Re: Improve mileage 350 with Quadrajet
 

If it's a 90C thermostat then it should begin to open at 90C not 80C. Your thermostat is worn out.

Gasoline has 114,100 BTU/gallon. Propane (LP) has 75,000 BTU/gallon. So. One US gallon of LP has 34% less energy than an equivalent US gallon of Gasoline.

@14-15 US mpg on gasoline is pretty good fuel mileage. You should get 34% less or... 9.2-9.86 US mpg on LP. I'd say you've arrived.

Re: Improve mileage 350 with Quadrajet
 

hi HAtzie,

thanks for the reply.

I have taken the thermostat from the car and tested it in water. heated it untill it cooked and in the mean time watched the thermostat open en then let the water cool and see the thermostat close.

The thermsotat is just fine. That test is somewhere here in my posts. It's just my onboard T-guage that seems to be of by a little...

Re: Improve mileage 350 with Quadrajet
 

I have a '78 swb step side with a 250 straight six and 3.73 rear gears, it originally had a 3 speed that got 12mpg on the highway. After swapping in a T5 with a 0.8 5th gear my mpg jumped 40% to 17 mpg on the highway.
Have you ever thought of a TH700 trans?

Re: Improve mileage 350 with Quadrajet
 

I did, but I have a 4WD and the right TH700 to find is a b1tch here in Europe...

and I have a TH400now that shifts perfectly...so I am a bit scared of swapping for a TH700...never know what you get and I hear a lot of bad talk about it...

Re: Improve mileage 350 with Quadrajet
 

its only so bad because it let someone down because they dont maintain there cars and truck proberly

Re: Improve mileage 350 with Quadrajet
 

oke, next chapter in this topic.

got my hands on a second hand MSD 6AL (model: 6420). Installed it yesterday. Engine is running fine now. dont really notice any big improvement. Need to open up the gap in the spark plugs a little...

I'll be back with results in two weeks.

Re: Improve mileage 350 with Quadrajet
 

okay guys, some results...

after my first 80 miles I got a MPG of 8,16

and the second 96 miles I got a MPG of only 7,83

while before wit the normal HEI I got 8,7 - 8,9 MPG

How is it possible that with a better ignition I get a lower mileage

In between I even opened up the gap from .8mm tot 1.1mm for a better spark...but I get no improvement...

If you guys dont have any tips I am gonna put the old HEI back in...

please help!

Re: Improve mileage 350 with Quadrajet
 

continuing my search for improvement in mileage I found this pages and tips on

HEI Tuning Secrets
http://www.73-87.com/7387garage/drivetrain/hei.htm

I decided to make my own Timing Tape using the information of this url:
http://www.crankshaftcoalition.com/w..._a_timing_tape

I took measurements of my Balancer 2nite and found the circumference is 695mm (27,34 inch). So:
1 degree is (1/360)*695 = 1,93 mm
10 degrees is (10/360)*695 = 19,3 mm
20 degrees is (20/360)*695 = 38,61 mm
40 degrees is (40/360)*695 = 77,22 mm
60 degrees is (60/360)*695 = 115,83 mm

Re: Improve mileage 350 with Quadrajet
 

hmmm good info...

Re: Improve mileage 350 with Quadrajet
 

how did you setup your timing?
initial?
mechanical?
vacuum?

total @ ?? rpm?

Re: Improve mileage 350 with Quadrajet
 

i think i started at 8
I've played it back and forth
not realizing the vac advance was still an issue(sticky)
I've cleaned the vac advance a few times
weights/vac rod were seized when i got the truck
but this time was the last time ,ordering a new one (dist)next
in my pic you can still see a mark where it was rusted solid
I've moved it(rod) out of the way to clean/file the hole and flat area

Re: Improve mileage 350 with Quadrajet
 

Overdrive will help you a lot!!!
700 swap from a 350 Turbo is relatively easy and you just need a kit from Advance Adapters for about $150. Your problem is the output shaft from the 400 Turbo is larger and therefore the gear in the transfer case is too big for the adapter shaft and no one I can find makes a kit for this. You can change the gear in the transfer case and it will work great. Better, but more expensive is to install a 4LE-80 with an electronic controller. A Gear Vendor Overdrive is excellent, also.
MSDs won't change your mileage unless you have a problem with your stock ignition, no matter what they say. Proper mechanical and vacuum advance, good secondary ignition parts and proper electrical supply to the primary side are all you need. The plug gap should be about .04" and won't help mileage to increase it.

Re: Improve mileage 350 with Quadrajet
 

thanks robert....

I already did some research on changing tansmission, but for a TH400 in a 4WD it isnt easy and no plug-n-play...I read somewhere that the 4L80E might fit nicely, but you still need an adapter and only a couple of companys make them so you dont need the electronics...and they are expensive....

I did the ignition timing today using the new timing tab....!

made my own timing tape for my 8" balancer... 18mm per 10 degrees...

My initial timing was set at 11 BTDC (without the vacuum advance).

My total timing at unknown rpm was 32 BTDC. My Equus 3568 timing light is digital and isnt able to read RPM with the MSD 6AL connected.

Because LPG is allowed a little more advance, I adjusted to 14 BTDC and total timing advanced to about 34.

I then added the vacuum again and idle timing was something like 20-25? jumping al over the scale...

for some reason sometimes when increasing the rpm's the the timing was stuck at about 15-20 rpm....I then had to re-increase the rpm's and then I was able to normally read the timing again....I think this is because the Timing light isnt always able to read the sparks correctly of the pickup...

any body else have experience with this?

the problem is, that now my car is running perfectly on LPG, but almost wont run on regular gas...what timing are you guys using for regular gas?

I read somewhere that because my engine had all the smog-stuff connected that is might need different timing, because of lower compression? anybody know about that?

Re: Improve mileage 350 with Quadrajet
 

MSD and digital lights don't like each other. The MSD gives multiple sparks at lower rpm and the digital lights react so fast they can't decide which spark to count.

Re: Improve mileage 350 with Quadrajet
 

used the mr gasket timing advance kit and changed the weights and springs (black ones now).

car drives fine, no real improvement performancewise as far as I can judge....the springs that came out were stiff ass hell...the ones that went in were easy...

I'll report back with mileage in a week or two.

http://www.chargerr.com/THORN/MrGasket%20929G.jpg

I had to get gas today (LPG) and I ran 127miles and had to get 67.49 liter of LPG.

that makes like 7.0 mpg

then I checked my tire pressure and noticed it was only 25 psi where I normally load the front with 44 and rears with 51.

that probably influenced my mileage a lot...

will check again the next few weeks.

Re: Improve mileage 350 with Quadrajet
 

alrgihty guys.

I took the choke plate out today, because it only restricts my airflow and I run on LPG for 99,9% of the time anyway.

I need to get to know more about these quadrajets.

I know the choke Pulloff prevents opening op the secondaires until the engine has warmed up through the mechanism at I.

but how do the big plates at II open up? As far as I can see they do not connect to anything?

I checked by opening the choke by hand and checking if I can open the throttle all the way...and it does...but these two big flaps at the number II dont open up.

why?

picture:
https://lh3.googleusercontent.com/-2...ke_pulloff.jpg

Re: Improve mileage 350 with Quadrajet
 

hows it goin,
there is a spring under that over hang your pointing at
ajust with allen key,adds more or less "spring" to the bigger plates
they open with vacume,but lower is a stop for the bigger plates till the choke is off i usally bend it out of the way,round end with a inch or so rod threw it
i'll go grab one from the garage 2 show

Re: Improve mileage 350 with Quadrajet
 

I checked when I just came back from a drive. the choke pulloff blocks the secondairy flaps from opening, untill I turn of the engine. So I probably need to hook the choke-pulloff to a temperature controlled vacuum port on the intake manifold?

where do you have your choke-pulloff connected?

Re: Improve mileage 350 with Quadrajet
 

never mind!

solved it! I found that the chokepulloff activates by vacuum (so at idle and cruise) and then retracts and pulls the choke a little open (only necessary when choke is engaged). When you open up the throttle wide enough so you engage the secondaires, the manifold vacuum drops and will let the chokepulloff release the secondairy air valves. I read that is to make sure the engine doesnt BOG? when suddenly kicking full throttle.

Re: Improve mileage 350 with Quadrajet
 

found mine, one looks close
no idea what they are from,just cores really
the shot with the writting, is from the bottom looking up
you might even consider seeing if the secondaries could open a bit less, unless you get right on it

Re: Improve mileage 350 with Quadrajet
 

thanks john!

Re: Improve mileage 350 with Quadrajet
 

those kits are crap
throw it it all away and put the stock wights in with the heavy springs from the kit

Re: Improve mileage 350 with Quadrajet
 

hi INSIDIOUS '86,

why would I do that?

I run LPG 99.9% of the time. So I benefit from a fast and flat advance curve. Thats why I installed the lightest weights.

Why would I install the old weights and heavy springs? can you explain that to me?