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Well, I am not normally this type, but I don't have that much experience in the high compression NA realm. I've done quite a bit of research, but I can't seem to find exactly what I am looking for.
Other Items:
Primarily e85 (occasionally 93oct)
Ported Factory Intake Manifold w/VCM OTRCAI
3200-3400 Stall
6L80E Trans
3.45 Gears
Currently undecided on the camshaft, but I have reached out to a few notable folks for input. I realize I would most likely be leaving quite a bit on the table with the 821 heads, but I can't seem to find out exactly how much. Trying to stay away from spending more money on aftermarket heads unless there's a substantial amount of power being left on the table.
Option:
Just install a BTR Stage 3 cam kit in the L76 and save this 403ci engine for another build, installing a set of WCCH 245 cathedral port heads and a Fast102/NW102 setup I have on the shelf.
Questions:
How much power do you think the 821 combo would make?
How much power do you think the WCCH 245/FAST102/NW102 combo would make?
What chamber are you going off of to get 12.0CR? I can give you something similar I did for a customer (408) I sent my 821's over to FED to run their stage 1 CNC port, had them milled down to 64cc with a .040 gasket 12.6:1CR, Cam Motion (Steven) Spec cam on E85 it made 553whp through a 4L80E with a lock up converter. Same build but with FED's new 11* LS3 heads I gained a nice amount 593whp
What chamber are you going off of to get 12.0CR? I can give you something similar I did for a customer (408) I sent my 821's over to FED to run their stage 1 CNC port, had them milled down to 64cc with a .040 gasket 12.6:1CR, Cam Motion (Steven) Spec cam on E85 it made 553whp through a 4L80E with a lock up converter. Same build but with FED's new 11* LS3 heads I gained a nice amount 593whp
Thanks for sharing those results! Do you think the stage 1 CNC port really contributed much in the grand scheme of things? I am thinking the milling played a larger role in the power, but I could definitely be wrong. Did you go with the same combustion chamber size with the FED heads? Same cam grind too?
Anything above 520rwhp and a decent torque curve would be awesome. I wonder if the 6L80E is more or less efficient than a 4L80E.
I was using the stock 70cc chambers in the calculation and used 0 deck despite the fact most stock motors come in ~.005" out of the hole, which would raise the compression slightly. Did the SCR seem high? I might have to drop to dish pistons if I mill the heads in order to stay closer to 12:1.
I called Cam Motion earlier today, but I guess they were busy since I never received a call back. They are just up the road from me, and I've used them on a few builds in the past. Great grinds and customer service.
Edit: do you recall which intake manifolds were used?
Last edited by RacerBill; Jan 3, 2020 at 07:45 PM.
What chamber are you going off of to get 12.0CR? I can give you something similar I did for a customer (408) I sent my 821's over to FED to run their stage 1 CNC port, had them milled down to 64cc with a .040 gasket 12.6:1CR, Cam Motion (Steven) Spec cam on E85 it made 553whp through a 4L80E with a lock up converter. Same build but with FED's new 11* LS3 heads I gained a nice amount 593whp
if you don't mind me asking, what were the cam specs/intake used on those motors. Thanks!
Thanks for sharing those results! Do you think the stage 1 CNC port really contributed much in the grand scheme of things? I am thinking the milling played a larger role in the power, but I could definitely be wrong. Did you go with the same combustion chamber size with the FED heads? Same cam grind too?
Anything above 520rwhp and a decent torque curve would be awesome. I wonder if the 6L80E is more or less efficient than a 4L80E.
I was using the stock 70cc chambers in the calculation and used 0 deck despite the fact most stock motors come in ~.005" out of the hole, which would raise the compression slightly. Did the SCR seem high? I might have to drop to dish pistons if I mill the heads in order to stay closer to 12:1.
I called Cam Motion earlier today, but I guess they were busy since I never received a call back. They are just up the road from me, and I've used them on a few builds in the past. Great grinds and customer service.
Edit: do you recall which intake manifolds were used?
Stage 1 FED port on the 821s I saw a gain of 32whp/18rwtq over stock heads so worth a decent amount IMO. Yes both Stage 1 821s and their M311 shared the same chamber of 64cc and same cam.
Personally I feel the 6L80E is more efficient than the 4L80E.
Stage 1 FED port on the 821s I saw a gain of 32whp/18rwtq over stock heads so worth a decent amount IMO. Yes both Stage 1 821s and their M311 shared the same chamber of 64cc and same cam.
I wonder how much of the power gain on the modified 821 head was attributed to the milling or the porting. Are you saying the completely stock 821 heads made 521 rwhp? If so, I might just mill the heads, slap on some .040" head gaskets, and target 12:1 with a different piston then expect a little less power from using a stockish intake manifold. The increased power of the 403 stroker over a cam only L76 should be worth my time.
I ran a port match high ram 102mm.
I was afraid you'd say this. Again, I wonder how much a factory ported manifold would choke this setup.
Is anyone foolish enough (besides me) to build a higher-ish compression 402-408ci engine and use stock 821/823 heads?
Built a buddy a 416ci motor with stock LS3 heads/intake/TB running 1 3/4" long tubes and dual 2.5" exhaust, T56 Magnum, alum flywheel/McLeod RXT, 335/30/18's on 91 octane it made 560rwhp with a BTR Stg3 cam on a Dynojet. I'm guessing a 402 would make 25rwhp or so less with the same combo.
Built a buddy a 416ci motor with stock LS3 heads/intake/TB running 1 3/4" long tubes and dual 2.5" exhaust, T56 Magnum, alum flywheel/McLeod RXT, 335/30/18's on 91 octane it made 560rwhp with a BTR Stg3 cam on a Dynojet. I'm guessing a 402 would make 25rwhp or so less with the same combo.
Nice! Recall the SCR?
I'd say you're pretty close on the power difference, and it will be less than that too since this is going to be paired with an auto.
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403ci with 821 Heads 
593whp 
