Curious to see if anyone has done a basic stock swap of an LS1 and its corresponding automatic tranny into a 68-72 Chevelle that has tracked what their mpg average has been? If so any other details like rear ratio would be appreciated. I am thinking of swapping in stock LS1 in to a 70 elcamino for my parts runner. I have to travel 30 miles one way to get to any dealerships to pick up parts for my shop. THanks

Well I can't give any direct insight yet, but before with a 700r4(3:73 rear) behind a 350 with a 750 double pumper and a healthy cam I got right at 15 mpg highway. I am close to finishing up my LS1 swap and even with a cam I expect it to get around 20 mph highway. Mine is a 67 however but I don't imagine 20 mpg is a far reach for an ls1 swapped 68-72 with an overdrive tranny either. Hope that helps you out a bit.

I have a 03 Silverado SS with a 6 liter and a magnacharger. It has 4.10 gears and a 4L65E overdrive. I get 12-14 around town and 16-18 on the highway if I keep my foot out of it. Also keep in mind that my truck weighs 5750lbs with me in it.

I had a '93 Firehawk with an LT-1 and a 4L60E w/ 3.23 gears. I know it is not an LS-1 but it may give you a ballpark idea. I got close to 25 mpg on the highway in my Firehawk. I knew some guys with LS-1's and 6-speeds that got around 28 mpg highway. That body style is ovbiously lighter and more aerodynamic than our Chevelles so that is a factor. I would imagine that at least 20+ mpg is not unrealistic.

In my FRC C5 I was getting 18mpg around town and 28mpg on the hwy. After heads and cam mileage went down to about 16mpg if I were nice around town and hwy was about the same or even improved.

My '01 2500HD crew cab 6.0 LQ9 gets 14mpg city or hwy but my hwy speed is running the rpm's a little high.

Given decent rear gears and a steady "sane" freeway speed cruise of 65 or so mph I would hope it would get 23 mpg minimum.

The newer GTO's are in the same weight category, maybe even a bit heavier than our cars and manage to knock those mileage figures down with the 6-speed. However their body is more slippery.

I can pull 19 mpg out of my car at 75-80 mph and I have managed to get just over 22 mpg at 65 mph. That's with a Gen 1 SBC with a fairly large cam and a blower too. I have it running quite lean at cruise (15.5-15.7:1) with 50-52 degrees of timing. I'd like to go leaner than that but then it starts to surge no matter what I do with the timing. If I can pull those numbers down with my combination then a stock LS1 should be able to better that without even trying.

Another thing you might want to consider is a ECM re-tune especially if you won't have to emissions test your car... There is a "lean cruise" option already in the ECM for non-US market LS1's that eeks out a bit more mileage at the expense of higher tailpipe emissions (increased NOx). We don't get it enabled here in the states because the leaner than stoichiometric cruise, while returning better fuel economy, increases the emissions beyond what the standards allow. Enabling lean cruise usually nets about 2-3 mpg increase in mileage at steady throttle light load conditions.

You should have no problem getting low 20s.
Check out LS1tech in the Conversions & Hybrids section. There may be some A-body swap cars on there.
http://www.ls1tech.com/forums/forumdisplay.php?f=28

I get 25-27 mpg in my GTO (2006), but that's with an LS2 (similar) and 6-speed, using 3.46:1 stock gearing...The auto versions (4-speed) probably get 3-4 mpg less easy...In the City, I'm at about 15-16 mpg, which isn't too bad IMO (with moderate driving, not flooring it everywhere, lol).

I will be putting 6-speed and 4.10's in my Chevelle, but with 'regular' SBC and would think 20mpg or so should be doable.

I did a 350 throttle body/700r4 out of an 89 truck into a 71 el Camino with 2.56 gears and would pull 22-23 mpg at 75mph all day. I would hope the ls1 could pull the same.

Mike

Ok, so anybody have MPG for a stock LS1/4L60E in a 68-72 yet? It kinda got off track. . . .

Mileage is going to vary so much as not to be of any value. Everybody drives differently. My brother has the exact same truck I have (2007 Silverado 6L L465E and 4.10 rear) and I get 2-3 more mpg than he does. I get 12-14 around town and about 17 on the highway at 70 mph. I'm sure you would get much better than that in a Chevelle.

I had a '93 Firehawk with an LT-1 and a 4L60E w/ 3.23 gears. I know it is not an LS-1 but it may give you a ballpark idea. I got close to 25 mpg on the highway in my Firehawk. I knew some guys with LS-1's and 6-speeds that got around 28 mpg highway. That body style is ovbiously lighter and more aerodynamic than our Chevelles so that is a factor. I would imagine that at least 20+ mpg is not unrealistic.

The weight difference between a loaded 4th Gen TA and Chevelle may susprise you and be close. The 4th gens can get over 3500lbs. Even an Iron block LSx with Aluminum heads should weigh in less than an aluminum headed SBC.

Ok, so anybody have MPG for a stock LS1/4L60E in a 68-72 yet? It kinda got off track. . . .


The gears and tire size you run will have a big impact. I would expect 20 up to 25mpg with 3.23 to 3.42 gears depending on details of the swap (year, weight, mods gear, tire size driver etc). A few links to sift through and get a feeling.

The first link someone posted up a 5.3 with LS6 cam and intake which would be a strong relatively cheap gas mileage setup.

http://www.chevelles.com/forums/showthread.php?t=296652&highlight=mpg&page=2
http://www.chevelles.com/forums/showthread.php?p=1900435&highlight=mpg#post1900435

Keep in mind Andrew in the 2nd link has a single overdrive and IIRC 3.73s. I lost 3mpg (31-30mpg to 27-28mpg) on the hwy by switching from 3.42s to 3.73s with a double overdive T56 in a 3100lbs C5.

Not a Chevelle but our `87 Cutlass G-5 car with SLP cammed LS1/T56/4.10 gears gets up to 28MPG if you really drive it for gas milage on a long highway trip. Realistically we average about 22MPG, not bad considering we like to beat on it. ;) Mark SC&C