2.4 is the most common ratio that I've seen. A low buck upgrade would be to take a 8 1/4 2.76 rear from a slant six car and swap it in. My friend took the rear out of my CMX and put it in his Imperial. The parts just aren't as plentiful as they used to be. You're on the right track with 3.23 and a 999. Now if you were thinking about a A500 overdrive swap 4.10 would be my choice.
80 Mirada 318 tweaks
- Thread starter MiradaCMX80
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This item is for the '97 and newer 8¼'s and will not fit his differential (unless he gets custom axles made).
BudW
I have to disagree. 27 splines for our cars and 29 splines for the newer trucks. Here's another option and the one that's in my car.
Mopar 8 1/4" Spicer "Trac-Lok" Differential
Mopar 8 1/4" Spicer "Trac-Lok" Differential
jasperjacko
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MiradaCMX80
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This is very tempting. 3.55 is a little steep, but it'd work. I'm hunting for a B-Body 8.75....I have a lead on two so far.
AJ/FormS
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3.55s with a 2.74 low and 215/70-15s will make 3000=23 mph. That's normally pretty good.
But with a super low-stall TC, and a starter gear of 9.73 you have no hope of spinning the tires, so you'll be waiting and waiting and waiting for that 23 mph to come around. Even with a roaring 4bbl.
With an advertised torque peak of 1600, that points to a power peak of 3100, and explains the 130 advertised horsepower.
Now; opening up the exhaust, installing a 4 bbl, and a retune, might increase your operating rpm say 200 , and and the power might increase by IDK lets say 10% at the best, which amounts to 13hpNET.
On a 3600 pound "race weight" car, that comes to a decrease of .0036 pounds per horsepower.
What does that come to in dollars spent per horsepower? IDK, a lot I guess.
Will it be quicker?
Well with 60% more rear gear, yes it will, but quicker to what speed?
With a power peak now 3100+200=3300, the shift rpm might be 3600, which with your gearing is 26 mph. On the 1-2shift, the Rs fall to 2000, and the TC is already stalled-up long ago so of no help at all, so yur speed thrill is done........ at 26mph. Dollars spent to thrill ratio? Possibly/ probably, a huge disappointment.
But you gotta start somewhere, and gears and TC were #1 on my list, so you are on the right track.
Honestly; I'm not trying to to be a kill-joy. I'm just trying to get you to see the big picture. That 130hp engine is a slug and is the next thing that has got to go, along with that TC.
But with a super low-stall TC, and a starter gear of 9.73 you have no hope of spinning the tires, so you'll be waiting and waiting and waiting for that 23 mph to come around. Even with a roaring 4bbl.
With an advertised torque peak of 1600, that points to a power peak of 3100, and explains the 130 advertised horsepower.
Now; opening up the exhaust, installing a 4 bbl, and a retune, might increase your operating rpm say 200 , and and the power might increase by IDK lets say 10% at the best, which amounts to 13hpNET.
On a 3600 pound "race weight" car, that comes to a decrease of .0036 pounds per horsepower.
What does that come to in dollars spent per horsepower? IDK, a lot I guess.
Will it be quicker?
Well with 60% more rear gear, yes it will, but quicker to what speed?
With a power peak now 3100+200=3300, the shift rpm might be 3600, which with your gearing is 26 mph. On the 1-2shift, the Rs fall to 2000, and the TC is already stalled-up long ago so of no help at all, so yur speed thrill is done........ at 26mph. Dollars spent to thrill ratio? Possibly/ probably, a huge disappointment.
But you gotta start somewhere, and gears and TC were #1 on my list, so you are on the right track.
Honestly; I'm not trying to to be a kill-joy. I'm just trying to get you to see the big picture. That 130hp engine is a slug and is the next thing that has got to go, along with that TC.
MiradaCMX80
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Not a killjoy at all...I really appreciate the info and math. I was unaware that the 318's were choked THAT bad. And the axles in these cars...holy crap. My line of thinking went back to say, a 1970 Dart 318 A904 3.23 car. They did ok. Not barn burners by any stretch, but they did ok. My Mirada is totally different, and now I understand why. This is why I read a lot and ask a lot of questions 
I can tell you the car shifts 1-2 at 4000 rpm according to my new tach. As soon as I replace the sending unit, the car is going for 2 1/4 h-pipe dual exhaust, and we are looking for a 3.23 axle. I'll drive the car this way until I pull the engine this winter for a reseal/refresh. Considering Magnum heads and a new cam with a small 4 barrel, at which time I'll work on the trans and TC to match the combo. At least for now, the car will sound decent and the 3.23 will pep it up a little bit around town.[/QUOTE]
I can tell you the car shifts 1-2 at 4000 rpm according to my new tach. As soon as I replace the sending unit, the car is going for 2 1/4 h-pipe dual exhaust, and we are looking for a 3.23 axle. I'll drive the car this way until I pull the engine this winter for a reseal/refresh. Considering Magnum heads and a new cam with a small 4 barrel, at which time I'll work on the trans and TC to match the combo. At least for now, the car will sound decent and the 3.23 will pep it up a little bit around town.[/QUOTE]
Sounds like a good plan, but I wouldn't even bother trying to wake up the 318 unless you're tearing the entire thing apart. Pistons need to be replaced to raise to the compression to a respectable level. Rather than a Mag head swap, do the entire the motor and get the benefits of a roller cam and higher compression. Mag 5.2 or 5.9, either will work great.
MiradaCMX80
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Considering it, since I can make it look like my LA. Don't mind if it's a flat tappet cam. Even with Mag heads, the squeeze is still that low? Geez...I'm getting ahead of myself....I'm still working on the stupid sending unit issue!
Then the axle!Mikes5thAve
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Don't over think it. Do 4bbl or axle, whichever you get first and go from there. It'll be an improvement and if you want to change heads or engine later you've already got a start to getting parts.
kkritsilas
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The 318-2V/BBL was factory rated at 120 HP peak. The Canadian/California 318-4V/BBL was factory rated at 160 HP peak.
I had an '81 Mirada that came with 318/ 2bbl, and 2.76 rear. The spider gears went bad, and I replaced the axle with a 2.49 from a parts Cordoba. That was worse, so I finally found a 2.94 Sure Grip from a cop car, and bolted it in. I took an 1985 318 roller cam 2 bbl engine, and reworked it. Left the short block alone except new seals and new oil pump. Ported out a set of 308 heads and a Thermoquad intake. Put a .444 hydraulic cam in it, double roller timing chain, and a recurved distributor. With headers and 3 inch pipes and mufflers, I was making over 300 hp. Got it in the low twelves at an eighth mile track. Plus built a homemade shift kit to the 999. Poor man's hotrod.
MiradaCMX80
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That's awesome. Didn't the late 80's roller 318's have more compression to begin with than the 70's early 80's 318's? I keep reading about 302/308 heads. A lot swear by them if you put the work into them...and a lot say they're over-rated and go with the Magnum heads.
I spent about two whole days porting them out. But I didn't have carbide bits. Just what I could find at Tractor Supply. They are good flowing heads when you open them up. Plus I put the headers and 3 inch pipes.
jasperjacko
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is that low 12's in the 1/8 mile?
