tuxedo

Besides the differences in lifters. What area of RPM does each respective engine perform the best in regards to torque/hp etc. I have heard the 30/30 Duntov cam in the L-76/365hp with solid lifters is duplicated as much as possible in the L-79/350hp with hydraulic lifters. Which would I guess make the L-79 a more mild version of the L-76. :chevy

SWCDuke

The 30-30 cam definitely makes more top end power, but at the cost of low end torque relative to the 151 cam in the L-79 - about 20 percent less at 2000 revs according to many engine simulation I have run.

That's why I recommend the LT-1 cam for all L-76 rebuilds, including the pre '64 versions with the Duntov cam. The LT-1 cam makes about the same bottom end torque as the 151, but more top end power. The 30-30 makes marginally more top end power than the LT-1 cam with a little less roll off between 6000 and 6500 than, but the price you pay at the bottom end is not worth it on a street engine.

The Duntov is a little weaker on the bottom end than the 151, but makes about the same peak power, and the LT-1 cam makes more torque/power across the entire range than the Duntov.

The 151 cam is a good Duntov or 30-30 replacement for those who don't want to retain mechanical lifters, but the LT-1 cam is best for any mechanical lifter engine restoration or for those who want to switch from a hydraulic to a mechancial lifter cam in order to gain more top end power and more useable revs.

BTW the 30-30 is not a "Duntov 30-30". Zora did not design it. He did personally design the "097" cam that was THE mechanical lifter cam from '57 to '63, which is why it is called the "Duntov cam". The 30-30 is just that - the "30-30 cam". No Duntov.

Duke

BobG

Duke...sounds interesting to me, as I'm going to be doing an L76 rebuild in the very near future. Any chance you might have the cam specs on the 30-30 and LT-1 cams? I'd like to run them through my dyno 2000 sim. And maybe even a part number on the LT-1 cam? Thanks a bunch.

SWCDuke

Here is the latest data I am using. The numbers are based on actual lift-crank angle data and have been "tweaked" to fit the symmetrical profile assumption of Dyno 2000. The cam lobes are actually asymmetrical. Lift is based on actual valve lift at a 1.44:1 rocker arm ratio at max lift (as measured on my engine) and the clearance is set to take up all the lash at the top of the clearance ramp with a 1.37:1 rocker ratio (also measured on my engine). The rocker ratio is not 1.5. It is not even constant- starts at 1.37 at the top of the ramps and maxes out at 1.44 at max lift.

30-30: seat to seat duration 310/310; IC=110; LSA=114; Lift = .436/.436

LT-1: seat to seat duration 292/310; IC=110; LSA=116; lift = .417/.436

OEM part number of the LT-1 cam is 3972178. I don't think you can buy it through GMPD anymore but Federal Mogul Performance Parts make an exact replica.

Duke

BobG

Duke...thanks for the info. I had thought about going hydraulic cause I didn't want to hassle with valve adjustments. But I'm wavering a little bit now. Do you happen to have any head flow data, or do you use a standard head when you do your DD2K sims?

SWCDuke

I don't have any flow numbers. I just used the standard head for the production engine, and the "pocket porting" option for my engine as built with the LT-1 cam. Pocket porting, and port matching is worth is because you gain top end power without much impact on low and mid range torque.

DD2000 may not give absolute numbers that are accurate, but when you're comparing specific parts, like cams, with everthing else unchanged I think the comparitive data is pretty reliable.


Duke

jimgessner

My 2 cents: The LT-1 works better in road race conditions. Duke is correct. It has better low end than the 30-30 which gives it better torque off the corner .........and first man out of the corner is usually first man home.

Ahh yes, and there is no better sound than a solid lifter Chevy small block thru a set of off road mufflers.
Regards,
Jim