[BuzzLOL]

The 204/214 durations performance truck cams for stock engines mentioned above (and below) are good cams, but bigger than the 194/202 cam you have and will make the MPG problem even worse... The problem is in 1970's, Chevy dropped to early 1950's static compression ratios of high 7's:1, but kept the bigger 1960's cam sizes used for 8.5 - 10:1 compression ratios to keep HP ratings from dropping back so low again... for advertising/competitive reasons... One way for more MPG is going to the heavy truck smaller 184/194 torque cam which will raise the dynamic compression ratio and MPG, but will lower your already tepid HP/RPMs... or maybe Comp Cams has a special truck flat tappet cam with more lift at those same low durations numbers to retain HP... Or could go roller lifters/cam at short durations, but higher lift, like GM did to cure the problem in the 1996 - 2002 Vortec truck engines along with higher compression ratio giving much better MPG and even a boost in power from your current level... but that roller cam setup would cost nearly a $1,000 minimum to do in your engine...

Other solutions:

Change to flat top pistons for a boost in compression ratio to around 9-9.5:1...

https://www.summitracing.com/parts/sum-17350-00/overview/make/chevrolet

Chevy SBC 350 Flat Top Pistons Moly Rings Kit 030 355 | eBay

Swap Vortec heads on for ~8.5:1...

Swap in a new ($2100) or used Vortec engine (9.1:1 and short durations roller lifters/cam)...

Remember, the gas savings will eventually pay for the parts if still driven enough...

The swap from well-tuned Q-Jet carb. to EFI will be expensive and not make a noticeable difference in MPG... the newer engines get vastly better MPG and HP mainly because of internal improvements to the engines as I outlined above... 11:1 compression ratio with aluminum heads is common now... direct extremely high pressure gas injection like a diesel uses is also the top MPG getter now...

Your truck prolly gets about 7 - 9 MPG city and 9 -11 MPG hiway... new trucks are more like 17 city and 23 hiway... simple improvements can prolly get you up to 15 city and 20 hiway... The Q-Jet was the best MPG carb. ever... and can also support a 400+ HP engine...
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[BuzzLOL]

I had forgot to mention that I had removed the stock exhaust manifold and install a set for Doug Thorley headers that had given me noticeable improved power when I drove with the camper.

Replacing the heads would be great but an extra $1k-$1.2K would put me way over my budget and Mama would not be happy with that extra cost, but @ $200 for a cam and lifters would work if I saw a modest improvement in performance and mpg.

I going to have to rethink the EFI vs Carb.

Yes, the engine you have is about 225 grossHP... stock iron manifolds/single exhaust knocks that down to about 175 HP or lower... headers and dual exhaust brings that back up to about 225 HP again... so a noticeable difference... as is usually said, (budget)headers give about the most power per dollar spent...

My old '86 Monte Carlo 305" V8 Q-Jet carb. was rated 17 MPG city and 25 MPG hiway... 10 years later a new mustang with 302" V8 and EFI had the exact same ratings... so that tells you the 'magic' of EFI...

A smaller cam would prolly get you 1 or 2 more MPG... but, as I mentioned above, NO "performance" increase, a drop in HP... but prolly a little increase in off idle and lower RPMs torque which would help cruising a camper... Depends on what your plans are for the truck...

Lowest cost option giving the biggest boost in MPG and also more power would be swap pistons... and keep cam, intake, carb... (inspect the cam closely to make sure no wiped out lobes)... that gives about 275 HP...

Domed pistons (not linked above), mild performance cam, and high rise intake manifold (trucks usually have room) can give around 325 - 375 HP with still much better MPG... the higher number assuming your stock heads have the car/light truck valves (1.94"/1.5") and not the smaller heavy truck (1.84"/1.44") valves and smaller ports... Like I said, depends on your plans for the truck...
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[BuzzLOL]

The #339 heads are small valve heads(1.72/1.5), so, you may not see a big improvement. A good budget choice for you would be a set of later model (87/95) #193 swirl port heads.

OK, I hadn't seen Eric's posting when I posted the above... the HP numbers are going to be quite a bit lower than what I posted above and these heads are prolly going to be limited to about a 200 HP max build no matter what you do...

However, changing pistons can still give a good bump up in MPG since they are still big chamber heads giving too low compression ratio...

Too bad you aren't closer to this member who just inherited a brand new Vortec 350" engine... don't know if he has any plans for it or wants it:

http://www.hotrodders.com/forum/motor-448730.html
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[BuzzLOL]

This is excellent advice. It's what I was thinking too.

Leaving things stock ??? How'd you get on this forum ??? ... R U Nuts ??? ...LOL !!!

 

[BuzzLOL]

Since the gas mpg sucked back when i use to drive it, we thought we would do some easy but moderate improvements under the hood.

we might think about a cam swap since the engine is on a stand. He couldn't recommend which one for my setup since he is a Ford guy.

what does the forum suggest for good mpg and overall torque? Is it worth the $$'s or stay with the stock cam?

I had forgot to mention that I had removed the stock exhaust manifold and install a set for Doug Thorley headers that had given me noticeable improved power...

but @ $200 for a cam and lifters would work if I saw a modest improvement in performance and mpg.

I going to have to rethink the EFI vs Carb.

I guess I now need to determine the right cam to choose.

Mike and Philip

Looks like Mike really wants to make some improvements...

 

[BuzzLOL]

The EFI offers alot more benefits.Better, quicker starts, especially in cold weather

Actually, nothing starts quicker than a Q-Jet warm or cold... the newer EFI cars crank over two or three times as the computer figures out where the engine parts are and then it starts... But a Q-Jet car in good tune just starts most of the time, you don't even hear the engine crank over...

 

[BuzzLOL]

Then he ought to save the money to build what he wants. $200-500 is not going to get it done ... spend it on items that can be used when the money allows for upgrades that are going to make a real difference - i.e. - headers.

As has been mentioned twice above, he already added headers...

Actually, the $86/set pistons I linked above plus some gaskets and a carb. tune may give everything he really wants... much better MPG and a little boost in HP and torque everywhere...
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[BuzzLOL]

That's simply not true.If an EFI has to turn over that much, there are other things going on. The computer doesn't have to figure anything out.No sitting there keeping it runni g til it warms up.

Not true, you need to go out and start your old truck and listen how many times the engine turns over... The sensors do nothing until something spins past them, then they send a message to the 'puter, which has to interpret them... also, no need to keep a Q-Jet engine running, just put in gear and drive off... When I drive a newer EFI vehicle, I often embarrassingly turn the key off starter position too soon and it doesn't start, because I'm not used to waiting for it to start after going from a Q-Jet vehicle...

Don't know yet just what Mike is looking for... Those 65cc Swirl heads will only give ~8.5:1 with the stock dished pistons with 4 eye brows and huge champfer around the outside edge... plus his -339 heads only have 89K miles so should only need some new valve seals to go another 100,000 miles... some stronger flat top hypereut pistons would be a good upgrade with no other changes to the engine since then the short block would be ready for any future upgrades like heads or cam...
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