1956 Duntov code 449

[Frank C.]

How can a '56 be verified as a true Duntov code 449?
No supporting documentation is available.
The car has the original 265 w/2 correct 4bbls.

[David B.]

Re: 1956 Duntov code 449

The only difference between RPO 448 and 449 was the cam profile installed. The RPO 449 cam part number was 3734073. The Engineering/production change was made 3-12-56. Both were not used with auto transmissions. Obviously, if your car was built prior to 3-12-56 you likely have the 448 installed cam.

[Joseph L.]

Re: 1956 Duntov code 449

I think the question you are asking is how to tell whether a 1956 car/ motor was a factory RPO 449 car.
The motor will be stamped GU on the pad. These became available after VIN 2500. The high lift cam has more duration than the RPO 469 225HP motor cam and they share the same lift. Otherwise there are no other differences.

Neither of the 1956 cams was a "Duntov" 097 cam but they were solid. The RPO 449 cam had the same duration as an 097 with more lift (0.395/0.401 vs. 0.404/0.413).

[Duke W.]

Re: 1956 Duntov code 449

What's RPO 448? I don't see it listed in the NCRS Corvette Spec Guide.

I'm certain that the RPO 449 camshaft is EXACTLY the same as the 097 except for the rear cam bearing notch for the early SB oiling system. Gross lobe lifts that include the .008/.012" high clearance ramps are .2625/.2665" The only difference between the exhaust and inlet lobes is the exhaust lobe clearance ramp is .004" higher. The engineering drawing lists lobe life to five decimal places every cam degree and above the top of the clearance ramp each exhaust lift point is .004" greater than the inlet side.

Even though Duntov referred to the cam as "high lift" it actually had slightly less lift that the regular production cam. By increasing duration and reducing lift slightly he was able to get another 1000 revs valvetrain limiting speed with the regular production valve springs.

It's my understanding that if 449 was ordered the cam and lifters came in the trunk for dealer installation. OTC the cam was about 35 bucks plus the lifter set, so the 449 option price of $188.30 must have included a labor allowance for the dealer service department to install the cam.

Duke

[Frank C.]

Re: 1956 Duntov code 449

Thanks, all, for the information.
The car I was considering, said to be "possibly" a code 449, is definitely not so.
Again, thanks.

[Joseph L.]

⁰ duration (228⁰ intake and 230⁰ exhaust duration @.050"), .394" intake and .400" exhaust gross lift (with 1.5:1 stock rockers), and 108* lobe separation.

The 097 is the cam that all the high HP motors in 57-63 had. These operate very well on the street in a 283. It would be curious to see what a 265 with the 097 or the 077 cam is like to drive.

Joe

[Jim L.]

Re: 1956 Duntov code 449

That's good info, Joe. Thanks. Does anyone reproduce the 077 cam?

[Duke W.]

Re: 1956 Duntov code 449

From Karl Ludvigsen's "Corvette: America's Star Spangled Sorts Car", page 47:

"...Duntov proposed a new camshaft design that he felt would give him the power increase he needed. Though it had less lift that the then current factory high perfromance cam..."

There is also a table with timing and lift data for three cams:

1955 standard, 12-54/52-20, 0.336/0.343"

1955 Power Pack, 22-63/66-24, 0.404/0.413"

Duntov Mark I, 35-72/76-31, 0.393/0.399"

Those are gross lifts (including the clearance ramps) assuming a 1.5:1 rocker ratio. So dividing by 1.5 to determine gross lobe lifts for the Duntov cam yields .262/.266". The '63 Corvette Shop Manual specifies gross lobe lifts of .2625/.2665".

I'll also add from Chevrolet drawing number 3736098 that the LSA is 110.5 degrees, the inlet POML is 108.5 degrees ATDC, the exhaust POML is 112.5 BTDC and the lobe are symmetrical. The ...098 is the finished camshaft part number, but what Chevrolet sold over the counter was an ASSEMBLY of camshaft and indexing pin, which is 3736097.

BTW, from measurements I made back in the seventies the actual rocker ratio is about 1.37:1 at the lash point and 1.44:1 at full lift, and the top of the Duntov cam's constant velocity clearance ramps above the base circle are .008/.012"

The above is from Ludvigsen's first Corvette book published in the early seventies. I understand he revised and republished it a few years ago, but I don't have the new version. If anyone does can you check to see if the above was changed in the new version.

Duke

[Bill B.]

Re: 1956 Duntov code 449

Hi Duke,

I have the latest edition of his book at home in CT, but I'm in NC right now. I'll check and let you know when I return mid next week unless someone here beats me to it in the meantime.

[Duke W.]

Re: 1956 Duntov code 449

Thanks! In the meantime here's more evidence... from Jerry Burton's Duntov biography, page 203.

"Duntov knew a thing or two about camshafts, both from his own racing days with Talbot engines and his Ardun overhead valve conversion. So he ordered two camshaft's built that used the same profile as his Ardun Ford camshaft. The design order was written up on July 31, 1956. [I believe this is and error and should be July 31, 1955. A nearby photo caption states "...testing versions of the new camshaft in late 1955...] In fact, he gave the Ardun specifications, written in metric, to Fred Frincke, who then had them translated into English measurements. The cam had less lift than the factory high performance cam,...

Duke

[Mark F.]

Re: 1956 Duntov code 449

From Karl Ludvigsen's "Corvette: America's Star Spangled Sorts Car", page 47: "...Duntov proposed a new camshaft design that he felt would give him the power increase he needed. Though it had less lift that the then current factory high perfromance cam..." There is also a table with timing and lift data for three cams:

• 1955 standard, 12-54/52-20, 0.336/0.343"
• 1955 Power Pack, 22-63/66-24, 0.404/0.413"
• Duntov Mark I, 35-72/76-31, 0.393/0.399"

....The above is from Ludvigsen's first Corvette book published in the early seventies. I understand he revised and republished it a few years ago, but I don't have the new version. If anyone does can you check to see if the above was changed in the new version. Duke

The new book has that table on page 123 - doesn't look like any changes were made...

		Duntov Mark I	1955 Power Pack	1955 Standard
Inlet Opens	BTDC	350	220	120
Inlet Closes	ABDC	720	630	540
Exhaust Opens	BBDC	760	660	520
Exhaust Closes	ATDC	310	240	200
Overlap		660	460	320
Inlet Lift		0.393"	0.404"	0.336"
Exhaust Lift		0.399"	0.413"	0.343"

[Duke W.]

Re: 1956 Duntov code 449

Here's some more food for thought. I can't remember who wrote most of the attached paper, "Corvette Cams", but I'm about 99.9 percent certain that I authored page four as it sounds like my writing, and all the data presented is based on my analysis of OE cam lobes for which I have most all the engineering data which consists of lobe lift, in inches, to five decimal places every cam degree.

It starts out with what I believe is an error in the first sentence, as it's my understanding that ALL '55 small blocks whether used in passenger cars, trucks, or Corvettes had mechanical lifter camshafts.

In the fourth paragraph and the listing on page 2 it states ...077 cam lift as 0.404/0.413, but based on the information in the Ludvigsen and Burton books I believe this is an error.

The 3911068 valve spring did not go into production until 1967. The spring it replaced that dated to '57 had a slightly lower rate, seat and open force.

The 30-30 cam has a 114 deg. LSA with POMLs of 110/118 (Note that LSA =(IPOML + EPOML)/2)

The Duntov cam .050" lifter rise duration net of the clearance ramps is about 220 degrees, very close to the L-79 cam, but the latter has less overlap than the Duntov that actually makes it a better road engine cam because the Duntov's higher overlap hurts low end torque, but doesn't really improve top end power with OE manifolds. I know some 283 owners replaced the OE cam with the L-79 cam and I've also recommended custom grinding the Duntov lobes with a IPOML of 110 and a LSA of 114. I know that Crane had Duntov lobe masters and could grind the cam, but I understand they have been purchased by Comp Cams and don't know what happened to their lobe master library.

The '55-'56 SB oiling system has a required cast-in "notch" in the rear cam journal for lifter gallery and rocker box oiling. The '57 up did not and though a notched cam would probably be okay in a later block a cam without this rear journal notch in a '55-'56 block would prevent lifter galley and rocker box oiling, so since function changed a new part machined from a changed casting was required, and my contention is that the lobes and lobe indexing of both the ...077 and ...097 is identical. The only difference is that the ...077 has the cast-in notch in the rear bearing journal and the ...097 does not.

A similar situation exists with '65-'66 big block oiling and '67-up oiling.

Duke

[Joseph L.]

Re: 1956 Duntov code 449

I'm half wrong on the 1955 passenger cars. Powerglide motors used hydraulic cams. See the 1955 shop manual. I will have to correct that at some time.

Joe