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alsalp
Tribal Scout

4 Posts

Posted - 16 Mar 2017 :  7:42:21 PM  Show Profile  Reply with Quote
I'd like to hear suggestions for a cam that would optimize mpg

I have a 68 Tempest wagon with a rebuilt 71 350 short block (.040 over) and 73 #46 heads. I don't know what cam is it. It seams to be a "stock replacement" cam installed during a rebuild. The engine sat around 20 years before I acquired it.

This replaced my tired original 2bbl 68 350. The fresh engine dropped a few mpg's from the old engine. This probably has something to do with going from 72cc #17 heads to 96cc #46 heads. (17 to about 14 mpg's)

I'd like to rebuild the higher compression heads and figure out the best cam for a daily driver to max mpg.

Up to this point I have been running a Q jet on an Edelbrock performer manifold with a th350 and 2.78 gears

In addition I am going to swap in a 700r4 (~1700 rpm at 70mph?) and am going to adapt GM TBI out of a chevy 350 truck (yes I know all about the aftermarket EFI)


alsalp
Tribal Scout

4 Posts

Posted - 16 Mar 2017 :  7:45:37 PM  Show Profile  Reply with Quote
TBI I told needs about 17 inches of vacuum

What cam would be or other things should I consider?
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cortcomp
Coyote

USA
5335 Posts

Posted - 16 Mar 2017 :  8:36:46 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Lower RPMS don't automatically mean lower MPG...you will be "lugging it" with that gearset and OD or have a loose converter bringing your RPMS right back up. Your timing won't be very advanced at all. I'm running a 700r4 and 3.70s and i'm at about 80mph converter locked at 2500. That's about good for a smaller motor, considering it has a lot less torque than the bigger 400+ engines. The lowest numerically gear i'd consider with OD is probably 3.42 or 3.23. As mentioned a lot here, you want your timing all the way in by your normal cruise RPM for the most efficiency.

I did run 2.56s and OD (stick shift) for a minute, but it was a high compression 428 with a good amount of torque. It was a lot snappier with the 3.42s and even more so with the 3.91s (i felt the 3.91s were a bit much, 1st gear was done in a split second.)
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alsalp
Tribal Scout

4 Posts

Posted - 16 Mar 2017 :  10:29:20 PM  Show Profile  Reply with Quote
I'm not opposed to changing the rear end ratio. Incidentally, are BOP gear sets the same as chevy 10 bolts? If not what is a good source to re gear a BOP 10 bolt?

what cam do think would be best for a #17 head 350?
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cortcomp
Coyote

USA
5335 Posts

Posted - 17 Mar 2017 :  09:59:13 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Nope, the BOP 8.2 isn't the same as the chevy 8.2. 8.2 axles bolt in, no c-clips, different posi type from the factory. I don't do any rear end work, but when i'm looking for pricing or availability, i look at summit to get an idea.

Jim at jdrace.com is a great resource for differential information.
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 17 Mar 2017 :  10:45:38 AM  Show Profile  Reply with Quote
Ball park compression ratio is 7.3 to 1.. Smog era car would run around 8 to 1..
9 to 1 would be allot more efficient.
I used .012 piston to deck.
- http://www.wallaceracing.com/cr_test2.php -


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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alsalp
Tribal Scout

4 Posts

Posted - 18 Mar 2017 :  1:18:29 PM  Show Profile  Reply with Quote
Anyone have a cam suggestion?
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phil400
Cochise

Canada
456 Posts

Posted - 18 Mar 2017 :  5:32:31 PM  Show Profile  Reply with Quote
Summit 2800.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"
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Phil
The Great White Buffalo

USA
7219 Posts

Posted - 18 Mar 2017 :  5:45:40 PM  Show Profile  Reply with Quote
Stick with an 067 or 066 on that or even a 2800 Sunmit. I had a 79 TA I put a 350/6x4 rebuiltd (but with updates including an 067 cam) . I also swapped in a TH-350/stock convertor as it had also been updated including a nice shift kit plus I had tuned it to shift right at 5000 consistently at WOT (the TA was originally a 301/4-speed car), 3.08 l/s, Perforner intake, 600 Holley VS, cheap Casler 4 tube headers and it ran 14 flat and got good mpg for its time. It was a great all around cruiser too. Naturally I optimized the tune on the HEI and Holley.

Today I would have run a well tuned Qjet without question and it would have ran better, cleaner and with higher mpg. It pulled like a locomotive with that cam (and taller gear) which the 350 seemed to like a lot. I'd also recommend spending a little time fitting that intake nicely to the heads as there's room for improvement, especially with later Edelbrock intakes.. It's a game of "every little thing helps". With your higher compression heads, you should be able to achieve even better results.

Of course I personally wouldn't use a 700 as I much prefer the 200-4R as it has many advantages but that's your call.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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