Inliners International Forums General Discussion Hi Performance Stock 250 1bbl vs 4bbl Clifford vs 4bbl Offy

I just converted my stock 250 to a 4bbl.
Started off as a stock 250, stock single exhaust, powerglide-3.08 Nova.
Tried both Clifford 4bbl intake and also the Offy 4bbl intake.
Tossup between the Clifford and Offy intakes, but both of them gained a clean 0.2 sec and 2 mph over the best 1bbl intake and carb setups I had.

That change equates to a gain of about 0.3 sec and 3mph in the 1/4 mile, and calculates to a gain of about 15hp in the Gonkulator from just adding the 4bbl and intake.

I tried many different carbs on each intake so the above is just a summary. One interesting note, during all this thrashing, the 4bbl setups got BETTER gas mileage than the 1bbl Rochester carbs.

The above started out in the "Engines" section but I posted it here too since it might be a better fit.

MBHD Hank asked about the testing above -
Most of the testing I do is Gtech, but some at the strip - which also serves to compare the Chrondeks and the Gtech on the same run. They are NOT the same, at least my Gtech is a couple percent optimistic, but that is ok as it is consistent once you get used to it. Also, the Gtech spits out MPH via a different measurement than at the track. So I calibrate the Gtech results to what the Chrondeks would say at the track, and also correct all runs for weather and weight of the car (even down to how many gallons of gas and my tools). Trying to make it as comparable as I can.

I plan a more full writeup at some point but here is a summary.
This is a stock Nova powerglide 3.08, about 3040 lb including me, some tools, and an extra carb or two. Stock single 2" exhaust, mystery muffler sounds pretty healthy but it is not a flowmaster or polished stainless magnaflow or anything.
The 250cid in there is stock, loose but not tired, just very low friction (and kinda low oil pressure....).
I tried a lot of 4bbl carbs on each intake, Holley, Carter/Edel, Autolite, Rochester. For the 1bbl intake, I ran just the Rochester B jug but 3 different venturi sizes.

Quick Summary: Best 6 Runs by Intake, and the best 1bbl run (way down on the ranking list)

60ft
1. Offy+390cfmHolley – 2.574
2. Clifford+610cfmAFB-2.580
3. Offy
4. Clifford
5. Clifford
6. Clifford
17. Best 1bbl Run-2.609

660ft-ET
1. Offy+450cfmHolley-11.238
2. Clifford+610cfmAFB-11.266
3. Offy
4. Clifford
5. Offy
6. Clifford
14. Best 1bbl Run-11.429

660ft-MPH
1. Clifford+390cfmHolley-62.870
2. Clifford
3. Offy+450cfmHolley-62.506
4. Clifford
5. Offy
6. Offy
27. Best 1bbl Run-60.607

I was kinda surprised that the Clifford did as well as it did down low, since it looks like a big tunnel ram compared to the Offy. And, I was surprised that both 4bbl intakes launched better than the 1bbl intake/carbs - and that the 4bbls were getting better gas mileage. Then again, the primaries of the 4bbls are about the same size as the bigger 1bbl carbs so maybe some of this makes sense.

The secondaries were starting to open, some of them just barely, but none were fully open for sure, as I checked with the paper clip test.

My bottom line right now is kinda that, if I were at a swap meet, and had the chance to pick up either a Clifford or an Offy, I'd get whichever one I could get the best deal on, at least for the type of build above. In cold weather the Offy probably has an advantage, better cold behavior, less puddling, etc - but for builds beyond the stock level the Clifford should gain an advantage so it is a tossup but a close call, closer than I thought it would be at least on this near-stock comparison.

DeuceCoupe
Thanks for that.

It does take a lot of time & effort to do these sort of tets,much appreciated

So according to your findings the Offy does outperform the Clifford, not by much,, but your testing the Offy is the winner, other than the MPH test,where I always stated the Clifford will make more top end power.
That's interesting.

DeuceCoupe
Are you the person that was doing the testing for Tlowe that he mentioned a while ago, or is there someone elso doing the same type of testing?
Again ,thanks for proving a point.

Just as I have tested so many years ago,the Offy is a better street intake manifold,no rumors ,just real world testing.
My Combos were not stock though,smallest cam I ran was .500" lift .224 @ .050 duration @ .050

When you run a bigger cam the difference is even more apparent,as the signal to the carb is even worse.

DeuceCoupe,

Over all,how did you feel about which intake seemed more forgiving on jetting,able to carborate better.
How about top gear roll ons,,, from low to high rpm,any testing ?
For example,going 35 MPH,, 2nd gear,no downshifting into 1st & go to 60 MPH,,,see how long it would take.

MBHD

Duece,
I am glad you took the time and effort to do this testing! This is the kind of real world testing that can help sort out rumors.

It is obvious from the #'s that at this power level (very low) the big Clifford did not kill the low end performance as it is always blamed to do. Both intakes are pretty much equal.

Hopefully you do some more tests with your 292. Maybe even with a bigger cam ,headwork and free flowing exhaust. Tom

P.S. This testing was Dueces idea. I supplied the Offy intake for testing and a Rochester 4GC 4 bbl.

Hank,
Yes, it's me.
This started out as just a carb shootout for a few carbs I was rebuilding, and the Clifford intake was all I had. Then Tom offered the Offy intake as a loaner and the shootout expanded.

I did not find one intake or the other more sensitive to jetting, etc - both gave a wide range of times depending on which carb was on top - even carbs of the same basic model (about half a dozen different Autolite 4100s, all 500cfm, all stock or near stock jetting, but as much as 0.4 sec and 3mph diff in the 1/8 mile!)

As far as driveability, in both cases I had the intakes bolted to the stock iron exhaust, but a plate in between for a bit less heat convection. The Clifford is slower to warm up and puddles gas in the intake on those chilly (50F) California mornings. That problem would get even worse on a brisk 10-below Michigan morning. I drove v8's with blocked heat crossovers in the Michigan winters and it was similar to warming up the Clifford from 40F or so out here.

That said, once warmed up, both intakes are very driveable, at least with this stock cam I can't tell the diff on that part (Warm, that is).

"How about top gear roll ons,,, from low to high rpm,any testing
For example,going 35 MPH,, 2nd gear,no downshifting into 1st & go to 60 MPH,,,see how long it would take."

On your question, since the 250 testing is done, all I could do is dig thru some of the Gtech data to answer it. I was able to compare, not top gear but 1st (1.82) gear over the 2300-3200rpm interval. See the two page excerpts below from the writeup I have started. I hope they answer your question, with the Offy showing a 2.9% advantage in that range.






The excerpts (2300-3200), and tlowe's dyno tests, and your own experience, all seem to be consistent with the statement that the Offy tends to be better below 3000-3500, and the Clifford better above that.

But then there is one more mystery -
I looked at the 60ft data for the same carbs/intakes in Table 1.
Clifford
2.615 average
2.580 best
2.710 worst

Offy
2.654 average
2.574 best
2.883 worst

So the Clifford beat the Offy in 60ft?!
Admittedly some luck is involved since the launch is kind of subjective - you can't just stomp on the pedal, so technique clouds those results unlike the 2300-3200 interval which is a pretty clean comparison.

More fun to be had!

Anyone have the actual manifold volume of either?
Leaving out the diffs in runner shape, if the plenum is worth some power, how much power would a 2" spacer add (estimate: 25-30 cubic inches)...

DeuceCoupe,

nice write up/post!

I am sure since you are using a stock cam w/not much valve overlap,the intakes would act/drive close to being the same.

When you run a camshaft w/more duration on the Clifford,the carb gets a poor signal & could bog,miss, stumble, & would take longer to recover from a stumble to clear out.

That (stumble, & would take longer to recover from a stumble to clear out) is the most apparent problem that I used to notice when running a Clifford intake.

I later switched to running a Clifford intake & keeped it installed,,,, but only when I had a higher stall converter & low rear gears , because ultimately,, the Clifford made more power on the top end.

MBHD

DeuceCoupe,

just wondering if you are going to post up your findings or write an article for the 12 port?
Thanks again for doing these tests.


MBHD

Hank,
For sure I will write up the saga in some form, not sure just what yet. Progress is slow especially with the holidays and weather.