NCRS Standards

[Joe C.]

Re: My answer to that would be

Mike, you hit the nail on the head! "Let us be CONSISTENT".

Joe

[Joe C.]

Compression

Joe:

I think that I can safely say that, around these parts, the term "low compression" means post 1970, Clean Air Act compression. I am fairly sure that that is what Mike was talking about.

What did Bill Clinton say in his defense, "it depends on what the meaning of 'is' is".

Joe

[Joe C.]

Re: LT1 Cam???

Joe:

I must take issue with your assertion that the LT1 cam represents an upgrade, and thus replaced the 30-30 in "service".

Consider what the "bean counters" were thinking in that era leading up to 1971, when the Clean Air Act tightened the noose on the muscle car era.

First of all, even BEFORE this happened, the MKIV engine was rolled out, and was marketed as God's answer to peanut butter and jelly sandwiches. So, what happened next, lots of them were sold, and this effectively caused a deemphasis of attention to the smallblock. Chevroled promptly discontinued the L76/L84. Now, this left Chevrolet without a SHP (meaning: solid lifters, effective rev limit 6500RPM)smallblock. So, what did the bean counters do next? Well, they told the engineers to bolt a large pan and balancer to the L79 (hydraulic lifters), and called it a SHP!

Okay, fast forward to 1969 (the year after the CAA was enacted). The engineers could see the handwriting on the wall. They knew that they would have to develop a fairly potent SHP smallblock that could be designed to perform acceptably with the anticipated lowered compression which would be implemented in 1971. They also knew that, if they ressurected the L76/L84 30-30, that it would fall flat on its face with lowered compression. So, they rolled out the LT1, in "high compression" form for 1970. It lived on for 2 more years in "lowered compression" form.

Joe

[Joe C.]

Re: Sooner or later ..............

Jim:

I'm with you! I enjoy driving my L76 with 30-30 cam (I shouldn't have to say that, should I), and domed original (style) pistons. It runs beautifully on unleaded premium. It starts quickly, does not detonate, runs reliably, does not foul plugs, and I LOVE TO DRIVE IT! So, what is the problem?

Joe

[Joe C.]

Re: NCRS Standards

Terry:

My L76 is not detuned. Just for folks who may not fully understand. I have domed pistons in her (as original). I also have the timing jacked up a few degrees past spec. (whoops....that's not original ). It runs great with unleaded hi test, and NEVER detonates, even if I lug the engine.

Joe

[Joe C.]

Re: NCRS Standards

Joe:

I agree fully. I just don't see the benefit of the LT1 over the 30-30. IMHO, the LT1 was a "transitional" design, invented to bring us into the emissions era. If I was going to recommend a camshaft, I certainly would choose a modern design.

Joe

[Clem Z.]

lower CR engines

when GM went to lower compression ratio engines they needed a cam with less overlap to build cylinder pressure so i would guess that is why the 30-30 cam went away

[Terry F.]

Re: NCRS Standards

It does not always work out that way. I am glad yours did ok. Did you use factory original high domes? It is my understanding that many newer pistons have changed over the years and are not the same configuration as factory. I am not an expert, only repeating what the parts people tell me. As I recall they said it was to help run on the newer gas. Thanks, Terry

[Mike M.]

Re: NCRS Standards

Duke,
Do you recommend installing the LT-1 cam straight up or slightly (maybe 4) degrees advanced? I intend to follow your recommendations when and use an LT-1 cam I rebuild my '63 327/340. And since I have extra sets of 461's laying around, I'll pocket port a set of those and keep the 461x's stock.

Thanks,
Mike

[Dave F.]

at the 9" rearend store :-) *NM*

[Chuck R.]

Re: Your bad Dave

And I'm worse

I just might drop one of them spherical headed jobbies in it instead of that ole Granny Smith 327/300

Ok I'm done no more wise cracks, back to business.

Chuck Rice #32205

[Dave F.]

Re: Your bad Dave

Just trying to help out. A hemi in a shark would be interesting....

[Duke W.]

Re: NCRS Standards

Heaven forbide! Can I offer advice publically without being castigated?

As a rule advancing a cam will enhance low end torque at a slight expense to top end power and vice versa if advanced. The OE indexing provides good torque bandwidth and excellent top end power, so I think it should be installed with the OE indexing. A Corvette owner recently rebuilt his L-79 with nicely pocket ported (he had them flow tested and the numbers were excellent) 461s, LT-1 cam, Crower Sportsman rods, and the OE type Speed Pro domed forged pistons with a measured CR of 10.35:1 using a composition head gasket. (I won't mention his name to protect him from possible vigilante squads attempting to burn his house down for installing the "wrong" cam.) Everything else is OE including the manifolds and carb, so external appearance will be identical to original.

He also had the engine tested on a lab dynamomter, and the results can be compared to the OE SAE gross ratings. Torque was a bit less than expected at about 338 lb-ft @ 4500, but the bottom end of the 80 percent bandwidth was 2000 and it held just below this all the way down to 1500. A signficant rise in torque didn't occur until about 2500 and then there was a good rise from 3000 to 4000, which is the "surge" we typically feel with SHP engines.

Torque dropped off so modestly beyond the peak that power was still climbing at the 6400 observed redline. Peak power was 359. This may not seem like much of an increase compared to the OE rating, but I also have lab dyno data on a stock rebuilt 40-over 327/340 and it made 343 lb-ft at 3800 and only 294 HP in the 5000-5500 range. Because power had obviously peaked it was not tested beyond 5500, and they did not test below 3500, so I don't know what the low end torque looked like. Both the above real world tests correlated reasonably well with simulations and helped me dial in models for various engine components.

"Mr. X" has a very nice engine and should enjoy countless hours of running it the way it was designed to run. A vehicle exhaust system, fan, and SAE standard correction conditions (yields 4.5 percent less power than standard sea level conditions) and driveline loss will yield lower rear wheel number, but it should approach close to 300 RWHP with the bottom end of the 80 percent torque bandwidth still in the 2000 range.

Duke

[Joe L.]

Re: NCRS Standards

kenny-----

The chance that I will run it through the 1/4 mile is near zero; not a DEFINITE never, but very close to that.

[Steve Pettit]

Re: NCRS Standards

Duke,

Please keep the advice coming. I always feel that if it doesn't apply to me I can just ignore it. But you and the others have helped me greatly and I appreciate it.

Regards,
Steve