offy dp/holly 390 vs offy c/2100
#1
offy dp/holly 390 vs offy c/2100
The head is coming off my F250 4wd. When I put it back together, I have a choice of intake combos:
1) offy dual port with holley 390 on 1" spacer, which is what I've been running for the past 10 years with zero problems.
2) offy C with 1.08 2100 2bbl from an '80 351M.
Truck is used on farm and road, with occasional towing. Already have efi dual exhaust manifolds. Primary interests: fuel economy, adequate power.
Comments, input, experience?
1) offy dual port with holley 390 on 1" spacer, which is what I've been running for the past 10 years with zero problems.
2) offy C with 1.08 2100 2bbl from an '80 351M.
Truck is used on farm and road, with occasional towing. Already have efi dual exhaust manifolds. Primary interests: fuel economy, adequate power.
Comments, input, experience?
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#8
Well dang, I have a D-P/Holley390 I got for seventy five bucks and was planning to use on my heavy step-van w/300/240-head/EFI exhaust.
Flyer, would you care to expand on this? I know the subject has been nearly beaten to death, but you have more credibility than all of the amateurs and their personal opinions.
Offenhauser spent a lot of time developing the Dual-Port for a bunch of different engines, and I supposed it could have some benefits (throttle response and good lower-rpm mixture maintenance) for a heavy truck . . . ??? This is not to say it would be as good as an individual-runner carbs set-up, or a good EFI system, but for those of us old dogs who prefer carburetion . . . .
Flyer, would you care to expand on this? I know the subject has been nearly beaten to death, but you have more credibility than all of the amateurs and their personal opinions.
Offenhauser spent a lot of time developing the Dual-Port for a bunch of different engines, and I supposed it could have some benefits (throttle response and good lower-rpm mixture maintenance) for a heavy truck . . . ??? This is not to say it would be as good as an individual-runner carbs set-up, or a good EFI system, but for those of us old dogs who prefer carburetion . . . .
#9
OK. The OP wants Fuel economy and towing power, mainly at low engine speeds as I see it.
Either combination will give a substantial increase in power over the original YF carb so don't dismay Smitty. Besides if you decide to fold on the 390/DP combo I will buy it from you at substantially more than you paid for it, or ebay patrons will probably give you even more.
The wall in the middle of the DP divides the ports into two unequal openings. But the surface area around the port is substantially more leading to increased boundary layer effect for the DP compared to the C, I'll bet the flow on the DP is substantially less than a C. Combined with four idle circuits in the 4V you get less max flow, more idle fuel consumption and a carb that seems prone to having tip-in starvation issues that are rectified by a much richer accellerator pump shot, another economy hit.
If you have either setup I'm sure you will be happy with it. My son uses a tuned-up 390 and I have a few 2100 carbs that also work well. Good luck with your projects.
By the way OP, don't be in too big a hurry to start changing jets in the 2100/2150. My experience is if you are using one from an EGR equipped engine on an EGR equipped 300 or using a non-EGR carb on a non-EGR 300 the jetting is close to right.
Either combination will give a substantial increase in power over the original YF carb so don't dismay Smitty. Besides if you decide to fold on the 390/DP combo I will buy it from you at substantially more than you paid for it, or ebay patrons will probably give you even more.
The wall in the middle of the DP divides the ports into two unequal openings. But the surface area around the port is substantially more leading to increased boundary layer effect for the DP compared to the C, I'll bet the flow on the DP is substantially less than a C. Combined with four idle circuits in the 4V you get less max flow, more idle fuel consumption and a carb that seems prone to having tip-in starvation issues that are rectified by a much richer accellerator pump shot, another economy hit.
If you have either setup I'm sure you will be happy with it. My son uses a tuned-up 390 and I have a few 2100 carbs that also work well. Good luck with your projects.
By the way OP, don't be in too big a hurry to start changing jets in the 2100/2150. My experience is if you are using one from an EGR equipped engine on an EGR equipped 300 or using a non-EGR carb on a non-EGR 300 the jetting is close to right.
#10
The wall in the middle of the DP divides the ports into two unequal openings. But the surface area around the port is substantially more leading to increased boundary layer effect for the DP compared to the C, I'll bet the flow on the DP is substantially less than a C. Combined with four idle circuits in the 4V you get less max flow, more idle fuel consumption and a carb that seems prone to having tip-in starvation issues that are rectified by a much richer accellerator pump shot, another economy hit.
I have a DP on my '81 and a C on my '84. I've spent many frustrated hours, days, weeks, (years?) trying to get the carb on my DP tuned in just right. Tip in starvation is a royal pain. I've had up to a size 40 on the accel pump to rectify this.
That said, once you get it tuned in, it is a snappy setup. Right now, I have a 465cfm Holley that really screams, and I'm getting 13 - 14 around town and 17 on the freeway.
On the flipside, any carb I throw on the Offy C is a "set the idle and forget it" sort of deal. The 390 I put on it ran great. The 600 I have on there now runs great.
If I had a choice again, I'd choose an open plenum (the C) over the DP.
That's not to discourage anyone from using one. Just that, if you have the choice, choose the C. The DP is a fine intake, just not as easy to tune.
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