Air distribuiton in LT1 intake
Thread Starter
Banned
Joined: Aug 2001
Posts: 3,505
From: looking for a flow bench so Brook and I can race
Air distribuiton in LT1 intake
I was thinking (and this could work well with my good)
the LT1 intake has some serious air distribution problems (well from what i've been told)
Two things-
first thing being the one i've thought about for more than 15 sec
get 2 junk intakes and an extra TB (anyone care to donate
)
but the front off one--
weld it to the top of another so the TB is on the top of the intake.
woudl this not help equalize the air discipation?
even taking 8runners from TB to the individaul ports maybe??
the second being spraying nitrous throught he rear of the intake-
wheater it be a dry shot through the EGR opening or addicing a second opening, puttin in a TB plate for a wet kit and then "closing" the opening?
yea i know there are fogger system-
but who wants to be ordinary
Challenge everything
Think outside the box
the LT1 intake has some serious air distribution problems (well from what i've been told)
Two things-
first thing being the one i've thought about for more than 15 sec
get 2 junk intakes and an extra TB (anyone care to donate
)but the front off one--
weld it to the top of another so the TB is on the top of the intake.
woudl this not help equalize the air discipation?
even taking 8runners from TB to the individaul ports maybe??
the second being spraying nitrous throught he rear of the intake-
wheater it be a dry shot through the EGR opening or addicing a second opening, puttin in a TB plate for a wet kit and then "closing" the opening?
yea i know there are fogger system-
but who wants to be ordinary
Challenge everything
Think outside the box
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Some thoughts:
On a plenum-type inlet manifold, the throttle body just lets air into a big box (plenum). As the air rushes thru the TB and enters the much larger plenum, it slows down and the pressure increases (or is at least less negative). Mr.Bernoulli explained that to me; I'm very old. Each cylinder has an opening (port) into that box from which it can draw air. There is really no direct flow from the TB directly to each port.
I use the strange cow analogy to visualize how the air gets to the cylinders. Think of a cow with 8 teats rather than 4 (that's the strange part). The udder is the plenum. Now visualize the milking machine getting a squirt out of each one in a 1-8-4-3-6-5-7-2 sequence.
As long as the udder is full of milk, there's not much problem getting enough from each "port". It really doesn't matter too much where the air enters the plenum, or the milk enters the udder; getting it out is the problem.
My take is the LT1 manifold has inlet runners which are just too darn short for decent tuning. They are straight, and can probably be made large enough to flow sufficient air. Making them 2-3 inches longer is the problem, IMO.
I believe the LS1 truck engine breathes from the top because there is hood clearance. Most cars don't have that luxury.
For you urban dwellers, my cow analogy might not be too clear. And no, chocolate milk doesn't come from brown cows. It's brown because it's what's sucked up off the milking parlor floor.
.
.
.
.
.
.
You can stop laughing at my analogy now.
On a plenum-type inlet manifold, the throttle body just lets air into a big box (plenum). As the air rushes thru the TB and enters the much larger plenum, it slows down and the pressure increases (or is at least less negative). Mr.Bernoulli explained that to me; I'm very old. Each cylinder has an opening (port) into that box from which it can draw air. There is really no direct flow from the TB directly to each port.
I use the strange cow analogy to visualize how the air gets to the cylinders. Think of a cow with 8 teats rather than 4 (that's the strange part). The udder is the plenum. Now visualize the milking machine getting a squirt out of each one in a 1-8-4-3-6-5-7-2 sequence.
As long as the udder is full of milk, there's not much problem getting enough from each "port". It really doesn't matter too much where the air enters the plenum, or the milk enters the udder; getting it out is the problem.
My take is the LT1 manifold has inlet runners which are just too darn short for decent tuning. They are straight, and can probably be made large enough to flow sufficient air. Making them 2-3 inches longer is the problem, IMO.
I believe the LS1 truck engine breathes from the top because there is hood clearance. Most cars don't have that luxury.
For you urban dwellers, my cow analogy might not be too clear. And no, chocolate milk doesn't come from brown cows. It's brown because it's what's sucked up off the milking parlor floor.
.
.
.
.
.
.
You can stop laughing at my analogy now.
Registered User
Joined: Feb 2002
Posts: 35
From: Leonardtown, MD
Now that I've stopped laughing over the 'cow analogy' (which was a good explanation for some of us 'rural' types) ...
I think a good point has been made and that is that the LT-1 intake really doesn't affect air flow as much as we would like to think. It really acts like more of a storage chamber for air. The pressure difference between the intake plenum and each cylinder is what determines how much air the engine will consume. Remember, there is a vacuum (or negative pressure) created by the intake valve opening and closing events and motion of the piston in the cylinder. The velocity of the air will be increased if a greater negative pressure difference exists between the cylinder and the intake plenum. Of course, cam timing and lift can help control this pressure difference (but that's another discussion). Assuming the intake plenum is continually supplied air at a rate consistent with what is being consumed by the cylinders, I don't think much can be done to improve the intake by altering the physical location of the throttle body. If it was shown that the throttle body location represented an impediment to the filling of the intake plenum, then there would be a benefit to moving it. But, that doesn't seem to be the case with the LT-1.
Trey, if it was shown that the front cylinders consumed so much of the available air entering the intake plenum that the rear cylinders were suffering, I would agree that your idea would work to help equalize the cylinders. But, I've never seen any data suggesting that to be the case.
Just my 2 cents...
Brian
I think a good point has been made and that is that the LT-1 intake really doesn't affect air flow as much as we would like to think. It really acts like more of a storage chamber for air. The pressure difference between the intake plenum and each cylinder is what determines how much air the engine will consume. Remember, there is a vacuum (or negative pressure) created by the intake valve opening and closing events and motion of the piston in the cylinder. The velocity of the air will be increased if a greater negative pressure difference exists between the cylinder and the intake plenum. Of course, cam timing and lift can help control this pressure difference (but that's another discussion). Assuming the intake plenum is continually supplied air at a rate consistent with what is being consumed by the cylinders, I don't think much can be done to improve the intake by altering the physical location of the throttle body. If it was shown that the throttle body location represented an impediment to the filling of the intake plenum, then there would be a benefit to moving it. But, that doesn't seem to be the case with the LT-1.
Trey, if it was shown that the front cylinders consumed so much of the available air entering the intake plenum that the rear cylinders were suffering, I would agree that your idea would work to help equalize the cylinders. But, I've never seen any data suggesting that to be the case.
Just my 2 cents...
Brian
Registered User
Joined: Oct 2001
Posts: 1,462
From: smog zone adjacent to a great lake
Originally posted by bn_bullet
I think a good point has been made and that is that the LT-1 intake really doesn't affect air flow as much as we would like to think. It really acts like more of a storage chamber for air. The pressure difference between the intake plenum and each cylinder is what determines how much air the engine will consume...... Assuming the intake plenum is continually supplied air at a rate consistent with what is being consumed by the cylinders, I don't think much can be done to improve the intake by altering the physical location of the throttle body.....
I think a good point has been made and that is that the LT-1 intake really doesn't affect air flow as much as we would like to think. It really acts like more of a storage chamber for air. The pressure difference between the intake plenum and each cylinder is what determines how much air the engine will consume...... Assuming the intake plenum is continually supplied air at a rate consistent with what is being consumed by the cylinders, I don't think much can be done to improve the intake by altering the physical location of the throttle body.....
Trey, if it was shown that the front cylinders consumed so much of the available air entering the intake plenum that the rear cylinders were suffering....Brian
Registered User
Joined: Jul 1999
Posts: 3,647
From: Winnipeg, Manitoba, Canada
How would you go about elongating the runners 2-3 inches?
Anyone on the net do this?
Did anyone ever get that plastic intake manifold off the ground?
Anyone on the net do this?
Did anyone ever get that plastic intake manifold off the ground?
Last edited by Gripenfelter; Feb 14, 2003 at 01:35 PM.
Registered User
Joined: Aug 2001
Posts: 2,400
From: Michigan's left coast
Originally posted by OldSStroker
As long as the udder is full of milk, there's not much problem getting enough from each "port". It really doesn't matter too much where the air enters the plenum, or the milk enters the udder; getting it out is the problem.
My take is the LT1 manifold has inlet runners which are just too darn short for decent tuning. They are straight, and can probably be made large enough to flow sufficient air. Making them 2-3 inches longer is the problem, IMO.
As long as the udder is full of milk, there's not much problem getting enough from each "port". It really doesn't matter too much where the air enters the plenum, or the milk enters the udder; getting it out is the problem.
My take is the LT1 manifold has inlet runners which are just too darn short for decent tuning. They are straight, and can probably be made large enough to flow sufficient air. Making them 2-3 inches longer is the problem, IMO.
As stated in the other intake thread, I feel that the udder, uh, I mean plenum, has too little volume for a 5.7+ L motor.
In the motorcycle world, airbox volume is known as a significant factor. While most bikes have individual throttle bodies, you can think of their arrangement being rather similar to the LT1 at WOT - a volume of air with individual runners to each cylinder.
Seems that most bikes work well with airbox volumes at least 10x that of an individual cylinder, and volumes over 20x seem to work even better. I've seen some graphs compared the airbox pressure of a Suzuki TL1000R (1000 cc twin, 5 L airbox) to that of a Hayabusa (1300 cc 4-cyl, 10 L airbox), and there's a night-and-day difference in average and instantanious pressure.
I seem to remember someone stating that the LT1 manifold had about 4 L of volume. If that's the case, then the plenum volume is less than 6x that of an individual cylinder on a 5.7 L V8, and the problem only gets worse with more displacement.
Registered User
Joined: Jan 2001
Posts: 2,148
From: Bay Area, CA
The small manifolds on older SBCs didn't seem to kill them too much though, unless I'm missing something?
The LPE intake was sure pretty big, but most of its gains were TQ, although an extra 50# of TQ is nothing to complain about.
The LPE intake was sure pretty big, but most of its gains were TQ, although an extra 50# of TQ is nothing to complain about.
Thread Starter
Banned
Joined: Aug 2001
Posts: 3,505
From: looking for a flow bench so Brook and I can race
Originally posted by Eric Bryant
As stated in the other intake thread, I feel that the udder, uh, I mean plenum, has too little volume for a 5.7+ L motor.
In the motorcycle world, airbox volume is known as a significant factor. While most bikes have individual throttle bodies, you can think of their arrangement being rather similar to the LT1 at WOT - a volume of air with individual runners to each cylinder.
Seems that most bikes work well with airbox volumes at least 10x that of an individual cylinder, and volumes over 20x seem to work even better. I've seen some graphs compared the airbox pressure of a Suzuki TL1000R (1000 cc twin, 5 L airbox) to that of a Hayabusa (1300 cc 4-cyl, 10 L airbox), and there's a night-and-day difference in average and instantanious pressure.
I seem to remember someone stating that the LT1 manifold had about 4 L of volume. If that's the case, then the plenum volume is less than 6x that of an individual cylinder on a 5.7 L V8, and the problem only gets worse with more displacement.
As stated in the other intake thread, I feel that the udder, uh, I mean plenum, has too little volume for a 5.7+ L motor.
In the motorcycle world, airbox volume is known as a significant factor. While most bikes have individual throttle bodies, you can think of their arrangement being rather similar to the LT1 at WOT - a volume of air with individual runners to each cylinder.
Seems that most bikes work well with airbox volumes at least 10x that of an individual cylinder, and volumes over 20x seem to work even better. I've seen some graphs compared the airbox pressure of a Suzuki TL1000R (1000 cc twin, 5 L airbox) to that of a Hayabusa (1300 cc 4-cyl, 10 L airbox), and there's a night-and-day difference in average and instantanious pressure.
I seem to remember someone stating that the LT1 manifold had about 4 L of volume. If that's the case, then the plenum volume is less than 6x that of an individual cylinder on a 5.7 L V8, and the problem only gets worse with more displacement.
what about a 383 with a big cam
anyone think i'd benifit much from a sheetmetal intake?
should i get a 58mm TB?
52mm ported by shannon.
of coarse it will all help-
but cost effective power gains?
or keep saving for FAST and progressive nitrous system?
Thread Starter
Banned
Joined: Aug 2001
Posts: 3,505
From: looking for a flow bench so Brook and I can race
Originally posted by Gripenfelter
Does the LS1 intake perform better at higher rpms?
If so why?
Hogan is $$$$$$.
Surely someone on this board must have the know-how to mod intakes to have slightly longer runners.
Does the LS1 intake perform better at higher rpms?
If so why?
Hogan is $$$$$$.
Surely someone on this board must have the know-how to mod intakes to have slightly longer runners.
how hard can it be to make sheetmetal intake once you can weld?
I cant see parts costing more than $100.
Why dont we make some kind of Cz28.com intakes?
Registered User
Joined: Jul 1999
Posts: 128
From: Tx
As I see it, the question pertains to the "fixing" of port to port variation through intake manifold modification?
My question to you is this.... Why go to such lengths when the bulk of the "problem" is in the cylinder head design? There are modifications which should be performed to maximize the LTx intake design but none are going to "fix" the volumetric cylinder to cylinder variation you'd see in a steady state flow test. The "fix" in that case would be through use of a cylinder head with "like-port" design, eg, the LSx or splayed valve designs. Not to say that the situation cannot be improved upon... it's just that effectively doing so is beyond the capability of most. For instance, simply making a runner "larger" will bring about better equalization but at what cost to performance? Is the larger port still as efficient as it was?
To the question of primary runner length, what are your goals with the engine? Simply adding 3-4 inches of runner length (runner volume) would increase the inertial supercharging effect but only with some sacrafice at a higher rpm. So, the goal of the design comes into question. What is our target torque peak and how do we size the runner to achieve that goal? What plenum volume? What included runner taper angle etc.? You can come close to "optimal" designs with some basic formulae but you will need wave modeling software to arrive at a better design.
On the issue of plenum volume. I agree that the LTx could use more plenum volume and some gains have been found in that area. Generally speaking on the subject, a larger plenum volume (up to 1.3 x engine displacement for 4-stroke engines) is usually about as large as is necessary. Any larger and you run into laggerdly throttle response... especially with a single throttle body. The further the throttle placement and the greater the volume (throttle to valve) the longer the response time. This is why many of the latest engine designs (BMW etc) are using one throttle per cylinder as close to the cylinder as possible. I'm assuming that the motorcyle engines in mention are running individual runner w/throttle bodies at each runner as well?
This is a rather ironic subject though because everyone wants a "longer runner length manifold design" but the answer isn't so far away...... the Accel SuperRam. But generally people frown when the SuperRam is mentioned and I'm still at a loss as to why? On a side note, I don't think the intake is being made for the LTx any more, most likely due to a lack of interest. You can't remain profitable trying to sell a product noone wants to use. For a 6-speed car with a stroked engine I think it's the wrong approach but that all depends on your goals. For maximum power (LTx engines here) my goal would be to spin the engine to 6500-7000 rpm and make as much power in that higher rev range as possible. That seems to be the goal of the majority working within the confines of the stock ECM and the engine doesn't need a total redesign to do that. More plenum volume will provide a broader torque band in the midrange (I've seen this in my modifications of the manifold) but the overall runner length is just fine for what most people are after. Increase the trajectory angle (raise the runners) and you get a better flow coefficient at higher lift/diameter ratios. Increase pressure recovery through modification of the inlet opening (requires internal manifold modification and removal of the top). You can also increase manifold volume by metal removal in the base of the manifold along with an increase with a taller shelled-cap on top.
How much would you be willing to pay to increase the average hp and torque of a strong 1.5hp per cid let's say 3%? I have seen some excellent gains in twin plenum designs but they aren't cheap to design or manufacture.
Those of us who build manifolds are out here and we're listening it's just a matter of supply and demand. If there isn't a true demand (money in hand and ready to pay) then there isn't going to be a supply. It's really as simple as that.
Trey,
There's more to it than welding. You will need to build jigs to do it right and then you're going to need machined flanges. The runners will also need machining so that they are planer to the plenum body. I CNC machine the aluminum runners at various taper angles from 2-4º included and lengths. They are 2 halves which fit together very precisely and are then welded. If you need any help with supplies let me know. I can also point you to some sheetmetal manifold supplies I've found. Or, you could use a Dart, Edelbrock etc. tunnel ram and modify it accordingly.
Take care
My question to you is this.... Why go to such lengths when the bulk of the "problem" is in the cylinder head design? There are modifications which should be performed to maximize the LTx intake design but none are going to "fix" the volumetric cylinder to cylinder variation you'd see in a steady state flow test. The "fix" in that case would be through use of a cylinder head with "like-port" design, eg, the LSx or splayed valve designs. Not to say that the situation cannot be improved upon... it's just that effectively doing so is beyond the capability of most. For instance, simply making a runner "larger" will bring about better equalization but at what cost to performance? Is the larger port still as efficient as it was?
To the question of primary runner length, what are your goals with the engine? Simply adding 3-4 inches of runner length (runner volume) would increase the inertial supercharging effect but only with some sacrafice at a higher rpm. So, the goal of the design comes into question. What is our target torque peak and how do we size the runner to achieve that goal? What plenum volume? What included runner taper angle etc.? You can come close to "optimal" designs with some basic formulae but you will need wave modeling software to arrive at a better design.
On the issue of plenum volume. I agree that the LTx could use more plenum volume and some gains have been found in that area. Generally speaking on the subject, a larger plenum volume (up to 1.3 x engine displacement for 4-stroke engines) is usually about as large as is necessary. Any larger and you run into laggerdly throttle response... especially with a single throttle body. The further the throttle placement and the greater the volume (throttle to valve) the longer the response time. This is why many of the latest engine designs (BMW etc) are using one throttle per cylinder as close to the cylinder as possible. I'm assuming that the motorcyle engines in mention are running individual runner w/throttle bodies at each runner as well?
This is a rather ironic subject though because everyone wants a "longer runner length manifold design" but the answer isn't so far away...... the Accel SuperRam. But generally people frown when the SuperRam is mentioned and I'm still at a loss as to why? On a side note, I don't think the intake is being made for the LTx any more, most likely due to a lack of interest. You can't remain profitable trying to sell a product noone wants to use. For a 6-speed car with a stroked engine I think it's the wrong approach but that all depends on your goals. For maximum power (LTx engines here) my goal would be to spin the engine to 6500-7000 rpm and make as much power in that higher rev range as possible. That seems to be the goal of the majority working within the confines of the stock ECM and the engine doesn't need a total redesign to do that. More plenum volume will provide a broader torque band in the midrange (I've seen this in my modifications of the manifold) but the overall runner length is just fine for what most people are after. Increase the trajectory angle (raise the runners) and you get a better flow coefficient at higher lift/diameter ratios. Increase pressure recovery through modification of the inlet opening (requires internal manifold modification and removal of the top). You can also increase manifold volume by metal removal in the base of the manifold along with an increase with a taller shelled-cap on top.
How much would you be willing to pay to increase the average hp and torque of a strong 1.5hp per cid let's say 3%? I have seen some excellent gains in twin plenum designs but they aren't cheap to design or manufacture.
Those of us who build manifolds are out here and we're listening it's just a matter of supply and demand. If there isn't a true demand (money in hand and ready to pay) then there isn't going to be a supply. It's really as simple as that.
Trey,
There's more to it than welding. You will need to build jigs to do it right and then you're going to need machined flanges. The runners will also need machining so that they are planer to the plenum body. I CNC machine the aluminum runners at various taper angles from 2-4º included and lengths. They are 2 halves which fit together very precisely and are then welded. If you need any help with supplies let me know. I can also point you to some sheetmetal manifold supplies I've found. Or, you could use a Dart, Edelbrock etc. tunnel ram and modify it accordingly.
Take care
Registered User
Joined: Dec 1999
Posts: 1,697
From: Petersham, MA
Originally posted by Eric Bryant
Seems that most bikes work well with airbox volumes at least 10x that of an individual cylinder, and volumes over 20x seem to work even better. I've seen some graphs compared the airbox pressure of a Suzuki TL1000R (1000 cc twin, 5 L airbox) to that of a Hayabusa (1300 cc 4-cyl, 10 L airbox), and there's a night-and-day difference in average and instantanious pressure.
Seems that most bikes work well with airbox volumes at least 10x that of an individual cylinder, and volumes over 20x seem to work even better. I've seen some graphs compared the airbox pressure of a Suzuki TL1000R (1000 cc twin, 5 L airbox) to that of a Hayabusa (1300 cc 4-cyl, 10 L airbox), and there's a night-and-day difference in average and instantanious pressure.
When I ported the intake on my WS6, we just tried to open up the internal plenum area as much as possible. Is that as good as it gets without a custom sheetmetal intake?
Registered User
Joined: Jan 2001
Posts: 296
From: Clawson, MI
I really don't think the air distribution is as bad as everyone makes it out to be, from what I've seen on the engine dyno. I did some testing with a ported LT1 intake, there was less .5 in. of vac. at wot. On the EGT's I had seen a differences of 125 deg from hottest to coldest, that's not all that bad. I will have to say low rpm air distribution does suck and thats why you see the 4 back plugs looking rich, if you were to shut it off right after a run you would not see this. I have also done some testing with a lager plenum intake 330 ci ver stock of about 175 ci. Gain I had seen were about 5-6hp from 5000-7000, and peaking at 7600 with about 20hp.
Comb was a 350 ci stock short block with LT1 heads, hyd roller making 560hp with stock ported intake.
Comb was a 350 ci stock short block with LT1 heads, hyd roller making 560hp with stock ported intake.
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Joined: Jul 2000
Posts: 520
From: MD
Hum… never really gave “why this happens” adequate thought before…, but the more I’m thinking about it the less I think that we’ve hit on the problem. Based on what I’ve seen and how they tend to ‘blow up,’ well, we’re missing something.
I’m with squinn on that the black plugs after some normal driving are not an indication of what we’re discussing. If anything the back cylinders would tend to run leaner, especially based on the fairly common occurrence of breaking pistons or head gaskets at 7 and 8.
Without really thinking about it I’ve always assumed a velocity/airflow explanation. That it’s easier to make a gradual 90* turn then a quick one so the front cylinders, right after then throttle body will get the least airflow since air coming through the throttle body will have to change direction most severely to enter those runners. I don’t think that that is a valid explanation since that would imply that the manifold plenum isn’t working as a plenum…
OldSStroker, I would think that whether you believe that the runners are long enough to tune is not really an issue here, since if anything, short runners would act as more of an extension of the plenum and lessen this effect as well as being generally less sensitive to any pressure pulses or anything else that would mess with air distribution. BTW, I used to like chocolate milk…
Mr. Horsepower, can you define “fixed port?” From your description it sounds like you’re suggesting that the issue is that on an SBC you’ve got intake runners that basically follow 2 patterns, and the difference is what causes the difference in flow. Seems to me that that would split the distribution in a 4 and 4 pattern (4 turning left or rear, and 4 doing the opposite) which it does not appear to be. (BTW, as far as I know the superram isn’t made at all anymore, but the LT1 version was discontinued early on because no one was really interested)
And I’m not sure that I believe it to be a plenum volume issue either, since I don’t know that I’ve heard of any similar inherent distribution issues with stock TPI manifolds (which have a similar plenum volume), or even more so, converted carb style manifolds which have significantly less plenum volume. To the contrary, a converted single plane is usually touted as a solution to distribution problems, and you can make a fairly strong argument that the plenum is smaller and the runners are not significantly longer…. Also, if this was a plenum volume issue I’d imagine you’d see 5 and especially 7 as running richer then the rest since they’re going to be filling one right after the other and are physically located next to each other drawing air from the same part of the plenum.
I’d love to hear a discussion why some of my conclusions/thoughts here are incorrect or what else would be the cause…
I’m with squinn on that the black plugs after some normal driving are not an indication of what we’re discussing. If anything the back cylinders would tend to run leaner, especially based on the fairly common occurrence of breaking pistons or head gaskets at 7 and 8.
Without really thinking about it I’ve always assumed a velocity/airflow explanation. That it’s easier to make a gradual 90* turn then a quick one so the front cylinders, right after then throttle body will get the least airflow since air coming through the throttle body will have to change direction most severely to enter those runners. I don’t think that that is a valid explanation since that would imply that the manifold plenum isn’t working as a plenum…
OldSStroker, I would think that whether you believe that the runners are long enough to tune is not really an issue here, since if anything, short runners would act as more of an extension of the plenum and lessen this effect as well as being generally less sensitive to any pressure pulses or anything else that would mess with air distribution. BTW, I used to like chocolate milk…
Mr. Horsepower, can you define “fixed port?” From your description it sounds like you’re suggesting that the issue is that on an SBC you’ve got intake runners that basically follow 2 patterns, and the difference is what causes the difference in flow. Seems to me that that would split the distribution in a 4 and 4 pattern (4 turning left or rear, and 4 doing the opposite) which it does not appear to be. (BTW, as far as I know the superram isn’t made at all anymore, but the LT1 version was discontinued early on because no one was really interested)
And I’m not sure that I believe it to be a plenum volume issue either, since I don’t know that I’ve heard of any similar inherent distribution issues with stock TPI manifolds (which have a similar plenum volume), or even more so, converted carb style manifolds which have significantly less plenum volume. To the contrary, a converted single plane is usually touted as a solution to distribution problems, and you can make a fairly strong argument that the plenum is smaller and the runners are not significantly longer…. Also, if this was a plenum volume issue I’d imagine you’d see 5 and especially 7 as running richer then the rest since they’re going to be filling one right after the other and are physically located next to each other drawing air from the same part of the plenum.
I’d love to hear a discussion why some of my conclusions/thoughts here are incorrect or what else would be the cause…