Mean....it's ground on a 106 with a 4 deg adv. If I set the crank sprocket straight up, the ICL is 102. I've got the cam in on a 106 ICL with the crank gear 4 degrees retarded.

I didn't say that using a simple table based on cubes and valve size made any sense. However Vizard is using that plus the overlap (which is at least based on based on use and size) to determine duration. For our application, which i'd like to limit to 7000 rpms, i think a duration in the 260s is about right. According to the cam companies, they'd recommend something bigger on a 106 LSA and Vizard would go with a 104, but i think it would be a lot easier to tune and drive with a 110 without giving up much power. However, the bottom end is buttoned up and the cam is what it is.

btw, in the mag article i mentioned above, Vizard put in a cam on a 104 LSA and advanced it 6 degrees so it had a 98 ICL. I thought that was kind weird...especially since he was trying to squeeze in all the lift he could. Unfortunately, i never got the last installment in the multi-part series to see how the engine performed.

 

I don't have a lot of time for this but will try.
To compare a solid to like hyd look for a hyd with similar lift numbers from the same mfr.
Subtracting 5* from advertized duration numbers is a general rule for solid cams. Just like u need to subtract the lash value from vlv lift to get the actual vlv lift on a solid cam. Now u can easily see that a cam with large lash value will act shorter than the same cam with a smaller lash value. Some of the new "tight lash solids" are only .012" lash where many of the older solid cams used .030" lash and u can expect a proportional difference in actual duration.
U can always buy 2 small "V blocks" and use a dial indicator to measure your solid cam - most serious builders run out each lobe to verify the cam specs before install (they have to have some quality control for the money spent on expensive builds).
BTW Vizard uses the full duration figure (from .003" to >.010" off the seat) which is measured different for each mfr rather than at .050".

As for choosing a correct cam u just have to keep crunching the numbers and sort things out Ralph. I was surprized myself to learn to use the full duration values when i had read cams advertized by the .050" value for years in the mags. I'm sure u would enjoy the Vizard books as i can tell u are ready for them. And don't be afraid to read them more than once as some of the tech concepts just take more effort/time. I reccommend sb Chevy Vlv trains and Camshafts.
All i can say that when people ask for cam advise i try to recommend a reasonable overlap cam but forum members just install a large overlap cam with too little compression anyways. So all i can say is that plenty of corvette enthusiets come and go and i don't read many bragging thier low compression eng with large overlap/duration as fun to drive.

Another BTW, i have posted this info before here and maybe a search would help ya. Hit the books Ralph.
Good night. cardo0

1 more funny thing , my new cam was ground way advanced too and had to retard mine 4* also - sounds like we're on the same plane as far as degreeing cams goes (yes mine is a solid too ).

 

After reading this thread last week, I spent most of my free time reading and studying cams. From what I understand, and I still don't think I have a complete grasp on the subject, the correct way to make a cam decision would be to first decide on the LCA based on your engine and valve size, second would be to decide on how much overlap you could live with.
Question is, wouldn't this then dictate your duration and to an extent your lift.
In the past the first thing I looked at was duration and lift.

Dennis

 

SWCDuke -- How do I calculate sq-in-deg?

 

Duke uses the "Engine Analyzer" program for those computations. You can get the program for around $100. It's a pretty slick piece of software, Duke let me check it out while at his house a few weeks ago.

 

It absolutely would. He's asking us to start with overlap and LCA based on engine size, valve size, and intended use, and then go backwards from there to determine duration. Lift will be a function of how agressive the cam's profile is.

What's got me concerend is why all the cam manufacturers with their dynos and years of research sell mostly cams in the 106-112 range. And then there's GM with 112+. Maybe GM sacrifices some performance for a smooth idle. (?)

Just when we think we know everything...

Mike

 

The aftermarket uses 110 centers because they cater to the race industry. An open header exhaust system with cams ground on 110 C/Ls or less work fine but when installed with a complete exhaust system you loose your low end torque due to the resulting back pressure.

Plus the average Joe likes that rumpty rump that a 110 C/L results in. Its all in the marketing

 

I think Scott may be on to something. Nearly all the guys in a car club that I belong to think this way. Just last week one of them lost a cam. They all run flat tappet cams no need to spend the money for a roller because they only care about the idle. When this guy lost his cam and ordered a new one he got more duration. I told him that it would not be street able and have poor low-end torque, the reply was Oooh I don't care how it runs I just want it to sound good.

 

Yeah, guys like that are about 90 percent of the market.

Duke

 

[QUOTE=black bart]...because they only care about the idle. QUOTE]

Whoops, count me as somewhat guilty. I've always wanted an idle reminiscent of the 270hp 283 Corvette engines.

Thought I might go with a tight LSA cam in my new 327, but Duke and the guys pretty much have me talked into an 70-72 LT1 cam. What should that sound like at idle? When I see a cam with 242/252 duration at .050", I'm thinking big-time rumpety rump, but apparently not.

The big cam syndrome you're talking about also means big lift, which can lead to coil bind, retainers hitting guide bosses, and pushrods hitting guide holes. Not to mention horrible low-mid range performance due to a very low DCR. So, these guys end up with worse performance than they'd have with a stock 300hp cam.



Mike

 

That cam sounds awesome, it idles a little better than a 30-30 cam but similar and it has the most wicked exhaust note you'll ever hear at 7,000RPM due to the exhaust valve opening up pretty early. Ping Mark and ask him about it.

 

Scott -- What is Mark's user name? I also want to ask him about vacuum.

Mike

 

His name is ghostrider20

 

Last week I ordered a new billet SR cam from Comp Cams. My 427 is coming back together after breaking the crankshaft. So my 427 is just waiting on my new custom comp cam. I went to the lobe pages and picked out lobe # 4124 and #4126. They are for endurance road race motors and might be relatively easy on my valve train. The problem with street or even what CC calls extreme lobes is the lack of lift. These endurance lobes have a good ratio of .050 duration to .200 duration. I’m making the assumption that you know what I’m talking about? I’ll have 248/250 @.050 with .662/.666 lift with 1.6 ratio My original XR280R cam that went bad was 242/248 with .608/.614 lift with 1.6. I was running 1.65 on the intake to get a little more in the cylinders. It just didn’t have the bark like my 383 has, so it needed a little more cam.


I did think long and hard about what LCA to have it ground on. In the past i always had them make 112 LC on the custom grinds. But with my freeflowing three inch exhaust with a 4 inch ovaled "H" pipe I figured I would just go for it.

I went for 110 lc with no 4 degrees of ground in advance. That puts max TQ at 4500-5000 rpm and max HP right in the 6000-6500. I have a two piece comp cams cover so it's not that difficult to just try anything from+2 to -4 degrees.

IVO = 18 IVC = 50
EVO = 59 EVC = 11


New TKO600, mcleod blowproof bell housing, 22 pound billet steel 168 tooth flywheel, and 4.11 rear gears