M1 or Port-Matched LD4B on 408

rmchrgr said
If the LD4B is making 523 HP and 522 ft lbs of torque, KEEP IT! My 416" motor has more Ricky Racer go-fast parts but makes less power and torque than your milder 408.

Switching to the single plane will essentially move the usable RPM band up which IMO makes little sense for street driving and road courses. Drag racing, yes but because that's only WOT. Can't vouch for your driving style but you generally don't stay at WOT for long periods on the street or road courses. Having more torque available at a given RPM would be of more benefit.

Staying with the LD or any dual plane will theoretically keep the torque peak in a more usable RPM range. Maybe an LD340 or as suggested already an RPM Air Gap would be what you want? The AG gives up very little on the top end, probably be a better choice over an M1.

Torque benefits you most coming out of turns, the car will accelerate quicker at a lower rpm and would be easier to rev match. Don't think you want to slow for a turn then alternately have to zing it to 7 grand to get to where the torque starts coming on.

Sniper - I had mistakenly thought that EFI on a dual plane was a no-go becuase of fuel distribution issues but I was corrected on that by a well-known builder. If the combo does OK with the dual plane and a carb, it will be fine with EFI.

Maybe I'll post an ad sometime asking if anyone wants to trade for an RPM Airgap. I honestly don't see what I need the M1 for unless I was doing a turbo build or drag racing as you said.

AJ/FormS said
Jus thinking
5 to 6 seconds gets you 60 mph.
300/350 is more power than most street chassis can handle. From zero to 60, you will only pass thru the power peak once, and in all likelyhood will be roasting the tires at WOT. So on the street, pick one with nice manners for cruising 30mph in Drive at like 1200 or something,lol.
But you didn't build your combo for street, yet you say 50% street, so, it kind needs to be civil.
The LD4B is already port matched.

5 to 10 minutes warm up, at what ambient.
I agree that the street tune in the 850 might need some help. She might need a bit more fuel from the transfers and a little less idle timing, to get the rpm back down. Yeah I'm guessing.

I'm pretty mellow on the streets. On the freeway I try to cruise at 60 mph in 6th gear.

Anywhere between 50-90F.
Everyone says that, but I've had two people look at it and set the carb and timing exactly the same. She idles at about 850 RPM. She just dies if you try to move her before the water temp reaches 150F. If water temp is around 150F and I am at a stop sign and try to slowly ease from the stop, the car wants to die. She runs at 190F all day and doesn't have any problems once at temp. That's the reason for wanting to go EFI.