Kennedy & The Dalai Lama delivered my '48 coupe last week just in time for Shades of the Past. I've been driving it every since and I love it. It's showing almost 1000 miles on the odometer. The engine in the coupe was originally built for my Deuce roadster pick up. When I traded the RPU off I decided to just use that engine in the '48. It sounds like feeding time at the zoo but it's not performing like I had hoped. It has a .030 over 283 with a Comp Thumpr cam, roller rockers, Power Pack heads, Performer intake, and a 600cfm Edelbrock carburetor. This is backed by a 700R4 trans (with TCI lockout) and a 8" Ford rear end with 3.50(ish) gears. Rear tires are big at 265/50/20". I do an equal amount of driving on city streets and the interstate. It's a fair mix of 30mph cruising and 80mph blasts. I'm getting about 15mpg. It runs good and once it's wound up, it'll flat fly. It doesn't have much low end power/torque though. I know this is common for a 283. My daily round trip is about 60 miles. When I have one running, I like to drive my hot rod a lot. I really can't afford to get less than 15mpg considering the miles I cover. Questions: Can I do something to what I have here to generate a substantial gain in low end power/torque? A head swap perhaps? Should I just build a 350 instead? If I stepped up and built a 383, would the gas mileage absolutely kill me? TIA, Jim
I'm just finising up a roller 305 to replace the 283 in my `63 C-10 pickup with the goal being better MPG and more grunt. It won't have much left after about 4500 revs but I don't visit up there anyway. I've heard of 283's getting good fuel milage and I'd say the biggest factor with yours is the Thumper cam. I have heard good things about the Melling MTC1 cam. A nice boost over stock but still mild and of course cheap.
If the 283 runs well, I'd look at the gearing first. I read somewhere that the 2.73 was the economy ratio behind the 283/auto back in the day. However, with economy comes a less fun response under your foot, as you already know. However, it may be a more pleasurable commute seeing the RPMs drop.
Jim,,,I'm not gonna be any help with performance enhancement or gas mileage and don't normally like the big wheels but I looked at the coupe long and hard at the Shades of the Past show last week and gotta admit the car has a great look. I didn't realize it was yours until we talked Saturday. Have you made any attempt to get back in touch with George? HRP
X 2 on the cam. Put in a smaller one, for more bottom end. Something that can move a motor home, would be better if moving your coupe.
You built your engine to operate most efficently at high RPMs and it does. If you want it to be efficent at low RPMs, you'd be wise to swap the cam for a short duration cam. Maybe one of those 262 degree RV grinds. With your high gears you may pick up 3-4 MPG with the cam swap. Personally, for only 3-4 MPG gain, I'd keep my thump'r cam but I love a lumpy cam at idle enough to pay for it with 15 MPG..
Thanks guys. I researched overdrives, tire diameters, and rear end gears at some point years ago and had determined that this combination should work out well in the RPM/mileage dept. I certainly don't think a taller rear gear will help low end power but I'm no mechanical engineer so..... I appreciate the advice. I'm listening. The people at Comp recommended this cam for the driving I told them I'd be doing. You gotta bet that they are like Rocky though and are willing to give up 4mpg for the lumpy cam. Thanks for the kind words Danny. I haven't talked to George. I'm waiting on the stars to align on that one I guess.... JH
Deeper gears is your best and cheapest option. Dump a 4.11:1 in it and you will see a real improvement. That comp thumper cam probably isn't helping you any either, it is not made to perform just to sound like it is performing. I know that it is probably too late to think about a cam change but there are better options for your 283.
Gotta tach? What's your revs at 70 mph? Late model V8/RWD stuff can get pretty good mileage, but they always keep the rpms around 2200 at cruising speed to get it. Just my 2 cents. Rich
They also have a computer that advances and retards the timming as well a some have variable cam timming, and constant fuel delivery changes. Basically the computer tunes it to run at the conditions it is encountering. An engine that is bult to run in a specific RPM range as ours are as a rule, needs to be operating in that RPM range to operate efficiently.
It's not too late for anything! I just want a little more power on the botom end without losing any more MPG. Thanks! JH
I am not help much on your mileage issue, but if you ever decide to sell your 48 let me know. I seen it at the shades run and it is perfect.
If you run the numbers, you'll see what the problem is: 65 mph, 3.50:1 gear, .70 OD, 30.4" dia tire = 1760 rpm. This is not in the torque band of a big cam 283 ci. Put a vacuum gauge on it and you'll probably see low vacuum at cruising speed.
I would say a gear change-right now at 65 you should be turning around 1780 rpms with changing to a 4.11 that would bump you up to 2100 rpms. That would get you a little bit closer to the sweet spot for your motor. its not a drastic difference but I think you would notice it performance wise-and it might not affect mileage as much as you think. It will be working the engine alot less up hills, getting to speed etc.
Big cams and milage don't go together. Thats why big cams and stock type fuel injection don't work in closed loop it must idle at 14.7 mixture and high over lap cams can't they need to be richer. So you richen the idle but the idle curcuit is some what used untell about 2000 rpm. where alot of your driving takes place.
Those Thumper cams were designed for giving a radical idle, not performance or economy. They are fair ground cams. They get the sound through lots of overlap and really long exhaust duration. They have like 15 to 20 degrees more exhaust duration than intake. With all that overlap and long exhaust duration, you are just sucking unburned gas straight out the tailpipe. Like others have said, lose the cam and get something with far shorter duration. I am assuming 9.5 or less compression? I'd go with something in the 205-210 degree at .050 intake and 210-220 degree at .050 exhaust, smaller would be better for cylinder pressure and economy. A tight lobe center like 108-110 will give a little chop and promote midrange power. As much lift as you can get. That said, I drove a 3600 car with a 9.5:1 302 with a 220-228 duration cam, 108 lobe centers, 3000 stall converter and 3 speed auto with 3.89's and 27 inch tires everyday for about 10 years. Even taching at 3,500 rpm on the highway, at steady speed it got around 17 mpg and had plenty of passing power. Lower gears like a 3.25 or 3.50 and a tighter converter probably would have put me closer to 20 mpg, but I wasn't really looking for max economy, it was just a fun little hopped up cruiser. Try to maximize the torque peak to be near cruise rpm for max economy. If it is geared to run at 2200 rpm at 70 mph, try to use a cam that will make peak torque around that rpm. Many factors to consider here, like gear ratio, tire size, compression ratio, vehicle weight, etc., but that Thumper cam is a big culprit. Those heads don't flow all that well, so why not cam it to match the rest of the combo? Will probably be quicker, as well as more efficient. If you are hell bent on having a rough idle at cruises, just pull a plug wire a block or so before you pull in. For what it's worth though, I like a radical idle too, so long as the engine can back up it's bark. I have a truck with a 260-266 @ .050 cammed 11:1 big block that gets 6 mpg sitting the driveway with the key in my pocket, hauls ass and I drive the shit out of that thing.
I would change the gear a 3.5 gear is too much gear for those tires behind a 283. If you are willing to change the cam get a GM cam or a copy of one, like a 300 horse 327 cam or a 330 horse 350 cam. Either will still be a little lumpy with your 283 and both will improve your low end grunt. I would say to run an L-79 cam but in the small displacement engine the 350 horse cam is going to put your cruising range too high for what you want to do.
Ha! Thanks man but this one is a keeper. Some shrewd horse trading resulted in my uncle building it for me. He is the reason I love this stuff like I do. This is the second one I've had that he built. I'm not going to let this one get away. It means more to me than just the sum of it's parts. I'm all for changing what I need to make this a true interstate eater. The lumpy cam is amazing but I'll yank it out in a minute if I need something a little more tame. Rear gears aren't sexy anyway so I have no problem swapping them. Question: What about my heads? Should I consider something a little better or are they fine for what I want this car to do? Thanks guys! Jim
Those heads should be fine for a low rpm interstate cruiser. Small ports to keep velocity up. Cam it accordingly, it should last for a long time and get great economy with good low rpm grunt. I have a buddy running a 283 with power pack heads, unknown (stock?) compression, a little Summit 204-214 @.050 on 112 lc cam, and a 600 Holley on an old C3BX manifold in a 56 Buick with a 200R4 and I think a 2.73 rear and tall-ish 225-70-15 tires (I think). Even with those mis-matched rear gears, it scoots out pretty good, respectably at least, and it's a big, heavy car. He said he got 22-23 mpg going across the desert to Vegas crusing at 80-85 mph the whole way with 4 people in the car and all their stuff.
Here's a thought. If you don't want to swap the cam, but you have 150 bucks or so, you can try a set of Rhoads lifters. They are designed to bleed off a precisely metered amount of oil pressure, which actually reduces the amount of lift at the valve under low-RPM conditions. When RPM climbs, the oil pressure bleed is overwhelmed by the increased volume coming from the pump, and the lifters restore full lift to the valves. The only downside I know of is they make some noise at idle. http://rhoadslifters.com/sc2/agora....69*oQ83x4&xm=on&product=Original_Flat_Tappets
I don't want to "patch" it. I think I'm going to swap the cam and rear gears. Thanks guys! JH Sent from my DROID device using the TJJ mobile app
I'm in the planning process of a similar situation. It will be a daily driver, car is approx 3500 lbs, I'm planning a 283 cause I like them and have 3.55 gears with a .82 overdrive, effectively dropping the final gear to approx 3.08. I have 2 options, 1 cheap, 1 a bit more, and I know I'm going to end up spending the money to do it right in the end. Cheap: I have a set of used .030 283 pistons with what measures out as a 10cc dome. With a 55cc chamber, that's 12.5:1 compression. I also have an old Crower solid cam, it's 224/230 @.050. With a set of 305 heads it would run real hard, but I'm not sure for how long. Expensive: I'll end up buying a set of heads from Trick Flow designed for a 305 and a roller cam. Run a cam somewhere around 210-220@.050 with as much lift a I can get, keep the compression in check around 10-10.5:1. Let the short duration build cylinder pressure. More bottom end, better driveability, better fuel economy, and still fun when i step on it. Devin
Jim, with your overdrive trans you are lugging the engine. Best rear gear with tall tires & your overdrive trans will be a 4:11 or even a 4:30. It may sound crazy but your milage will improve. I've always wanted a patina hot rod like yours! Sorry to hear about your grand dad, Bob Perreault
You may be running the engine at too low an RPM for the "sweet spot" of that cam. Try doing a milage loop, say 60 to 100 miles with car in "D" instead of overdrive, and see if you get better mileage with engine running at the higher RPM. Just a test, and may help guide you in the right direction.
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