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So I’m back again. I’ve recieved good advice from here in the past, figured we’d give it another shot.
So my uncle and I are setting up my little brother a new motor for his truck for his graduation gift.
But then we found out his new job was gonna take him to the middle of New Mexico. And the closest gas station with premium gas is almost a 2 hour drive from his house on the ranch. The main gas station he will be using has 87 octane and diesel.
We are trying to figure out if we can build a 6.0 with more kick than a stock one that will run reliably on 87 octane. If we do stock compression, ported heads and ported intake and a bigger cam will that make it non drivable on 87?
Figure out your compression ratio. Keep it at 10:1 or less and you're gold. More, and he'll be buying 91.
Leave the intake alone; it flows pretty well already. Get some 243/799 heads if needed. They came on all the Gen IV 5.3/4.8's, so are easy to find.
Use a drop-in truck cam from TSP or Cam Motion. Keep the durations at 216/220 or less.
Figure out your compression ratio. Keep it at 10:1 or less and you're gold. More, and he'll be buying 91.
you think so?
If it really gonna be that simple? We might be able to get his old lq9 down to that point. I think it’s got milled ls3 heads on it. Full height + ls9 headgasket might get us into the right zone.
Couple that with efi instead of the current carb and we might be in business.
A carb RAISES octane requirement because of the uneven fuel distribution that is unavoidable with carbs. I did not know you were running a carb.
The LQ9 came stock with 10:1 compression, and were rated for 87 octane Regular gas. That low of octane requirement with that much compression is more easily possible with a good fuel injection system.
A carb RAISES octane requirement because of the uneven fuel distribution that is unavoidable with carbs. I did not know you were running a carb.
The LQ9 came stock with 10:1 compression, and were rated for 87 octane Regular gas. That low of octane requirement with that much compression is more easily possible with a good fuel injection system.
I understand the carb messing with stuff. The lq9 in his truck is a 408 now with 10.9:1 I think. It is currently carbed, but will be leaving soon. Won’t be hard to go back to efi. We just have to dig out the wiring harness and a few other fiddly bits. The ecu is still in the truck just unplugged. I need to get all the details to make sure we can make it happen. The spare block for my truck might work as a donor as well. It’s 9.5:1. Overbuilt bottom end, but that won’t hurt anything.
I’ve heard the lq9 in stock form was capable but not happy on 87.
Where in NM? That matter because altitude has direct relationship on cylinder pressures. Some town in central NM are over 6,500' ASL. High altitudes can tolerate a higher compression ratio. At low altitudes, cylinder pressures will go up. And it's generally a lot hotter at lower altitudes, which can also increase your octane requirements.
What you're really interested is dynamic compression, and not just static compression. Dynamic compression includes static compression, cam design, altitude, etc. http://wallaceracing.com/dynamic-cr.php
Where in NM? That matter because altitude has direct relationship on cylinder pressures. Some town in central NM are over 6,500' ASL. High altitudes can tolerate a higher compression ratio. At low altitudes, cylinder pressures will go up. And it's generally a lot hotter at lower altitudes, which can also increase your octane requirements.
What you're really interested is dynamic compression, and not just static compression. Dynamic compression includes static compression, cam design, altitude, etc. http://wallaceracing.com/dynamic-cr.php
It’s his personal daily so it really needs to be able to go from sea level and up.
To be honest I don’t know exactly where he is gonna be. He’s made 3 trips out there, and damn near got stranded the first time.
in my experience that stuff doesn’t work. Adding race gas has worked for me in the past when I was in a bind. That is on the table, he just doesn’t really want to do it. If we do then we can do the old plan.
Doing a Cummins 12v swap is also on the table. 🤮
We think we can get a peppy motor with 87, it’s just gonna take some finesse, and it’ll cost more to do so than with premium.
Any room for a bigger fuel tank? Or another tank on the other side?
‘I wonder what’s the hp tq loss difference in a stock lq9 on 87 vs 93?
you know with a 12 valve swap you’ll get good mpg, torque and can gear it low.
im biased and love 12 valves as I’ve had several in my life
Any room for a bigger fuel tank? Or another tank on the other side?
‘I wonder what’s the hp tq loss difference in a stock lq9 on 87 vs 93?
you know with a 12 valve swap you’ll get good mpg, torque and can gear it low.
im biased and love 12 valves as I’ve had several in my life
Its currently got a 35ish gallon tank, and the other side has his air compressor and air tank and stuff. Some of the question is how much he’s gonna use his personal truck for work.
Thats a a very good question on the lq9. I’d like to know the answer to that.
I have a 12 valve swapped k20 blazer and it’s getting an LS as soon as I find the time to do the swap. It gets about 15 or 16 mpg and has been nothing but trouble for me. Turned up the power and **** started breaking. It was at about 500 hp, and I already have had to replace main bearings and rod bearings. Then the injection pump went out. Then the goddamn dowel pin fell out and destroyed the whole sombitch. I quit at that point. I’ll be putting some LS in it. I’m feeling an LS3.
Not to mention that in my opinion the sounds the 12 valve makes are nowhere near as good as the LS.
01-18-2019, 10:01 PM
Questions about low octane fuel 
