M1 or Port-Matched LD4B on 408

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MuuMuu101 said:
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.
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It sounds like the LD works. I mean, there probably aren't many small blocks out there with that particular intake making anywhere near 523 HP. As I understand it, intakes with small runners increase the velocity of the A/F mixture going through the intake tract which translates into more torque. Not sure what an AG would gain you, maybe a few HP? It is fun to swap parts though, can't hurt to give it a shot.

MuuMuu101 said:
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.
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Have you tried a different carb to see if the symptoms are the same? Not something random but a known good running carb. Might be worth a try, easy enough to do.

Or, take a big swing at something and adjust a parameter to the edge of spec to see if it has an effect one way or another.

Sorry if I missed it but do you have an A/F gauge hooked up? They can help make the tuning process go quicker.
 
rmchrgr said:
It sounds like the LD works. I mean, there probably aren't many small blocks out there with that particular intake making anywhere near 523 HP. As I understand it, intakes with small runners increase the velocity of the A/F mixture going through the intake tract which translates into more torque. Not sure what an AG would gain you, maybe a few HP? It is fun to swap parts though, can't hurt to give it a shot.

Have you tried a different carb to see if the symptoms are the same? Not something random but a known good running carb. Might be worth a try, easy enough to do.

Or, take a big swing at something and adjust a parameter to the edge of spec to see if it has an effect one way or another.

Sorry if I missed it but do you have an A/F gauge hooked up? They can help make the tuning process go quicker.
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I just figured an Airgap would be more useful to me than an M1 if I were to use it on a different engine not this engine in particular. Or, I'll just sell the M1 intake. I think I'm going to leave the LD4B as is.

For the engine I have now, I don't have a spare carb and honestly, I'd have to teach myself how to tune one. This car in particular, I'm hesitant to change anything, like a carburetor tune, because I hate having down time on it if I do something wrong, which I will probably do. Right now, I don't really have any time to invest on working on the car as I just bought a house and have to do some work to it and I'm getting married in February.
 
It would be interesting to see the flow numbers between the Air Gap and the LD4B.
 
MuuMuu101 said:
I had a manual choke on it and it was sticking causing serious drivability problems. So I removed it and left it wide open.
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Well dang dude, if that don’t sound like the problem right there....
Did you enrich the carb after the choke was removed?
 
MuuMuu101 said:
I had a manual choke on it and it was sticking causing serious drivability problems. So I removed it and left it wide open.
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Put it back on and fix the sticking. That's the correct thing to do.
 
My 367 requires no choke at all at 50-90 Ambient. My 750DP has never had a choke on it, I bought it from a friend in 78 without one.
Yeah the low-speed is a little fat, that's what it takes to idle down to 550 warmed up at 5 to 7 degrees advance, so I can drive it at 4 mph, with a 230 cam in first gear.
At 50*ambient, and 14* idle-timing, it will take a few blips to load the AirGap up, and then I can back out of the carport,and drive away. The aluminum heads take about 3 miles to warm up, or maybe it's the AG, whatever, and then I can see the SpeedO pick up a few mphs.
 
AJ/FormS said:
My 367 requires no choke at all at 50-90 Ambient. My 750DP has never had a choke on it, I bought it from a friend in 78 without one.
Yeah the low-speed is a little fat, that's what it takes to idle down to 550 warmed up at 5 to 7 degrees advance, so I can drive it at 4 mph, with a 230 cam in first gear.
At 50*ambient, and 14* idle-timing, it will take a few blips to load the AirGap up, and then I can back out of the carport,and drive away. The aluminum heads take about 3 miles to warm up, or maybe it's the AG, whatever, and then I can see the SpeedO pick up a few mphs.
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Now that your bragging about it, did you jet it properly after you removed the choke?
(Your not helping)
 
That's not a brag.
There is so much information in that one short post, mostly contrary to the accepted party line, that most will dismiss it , just like they do so many other things.
If a person pays attention to what his street-engine is saying, that person could have a carburated engine that runs as good or nearly as good, as any bolt-on EFI system. Let me rephrase that ;You couldn't give me an EFI system to replace my 750DP.
 
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my 360 starts well with a 750 avs and no choke at 30 degrees air temp. not jetted super rich, ld 340 with center divider cut down 1/2" and blocked exhaust crossover. 4 gear manual and 4.30 gear and 28" rear tire. will not idle for about 10 minutes, but I can drive off in about 2 minutes after fire up and go as slow as about 10 mph
 
AJ/FormS said:
That's not a brag.
There is so much information in that one short post, mostly contrary to the accepted party line, that most will dismiss it , just like they do so many other things.
If a person pays attention to what his street-engine is saying, that person could have a carburated engine that runs as good or nearly as good, as any bolt-on EFI system. Let me rephrase that ;You couldn't give me an EFI system to replace my 750DP.
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Sorry to see the thin skin again, but you still haven’t answered the question to my off handed compliment.
Thanks for helping out again.
 
"I have a 408 built by IMM engines. I currently have a port-matched LD4B on it and am making 523 hp @ 6000 rpm and 522 ft-lbs @ 4500 rpm on their engine dyno. I'm planning on installing a Holley Sniper on the car (hopefully before next spring, not sure if I'll upgrade to a Holley EFI Dual-Sync distributor). Is it worth it to replace the LD4B for a Mopar M1 intake (no port work done)? I figure the intake is a big restriction as the LD4B was meant for 273/318's. But how much of a hp/tq increase do you think I'd get? Do you think it will ruin the driveability with the EFI?"


Why not ask Brian what he thinks?
 
TX9 340 Plymouth said:
"I have a 408 built by IMM engines. I currently have a port-matched LD4B on it and am making 523 hp @ 6000 rpm and 522 ft-lbs @ 4500 rpm on their engine dyno. I'm planning on installing a Holley Sniper on the car (hopefully before next spring, not sure if I'll upgrade to a Holley EFI Dual-Sync distributor). Is it worth it to replace the LD4B for a Mopar M1 intake (no port work done)? I figure the intake is a big restriction as the LD4B was meant for 273/318's. But how much of a hp/tq increase do you think I'd get? Do you think it will ruin the driveability with the EFI?"


Why not ask Brian what he thinks?
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You know, I was wondering the same thing.
 
Plenty of people have pulled a dual plane off a 500 hp SB mopar, put on a single plane and slowed down. Just a thought.
 
crackedback said:
Plenty of people have pulled a dual plane off a 500 hp SB mopar, put on a single plane and slowed down. Just a thought.
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How true that is. It’s been said over and over again, printed over and over again, dual planes are best for street & street strip. Single planes are best left for race engines.

Everyone will see a dyno test and fall over themselves to use the single plane because it made 40+ hp more than the dual plane. Then they curse it out for its less than desirable street manors, slower 60’ & crap mileage.

What’s even funnier is when people start to throw stones at the performance under 3500. With the single plane, you should be ignoring it completely because a single plane is only at the beginning of its power band at a Minimum! The camshaft should be matching that rpm range as well.
 
rumblefish360 said:
Nuff said???
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Its not just a simplistic question of Single vs Dual plane, but in the OP specific case,,a TINY dual plane vs proven Single plane and (most importantly) on a 408" with a decent cam making peak hp at 6000rpm.

It's not unreasonable to think a M1 would work considerably better on a 408" in every way WHEN compared to the LD4b. If MUUMUU already had a Performer RPM, that would change everything and I'd strongly side with keeping it as is but not with a LD4B. The LD4b is just too small for that size engine.

Also, I'd often suspect a good part of the "less than desirable street manors, slower 60’ & crap mileage" that the single plane gets the blame for is misplaced. The majority of "issues" after a intake swap could easily be contributed to just poor tuning or most often ZERO tuning whatsoever. BUT add a good self-tuning EFI to the mix and again, that changes EVERYTHING! Again, my M1 with multi port EFI no such issues but it was tuned very well(A/F & timing). But I'd happily admit that when I had the SAME setup running on a 750 AFB, it ran worse in every way. Yeah, it was not the intakes fault lol.
 
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And without a doubt every build is different and has the ability to use different parts with varying degrees of success.
The video I posted is a small 350 and typical of how the two intakes act on engines of THAT size.

I stick by my comments.

myduster360 said:
Its not just a simplistic question of Single vs Dual plane, but in the OP specific case,,a TINY dual plane vs proven Single plane and (most importantly) on a 408" with a decent cam making peak hp at 6000rpm.

It's not unreasonable to think a M1 would work considerably better on a 408" in every way WHEN compared to the LD4b. If MUUMUU already had a Performer RPM, that would change everything and I'd strongly side with keeping it as is but not with a LD4B. The LD4b is just too small for that size engine.

Also, I'd often suspect a good part of the "less than desirable street manors, slower 60’ & crap mileage" that the single plane gets the blame in misplaced. The majority of "issues" after a intake swap could easily be contributed to just poor tuning or most often ZERO tuning whatsoever. BUT add a good self-tuning EFI to the mix and again, that changes EVERYTHING! Again, my M1 with multi port EFI no such issues but it was tuned very well(A/F & timing). But I'd happily admit that when I had the SAME setup running on a 750 AFB, it ran worse in every way. Yeah, it was not the intakes fault lol.
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