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Discussion Starter · #1 ·
I was wondering if you guys would think it would be worth it for me to swap the 3.42 rear gears in my car for 3.93? I was thinking of doing it because I would think it would result in better performance, as long as I get better tires, and wouldn't really hurt highway gas mileage, because with my cam I would think the higher gear would put me more in the torque range I want when cruising. Right now, i need to be going 75+ to really make use of 5th gear.

Here are the specs on my car:
350 engine
-1.94/1.50 open chamber iron heads 462624
-9.6 compression
-Cam .454"/.480" 272/284
Hooker Competition Headers
TKO-600 w/.62 OD
25.85" Tires

Thanks in Advance
 

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Discussion Starter · #3 ·
Yea, I have used that calculator. If you take a look at 70-75mph, which I would say is my average on the highway, than its a difference of 300+ rpm. And I was trying to figure if the extra gear would actually push by enough rpm closer to my peak torque that it would not hurt gas mileage on the highway, but I would get a bonus in acceleration.

Thanks
 

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Going to a lower gear will hurt your gas mileage. It sounds good on paper but I have never seen a lower (higher numerical) gear improve gas mileage. Think about the overdrive transmissions, most cruise under 2000 rpm and the torque peak may be much higher. Lowering the rpm is the most effective way I know to improve gas mileage along with good driving habits.
 

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I agree with sleeper.

Any time you increase your engine rpm you will hurt gas mileage. Fortunately it will also give you a slight increase in performance but definitely one you can feel in the seat of your pants. I wouldn't suggest going any higher though, a 4.10 is a bear to drive anywhere but around town.

Tom
 

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3.42 is a good cruiser gear ratio. Going to 3.93 will add torque. Torque is good. Using the available torque more often (come on, we know you will test those gears more often then you do now) will decrease you gas mileage. Switching to a 3.55 or 3.73 gives you a noticeable increase in get-up-and-go and will save you a little MPG over the 3.93's. If you spend most of your time on the freeway, your mileage, in 5th gear shouldn't decrease significantly, but it will decrease. Nice motor specs.
 

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3.42 is a good cruiser gear ratio. Going to 3.93 will add torque. Torque is good. Using the available torque more often (come on, we know you will test those gears more often then you do now) will decrease you gas mileage. Switching to a 3.55 or 3.73 gives you a noticeable increase in get-up-and-go and will save you a little MPG over the 3.93's. If you spend most of your time on the freeway, your mileage, in 5th gear shouldn't decrease significantly, but it will decrease. Nice motor specs.
There is no such gear as a 3.93 in the G.M. arsenal to my knowledge. It goes from 3.42 in the ten bolts to something like 3.73s and then to 3.90s. I'd keep what you have and get a lower geared O/D transmission for more low end and better hiway cruising. The 200-4R has a 2.75 low gear and the 700-R4 has a 3.06 low plus they both have overdrives. A couple of companies are now beefing up both of these transmissions for more powerful engines.
 

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Discussion Starter · #8 ·
Harold
My fault, it is a 3.90 I was thinking of. I'm not going to get a new transmission though, because I love my TKO-600. Apparently, I just didn't plan it out right and should have gotten the one with the high OD gear. Swapping it though, would not be worth the price though.
 

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Anywhere from 3.73-4.11 will work great with your TKO-600.
 
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Imho, install an Isky 264 Mega hy-cam and you will be good to go at 9.6 to 1 CR. regardless of gearing.

264/214, 108, .450" lift.

I bet it will be darn near midrange explosive in your engine regardless of it being an older cam.

Or this little-bitty Clevite solid lifter cam!!

Part Number 229-1998 spec'd at;

258/219/270/229, 114/110, .456"/.479" gross lift and it need's .022" lash on both sides. (You want to up this one a schosh, then run 1.6 ratio rockers on it)..

Please notice that I am looking at older SMALLER cams here b/c of your cruise rpm when in OD is all.

And I know that there are more modern cams out there, but imho, when you factor in longevity, I think the older cams will last longer like stock even if a bit of hp is left on the table.

Please take the ol' man w/ a grain of salt here b/c I would run these if it was mine b/c I'm just NOT a fan of XE cams unless it's a cam from UDHarold!!

pdq67

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