Next gen 8100 V8 - Page 2

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Thread: Next gen 8100 V8

  1. #16
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    Quote Originally Posted by Sierra12 View Post
    That's true, and that leads to the question of a tall deck LS/LT.
    now that’s another option if say the deck height is raised to 10” or 10.2” like the old truck blocks. You might be able to swing a 4.25” or 4.5” crank in something like that and set the rpms lower than 5,000 rpm for added durability.

    I’d be looking at higher lift out of the cam and valves, at lower rpms, a longer valve and springs can be used to make it reliable at that rpm range, a bit like what the Ford 7.3 is doing.
    Last edited by jpd80; 10-08-2019 at 05:21 PM.

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  3. #17
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    Re: Next gen 8100 V8

    Quote Originally Posted by ogg vorbis View Post
    I'm more lucid when I'm NOT posting at 5am I did some more math.

    I'm not a fan of just throwing LT1 heads on a larger engine and calling it a day. The intake pumping losses are OK for the 7L, but the exhaust pumping loss goes through the roof. I can tell the Ford 7.3 uses similar size valves because the torque curve is a mountain instead of a flat line.

    A 7L calls for 2.126" x 1.71" valves. That might not fit in a 4.065" bore, and a 4.125" is not great in a standard deck block. Not a good engine.

    A 7.4L calls for 2.19" x 1.77" valves. 430 bhp @ 4900, 525 lb*ft and 415 lb*ft @ 1500 (although I'd gladly give up 25 peak torque for 20+ low end torque). Another route is a small block with 4.6" bore centers and 9.5" deck. 4.25" bore x 4.0" stroke. It gains a fraction of an inch in every dimension. The optimal external size and weight for the displacement. The LT can't grow this big, and small bore is a waste for a BBC.
    Any LT based HD engine larger than the 6.6L will have to be a RB (Raised Block) or "Tall Deck" with the 4.065" Bore to maintain the durability and think that 7.2L (4.25" Stroke) would be the realistic Maximum since using a 4.185" B Siamese Block and 4.25 S would not have enough cylinder cooling for HD use. The 7.0L makes the most sense since GM already has the Forged Crank with the 4.125" Stroke that should be strong enough for HD usage and deliver power numbers similar enough to Ford's 7.3L to be competitive.

    Think a new "Big Block" would have a Bore/Stroke Similar to Ford's 7.3L 4.22" B x 3.976" S and think the LSX 7.4L 4.25" B x 4.00" S would be the one used for 2500/3500/4500 and go to 4.25" B x 4.37"S for 8.1L Engines that would be more for Commercial use. The larger Bore provides enough room for the valves without creating too much added Bore friction.

    Think it will matter how much GM is willing to spend on a HD engine larger than the 6.6L and don't think they would use the old 8.1L Block to base it on, but could be an option. Not sure how "Modern" (Size/Weight/Strength) the old 8.1L Block is in relation the Ford's 7.3L. If GM could use Modern casting techniques on the block and add "LT" Heads modified for "HD Truck" use then it would be a viable option.

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