Guys,

I need someone to educate me on lobe separation angle and how that affects and engines performance when you start looking at aftermarket cams.

I have read that the wider lobe angles are better for engine vaccum and idle.

The shorter lobe seperation angles are better for making more torque and power but at the expense of idle quality and engine vaccum.

Is this correct or am I totally off base? I'm starting to look at cylinder heads and cams for my car that I would like to buy in the future at some point so I'm trying to go to school on camshaft related information like lobe seperation angle.

 

You are right for the most part. It really depends tho on engine type and cam duration too. Overlap effects need considered.

A 230/236 deg cam on a 113 has more overlap than a 218/224 cam on a 108 lsa. The overlap has influence on idle quality and vacuum, as well as trq curve. Power curves would be different but that 108 lsa cam may end up being easier to tune since it has less overlap. So lsa alone isnt enough to make a decision.

But for a given combo, using same cam lobes and duration, if you had one with wider lsa say 113 vs a narrow lsa of 108, the narrow one should have a peakier trq curve as well as hp curve, making more low to mid range numbers but falling off earlier after peak rpm. Wider should carry curve out longer making a broader curve but possibly less average hp/trq but can depend on intake manifold and exhaust setups too since they have influence on power curve shape.

 

Thanks for the advice. Ok that makes more sense then why the OEM manufactures use cams that usually have a wider lsa then a comperable aftermarket cam.

Does the lsa affect emissions to? I live in California so I have to deal with both a visual and tail pipe emissions test every couple of years.

 

Yes overlap by duration and lsa can change emissions but also alot of that is in the tune. After seeing what the cali guys are getting away with for cams out there, i have to say most is in the tune and good cats or else they have someone writting them tags

 

http://www.summitracing.com/parts/NAL-10185071/

What about this, it's the ZZ4 cam. I know the ZZ4 is a warmed over L98 style engine with a carb on it.

Would this cam work well for a street driven L98 TPI engine? It's got high lift numbers compaired to some of the other TPI aftermarked cams that I have looked at.

 

Yeah that cam does well. Long duration split on exhaust seems to compliment stockish head type intake/exhaust flow ratios and shorty header systems that dont scavenge as well. Its low duration and friendly 112 lsa makes it stable. Plus it can be found for cheap. Stock heads need modded to handle the lift but it would be a good cam

 

Thanks for your help on this. That makes a lot more sense now.

Also sheds some light on why some of the newer cars that are available now that have high lift cams (like the LS3) have wide lsa's so they are more friendly in terms of idling and emissions requirements.

I also get why most of you guys on here that have custom built your motor to your own personal specifications like shorter lsa's. Since you guys built the motor to your own personal taste you have a lot more control over all aspects of the engine so an extremely wide operating band may not be as ideal in that case.

My L98 is internally 100% stock. I've also seen other cars that have had mild aftermarket heads or stock heads run with the ZZ4 or ZZ9 cam before as well.

 

Narrow LSA gives a cam that rump, rump sound but the trade off is drivability. You wouldn't want a 104 or 106 LSA in a street vehicle. 110 or 112 is a better choice.

The bigger the cam, the more the LSA changes. To make good power, the LSA starts to drop up to a certain lift/duration then the LSA starts to open up. My BBC cam has 0.800+ lift and my cam grind has 114 LSA and idles smooth just over 1000 RPM. It's very hard to find a narrow LSA with a big cam. My powerband starts a little over 5000 rpm and peaks somewhere below 8000 rpm. The wide LSA makes power in that wide rpm range. With only 2 gears, I use that wide range. When I shift, the rpms only drop back to 6400.

If I had a multi speed transmission with rpms climbing and dropping quickly as it goes through the gears, a cam with a narrower LSA would be a better choice.

 

Ahh see. That makes a lot of sense now. For my car I was looking at something really mild like the ZZ4 cam. There are simular cams out there to that grind that have different lsa's. At least now I know some more information when I'm looking at different cams.

 

Also note that lsa changes opening and closing positions of valves in relation with the piston position and thus change piston to valve clearance. Sometimes wider lsa's are used to keep clearance up. Ls1's are like this to a degree. Generally those heads like wider lsa's but most cams that are bigger remain on wide lsa's because of piston to valve clearance.

Some pro stock motors use 117-120 lsa's. Their heads are the best available for automotive internal combustion engines in n/a racing but since they turn such high rpm the duration is large and they may have too much overlap with common 110-112 lsa's so they are forced to go much wider.

Again a 218-224 cam on a 113 is wide since duration is low but a 286/296 cam on a 113 isnt as wide since duration is different. Need to look at overlap area

 

Roller cam vs. flat tappet cam makes a huge difference too. Roller lobes allow much more aggressive ramps which provides faster opening and closing of the valves. This produces much more actual full open time per degree of duration. You'll notice that a good hydraulic roller cam has much more lobe lift per degree of duration than a flat tappet cam of similar duration. The roller cam will also produce better idle quality, vacuum and engine efficiency than the flat tappet cam. This leads to a more powerful, more drivable engine.

 

Engines with better flowing heads, such as the LS series, will tend to run wider LSA's for best power. Because of the superior head flow, less overlap is required to help with cylinder filling, so they'll make better average power with the wider LSA.

 

Not near seated. Again, only if looking at the 0.050" numbers. Look at comp's shelf hydraulic SBC cams. Whether you look at the popular 224/230-110 cam, or a tamer 206/224-110, either way you find less duration at 0.006" with the non-rollers. This is what gives clean emissions, good idle quality, good vacuum and good low-RPM torque. The roller will give more power due to the superior cylinder filling, but not at idle speeds. If you're going to run a 3500-stall converter, then this doesn't matter. But for those happy with stock 1200-stall torque converters, or those who hate to needlessly rev the engine before engaging the clutch, it's critical. Having driven a mild 350 that would happily cruise at 830 RPM at 30 MPH, with a HF cam and a functioning lockup converter, I vouch for the value of off-idle torque. Intake closing at 0.006" is far more important for this than intake closing at 0.050", and for this, exhaust opening also matters enough to feel.