I’d pass on the quadrajet, the TQ is a much better carburetor. You’ll end up going down the rabbit hole and talking to a bunch of chivvie guys and what do they know? Nothing,otherwise they’d own mopars.
road car cam for my 318
- Thread starter str12-340
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A quadraJet is a good carb, when done right. Problem is it takes more work than a TQ and isn't designed as well. But when done right it will run 10 sec quarters and in another application, get 20 mpg on a 350 engine. You could always count on Chevy to snatch defeat from the jaws of victory. Bean counters ruled the roost, not engineers.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I see I'm late to the party and unwilling to read all three pages. So if someone has already mentioned this, my apologies. Your cam is;
272/272/110/52* overlap. In at split-overlap of 110, the Ica is 66, Compression is 114 and power is also 114. With headers, running at 65=1800 rpm, that's a lousy economy cam.
Advanced to 106, the compression becomes 118, and the Power to 110. which is way better. Overlap is still 52, but the exhaust is now closing 4* sooner. Put some log manifolds on that to kill the overlap and watch what happens. Then, at the other end cruizing at 65=1800 with that cam, even advanced, with a factory type distributor is a bad recipe. That combo will want Cruize-timing to be up around 45 degrees, or more. Have you tried getting there? IDK where you have the Base-Timing set at, but if your mixture screws are not centered in their range, to slightly lean, I'd be willing to bet she's running fat....... all the time; the Idle mixture screws are for idling on, whereas the transfers are your Primary cruizing fuel supply.
If you run a LOT of Idle-timing, then the Power-timing has to be limited and slowed down, to not detonate at PT never mind WOT. If the throttle is nearly closed while cruizing, the VA cannot work.
Here's an example.
Let say you are running 20s at idle.. Thus the Distributor cannot bring in more than 15/16 for power, and say that happens at 3400.
Firstly, the throttles will have to be nearly closed to run that 20* which means the transfers will be nearly closed, which means that the mixture screws will have to be cranked open to supply idle-fuel. As a result, as soon as you open the throttles, and the Transfers come on line, the AFR will go rich.
The second thing that happens with 20* of idle-timing is that the the Vcan gets no signal from the sparkport, until you open the throttle a long ways then it comes in ok but when you get to ^5@1800, you back off to cruise, and anything can happen at the spark port. Maybe you lose all signal/ maybe 50%. But here's the thing, typically the Vcan is only good for say 10 to 13 degrees. Losing even half of it is a very big deal.
Suppose your Distributor starts advancing at 1000 rpm and all 16* are in at 3400. Thus the rate of advance is .67 degrees per 100 rom. so then, at 1800 cruise, the D is supplying ~5 degrees. thus your all-in timing is 25, IF your vcan is bringing in 15*, this comes to 40*. What if your engine wants 56*, or more, like mine does? Guess what, if that is true, your cruise-timing is 16* retarded! So she NEVER develops peak combustion pressure, and what there is of it, is chasing after the piston that is running away from it.
And so, those expanding gasses may enter the headers still burning and for sure still expanding. Which totally disrupts scavenging. Which in your case, while cruising, is probably a good thing, lol.
Now;
Your cam has Compression plus Power duration of 228* and overlap of 52*
My former cam had Compression plus Power of 227*, and overlap of 53 * it was spec'd as 223/230/110@050, which I later learned was 270/276 advertised. I tuned that beast to over 30 mpgUS, running at 65= 2100, running the cam 2* RETARDED, because she already had 11.3 to 1 Scr. It liked up to 63* of cruize-timing in certain situations but most of the time I ran 56*, now at 65=2240 (different trans, different rear gears.).
Now I gotta tell ya, my cylinder pressure with that cam, easily ran to 195psi in at the recommended plus 4*.
Now I'm not saying that you need to run your cruize timing up to 63*, lol. What I am saying is that cruise-timing for best economy is nearly critical.
To find the window, I installed a dash-mounted, adjustable timing module, with a range of 15degrees, and in the coming weeks before the gas-mileage run, I got intimately acquainted with what my engine wanted and changed the distributor dozens of times, to make it happen. And changed the low-speed fuel delivery nearly as many times.
and then it happened, I found a shortcut. And I'll give to you for free.
Warm up your engine, I run 207*F.. Rev up your engine to cruise rpm and maintain it there. Next, without regard to reading the timing, just pull in some timing, little by little, keeping the rpm steady. Keep advancing it until more advance produces no more rpm. Now read the timing@cruise-rpm. What you read is what the engine wants, at that rpm, with no load. From that number I subtract 3 degrees for load-compensation, and then I go build my advance curve to make that final number happen. Had I known this when I started, I couldda saved myself a lotta time.
From this starting point I just leaned it out until it was too lean, signaled by misfires and such, then put a lil fuel back in. Then road-tested with the dial back, looking for the perfect cruise-timing. My window was 56>60 @2240rpm, , sometimes as much as 63 degrees.
Just so you know, My combo likes
14* Idle timing plus
14* by 2800 distributor; 20* in by 3400/plus
22* in the Vcan, asap, plus
whatever more I can add with the dial-back, usually at least 6*
I liked that Hughes cam. I was very sad when it dropped lobes.
For pure economy, yeah, I'd look for a cam like the big guns here have already recommended. and or, run the one you got a lil faster to get it out of reversion.
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