: lt1 GREAT MPG



v90hamm77
04-21-07, 08:51 PM
I cant believe I got 410 miles out of a tank of gas. I refilled 5 minutes after the low fuel light came on I probaly could have gotten more. Those plugs and wires came through for me.

I~LUV~Caddys8792
04-21-07, 11:22 PM
Is that in city, highway or a mix? If it's city, then 410 miles out of about 21.5 gallons of gas (tank is 23 gallons, give or take a few gallons for safety so you don't run out when it says E)...that's 19.5 MPG, damn good for a 4500 lb land yacht!

cadillacmike68
04-21-07, 11:44 PM
I get 15-17MPG in mixed driving with my 186,000 miles 1995 Fleetwood. I checked mileage on a short (70 miles) highway during which i eased up on the gas a bit - kept it around 75MPH, I got 23MPG on that short run.

I took it to Atlanta from Tampa and got over 20MPG total for abput 1,000 miles. Again while in and around town mileage tanked. I got the fuel pump and sending unit in the tank replaced some time ago, so the problem with the gas gauge lying to me is gone!

I replaced the plugs and wires at around 120,000 miles. The plugs are due again soon, but no driveability issues have arisen.The optispark distributor also had to get replaced a few years ago, because the WP leaked on it :thepan:

The alternator went twice. Other than that it's been pretty good.

JTraik
04-22-07, 09:14 AM
I have gotten 550 miles out of a tank with my '93 Caprice 9C1... not bad for a first gen 350.

caddycruiser
04-22-07, 09:27 AM
Yeah, I've been trying to eek out 400 from mine, but am right about on the verge. Every time I calculate it, I'm right at 16-18, with mostly highway driving (of course, at 75+ the whole time) and once a week coasting around town.

Right now I'm also running a K&N FIPK intake and a custom PCM tune by our own N0DIH, neither of which really made a change in the mpg regard, but are still an improvement in various ways. I think, however, buying mine at 117k and really having no idea of what's been done, it very likely could use fresh plugs, wires, etc., to help it out a bit more at this point--probably could help take care of some recent slight surging/vibrating at a red light, and some general bogginess from time to time.

That said, I've never been able to make it sip the way either our '92 Roadie or '93 FWB L05's do, but that seems fairly common...just as JTraik also gave an example of.

cadillacmike68
04-22-07, 01:09 PM
Simple math says we should get 575 miles to a tank with the EPA estimates (the old one)

yeah, right.. :lies:

but I got 400 miles to a tank a few times- that is when I kept the speed below 75! :tisk:

v90hamm77
04-22-07, 03:26 PM
This was a mix of city and highway with the AC blowing. On the highway I set the cruise at 75-80. Its all stock except for new plugs and wires.

N0DIH
04-23-07, 09:03 AM
With city highway mix I drive to work and back everyday, I see 16.2ish with E85, 19-19.5 with gas (no ethanol), and all time high of 21 highway. With 3.42 gears.

Temp is the big variable. In the 50-60F range I have always got best mpg. No AC on. In the 30-50 range I am in the mid 18's, In the 0-30 range, I am down to 17-18. Below 0 I see 16's to 17's. I have never got lower than 16 on gasoline.

The new EPA ratings on my car are reasonably close now with me assuming the 2mpg penalty for the V4P package (according to one website the V4P package was rated 17/23 mpg, so make that 17/21 and that is dead on for what I see)

I want to replace my wires soon, mine probably have 100K miles now.

96Fleetwood
04-23-07, 07:16 PM
You guys are lucky. My brother is getting 17 mpg with city/highway driving in his 1994 LT1 Roadmaster.

I am getting 15 mpg with city/highway driving... then again I might have a heavier foot.. or I just like to hear the sound of the Borla with some throttle applied.

N0DIH
04-23-07, 08:26 PM
How refined is your tune? Ever run any datalogs to see how it is running?

Old Fleetwood
04-23-07, 09:10 PM
I haven't followed mileage closely except once and that was 23 highway. Then again, the Highway was absolutely freaky with traffic running from 85 to 40 and nobody holding any decent average speed.
Towing I never checked.
What's VERY interesting is a friend's Chrysler minivan. He consistently gets NO BETTER than 18! That's with the big V-6 and 4 passengers.
Chrysler Cordoba 360 V-8 best ever road mileage 25 - One time.
With my 318 V-8 in my Dodge B250 Van/Wagon weighing 6,000 plus, I got 14 mpg fully loaded from Hartford, CT to Burlington, VT, Fillup to fillup, all highway driving. And that's like pushing a 4x8 sheet of plywood through the air at 70 miles an hour.
So the mileage for the big Cadillacs isn't so bad.
My God - You're travelling in a helluva lot more luxury than anybody in a minivan!

JTraik
04-24-07, 09:45 AM
I drove my '68 back from Des Moines and got an average of 16.5mpg. That was with poorly tuned engine. I told the guy to change the plugs and wires before I picked it up, get it home, poke around and realize he gave me cheap plugs.... didnt install the ones difficult to access and the wires were pretty original looking.... the car wasnt timed very well and the carb was very dirty!

3rd
04-24-07, 02:10 PM
wut can I do to get better mileage on my 1970 deville?

caddycruiser
04-24-07, 02:17 PM
wut can I do to get better mileage on my 1970 deville?

That's a big, heavy, gas sucker of a car, so really you're best bet--as with any car--is just making sure it's performing at its optimum level as frequently as possible, with a recent tune up and check.

3rd
04-24-07, 02:55 PM
That's a big, heavy, gas sucker of a car, so really you're best bet--as with any car--is just making sure it's performing at its optimum level as frequently as possible, with a recent tune up and check.

ok, thanks

Destroyer
04-25-07, 03:40 PM
Wow thats great, best I can do with my '91 is 250 miles thats with $60 -$65 fill ups. The carb and L98 355 sure helped with performance but at a huge expense at the pumps. I have the distributor advanced but the car feels like a pig when I have it timed right. I should find a good compromise where its still quick but gets better mpg's.

Old Fleetwood
04-25-07, 04:04 PM
Time to :stirpot:

Maybe everybody likes a cushy ride, but I like to keep TIRE PRESSURE up to the maximum pressure noted on the tire sidewall.
The boaty Cordoba I had cornered better, got better gas mileage and seemed to even ride smoother. Maybe that was a function of Mopar's torsion bar suspension. I dunno, but full sidewall pressure worked for me and is working for me now with my 1995 FWB with Coopers.

N0DIH
04-25-07, 04:26 PM
The V4P package requires 35 psi while towing, 30 while not. I like it at 38, but when the roads are rough it can be sort of rough too (Chicagoland roads suck....)

N0DIH
04-25-07, 04:30 PM
Get the L98 EFI system and drop on and that should do well.

You can get a PCM for $50, need some custom PROM work and then get a TPI intake or even an LT1 intake (will need some mods, as it doesn't have a distributor hole, L98 TPI is preferred) and make it a killer high torque L98 again. They said the L98 low end was stronger than the LT1. Getting a LT1 B/D Body cam and it really should do well for mpg.

I have found too high timing will hurt mpg too, so vary it and see what you find. Shoot for around 40 degrees cruise timing and 32-34 at WOT.


Wow thats great, best I can do with my '91 is 250 miles thats with $60 -$65 fill ups. The carb and L98 355 sure helped with performance but at a huge expense at the pumps. I have the distributor advanced but the car feels like a pig when I have it timed right. I should find a good compromise where its still quick but gets better mpg's.

I would expect more like 300-350 miles on a tank min on that car highway. 250 is getting far worse than I get with E85 and 3.42 gears dogging the heck out of it. That is in the 12's or less isn't it?

JTraik
04-25-07, 09:08 PM
Time to :stirpot:

Maybe everybody likes a cushy ride, but I like to keep TIRE PRESSURE up to the maximum pressure noted on the tire sidewall.
The boaty Cordoba I had cornered better, got better gas mileage and seemed to even ride smoother. Maybe that was a function of Mopar's torsion bar suspension. I dunno, but full sidewall pressure worked for me and is working for me now with my 1995 FWB with Coopers.

Yeah my friend has a 77 Newport... Chrysler likes those weird suspension setups, torsions and leaf springs on their fullsize sedans :rolleyes: I prefer coils all around but anything really works. He says he gets a pretty stiff and responsive ride from his Newport but not as cushy as he really wants, he rode in my '68 and seemed to think it was a smoother ride. His newport also has a much more beefy front sway bar. I like those old Mopars ALOT, second to the Caddies easily.

N0DIH
04-25-07, 10:16 PM
Oh, and to mention, the aura of having a TPI under the hood, looking like it was meant to be there.

Pick up the stuff and drop on by!


Wow thats great, best I can do with my '91 is 250 miles thats with $60 -$65 fill ups. The carb and L98 355 sure helped with performance but at a huge expense at the pumps. I have the distributor advanced but the car feels like a pig when I have it timed right. I should find a good compromise where its still quick but gets better mpg's.

Destroyer
04-26-07, 07:42 AM
Oh, and to mention, the aura of having a TPI under the hood, looking like it was meant to be there.

Pick up the stuff and drop on by!Guys at Summit racing said it would have been pretty easy to put the TPI stuff in it as well when I was purchasing the intake and carb. I have had several L98 powered cars, and in some ways prefer them to the LT1, simplicity being the major reason. Low end is similar between the LT1 and L98 but the TPI L98 runs out of steam in the upper rpm's whereas the LT1 feels stronger. The carb setup on the L98 seems to have given it more upper rpm power than it had with the TPI at the expense of off the line throttle response. Regardless, if I kept this motor in the car I might be tempted to go back to TPI but I'm looking to get a 383 Vortec stroker motor for it or possibly a 454 or 502 BBC. I do agree that a TPI would look sweet under the hood and IMO, GM should have been putting TPI motors in the Fleetwood since '85 instead of using 307's and TBI truck motors.

96Fleetwood
04-26-07, 02:08 PM
GM should have been putting TPI motors in the Fleetwood since '85 instead of using 307's and TBI truck motors.

Amen! :thumbsup:

N0DIH
04-26-07, 02:31 PM
Personally they should have never allowed less than 5.7L and 300 lb/ft torque in the D body.... Any less is just plain wrong....

z06bigbird
04-26-07, 03:35 PM
I get best mileage by parking car in garage for a month or two.

LOL

Destroyer
04-26-07, 03:35 PM
Personally they should have never allowed less than 5.7L and 300 lb/ft torque in the D body.... Any less is just plain wrong....
I think the Fleetwood, being the flagship car should have had the 5.7 TPI while others (D bodies) should have had the 5.0 TPI Chevy with the 5.7 as an option.:thumbsup:

N0DIH
04-27-07, 12:18 AM
Even if we limited ourselves to the era GM parts bin, just think, a 1985 Fleetwood with a 5.7L TPI, an L82 cam ("The L82 cam is used in the GM 290 HP crate engine, with 8.5:1 compression, knock offs of the 882s, headers, stock 4 bbl intake, stock Q-Jet, stock HEI set at 8* it gives 290 HP @ 5,100 /326 ft/lbs @ 3,750."), 3.42 gears for towing, 3.08 for std applications.

This would have started the Cadillac performance much much earlier. And I would bet the Impala SS would have surfaced much sooner...

pimpin88
04-27-07, 12:01 PM
I have gotten 550 miles out of a tank with my '93 Caprice 9C1... not bad for a first gen 350.

I've gotten 550+ in my 92 Roadmaster with 3.08's. Definitely not bad.

My last highway trip up to Toledo was in the middle of the night, absolutely no traffic and the cruise set at 60mph. I got 30mpg on the way up there and 29 on the way back!!! :bouncy: