the throats were cut for the larger valve, you'd be best off leaving them be and opening the chamber to unshroud the 2.02 valve. The i.d. of the bowl should be approx. 77-80% of valve diameter. Installing intake seats is as much work as finishing the 2.02 conversion right anyway and would require blending on top and bottom of the new seats. Sticking 1.94's back on 2.02 cut seats will leave them a bit deep, but we've run them that way and they flow good.

[dq409]

Thanks Firepower,,,,dq