ViciousZ

iTrader: (1)

The less the duration, the more low-end power a cam will make, right? And besides giving higher vacuum and smoother idle, a larger lobe separation will raise the powerband, yeah? So... if a cam had low duration and high lsa, like 210 220 dur and 114 lsa, what's it gonna do? Will the low duration and high lobe separation kinda be working against each other? I put this cam (comp 304) in my new 355 engine, but now I'm starting to wonder if it was such a good idea. It's a tpi motor with ported vette heads, headers, and superram base, and runners and plenum are soon to come. What do you guys think?

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91 Z28
Come see The Vicious...

five7kid

iTrader: (14)

I'm not the most guru-ish out there, but I think you've got at least one piece wrong. IIRC, a larger LSA will improve vacuum and idle and tend to LOWER the powerband. So, a high duration and LSA will "tend" to work against each other, but can also produce desireable results, especially in a computer controlled engine.

My cam has 216/234 duration @ .050" lift, and 114 LSA. It will rev to 6000, but will also idle smoothly at 500 with a CC carb and has yet to set a code.

If emissions and CC weren't an issue, the cam grinder would probably pick something like 108 LSA to get even more RPMs out of that duration.

Perhaps a real guru can set me straight if I'm wrong.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2300 stall TC. Ported World 305 heads, Crane PowerMax 2050 cam. ZZ3/4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster 80. 2.93 limited slip. Spohn SFCs waiting to be installed. AMSOIL syn lubes bumper-to-bumper. Daily year-round driver. Best ET, speed TBD...
57 Bel Air, my 1st car. '66 396, 9.7:1 forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 700 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

Vader

Viscious,

Don't take this as Gospel, since camshaft design is more of a Black Art than a science, or at least can seem that way. There are really very few hard, fast, all-encompassing rules that apply to cam design since there can be so many other variables in the final engien configuration. A cam profile that most of us would consider "lame" does very well in a smaller engine with well designed heads and monster valves, and can operate for long periods at some wicked RPMs.

So, for the generalizations, a typical cam installation that uses a lower duration at the same lift will typically create more power at a lower RPM and less power at a higher RPM. Since the cylinder sealing is better due to the shorter duration, vacuum and compression are increased at lower RPMs, creating more power. At the same lifts, a longer duration profile with necessarily more overlap will make less power at lower RPMs (due to poorer cylinder sealing and lower vacuum), but will have more time "built in" to allow better intake and exhaust flows at higher RPMs. The short-duration profile at high RPMs tends to cut off the fuel charge before it reaches optimum velocity in the intake ports, and starves the engine a bit.

The hybrid of these to typical ideas is the high ramp, short duration profile that can only be done effectively with a roller lifter. This profile allows for respectable cylinder sealing and vacuum (which the TPI ECM is going to prefer) and still allows better flow through higher net lifts and better ramp profiling - or getting the valves open farther, sooner than the factory cam would, then holding them open farther, longer than the factory cam. Whereas the initial opening points and eventual closing points of the valves can be about the same as the factory grind, the speed at which the valves move between those points can be increased substantially. This can allow for a lot better flows with relatively "mild" numbers. This "area under the curve" is what tells the real story in cam design. Granted, the high-ramp, faster moving valve train is going to need much better springs to control the valves, and should get better components throughout the valve train due to the added stresses, but it is very streetable with the right parts.

As for your choice, the longer LSA is going to be more friendly to the ECM and engine control scheme, and the additional lift and improved duration over the stock profile are going to provide better flows that shouldn't overwhelm the heads and valves. I understand that you have done some porting work, but unless the intake ports are above 180cc or so, the need for more cam might not be apparent. The headers and SuperRam will certainly help in flows and could indicate more duration for top end power, but the TPI is mostly designed for torque, even with the SuperRam. A MiniRam would change that, but you'd still want to have some respectable torque on the low end. Compare the cam profile curve to one designed to replace an LT1 cam and see if the area is way off - I doubt it is that much different, and would expect that the greatest differences are in lift wiht a little more duration, and not big change in LSA and overlap.

The second Comp I install in an LT1 was 230°/244°, .510"/.540", but still has 112° LSA. I wouldn't want to go any deeper into the cylinder without some heavy PCM and gearing work, and some serious stall speeds on the converter, since low-end would be really shameful.

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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
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Tom84L69

The lobe separation also affects the sound of the engine. The lower the number, the more "lope" the engine makes, or the rougher the idle. My car has a 108 lobe seaparation and idles rough and sounds cool. It also pulls really strong till about 6500 rpms.

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84 Z28 L69. 5 speed with 3.73 posi (broken)Ported heads, intake, 10:1 comp. 230/230 .480 lift cam @.050" w/108 LSA

Triumph Spitfire SCCA roadracer. 1.1 liter 4cyl w/ 14:1 comp.
turns on rails!

Sitting Bull

There is a good article on this cam and valve train biz in the latest Super Chevy.

SoCo80p

iTrader: (5)

a 210/220 on a 114 will idle like a stock cam , it will make alot of off the bad torqur but is pretty weeny. i would forsure go a bit bigger then that .

ViciousZ

iTrader: (1)

I'm sticking with the TPI, might as well make the cam match. The powerband was listed as 1400-5400. Besides, it's already in the engine, so it's a little late for second thougths. The lift is .533 .544 with a 1.6, that's not so weeny. But for some reason the engine has no torque. ??? That's what I'm trying to figure out.

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91 Z28
Come see The Vicious...

five7kid

iTrader: (14)

No torque? You have it running then?

I see you have 3.73 gears. That's good. I didn't see any mention of a higher stalling torque converter. That is key to getting the engine up into it's torque band when you raise the powerband of the engine like you have with this cam.

You have some mismatched parts, too. Those are stock runners, right? You are correct about needing to have things matched to each other, and until they are, things will suffer.

It's good to see a member of the fairer gender wrenching. Those pictures were a little posed, though, right? I mean, you are ENTIRELY too clean!

Can we assume you're going to KU? My sister has lived in Lawrence for years. Brother lived in Wichita back in the late '70's, I was only there twice - once when freezing cold, once when boiling, muggy hot. I'll take Colorado (even though I'm a native Husker).

ViciousZ

iTrader: (1)

Yup, it's runnning, got about 1100 miles on it and going to the track this weekend, if the nice weather holds.
In my own defense I must add that cleanliness is next to G0dliness. Especially in engine building. They are not posed, I'm just **** and insisted on having not a single spec of dirt anywhere near my engine. If you want some greasier pix of me I'm sure I have plenty. As for the 'mismatched runners' I'm a little low on cash right now. It seemed more logical to replace the upper plenum and runners later, as opposed to a cam swap. If you'd like to contribute to the 'superram fund' let me know. And my 700R4 is about ready to kick the bucket, so why waste money on a stall when I ought to be saving for my T56? Sure do go to KU, and I'm also a native Husker. Small world, eh?

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91 Z28
Come see The Vicious...

five7kid

iTrader: (14)

Certainly no problem with cleanliness. Just jerking your chain.

Can't disagree with that. Just pointing out one possible reason for your apparent low torque.

I have similar funds going that need contributions. Have to pass on yours.

Same as the runners. All in due time.

Huskers for the Roses, that's what I say!

mtx28

well vader and others have covered cams pretty well, i'd just like to add my 1c in and say that a cam should be more of a tuning aid, rather than building your engine around it(not saying you did). too many poeple pick the cam they want, then try to match the rest of the engine to it.. I dont see that as the way to go. I think you have a good cam for your motor, but I think that since you've built the new motor you will really notice a difference on the top end, ie above 4k rpms, when you swap out(or port which is free) the plenum and runners. it cant hurt to port them... maby i missed it, have you already? I still feel aftermarket pieces would be better, but hey, they do cost money right? In any case, nice engine, nice car, and just tell me.. where the hell do you find a girl that is into cars?? only girls around here that like cars are the ones that just got a new suv. my luck.. hard at work just like always oh yea, one more thing, you said your looking for a T56, check out the classified board on www.ls1.com , they usually have one for sale. if not, just register and post a wanted ad. good luck

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74 Z28-- 383/400 SOLD

LS-1, come to me now

five7kid

iTrader: (14)

mtx, building the engine around the cam is one of the BETTER approaches to this. All too often, people will do silly things like spending thousands of dollars on things like a tunnel ram and 220 cc heads, but not consider what the cam needs to be to make it run, and end up with less power than they had before. Or, get the right cam but don't build around it, and end up in the same place.

Vicious is somewhat in the latter catagory, but she knows that and has a plan to correct it. The real issue is that you have to put together a "package", not assume that just replacing one piece, like the chip, will take your LO3 from the 16's into the 13's.

It would seem that you can find at least one car gal in Lawrence, Kansas. In the past couple of years, I've seen a lot more women running at Bandimere, a big difference from 20 years ago when I knew of a grand total of 1. About the same percentage of them wrench their cars as do the guys.