Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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Currently I have the LT4 HOT cam (218/228 at .050, .525/.525 lift) and I've been thinking about going bigger as far as duration. My valvetrain is up to snuff but I'm afraid that a bigger duration will move the power band too high since I have a stock bottom end that I'm not sure can hold up to over 6k rpm repeatedly. Thoughts?
My specs: Corvette L98 block .030 over, crank, and rods. Hypereutectic pistons. Rotating assembly dynamically balanced. ~9.5:1 CR. Pro topline iron 200cc heads with roller cam springs, Magnum roller tipped rockers, factory roller lifters. 600cfm Holley single pumper with vacuum secondaries. Currently I have a World Products Sportsman II intake that I hear is crappy but I will possibly be swapping to a Weiand Stealth in the near future. Car is a daily driver.
__________________ '87 Burnished Copper Camaro LT. L98 with Pro Topline heads, LT4 hot cam, LT1 intake conversion. T56 trans and some suspension goodies.
Oh, I don't know. How about a Comp XR276HR, 276/282, 224/230, .502/.510. They say 1900-5600 RPMs. Dual pattern. Slightly less lift, more .050 duration. Should be more civil than the HC, and outrun it.
Originally posted by Section162 I don't know a lot about cams, so I was surprised that you said this about a cam with apparently more duration. Can you explain why this is?
No, not really. But, what I've seen is those guys know how to get a wider powerband out of an engine. And, you're dealing with a cam developed by the factory for EFI vs. a cam developed by the aftermarket for carb.
The heads will be able to flow, there's no issue about that. i would definitly stuff something a bit more aggressive than a Hot cam, as was suggested above. Judging from the flow charts, I would look to about .550" as peak lift. Yes, the heads do support more, however, typically, as you increase lift into the high .500's and even .600 range, duration becomes impactical. Judging by the intake, I am guessing this is a carbureted application.
I would agree with five7 on the XR276HR suggestion (obviously ground on a factory roller core). CCA-08-423-8 is the cam being talked about, as seen on Summit's web site. Use the appropriate valve springs and Magnum 1.6 ratio rocker arms.
The biggest issue with the Comp cam versus the HOT cam, in my mind, is that the HOT cam was made to bring out more power out of a factory engine. It was designed with set parameters that it had to comply by. Paremeters of the LT4 engine. The Comp's grind, or any Comp grind for that matter is manufactured to bring out the most power for an given engine. They more or less say "here's a cam, it's up to you to make it work."
Edit: I just looked up the HOT cam specs. It has 279/287° of advertised duration. So, it has more seat duration with less .050" duration. THe HOT cam will have slower ramp rates. It opens the valve slower and keeps it at a higher lift (where the power is made) for a shorter amount of time than the Comp grind. The hot cam will be friendlier on the valve springs because of the less-aggressive ramp rates, however, because of that, the Comp grind will out run it.
Hey that's good thinking comparing the advertised to .050 durations. I'm going to check with the shop exactly what springs they put on my heads in case I could still use them with the new cam. I wasn't really planning on changing the cam this year so I'm somewhat reluctant to spend too much. I was also thinking about converting to solid roller lifters... until I saw that Comp's retail on them is over $500 just for the lifters!
Oh, also, I just swapped to a 600cfm carb from a 750 because I was having persistent bogging problems with the bigger carb. I wonder if with the new cam I'll need a 750 again. I might regret selling the old carb to my friend now lol.
Last edited by Ukraine Train; 03-04-2005 at 07:19 PM.
I'll offer my $.02. The Hot Cam is a good cam, but if you want something more aggressive don't sacrifice lift to do it. As long as your valve train can handle it, run as much lift as possible. This will allow you to get the most air into the cylinder for a given duration, giving you the most bang for the buck. This also keeps your street manners and fuel economy.
I run the LT4 Hot Cam and made 365 horsepower with 1.6 rockers. I had been to the dyno many times and had tweaked every last bit of power out of it. I replaced my rockers with a set of 1.7's and immediately gained 14 horsepower and a healthy torque gain all the way across the board. My records also show an increase in fuel economy.
You should never have to sacrifice lift to get duration, in fact a higher duration allows a higher lift because it would result in a less aggressive ramp rate.
The cam I really want personally is a 220/230 .600/.600 112 with 1.5 rockers. Unfortunately such a cam doesn't exist and it would only cost me a mere $1200 to get it ground. I said no thanks.
