rice0209

LT4 Hotcam in 5.7 Vortec

11 posts in this topic

Anyone have any experience with the LT4 hot cam and the 5.7 vortec?

 

I have started my search for a vortec 350 that i can rebuild all the way up a) for the experience, b) because i've always wanted to completely rebuild an engine, and c) because i love my ZR2 and want to give it more power as it retires to a 3rd vehicle for us. While i have this engine on the stand, i want to do the hard work now, and not later, so cam is one of my main concerns as i plan this out.

 

It will be used as a daily driver for a couple more years (lots of interstate driving), and then it will be a utility vehicle / 3rd vehicle. Home depot runs, occasional small trailer tow when i go to the sand dunes. Again, I love my Z and want to also use it as my hobby vehicle.

 

From what i researched, i don't look to lose any torque with the LT4 hotcam kit (1.6 rockers, etc) and might possibly increase torque through out the rpm range as well as signicantly increase horsepower, especially in the upper rpms. What do you guys think about this cam and a ZR2 350 swap? Good idea? Bad idea?

 

Also, i am reading that you can get beehive springs and comp cam retainers that require no machining to the heads, but does going with the beehives sacrifice anything versus doing the machining and putting in the lt4 springs that come in the LT4 hotcam kit? is one better than the other, because generally shortcuts come at a sacrifice of something.

 

Thanks in advance for your help!

 

Chris

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If you are going for full rebuild wont cost much more to have the heads machined to accept the LT4 springs. And if you don't want to run into any kind of problem i suggest you do the head work and do it right the first time.

 

As for the cam exp. i have never ran one but would expect a little loss of power and torque down low where you need it most. I bleive that cam is spected at around 1700-1900 to 6500 you realy need a cam that is around 1200 to give you the power where a truck needs it at.

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I think it really depends on how you will be using the truck the most. From what I have read, that cam has its best power in the mid-RPM range as already mentioned. So you'll need more stall on the converter, which generates more heat = not ideal for towing. I have heard lots of people using the 1996 LT4 cam with good results..

 

Or, build yourself a 383 if you want good HP/TQ like the HT383E GM has for replacing L31 blocks. Then just use the Ramjet 350 cam.. :)

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Here is a table that shows the increase of HP and Torque from a ZZ4 engine to the LT4 hot cam equipped "ZZ4".

 

Now I don't know how an L31 Vortec truly compares to the ZZ4. I know the heads are aluminum, so lightly less in weight, and the ZZ4 i believe already has 1.5 rockers. I am sure it generates a little more horsepower.

 

My thoughts are, even if the L31 is a step down from the ZZ4, if I can achieve similar increases in horsepower and torque through out the rpm range, than there really is no loss for me.

 

But the torque converter does bring up a good question. What do you guys think after looking at this chart? Do you think a similar trend (increase in HP and TQ) would occur in taking an L31 vortec, putting in the hot cam kit which includes 1.6 rockers, LT4 springs, and also adding the GM Perf Parts roller lifters? I am not really looking to match the numbers on the chart exactly as i am sure there are enough differences in the L31 and ZZ4, but if the cam has increases similarly across the rpm range, i think that would be a great upgrade. BVD80, I know you said the torque converter might need to be changed. Given the info in that chart, do you think its reliable enough to use in assessing the stock Sonoma TQ converter and if it will work after the cam change out?

 

Cam Chart - ZZ4 to LT4 hot cam kit - from GMPP catalog

 

http://www.cis.udel.edu/~davis/z28/buildup/cam/

 

Thanks again guys!

 

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Oh yeah, also, as far as how i use the truck most, i have to be honest, this will be a daily driver. My drive is mostly interstate, 70mph to 80mph speeds. Both my home and work are within a mile or so of the interstate so not a whole lot of stop and go at all.

 

Other than that, I do my cruising between home depot and auto parts places and what not. As i said above, i may pull a small trailer, maybe once a year, and may haul heavy loads in the bed like when doing landscaping and stuff like that, but the majority of the time, the truck will not be hauling or towing anything and will be just me, wanting a truck that has plenty of power, puts me back in my seat a little, and most of all, doesn't give me crap when i am on interstate, hit a long drawn out hill, and my truck acts like it just had a 5000lb trailer hitched up. The headers, high flow cat, borla exhaust, cold air intake, TB spacer, etc helped to smooth out my power, but its still not enough.

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There is definitely a difference between a ZZ4 and L31. The ZZ4 has a 10:1 compression, aluminum 58cc heads, different fueling/intake and uses a carburetor.

 

I'm still thinking that might be too much cam for a heavier truck. The duration is rather high at 218/228 and that means the power-band is up much higher to get good power. It might be nice for a while, but I think it will get really old. From that chart, it looks like it starts making a difference in power over the ZZ4 at 3K+ RPMs. You may have to get a converter close to 3K also to match that cam. I'm no expert on cams, but that's my take on it.

 

I think its best to find a cam that gives you some serious torque throughout the RPM range. That will give you the ability to tow when needed and throw you back in your seat when needed also :) The V6 is a joke in these trucks. I even think a stock L31 is not enough :wow:

 

 

 

I'm sorta in the same boat as you right now. I'm wanting to upgrade my cam, but keep it reasonable too. I thinking I'm going to use the Ramjet 350 cam (already have 2 of them!), Comp Beehive springs, retainers and possibly 1.6 roller rockers..or just use my 1.52 roller rocker I have already. The stock L31 cam is just not enough and loses power as RPMs go way up.

Edited by bvd80

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The stock L31 cam is just not enough and loses power as RPMs go way up.

 

Ain't that da troof !!

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Yeah, I know i definitely don't want to leave the stock cam in. This whole engine will come completely apart so i want to make good changes while its easy to do so. I am starting to look into the ramjet cam and try and compare it to the other cams i have looked at.

 

I really like the idea of a gmpp cam going in. I don't have anything against many of the other cam or cam companies, but most of these GM cams have been put in plenty of engines and are very proven.

 

With that said, i welcome any suggestions on a good cam that will develop power throughout the rpm range as I do the majority of my driving on interstate, but i don't want something that doesn't have any low end power.

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Yeah, I know i definitely don't want to leave the stock cam in. This whole engine will come completely apart so i want to make good changes while its easy to do so. I am starting to look into the ramjet cam and try and compare it to the other cams i have looked at.

 

I really like the idea of a gmpp cam going in. I don't have anything against many of the other cam or cam companies, but most of these GM cams have been put in plenty of engines and are very proven.

 

With that said, i welcome any suggestions on a good cam that will develop power throughout the rpm range as I do the majority of my driving on interstate, but i don't want something that doesn't have any low end power.

 

 

 

Yeah, that stock cam sorta sucks for mid-higher RPMs. Now, I am not sure how much more power a Ramjet 350 cam will make, but it can't be any worse that the stock one, for sure. I think I'm gonna use it, mainly because I already have one and its a GM product that's proven itself already. Then I'll use the Comp 26915 Beehive springs, 787 retainers and 648 valve locks.

 

Seems like most people with L31s are using either the 1996 LT4 production cam, LT4 Hot cam, ZZ4 cam, or some form of Comp cam.

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The biggest thing you need to keep in mind that this is a truck and it will be used as such. The LT4 Hotcam is a hot-rod cam. It has high rpm power and that cool factor with a somewhat choppy idle. I had debated about using it in my build, but it really doesn't make sense for a daily driver. Even though my Blazer is no daily anymore, I still thought it through and went with a truck cam for practicality. Several manufacturers make truck cams that produce good torque.

 

I ended up building a 385 cu in stroker and used the gm cam out of their HT383. That along with 1.6 roller rockers seems to work well. Now if I could just get everything buttoned up and the bugs worked out maybe I could get out there and enjoy it a little.

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I ran the "Hot Cam" in my LT4 powered-Z28. That cam likes to rev, and REALLY picks up around 2500RPM.

 

It's a pain in the dick to tune too....

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