IMHO; as long as you can afford it, there is not a single sensible reason in the world that should keep you from playing with your slantsix!
What kind of intake?
Olaf.
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| Extra aluminum intake. 4 barrel project? https://slantsix.org/forum/viewtopic.php?t=46545 |
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| Author: | /6Vanner [ Tue Oct 04, 2011 9:13 pm ] |
| Post subject: | Extra aluminum intake. 4 barrel project? |
Any thoughts, ideas, reasons why i shouldnt do it? |
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| Author: | Reed [ Tue Oct 04, 2011 9:32 pm ] |
| Post subject: | |
Mainly you shouldn't do it because a street driven slant six in a van really doesn't need a four barrel carb. A van really doesn't need a carb bigger than a one barrel- the motor just won't see the RPMs necessary to need a bigger carb. The biggest carb I would put on a stock street driven slant six in a van would be a two barrel, such as the Carter BBD or Holley 2280. |
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| Author: | olafla [ Tue Oct 04, 2011 9:34 pm ] |
| Post subject: | |
IMHO; as long as you can afford it, there is not a single sensible reason in the world that should keep you from playing with your slantsix! What kind of intake? Olaf. |
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| Author: | Brussell [ Wed Oct 05, 2011 6:40 am ] |
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Hi Reed, is there something different about having a slant 6 in a van? Or are you saying that because of the way a van handles? Thanks! But regardless why not have something funky on your car? haha |
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| Author: | /6Vanner [ Wed Oct 05, 2011 11:29 am ] |
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its a stock 87 aluminum intake. I was thinking a small 500 or 600 cfm 4 barrel, I figured more air more fuel more go.... Thats why i ask! |
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| Author: | Reed [ Wed Oct 05, 2011 2:01 pm ] |
| Post subject: | |
It mainly has to do with the maximum RPM a street driven slant six sees and the torque requirements of a big heavy van. The slant six is a small engine. Even running at 4500 RPM, a speed most street driven slant sixes rarely achieve, a slant six with 83% volumetric efficiency only needs 243 CFM flow through the carb. Street driven slant sixes rarely see more than 3500 RPM. At a more realistic 3500 RPM a 225 with 83% VE only needs 189 CFM. If I remember correctly, the average one barrel slant six CFM rating is ~210. The "Super Six" two barrel carbs flow ~ 280 CFM. Even a 390, 450, or 500 CFM four barrel carb is too much for a stock street driven van. Even a moderately built slant six used as a daily driver simply doesn't need a even a small four barrel carb. Additionally, vans are big heavy vehicles to get moving. A motor in a street driven van benefits more from low RPM torque than from high RPM horsepower. Smaller carbs make better low RPM torque. Frankly, if I was building a motor for a van, I would keep a one barrel carb and focus on compression and cams. A four barrel intake can certainly be built out of a stock one barrel, intake, but I don't think it would be worth the trouble in the end. If you want better pickup, then I recommend focusing on gearing in the rear axle before a four barrel carb switch. |
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| Author: | 65CrewCabPW [ Wed Oct 05, 2011 5:46 pm ] |
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This talk of CFM is misleading. One, because 2BBL carb CFM is rated at MUCH HIGHER vacuum ( lower pressure ) than a 4 bbl. A 280CFM 2 bbl does not flow anywhere near half of what a 450 cfm 4 bbl does, given the same pressure differential. Yes, it's true that a slant six won't pull large CFM at anywhere near normal rpm's, but it's also true that in real life, the 1 bbl and 2 bbl carbs are rated as if they had far more vacuum behind them than a 4 bbl does. So, experience says that you CAN flow more air with a larger source of air. Frankly, I'd go for TBI, not a carb, so you can get as close as possible to full atmospheric pressure in the manifold - meaning as high as possible VE. |
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| Author: | olafla [ Wed Oct 05, 2011 6:07 pm ] |
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Also, the plenum chamber under the carb in a stock 1-bbl manifold, is very small for a 4-bbl carb, I think you are better off listening to Reed (this time!  )Olaf. |
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| Author: | Rick Covalt [ Wed Oct 05, 2011 6:08 pm ] |
| Post subject: | 2 barrel |
I do know that just switching to the 2 barrel (Holley 2280) in my 85 truck made a world of difference in how it drove power wise. I would never go back to a single barrel with it. And it got almost 19 MPG running to the Elk Creek race with a full load of stuff in the bed doing 65 on the highway. Rick |
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| Author: | Reed [ Wed Oct 05, 2011 8:07 pm ] |
| Post subject: | Re: 2 barrel |
Quote: I do know that just switching to the 2 barrel (Holley 2280) in my 85 truck made a world of difference in how it drove power wise. I would never go back to a single barrel with it. And it got almost 19 MPG running to the Elk Creek race with a full load of stuff in the bed doing 65 on the highway.
What was on the truck before the switch? Was it a lean-burn system? Was it a worn out original carb? Before an accurate comparison can be made we need to know what was fueling the engine prior to the swap. I envy your 19 MPG. Stick shift? Gearing? What have you done to the ignition system? Rick Fuel economy might improve based on switching to a two barrel, but there are too many other variables to consider before a blanket statement like "two barrel carbs improve economy" can be made. All things being equal, in a stock motor in a daily driven van, I would recommend a good condition one barrel carb over a two barrel carb, and wouldn't recommend a four barrel carb at all. If you have done extensive modifications such as bigger valves, a custom cam, etc... then a two barrel might be a better choice. However, a four barrel won't be a good idea unless you build a serious motor and change the gearing in the van. Don't take my word for it, look at OTHER PEOPLE'S EXPERIENCE. That article is about Ford inline sixes, but the concepts and results are comparable (inline six cylinder motor, similar displacement). |
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| Author: | /6Vanner [ Wed Oct 05, 2011 8:25 pm ] |
| Post subject: | |
This is a great discussion guys. Gives me lots to ponder as i keep working on this beast. I would have a stroke if i got 19mpg. My van with a 300lb interior and keepin a steady 65-70 gets about 13 on the highway. |
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| Author: | Rick Covalt [ Thu Oct 06, 2011 3:28 am ] |
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My truck was a short bed, D-100, bone stock automatic with the factory lean burn. I put the 2280 carb and HEI on at the same time. The truck ran OK before it just ran noticably better with the 2 barrel/HEI. The rear gearing is 3.21. I never had it on a trip with the lean burn, so I am not sure what the mileage was. Rick |
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| Author: | Reed [ Thu Oct 06, 2011 3:53 am ] |
| Post subject: | |
In that case I am not surprised you got better performance and economy by replacing the lean burn with HEI and a non-computerized carburetor. Lean burn systems are terrible for power and economy. 19 mpg is very good for a loaded slant powered truck. You must have a good combination. I would think comparble and possibly slightly better results could be achieved with a one barrel carb, but I wouldn't mess with your setup since it works so well. |
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| Author: | /'d Box [ Thu Oct 06, 2011 6:05 am ] |
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/6vanner, I agree with the idea that a 4bbl is overkill for stock(ish) tune applications. I have an '85 SWB B250 with a converted MP ignition and has a MP 2bbl manifold with a Weber 32/36 on it. I finally have it tuned right and love it over the 1bbl. I tried the Weber 38 but prefer the progressive nature of the 32/36. There are a number of mods that need to be done using the Webers (linkage, adapters) that may be more than it's worth for some, but I do like to tinker. After driving and wrenching 'modren' cars for the last decade, it's a pleasure working on this thing. Years ago, I helped my dad build a '84 CJ7 258 with a Clifford set-up (manifold, cam, head work, etc) with a small Holley 4bbl and ended up switching to the Weber 38 and I think the 2bbl worked alot better in that applications. FWIW. |
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| Author: | kesteb [ Thu Oct 06, 2011 10:32 pm ] |
| Post subject: | Re: 2 barrel |
Quote: Don't take my word for it, look at OTHER PEOPLE'S EXPERIENCE. That article is about Ford inline sixes, but the concepts and results are comparable (inline six cylinder motor, similar displacement).
Boy talk about comparing apples and oranges. The small block ford 6 has about the worst cylinder head/intake combination that you can find on any domestic 6. The best modification that they can do is swap the head and intake for one from Australia. Which by the way, would be a 2v intake with a Holley flange suitable for the 2300 series. The reality is that the primaries on a 4v will be about the same size or smaller then a BBD. So it would have the same characteristics of a 2v carburetor until you mash the throttle pedal. The carburetor would also be new and calibrated for today's fuels. Something a used Holley 1920 or BBD is not. Modifying a 1v aluminum manifold most like won't be the best thing to do. As was mentioned the plenum is to small. |
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