Anyone have experience with 2.76s or 2.94s behind a commando box? I'm looking for something a little more fuel sipping, but I don't wanna be burning the clutch when I'm just around town or in traffic. I do still wanna have plenty of fun with it. So if not that, then I may be going with an a833od+ 3.55s
(Car is 2700lbs the 360 makes about 380ish hp)
Your 380hp 360 has the 288/292/108 cam in it so the bottom end at 9/1 Scr is gonna be pretty soft.
But you got the 2700 pounds going for you. Still IMO that's not a very good street combo, to try and get fuel mileage out of, and Here's why.
288/292/108+4/ 74 overlap/ 112 compression/102 power/9.0 Scr
First; 74* is a lotta overlap, so the slower you run that engine, the more reversion you're gonna get. Reversion kills low-speed torque and with it;fuel economy. I'll guess for fuel economy, she'll want to run at 2400 or better.
Second; it only has 102* of power extraction. Meaning the exhaust is still gonna have a lotta energy in it when it leaves the pipe, energy that couldda been used to propel the vehicle.
Third; That 112* of compression together with just 9.0 Scr makes for weak low-rpm torque; so no matter what, you will always be driving deeper into the throttle than you would with more Scr or more compression degrees.
Fourth. Even if it was possible to get just 10% better mileage, how much are you willing to spend to get it and how many miles will it take to break even? Rhetorical question.
So as for fuel economy that combo is fubarred no mater what gears you run.
>After a lifetime of A833 shifting on the street, the happiest I have been is to have second gear set up right for me, and let the rest be what it will be. If you do this, 300/330 hp is all you need. And that spells really small cam.
For you, the question is where do you want to be in second gear?
With 2.94s and;
With the 2.66 box,that gives you a starter gear of just 7.82. This will be like starting in second gear with 4.10s the gear that that cam likes.
With the Commando box, the starter will be 9.08, now like starting with; 3.42s and the standard box. By itself this doesn't look that bad, but the Wallace calculator says your Dcr is just 7/1, so these numbers mean lots of clutch slipping every time you gotta start from zero mph.
A good fun starter gear for that combo is gonna be 11/1 or better; which is 4.10s with a 2.66 box and 3.55s with a Commando box.
Now second gear is the next big deal. 6.50 is usually a good target, but with your 7/1 Dcr Ima thinking 7.5 .With either box, second gear is 1.92 , so second wants at least 3.91s..
Third we don't care. As a streeter, we're never in it and pulling hard.
And that leaves just the hiway gear.Remember I guessed the minimum hiway rpm to be ~2400 which with 27" tires , is a final drive gear of 2.94s, alrightee.
Ok so lets look at that;Second gear is priority one and either non-od box says 3.91s are the gear of choice. And that means you can run the 2.66box which wanted 4.10s in first; 3.91s is close enough.
Yabut 3.91s makes for a buzzzy 3160rpm at 65mph.. This is more than 2400 so that's good. But it could be a lot slower.
Analysis;
Bottom end is just too soft, we need an overdrive.
But with the overdrive box, second is 1.67, so 7.5/1.67 says she wants 4.56s to make second gear exciting.. And 4.56s with a .73od makes 65=2700. Ok better than 3160 but First gear is whack-O at 14.09. and fourth is again rarely used. IMO there is no way this is gonna work.The current combo will never be happy with the overdrive box. The 1-2 split is just too wide. Well that's not exactly right. It never worked fo me cuz I was aiming for low-ET at 60 mph., which means running thru the power-peak twice and finishing up about 200/300 after peak horsepower. If this is less important to you, then maybe You could make it work for YOU.
I tried this nearly exact thing with 4.88s,4.30and 3.91s, but my cam was a 292/292/108... and my Scr was 11.3. I gave up and sold that cam.
As for gas mileage, I'll tellya what worked for me;
a 223*@.050 cam at 10.9Scr and any box/any gears,lol.
270/276/110+4/53 overlap/119 compression/108 exhaust/10.9Scr
This combo made enough power that at 3650 pounds and 750ft elevation it went [email protected] on the only timed run it ever made, with 3.55s and the 2.66 box, and 245/60-14s. The Wallace calculator makes this 335hp.
And I do mean any box/any gears, that 223cam at 10.9 Scr is a torque-beast; I tried everything from 2.76s to 4.30s, and any box and including the GVod behind the Mopar od box with 3.23s; yes 65=1450 and she was down with that.
For you, at 2700plus driver and gear say 2900. and with 335hp, the Wallace says [email protected] is theoretically possible.
But before you get too excited, I was running aluminum heads and over 180psi cylinder pressure; Few people have run that with iron heads. Mine ran on 87E10. And that was where the savings was. Traditionally, here in Manitoba there is a spread of about 25% or more between 87 and 91. Over 10 to 15 years, or 125,000 miles; that adds up to a lotta money.
