GM L31HD and cam choice

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rangrayy

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ZZ4 cam specs here...

Duration @ 0.050" Lift: 208/221
Lift: .474"/.510"
Lobe Separation: 112

I am somewhat of a neophyte and I don't know what a 411 is so I guess the answer is no. My truck is OBDII that much I know.

Have it running yet with a sound clip? If it’s a stock 98 then it’s he black box.
 

slowburb

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I wouldn't suggest the LT4 hot cam for this buildup. Too much cam. I don't suggest the stock LT1 or LT4 cam to anyone looking to build up a truck motor. They're meant for light cars with stick shifters.

The ramjet cam is the ideal cam here. Maybe the ZZ4 cam, but it would give up some off-idle torque to the ramjet cam.

Plan on changing valve springs. The stock valve springs are not ideal even for the stock cam. Remember though, you have to pick a cam before you choose valve springs.
 

toomanyhobbies

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I do have a video at idle but I am not high tech and I don't know how to post photos or videos here. It doesn't run great because it hasn't had the tune yet but it's warmed up in the video so it idles pretty smooth. It sounds pretty good. I have ebay stainless shorties on it with a full stainless single magnaflow XL two in two out (to keep the crossover which everyone told me is better). If you PM me I can email it to you.

I went for the BBK throttle body and the Jet MAF with EGR delete. That's about it.
 

rangrayy

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I wouldn't suggest the LT4 hot cam for this buildup. Too much cam. I don't suggest the stock LT1 or LT4 cam to anyone looking to build up a truck motor. They're meant for light cars with stick shifters.

The ramjet cam is the ideal cam here. Maybe the ZZ4 cam, but it would give up some off-idle torque to the ramjet cam.

Plan on changing valve springs. The stock valve springs are not ideal even for the stock cam. Remember though, you have to pick a cam before you choose valve springs.

I was leaning with the ramjet or the one in the 383HT motor(marine) and I had already planned on changing out the springs.
 

rangrayy

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Or drop the induction cfm down to 300 still not a bad combo. 292hp@4000rpm and 478ftlb torque @2000rpm

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I was playing with the numbers on the CamQuest and I wasn’t sure on induction airflow total but figured 500cfm would be a safe bet. Along with small tube headers, not sure either, with the XR258HR am impressive 311hp @4000rpm with 485ftlb torque @ 2000rpm.
 

rangrayy

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Specs on the ramjet cam:
Duration: 288/308 [email protected]: 196/206 Max lift w/1.5 roller rockers :.431/.451 LSA:109

XR258HR
Duration: 258/264 [email protected]: 206/212 Lift std rocker: .480/.488 LSA:112

Feels like the second cam is the better choice. I do not know how to read cam numbers very well but I do understand some. I do not understand how the ramjet has a higher duration than the XR258HR but then has a smaller .50” duration than the XR258HR.
 

slowburb

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Those images look like fake news to me. Seriously.

There is a LOT more to identifying a cam lobe than using the advertised duration vs. duration at 0.050", but it is intended to *help* determine the overall shape. What you're looking at are numbers to determine the lobe ramp intensity or "steepness" of the lobe. The GM cam has more of a gentle, gradual ramp, while the comp cam has a steeper ramp. Generally speaking the steeper the lobe the more power, but with a trade off for valvetrain noise and longevity. This is scraping the surface of camshaft design theory. If you want more explanation, let me know.
 

rangrayy

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It’s just a computer simulation. I’m not the type that’ll put in that cam and automatically say, “yeah I’m getting 310hp and 485ftlb of torque because a computer told me so.” There are variables I bet the software doesn’t even consider when it makes its predictions.

What you explained makes sense which makes sense why the ramjet would be the best choice. Spreading it out over the curve, if that’s the correct term.

Share the knowledge if you feel inclined to.
 
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