I searched, and couldn't find the info I was looking for. Anybody have real number MPG for mostly stock 350/4 and 455? I can't decide what to build for the convertible. I understand the performance, sound, fun, all of that. But as money gets tighter, and gas gets more expensive, it changes things a little. I am also re-thinking my rear gear. I want to drive the car most of the time. Thanks for any information.
That is interesting Mark - I would be curious to know the difference in MPG as well between the two Buick engines. As for your rear gear - I have a rebuilt 3.23 (done by Ken Geiss of Everyday Performance) which is great around town and on the highway. 3,000 RPM at 70 mph.
I have had decent luck getting resonable mileage out of both engines. I have had 455's that got a good of mileage as the 350's because it did not have to work as hard, but these were bone stock drivetrains with modest gear ratios. 16-19 mpg's seems to be the numbers that I remember.
I can tell you the best that I have been able to do with my mildly built 455 is about 14mpg, on the interstate . 3:31 rear end, 26 inch tall tires, TH400, KB118 cam, Osborne rebuilt original Q-Jet. 60MPH=3000RPM, if I remember right. I've done anywhere from 8 (or worse) to 12mpg running around town.
That's helpful. I have cars with both, but never check the mpg. Guess I should. If the 455 can end up with that kind of mileage, I'll go that route with the car. I'll have to figure out the tire I will use and get the rear ratio. I was thinking maybe 3.08. But maybe 3.23 would be the way to go.
>>Hi Mark, I forgot to mention that I run 255/60/15 tires all around with my 3.23 posi rear so it acts a little higher.
For comparison, my wife's 2006 Nissan 4wd Pathfinder with a V6 gets about the same mileage as my 455. I'm guessing it's a little more flat where you are, so my car might do better there.
Flat? I can watch my dog run away for 3 days. The only 455 we run, is the 464, and it's not a good judge for fuel economy. I'm not looking for great mpg's, but wanted to make sure it wasn't too terrible. Sounds like a 455 goes in for now if I can afford to put it together. Cheap way would be a 350/350 and stock open rear. I have those sitting around everywhere. I want to do the 455/TH400, and posi rear with gear. To do that, I have to freshen up a 455 I have, get Tyler to build the TH400, and build the rear. Not a whole lot of money, but much more than the 350 combo. Tyler says build it like I want it (455), even if it takes me longer. Guess I better sell some parts.
I think it depends on set up also. Using a OD transmission, will get you better milage while running a lower rear gear. also a gear vendor overdrive will help also. Tim
Where you drive and how often you have the secondaries open make all the difference in the world. I have to admit I've never checked my mild 350's mpg around town. At interstate speeds from the west coast to ND in 2004, I averaged around 20.With a 2.56 rear, TH350 trans. I'd guess low teens around town.
The only useful data you're going to get will be from someone who's swapped and had both engines in the same car without other setup changes like weight & gearing, and without a big change in driving habits between both engines. Then you have to hope they bothered to check fuel economy before & after. Devon
Both Billy A and myself get about 17-18 MPG + (U.S. gallon) with our warm 462's.This is steady highway cruising at 65-70 MPH.The secret is lots of timing advance,relatively lean primary jetting (both have big Holleys),3.08 gears,28" tires and pretending there are eggs under the accelerator.Not bad for 475-520 HP. Old age helps too!!! Rod
I've heard of 20 mpg with a stock 455 in a GS, and I've gotten 16 mpg with a stock 455 in an Estate wagon. Proper tune makes a big difference!
Devon, the information people are providing is exactly what I was hoping for. Thanks again everybody. My concern was that if I built a mild 455 for the car, it would be impossible to get decent mileage. Sounds like, the fuel economy can be very similar between the 350 and 455. Not a huge gap anyway. I've been around this board for a while. Ya'll all know I'll get about 6mpg and sell a kidney for gas money.
Youll have to convert this; But my 1996 Lumina Van gets about 10L/100km (23.5 USMPG) (it used to get about 9 but its getting old now, going on 400 000kms). My Buick 350/2bbl with TH350 and 2.73 rear gear got slightly better than my van close to 9L/100km (24 USMPG). This was a difference of about $5 in gas per week. Driving to school each day which was highway morning, and bumper to bumper after noon. I drove the speed limit (ie: no faster than 62mph) My previous buick had a very tired 350/4 with TH350 and 2.56 and i didnt drive it enough. But i remember if i didnt speed, i didnt really need third gear. I could drive in 1st to about 80km/h and in second at 100km/h at about 2600rpm. (i needed it to rev that high becuase it burnied oil and would have fouled the plugs). I would bet a stock 455, with a healthy exhaust and intake system and a 2.56 would beat everything, because youd never need to rev over 1400rpm. (ALL of the figures above were calculated using distance from googlemaps and keeping track of gas receipts in litres).
i always got around 15 with my spirited driving no matter if it was with the stock 2.56 and 215-60s or the 3.08s and 275-60s I can manage 20mpg if i'm really easy on the throttle and watch my rpms and what not.. as of now, I get a bit worse then 15 due to a leavy tank, gas lines, and out of tune carb..
Another thing i wanted to mention; carb selection. Make sure its a 4bbl if its a 455. Dont use a holley, q-jet or edelbrocks would be nice. Mainly because they arent as sensitive to temp/humidity change. Your driving habits will dictate how much fuel you use. Ie; WHERE do you drive? If its all highway, go with the 455. If alot of it is city/rush hour/bumper to bumper, go with a 350/2bbl.
I can get almost 20 MPG on the Skylark and the LeSabre is around 13-15. I tend to drive the Skylark a bit more briskly, but due to weight and transmissions, I'm not sure it's a good comparison. Your right foot will be the biggest factor.
The only time I've checked my mileage I got a solid 200 miles on the 20 gallon tank for a whopping 10 mpg. That's a 455, mild cam, headers, TH 400, going an indicated 70 mph, ALL highway miles! After that, I don't check it anymore. Too depressing. As for a 350, I bought a '76 Regal brand new. Best mileage I ever saw with it was 15.5 hwy. Neither would win an economy contest but that's not why we have these cars, is it?
