Quadrajet Problem Solving > Quadrajet Parts and Numbers

My M4MED Q-Jet and my FJ-60 Landcruiser 383 swap in

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Cliff Ruggles:
Cams with tighter LSA's increase overlap, all else being equal.  They also pull power down in the rpm range, and narrow up the power curve some.

This is why the factory cams have very wide LSA's.  The idle good, broad power curve, and still pull hard at high rpm's.

Aftermarket camshaft advertise much quicker opening/closing ramps (shorter seat to seat timing), and claim the better lobes make up the difference in opportunities to move air, so they can pull down the LSA some.  This also provides some "attitude" at idle and low speeds.

What it really does from what I've seen here, is raise cylinder pressure sharply in a narrow rpm range, and early in the rpm range.  This can increase octane requirements significantly, and in extreme cases cause tuning and detonation issues......Cliff

dougbert:
Cliff I appreciate this information on the CAM principles.

Since I have been studying the Comp CAMs, I am learning "their" viewpoint.

The Extreme 4x4 line I am looking at, has 111 LSA and 107 ICL, while their Extreme Energy is 110 LSA and 106 ICL.

Their Thumper line have 107 LSA and 102 ICL.

They then vary the durations and lift within each of those family lines.

So I see the effect you are talking about,  tighter LSA and ICL, the more overlap, etc.

What I am also trying to compare/understand is what stock production used for LSA and ICL.  I am a software engineer and love numbers to compare things with.

I am ignorant on these things, but hope to learn fast.

thx

doug

dougbert:
I found on the web Vortec CAM specs (If they are true anyway)

The Vortec 350's/305's all use the same cam grind. In fact the B/D body Lt1 350's and B/D 4.3V8's use the same cam as the vortec 305/350's do.191º/196º 0.414"/.428" lift on a 111º LSA.

endquote

So the CC 4x4 series have the same LSA, but more duration and higher lift.  Things are making more sense to me.

doug

Cliff Ruggles:
Look a bit further into factory camshafts for the higher output engines. 

A very good cam for a SBC is the LT4 "Hot" cam, hydraulic roller.

http://www.summitracing.com/parts/NAL-24502586

A 355 needs at least 10 to 1 compression to effectively use it, 9.5 or so in a 383 build.  EASILY makes 400hp in a well set-up 383 or 400.  Good idle, strong off idle, and broad power curve.

Also consider, when playing around with cams, CID, compression, etc, for every full point of compression increase, the cam needs to be increased apprx 10 degrees in duration as well, or cylinder pressure goes up accordingly.  This assumes the base cam was a good choice right to start with.

I've dyno'd Comp's XE flat cams, and street/strip evaluated them......and if I told you the results, and what I thought of them, they would put a "contract" out on me!.....FWIW.....Cliff

dougbert:
Interesting. I know that CAMs bring many variations and different results, and it is difficult for a novice to "get it right" the first time out. But I can try.

Unfortunately, the block I have is a 1983 350 and not the LT4, though I will see if they have one for the older SBC (but probably not). Thank you for the reference. I will keep that for "future" projects.

interesting insight on CC

doug

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