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Discussion Starter · #1 · (Edited)
Anyone know the valve open/close specs of the GM L79 cam?
I am not an expert or know much,but I am building a 4" bore motor with 5.7 rod,11:1 pistons,3" stroke. One cam mfr. sells a cam patterned after the L79 cam with an intake closing point of 41 deg. ABDC @ .050".
Using an internet compression calculator I am getting a very high DCR using 41 ICP.
Did the original factory cam have a much higher closing point or am I missing something here?
 

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Here's some spec's I've come up with but suggest you verify:


68 327 L79 hyd p/n 3863151 c/n 3863152

350hp

Int opens BTDC Int Closes ABDC Int Duration ILC Int Lift
40 86 306 113 .447

Ext opens BBDC Ext Closes ATDC Ext Duration ELC Ext Lift
88 38 306 65 .447
 

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Discussion Starter · #3 ·
Thanks Z15CAM, those are advertised specs. When I use the 'supposed' 41 deg @ .050" I get over 9:1 for DCR. Does this agree with the original factory DCR ? If so,,,then the pressure bleeds off at low RPM? If not then 41 must not be the right figure???
 

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You cant use the .050 numbers to compute DCR. You have to use seat timing. The numbers will vary a bit depending on where the cam is actually measured (gm used something like .001", crane uses .0045", comp uses .006", etc). I believe that cam is about 291* at .0045", and about 287 at .006".
 

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Discussion Starter · #6 ·
Using the kb-silvolite calculator that asks for the ICP @ .050 +15 gives a high DCR so it can't be right.Using 290 does make a difference. The original factory 11:1 pistons in the L79, 302, and other motors was a piston head volume of -11, I am presuming?
The heads were 62cc chambers but does anyone know what head gasket thickness was used?
 

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i would think that would be a good hydraulic cam to put on a 302.
but, really, why not go with a solid to keep the heritage of the 302 intact?
 

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.020" thick steel shims!

Yes, go w/ a solid lifter cam in the little bugger b/c it will want to wind right up HIGH!!

And don't forget good valve springs too, at least Z-28, (i.e., -140's), as well as say an Isky Z-30 solid lifter cam!! Or a CC 294S solid lifter cam...

That is, if you don't want to run the great old 30-30 cam in it like it came w/ stock..

pdq67
 

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Discussion Starter · #9 ·
Thanks guys. Well,you know I've been wrestling with the desire to use a solid cam. I've never ran a solid before and don't know how well it would work seeing that I want to be able to drive it everyday ( not long distances) and with promising myself that I wouldn't 'over cam' yet another motor,I set a max.lift of 460" and my parts catalogs don't list many solid cams that small unless the overlap is way high. But then PDQ67 does brag on that little bitty 097;) maybe that one or does anyone sell the modern (exact specs) version of the old #3849346 solid?
 

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Using the kb-silvolite calculator that asks for the ICP @ .050 +15 gives a high DCR so it can't be right.Using 290 does make a difference. The original factory 11:1 pistons in the L79, 302, and other motors was a piston head volume of -11, I am presuming?
The heads were 62cc chambers but does anyone know what head gasket thickness was used?

+11 not -11.:thumbsup:
 

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Put any onna these little solid lifter cams in her and daily drive her ALL you want... Just use at least Z-28, (i.e., -142), valve springs....

CC's 270S;

Isky's Z-20;

The little Crower; and of course

The old stock, Duntov -097 cam.. I'd use 1.6 ratio rockers on it to up it's about .385" lift to about .410" lift.

AND don't be fooled by it being a little-bitty bugger b/c it was used in the 340 and 360hp/327 engines as well as the smaller hi-po, 283's too just before the 365 and 375hp/327 engines that used the great old 30-30 solid cam.

pdq67

Ps., you get her up to 11 to 1 CR. and then run an Isky Z-30 if you don't want to run the old 30-30 cam!!!!! And hold-on...
 

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Discussion Starter · #12 ·
One more dumm question on this. The suggested 290 to be used as the intake closing point is the duration in degrees that the valve takes to close?
If so,,,I am getting a static cr 12.09 and dynamic cr 9.09 with 58cc heads and .016" gasket sooooo,,,,It probably won't last long with this cr even on race fuel???
 

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Using EA3.0, and a true 11.0-1 compression, and the -151 hydraulic cam, I get 195psi cranking compression. In my experience, this program is always dead on to about 10psi too low. With a sharp tune, it looks like it would just work with some 93 octane fuel (and some relatively deep gears). Using stock 2.02/1.60 double hump heads, a performer rpm intake with the exhaust cross over blocked, a 750 vac sec carb, 1 5/8"x32" headers, and a 800 cfm exhaust system, I show [email protected] rpms, [email protected] rpms, and a torque peak of 340 ft-lbs @ 4500 rpms. The torque curve is pretty soggy under 3K rpms. With no other change other than switching to a 30/30 solid cam, cranking compression drops to 171psi (89 octane easy), but it doesn't have a performance advantage until 5K rpms and up. I then changed cams to the gm LT-1 solid -178 cam...it equals the -151 on the low end and equals the -346 solid on the top end, losing only 6hp at 6K rpms. It also shows 191psi...again with a sharp tune and some gears (that this is really going to need) it could just work on pump gas.
None of those 3 cams really do anything until about 3000-3500 rpms...typical of a small inch short stroke engine. Gear it accordingly and have fun.
 

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....... With no other change other than switching to a 30/30 solid cam, cranking compression drops to 171psi (89 octane easy)....
89 octane?
 

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302 w/ a 4"b x 3"s here........

I get 10.77 CR. w/ 66 cc big valve stock type double humps, +11 dome cc, .015" thick shim's and a .025" DITH piston depth.

From here..........

http://www.campbellenterprises.com/Race math calculators.htm

And 11.43 CR. w/ 62 cc heads........

So I figure 64 cc heads should be right at 11 to 1 CR..............

AND I always forget about the old -178, the 330hp/350 solid lifter stock cam, SORRY!!!

pdq67
 
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