What did you do to your NBS GMT800 Tahoe/Yukon Today?

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Walchit

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Well, dammit.

You gonna do any work to them heads? They're actually a bit of an underdog and just need some mild porting and maybe some stock intake valves from the 799/243 heads. Good for low- to mid-range torque.

I was just lapping these valves in now. I'm a complete noob, and did a little research on porting and decided against it. Mainly because I thought these were designed more for torque, and I didnt wanna mess anything up.

This lap look alright? I also had found conflicting info on valve lapping so I just went for it, lol
 

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Scottydoggs

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I was just lapping these valves in now. I'm a complete noob, and did a little research on porting and decided against it. Mainly because I thought these were designed more for torque, and I didnt wanna mess anything up.

This lap look alright? I also had found conflicting info on valve lapping so I just went for it, lol
looks good to me. i went and used a drill to lap em in a older engine i freshened up. ported the heads too. something ill never do myself again. way to much work and time. id rather just pay for it. ported heads dfone.jpg
 

Rocket Man

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looks good to me. i went and used a drill to lap em in a older engine i freshened up. ported the heads too. something ill never do myself again. way to much work and time. id rather just pay for it. View attachment 367512
I agree on the porting. I still remember how much work I put into a set of 427 Cobra Jet heads for the 460 Ford I was building for my boat and that was 40 years ago. I’ll never do it again. :mad:
 

Scottydoggs

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I agree on the porting. I still remember how much work I put into a set of 427 Cobra Jet heads for the 460 Ford I was building for my boat and that was 40 years ago. I’ll never do it again. :mad:
sad part is i actually did a good job. that was for a blown 3800 v6 that i used a na bottom end with. most top swaps as they call it make 8 psi min on the stock blower pulley, i was making 6 psi. less boost= more flow. ended up putting 13 psi through it after a ic and a 2.8 pulley.
 

Rocket Man

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sad part is i actually did a good job. that was for a blown 3800 v6 that i used a na bottom end with. most top swaps as they call it make 8 psi min on the stock blower pulley, i was making 6 psi. less boost= more flow. ended up putting 13 psi through it after a ic and a 2.8 pulley.
I ended up putting a Weiand blower on that engine but I had a friend help with it. I was out of my knowledge zone by that time. I have no idea how much boost or HP it was throwing down but somebody told me at the time it should bave been about 800-900 tq and 1000hp. I was in my early 20’s and drinking and drugging heavily. I only got to run it with the blower for one summer because I lost pretty much everything due to my bad habits. My truck was zebra striped so the popo would know I was a habitual offender and pull me over on sight. My license was taken for 7 years. The boat sat at my sisters and there must have been water left in the block over that winter because it cracked; all the freeze plugs were blown out. But that was one fun summer. That jet boat would literally jump out of the water and onto a plane instantly, threw 100’ rooster tails. I even got a ticket for recklessly endangering in it by the marine police but when I went to court they didn’t even know what to do with a marine ticket so it was dismissed. Back then you could drink and drive on the water too. Since cell phones weren’t even invented back then, the only pics I had were actual pics that I kept in an album. I lost all my belongings a few times during those years including all my pictures. All I have left are memories and a lot of those are pretty hazy lol. I lived pretty hard and fast during my younger years, I was pretty wild. :cool:
 

Walchit

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I think I did it boys!
@Scottydoggs I used the suction cup on my drill, Idk if I went too far, or not enough, or just right. I guess we will see.
@Rocket Man I've lost a good amount of shit due to drugs and alcohol also, nothing that bad ass though.
 

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Scottydoggs

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I think I did it boys!
@Scottydoggs I used the suction cup on my drill, Idk if I went too far, or not enough, or just right. I guess we will see.
@Rocket Man I've lost a good amount of shit due to drugs and alcohol also, nothing that bad ass though.
once you see the sides of the valve and the valve seat are both a polished match your all set. your pic looked perfect.

i closed the chuck on the top of the valve and pulled on it lightly. slow and light pressure.
 

Walchit

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I'm gonna regret starting this in a few hours I bet...
Practiced on one of the rockers I got the other day, and the cast iron pan didn't break! Lol
 

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iamdub

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I'm a complete noob, and did a little research on porting and decided against it. Mainly because I thought these were designed more for torque, and I didnt wanna mess anything up.

Better safe than sorry! Are those the heads you got for $50? Are you sure they're not cracked or warped?


This lap look alright? I also had found conflicting info on valve lapping so I just went for it, lol

As the others said, you're good. You've got a lot of matched surface there
 

Walchit

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@iamdub
No these are the heads that came on the used engine from the junkyard, 294k, pressure tested at the machine shop. I only got those other heads because I thought I was getting an updated valve cover. Lol

I gave up on cleaning these rockers and putting the trunions back in.
 

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