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alsalp
Tribal Scout

6 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

6 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
5440 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

6 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
5440 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
3505 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

6 Posts

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

Canada
504 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.
77 T/A sold
85 Monte Carlo SS sold
83 Mustang GT sold
"Let me tell you what Melba toast is packing"
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Phil
The Great White Buffalo

USA
7284 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. LS swaps in Pontiacs should only apply to Fieros.
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alsalp
Tribal Scout

6 Posts

Posted - 28 Dec 2017 :  1:02:10 PM  Show Profile  Reply with Quote
how about a 068 vs 067 cam
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Lee
Sitting Bull

171 Posts

Posted - 28 Dec 2017 :  4:30:57 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
If you raise the compression ratio very much, then you run into detonation issues with a short duration camshaft. You are talking MPG's, but is that the goal or is it MP$'s?

High compression small cam will require premium gasoline, while the lower CR could run on the cheapest gas. 17MPG with premium could cost you more per mile than 14MPG with 87 octane.

If you want to maximize efficiency at 1700rpm, then it will be a cam with rather small intake duration. To best optimize it, a custom grind will probably be needed. But that will add a couple hundred dollars to the cost.

You have not mentioned your exhaust, and that will make a difference in cam selection as well. Small tube headers with a free-flowing exhaust would be my first choice, R/A manifolds second choice.

As a cheap, general suggestion, Summit 2800.

CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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alsalp
Tribal Scout

6 Posts

Posted - 28 Dec 2017 :  8:57:35 PM  Show Profile  Reply with Quote
i have dual 2" exhaust with standard manifolds. I would like headers but am concerned that they might interfere with my column shift linkage
Anyone know of headers that clear column shift linkage? Also I'll be running FITECH fuel injection
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tjs44
Crazy Horse

USA
533 Posts

Posted - 28 Dec 2017 :  9:43:03 PM  Show Profile  Reply with Quote
just get the ram air exhaust and forget headers.They should be a good fit.
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