GTOguy

I am no engineer, but I would never install a camshaft retarded on a non-blown, street driven car. Low range and mid range suffers, fuel mileage suffers, it runs hotter, all at the expense of more power at the top end. I would install a cam advanced slightly or straight up.

SWCDuke

Look at the inlet valve timing of modern Corvette engines. When you have good head flow a short duration cam with late indexing is the way to go if you want the broadest torque bandwidth from off idle to redline.

In fact, the inlet event of the McCagh Special is near identical to the LS2 and LS3 inlet lobe in terms of both duration and indexing.

Then you tailor the exhaust timing to achieve target effective overlap, which in the case of the McCagh Special had to be the same at the OE 300 HP cam to achieve the same idle behavior, and because massaged OE heads have a very high E/I flow ratio (as do the new Trick Flow al. double hump heads) exhaust valve opening can be retarded, which results in LESS duration than the inlet event. I bet you never heard of that either, but it flat out works for a high torque bandwidth vintage engine with high E/I flow ratio massaged heads.

You should read the Tale of Two Camshafts article posted here in a thread started by me. I has all the reasons why it works so well for a vintage road engine with massaged heads. Engineers know a lot more about engine aspiration now than back in the sixties, and that's why modern cam timing is very different from both vintage OE and hotrod cams.

Duke

GearheadJoe

I think the terms "advanced" or "retarded," by themselves, don't provide enough information to know what is actually happening. At a minimum, you need to know "compared to what?"

For example, the cam I put in my 383 has 4 degrees of advance built in by the manufacturer. Most aftermarket cams have some advance built in.

On Duke's suggestion regarding DCR and detonation, I retarded that cam by 4 degrees. Technically, this made the cam "straight up." So, I retarded the cam, but the position is now what would be called straight up.

I have not studied the McCagh cam enough to know, but Duke may have specified that cam with a lot of built-in advance. So, retarding that specific cam by a few degrees may still have left some remaining advance compared to the straight-up position.

BTW, if you are reading this Duke, don't you also recommend installing the L46 offset 4 degrees from the OEM position? Was that done in your simulation?

65tripleblack

Most likely since the 962 was designed for a 350, then advanced for a 327, and retarded for a 383.

SWCDuke

You've touched on a subject that I've been harping about for a long time. All this hotrod cam lingo "advanced", "retarded", "straight up" is a bunch of confusing gobbledygook.

A cam can be advanced or retarded from some reference point, and the proper reference point is the AS DESIGNED/MANUFACTURED INLET POML.

"Straight up" in hot rod lingo means the IPOML and EPOML are the same, but nothing else about the cam, and most guys don't understand this. The L-46 cam as-designed/manufactured POMLs are both 114, so it is "ground straight up" in hot rod lingo, and the L-79 cam at 110/118 it is "ground with four degrees advance." If you install the L-46 cam at 110 it is INSTALLED with four degrees advance.

Again the as-designed/manufactured IPOML is the reference point, not the relative values of the POMLs. You don't grind a cam with advance or retard. You grind it to the design spec (unless you intentionally have it ground with a different IPOML, which would be a custom order), but you have the option to INSTALL it advanced or retarded with an adjustable timing set.

The McCagh Special has a LSA of 112, IPOML of 116 and EPOML of 108, so in hot rod lingo it's ground with four degrees RETARD. Retard the IPOML to 120 and it has EIGHT DEGREES RETARD!

I started the McCagh Special design by fixing the IVO and EVC points to get the desired effective overlap of about 0.9 sq-in-deg in order to achieve the required smooth base engine idle behavior that was a primary design requirement for the original application. Then using a fairly long exhaust duration I experimented with IVC point until I got the highest percent of peak torque at 2000. (The target was 90 percent.) Then I advanced/retarded the whole cam to achieve a bit more optimization by looking at average torque power from off idle to design speed while keeping an eye on torque at 2000.

Finally, keeping EVC constant I experimented with the EVO to get the get the highest torque at 2000, then advanced and retarded the whole cam to get the best average, then went back and started the whole process again with this staring point and ended up with shorter exhaust than inlet duration because of the high E/I ration of massaged OE heads.

It was an iterative process over a period of weeks that I worked on when I got bored, had nothing better to do, and needed some "brain exercise". It was not until I compared the final McCagh Special design to modern LS lobes that I realized I stumbled onto something that GM figured out 15 years prior- relatively short inlet duration (with good flowing heads), but phased later than traditional designs provides the broadest torque bandwidth from off idle to design speed - but like I said in the article, GM Powertrain has more resources than I do.

The McCagh Special exhaust event is significantly different than LS-cam exhaust events because of the big difference in E/I flow ratio between massaged vintage and modern LS heads. Try to find an off-the-shelf design that has shorter exhaust than inlet duration. The reason is because OE massaged heads yield a much higher E/I flow ratio than OE-machined vintage or modern LS heads. GM compromised the exhaust port design to get the highest efficiency inlet ports and to off set this opened the exhaust valve somewhat "early" that yields longer exhaust than inlet duration, something they learned back in the sixties, but massaging vintage heads increases the E/I flow ratio, so the optimum design has LESS inlet than exhaust duration.

I've heard endless arguments about single pattern versus dual pattern (usually longer exhaust than inlet duration) that usually quickly go into he ozone, but it's real simple. If the E/I ratio is about 0.75 a single pattern will usually work best. If it's closer to 0.65 a dual pattern with a few degrees longer exhaust duration is usually best, but if the ratio is close to 0.8 a SHORTER duration exhaust lobe will provide the best torque bandwidth. This is for road engines with OE type exhaust manifolds and pipes. Racing engines with headers and open exhaust have very different valve timing requirements - apples and oranges.

Out of this fell IPOML, EPOML, and LSA. They are byproducts of the design, NOT DESIGN PARAMETERS OR SPECIFICATIONS. Hot rodders just don't understand this but OEM engineers do because they design cams the same way I do. Hotrodders get into these discussions about LSA, centerlines, advanced, retarded, straight up, but it's all nonsense. Engineers design timing points, IVO, IVC, ECO and EVC, and on asymmetric lobes the "centerlines" are not the same as the POMLs. The LSA is simply the arithmetic average of the two POMLs, but this doesn't tell you anything about effective overlap unless you know the durations.

There are two OE lobes within a couple of degrees of the final design durations. Crane has lobe masters for both, so it was just a matter of specifying the lobe masters and the POML for each for Crane to grind the cams.

Regarding advancing the L-46 cam, I ONLY RECOMMEND THIS ON SHORT STOKE 327s. For a given cam design, retarding the cam in an increased stroke configuration will usually improve average output across the entire rev range and vice versa for a short stroke engine. As stated in the prior post, the L-46 cam was designed for the 350, so on a 327 it should be INSTALLED advanced four degrees with an adjustable timing set to bring the IPOML back to equal the L-79s 110 from the 114 as designed/manufactured. Likewise, if you choose to install a L-79 cam (which I would not recommend) in a longer stroke engine, particularly a 383, retarding it a few degrees will likely provide the best average torque/power and best overall torque bandwidth up to a reasonable design speed of 6000 to 6500.

If you don't do this the maximum useable power range on a 327 with massaged OE heads will extend beyond the reasonable valve train limiting speed of about 6500+ with carefully set up OE valve springs. If you want more revs and power in a short stroke engine the answer is the LT-1 mechanical lifter cam, which has a valve train limiting speed of about 7200 with carefully set up OE valve springs and with massaged heads the power peaks at 6500 on a 327 with a little rolloff to 7200 and signs of insipient valve float at 7250.

Above 7200 bottom end considerations and the OE wet-sump oiling systems can be limiting factors that can lead to catastrophic engine failure.

No one has yet opined which cam is which and which one they think is preferable for typical vintage Corvette service. Hey, just flipping a coin you have a fifty percent chance of getting the right answer.

Duke

65tripleblack

I'll answer because the Stupid Bowl is already getting to me with the idiotic commercials. So I'm taking a break from the Tom Brady Show.

I though it was a rhetorical question. Your cam is obviously graphed dark blue/green; the 962 is graphed light blue/red. Your cam gives very peaky torque and horsepower plots. The 962's are flatter with much more gradual drop off past the power peak. Neither are nearly as flat as those of a roller cam.

If a guy wants to burn a lot of rubber then your cam is best. It would also be better for a dump truck or school bus. The 962 is better if a guy likes more RPM and bragging rights to higher horsepower. For my money, installing your cam into an engine is tantamount to emasculating it. There is no such thing as a free lunch. Juggling cam lobes is same as juggling three rotten apples: in the end none are edible.

For me, neither is satisfactory. Actually, a good, mild hydraulic roller cam will give stump pulling torque exceeding your cam, along with scorching and fun filled top end power far beyond that of the 962. In this day and age, it makes no sense to be fooling around with 70 year old technology, which is also sensitive to ZDDP concentration, when a proven technology is so much better on all counts.

Hate to bring this up again, but my 327 with roller cam makes 341 ft-lbs @ 2000 and peaks at 435 ft-lbs between 4000 and 5700 RPM with 90 percent bandwidth between 3000 and 6500 RPM.

EDIT: You should add a third plot of the simulation using the 327/300 (929) cam for clarity and comparison. You might sell more "Special" cams that way.

SWCDuke

The McCagh Special is basically an optimized 300 HP cam that's specifically designed for the flow characteristics of massaged OE or similar flowing aftermarket heads while maintaining typical 300 HP general operating characteristics like stump pulling low end torque and the smooth 500 @ 18" idle behavior. The target audience is base engine owners where the owner wants to maintain OE appearance and general operating characteristics, but wants more top end power and useable revs. It yields base engine low end torque and idle behavior with L-79 top end power and useable revs with suitably massaged heads and a CR in the range of 10-10.3:1

The ...929 cam makes similar low end torque but less power and revs, even with massaged heads. I wouldn't consider the ...929 unless the heads are unmodified other than a valve/guide/seal job. It's a good cam for a "stock rebuild" base engine. The L-46 cam, which is the best of the SHP hydraulic cams is a better comparison and adding more configurations makes the graph too busy and tough to read.

I don't "sell" the McCagh Special cam and have no financial interest in it. Interested parties buy it directly from Crane, but I prefer to talk to them before they proceed so they understand the unique requirements - head flow and compression ratio that it's specifically designed for.

Since I'm boycotting the NFL (don't like the behavior of some of the players and most of the owners) I spent the afternoon splitting a load of cedar firewood, but I heard it was a pretty good game.

Duke

cv67

Damn strong for a little 327, build details? Not trying get off track just caught my eye

65tripleblack

Yes, I seem to remember that it's a hybrid using lobes from a 929 and a 962 with widened lobe centers of 116 or 118 degrees. And that's why I asked you to graph all 3 cams on your EA simulator. It's a shame that your x axis is sooooo truncated in your plot. It would be better if you could re-scale the graph so that the x/y ratio is larger.

I wasn't saying that you're earning remuneration from your cam's sales. I meant "sell" to be a synonym for "hawk", "extol", "hump", "peddle", etc.

As far as the game...............I reluctantly watched it with the players' lack of patriotism in mind. Rest assured that if Colin Kaepernick were somehow involved, then I would NOT have watched it. Actually a very exciting game, which is very unusual. It was more like a Conference Championship game because the teams played as if they were very evenly matched..................although The Brady Bunch was favored fairly heavily. It came close to going into overtime! I was happy to see Philly win even though they are bitter rivals of the NY Football Giants. Lesser of 2 evils.

65tripleblack

PM sent.

SWCDuke

That was the first design (Special 300 HP cam) that didn't perform as well as the McCagh Special, which swaps the 929 lobes, leaves the LSA at 112 deg., with the IPOML indexed at 116 deg. ATDC.

The full story is in the "Tale of Two Camshafts" pdf that is on the CF in a thread started by me.

The McCagh Special came about due to Mike's long time friendly rivalry with Dennis Clark. When Mike got word that Dennis was in the project he wanted in, too, but since his '57 cheater motor has a Powerglide I wanted to modify the design for more low end torque. Dyno testing revealed it made both more low end torque and more top end power, and the article includes an analysis of why I think this turned out to be the case.

Duke

Vettrocious

Just thought I'd report that I'm in Florida for a while, the engine build is reduced to collecting ideas and some parts, until I get back

Mike

65air_coupe

You've gotten lots of good advice and I can't really add much but to say you'll enjoy the process and especially the results. I set off to do pretty much the same and veered off only slightly by building a 406 instead.

I used Trick Flow heads and Crane gold roller rockers as well but the big difference in my build was the choice to go with a roller cam using OEM components. That path required some modifications to the lifter valley but in turn reduced the costs of going to a roller by allowing the use of OEM components along with their proven reliability. While I don't have a basis for comparison like DZAUTO has, I love the performance of a roller cam.

One other note, I also chose hyper-eutectic pistons but as an inexperienced builder, I also followed the guidelines of the ring manufacturer for end gaps which resulted in a broken piston and a complete tear-down to replace all of them with new rings and a larger end gap!

SWCDuke

If you install KB hypereutectic pistons, you have to follow THEIR recommendations for top ring gap, which is wider than conventional pistons due to the high placed top ring that runs hotter than conventionally placed top rings.

The instructions are clearly noted on the web site, and I'm pretty sure each piston comes with instructions in the box.

This is a common mistake made by both DIYers and "professional engine builders". Of course, they usually all blame the pistons and rarely accept responsibility for NOT READING THE INSTRUCTIONS!

And if you don't, the inevitable result is ring butting, which breaks the piston's top ring land.

Duke

65air_coupe

That's precisely correct except for the small detail that the only instructions I had were from the ring manufacturer. Since I'm not the type to lay blame elsewhere, I just chalked it up to a learning experience, which is why I chose to pass that experience on to others.

larrywalk

Hey Triple,

I also have a triple black '65 L76 - at least it was before I had it painted silver pearl in 1977. It's nice to read your posts; I'd also like to learn of your build!

Thanks, Larry

GearheadJoe

Okay, here is an update on block clearance with a 2.0" small-journal rod. Attached are photos of the block clearance in one particular cylinder of a block that has the cast-in clearance notches.

The first photo shows a Manley Sportsmaster 2.0" journal rod with the as-received bolts that Manley provides. The second photo shows the same rod and cylinder, but with a different bolt that has a shorter head. This bolt is from a Scat Pro-Stock rod and is sufficiently strong, but it's a bit longer than the Manley bolt.

I'm not sure whether it would be okay to use the Scat bolt in the Manley rod, but several people I have talked to say it would be okay to shave down the top of the Manley bolt head to match the lower head height of the Scat bolt.

The Eagle SIR 2.0" journal rod has only .020" less clearance than the Manley 2.0" rod and costs a lot less than the Manley. The SIR rod is not as strong as the Manley Sportsmaster, but it would probably be fine for under 450 HP and under 6000 rpm.

I'm really liking the additional block clearance and cam clearance of these two 2.0" journal rods. I think the reduced rod journal would be fine if the crank is forged and it has large-journal mains.

65tripleblack

PM sent.