Monte Posted October 5, 2003 Share Posted October 5, 2003 Good explanation of LSA & ICL & how they relate to power I often here many people talk about the subject of LSA and ICL. (Lobe Separation Angle, Intake Center Line ) Most people think that a wider LSA cam makes more cylinder pressure. That is not exactly correct. I have seen this subject widely debated between racers and on the net. I found this posted on a web site. This is some good reading. It is one of the simplest explanations of a very complicated subject that I have seen. Enjoy. XXXXXXX----------------------------------MadMarv Team Member posted 10-04-2003 08:54 PM -------------------------------------------------------------------------------- I'm sure this has been explained numerous times before.. but I'm still sort of confused. I'm cam shopping, sorta anyway, and plugging with the DCR calc at the same time. Can someone run down lobe sep and icl in general? then explain how they matter in vehicle behavior? then explain how a 114 lobe sep with 112 icl would be different than a 110 108? if the total advance is still 2 deg? if you have time, same theory on 114/108 and 110/104? What would be the difference? I'm getting ready to call crower, crane, comp, lunati (non-harold) and see what they have to say. I'm going to ask what difference it would make if I switched from 3.90s to 3.31s or 3.42s(but I'd have to buy 3.42s). I am gonna call UDLunati when I'm ready to make the purchase. I'm using the DCR thing, but it just seems to hate big cams. I can't see how bigger always would equal worse. If anyone wants to know, I'm looking for a way to squeeze 625hp out of a NA 454 w/ a hyd roller and rect ports, mainly via just a cam swap. Suggestions welcome. Matt -------------------------------------------------------------------------------- From: Northboro, MA | Registered: Aug 2000 | IP: Logged | 69 Ratt Vette Tech Team posted 10-04-2003 09:19 PM -------------------------------------------------------------------------------- In general the wider LSA will make a broader tq curve and higher peak hp, but less mid range tq. When selecting a cam for an auto or 2 spd you want a LSA in the 104-108 range, cams for a 4-5 spd are usually in the 110-114 range, pro stock is more than that. Also forced induction or nitrous cams are wider LSA's. Wider LSA's usually idle better and are more streetable, check the cam specs on new motors (LS-1's etc.) Just for a comparrison my 454 +.030 runs ported Oval Edelbrock Ovals, Vicotor Jr, Holley 1000 and a solid roller (255 / 262 at .050 .652 lift on a 112 LSA installed at 110.5 ICL) the car goes 125 mph in the 1/4 on the motor (approx 3450 lbs). It has a relitively radical sounding idle (1200 rpms) but will pull 6th gear (3.70 x .62) at 1500 rpms You need to list you combo to get better advise than that. You are going to need a good set of heads to make 625 hp with a 454 unless you go to some higher compression stuff -------------------------------------------------------------------------------- From: Huntingtin Beach | Registered: Jul 2002 | IP: Logged | Pat Kelley Tech Team posted 10-04-2003 09:45 PM -------------------------------------------------------------------------------- That is a whole slug of questions. Entire books have been written on the subject. Basiclly, tighter Lobe Seperation Angle (LSA) causes the peak torque to be higher, and located lower in the rpm band. A 108 LSA, while having a higher torque peak, has less torque at lower and higher rpm than a wider LSA cam given the same duration. It has a narrower torque band. Average torque is lower with a tight LSA. The advantage of a tighter LSA is the quick rise to the higher torque peak. This work great for drag racing cars which can operate in a narrow rpm band. The more gears your trans has the tighter LSA you can run since you can keep the engine in the narrower torque band with the extra gears. Most street cams have a wider LSA which broadens the torque curve. The advantage is an increase in low end torque with a steady rise to the peak (which is lower than a tight LSA). The curve stays higher well past a tighter LSA cam's curve, which can cause the wide cam to make more power at top end. As for the Intake CenterLine (ICL), the curve stays the same but it is moved up or down the rpm range by advance or retarding the cam. Advancing the cam causes all cam events to happen earlier. For example, the intake closes earlier when the cam is advanced. This traps more mixture in the cylinder and makes more torque at lower rpm. However, there is less time for cylinder filling at high rpm. With less or no advance, the intake closes later. This traps less mixture at low speed but allows the engine more time to fill the cylinder at high rpm. I'm guessing you know what LSA is. The DCR calculator loves or hates nothing. It really couldn't care less what cam you use. Would you say a torque wrench hates high or low torque? If you want to run a big cam with low compression, you can. However, the engine won't like it much. The DCR calculator is just a tool to help match compression with duration and ICL. If your CR is low the engine won't like a big cam, the DCR calculator is just helping the engine tell you this. -------------------- Pat Kelley 66 El Camino, daily driver 67 El Camino, Bracket car (7.36, 92.96, 1.62 60', 1/8 mile) 355 powered Pat's Page (Dynamic Compression Ratio Calculator, car specs, Spark plug reading info) -------------------------------------------------------------------------------- From: Pomona, CA | Registered: Oct 98 | IP: Logged | 69LS1 Team Member posted 10-05-2003 12:10 AM -------------------------------------------------------------------------------- I dont know if this example will help at all but if you have two cams...Both lets say 270 deg adv duration....one ground on a 114 LSA and one ground on a 108 LSA...Same lobe just a different LSA. Lets say the 114 LSA cam had timing figures of: IO = 18 and IC = 72 EO = 66 and EC = 24 If you add the IO of 18 and the EC of 24 the sum would = 42 degs of overlap. The same lobes ground on a 108 LSA would have : IO = 24 and IC = 66 EO = 60 and EC = 30 If you add the IO of 24 and the EC of 30 you would have 54 deg of overlap. You can also see that with the 108 cam the intake is closing sooner and would build cyliner press sooner that the later closeing 114 lsa cam would.The 108 LSA cam EO later for a longer power stroke than the 114 LSA cam has. The 114 LSA cam would likely idle abit smoother than the 108 LSA cam due mainly to the lower overlap but the 108 LSA cam would likely come on Harder and be snapier when you got into the cams RPM range.The 114 LSA cam would likely not hit as hard and be smoother power and really pull abit later in the RPM range. Not to dispute anything here but many times especially with small blocks under 370 CID a tighter LSA cam will many times make more power throught the entire RPM range than a wider one would. When you get into some really small cams often times they are ground on a tighter LSA...UD Harolds SB 246/254 H (192/199 @ .050 ) in on a 108LSA and Iskys Mile a More cams ( 194 @ .050 ) are also on a 108LSA....They also offer a 256 H (202 @ .050 ) on a 108 LSA...One of Chevys OE 305 cams was ground on a 110 LSA from the factory... As you can see the LSA basically changes where your cam timing happens.Good , bad or indifferent but the right lobe on the correct LSA cam really make a difference depending on your combo's needs. -------------------- Al. 1969 El Camino -------------------------------------------------------------------------------- ------------------ 70 Monte Carlo. 355, 10.4 to 1, AFR 210's, 1 3/4" super comps, solid roller 585/597 260/266 @.050 on 112LSA, Edelbrock tunnel ram w/2 600 hp's, 4,000 stall, 4.11. 3800 lbs. 4000lbs with me in it, 12.4 @ 111 mph, 2.000 60' time, launching at 1/2 throttle for 60' to keep from spinning the tires. With that mph it should be between 11.8 and 12.2 once I get it to hook up. New Times coming for the new rear end set up and 200 shot of nitrous. Link to comment Share on other sites More sharing options...
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