SB M1 Single Plane plenum - Long
#427494
08/03/09 04:56 PM
08/03/09 04:56 PM
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Joined: Jan 2003
Posts: 4,084
Indiana
W5Duster436
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Been fighting an issue with my car being fairly sluggish for quite some time and may have finally fixed it but wanted to see if anyone else has had this happen. Basically my setup is: 345 11.5:1 Fully ported X's 275/275 .585/.585 Solid Hooker Super comps Fully ported M1 intake QFT Q-950-AN Mallory SS 32 and 6AL box 3.91 then 4.30 gears Basically after putting the engine the first time it never felt right and would absolutely struggle to hit 7k. Took it back apart and with the help of Rob Y. found out the springs were way too weak for this cam even though they were originally the ones called out for. Had the spring issue fixed and had the heads fully ported at this time as well with all the other goodies. Put it all back together and STILL the thing just felt like it was hitting a wall at 1/2 - full throttle. More hours spent on the phone with Rob who graciously put up with my million questions.  Borrowed an LM-1 and the carb was a bit rich but nothing that should have caused this. Finally about had enough over the weekend and took the car to the engine builder who did the heads and after verifying ignition and everything looked at the intake and commented how the plenum went right into the runners. Put a 1" spacer on it with the 4 bore holes and holy smokes it pulls like a freight train now and will hit 7300 instantly. Has everyone else running this intake had to put spacers on due to the same issue? I always wondered why the indy 360 intake had such a tall plenum and I guess now I know. Now if I can get the A/F ratio correct (11.5 WOT) I'll be doing even better. It's obvious this 950 is probably way too big for the engine but planning on building a stroker I didn't want to buy two carbs. The car idles around 13.0 A/F but at cruise (60 mph 3400 rpm) it appears that it is running on the transition area at 11.5 - 11.8 A/F. Give it a little throttle and it'll go to 12.2 or so. What is the best thing to clear this up? Currently has 74/78 jets but when I previously went to 70 or 72 in the primaries when I would get into the throttle right before secondaries it would go totally lean around 15 A/F. Sorry for the long post but feels good to finally be getting close and couldn't have gotten here without moparts members! 
'70 Duster - SDSS 436 W5 4spd (Gone)
'71 Dodge D100
'70 Dodge W100
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Re: SB M1 Single Plane plenum - Long
[Re: W5Duster436]
#427495
08/03/09 05:05 PM
08/03/09 05:05 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
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I Live Here
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Kalispell Mt.
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The car idles around 13.0 A/F but at cruise (60 mph 3400 rpm) it appears that it is running on the transition area at 11.5 - 11.8 A/F. Give it a little throttle and it'll go to 12.2 or so. That comment right there makes me think the power valve is opening too early. Once you introduce more air it leans it out, kinda suposed to add more fuel as you mash the gas harder. I would check out the power valve and see what you vaccume is at cruise then see what number valve you have, the number should be about 2 numbers lower than your cruise vaccume.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: SB M1 Single Plane plenum - Long
[Re: W5Duster436]
#427497
08/03/09 07:22 PM
08/03/09 07:22 PM
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Joined: Jul 2006
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On the south side of Nowhere
S/ST 3040
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Quote:
Finally about had enough over the weekend and took the car to the engine builder who did the heads and after verifying ignition and everything looked at the intake and commented how the plenum went right into the runners. Put a 1" spacer on it with the 4 bore holes and holy smokes it pulls like a freight train now and will hit 7300 instantly
That sounds like one hell of an improvement for a carb spacer.
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Re: SB M1 Single Plane plenum - Long
[Re: MR_P_BODY]
#427501
08/03/09 08:44 PM
08/03/09 08:44 PM
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Indiana
W5Duster436
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2" would never fit under the hood. When the engine was first built in '88 it had a tunnel ram and would hit the higher rpms instantly. That's how I knew when I rebuilt it that something was wrong. It was just sluggish getting to the rpms. Engine was the same except better ignition, headers, and fuel and performed worse!
This M1 that I have is also the first version that didn't have heater provision etc. Makes me wonder if they improved this plenum when they came out with the newer version.
Like I stated before I always wondered why the Indy had such a tall plenum.
I guess I may throw a super sucker 1" on it and see if it even makes an improvement. It may also be that the Q-950 was just too much for the intake without the spacer.
Dunno.
'70 Duster - SDSS 436 W5 4spd (Gone)
'71 Dodge D100
'70 Dodge W100
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Re: SB M1 Single Plane plenum - Long
[Re: W5Duster436]
#427504
08/03/09 11:12 PM
08/03/09 11:12 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
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Kalispell Mt.
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Cruise is when the PV is working (or technically needs to be not working)so why do people insist on setting it for idle vaccume  The idle mix is run from the idle circuit, cruise is run off the main jets and wot is run off the PV. Actually they stack up and full throttle will get some fuel from all those sources. If idle is right then move on to the main circuit where your car is haveing it's issues, then to get full throttle right you have to work on the PV circuit, however most people just change the jets because it is the easiest way to change WOT and cruise ratios be darned.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: SB M1 Single Plane plenum - Long
[Re: HotRodDave]
#427505
08/04/09 09:56 AM
08/04/09 09:56 AM
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Joined: Jan 2003
Posts: 17,864
S.E. Michigan
ZIPPY
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Quote:
This M1 that I have is also the first version that didn't have heater provision etc. Makes me wonder if they improved this plenum when they came out with the newer version.
It wasn't changed, the newer intake has the same plenum as the old one.
While I agree it IS small, I'm pretty surprised it acts as dramatically horrible as you describe on a 340ci motor. They usually do respond well to spacers, but not quite that dramatically.
When I opened this thread I thought I was going to see something like "plenum too small for a stroker combo/picked up 25HP with a spacer" which is very common. From looking at it, I have to guess it was really designed for 340ci or less.....but that's exactly what you have, so I can't offer much more.
Trial and error testing always wins, glad to hear you got it to do what it needs to do and found out what it wants.
I would be looking to see if the small side of the weird quasi-spreadbore flange isn't restricting flow by overhanging the barrels. Usually the carb flange takes some grinding to get rid of any restrictions.....if that turns out to be a visible issue, then when corrected it'd be interesting to see what a second spacer test would do.
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Re: SB M1 Single Plane plenum - Long
[Re: ZIPPY]
#427506
08/04/09 10:25 AM
08/04/09 10:25 AM
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Indiana
W5Duster436
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It must be the combination of this particular carb (too big) and the intake. Thought maybe someone else ran into the same problem. Made sense when I read the thread about the fuel hitting the bottom of the plenum and not dispersing correctly. It's hard to describe but the car would just basically struggle past 6500 getting to 7K. Also at part throttle it always had a real tinny sound from the exhaust. After the spacer was put in the whole car seemed to be a bit smoother over the whole throttle range. Hammering it now it shoots to the rev limiter much easier. Even at a 1/2 throttle burst it felt like something was holding it back. Even felt like a car with severely retarded ignition. That was one of the first things I thought it could be and had a thread about the timing mark being off on the dampener but it was checked and dead on. I may take it to a chassis dyno just to see the difference between having the spacer or not. Quote:
I would be looking to see if the small side of the weird quasi-spreadbore flange isn't restricting flow by overhanging the barrels. Usually the carb flange takes some grinding to get rid of any restrictions.....if that turns out to be a visible issue, then when corrected it'd be interesting to see what a second spacer test would do.
I didn't really look but i know when they ported the intake they did a lot of grinding/rounding etc. in the plenum area as well.
'70 Duster - SDSS 436 W5 4spd (Gone)
'71 Dodge D100
'70 Dodge W100
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Re: SB M1 Single Plane plenum - Long
[Re: Streetwize]
#427510
08/04/09 12:53 PM
08/04/09 12:53 PM
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Joined: Jan 2003
Posts: 4,084
Indiana
W5Duster436
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Try it with/without the spacer and let us know the results. My bet is it's as sluggish as mine was. Like I said though it could just be my combo with the extremely large cam and oversized carb.
'70 Duster - SDSS 436 W5 4spd (Gone)
'71 Dodge D100
'70 Dodge W100
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