six barrel

rumblefish360 said
Expensive key factor highlighted.

budnmic said
How to adjust for fuel economy? '70 AAR 6 barrel motor in a 1969 fastback with overdrive 4speed.
any thoughts???

3.55 x0.71 x0.78 =1.97; That was my double O/D. It comes with a 3.55 x3.09 =10.97 starter gear.
My thoughts:
Now, with an A500LU, the final drives become;
1.97/.69od=2.85; so anyone can do it on the relatively-cheap, cuz;
2.76s x.69= 1.90, with a starter of 7.56; or
2.94s x.69= 2 .03, with a starter of 8.06; or
3.23s x.69= 2.23, with a starter of 8.85;
So just choose an appropriate stall.
>Who doesn't have at least one of these gears laying around, and if not, people practically give them away.

>But to be fair, OP already has the 3.09-1.67-1.00-.73o/d, so this, to me,when it comes to fuel-economy only; is a no-brainer;
3.55 x.73=2.59; and 65= 2200; which is a GOOD number for a 220* cam, with a long power-extraction cycle. You can still make 300/330 hp on that cam, enough to satisfy all but the the most hungry streeter.And it has a starter of 10.97. The 340 cam being 228/235/114 will want to cruise at 2400 or higher.
So;
>just install a fat-.200, solid-lifter, cam in there of about [email protected], and call it done. The rest is in the tune. And some is in the chassis. and a little is in the aero.
>Besides, that o/d trans needs a small cam to work right; the splits are wicked far apart, especially the one that counts most for a streeter, namely, the 1-2, which is .54 . I suffered that trans for 3 or 4 years behind my hi-torque 360, before I couldn't take it any more. I bought the GVod strictly to be able to split those wide gears. That it had an overdrive was just icing. I ran it with a Hughes HE2330AL, which was s hydro at [email protected]. I was very happy. I wouldda been a lil happier with a solid, one size bigger at .050. even if it meant sacrificing a lil extraction.
>A 2nd gen manual-trans Barracuda is pretty good on aero. Get one up to 65 mph, and then put it in neutral and see how far it coasts; it can be pretty amazing.

My tip for economy is this;
People put way too much faith in the intake duration, and not nearly enough thought into the extraction and overlap.Here are some cams in all their durations(advertised), arranged as;
intake/compression/extraction/ exhaust/LSA/ overlap/ Ica
268/116/104/276/114/44/64 the 340 cam
268/119/113/276/108/56/61 same cam with LSA tightened up.
>Notice that the extraction has jumped NINE degrees! That is huge.
> notice that the overlap has jumped TWELVE degrees!
> Notice that the intake is closing 3 degrees earlier. That is, in terms of compression building, the equivalent of running one size smaller cam.
> but there is no free lunch; the powerband of this 108LSA cam is NOT suited to those wide od ratios, and it will want to cruise at a higher rpm to slam the door on scavenging with 56* of overlap AND, most importantly, I doubt it will get any better fuel-economy than the 44*overlap cam.......... even geared optimally. It may not be any worse either. But I would never recommend either of these cams for fuel economy.

For fuel economy, in terms of camshafting you need;
to limit the overlap,
to maximize extraction,
optimize the cylinder pressure,
be aware of the powerband requirement of your transmission,
and optimize the cruise rpm according to what comes of your figuring.
Lets look at the 318LA cam;
240/130/122/248/112/20/50
>We know this cam can make great torque in a low-compression 318, because the Ica is just 50* so it traps a lot of just-inducted mixture and idles at a hi-vacuum, usually 18 to 20 inches.
> this cam makes great fuel economy because extraction is 122*, which is a lot; probably a lot more than it really needs, and because the overlap is just 20 degrees, not enough to scavenge with log manifolds.
> and the 112* of LSA, makes for the right powerband for the TorqueFlite splits.
So this cam is great for it's intended useage.

So the question is;
how can we incorporate this information into your 340/od trans combo?
Ok first, the 268/276/114 numbers are not bad numbers by themselves. What is bad is that they are big compared to their .050 ratings. Yeah I realize that those ramps are there for a long street life. But com'on, who puts 120,000 miles on their hotrod engine without ever freshening it; the rings will be gone LONG before that 268/276 cam wears out. So IMO, those long ramps are costing me money at the pumps every daymn time, that I would rather put into new rings from time to time.
Ok so that 340 cam is advertized at .050, as 228/235/114. These are the important numbers. Those are good numbers. What is not good is 268-228=40 degrees, which is actually pretty good, until you realize that the intake valve on that hydro cam is still open .008 x 1.45effective rocker ratio = .012, at that 268. it may not close until 20 or more degrees on down the road, (IDK the actual number so guessing), and that is why that 340 hydro-cam is known to be a gas-hog.
If you could find a 268 cam that actually closed the valve tight at that duration, and still be [email protected] you'd have the best of all situations. But that is not possible. So when it comes to fuel economy with a small engine, AND performance, you gotta do three things;
1) yur gonna have to bias your combo one way or the other
2) swap that 340 cam out. You didn't mention what cam is in your engine, but only offered 71-340, so I'm guessing the cam and compression are still 1971 status. and
3) the best way to cover those TWO bases of performance AND economy, AND those wide split of the overdrive 4-speed, is with a short-period, wide LSA, solid-lifter cam.

To that end, IMO, I recommend to KEEP the 114 LSA. And that is gonna be the first hurdle. But, it will allow the later closing of the exhaust, and the earlier opening of the intake, without the overlap penalty.
Next, assuming a true Scr of 10.5, you can afford to decrease your compression degrees ,a lil.
But you want your extraction degrees to be as large as possible, certainly more than 104*, but does not need to be as high as 122*, lol. 112 is a good number.
Ok so I get something like this;
262/116/112/266/114/36/64
Notice the extraction is up to 112, and
the overlap is down to 36, but
I left the compression at 116, for an Ica of 64, to work with your current Scr. At 10.5 your pressure is already borderline too high for iron heads and pump gas. So I cannot make the compression duration any bigger.
Now, the 340 cam is 228/235 At .050, so we don't want to sacrifice too much power, so on this 262/266 cam, it will need similar specs, and that means the acceleration ramps from advertized to .050 need to be 262-228=34* And that means your only choice is a flat-tappet cam. And @Wormryder has the scoop on which one to get, with the fatest .200 numbers. But I warn you, a cam like this will idle almost dead smooth, with a lil clatter from the valve train. Just like millions of slantys do. But be not deceived, the only thing you give up with this is the slight 340 burble.

Is there a cheaper way to do this?
Well as it happens, yes.
Just install a 273 rocker gear, and run your hydros loose on the exhaust side, and retime your cam. You can gain up to about 8 degrees of extraction, going from 104 to 112 extraction, and give up nothing on the intake, and the 340 cam is already ground on a 114LSA.
But there is no free lunch here; you will have to keep your eye on the valve lash, and if it suddenly increases, the cam is done. No one can predict the day and the hour when this might occur; I said might occur.
Would I do it?
I already did, twice even. I'm coming 68, so binaround for a while. And I started out a broke-azz, high-school-dropout, kid,with no internet, and living on the cusp of technology, making 85cents an hour part-time. So with no learning and no schooling, and no one to tell me "that won't work", I tried stuff out for myself. Time is the one thing I had lots of.