408 build, L92's vs. 317's on stock converter
10-24-2011, 03:11 PM
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408 build, L92's vs. 317's
I have a 99 silverado 2500 currently with an LQ9 and a small cam. I am planning on building it up to a N/A 408 but I need some advice on what to do with the heads. This truck will be an around town truck that does occasional towing of a 9000 pound trailer. This is a budget build and the goal is 400rwhp through the 4L80E. I am planning on using the stock converter. I have read about the great numbers being made when using the L92 top end parts but I am trying to decide if its really worth the extra money considering my cam choice and how the truck will be used. If I bolted my current 317 heads and stock truck intake onto the 408 all I would need to make it go would be a new set of injectors. This wont be a drag truck so I was thinking either stick with my stock cam (comp 212/218 114 LSA) or maybe a TSP 224. I probably will go with the 224 as my current cam seems pretty small for a 408. If I were to put the L92 heads and truck intake on this 408 I would have to buy those parts plus a new 90mm cable driven throttle body and whatever else I would need for the fuel system. I want this to be a torque engine with usable power everywhere.
Do you think my current top end parts with the 224 cam or even my current 212/218 cam will allow me to reach my 400 rwhp goal or is it worth it to go with the L92 heads, intake and the 90mm throttle body? If I stayed with my 317's that would save me lots of $$$$ and I could spend a few hundred on having someone port and polish them for a little more power.
Thanks for your input.
Do you think my current top end parts with the 224 cam or even my current 212/218 cam will allow me to reach my 400 rwhp goal or is it worth it to go with the L92 heads, intake and the 90mm throttle body? If I stayed with my 317's that would save me lots of $$$$ and I could spend a few hundred on having someone port and polish them for a little more power.
Thanks for your input.
Last edited by chevy6.0fan; 10-24-2011 at 08:59 PM.
10-25-2011, 11:23 AM
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Just one guy's opinion, but I "think" you'll be out of flow on the 317s long before you get to 400HP on the ground, especially through a 4L80. We have a similar set-up running the LQ9 via 243 heads and a 222/224 cam, 112LSA. It's got a rough idle already and we ran out of oomph at about 350HP to the wheels through a manual.
If you compare the various configurations (even up to the LS2 in a Corvette, running 11:1 compression) it looks like the 317/243 heads with the cathedral ports were designed and modeled to get to airflow sufficient to 400-425HP AT THE FLYWHEEL...
I think it will be much easier to get to your numbers on LS3 style heads-- they are cheap and flow great.
If you compare the various configurations (even up to the LS2 in a Corvette, running 11:1 compression) it looks like the 317/243 heads with the cathedral ports were designed and modeled to get to airflow sufficient to 400-425HP AT THE FLYWHEEL...
I think it will be much easier to get to your numbers on LS3 style heads-- they are cheap and flow great.
10-25-2011, 03:38 PM
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^^ What he said...^^
Running N/A I think the heads really are the bottleneck. It would be a waste to bump displacement to 408 and leave so much power on the table in the heads...
10-25-2011, 07:23 PM
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Sounds like if I want to meet my goal I'm gonna have to just pony up for the L92's. If I go this route I just have a few questions about making it all work on a 99. The fuel rails are different and the truck has a cable going to the throttle body so I will need a new TB and way to make the fuel system work. What do the stock injectors on an L92 truck intake flow? The guy at TSP told me I would probably need at least 36# injectors. If they wont work then I was thinking about picking up some 8.1 marine injectors but I dont know how those would fit on the GEN IV intake manifold.
10-25-2011, 08:18 PM
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in a diffrent note my cousin has a 414stroker with afr's and only did 403 rwhp ... his cam is a 227/233 which we have come to learn that it leaves a whole lot of power in the table
10-25-2011, 08:24 PM
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IIRC, the stock injectors on an L92 intake are 30#. You will need bigger injectors, injector pigtails, Wix fuel filter part # 33737 for the fuel system, and a bracket for a 90mm DBC throttle body. A few other small things, but nothing major. I have an L92 intake complete for sale if your interested. You can also use the LS3 injectors which you can find for cheap, and they are 42#. They do require spacers, but if you do some searching on here you can find the info. Search, Cheap injector mod or something close to that and it will come up. Good luck on your build.
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10-25-2011, 08:27 PM
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this is true but in my unexpert opinion a 212/218 cam also leaves a whole bunch in the table in such bid displacement motor ..
in a diffrent note my cousin has a 414stroker with afr's and only did 403 rwhp ... his cam is a 227/233 which we have come to learn that it leaves a whole lot of power in the table
in a diffrent note my cousin has a 414stroker with afr's and only did 403 rwhp ... his cam is a 227/233 which we have come to learn that it leaves a whole lot of power in the table
10-26-2011, 12:21 AM
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I think some of these low HP issue's are with the combo and tuning. That baby cam isn't gonna work with the L92's. My 370 made 504rwhp, but then again..the L92 head and 6.0 block casting's were the only GM part #'s in it.
10-26-2011, 04:50 PM
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IIRC, the stock injectors on an L92 intake are 30#. You will need bigger injectors, injector pigtails, Wix fuel filter part # 33737 for the fuel system, and a bracket for a 90mm DBC throttle body. A few other small things, but nothing major. I have an L92 intake complete for sale if your interested. You can also use the LS3 injectors which you can find for cheap, and they are 42#. They do require spacers, but if you do some searching on here you can find the info. Search, Cheap injector mod or something close to that and it will come up. Good luck on your build.
Stock LS3 injectors are reputed to be 59#, since the same part number is used on the LSA and LS9 motors to support boost. For Gen IV, GM upsized the L92 and LS3 stock injectors to allow use with E85, which has much higher fuel consumption to maintain stoich.