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327/300 cam suggestions

 
Old 02-11-2019, 07:30 AM
  #21  
tbarb
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Originally Posted by plaidside View Post
Duke,
Maybe I missed it but what is IPOML?
Thanks,
Joe
Joe,

Duke is referring to intake point of maximum lift, he likes the 350/350hp cam more but I don't know the lobe specs and how it differs from the 327/350hp camshaft.
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Old 02-11-2019, 01:27 PM
  #22  
wilcar
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I had a 76 l82 with AT and 3.36 rear and I used an Isky 264 mega cam which provided much better low and mid range power than the L82 cam. 214-214 dur at 050 .450-.450 lift 108 lsa. A friend had a pretty stock 327 in a nova with AT and 3.08 rear and he really liked the 264 Isky.
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Old 02-11-2019, 02:39 PM
  #23  
SWCDuke
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Originally Posted by bowtyebob View Post
One more reply to your query.... Most of the replys are correct ....almost. A blueprinted L79 cam (from Crane Cams) is absolutely the away to go. It worked in '67 and will work just fine today. Keep in mind that just swapping the 300HP cam for an L79 cam will yield a loss in compression of about one point because of the increased duration and overlap. If you swap the cam you really ought to replace the pistions with the L79 11:1 pop-up pistons as well to maintain the engines static compression ratio. I have done this 'conversion' before and have been completely satisfied with the results. As for the distributor, I recommend using a B20 which will start the pluinger advancing slightly sooner (6"-7"in) than the 300HP canister, but is not as 'aggressive' as L79 canister that would probably cause some detonation (if used with the L79 pistons) under moderate acceleration in the mid-rpm range. No, there really is no need to use the L79 intake manifold OR the larger valves that would ONLY give a wee bit more horse power above 5500-6500 RPM at the expence of a slight loss in low-end driveability and increased fuel consumption because of slightly lower low-mid range flow velocity.
Swapping the cam with the L79 version, using the L79 pistons and a B20 vacuum, and setting the initial timing to about 10 degrees should result in a steady, reliable 'L79' 700 RPM idle, NOTICEABLY more power to 6000-6500RPM (no more 'nosing over' at 5200RPM), and excellent low-end response with little to no loss in fuel mileage.
In order to change the pistons the whole engine needs to be disassembled. The slightly lower SCR and DCR when you install a L-79 cam in a 300 HP engine does not justify the cost and time unless the engine actually needs a complete overhaul. The L-82 was basically a low compression version of the L-46. The SCR was dropped two points to satisfy the Fourteenth Floor's mandate that all engines operate on 91 RON unleaded fuel, and it certainly was stronger than the base engine.

In the early seventies a buddy bought a '67 300 HP Couple with the WR four-speed and 3.36 Posi axle, which was the same drive train as most L-79s. The odometer showed about 65K miles, but was broken (and he had fixed), and it showed a little blue smoke on overrun. He liked the car, but wanted it to sound like a "real Corvette engine" with more top end power and revs, and he was concerned about the blue smoke. I suggested swapping in a L-79 cam, N-11 exhaust, and new valve seals. (A compression test showed that the engine was healthy, internally.) I insisted on all GM replacement parts, and I got a "trade discount" from a local dealer, so we made the deal. We also replaced the OE nylon sprocket timing set with a truck roller chain set. The nylon sprocket looked okay, but I knew of several that had shredded teeth, so it had to go. The guides had some wear, but not enough to justify refreshing the heads, and the new valve seals eliminated the slight blue smoke on overrun.

The new N-11 exhaust was unbelievably inexpensive compared to what NOS examples go for today. Total parts cost was probably a few hundred bucks, but he was making good money for the time, so the expected result, which was achieved, was well worth the expense and time.

The OE 355 16 12" VAC was okay since L-79 idle behavior is 750 @ 14", so the OE VAC passes the Two-Inch Rule with the L-79 cam, and we quickened up the centrifugal curve with lighter springs. All work was done in his garage over a couple of weekends with basic hand tools... no need to pull the engine. We painted the cast iron manifold with silver header paint and also installed a set of "Corvette" valve covers, so to casual observation, it looked like a real L-79.

The final result didn't appear to lose much low end torque that I attributed to the quicker centrifugal curve, and it felt like a real L-79 in the upper rev range and was pretty much equal in performance to my 340 HP SWC.

He was very happy with the result. The L-79 cam and N-11 exhaust certainly made it sound like a "real Corvette engine", and compared to the OE 300 HP configuration it ran like a scalded cat from 4000 to 6000.

He was very happy with the car until he sold it in the late seventies.

Duke

Last edited by SWCDuke; 02-12-2019 at 11:44 AM.
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Old 02-11-2019, 05:35 PM
  #24  
MikeM
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Originally Posted by SWCDuke View Post

He was very happy with the result. The L-79 cam and N-11 exhaust certainly made it sound like a "real Corvette engine", and compared to the OE 300 HP configuration it ran like a scaled cat to 6000 revs.

He was very happy with the car until he sold it in the late seventies.

Duke
Exactly right! You want your 300 to come alive. No need for all the theory or changing pistons, heads, valves and all that stuff. Just stick an L 79 cam in the bugger and you're in business. .

I don't care for the 350/350 cam because it doesn't have the "come on" feel at a certain rpm. the L 79 cam does. Just MY OPINION!

Last edited by MikeM; 02-11-2019 at 05:36 PM.
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Old 02-12-2019, 11:14 AM
  #25  
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The '65 L-79 distributor I overhauled a few years ago and wrote up in a thread started by me had a very linear pull from off idle to redline that I attribute to the quicker centrifugal curve we implemented - all in by 3500 instead of 5000. The curve is non-linear and most was in by 3000. My 340 HP engine always had that "come on the cam" feel even after I implemented the very aggressive 365/375 HP centrifugal curve, and I attribute that to the Duntov cam's higher overlap relative to the L-79 cam.

The L-46 cam (advanced four degrees on 327s) is so close to the L-79 cam that I can't imagine there would be any difference in SOTP feel, everything else equal, including the spark advance map, and the spark advance map has a HUGE effect on torque bandwidth, especially the low end. The reason I prefer it is because it's a later design that has better lobe dynamics, so it's easier on the valve train.

Duke

Last edited by SWCDuke; 02-12-2019 at 11:57 AM.
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Old 02-12-2019, 11:32 AM
  #26  
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Originally Posted by tbarb View Post
Joe,

Duke is referring to intake point of maximum lift, he likes the 350/350hp cam more but I don't know the lobe specs and how it differs from the 327/350hp camshaft.
L-79 cam: 222/222/110/118/114/.298/.298 (same lobe on both sides)

L-46/82 cam: 224/224/114/114/114/.300/.307 (different inlet-exhaust lobes, primarily dynamics)

L-46/82 cam advanced four degrees: 224/224/110/118/114...

The two degrees difference in duration and few thou difference in max lobe lift is insignificant, and advancing the L-46/82 cam four degrees means the IPOML and EPOML are the same as the L-79 cam, and, of course, the LSA is the same because it's fixed.

The following formula is valid for all cam designs. Once you know any two of the variables, the third cam be computed.

(IPOML + EPOML)/2 = LSA

Duke
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