double hump heads ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jeff69cst/10 · 05-02-2002, 09:35 PM

What is so special about them?
I have a set of the that came off of my original motor,should I keep them and redo them and put them back on?
They are not 2.02,they are 1.94 or slightly smaller.

------------------
69 CST/10 350/400TH lwb fleet,1 owner
79 K/20 4x4 built & lifted
Sheridan,IN

Longhorn Man · 05-02-2002, 09:58 PM

Now that teh vortecs are out there.....absolutly nothing special

------------------
'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite.
If you need a pic posted, E-mail me at longhornmail@yahoo.com
Andy, in Columbus Ohio

Stroker · 05-02-2002, 10:13 PM

I wasn't aware that the dbl humps were installed on trucks, but then again I've seen an original 350 in a 68 c10. That truck had been in the same family since new and the engine had never been out. What casting number are the heads? The dbl hump heads were the best Chevy had to offer in their day and are still a decent head. But usually by the time you COMPLETELY rebuild a set the price is comparable to a new set of vortech heads with better flow and combustion chamber design. It really depends on how much work the heads need. Be sure to check for cracks they are not uncommon on 30 year old heads. Personally I would sell them, they are still very popular with a lot of hot rodders and I've seen them sell for $100-$200 as usable cores. I would put that money toward a newer design like the vortech.Just my .02 worth.

dmnall · 05-03-2002, 03:11 AM

Well it depends on the Casting of the Double Hump Heads!! I am running 462 (last 3 digits of Casting Number) and they are great heads but the problem with first 4 Castings of the Large Double Hump is no accessory Holes and High Compression!! To get anything below 10.5:1 Compression w/ these heads are Dish Top Pistons! I am running Flatop which I am around 11.5 - 12:1 Compression Ratios and my heads have 2.02 Intake and I have to run 91 and Above Octane Rating just to get my 350 to run right!!

If my Heads were to go belly Up, then I would either go w/ GM's Aluminum Fastburn Vortec Heads w/ 2.02 Valves or Edelbrock's Etec 202 Heads!! I prefer the larger Valves for More Top End and better performance!! Vortec's are nice because they flow nice and you can get a set of steel ones new for about $500 and 100 - 250 for used and Fastburn are around $ 1000 and I have seen a set of these go for around $ 500 used!!

------------------
Truck #1 68 Chev LWB Fleet w/ Wood Floor (Sucks Gas and Hauls Ass!) and in process of Body Work...

Truck #2 1994 GMC Sierra SL w/ 4.3L Vortec V6, 4L60E Auto!!

*Randy70C-10* · 05-03-2002, 07:16 AM

dmnall is on the money, smaller combustion chambers produces high compression. I ran a set with 58cc chambers and flattops, with around 10.5:1 compression in a 283!!!

**MikeB** · 05-03-2002, 07:56 AM

Back in the 60s, 98 octane fuel was plentiful and only 35 cents/gal, so 11:1 compression was no big deal. And the cams used tons of duration to achieve high lift, so a lot of that compression was bled off by very late intake valve closing. I expect Vortec heads with better springs and screw-in studs would work just as well, if not better. Heck, I hear the Vortec outflows a basic Bow Tie head! Also, the World products SR Torquers are good heads and don't require a special manifold or valve covers like the Vortecs. As a user of Dart Iron Eagles, I can't recommend them due to shoddy castings and other problems.

------------------
MikeB
69 C-10 Fleetside, mild 383, Dart Iron Eagle heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash.

Mike C · 05-03-2002, 07:57 AM

Small chamber SBC heads (64cc) add about 1 pt of comprssion compared to the large chamber (76cc) heads. Your typical 8.5:1 flat top with 4 valve reliefs motor will be 9.5:1 with the double humps. No where NEAR the 11 & 12-1 mentioned previously. Small chamber heads are worth 20hp more than large chamber heads even after taking into account compression. Every engine Chevrolet ever had that was more than 10:1 had a piston with at least a small dome. Like mentioned previously, the biggest drawback to the early heads is no accessory holes fowllowed by the fact that they do not have hardened exhaust seats. It costs as much to R&R an old set of heads as it does to just buy the Vortecs. You do have the added expense of new valve covers and an intake, which is more leakage prone than the older ones that have 4 more bolts.

------------------
70 GMC 3/4 ton Sierra Grande 402/TH400
72 Jimmy 4WD 4spd 4" & 35's
64 Corvette Coupe
68 Camaro 'vert TPI & TH700
69 Z/28 355 12.6's @110
72 Datsun 240Z-ol' reliable

*Randy70C-10* · 05-03-2002, 08:16 AM

You can still achieve slightly higher compression by boring .060 and using aftermarket 2 relief pistons. Boring .060 is common in 283's, with room to bore up to .120 over.

*Randy70C-10* · 05-03-2002, 08:19 AM

(slightly higher than 10:1) that is!

------------------
Yeah, that's right. My name is Randy too!
WWW.Randysrods.freeservers.com
1970 Chevy C-10 shortstep
30 Ford Model A Coupe 4 inch chop, 350, GMC 671 blower-Hell yeah it's fast!
87 Harley Sportster(couldnt get a 350 to fit)
Self Propelled Lawn Mower
Built in USA!!!!

Virginia Beach, VA.

69 longhorn · 05-03-2002, 08:25 AM

Also decking the block,& milling the heads can put a 350/flattop in the 11 to 1 range(assuming minimum quench clearance). As a rule though,a flattop 350(stock parts &deck/040 gasket) will fall into the 9.5-9.6 range with a 64-66 cc chamber.....69 longhorn.

*Randy70C-10* · 05-03-2002, 08:28 AM

Mine where milled to 58cc's, but the machine shop must know what they're doing or your intake will never bolt on correctly!

**MikeB** · 05-03-2002, 08:44 AM

Mike C -- My spreadsheet shows 9.96 for a 355 with stock deck height, .038" gasket, flat-top pistons (-4cc), and 64cc chambers. A 383 with .005" deck and .038" gasket with flat top pistons and 64 cc chambers yields 11.2:1 CR. A 355 with same is 10.5. A 406 is 11.75. So, the 11-12 numbers were only correct for a stroked motor with short deck height.

------------------
MikeB
69 C-10 Fleetside, mild 383, Dart Iron Eagle heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash.

05-02-2002, 10:13 PM	#3
Stroker Registered User Join Date: Mar 2001 Location: Moore, Ok Posts: 1,149	I wasn't aware that the dbl humps were installed on trucks, but then again I've seen an original 350 in a 68 c10. That truck had been in the same family since new and the engine had never been out. What casting number are the heads? The dbl hump heads were the best Chevy had to offer in their day and are still a decent head. But usually by the time you COMPLETELY rebuild a set the price is comparable to a new set of vortech heads with better flow and combustion chamber design. It really depends on how much work the heads need. Be sure to check for cracks they are not uncommon on 30 year old heads. Personally I would sell them, they are still very popular with a lot of hot rodders and I've seen them sell for $100-$200 as usable cores. I would put that money toward a newer design like the vortech.Just my .02 worth. __________________ 72 SWB parts and pieces Oklahoma

05-03-2002, 03:11 AM	#4
dmnall Registered User Join Date: Apr 2001 Location: Goleta, CA Posts: 505	Well it depends on the Casting of the Double Hump Heads!! I am running 462 (last 3 digits of Casting Number) and they are great heads but the problem with first 4 Castings of the Large Double Hump is no accessory Holes and High Compression!! To get anything below 10.5:1 Compression w/ these heads are Dish Top Pistons! I am running Flatop which I am around 11.5 - 12:1 Compression Ratios and my heads have 2.02 Intake and I have to run 91 and Above Octane Rating just to get my 350 to run right!! If my Heads were to go belly Up, then I would either go w/ GM's Aluminum Fastburn Vortec Heads w/ 2.02 Valves or Edelbrock's Etec 202 Heads!! I prefer the larger Valves for More Top End and better performance!! Vortec's are nice because they flow nice and you can get a set of steel ones new for about $500 and 100 - 250 for used and Fastburn are around $ 1000 and I have seen a set of these go for around $ 500 used!! ------------------ Truck #1 68 Chev LWB Fleet w/ Wood Floor (Sucks Gas and Hauls Ass!) and in process of Body Work... Truck #2 1994 GMC Sierra SL w/ 4.3L Vortec V6, 4L60E Auto!! __________________ 1968 C10 Truck LWB Fleetside 1968 C10 Truck SWB Stepside 1994 K2500 Ext Cab Fleetside 2008 Honda Civic Si lease

05-03-2002, 07:56 AM	#6
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,544	Back in the 60s, 98 octane fuel was plentiful and only 35 cents/gal, so 11:1 compression was no big deal. And the cams used tons of duration to achieve high lift, so a lot of that compression was bled off by very late intake valve closing. I expect Vortec heads with better springs and screw-in studs would work just as well, if not better. Heck, I hear the Vortec outflows a basic Bow Tie head! Also, the World products SR Torquers are good heads and don't require a special manifold or valve covers like the Vortecs. As a user of Dart Iron Eagles, I can't recommend them due to shoddy castings and other problems. ------------------ MikeB 69 C-10 Fleetside, mild 383, Dart Iron Eagle heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

05-03-2002, 07:57 AM	#7
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,723	Small chamber SBC heads (64cc) add about 1 pt of comprssion compared to the large chamber (76cc) heads. Your typical 8.5:1 flat top with 4 valve reliefs motor will be 9.5:1 with the double humps. No where NEAR the 11 & 12-1 mentioned previously. Small chamber heads are worth 20hp more than large chamber heads even after taking into account compression. Every engine Chevrolet ever had that was more than 10:1 had a piston with at least a small dome. Like mentioned previously, the biggest drawback to the early heads is no accessory holes fowllowed by the fact that they do not have hardened exhaust seats. It costs as much to R&R an old set of heads as it does to just buy the Vortecs. You do have the added expense of new valve covers and an intake, which is more leakage prone than the older ones that have 4 more bolts. ------------------ 70 GMC 3/4 ton Sierra Grande 402/TH400 72 Jimmy 4WD 4spd 4" & 35's 64 Corvette Coupe 68 Camaro 'vert TPI & TH700 69 Z/28 355 12.6's @110 72 Datsun 240Z-ol' reliable __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

05-03-2002, 08:25 AM	#10
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	Also decking the block,& milling the heads can put a 350/flattop in the 11 to 1 range(assuming minimum quench clearance). As a rule though,a flattop 350(stock parts &deck/040 gasket) will fall into the 9.5-9.6 range with a 64-66 cc chamber.....69 longhorn. __________________ http://community.webshots.com/user/hotrodhorn

05-02-2002, 09:35 PM	#1
jeff69cst/10 Registered User Join Date: Jan 2002 Location: Sheridan,IN Posts: 92	double hump heads ? What is so special about them? I have a set of the that came off of my original motor,should I keep them and redo them and put them back on? They are not 2.02,they are 1.94 or slightly smaller. ------------------ 69 CST/10 350/400TH lwb fleet,1 owner 79 K/20 4x4 built & lifted Sheridan,IN __________________ 69 CST/10 350/400TH lwb fleet,1 owner 79 K/20 built & lifted 85 K/5 4" lift 6.2 Diesel Sheridan,IN

05-02-2002, 09:58 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Now that teh vortecs are out there.....absolutly nothing special ------------------ '69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it. FINALLY got the HORNIAC...a '70 one ton Longhorn with a Pontiac 350/350 and lots of 'personality'. Check out The Longhorn Webite. If you need a pic posted, E-mail me at longhornmail@yahoo.com Andy, in Columbus Ohio

05-03-2002, 07:16 AM	#5
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	dmnall is on the money, smaller combustion chambers produces high compression. I ran a set with 58cc chambers and flattops, with around 10.5:1 compression in a 283!!!

05-03-2002, 08:16 AM	#8
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	You can still achieve slightly higher compression by boring .060 and using aftermarket 2 relief pistons. Boring .060 is common in 283's, with room to bore up to .120 over.

05-03-2002, 08:19 AM	#9
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	(slightly higher than 10:1) that is! ------------------ Yeah, that's right. My name is Randy too! WWW.Randysrods.freeservers.com 1970 Chevy C-10 shortstep 30 Ford Model A Coupe 4 inch chop, 350, GMC 671 blower-Hell yeah it's fast! 87 Harley Sportster(couldnt get a 350 to fit) Self Propelled Lawn Mower Built in USA!!!! Virginia Beach, VA.

05-03-2002, 08:28 AM	#11
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	Mine where milled to 58cc's, but the machine shop must know what they're doing or your intake will never bolt on correctly!

05-03-2002, 08:44 AM	#12
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,544	Mike C -- My spreadsheet shows 9.96 for a 355 with stock deck height, .038" gasket, flat-top pistons (-4cc), and 64cc chambers. A 383 with .005" deck and .038" gasket with flat top pistons and 64 cc chambers yields 11.2:1 CR. A 355 with same is 10.5. A 406 is 11.75. So, the 11-12 numbers were only correct for a stroked motor with short deck height. ------------------ MikeB 69 C-10 Fleetside, mild 383, Dart Iron Eagle heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.