How bad is this tire/gear combo killing me??

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SleeperScamp

SleeperScamp

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70 Duster 340 4spd.. 275/60r15 with 3.23 Gears... Engine is 40 over 10.5 to 1, X-head 2.02 valve with some port work done...750 Edelbrock, LD340.. Car seems like a dog to me.. Is it the to tall tire with not enough gear? I don't like the tires on it and will be changing soon to something smaller. Just wondering if the tire change alone will be much improvement or do I need a gear change??? Thanks for any input..
 
10.5:1? What are the cam specs? What are you shifting at? Is it pulling hard once it gets past 3000?
 
change 750 eddy to 750 holley double pumper..
 
Get on one of them RPM calculators and play around with it. Shorter tires will not help out that much. Need a gear change. Going to bring your cruising RPM up too though.
 
Don't know what your cam specs are but it sounds like you need at least a 3.91 gear. Tires are probably OK.

Small blocks like/need gears.

I know Comp Cams suggests what gears to use with a particular cam.

Check out the Wallace Racing website, use their gear ratio/tire calculators.
 
jimmyray said:
10.5:1? What are the cam specs? What are you shifting at? Is it pulling hard once it gets past 3000?
Click to expand...

I cant confirm anything for sure.. I need to go back and talk to the previous owner to find out exact details but this was some notes he had when I bought the car..." 40 over 10.5 2 relief,Mopar Performance 424 HYD ??? No Idea on that one never heard of such... And to be honest I'm just going by seat of the pants taking off to see how it "pulls"
 
i am running a 275/60/15 on a 15x10 rim with a 2.91 rear and i can burn em off all day long. i have a 727 and when i get on it, that puppy pulls. maybe our definitions of a dog may be different, but my duster will get it. maybe carburetion.i just re- read and saw it is a four speed.
 
You really need to find out cam specs. Sounds like you just have the wrong mix of parts. Small cam,high gear,tall tires.
 
I have a set of 4.10 gears. If I went with a 255/60 15 How " streetable" would that be?
 
My Chevy 2wd short box goes high 14's with a 350 that makes not much more than 325hp with 3.20 gears on 275 60 15 tires and an open diff so I can't see how your car would not be a bit quicker than you think.
 
With the 255/60 Is there much difference in a 4.10 compared to 3.91?? I looked at those calculators and was to dumb to figure it out..
 
I'm running the same tires and rear on my car I only have a 318 with simple bolt ons but i think it would have ran high 14s maybe low 15s. got up and ran pretty darn good. maybe your out of tune or used to some really wicked cars? with that kind of compression that thing should go like a raped ape i would think. something doesn't seem rite to me.

gears will help the get up and go but you might be revving the piss out of it on the highway. I don't think i would run anything more than 355s on a street car without OD. just my opinion.
 
More gear.....

Less Carb.... if it can't breath. Holley 650 DP is plenty

I Run/Ran 275/60/15 with 4.56 about 3300@60mph not your daily driver....
 
The car was originally set up for a ~25" tall tire. You now have a tire that is 3" taller or ~13.3%. So you've taken the 3.23 rear and effectively made it a 2.8 ratio with the taller tire. If you want it to run similar to the stock set up, you need to install a 3.73 gear.

That's a tall effective ratio set up for a 4 speed car. Especially a 340. Put/try/borrow a shorter tire on it see how it wakes up!
 
The tires are going to be changed for sure.. I just dont like the looks of them. Too big for my taste.. I'll try new tires first and go from there.. Thanks for all the input...
 
SleeperScamp said:
With the 255/60 Is there much difference in a 4.10 compared to 3.91?? I looked at those calculators and was to dumb to figure it out..
Click to expand...

For the calc I posted all you gotta do is this:

275
60
15
1 (final drive ratio,its the same for auto or non od manual)
4.10 (or whatever gear you want to see.)
 
73AbodEE said:
i am running a 275/60/15 on a 15x10 rim with a 2.91 rear and i can burn em off all day long. i have a 727 and when i get on it, that puppy pulls. maybe our definitions of a dog may be different, but my duster will get it. i would guess it may be in your converter??? i dont know if you have an auto..but just a thought...
Click to expand...



This guy is 100% correct. I had a built 340 here with 355 gears in a 72 Charger. He wanted gears because it only went 15's . We put 410's in . No real improvement. We put two little 14 inch tires on and you couldn't spin them from a kick. We installed a cheap GER 3500 converter. It was like night and day. We put the 355'd back in . It got into the 13's. Do the converter first. If you put a bigger cam in you will need at least a 3500 and you will find it only stalls about 2800 behind a mild SB. No brainer.

340 cars came with 3000 stall. If you hold your brake on and peg the throttle. Where your tack stops this is your brake stall. It should be at least 2800. With a stock motor. Your motor will also play a part in where it stalls. A BB will stall the same converter higher then a small block. If your converter doesn't stall atleast to where your peak torque starts your car will be a dog off the line.
 
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