3:55 gears to 323 gears

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The difference will be quite noticeable.

I just swapped in a 3.23 for a 2.94 in a B-body with 15" tires. I noticed the difference just backing out of the garage! :)
...and how did the performance change.I am thinking of using 2.94 in place of my existing 3.23
...stock 340 and 14" tires.
 
...and how did the performance change.I am thinking of using 2.94 in place of my existing 3.23
...stock 340 and 14" tires.

I got 2.94 gears and 26" tires, with a 380hp/360 crate engine have to drive in 2nd in town or it lugs. It goes ok from a light but be better when I go 3.91-4.30 haven't decided how deep yet.
 
I curve my distributors for about 15-18 initial timing at 800 rpm, with mechanical going to about 34-36 at 2000-2200 rpm and finally at 54-56 degrees total advance with the Vacuum advance hooked up for cruising speeds. My cars all perform very well like this for street cars.
For an automatic; I'm with you on this.

except with a 4 speed car;
For these,I delay the all-in to 3000 to 3400, depending on the cylinder pressure.
54 to 56 is a pretty good cruise-timing number.
But the full-timing so early in a hi-compression manual trans car, gets too jumpy for me in first gear,with numbers that high.
Conversely; with a dead cold engine, at say @68*F, she likes a lotta idle timing, like 22/25 . it seems to take a lotta lotta time to heat all that aluminum up.
 
that 380 hp crate engine has the long duration .510 cam?
ya it's like 288/296 or 230/236 @ .050" 108 .510"/.513" might be a little off on specs.

screenshot_20171212-084647-png-png-png-png.png
 
That's a nice torque number at 2500!
My stock 340 actually has a smaller cam than stock...at .204 / .214 and has a ton of lo end torque.Pulls hard from 800 rpm up and it just may work with the .294"s
we'll see?
 
That's a nice torque number at 2500!
My stock 340 actually has a smaller cam than stock...at .204 / .214 and has a ton of lo end torque.Pulls hard from 800 rpm up and it just may work with the .294"s
we'll see?

To be fair I only got to drive it for a week with a trip permit when I bought it don't know how well he had the timing and carb setup, but seem soft under 2000 rpm.
 
For an automatic; I'm with you on this.

except with a 4 speed car;
For these,I delay the all-in to 3000 to 3400, depending on the cylinder pressure.
54 to 56 is a pretty good cruise-timing number.
But the full-timing so early in a hi-compression manual trans car, gets too jumpy for me in first gear,with numbers that high.
Conversely; with a dead cold engine, at say @68*F, she likes a lotta idle timing, like 22/25 . it seems to take a lotta lotta time to heat all that aluminum up.


Yes, mine are all automatics. :thumbsup:
 
...and how did the performance change.I am thinking of using 2.94 in place of my existing 3.23
...stock 340 and 14" tires.

Well, this car used to have 14s and the 2.94 and it was very similar to where is is now with the taller 15" tires and the 3.23.

If yours is an automatic it should be fine. With a manual transmission I like the 3.23 with 14s.
 
On another note
But honestly, the biggest hindrance to fuel-economy is not having enough ignition timing, and or having the exhaust valve open too early, made worse when both are in effect; and/or operating in the wrong rpm for the specific cam.
All the math in the world goes right out the window, when trying to make a 292 cam operate at 1600rpm, it will just spew unburnred gas into the headers, and if/when it catches fire in there, it will make it all the worse.So some common-sense has to prevail.
Generally, I have found 2200 to be the lower limit of a hot street cam, and the engine will want more ignition timing there, than is generally possible to give. Mine has liked up to 60 degrees there.How can a guy meet that need? No stock or modified parts can achieve that. At the best; if you cranked the mechanical to 38* and modded your Vcan to get 22*, there is your 60*.. But just try and drive that hummer at 2200 at WOT, with 38* of lead. Furthermore; what will the idle timing be with such a set-up?, and what will be the idle-speed? Yur not gonna successfully marry this tune to your street engine. You will require a stand alone timing computer.
If you don't give the engine the lead it wants a cruising speed, fuel-mileage will suffer.

It's all about maximizing the cylinder pressure at just the right time of crank-rotation, to maximize the energy-transfer of the expanding exhaust gasses, to the crank and to the rear wheels following.
So the key player to good fuel-economy, is the running cylinder pressure, at cruising rpm..

This is how, the stock lowly LA318 can make fuel economy with it's atrocious sub 8/1 Scr and subsequent meager cylinder pressure of barely into the 130s. With 2.76 rear gears the rpm mathes out to 65=2230 in loc-up. The peak efficiency of that LA comes at about 2400rpm.
That 318 cam has specs of
240/248/112+4/Ica of 48*/132comp/120power/ Effective overlap of 16*
Check it out;132* of compression from an Ica of just 48*. That traps a lotta aircharge, preventing it from backing up into the intake. The meager overlap means very little,if any, exhaust dilution. But the thing I really want guys to see is the 120* of power extraction. That is a lot! And by the time the exhaust exits the chamber, there is not much energy left in it.
If you get the ignition timing right, you can impart a lot of pressure to the short 3.315 stroke, which will be down to 2.89effective. The cylinder pressure is expected to be 140 at sealevel, with a VP of 116.
VP of 116 is what most of us are used to seeing/feeling with our 318s, and more often than not , with 2.76 rear gears. We know how that feels; albeit with a 2bbl and single exhaust.
If you assume a 7/1 pressure rise, due to heat, then one could expect a new engine with 140 x 7=980 pounds of pressure at WOT from this engine during it's peak efficiency. That's not bad.

But if you bump the Scr to 9/1, then the cranking cylinder pressure might rise to 160psi, and at the same 7/1 expansion ratio, this now mathes to a potential of 1120psi at WOT; a 14.3% increase. As to torque, this is like an across the board increase of 14.3% in rear gear or from 2.76s to 3.15s. Or in terms of peak power, about 20hp.
Now that is something; same engine, only the Scr was increased.
But what is the first thing a newbe says? He says; "not taking the short apart". And most of the time that 40 year old engine is still on the original rings! With gaps you can drive a truck thru, and the rings are coming into the hole under the ridge and spewing compression straight into the crankcase. You know; 980psi leaking thru that monster gap.

So he puts a too-big cam in there, and the cylinder pressure falls to 120 , and 120x7=840 running at WOT, so the torque has fallen to 86% so it feels like the 2.76s have turned to 2.37s ....... and here he comes with "what do I do now?", and the only solution is a higher stall and bigger gears.
In the meantime, the fuel economy is so low, he dares not drive it anywhere.
To my thinking this is a ridiculous thing to do.
If I wanted performance from a 318, the very very first thing I would do is bump the pressure up. And that is what the factory finally did when the 5.2M came out.
You have to be kidding all this to calculate Fuel economy? we're talking 50 year old cars. Buy a new dart or a srt neon for economy. V8's are not for fuel economy there for racing . I would get higher gears to go faster to get there quicker the hell with economy. In 72 I had a 65 426 plymouth conv 4 spd. it had very high gears compared to the 410's in the R/T. we use to measure how far the roof would lift off of the bows at the end of third. Mid way through 4th frank cracked his window and blew the back window right off the zipper.
 
OP asked
I answered
Have a 1969 Dart Swinger 340-4speed 11.1 compression hydraulic cam .510 lift 245/60/14 tires 3:55 gears. 2900 rpms at 60 mph mostly highway driving. Would there be much difference in rpms and gas mileage going to 3:23 gears at 60 mph? Any info would be appreciated thanks.
 
Until you gear or o/d for a cruise rpm at or below 2000 rpm no changes will make much difference. Especially with a performance build.
 
Gas mileage is the worst thing to usually spend your money on.
You have to put crazy miles on your to recoup.

whatever your car gets with a good tune it’s hard to increase by a lot. Even modern midsize cars don’t get the greatest. My V6 avenger only gets 22 mpg mixed driving. Say you put on 2000 miles a summer at 10 mpg at say $3 a gallon that’s $600 a year, even if it was possible to double it to 20 mpg that’s a $300 savings, know how much time and money it would take to double that, say you could with $3000 in upgrades it would take 10 years to break even.

it’s cheaper to usually to just dump it into the tank, now if your upgrading for performance with and eye towards mileage and driveability Then it don’t matter cause your not concerned to recoup just a better experience.
 
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