2 or 4 barrel?
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Junior User
Joined: Apr 2005
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2 or 4 barrel?
My 360 is currently under a rebuild. Soon it willo be a 390 and hopefully it will have more guts than before. My question now is should I keep my holly 500cfm 2 barrel, Or would I really like a 600-650cfm 4 barrel? Mileage isnt going to be really important but I want this truck to move when I am done. I doubt that it will see more that 5500rpm. Unless a 4 barrel is going to give me a huge increase in acceloration I will stay with the 2.
Fleet Mechanic
Joined: May 2004
Posts: 1,436
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From: Montana
either or but a new carb means new intake which means more cash. I like 4 barrels but i ran my 2 for a long time happily. I gather your mileage will increase with a four and maybe even your throttle reponse, a 600 holley vac secondary....I believe the primaries are small and give nice response. I bet you will be happy with a four and when you do your rebuild you will want it.
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Junior User
Joined: Apr 2005
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It will be a 390 with 360 pistons problaly 30 or 40 over, stock truck 390 heads(rebuilt), headers, the cam is still questionable. I like a little bit of idle lope but I dont want it to be exessive. If I keep the 2 barrel it will just be a stock iron intake. The 2 barrel is new so it should do ok if I use it. If I decide on a 4 barrel, I will buy a dual plane alluminum which would be really nice. Those stock iron intakes are HEAVY. I think since I am used to driving a 91 toyota pickup, this truck will at least seem fast. I hope it turns out alright.
Posting Guru
Joined: Jul 2003
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From: Eureka, Ca.
Most people here seem to recomend the Comp 941 cam. for what you are wanting. as for the carb...stick with the 2 barrel and see if you are satisfied. If you find yourself wanting more upper rpm power then try the Edelbrock Performer RPM intake and a 650 or 750 4 barrel.
Lead Driver
Joined: Apr 2001
Posts: 6,175
Likes: 21
From: Texas
My 2 cent opinion. If you already have the engine apart, do the intake swap now and go to a 4 barrel carb. Get a dual plane aluminum intake like the Performer RPM from Edelbrock.
I guess, it depends on your budget and how bad you need the truck running.
I guess, it depends on your budget and how bad you need the truck running.
Senior User
Joined: Sep 2004
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Your mileage will be a wash......
I run a 2bbl holley on my stock 390 in a '75 highboy with 4.1 gears. She gets up and goes and doesn't look back. The reason I run my 2bbl is the steep grade I live on. I live in the foothills of the Cascades, and I have a problem staying out of the secondaries going up my road, so I figure I'd better run the 2bbl.
Eatin' chivys & ****tin' Dodges.
I run a 2bbl holley on my stock 390 in a '75 highboy with 4.1 gears. She gets up and goes and doesn't look back. The reason I run my 2bbl is the steep grade I live on. I live in the foothills of the Cascades, and I have a problem staying out of the secondaries going up my road, so I figure I'd better run the 2bbl.
Eatin' chivys & ****tin' Dodges.
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Postmaster
Joined: Jul 2003
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From: iowa
I would switch to a 4bbl intake and carb. I did this once if my memory serves me right. Bottom line intake would be an "S". THe rpm would be nice but as kurt has said there is a port mismatch to later stock haeds such as d2 and c8's. I measured the rpm runner exit at 1.99 inches while the head is 1.92-1.93. So, the intake ports of the cylinder heads should be opened up a smudge. I have not seen how placement is. There might be a bigger mismatch than .06-.07 even. I have ported my heads and have the opening to 2.18 in order to accomodate the old intakes.
As for the carb, I noticed a 4bbl wasn't a huge diffrence on bottomend power over a 2bbl but mid and top is a lot better. One other thing to remember is the 2bbl is rated at more iches of mercury than a 4bbl so a 500cfm 4bbl flows more than a 500cfm 2bbl.
I think the crane 343941 is too big for a 4wd or automatic. And since you have stock heads, something like a 343901 or comp equal cam would do. But thats me MR. Small Cam. If you have a 2wd sport truck that will see over 4000rpm then go ahead and run the 941 cam.
As for the carb, I noticed a 4bbl wasn't a huge diffrence on bottomend power over a 2bbl but mid and top is a lot better. One other thing to remember is the 2bbl is rated at more iches of mercury than a 4bbl so a 500cfm 4bbl flows more than a 500cfm 2bbl.
I think the crane 343941 is too big for a 4wd or automatic. And since you have stock heads, something like a 343901 or comp equal cam would do. But thats me MR. Small Cam. If you have a 2wd sport truck that will see over 4000rpm then go ahead and run the 941 cam.
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Elder User
Joined: Mar 2003
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From: Phoenix Az, by way of Fre
Originally Posted by fordeverpower
One other thing to remember is the 2bbl is rated at more iches of mercury than a 4bbl so a 500cfm 4bbl flows more than a 500cfm 2bbl.
I've seen people corrected for that statement before...
Either way...
I'm running the Holley 500cfm 2bbl and like it just fine.
Throttle response and off idle-low rpm power are great.
If i had the money at the time of the rebuild, I'd have sprung for the 4bbl intake and a 600-650 4bbl carb.
I doubt throttle response or off idle power would be greatly effected, and I cannot help but think running around on small primaries of a 4bbl would be more efficient that running around on the #86 jets my 2bbl requires.
My .02
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Originally Posted by fordeverpower
I think the crane 343941 is too big for a 4wd or automatic. And since you have stock heads, something like a 343901 or comp equal cam would do. But thats me MR. Small Cam. If you have a 2wd sport truck that will see over 4000rpm then go ahead and run the 941 cam.
I wouldn't want to go any bigger than the 941 with the stock torque converter though. The 941 cam turns on about 100rpm after the torque converter stalls. Often times I'll go a few feet, THEN get the burnout.
But yeah, if you're going to be hauling trailers all day, then 901 may be a better choice.
On the carbs: 2 barrel carbs are rated at 3" mercury pressure drop, 4 barrels are rated at 1.5" mercury. So, a 500cfm 2 barrel will flow less than a 500cfm 4 barrel. That's just the way it is. I can site multiple sources...
Edit: On the port mismatch with the RPM intake to the later style port heads (C8's, D2's, etc.) There is quite the mismatch. Hold a gasket up to the intake, align it with the bolt holes, mark the dimensions on the gasket. Then, compare this to the head. You'll see what I mean.
Last edited by rusty70f100; Aug 1, 2005 at 06:46 PM.
Postmaster
Joined: Jul 2003
Posts: 3,934
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From: iowa
yeah i'm pretty sure about the carb ratings.
Kurt, I am becoming more convinced every week to opt for something a little bigger than the old 901. I will see how the new motor reacts. I have done a cam change before without moving the engine 1 centimeter why not one more time. Now if i could find a manual 2wd shortbox i would be in heaven and go bigger yet.
Kurt, I am becoming more convinced every week to opt for something a little bigger than the old 901. I will see how the new motor reacts. I have done a cam change before without moving the engine 1 centimeter why not one more time. Now if i could find a manual 2wd shortbox i would be in heaven and go bigger yet.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by cleanLX
You sure about that?
I've seen people corrected for that statement before...
Either way...
I'm running the Holley 500cfm 2bbl and like it just fine.
Throttle response and off idle-low rpm power are great.
If i had the money at the time of the rebuild, I'd have sprung for the 4bbl intake and a 600-650 4bbl carb.
I doubt throttle response or off idle power would be greatly effected, and I cannot help but think running around on small primaries of a 4bbl would be more efficient that running around on the #86 jets my 2bbl requires.
My .02
I've seen people corrected for that statement before...
Either way...
I'm running the Holley 500cfm 2bbl and like it just fine.
Throttle response and off idle-low rpm power are great.
If i had the money at the time of the rebuild, I'd have sprung for the 4bbl intake and a 600-650 4bbl carb.
I doubt throttle response or off idle power would be greatly effected, and I cannot help but think running around on small primaries of a 4bbl would be more efficient that running around on the #86 jets my 2bbl requires.
My .02
4V CFM X 1.414 = 2V CFM
2V CFM X 0.707 = 4V CFM
