Project LSZ: 799 Problems And Our Heads Are One

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Update by Tom Suddard to the Nissan 350Z project car
Dec 5, 2017

When we tore down our $400 LS1, we discovered some positive things and some negative things. We also discovered a horrible thing: The stock 853-code heads, which are regarded as some of the worst flowing to ever top an LS-based engine. We didn’t quite know what our engine’s destiny would be, but we knew there was no sense in building a stout bottom end and then topping it with terrible heads.

So, we went to the internet for advice. We didn’t want to spend big money on a fancy set of CNC-ported heads, as we’d already used up most of our budget on that beautiful K1 Technologies rotating assembly.

According to the internet, some of the best cathedral port LS heads available have a 243 casting code, and would have originally come on 2001 or newer LS2 and LS6 engines. They have larger intake and exhaust runners and a smaller chamber, meaning more compression and better airflow. The LS6 heads even have fancy hollow-stem intake valves and sodium-filled exhaust valves, along with stiffer valve springs.

There was one issue, though: 243 heads are expensive. Everybody seems to have figured out that these are great-flowing junkyard heads, and we saw prices around $700 for a set. Fortunately, they have a budget alternative: heads with a 799 casting mark are more or less identical, but all came equipped with normal solid valves and normal valve springs. We scored a good used set off of eBay, complete with valves and springs, for less than $300.

And, well, that’s how we learned that it’s important to purchase used parts like this in person. Our used heads had cracks between the valve seats. We returned them to the seller, then turned back to our engine block and continued working. We’ll figure out heads another day.

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NickD UltraDork
2/5/18 3:39 p.m.

5.3L heads can have LS1-sized valves installed in them, and have a slightly smaller combustion chamber that will give a compression boost.

Jerry From LA
Jerry From LA SuperDork
2/5/18 3:40 p.m.

Good to see this one's still moving forward albeit slowly.  What years and models did the 799 heads appear in?


Tom Suddard
Tom Suddard GRM+ Memberand Digital Experience Director
2/5/18 3:47 p.m.

799 heads are from 2005 and newer 4.8 and 5.3-liter trucks.

Patrick GRM+ Memberand MegaDork
2/5/18 3:54 p.m.

FYI the front drive 5.3 engines have 243 heads

noddaz GRM+ Memberand SuperDork
2/5/18 4:15 p.m.

JB Weld for the win!

dean1484 GRM+ Memberand MegaDork
2/5/18 4:49 p.m.

5.3 heads have been a well kept secret for a while.  How do you think you get 400hp from a 5.3 with just a cam change and a carb?  It is all about the stock heads on those being so good.  

Will UltraDork
2/5/18 5:36 p.m.

Been a minute, but aren't the rockers in 5.3 heads better than the LS1 parts?

JBasham HalfDork
3/19/18 12:04 p.m.

I'm loving this project.  But I have to say, I have always thought the reason motor-swappers pay up for an LS engine instead of a Ford was the turn-key package of HP and TQ.  None of that fussing around required with SBF.  This project is making me rethink that.

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