Here is a pic of Squirrel’s engine back when it was fresh . Just a normal everyday big block,,,,you know,,,,for the grocery shopping and church on Sunday ! Lol,,,,,just kidding,,,,Jim’s engine is much more radical than this . Tommy
I had a 750 Edelbrock on a 455 Olds with Aluminum heads and a reasonably big cam, and the gasmileage was about 7. I got about a third of that gas consumption knocked off by changing the metering rod springs, as they would pop up under normal cruising load. Though in this case I'd ***ume the high fuel pressure might be an issue
Get a Wide band O2 gauge , On SBC I like to tune off #6 but it depends what Intake using. Not all intakes designs flow the same . ( fuel mixtures runner to runners AFR) Timing Light , Vac Gauge , A avance kit if distributor is not one thats adjustable , 650 carb should be all cfms needed a true 5-6 psi pressure reading . Take Notes & adjust / tune accordingly. My 427 SBC over 670 hp 1,100 cfms gets 10 mpg.( I prefer Holley style carbs) Stop & go for 15 miles before out of town to open road driven average 100 on each drive plus 3-4 1/8 mile pulls every time. 3 speed trans.
Who cares. It’s a hot rod isn’t it. Mine may get 10 mpg. It’s part of the deal man. 2.73:1 gear? Probably runs down the road below idle right? Lol
As 19Eddie mentioned above, if you want to get right on the mark, you need to install a fuel/air ratio gauge. When my mileage ****ed, I got one, and found that I was running rich at light loads and highway speeds.. After testing and noting under which conditions the ratio was at or below 12:1, I was able to make a selection off of Edelbrock's installation/trouble shooting do***ent to select new jets and pins to get where I wanted to be. .. now I'm running between 13 and 16 most of the time, and 12 at idle, and yes, now I know what's going on with the carb while I'm driving. It's the only way to go. And yes, some folks think that reading the plugs works. And perhaps it was the only way to go 30 years ago.
I set up my AFBs with an AFR gauge, although it was on a different car at the time. Stock jetting, with primary metering rods on step leaner on cruise. The numbers on the gauge are not so great, and do scary things under certain conditions, but it runs good and goes fast and gets decent mileage for what it is and doesn't foul plugs. Usually setting up a carb with stock jetting works reasonably well, ***uming vital things like correct fuel pressure and float level, and that the carb is appropriate for that specific engine. Some guys can tune carbs to show great AFR numbers, but my experience is they tend to be a bit rich when they are running well. At least, that's how the aftermarket carbs are. Something like a stock Qjet on a stockish engine, you should expect to see pretty good numbers (and decent mileage, drivability, etc)
I ***ume Muncie gearbox meaning 4 speed and a fresh engine has tight tolerances? Was it at freeway speeds of 80 m.p.h.?
It still works if you understand carburetor tuning but it's become a lost art these days. The problem I see is people comparing plug readings from EFI systems to carburetors, which is incomparable. EFI systems run on the jagged edge of detonation for mileage and emission purposes. Carburetors are not capable of metering fuel like the EFI systems. A carburetor has to be tuned for a happy compromise between mileage and power w/o detonation. Joe
The tricky think about statements like this is that they overlook the fact that it might be wasting fuel at 8 mpg. What if it was tuned up right and running the right fuel pressure and it got 10, 12, or 14 mpg afterward? While 10 is not great, it is a lot better than 8.
70 miles on a new engine? Don't know they use for rings and bore finish on those but could still be some friction going on.
like Squirrel said ,, things get Scary with AFRs .. It takes a lot of experimenting & time to get every Runner / cylinder To same AFR even on all the cylinder , If people used a Dyno it Data data data !!! You wold be Amazed what the Littles adjustment will change in air mixture in intake , I have played with carbs / efi throttle bodies ((Multi ****erflies)) buy taken the shafts apart in a way that you could move each ****erfly independent, & Monitor AFR on each cylinder what is the AFR Affects different Cylinders, on Open runners on Dual plane ,,open plane , Tunnel Rams & Roots Blowers. Even the position on the carb / carbs mounting. There is a lot to learn , But I know most here are not into what I do & experiment with... its a Disease ( H-Power , Torque & Knowledge) Very time consuming . Mechanical injection can give you a better air fuel ratio on each Runner Almost exact. OT EFi programmable ECU injector in each Runner and that you can control the fuel on each cylinder and the timing on each cylinder ,, It's just amazing. Reading Plugs are almost impossible because of Fuel blends of today for off the pump Gasoline. I aways use Shiny plugs Easier to read then a black plug. 8 mpg is 454 1 ton & Ford truck 351 352 400 460s
My T has a bored & stroked 388" SBC , 2-450 mech sec Holley's on an edelbrock street tunnel ram , cruising small towns ( 2500 r.p.m. avg. )around here the car averages 16.5 m.p.g. carbs are jetted like they came. Even my '73 crew cab with a dump box that scales @7300 lbs with a 355 qjet , t 350. & 410 gears gets 12 m.p.g. average . I wish I could tell you a magic fix , but am at a loss ?
on my OT 75 c3500 crew cab Duly pull enclosed car trailer, I think it was a 780 Qjet it would burn tires off no trailer 10 mpg. Trailer on 7-8 mpg. I Put a small Qjet I think it was like around 620 cfms , Power was Very Noticeable lack of, 15 mpg ,,with trailer 13 mpg
I notice you are in Scotland. Are you allowing for the difference between a U.S Gallon and an Imperial Gallon? "In the Americas, a gallon is equivalent to 128 fluid ounces or 3.785 liters (American spelling). But in the UK, it's 160 fluid ounces or 4.546 litres (British spelling)."
Right, there isn't any benefit to just wasting gas, it won't go any faster. The problem is a mistuned engine fouls out plugs very fast, dilutes crankcase oil. 18 hwy mpg might not sound very good but doubling from 9 is pretty impressive when you think about it. It does take an understanding of carb circuits and distributor curving. Cars lose maybe 3 to 4 hwy mpg alone without vacuum advance. That's why everybody hated the 1970s, a V8 in a car could get probably 25 mpg when it was tuned right and run real good, though not when Detroit de-tuned everything to meet emissions. In those days I thought 11 mpg was set in stone.
I used to have a 462 Pontiac with an HEI/MSD 6A, Q-jet, mild can, SP TH400, and a 2.75 Ford 9" that got 19 mpg on the highway/12 mpg in town. It made loads of low end torque, had no problem blowing away the rear tires.
there is one on the car, but it wasn't installed when that picture was taken. It only helps a little.
I ran two Carter's on a blown 327... I could not get them not to bleed off after shut off until I regulated it down to 4.5 psi with a stock mechanical pump...
I had a Brand-New Spectre SBC fuel pump that flooded my Qjet. I set up my fuel pressure tester and cranked the engine and it was producing 12 PSI. Took it off and ordered a Carter M6900 that is internally regulated to 6 psi , works perfect for me.
My experience with Edelbrock carbs is that the Manual choke versions (1405 600cfm) are set up way richer than the electric choke versions (1406 600cfm) as an example. Both are 600's but the mileage is much better with the 1406, as much as 5mpg from what I observed, same engine, same truck. According to the Edelbrock carb manual the 1405 uses a 0.100 main jet and a .070 x .047 metering rod while the 1406 uses a .098 main jet and a .075 x .047 metering rod. Secondary jet size is .095 on both. The 1405 has an orange step up spring (5") and the 1406 has a yellow step up spring (4") so there is quite a bit of difference even though both carbs are 600cfm. I agree that the best way to set one up is with a wide band O2 and if possible a dyno run. Pay lots of attention to the advance mechanism in the distributor and the vacuum advance, full manifold vacuum to the vacuum advance usually nets the best mileage. I have seen many Chevy distributors with stuck, worn out mechanical advance mechanisms over the years. Just my educated guesses.
There must be something about Tri-5's and a Prius. I own a Prius C, and it is a far better daily driver than my dinosaur 57. Kerry , who has road racing experience [a good "Momentum" driver] managed to get 100 mpg out of it, while thrashing it home from the dealer [124 miles away] note ^^^^ this is imperial gallons Get all the basic tuning sorted on your car [timing, carb etc] then learn to drive it differently. [I don't mean "hypermiling" because life is too short for that]
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