1956 Special High-Lift cam option code 449

[Richard M.]

Re: 1956 Special High-Lift cam option code 449

What would you like to know?

David, Anything you know. Great history there to tell us about.

Curious, why did they choose the GT engine versus GU on the 56 Sebring cars? Related to ZF transmissions?

I'd love to hear the full story of that cam change you did too.

Rich

[Joseph L.]

Re: 1956 Special High-Lift cam option code 449

Sebring in 1956 was on March 24. The JM shows Corvette motors with the old style 2-bolt exhaust manifolds left the factory until VIN 1700 on March 31. JM shows GU motors were not available until VIN 2500 on May 17.

There was only one 1956 Sebring car with a 1956 VIN, and that was 1009. The rest were 1955 chassis with 1956 bodies. The GT motors may have been the only ones available at that time, with enough lead time to be fitted.

If we move forward with 65 GU motors, six of them would have been used in the six? SR1 cars. There are the 7 VINs listed in this thread. I have research on four other unconfirmed cars. There is a question on what the SR-2 cars used.

Remember, the 077 cam should have been available as a part and fitted into many of the 1956 Corvettes. Then you have a 265/240 HP. This is much like the 1957 RPO 684. What we are looking for are 1956 cars with the GU stamped original block.

Joe

[Ernest C.]

Re: 1956 Special High-Lift cam option code 449

Joe, I started this discussion because I have one with a GU block, VIN 3263 built o July 2 1956. I am 83 years old and was considering downsizing so I wanted to know as much as I could. This discussion has been enlightening. Thanks Ernie

[Duane M.]

Re: 1956 Special High-Lift cam option code 449

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[David B.]

Re: 1956 Special High-Lift cam option code 449

David, Anything you know. Great history there to tell us about.

Curious, why did they choose the GT engine versus GU on the 56 Sebring cars? Related to ZF transmissions?

I'd love to hear the full story of that cam change you did too.

Rich

Rich, The first GT engines were cast late 1955. The one I replaced the crankshaft on (not camshaft) was engine 0243504 F56GT cast L275. As explained to me, engines at this time were engineered primarily for powerglide transmissions. It was discovered that under severe usage with a manual transmission an oil leakage problem arose. The problem was corrected but there was not enough time to replace the crankshaft sent down from the Tech Center.
The early GT engines were first built and used in the passenger cars running at the Daytona Speed Week event, since this effort was headed up by Mauri Rose he made sure he had a little edge (he tried and failed to get Cole's approval to use the 'new 283 cu. in.). A group of 25 GT engines were not installed in cars at the factory but rather given to various VIP friends of Mauri's. Since they were better then the stock Corvette engine they were also used at Sebring. (not all Sebring engines were stamped GT) In addition, these engines were "reworked a little" at the Tech Center with a few slight modifications to help Chevrolet's team effort. The ZF transmission you mention (I owned both, another GREAT story) might have helped cause the clutch slippage which occurred in the #1 car. It was a crappy trans! OK maybe for a truck it was designed for.

[Richard M.]

Re: 1956 Special High-Lift cam option code 449

Duane, I see your first post! Welcome to the TDB! That is a great photo of your '56.

Rich

[Richard M.]

Re: 1956 Special High-Lift cam option code 449

Rich, The first GT engines were cast late 1955. The one I replaced the crankshaft on (not camshaft) was engine 0243504 F56GT cast L275. As explained to me, engines at this time were engineered primarily for powerglide transmissions. It was discovered that under severe usage with a manual transmission an oil leakage problem arose. The problem was corrected but there was not enough time to replace the crankshaft sent down from the Tech Center.
The early GT engines were first built and used in the passenger cars running at the Daytona Speed Week event, since this effort was headed up by Mauri Rose he made sure he had a little edge (he tried and failed to get Cole's approval to use the 'new 283 cu. in.). A group of 25 GT engines were not installed in cars at the factory but rather given to various VIP friends of Mauri's. Since they were better then the stock Corvette engine they were also used at Sebring. (not all Sebring engines were stamped GT) In addition, these engines were "reworked a little" at the Tech Center with a few slight modifications to help Chevrolet's team effort. The ZF transmission you mention (I owned both, another GREAT story) might have helped cause the clutch slippage which occurred in the #1 car. It was a crappy trans! OK maybe for a truck it was designed for.

David, Very cool story. Thanks for sharing the info. Rear main leaking? Was the crankshaft damaged due to the oiling problem?

I don't know much about the 4 speed ZF transmissions, other than they were made overseas(Germany?), and they were also used on the 70's mid-engine Pantera( a friend had one). Since GM didn't have a 4 speed then I guess they needed to outsource to be competitive on the track.

Rich

[James G.]

Re: 1956 Special High-Lift cam option code 449

All,

Need to include Bob Kunz barnfind 56 S/N 2762 which is one of 111. Car is pretty much all original with 41,000 miles on it. Bob sold the car to the grandson of the original dealer Paul Luehrs Chevrolet of Mascoutah, Illinois who sold the car new in June 1956.

https://www.motortrend.com/features/1604-possible-1-of-111-1956-corvette-with-duntov-cam-pulled-from-missouri-basement

Mike

The grandson had the car at the Cincinnati Regional show in April of 2019. - I spoke with him a number of times, I absolutely loved the car. It 2nd flighted if not mistaken.

[Michael H.]

Re: 1956 Special High-Lift cam option code 449

The grandson had the car at the Cincinnati Regional show in April of 2019. - I spoke with him a number of times, I absolutely loved the car. It 2nd flighted if not mistaken.

Yes you are correct, he also had it judged for Bowtie award and I think he got a one or two stars.

Mike

[James G.]

Re: 1956 Special High-Lift cam option code 449

Saw the car in 2013 on our way to Carlisle. Bob was very generous with his time and knowledge.

[Duke W.]

Re: 1956 Special High-Lift cam option code 449

It is not the 1957-1963 “097” Duntov cam. This Duntov cam (P/N 3736097, casting #3736098) had 287⁰ duration (228⁰ intake and 230⁰ exhaust duration @.050"), .394" intake and .400" exhaust gross lift, and 108* lobe separation.The 1956 cam used in GU motors is similar to the 097 cam. The GU cam (P/N 3734077) had 287⁰ duration (228⁰ intake and 230⁰ exhaust duration @.050"), lift of .404” intake and .413” exhaust gross lift.BTW, all other 1955-56 Corvette motors used a P/N 3711354 (casting #3711355) mechanical camshaft. It had lift of .404” intake and .413” exhaust, and duration of 264 intake and 266 exhaust.I would like to do a drive comparison of a 265 with a GU cam with my 270HP 1957.Joe

I don't know what your source is for the '56 Duntov cam specs is, but I believe it's in error. The lobe is exactly the same as the '57-'63 version... no difference in lift, either the lobe itself or the gross valve lift (including clearance ramps) times 1.5. The only difference between the two cams is the notch in the rear cam journal of the '56 version for lifter gallery and overhead oiling.

I've seen the engineering drawing for the '56-'63 version, but not the '56 version. There's a lot of erroneous camshaft data floating around the Web.

Also the ...098 is not the casting number. It's the actual finished camshaft part number, which is the drawing number. The ...097 is the assembly of cam and indexing pin, which is what was sold over the counter. In addition to the lobe data drawing #3736098 includes rough casting dimensions along with an instruction to embed the finished camshaft number in the casting. In the parts manuals this is referred to as the "ID number". AFAIK there was never an issued part number for the raw casting. The above applies to all other camshafts of the era.

Duke

[Duke W.]

Re: 1956 Special High-Lift cam option code 449

The following quote is from Ludvisgen's book, page 47, the original version published in 1973.

"Drawing on his considerable experience with pushrod-and-rocker valve gear, acquired with racing engines from the Talbot-Lago to the Ardun, Duntov proposed a new camshaft design that he felt would give him a the power increase he needed. Though it had less lift than the then current factory high performance cam,..." [my emphasis]

Included is a chart showing valve timing and gross valve lift at a 1.5:1 rocker ratio of the Duntov design and two existing cams.

Duntov Mark I: 35-72/76-31, .393/.399"
1955 Power Pack: 22-63/66-25, .404/.413"
1955 Standard: 12-54/52-20, .336/.343"

Jerry Burton's Duntov biography offers the following, page 203. Perhaps Ludvisgen was his source.

"The cam had less lift than the factory high-performance cam, but lifted the valves earlier."

I was always intrigued by Duntov's reference to his design as a "high-lift cam". Maybe he was trying to throw off the competition as to the underlying design philosophy. Knowing he could not change anything else in the valve train including the valve springs he opted for increased duration with about the same lift, actually marginally less. This softened valve train dynamics and allowed another 1000 revs of valve train limiting speed. Later designs based on Chevrolet's analysis of valve train dynamics with the Optron resulted in even softer action, beginning with the 30-30 cam design.

Years ago when I had a serious conversation with Ed Iskendarian about camshaft design he said that Ed Winfield was a proponent of "soft action" cams and Duntov knew Windfield from his days with the Ardun heads. Connect the dots.

Duke

[Joseph L.]

Re: 1956 Special High-Lift cam option code 449

Duke- AMA Specifications for 1956 and 1957 Corvette is the first place to start. Chevy by the Numbers is another reference.

Using the lift/duration specs-
Your first cam (Duntov Mark I) is the 1957-1963 097 cam. This is what is referred to as the Duntov 097 cam.

The '1955 Power Pack' is the casting #3711355 cam that came with 1955 Corvette 195 HP, 1955 Super Power Pack (there weren't many) and 1956 210 and 225 HP Corvette. Just like you quote, "The cam had less lift than the factory high-performance cam, but lifted the valves earlier."
That quote is comparing the 1955 195 HP and 1956 210 & 225 HP #3711355 cam to the 1957 097 Duntov cam.

The '1955 Standard' is the casting #3836686 1955 162 HP and 180 HP Power Pack

Joe