Any MPG Fans here??

L31MaxExpress said:

If I were purpose building an engine for fuel economy it would likely be a L99 4.3L Gen II engine. I would stroke it from 3" to 3.875" using a 6" rod. 3.765 x 3.875 bore and stroke for 345 cubic inches. Small bore limits the amount of timing needed and helps prevent detonation at high static compression ratios. Then it would get as much compression as physically possible and a smallish camshaft. Then I would use the aluminum LT1 heads milled down as far as possible. I would run it with a GenIV computer backed to a 6L80E automatic and 3.08 rear gear. The intake manifold would be a dual plane MPFI setup with a 90mm DBW throttle body on top. Small 1-1/2" primary Tri-y headers to optimize low-midrange torque production. For those that know GM well that is very close to the bore/stroke of a Buick 350 and those engines were well known as producing noticeably more torque than the 350 SBC. I did the tuning on a TBI swapped Buick 350 in an old Jeep Wagoneer (factory engine for that Jeep) and it had loads of low-midrange torque. That Buick 350 would spin 37s in 4 hi on dry pavement. That Jeep later had a 4L80E swapped into it and even on 37s the 350 chugged along at 70 mph effortlessly at 1,850 rpm.

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tayto said:

was there any marine dual plane intakes that had multiport but the regular SBC intake bolt pattern, NOT vortec? i was thinking about going TPI on my squarebody, but would rather keep the stock traditional air cleaner if possible.

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L31MaxExpress said:

I have seen some traditional pattern MPI intakes, but never really paid attention to which ones. Those engines had the 72* angle center bolts like a TBI head.

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L31MaxExpress said:

If I were purpose building an engine for fuel economy it would likely be...

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Erik the Awful said:

You won't.

Sorry, couldn't help it. @618 Syndicate is a bad influence.

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L31MaxExpress said:

If I were purpose building an engine for fuel economy it would likely be a L99 4.3L Gen II engine. I would stroke it from 3" to 3.875" using a 6" rod. 3.765 x 3.875 bore and stroke for 345 cubic inches. Small bore limits the amount of timing needed and helps prevent detonation at high static compression ratios. Then it would get as much compression as physically possible and a smallish camshaft. Then I would use the aluminum LT1 heads milled down as far as possible. I would run it with a GenIV computer backed to a 6L80E automatic and 3.08 rear gear. The intake manifold would be a dual plane MPFI setup with a 90mm DBW throttle body on top. Small 1-1/2" primary Tri-y headers to optimize low-midrange torque production. For those that know GM well that is very close to the bore/stroke of a Buick 350 and those engines were well known as producing noticeably more torque than the 350 SBC. I did the tuning on a TBI swapped Buick 350 in an old Jeep Wagoneer (factory engine for that Jeep) and it had loads of low-midrange torque. That Buick 350 would spin 37s in 4 hi on dry pavement. That Jeep later had a 4L80E swapped into it and even on 37s the 350 chugged along at 70 mph effortlessly at 1,850 rpm.

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0xDEADBEEF said:

I would go square or over square because of more efficient pumping.

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L31MaxExpress said:

I would want under square for the low speed torque increase from Idle to ~2,000 rpm. Think Chevy 292, Ford 300 or Oldsmobile 455.

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