Intake distribution issues

[Josh A]

Question for the intake gurus, sorry if it's a long post guys.
Engine I'm working with is 360 60 over, stoke stroke with 273 rods and speed tec pistons, 11.2 comp. Cam is hr 530/536 230/234@50 110lsa, Heads are promaxx cnc'd and milled to 60cc with 2.08 1.60 valves. M1 intake unported. Holley sniper efi.

Problem I was having was once around 2k and up afr was going crazy and missing and popping thru exhaust under light excelleration or even steady cruising unless you went from idle to full throttle then it would rip. Tried many other things to remedy but didn't help at all. So on a recommendation from my tuner i started adding spacers to increase plenum. Well that fixed my issues amazingly car runs like it should.

issue I'm at now is this intake needed 2.5" of spacers added to run correctly. Currently the sniper tb is above my hood line and into my hood scoop its so tall, and to me it visually looks terrible when I open the hood aswell.
Does anyone have any ideas I could try to remedy the issues and keep the m1 intake?
Also I've been looking at other intakes I see lots of people on here recommend air gap or a victor 340 not so sure I need a super victor. Any help or recommendations are welcome guys. Thanks

 

[Professor Fate]

First question that popped into my head was "What manifold are you running?" At the end you said "M1", but that doesn't help, since MP probably released a dozen manifolds under the M1 designation.

etc. etc.
So I ask, single or dual plane? Open or divided plenum? And then, what type of spacers- open or divided?
TBI systems like an open plenum so they get a better vacuum signal; and arguably work better on a single-plane manifold.
My swag is that you've got a a dual plane with a divided plenum, and you added open spacers to it- and as you added more spacers you stabilized the vacuum signal and it ran better.
If this is the case (I'm making a lot of assumptions here due to a lack of info) you could get rid of the spacers by having about an inch of the plenum divider removed. I've read the exact recommendation somewhere, but can't find it right now- but an inch is about right if my feeble old brain recalls correctly.

 

[Josh A]

First question that popped into my head was "What manifold are you running?" At the end you said "M1", but that doesn't help, since MP probably released a dozen manifolds under the M1 designation.
View attachment 1716270999View attachment 1716271000View attachment 1716271001View attachment 1716271003View attachment 1716271005etc. etc.
So I ask, single or dual plane? Open or divided plenum? And then, what type of spacers- open or divided?
TBI systems like an open plenum so they get a better vacuum signal; and arguably work better on a single-plane manifold.
My swag is that you've got a a dual plane with a divided plenum, and you added open spacers to it- and as you added more spacers you stabilized the vacuum signal and it ran better.
If this is the case (I'm making a lot of assumptions here due to a lack of info) you could get rid of the spacers by having about an inch of the plenum divider removed. I've read the exact recommendation somewhere, but can't find it right now- but an inch is about right if my feeble old brain recalls correctly.

I didnt realize mopar had that many intakes. But I am running the first intake pic you posted that is on the red and green rug. it's a single plane with spread bore flange. currently what is working is manifold flange to a open spacer then a thick gasket and then a tapered 4 hole spacer on top and then the tbi unit.

 

[mderoy340]

I run a carb so this may not apply.
I briefly ran that intake on my 360 with a square flange plate, 1" 4 hole HVH Super sucker and a 750dp carb. 3, 6, 7 cylinders were rich. I swapped to a Victor 340 square flange intake and 3 & 7 are rich. Car runs great with either manifold but I'd like to get the plug color closer.

 

[AJ/FormS]

My guess is that atmospheric air is getting into your headers, right at the header flanges.
> you didn't mention your exhaust, but I gotta assume yur running headers.
My 276/286/110 cam (230/237), has 61 degrees of overlap. I suppose that yours has about the same.
The job of the headers is to create a low-pressure area, behind the exiting hot exhaust gasses. This helps draw plenum mixture into the chamber.
But, at lower rpms, some of the low-pressure pulses, that are created by the headers, now telegraphed into the intake, has time to pull mixture right across the piston-top, parked at TDC, and out into the primary pipes, where, if it finds even a hint of fire, it will explode, sending a reverse hi-pressure pulse back into the chamber. If the intake is still open at TDC/overlap that pulse can easily make it into the plenum. So now, your poor sniper is having to deal with all those pressure pulses going in different directions inside the common plenum, and in the single-plain, those pulses are all of them, right under the throttle-valves, and I bet in close proximity to, the load-sensing vacuum device..
>IMO, the TB spacers are likely helping to contain and dissipate this mess.
>IMO, fixing the header leaks will fix the problem, or most of it.
>IMO, a dual-plane will help contain and dissipate the rest.
>FYI the Edelbrock Airgap on my combo pulls hard to 7000, which is my typical shift-rpm, when ramming thru the gears.
Do not think that, on the street, you may need more intake than the AirGap. Mine makes enough power to post 93mph in the Eighth.
------------------------------

My engine-combo is very similar to yours.
You said;

Engine I'm working with is 360 60 over, stoke stroke with 273 rods and speed tec pistons, 11.2 comp. Cam is hr 530/536 230/234@50 110lsa, Heads are promaxx cnc'd and milled to 60cc with 2.08 1.60 valves.

mine is;
Engine I'm working with is 360/40 over, 3.58 stroke
with 318 floating wristpin rods, and
KB107 pistons,
currently she is at 11.0 comp.
Cam is a Hughes 549/571 lift/ 276>286/110&230>237@050;
Heads are OOTB Eddies.
She runs an untouched Airgap/750 DP/no spacers.
She is getting fresh cold air from above the hood, and
She runs TTI headers with full-length 3" duals. And,
I run it at 207*F.

> IMO, she runs, perfectly at all throttle/load settings with no flat-spots and no hesitations of any kind.
> until recently, the plugs were new in 1999.
> As to Timing;
she will idle down to 500 in gear and smoothly pull herself along, at 5* advance. Her normal timing is 12>14 at idle, going to 28* at 2800, then tapering to no more than 34*@3400.
The V-can pulls in 22 degrees by 13 inches.
The cruize-timing is thus 50* at 2800, to which I can add up to 15 degrees from my dash-mounted, dial-back, timing module, but rarely does she run over 60*
At 2240=65mph, in GVod, the cruize-timing is usually about 14+10+22+6= 50*; but she gets a lil better gas-mileage at closer to 60*.

I know that cam. I've been running it since 2004. I run it straight-up with no advance. it likes a little bypass air from the carb.
In straight up, it doesn't clean up until about 2200>2400 rpm. Until it does, the vacuum is somewhat unstable. If I want to run something off the intake vacuum, I install a restrictor in the line, to smooth it.
I run a 4-speed/3.55s, so intake vacuum is always high enough to operate my power-brakes. Except for first thing in the morning. But by the time I get her backed out of the carport, the booster is on line.
Good luck.

 

[Josh A]

My guess is that atmospheric air is getting into your headers, right at the header flanges.
> you didn't mention your exhaust, but I gotta assume yur running headers.
My 276/286/110 cam (230/237), has 61 degrees of overlap. I suppose that yours has about the same.
The job of the headers is to create a low-pressure area, behind the exiting hot exhaust gasses. This helps draw plenum mixture into the chamber.
But, at lower rpms, some of the low-pressure pulses, that are created by the headers, now telegraphed into the intake, has time to pull mixture right across the piston-top, parked at TDC, and out into the primary pipes, where, if it finds even a hint of fire, it will explode, sending a reverse hi-pressure pulse back into the chamber. If the intake is still open at TDC/overlap that pulse can easily make it into the plenum. So now, your poor sniper is having to deal with all those pressure pulses going in different directions inside the common plenum, and in the single-plain, those pulses are all of them, right under the throttle-valves, and I bet in close proximity to, the load-sensing vacuum device..
>IMO, the TB spacers are likely helping to contain and dissipate this mess.
>IMO, fixing the header leaks will fix the problem, or most of it.
>IMO, a dual-plane will help contain and dissipate the rest.
>FYI the Edelbrock Airgap on my combo pulls hard to 7000, which is my typical shift-rpm, when ramming thru the gears.
Do not think that, on the street, you may need more intake than the AirGap. Mine makes enough power to post 93mph in the Eighth.
------------------------------

My engine-combo is very similar to yours.
You said;

mine is;
Engine I'm working with is 360/40 over, 3.58 stroke
with 318 floating wristpin rods, and
KB107 pistons,
currently she is at 11.0 comp.
Cam is a Hughes 549/571 lift/ 276>286/110&230>237@050;
Heads are OOTB Eddies.
She runs an untouched Airgap/750 DP/no spacers.
She is getting fresh cold air from above the hood, and
She runs TTI headers with full-length 3" duals. And,
I run it at 207*F.

> IMO, she runs, perfectly at all throttle/load settings with no flat-spots and no hesitations of any kind.
> until recently, the plugs were new in 1999.
> As to Timing;
she will idle down to 500 in gear and smoothly pull herself along, at 5* advance. Her normal timing is 12>14 at idle, going to 28* at 2800, then tapering to no more than 34*@3400.
The V-can pulls in 22 degrees by 13 inches.
The cruize-timing is thus 50* at 2800, to which I can add up to 15 degrees from my dash-mounted, dial-back, timing module, but rarely does she run over 60*
At 2240=65mph, in GVod, the cruize-timing is usually about 14+10+22+6= 50*; but she gets a lil better gas-mileage at closer to 60*.

I know that cam. I've been running it since 2004. I run it straight-up with no advance. it likes a little bypass air from the carb.
In straight up, it doesn't clean up until about 2200>2400 rpm. Until it does, the vacuum is somewhat unstable. If I want to run something off the intake vacuum, I install a restrictor in the line, to smooth it.
I run a 4-speed/3.55s, so intake vacuum is always high enough to operate my power-brakes. Except for first thing in the morning. But by the time I get her backed out of the carport, the booster is on line.
Good luck.

I am running full length Hedmans with full 2.5 exhaust out to the rear end. And a 904 with 3500 Stall and 4.30s out back.
Question though if I was pulling air would I not be getting weird afr readings with the air leak? As for now with the spacers my afr will float from 13.5 to 13.8 cruising down the road as my cruise afr is set at 13.5 on my handheld.
Sniper has no vacuum advance my timing is 20 initial and 34 total around 2800-3k, and only thing hooked to my tb base is pvc.
Glad u said something about a air gap as i debated swapping to a dual plane as one is for sale close to me for sale, just to try but was wondering about it as I drive my car aggressive also and normally shift around 5k or higher and my car regularly see's 7k aswell.
But alot of info says the intake is not that good up top so I haven't jumped, but I'd be pissed if I got another single and still had issues again without spacers

 

[AJ/FormS]

>As for the AG not being good on top, hang on;
even with 4.30s yur gonna be speeding at the top of Second Gear. And in first, as you know; it spins all the way thru. So what top are we talking about. lol.
I installed my AG waaaaay back in maybe 2001 or 2002 when they became available locally............ and I've never been sorry.
As for the air leaks at the header flange;
-If you got afterfires, you can bet you got fresh air in the exhaust
-if you got fire in the plenum , there's only one place it can come from which is past an intake valve. The how of it, you gotta figure out.
Your options are;
1) valves not closing, or not sealing, or something in the chamber, running hot enough to spontaneously ignite the fuel charge before the valve is closed, or as mentioned fire coming in during the overlap period.
2) As I think about it, this could also be due to bad cam-timing, but honestly if it was far enough out to be the cause, I doubt the engine would start. and
3) consider the Ignition timing. IDK how your EFI compensates for engine load. and if it doesn't then there is only one time the Ignition Timing can ever be right which would be at WOT, and over 3600 rpm. The entire rest of the time, the Ignition Timing would be retarded.
If the engine was running in such a mode, at Part Throttle, the mixture in the chamber, for a great deal of time is never gonna finish burning inside the chamber, and will have to finish up burning in the header pipes. and that means that the overlap period will be dead, for an instant loss of power. But, if the engine is simultaneously running rich, then the entire primary pipe, of every cylinder, could be filled with burning gasses. This is of course, very bad; cuz if the primary pipe ends up under pressure, when the exhaust valve next opens, and you have 61* of overlap, guess what; those higher pressure than what is in the intake plenum, are headed up to the plenum.
This is theory.
Does it happen in real life?
Well if your Sniper cannot add or subtract ignition timing in compensation for load, my guess is yes it can.

MY engine
which is very similar to yours, has up to 22* of Part Throttle load compensation, built into the distributor.

At idle, she is happy running at 25>35degrees. (but I only give her 14 max.)
By 2000/no load, she likes 40/45
By 2500/no load, she likes 50 to 55
By 2800 she wants 50 minimum, up to 60, just to cruise on.
But the Power Curve is 14*basic, >28*@2800 >34 by 3400.
These numbers produce cool-running in the Primaries and minimum fuel consumption.
Please tell me, the Sniper can control this.
If it cannot, you are gonna have to build your distributor with similar curves, and absolutely, you are gonna need Vacuum advance ..... and I prefer running it off the sparkport. If your sniper does not have a sparkport, (I wouldda never bought it) panic; the distributor can be made to work on full-time advance .

 

[Josh A]

>As for the AG not being good on top, hang on;
even with 4.30s yur gonna be speeding at the top of Second Gear. And in first, as you know; it spins all the way thru. So what top are we talking about. lol.
I installed my AG waaaaay back in maybe 2001 or 2002 when they became available locally............ and I've never been sorry.
As for the air leaks at the header flange;
-If you got afterfires, you can bet you got fresh air in the exhaust
-if you got fire in the plenum , there's only one place it can come from which is past an intake valve. The how of it, you gotta figure out.
Your options are;
1) valves not closing, or not sealing, or something in the chamber, running hot enough to spontaneously ignite the fuel charge before the valve is closed, or as mentioned fire coming in during the overlap period.
2) As I think about it, this could also be due to bad cam-timing, but honestly if it was far enough out to be the cause, I doubt the engine would start. and
3) consider the Ignition timing. IDK how your EFI compensates for engine load. and if it doesn't then there is only one time the Ignition Timing can ever be right which would be at WOT, and over 3600 rpm. The entire rest of the time, the Ignition Timing would be retarded.
If the engine was running in such a mode, at Part Throttle, the mixture in the chamber, for a great deal of time is never gonna finish burning inside the chamber, and will have to finish up burning in the header pipes. and that means that the overlap period will be dead, for an instant loss of power. But, if the engine is simultaneously running rich, then the entire primary pipe, of every cylinder, could be filled with burning gasses. This is of course, very bad; cuz if the primary pipe ends up under pressure, when the exhaust valve next opens, and you have 61* of overlap, guess what; those higher pressure than what is in the intake plenum, are headed up to the plenum.
This is theory.
Does it happen in real life?
Well if your Sniper cannot add or subtract ignition timing in compensation for load, my guess is yes it can.

MY engine
which is very similar to yours, has up to 22* of Part Throttle load compensation, built into the distributor.

At idle, she is happy running at 25>35degrees. (but I only give her 14 max.)
By 2000/no load, she likes 40/45
By 2500/no load, she likes 50 to 55
By 2800 she wants 50 minimum, up to 60, just to cruise on.
But the Power Curve is 14*basic, >28*@2800 >34 by 3400.
These numbers produce cool-running in the Primaries and minimum fuel consumption.
Please tell me, the Sniper can control this.
If it cannot, you are gonna have to build your distributor with similar curves, and absolutely, you are gonna need Vacuum advance ..... and I prefer running it off the sparkport. If your sniper does not have a sparkport, (I wouldda never bought it) panic; the distributor can be made to work on full-time advance .

The distributor is locked out and phased with a cap from holley. There is no vac can on these distributors either.
So I would say I can hook the ecu up to a laptop and have my tuner build me a timing map table to whatever the distributor will phase itself out to based off load or tps that's above my knowledge though, so I'll have to pick his brain on that a bit. I've watched him build a table before but not sure what the bases are besides rpm.
I'll do some checking tomorrow on the exhaust report back.

 

[Bewy]

With your current intake, you have 7 cyls that can interfere [ they are cross-connected ] with the cyl that is drawing air. With a dual plane, much less interference, only 3 can interfere. I have no experience with your type of EFI, but it maybe a factor to look at.