Camshaft confusion. Need help!

[Joseph W.]

As I posted on here awhile back, I’m working on a 1969 L89 project car.
Well, the heads are done and the block is at the machine shop.
The block has been decked, and rather than running the original 11:1 compression pistons, I’m going to go with 10.5:1 pistons.

Im struggling with camshaft selection. I’d love to run a solid lifter but I’m just not interested in going backwards if it fails.
Ive had several of my friends have cam failures and have read on about many others having failures on different forums.

So my plan is to run a hydraulic roller cam and get it as close as possible to factory specs.
I have a Howard’s roller in my other 69’ L71 and I love the sound of it. Unfortunately I haven’t drove it yet.

The problem is I don’t really know how to decipher the camshaft specs.
This is my first engine build and I realize how much vacuum a cam produces is important. Not only for the vacuum operated headlights and wiper door, but also can’t it also affect the distributor vacuum advance?
Im running the original TI system that has been rebuilt and restored to original by Dave Fiedler. The car is a 4 speed and has 3:70 rear gears.

After speaking to the rep at Howard’s Cams, I think I have it narrowed down to 3 choices:

See next post…..

[Joseph W.]

Re: Camshaft confusion. Need help!

IMG_1461.jpg
IMG_1460.jpg
IMG_1456.jpg
Below is the GM specs for the factory L71 and L89 cam
IMG_1463.jpg

[Owen L.]

[Joseph W.]

[Owen L.]

Re: Camshaft confusion. Need help!

Thank you for replying.
Assuming you went with a roller cam too?
Great advice, I never thought about what type of driving I’ll be doing and where I want the power band.

Actually, no, I went with a regular hydraulic flat tappet. My rebuilder insisted on breaking in the engine on his dyno, so I let him! I do have roller rockers though.

[Duke W.]

Re: Camshaft confusion. Need help!

The OE L-71 cam has a 114 deg. lobe separation angle. The inlet POML is 108 deg. ATDC. The 242 deg. .050" lifter rise duration is gross. Net of the clearance ramps it's 231, and this is the number you use to compare to hydraulic lifter cams

Consider how you drive the car, especially around town then look at the RPM range of the cams. IMO go with the mildest, which is 1800-, but IMO it should have a wider LSA for less overlap

Ask the cam grinders what vacuum is at 900 RPM idle speed, or whatever idle speed they can specify vacuum. The L-71 cam is about 14" @ 900. Any cam that pulls less vacuum at 900 will have less low end torque.

It's very common for guys to "overcam" their engine for the intended use. If you select a cam based on liking the lumpy rumpy idle you will probably end up with a gas guzzling dog that has poor low end torque and may not be very pleasant to drive in normal traffic.

As far as the VAC is concerned the OE signal is ported, so the OE VAC is probably okay for any cam. However, as long as the car doesn't have to be emission tested I recommend converting to full time vacuum advance. Then you use the Two-Inch Rule to select the best fit VAC.

Also , even if the block has not been decked, 10.5:1 pistons are meaningless. Variation in deck height/clearance during the Tonawanda broaching operation can result in CR being up to about 0.6 less than specified. Piston compression specifications are also based on a specific deck height/clearance and gasket thickness, which are often not specified.

You need to make all the measurements to compute the actual compression ratio. There is a paper on this subject in the restoration documents near the bottom of the sticky section. You should also study the tuning seminar, which explains the Two-Inch Rule.

The target compression ratio range you should select is a function of your available fuel octane, altitude and ambient temperature range, and inlet valve closing point. For the L-71 (with the OE cam) near sea level with 93 PON E10 I recommend 10.25:1 max and reduce 0.1 for each octane point below 93, so 10.05 for California 91 PON "premium" fuel, and I expect Joe Lucia would recommend less.

For a roller cam of similar .050" lifter rise duration the above should likely be reduced because the roller cam will have a somewhat higher DCR.

Going too high on compression can dictate a lazy spark advance map to keep the engine out of detonation, which will decrease power in the low to mid rev range where you spend 99.99 percent of your driving time, so it's best to go a bit conservative on the CR, so you can run an aggressive spark advance map, which will yield a much better performing engine than too high compression that requires a retarded spark advanve map to keep the engine out of detonation.

Duke

[Joseph W.]

[Duke W.]

Re: Camshaft confusion. Need help!

I was hoping Joe Lucia would chime in on this thread since he prefers and has experience with roller cams. My concern is that you will "overcam" the engine and end up with a torque shy gas guzzling hog that won't match your normal driving conditions very well.

So I emailed Joe with a link to this thread and asked him to comment.

It's somewhat difficult to compare roller hydraulic cams to flat tappet, either hydraulic or mechanical. For a hydraulic roller cam of the same .050" lifter rise duration as a flat tapped hydraulic the roller will likely have less seat to seat duration, but more total lift. This is because of the more aggressive dynamics. It's even tougher to compare a mechanical lifter flat tappet cam to either a flat tappet hydraulic or roller hydraulic lifter cam because part of the .050" clearance ramp duration is clearance ramp. In the case of the L-72/71/LS-6 cam the .050" lifter rise duration of 242 degress is 231 net of the clearance ramps.

You said your heads are done, so what valve springs are installed and what are the specs? Valve spring selection is based on cam selection and as a general rule you should follow the cam manufacturer's recommendation, except for OE cam grinds. For some inexplicable reason aftermarket grinders of OE equivalent vintage cams recommend significantly stiffer springs than OE, which it totally unnecessary and likely a factor in lobe and lifter failures.

BTW your engine likely had the second design big block springs... dual springs with an integral retainer and umbrella seal. If so, I hope you didn't through them away as an exact duplicate of this design is no longer available, but Joe had identified an aftermarket equivalent set up which is petty close and these should be used with OE equivalent cams.

My recommendation is to select a cam that has no less than the OE cam's 14" Hg manifold vacuum at 900 idle speed.

Duke

[Joseph W.]

[Duke W.]

Re: Camshaft confusion. Need help!

If your original springs are the second design as I described then I think they are okay to reuse, or Joe's recommended springs if you want to go with an OE equivalent cam. The first design single spring damper is prone to breakage.

I prefer to go with OE cams, although Joe prefers rollers. The camshaft is SO important in establishing desired engine operating characteristics... idle behavior, torque bandwidth and useable revs, and I think the OE cam is an excellent high performance cam for a road engine.

There are lots of reports of lobe lifter failures, but they are likely very small compared to those that succeed. Proper material hardness and Parkerizing along with break-in lube on the lobes and lifters, a ZDDP supplement with a 20-30 minute cam break-in along with C-category oil should go a long way toward obtaining a lifetime installation.

Let's wait and see what Joe has to say.

Duke

[Duke W.]

Re: Camshaft confusion. Need help!

Joe should be along, shortly. He's been on a secret mission for a secret government agency for the last few days

Duke

[Joseph W.]

Re: Camshaft confusion. Need help!

Thank you Duke.

[Gary S.]

Re: Camshaft confusion. Need help!

Joseph, sounds like you are using L89 aluminum heads? I think the rule of thumb is you can up the CR half a point due to the lower head temperature compared to iron.

BTW, I'm having an L36 and an L71 rebuilt this winter with Isky roller cams. They seem to use a little less lift than the Howard's cams. There is a point where you may have to have reliefs cut in the pistons for high lift.

Here's from the Isky catalog:

17078965487342838812727297495845.jpg

We're using the 265/275 (218/228 dur @ .050") cam in the L36, probably the 275/284 (228/238 dur @.050") in the L71


while we're waiting for Joe...here's an interesting article with dyno test about lobe separation angle effects:

https://www.motortrend.com/how-to/ca...e%20wide%20end.

[Duke W.]

Re: Camshaft confusion. Need help!

Note that the cams in the test all have the same duration, which is the ONLY way you cam use LSA as an overlap comparison, but the article doesn't explain why this is the case. (BTW I've never heard of a cam with a 101 degrees LSA. I think they meant 110.)

The only way to compare overlap with camshafts of different duration is to compute effective overlap in square-inch-degrees, which the Engine Analyser program computes based on high level inputs specs like .050" lifter rise duration and POMLs. This is the program I used to develop the McCagh Special Camshaft. Consider the following data for OE small block cams from the era.

Camshaft............. LSA (degs).............Effective overlap (sq-in-degs)

300HP....................112...................... .0.9
L-79, L-46/82..........114.......................4.5
30-30.....................114.......................8 +
LT-1.......................116....................... 5

Note that if you use LSA as a surrogate for overlap you would pick the 300 HP cam as having the most overlap, but by far it has the least. This is because the other cams have 20 to 30 degrees more duration.

Normally I don't use overlap as a design parameter (with one exception). Based on desired torque and power bandwidths and E/I head flow ratio I work with all four timing points, and LSA is a mere fallout once I've achieved the desired output characteristics and idle behavior.

That one exception is the McCagh Special cam, which uses the same lobes as the 300 HP cam, but swaps them... inlet lobe for exhaust and exhaust for inlet. Since one design requirement was to maintain the smooth 500 at 18" inches idle behavior I fixed overlap at 112 deg., same as the 300HP cam, then played around with the inlet POML until I found the indexing that gave the greatest average torque/power from 1500 to 6000 revs.

The end result moved the split overlap point (crank angle where both valves are open the same amount) from about 4 degs. BTDC to 4 ATDC. The inlet POML of 116 ATDC is 8 degrees later than the 300 HP cam and with the longer duration this places the inlet .050" lifter rise closing point only four degrees short of the L-79 cam. Meanwhile, the shorter exhaust duration and later indexing opens the exhaust valve later, which offsets the loss of low end torque that the later closing inlet valve would otherwise cause. This design proved to be ideal for the 10-12 percent increase in inlet port flow and 30-40 percent increase in exhaust flow that is typical from head massaging.

The most important information one needs to select a camshaft is a realistic understanding of how the engine will be used. For a for a high performance road engine my criterion is at least 80 percent of peak torque at 2000, limiting .050" lifter rise duration to about 230 degs., and effective overlap of no more than about 5 sq-in-degs. These are maximums and less okay. For a small block this is the LT-1 cam.

The bottom line is to select a cam that makes 80 percent of peak torque at 2000 or less and massage the heads for your top end power objective, and if you want to maintain OE idle behavior, maintain the same effective overlap (sq-in-degs).

Duke

P. S. Gary, I recommend you go down one notch on each selection... the 210/218 cam for the L-36 and 218/228 for the L-71. Also you might ask Isky what the beginning RPM range is in terms or percent peak torque. In my experience, more than 2000 for 80 percent makes for a somewhat soggy bottom end, which is not the best road engine choice for the way we use these cars nowadays, but let's wait to see what Joe says.

P. S. #2 I'll also state that these two engines would make for lousy unresponsive road engines in normal driving. Here's why. They have huge holes in the torque curves between 2500 and 3500 RPM, and likely 99 percent of normal road driving the engine will be at less than 3500 RPM. Also, tests with headers and open exhaust on a lab dyno can be deceiving. Headers and open exhaust with significant overlap work to increase torque and power, primarily in the mid to upper rev range, but ofter hurt output in the lower rev range as we see here. Backpressure from a street legal exhaust system, even with headers, will negate a lot of this increase, and manifolds even more, but manifolds will tend to reduce the size of the hole, but not eliminate it. Note that even with the differences in overlap the outputs are not that different. Any of these configurations would make a decent "street/strip" engine for someone who is into drag racing, but the best torque curve for the way most of us drive these cars is stump pulling low end torque and as flat a torque curve as possible to peak design revs, which is what the McCagh Special does for a 327/300.

In the case of these three camshafts the problem is not overlap, it's too much duration. Consider that the 505 net HP, 7000 redline LS7 cam has .050" lifter rise durations of 211/230 degrees.

[Gary S.]

Re: Camshaft confusion. Need help!

P. S. Gary, I recommend you go down one notch on each selection... the 210/218 cam for the L-36 and 218/228 for the L-71. Also you might ask Isky what the beginning RPM range is in terms or percent peak torque. In my experience, more than 2000 for 80 percent makes for a somewhat soggy bottom end, which is not the best road engine choice for the way we use these cars nowadays, but let's wait to see what Joe says.


Duke, the horse is already in the L36 barn! Just waiting for the exhaust manifolds to come back from ceramic coating. You may well be right about the cam choice and drivability, we'll see how I like it.
Using the same cam in the L71 might make an interesting comparison as then the difference between the two motors would just be the heads/valves and induction, assuming I stick with the plan for both to have 9.5:1 CR. Both have M21s, the L36 has a 3.55 axle, the L71 a 4.11.

Joseph, sorry for the hijack...

Gary