Hi guys, I just bought a custom ground roller cam to use in a Stealth Rammed 355. Here are the specs w/ 1.5 rockers

0.495"/0.530" i/e 222/230 i/e @.050 on a 114 lsa

I have a wideband (finally) and burn my own chips, but I still hope this cam idles fairly smooth. I'm sick of choppy idling cams that smell like gas at idle no matter what I do to fueling. I figure the 114 LSA and pretty conservative duration (for an aftermarket high HP build) should have this thing idling pretty reasonably smooth. What do you think?

 

ya thats a pretty conservative...itll idle real calm.

 

Do you know what the overlap is at .050"?

 

I don't, I am buying it new but I didn't have it ground, hopefully I'm getting the spec card with the cam when it comes in.

 

I had a 236/242 @050 XE that idled pretty smooth, the rollers are pretty calm, my 230/236 @050 flat tappet idles harder, makes the car shake...

 

its your LSA that determines rough idle or not, a high LSA will make an engine run smooth, and a low LSA will produce more low-end power, but your idle will suffer.

 

zz4 has very similar specs, and is 150 brand new on ebay all the time

just a suggestion . love the car

 

that that cam is pretty tame, it should make good power yet idle nicely. and it doesnt have all that much lift either

 

The overlap @ .050 is what will determine how your engine is going to idle. With a 355c.i. engine, i would say 10 degrees is pushing it. You can have 3 cams that have the same adv. duration and lift numbers, and they all three can act completely different. Open & closing events combined with L/S angle is what affects the idle. A good rule of thumb is (c.i)divided by(overlap @.050) example-406/13=31.2% ... this ratio is a good guide to help determine how a cam is going to idle. If you start to go below 30%, you will see how the idle starts to chop. EFI can tolerate more overlap@.050 than carb. engines, so keep that in mind as well, with proper tuning of course. I'd say much less than 25% with EFI and you will have your hands full with the idle issue.

 

That's not true except if ALL other specifications are identical AND the only difference is caused by a widening the LSA (and causing the overlap to decrease). Idle quality depends on the overlap between the time the exhaust valve closes and the intake opens. A 116 LSA on a 236/240 cam will idle rougher than a 110 LSA on a 210/216 cam. This is using .050 durations in all cases. But, what is seldom specified when people quote cam specs is the actual timing where the exhaust closes and the intake opens as that is what really determines the idle. You really need to analyze the cam cards specifications in detail to determine this.

The LSA's primary function determines the power band rpm range of the cam. A narrow LSA cam (110) tends to promote mid-range torque while a wide LSA will sacrifice mid-range TQ for a higher top end.

Large cams often will go with a narrower LSA because the large duration itself often promotes major HP so they often look to compensate by increase mid-range TQ while sacrificing a little at the top end. A short duration cam tends to be weak on HP so a wider LSA will help increase top-end HP while sacrificing little TQ.

But it is the overlap between the exhaust closing and intake opening that determines the idle quality more than anything else.

PS: I just noticed twinturbo406 said basically the same thing. So you add my vote as agreeing with twinturbo406's comments.

 

yes it should be pretty smooth but will still let people know it's cammed

 

Pennock, thanks (and thanks everyone else too!). This cam cost me $100 new, I got it in the mail the other day. Sounds like I'll be in good shape.

 

make sure you get a new prom burned or the cam will throw your computer and air/fuel ratio wayyyyyy outta wack

 

I don't get "proms burned", I burn them myself. I datalog and have a wideband O2. Only way to fly. I couldn't imagine running EFI with any engine mods without doing your own chip work (or having someone with a dyno and a wideband do it)

 

ok chill man i didn't know

 

LOL I can't chill its been a long day

 

Another member of the cult.