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Hey. I just picked up an L86 6.2 long block. It was a warranty take out for a collapsed lifter. A guy from the dealership had it hid in corner and the guy that I got it from had it hid in a corner for years. When I got it, we took the heads off and took the oil pan off. It looks really good. I see why they were hiding it. It's from a 2018 Silverado. It did not come with the high pressure fuel pump, injectors, or fuel rails. This is what scared off the other two guys. So, here is what I have so far on my 2017 5.3 RCBS. Ported 6.2 intake and throttle body, TSP longtube headers with hi-flow catted y-pipe, K&N CAI, custom tune, and 4.10 gears. What I want to do the 6.2 is, fuel system, TSP Stage 2 or so cam kit, DOD delete, ported heads, LT2 intake, and a matching converter. My truck has the 6 speed transmission, so it will need some upgrades. I want to find an exhaust shop to cut the end off of my y-pipe and make a true duel after that. From what I have added up so far, I am around $6,000 more to invest before I get it installed and tuned. Before anyone suggest it, I don't want a turbo or supercharger. So, here are my questions:
Fuel system for around 500 hp. Do I need an LT4 high pressure pump for this? I hear that these are on like a permanent back order.
Do I need LT4 injectors or will stock L86 work with this power level?
Do I need to upgrade my low pressure in tank pump?
Is the LT2 intake really much better than the ported L86 t.b. and intake?
The LT2 intake and and LT5 throttle body seem to be that way to go. Pros and cons?
What are some good parts for the 6 speed transmission?
Thanks in advance for some insight on this swap. I did a search and I searched the internet, but I really didn't find much at all for what I am trying to do. Cheers.
Kevin
Hey. A hundred views and no answers. No worries, I will answer my own questions and maybe it will help some people in the future. Here we go:
“Fuel system for around 500 hp. Do I need an LT4 high pressure pump for this? I hear that these are on like a permanent back order.”
Answer is, no. The stock LT1/L86 fuel system will accommodate around 550 NA horsepower to the rear wheels. I got this info from watching about 25 dyno runs, mostly on Camaros, as there are just a few on 500rwhp trucks. Also learned that even a 10% fuel lobe isn’t needed at this level unless you are using E85. And yes, the LT4 hp pump is almost impossible to find and it’s rediculesly
expensive.
“Do I need LT4 injectors or will stock L86 work with this power level?”
No. stock L86 injectors are fine at this power level.
“Do I need to upgrade my low pressure in tank pump?”
This is interesting. At sustained higher rpm runs, the stock in tank pump might not be able to keep the high pressure pump satisfied with the 75or so psig that is required. More on this in my conclusion.
“Is the LT2 intake really much better than the ported L86 t.b. and intake?”
No apples to apples comparison here. I already have a ported L86 intake and throttle body on my 5.3 and it works great. On the dyno videos that I have seen, it’s worth almost 10 hp and doesn’t really loose any torque. For the LT2 intake, it seems to just be about looks. That is, if you also buy the plastic cover. It’s the classic gain 10hp at the very top of the rpm range, or loose 10 lbs/ft of torque in the midrange. On the topic of the LT5 95mm throttle body, well, the LT2 intake apparently can’t be ported to that size because there isn’t enough material at the port entry. Also, the adapter that is needed is also necked down and is not 95mm by the time it enters the port. Also, I heard a guy quote the CFM requirement for the LT1 engine and this power level, and it is well within the range of the LT1/L86 throttle body. Now I don’t know who this guy is, so I won’t quote his numbers, but the GM engineers figured it out and I should go with them.
“What are some good parts for the 6 speed transmission?”
I am just going to run it until it explodes. The cam that I will be using uses the stock converter and when the transmission dies, Sonnex and others will come to the rescue.
So, in conclusion, I am just going to buy all brand new L86 fuel system components. I am going to order my cam with the 10% fuel lobe and if tuning shows that I need a little more fuel up top, I will upgrade the in tank pump. I am also going to upgrade the front cover so I can use a 3 bolt cam. I still might get the LT2 intake and LT5 throttle body and port it all to make it work. I already have 4.10 gears in a single cab short bed truck so I could miss a little midrange for an extra 10hp on top. All that being said, I have learned that the fuel system is good at 500hp, but it gets very expensive above that. I really like the LT series of engines as they run really well right out of the box. My daughter has a 2018 Redline SS and that car is just fast. I have a 2001 SLP SS with an LS7 and, well, that’s faster.
Funny. It stands for Regular Cab Bed Short. You’re probably more familiar with Regular Cab Short Bed. The RCBS is a far more elusive creature…..
(you did …..didn’t you?)
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L86 6.2 N/A Build for 2017 RCBS 
