Which cam and other questions

[eventhorizon66]

So if I had a cam in a 2.02 valved 383 that had a 110 LCA and 236° @ 0.050", and I wanted to find a more optimal cam.  I would first look at the LCA.  That should be narrowed to 106.  Now if I simply apply a 106 LCA to my current lobes, overlap will go up considerably and may peak torque/horsepower will shift upwards.  But I want the same powerband, so I would like about the same amount of overlap as the first cam had.  So I will now select lobes will less duration.  Lobes of the same intensity as before but with 228-230° @ 0.050" should fit the bill.  Now I will try to achieve the most lift I can with 1.6:1 or even 1.65:1 rockers.

Cam 1: 236° @ 0.050" - 110 LCA - .520" lift w/1.6:1 rockers

Cam 2: 230° @ 0.050" - 106 LCA - .522" lift w/1.65:1 rockers

Cam 2 will make significantly more average torque.  It does still have slightly more overlap, so the idle will be a bit rougher, but not much.

[eventhorizon66]

For lower-lift and duration cams though, you don't often see (or at least I haven't) a 106 LCA. Perhaps I'll keep an eye open for that some more. Curiously, what would the optimal LCA be for the motor I have? Specs are in sig below.

These rules for speccing cams apply across the board for NA gasoline engines (Towing to full circle track).

Based on David Vizard's advice, a 350 with 2.02" valves is typically best served with a 108 LCA.  A better cam than the XE268 might be one that uses XE268 intake lobes #5443 on both intake and exhaust on a 108 LCA at 4° advance.  Then use 1.6:1 rockers across the board.

BTW Vizard recommends single pattern cams for any street engine as they tend to make more low end torque and improve fuel effiency.  Dual pattern cams begin to pay off in the upper mid-range and top-end, and, before you ask, the LCA rules still apply to dual pattern cams.  Also when using dual pattern cams, I notice Vizard tends to use 1.6:1 rockers on the intake only and 1.5:1 rockers on the exhaust.  He recommends this because the exhaust side is much more sensitive to changes in the duration than in the amount of lift.  Higher ratio rockers on the exhaust side of a dual pattern cam may only serve to further reduce low end output.

[eventhorizon66]

SUX if you are genuinely interested in this topic I'd strongly encourage you to check out this book:

http://www.amazon.com/Build-Chevy-Small-Blocks-Budget-Performance/dp/1932494847/ref=sr_1_2?ie=UTF8&s=books&qid=1254072084&sr=8-2  (I've noticed a few typos in the new edition, but none that will alter your understanding of the material)

Here is a very informative Vizard article on cam selection: http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/index.html

Also you can check out more Vizard tech articles, as they become available, at this address: http://www.motortecmagazine.com/ (it's a new website and under construction so beware).

[TexasRed]

The thing to remember about Vizard is that he's also got to sell magazines. So take some of his advice with that in mind. (What's sells magazines? MAX POW-UH!)

[eventhorizon66]

You're right, he does make his living by authoring articles and books.  But to dismiss him, even partially, for this reason alone would be ignorant.  Everyone should be fortunate enough to get paid for doing what they love and contributing to their area of expertise.  And it's never been the max power figures that have impressed me about Vizard street engine builds, but the overall torque curve, which is more telling of "how" he got there, and his constant aim for total streetability with the power.

I'm not saying he is the "end all be all" of engine building, as he most certainly is not.  But for me personally, I just decided to find one "expert" to follow in my future engine building pursuits, since if I tried to follow the advice of as few as ten different people, I'd most certainly end up moving in ten different directions.  I feel David Vizard is a qualified expert and have chosen to follow his advice so I can make my decisions as easily as possible.  If Smokey Yunick had spent some serious time on street engines and then spilled the beans on everything I need to replicate his results, then maybe I'd follow his advice instead.

[TexasRed]

I'm not dismissing him at all ("I READ YOUR BOOK!" Patton talking about Rommel in North Africa). I just don't know what people consider streetability. I live in Houston currently so I deal a lot with traffic. So a better idle is going to be a benefit to me. Along with the fact that a lot of his stuff isn't for building trucks (a few are, but they require almost a lower rear end ratio) so I take his advice with the attitude that I'm happy to lose a little bit of power if it means my engine is smoother and possibly lasts longer.

OK, what's the min clearance on a stroker? I just started putting things back together after grinding and cleaning. Is .050 ok? .040? I may need to get a file so I can get one spot a little better now that I can see it's actually fairly close once I got where it was hitting clearanced. The dremel was putting filings everywhere.

[eventhorizon66]

I would think 0.050" would be OK.  Why not give your machine shop a call?

[TexasRed]

The day I picked up my block was the day they shut down.

[eventhorizon66]

You shut 'em down, huh?  Well I hope they did you right before they shut down, but you'll still need to find another machine shop.

As far as your clearance isue goes, I look at it this way.  How much is the crank/rod really going to grow/move around?  A piston can be run tighter than 0.030" from the cylinder head and it expands much more than the crank or rod.  You can go for more clearance, but sooner or later you'll hit water jacket (it's not unheard of on 383 builds).  If you're in the Houston area, these guys look like a reputable shop.  Give them a call and see what they say about your block/cam clearances.

[TexasRed]

I'm in NW Houston . . . .Pasadena's a bit of a drive. I read a few places that .050 is pretty standard. I'm fairly close to that so I think I'm good.

[eventhorizon66]

I wasn't suggesting going down there, just calling them.

[TexasRed]

Not sure why you deleted the Smart Aleck response.

Just an update, I'm never going to build another stroker again. Well, maybe, if I ever have more time and more money. I think next time I'll do the rod by rod method whereby I put a rod and piston in and THEN grind. That way I can clean everything up at one time and then build. So as soon as I finish clearancing everything (getting close) then I will probably start the final build (please God).

[eventhorizon66]

Not sure why you deleted the Smart Aleck response.

Just decided I might have come off as a [fill-in-the-blank].  I was just being goofy anyways.

So it's been fun, huh?  Hang in there and don't get impatient (careless) now.  Make sure everything is super clean before assembly and check, double-check, and triple-check everything as you go.  Keep us updated.

Just so you know for the future, these rods are supposed to make 383 building a snap (little or zero clearancing required).  Unfortunately they aren't cheap.

[eventhorizon66]

Any new updates on your engine build?

[TexasRed]

Not much other than I bought one of them ring compressors from OReilly's/HiLo (I think they're called Ring Breakers by some) and a Husky-brand torque wrench from Home Despot. Also some Delo as my breakin oil along with some EOS. Just gotta find time now. . . . .