i have a street/trackday '83 z-28 that has a rebuilt 355 with 750 carb, headers and a t-5 with 3.73 rear. it has at present a zz4 cam, but i realize i wanted more....would a different cam with a narrower LSA give me more umph? or should i stick with the 112 LSA and go with more duration?

 

A lower LSA will add more of a rump rump type of idle. A wider LSA will have a smoother idle even with more lift and duration. The cam in my BBC has a 112 LSA. With .748 lift and 286/298 @ .050 duration, it idles very smooth at 1000 rpm.

 

If it were me I would us a 108 lca just don't go over board on the duration.
Some thing like a isky 262 or 270 hyd. mega cam with 108 lca.

 

You haven't said what heads you've got.

 

The lower the LSA, the more the cam is geared towards upper RPMs, and the worse the idle will be. You need to factor in the rest of your combination before you decide. If this is a track car that sees some street use, a 110 cam may give you more power. If its a street car that seems some track use, a 112 cam may give you better idle, and better gas mileage. I have seen magazine tests and the difference between similar duration/lift cams and different LSA's is worth no more than 10 HP, but with the lower LSA cam the peak is shifted up higher a few hundred RPMs. Its your choice, really.

 

From what i've seen, duration effects where your powerband will be. Higher or lower in the RPM range.

LSA effects the "shape" of the powerband.

eg, a 114 LSA will have a long flat powerband, lets say it peaks at 300RWHP
Same duration cam, with 106 LSA, will have a shorter peakier powerband. It might peak at 320RWHP for example, and taper off quicker before and after the peak.

If you integrate under the curve, it's anybodies guess which will make more power. The idea is that if you keep the car in a narrow RPM range (6 speed tranny, close ratio, racing) you'll do better with a narrow LSA. If you've gota TH-350, and drive it around town, a wider LSA will probably be best overall.

And yea, longer LSA makes for a better idle. "They" also say that a narrower LSA makes more "midrange torque". Not sure how they define midrange, but I thought i'd pass it on. 110-112 is not a huge difference. I think supervisor42 mentioned to me that 2° in LSA is equal to 4° in duration sorta thing (you double it).

Also, Vizard says that a specific LSA is best for a specific displacement engine. I think he means when you integrate under the curve sorta thing. Anyway, he said 108 was best for a 350 sized engine. 110 for a 305 I think. 106 for a 400cid.

Thought i'd just pass along what i've heard.

 

It's really kind of a moot point, because unless you're going to be having your cams custom ground, you're not really going to be choosing between cams that are identical apart from the LSA. You're going to be choosing between cams with varying lift and duration (and sometimes LSA), intended for different applications.

Still need to know what kind of heads you've got. Power comes from the heads, and the cam has to be chosen to match. There's no point putting a huge cam on if you can't get enough air through the heads to use all that lift and duration. Likewise, there's no point choking huge heads with a tiny peanut cam.

 

thanks a bunch guys!...i've got the vette aluminum 113 heads on....small chambers ( 58cc ), small valves......1.52 roller tip rockers...flat top pistons with valve cuts... edelbrock perf. rpm intake...i thought i'd get the motor up to 350hp rwhp...but it's dynoed at only 280 rwhp...something's either wrong or this cam isn't delivering....motor pulls 20 " of vacuum at idle and pulls very strong...but i guess it runs out of breath....could be the heads. but i built it to zz4 specs...are the crate zz4 heads very different than the vette heads? would a switch to 1.6 full roller rockers help here?

 

The ZZ4 MOTOR is 355hp... not 355 rwhp.

Not sure what the difference in heads are, but here are the ZZ4 heads...

http://paceperformance.com/index.asp...D&ProdID=22850

Hope this helps!

 

but how much hp could you lose with a manual trannie? i'm thinking of a solid roller cam with 110 LSA..about the same duration and lift...maybe a little more lift....what do you think? would i get over 300 rwhp with that?

 

My ZZ4 cam, ZZ4 heads, and TPI intake made 280 RWHP and 380 RWTQ thru a T5, so you're right in the ballpark with your setup.
The L98/ZZ3 heads are identical. The ZZ4 heads are identical as well, except they have better springs, the LT4 stock springs.
A solid roller cam will have too much duration for those heads, they cant flow that much air. Stick to something smaller. I used an LT4 HOT cam to make the power and ET in my sig, with custom chip tuning. With a spring upgrade you could use the new hot setup, the XFI268HR.

 

thanks Kevin.....that's helping me alot! so, 268.....a little bigger than the zz4 cam?

 

Its smaller advertised duration which helps the idle, but a larger 0.050" duration, which means fast ramps and more power.