"New" L36 Cam

[Greg L.]

Well I'm close to getting my engine parts all lined up and was wondering what would be a good cam to use. The one in it now is quite large compared to what the original one was so it has to go...wish I had kept it but my buddy wanted it for his Chevelle so that is where it lives today.

Anyways, is there a modern version of the original 69 L36 cam, or is just the stock grind available? I was thinking that there may have been some improvments in the past 30 or so years in performance/mileage but still retain the stock idle?

Any leads are appreciated.

Greg

[Duke W.]

Re: "New" L36 Cam

"Modern cams" are a myth. Chevrolet had a good handle on valvetrain dynamics back then, and any "modern cam" which has more aggressive dynamics will require greater valve spring force/rate, which will take a toll on valvetrain durability, which is pretty much at the limit already on big blocks with the OE cams.

Valve timing should be matched to head flow so that the overall E/I ratio taking into account average flow coefficient yielded by the valve events is in the range of 0.75. Since pocket porting typically improves exhaust flow more than inlet flow, which significantly increases the E/I ratio (based on head flow alone) the valve timing requirement is very different from any OE or aftermarket cams.

My current research on SB cams for pocket ported heads indicates that the best combination is the L-46/82 inlet lobe, retarded several degrees and the late 300 HP cam exhaust lobe advanced several degrees. Total effective overlap is about the same as the 300 HP cam so it will have a smooth 500 RPM idle while making up about half the low end torque deficit of the LT-1 cam with about the same top end power. Power may only be limited by hydraulic lifter pump-up.

Bottom line is that both OE and aftermarket cams have too much overlap, but most aftermarket cams have WAAAAAYY to much overlap. Overlap and exhaust system backpressure, even the modest amount from the efficient Corvette exhaust system mix like amonia and bleach! Big blocks develop more exhaust back pressure than small blocks because they are pumping more air and exhaust products, so overlap is bad news.

Being as how I have never gotten a handle on the zillion different big block head and valve size combinations, I have not extended my research to big blocks at this time.

My SB timing numbers (for pocket ported heads) look very "weird" compared to OE cams and certainly aftermarket cams, but are amazingly similar to modern SB cams - LS1 through LS7 when taking into account raw port flow.

Racing engines where you have headers and open exhaust that can harness wave dynamics are a VERY different animal and require VERY different valve timing to maximize power in the upper third of the rev range with little regard for anything else. My street cam designs maximize torque bandwidth in the presence of modest exhaust backpressure.

The answer to your question is that the OE L-36 cam is probably the best medium performance BB cam on the market, and I recommend you install same whether you massage the heads or not, but you will gain 5-10 percent top end power and 500 more useable revs with head work without affecting low end torque or idle quality if you massage the heads.

I don't see the L-36 cam in my old FM Speed Pro catalog, but you should check with a FM dealer, GMPP, and the aftermarket vendors. I'm sure someone makes a reproduction.

The specs you are looking for are (inlet/exhaust):

Duration at .050": 214/218
Points of maximum lift-LSA: 110/120-115
Gross lobe lift: 0.27143/0.28235"

Duke

[Clem Z.]

GM cam and kit # 12364055 should be it *NM*

[Joe L.]

Re: GM cam and kit # 12364055 should be it

clem-----

That's the one. Crane-manufactured cam and lifters. The kit GM lists for about 180 bucks and can be purchased for about $150. It's a very good value. Get it quick, though. They are discontinuing a lot of these kits ( I guess they figure it's too good of a value), so this one might be next.

[Terry F.]

Re: GM cam and kit # 12364055 should be it

Joe, where is the cheapest place to buy the cam kit? Through the dealer? Terry

[Greg L.]

Re: GM cam and kit # 12364055 should be it

Thanks guys. I just did a search on this part number and it comes back as a 350hp-396 so I'm just wondering if this is in fact the same cam an L36 or is it GM's service replacement?

[Joe L.]

Re: GM cam and kit # 12364055 should be it

Greg-----

The 350 hp 396 (L34) and the 390 hp 427 (L-36) both used the same cam grind. The 65-66 version of the cam used a grooved rear journal; the 67-69 version had no rear journal groove.

The same cam was used for 385 hp 427 (passenger car) and for all 390 hp 454 (LS-5).

So, the GM #12364055 kit has "got you covered" for any of these applications. The L-34 application is probably the most common usage of this cam with respect to numbers originally produced. That's probably why it's advertised as a replacement for this application. But, it was used for these other applications, too.

[Joe L.]

Re: GM cam and kit # 12364055 should be it

Terry-----

I don't think you'll get them very much cheaper than you can get them from a source like GM Parts Direct.

[Greg L.]

Re: GM cam and kit # 12364055 should be it

Great, thanks Joe!

[Terry F.]

Re: GM cam and kit # 12364055 should be it

Thanks for the information. I was wondering about the 350 hp thing vs the 390 hp also.

Terry

[Steve Antonucci]

Re: GM cam and kit # 12364055 should be it

Joe,

I hate to pop this "expanded thread" in here, but here goes. The 396 ( L/34 )
had published HP numbers of 350hp. The L/36 had published HP numbers of 390hp.

What gives? Certainly the Vette's had far superior exhaust manifold designs,
but the cam, heads, carburetor were all the same. Even with that, the Vette
intake was the low-rise aluminum as opposed to the L/34 cast iron high rise.

So, where does the extra 40hp come from? Did all that come from the bore
difference?

Steve

[Duke W.]

Re: GM cam and kit # 12364055 should be it

The extra 31 cubic inches with the same stroke and cam should be good for about another 25 HP, but keep in mind that the SAE gross horsepower ratings of the sixties were as much a creation of the marketing guys as the engineers.

Duke

[Joe L.]

Re: GM cam and kit # 12364055 should be it

Steve------

Just a few comments: the intake manifold used for the L-34 was not really what I'd call a "high rise" design. I suppose it could be said that it was a "medium rise". However, it is higher than the "pancake" manifolds used for 1968-72 Corvette big blocks, necessary for hood clearance reasons. Also, the L-34 manifold was exactly the same as the L-36 manifold used for 1966-67 Corvette L-36. It was also the same as the manifold used for 1965 and some 1966 base big block engines (325 hp) used in many passenger cars and Chevelles.

Also, the L-34 was rated at 360 hp for the 1966 model year. For 1967 it was-"de-rated" to 350 hp even though nothing significant changed with respect to the basic engine. So, as Duke mentioned, horsepower ratings were quite "flexible" in those days.