Recommendation on Proper Gear Ratio

[hookem78613]

I have a 68 CHarger R/T and I am running about 575HP.  I have a 727, 3000 stall and 295-50-15 (26.7) in the rear.  I would like to run in the 12's or better and need to switch out the 323 gears. I was thinking of going with 3.90 or 4.10. I plan on driving it on the street too.  Is there a way to calculate this? 

Recommendations would be helpful.

Hookem

[69fourspd]

Here is a simple calcultaor to figure out top end....

http://www.mymopar.com/gearratio.htm

[hookem78613]

anyway to figure out if that will put me in the 12's?

[69fourspd]

That will depend alot on the power band and how fast the motor will rev, tire size....

[hookem78613]

The tire size is supposed to be 26.7(www.tirerack.com).

The power band is from 3000-6500 RPM.

[firefighter3931]

If you're making 575hp you should be well past the 12's and deep into the 11's....even with 3.23 gears.

Ron

[hookem78613]

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Maybe I wasn't all that clear.  I don't know where I am at because I haven't opened it up really. Still breaking it in. I just went through the motor again and tightened it up a bit.  The advertised HP of the motor was 575 from the Mopar Performance literature...so that's what I am going by.  I have a dyno sheet with 440 HP at the rear wheels before I went through the motor and with a crappy dual plane intake with adapter plates.  I also had everything rebalanced and trued up plus I swamped a single plane M1 intake and put some Forged 11:1 slugs in it.

My purpose it just to get some advise on the best setup so i don't go back and do things twice.  When I started i know I wanted at least 12 second ET's so that is where I am coming from.    I figured that a lower set of gears would also WAKE the motor up and keep it closer to it's power band of 3000-6000 and that would make it more responsive.

Am I not thinking clearly?   

[firefighter3931]

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Maybe I wasn't all that clear.  I don't know where I am at because I haven't opened it up really.

Ok, that makes more sense. I'm going to assume that this is your first stroker. The 3000-6000 powerband is a general range but in reality a stroker will make lots of power everywhere unless it's waaaay overcammed. The long arm crank creates a ton of torque and traction will be an issue. Adding a deeper gear only amplifies the problem.    What cam is in this motor ? Are you planning any extended highway cruising ?

Once that stroker is properly tuned you can forget about any traction with a street tire....even with 3.23 gears. 


Ron

[hookem78613]

You are correct in your assumption!  The specs on the motor are as follows:

575HP / 500 Wedge Mopar Performance Crate Engine ::Mopar Performance PN : P5007629
The 575 Horsepower 500 cubic inch wedge engine assembly is based on a heavy-duty cast iron, thick wall, thick deck, cross-bolted main block. The hi-flow aluminum Stage VI heads use large 2.140" intake and 1.810" exhaust valves. The 4.380" cylinder bores house 10.25:1 cast aluminum flat top pistons. The 292° duration, 0.453"/0.543" I/E lift camshaft is controlled by heavy-duty hi lift valve springs with dampers and umbrella valve seals. single plane M1 aluminum 4 bbl intake manifold.

The only thing I have done differently is put Forged slugs in it and bumped the compression up a little.

So do thing I'll be okay with the 323's?

[firefighter3931]

Hookem, that cam is the 509 hydraulic grind with a 1.6:1 rocker if i'm not mistaken. The 292* cam has ~250*@.050 duration so it's plenty for a street/strip 440 but will be fairly mild in a 500 incher. That being said, if you throw too much gear into it, the engine will nose over too early. The 3.23's will work fine inmo. I've seen a 70 charger > 440 with e-heads run 11.90's with 3.23 gears and it makes nowhere near the Tq that yours will. 

Personally, i prefer more grear and a taller tire to increase the contact patch. This helps the car hook up better. A taller tire with bigger gears can give you similar engine speeds for cruising if you're careful with your planning. On mine i will be using a 295/65/15 with 4.10's which is effectively a 3.6:1 final drive ratio.... pretty much the same as a 3.55 with a factory height tire.


Ron

[hookem78613]

You are correct.  I think it is the 509 with the 1.6 rockers.  Maybe I should have gone with another Cam while I was in there!!  But I figured if it aint broke......

What do you think about 3.73's?  I have a friend that has a 3.73 complet setup and he want 350.00 bucks for it.  Says it was in good working order when he took it out of his Coronet. 

He's got a set of MT ET's that are DOT approved but he want 800.00 for the wheel/tire set.  Just don't want to waste my money on things I don't need.  With the ET's will I need more gear? 

I guessing I may get more out of the street slicks that swapping the gears.

Hookem

[firefighter3931]

Hookem, 3.73's would be an excellent choice....good compromise for strip and cruising on the hwy. I would upgrade the tires while you're at it to a 28in tall. The MT drag radials are awesome....lots of guys run these at the track and say they hook better than slicks. I have the BFG drag radials for mine but you can bet when those are done....i'll be switching to the MT's. 

The 275/60/15's would be perfect for your 3.73's and the stroker. 

There's nothing wrong with that cam...it will make excellent power in your stroker. Plenty to get you into the 11's. You can allways upgrade later but i would keep it for now. 



Ron

[firefighter3931]

He's got a set of MT ET's that are DOT approved but he want 800.00 for the wheel/tire set. 
Hookem

Are these the bias ply ET streets...or the drag radials ? I would go with the drag radials right off the bat. Summit and many other venders carry them. These will work fine with an 8in rim.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MTT%2D3754R&N=700+4294923107+400206+4294922134+115&autoview=sku



Ron

[jg68]

McCormick tire carry's them also, if i remember right, the 275/60/15s were 150.00 each shipped, those are the ones i'm getting, but i'm stuffing em on 10" rims.

[daytonalo]

323 all the way , but please go ahead and install 410 so  a kid in a Honda can smoke you from 65mph on up

[firefighter3931]

323 all the way , but please go ahead and install 410 so  a kid in a Honda can smoke you from 65mph on up

Ummm....not likely !   

3.73 +28in tire @ 130mph = 5975rpm  That stroker should pull 6 grand no problem....wonder who'll get to 130 first ! 

Substitute the 3.73's for 4.10's and you get 120mph at just over 6k....and with 600+ flbs of Tq, you get there pretty darn quick.



Ron

[jg68]

323 all the way , but please go ahead and install 410 so  a kid in a Honda can smoke you from 65mph on up

Ummm....not likely !   

3.73 +28in tire @ 130mph = 5975rpm  That stroker should pull 6 grand no problem....wonder who'll get to 130 first ! 

Substitute the 3.73's for 4.10's and you get 120mph at just over 6k....and with 600+ flbs of Tq, you get there pretty darn quick.



Ron

I would like to have seen a rice burner whip up on my ride with 411s, as Macaulay Culkin would say "I DON'T THINK SO" 

Hey Ron, what would be the final gear with 355s & a 31" tire? I was told about 3.00

[firefighter3931]

Hey Ron, what would be the final gear with 355s & a 31" tire? I was told about 3.00

Hi Joe, that will be a highway screamer ! Your 3.0 is pretty close....i came up with 2.97 


Ron

[jg68]

Hey Ron, what would be the final gear with 355s & a 31" tire? I was told about 3.00

Hi Joe, that will be a highway screamer ! Your 3.0 is pretty close....i came up with 2.97 


Ron

Thanks, i'm hoping with the 28" tires it'll get me closer to 355s

[firefighter3931]

Hey Ron, what would be the final gear with 355s & a 31" tire? I was told about 3.00

Hi Joe, that will be a highway screamer ! Your 3.0 is pretty close....i came up with 2.97 


Ron

Yep, it'll be closer.....3.29 



Ron

Thanks, i'm hoping with the 28" tires it'll get me closer to 355s

[hookem78613]

Can you tell me what RPM I will be crusing on the highway at 65mph Using a 3.91 rear end with my 295-50-15's? 

Should I run a 6k rev limiter or can I go higher?  I think the 509 is specd up to 6 grand.

[firefighter3931]

Can you tell me what RPM I will be crusing on the highway at 65mph Using a 3.91 rear end with my 295-50-15's? 

Should I run a 6k rev limiter or can I go higher?  I think the 509 is specd up to 6 grand.

Hookem ; 65mph with 3.91's and a 26.5in tire is 3300 rpm according to the calcualtor. 

As for the rev limiter 6k is about as high as you would want to go with a hydraulic cam....beyond that the valvetrain becomes unstable anyway. 


Ron

[hookem78613]

Thanks!  I appreciate your help and understanding of all my crazy questions.  Been a big help.  I think I am going to go with 3.73's.

I think it really is the best all around option for me. I might keep a 4.10 or similar setup around if I really want to smoke em!!

Hookem

[firefighter3931]

You're welcome Hookem. I think you'd be happiest with the 3.73 grears.....enough low end grunt for the in town stoplight action and you can still cruise comfortably on the hwy. 



Ron

[phat69charger]

Hookem,

If your looking for a way of comparing what you have to what it could be if you changed things you can use this gearing calculator, it won't tell you how fast you'll run in the 1/4 in, but it will tell you the RPM and Speed that you will be operating at based on the information that you input: http://users.erols.com/dmapes/GEARCLC.HTM

There's a few post of the site about gearing here's one of my replys: http://www.dodgecharger.com/forum/index.php/topic,17425.0.html