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Post by island65cruiser on Apr 21, 2019 14:30:55 GMT -5
I just finished installing a Street Demon 625 CFM carb on my otherwise stock 65 Holiday Coupe. these are now made by Holley, and quality seems to be good. It came out really well, so I thought I would share some info. First, my problems with the 4GC were gas leakage, off Idle stumble, and secondaries not opening correctly. I thought about rebuilding the 4GC which is really damaged from lead free ethanol gas the previous owner used, but thought I would experiment with modern tech first, to eliminate fuel and other issues. The results are amazing. Right out of the box, the carb was perfect, only idle adjustment was needed. Bottom end response is quick, and smooth. Secondaries open fast and you can feel the immediate difference. And, it is only a $300.00 carb. They claim fuel economy will improve, but I can't confirm that yet. Big plus, no gas smell after car shuts off. The carb has a one piece, leak proof lower body.
Parts needed include a 1/2" phenolic spacer between manifold and carb. The Demon is 1/2" shorter than the 4GC. Also needed is a 66 Cutlass air cleaner base for the Quadrajet carb with a 5&1/8" neck opening. The stock chrome 442 lid fits this base. A New 30" steel fuel line is needed to reach the fitting located on the back of the passenger side of the carb. The throttle linkage rod needs a 1/2" "dog leg" bent into it to line up as the carb is wider than the 4GC. An "ignition on" 12 volt source is required for the electric choke. Done! Two hour job.
My car now starts cold, or hot immediately. No long cranking to pump fuel into the carb after sitting parked. No more spraying starting fluid into the intake. The best part is that the new carb is completely hidden under the factory air cleaner and the car looks stock.
If anyone cares, let me know, and I'll seriously check gas mileage, something i don't really care about. So far it seems promising.
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Post by ronniev1959 on Apr 22, 2019 8:42:18 GMT -5
Was size motor, do you think it's suitable with a 400 engine?
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Post by island65cruiser on Apr 22, 2019 9:17:52 GMT -5
Ronnie, I contacted Holley first, and the told me the most common mistake people make is to use too big a carb that is too much CFM for street use. I asked about the 750, and they said not to use on a stock motor. I used their on-line formula, plugged in cubic inches, 6,000 RPM red line, and answered their other questions, and it gave me the 625 CFM carb part number. This carb is like a ThermoQuad, or Quadrajet, small primaries, monster secondaries. The secondary butterflies and throttle linkage won't clear the manifold without a spacer. The mechanical secondaries open up more quickly and noticeably than those on the original carb.
Bottom end, around town performance is noticeably better. I havn't taken it on the freeway yet to see top end performance. Keep in mind my car is a driver, no headers, or hot rod upgrades. Also, I bought a factory refurbished carb direct from Holley on ebay, and saved over a hundred bucks. Same warranty and packaging as new. They are bench tested and adjusted after assembly, no adjustment was needed. I will post a follow up if I find any issues with the set up.
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Post by ronniev1959 on Apr 23, 2019 10:07:46 GMT -5
Sweet,answered all my questions right down the the ebay one. Thank you.My car has the stock carb which is questionable at best. It does have headers and a slight cam in it though
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Post by island65cruiser on Apr 23, 2019 20:21:29 GMT -5
I would suggest you call Holley tech support, they were really helpful. Headers and cam may make of difference on carb size. So far, the only problem I need to address is hard shifts, I think I may have connected that line to the wrong vacuum port. BUT, off idle, accelerating, secondary response, all really good. No mileage numbers yet, maybe by this weekend.
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Post by island65cruiser on Apr 28, 2019 13:16:36 GMT -5
I said I would update the post after I had a chance to drive the car a while. We went to a car show in Sarasota today, a 45 mile round trip. Drove up on Rt. 41, cool weather, no traffic, 35-50 MPH. Came home on suburban roads, 35-40 MPH limits, few stop lights. I topped of the tank and checked the mileage: 45 miles divided by 1.94 gallons is 23 MPG. I still don't believe it, but how can the numbers be wrong? I will check it again, but can it be that the Street Demon swap produced a 50% increase in local mileage? The cars runs great, no negatives at all, excellent cold and hot starts, smooth cruising and good acceleration. Seems to good to be true.
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Post by joepadavano on Apr 28, 2019 16:41:36 GMT -5
So first, you are surprised that a brand new carb performs better than the original that was "really damaged from lead free ethanol gas." Not exactly a scientific comparison.
Second, unless you have a clear plastic fuel filler neck with graduations every ounce, you have no idea how much fuel your car used. 1.94 gallons? Seriously? Based on what? When the gas pump clicked off? That's not even close to a precise measurement. It could have been 1.5 gallons or 3.5 gallons. And 45 miles is far too short to be meaningful. A one gallon fill repeatability tolerance on a two gallon fill is a 50% error band. A one gallon tolerance on a 20 gallon fill is a 5% error band. Don't get too excited.
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Post by island65cruiser on Apr 28, 2019 20:49:34 GMT -5
Whoa, slow down there cowboy, I said I found it hard to believe. However, lacking the high tech scientific mileage metering tools necessary to satisfy you, I did it the way we always did in the old days, fill it to the brim, drive it, and fill it to the brim. When I have a chance to take a longer road trip, I'll check it again, and get an average, which will satisfy me, and others who are not so particular. Even with that being said, It is certainly an improvement, and in no way disappointing. Take it for what it is worth to you. Of course, if you want to invest $300.00 to buy a carb and do your own test, be my guest, I would love to see your scientifically correct results, weighted for climate, barometric pressure, temperature, tire size, graded rolling resistance, and so forth. See, at my age, I don't have anything to prove. Just trying to be helpful. A couple of guys PM'd me and wanted more follow up, so I'm trying to do that. End result, I can see no down side to the swap so far.
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Post by ronniev1959 on Apr 29, 2019 10:41:44 GMT -5
Ya
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