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Discussion Starter #1 (Edited)
Hey all I have a 1970 Lemans with 350/350 combo bought from a junkyard and here is what I know and what I think I know.
Stock lower end w/ a mild cam (I think it has a mild cam because anything under 10deg of timing causes it to back fire out the carb)
Heads have been rebuilt and still uses stock parts, rockers torqued to 20ftlbs
Here is where it gets dicey I have a tomahawk single plane manifold with a 1406 eddy sitting on a 1in spacer, no power brakes.
my ignition is a MSD pro billet with no vacuum advance I have found it runs happiest at 14 degrees advanced and pulls 15 on a vacuum gauge.

It runs and drives great but a little sluggish off the line with a 2.73? open diff my concern is the MPG it gets about 11 about half freeway driving. Would my mismatch of parts cause this? It gets 89 octane in cali gas. The carb is set with the number 8 tuning chart mixture which leans it out some. This car was built on a vary tight budget.

Forgot to mention exhaust, stock manifolds running dual exhaust 2.5 with thrush mufflers no X/H pipe
 

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Hey all I have a 1970 Lemans with 350/350 combo bought from a junkyard and here is what I know and what I think I know.
Stock lower end w/ a mild cam (I think it has a mild cam because anything under 10deg of timing causes it to back fire out the carb)
Heads have been rebuilt and still uses stock parts, rockers torqued to 20ftlbs
Here is where it gets dicey I have a tomahawk single plane manifold with a 1406 eddy sitting on a 1in spacer, no power brakes.
my ignition is a MSD pro billet with no vacuum advance I have found it runs happiest at 14 degrees advanced and pulls 15 on a vacuum gauge.

It runs and drives great but a little sluggish off the line with a 2.73? open diff my concern is the MPG it gets about 11 about half freeway driving. Would my mismatch of parts cause this? It gets 89 octane in cali gas. The carb is set with the number 8 tuning chart mixture which leans it out some. This car was built on a vary tight budget.
So what kind of mileage do you think it should be getting, just curious. :yesnod:
 

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Add a vacuum advance for better mileage. No reason for a street car to run without it. Single plane manifold isn't doing you any favors either.

The 67-72 factory 4 barrel manifold is a copy of the old SD manifold from the early sixties and outperforms or is equal to most aftermarket manifolds.
 

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Discussion Starter #4
So what kind of mileage do you think it should be getting, just curious. :yesnod:
thanks for the replys I want to toss on a vacuum advance dizzy just for giggles, The intake was cheap so it went on, replacing a warped eddy p4b intake.

Well I have been reading around that some people are getting around 15-20 mpg I would be happy with 14, I am not looking for a miracle, just an improvement. Honestly that would almost put it on par with my truck and I could use them interchangeably, as this car may not be the fastest or prettiest but it is mine and I enjoy it to much to let it sit around :smile3:
 

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Put a bottle of Redline S1 complete fuel system cleaner in a full tank of gas and clean some of the system out.....
 

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thanks for the replys I want to toss on a vacuum advance dizzy just for giggles, The intake was cheap so it went on, replacing a warped eddy p4b intake.

Well I have been reading around that some people are getting around 15-20 mpg I would be happy with 14, I am not looking for a miracle, just an improvement. Honestly that would almost put it on par with my truck and I could use them interchangeably, as this car may not be the fastest or prettiest but it is mine and I enjoy it to much to let it sit around :smile3:


OK, 14 could be had. The vacuum advance should be a plus. However, the intake/carb combo is a problem. Go back to a factory Q-jet and carb and mileage will go up -smaller primaries and better fuel distribution. Additionally, if you wanted to get much better mileage, I'd install a shift kit for faster shifts and less slip as the gear change takes place, and install what is called and RV torque converter which is a tighter stall speed than factory. Get your timing sorted out and add a big open air element air cleaner and you could probably see 17-18 MPG at steady 70MPH highway speeds. Around town might be 13-14 with the stiff gears and stop/go traffic.
 

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X2 with Jim on the carb/intake .

Run a Q jet and a stock P4B intake.

The MSD distributor Definitley isnt helping either .

Get a stock HEI and run it. Check to be certain the mechanical advance is free and will move and also the vacuum advance must work.

You can run an adjustable vacuum advance can to help with economy.

Set timing at 12- 14 degrees initial.

Use stock weights on mechanical.

set the vacuum at a light spring setting and limit the timing to around 10 degrees full vacuum .

Run a ported source for best economy.

Check the plugs and set the gaps at .045 with the HEI setup.

R45S AC delco plugs may be a good choice here
 

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Discussion Starter #8
Thanks for the tips advice all! A little update I did try the 1425 primary jets which are .72 and I was getting a miss under light throttle, I fixed that by going to a 70x37 rod vs the 73x42 that had been in there. Pump shot is on the top hole. While it does run great question is did the smaller rods negate any mpg improvement that the smaller jets provide?
Maybe I just have to save my pennies and stop trying to make my current set up economical lol :)
 

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Discussion Starter #9
Update time, I am going to freshen up the cars original points distributor and run that for now and maybe down the road try the pertronix igniter conversion. This raised a new question for me however, can I run the original points to an MSD blaster II coil with a 6Al box? I have read that yes I can but I would like to hear from the experts. Thank you all for the support and input learning as I go.
 

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Update time, I am going to freshen up the cars original points distributor and run that for now and maybe down the road try the pertronix igniter conversion. This raised a new question for me however, can I run the original points to an MSD blaster II coil with a 6Al box? I have read that yes I can but I would like to hear from the experts. Thank you all for the support and input learning as I go.

Yes you can.IIRC the white wire on the MSD box is the points trigger wire.
 
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