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Discussion Starter · #1 ·
With the higher RPM cam and set up on my 468, it doesn't like to lug or pull down low. To give you an idea, it has 8" of vaccum at idle. So with my TKO (.64 OD) and 3.73 gears, it doesn't seem happy in OD until over 65 or so. I don't drive it that fast, there is usually too much traffic, so I am not really utilizing the OD.

I would like to switch my 3.73 gears to 4.10. to raise my cruising RPM 10%. Would 4.10's be rediculously low with a 2.87 first gear (28" tires)? This car will never see a drag strip. If just gets driven around town for fun, and freeway jonts of 10 miles or less.
 

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Our old L72 Chevelle has the M20 and 4.10s. Low gear was pretty well useless with any normal street tire that would fit the wheel well. Some of the semi street tires available today with their soft compounds might have enough bite. I'd be more worried about how the engine reacts to lugging along at under 2k rpm at highway speeds with today's pump gas.
 
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With the higher RPM cam and set up on my 468, it doesn't like to lug or pull down low. To give you an idea, it has 8" of vaccum at idle. So with my TKO (.64 OD) and 3.73 gears, it doesn't seem happy in OD until over 65 or so. I don't drive it that fast, there is usually too much traffic, so I am not really utilizing the OD.

I would like to switch my 3.73 gears to 4.10. to raise my cruising RPM 10%. Would 4.10's be rediculously low with a 2.87 first gear (28" tires)? This car will never see a drag strip. If just gets driven around town for fun, and freeway jonts of 10 miles or less.
Good plan:hurray::hurray:

I ran a 4.56 with a M20 and a 427 in the 65SS car. But I was all about street racing and gas was .35 per gallon for Sunoco 280.

It makes sense to me to put a taller gear in, why not take advantage of the TKO OD:yes::yes::yes:
 

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I think its a great idea! Wish I did, but I'm pretty close with the 3.90's. DOnt worry about 1st gear being too low - its suppose to be. I dont know anybody that cruises around in first anyway. With the 4.10's you'll be able to shift fromt 1st to 3rd to 5th and save some gas.
 

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Discussion Starter · #5 ·
Looks like 3 to 0 positive for the idea. I am not worried about traction. I live in an area where I can't run it hard anyway. In fact, I think it's gratifying to feel the wheels spin, something it never would do with the TH400. Now, rolling along at 2500rpm in 1st, if I stab it, the tires start spinning. That's fun! I am still breaking in the trans and clutch, so I haven't fully tested it to see what other fun and games are in store.

OK, let's get stupid.... What about 4.56's? TKO's also come in .82 overdrives, If I did 4.56's with my .64, it would be kinda like 3.73's with a .82, still an improvement over my TH400's 1.0 with 3.73's. I didn't put in the TKO for the OD, I did it to be able to row the gears. The OD was just a fringe benefit.

Would 4.56's be rediculous with a 500hp bb?
 

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In approximate terms, compared to a M20 or a TH350, 1st gear in a TKO will feel like

4.04 rear gears if you have a 3.55s
4.25 rear gears if you have a 3.73s
4.44 rear gears if you have a 3.90s
4.67 rear gears if you have a 4.10s
4.93 rear gears if you have a 4.33s
5.19 rear gears if you have a 4.56s

Hope that helps.
 

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Discussion Starter · #7 ·
Sooooo.... can anyone tell me what 5.19 approximate gears with an M20 or TH350feel like? :D That's what 4.56's with a TKO would feel like. Too low for even messing around?

4.10's still the most practical choice?
 

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Sounds perfect! 4.10:1 with a TKO!!! Talk to Kevin R on the NW section. He has a '66 with TKO600 and 4.56s. Your 0.64 OD is really beggin' for even more gear. I would say that 4.56s are getting pretty steep for a daily driver, but your OD RPMs are still more than respectable! 4.10s lug the motor down pretty low still at 65 MPH, but the first gear ratio is pretty respectable at 11.8:1.
 

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I used to have 4.11 rear with a 1st gear of 3.35 and it was too much, 1st gear was so low on the street if I touched the gas a bit too much instant redline, you could drop the clutch without gas and not stall it.

4.11X3.35 = 13.77 total

So I changed to 3.55 which I am very happy with.

3.55X3.35 = 11.89 total

Your first gear is 2.87 with 3.73 rear

3.73X2.87 = 10.70 total

If you change to 4.11 you will have

4.11X2.87 = 11.79 total

Which is basically what I have with mine, your engine is a bit more radical than mine but also is a big block so it should be good.
 

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It seems to be a concenus. :)

It does depend on your cam. A really torquey like an old RV cam might work fine with 3.55s. A radical cam might need 4.33s or more to cruise in OD at 60. It might be wise to ask the performance cam guys what the recommended cruising rpm range for a given cam is and compare that to your expected rpms at the mph you cruise at.

The more I look at this stuff, the more I think the cam is matched to the drive train rather than the other way around - for a street car that is.
 

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I have 410s with a TKO 600 and they work great,especially on the highway. If I ever go though the rear end I'm thinking of going to 390s just because I tend to short shift around town (3000/3200 rpm) and I think the 390s would give me a little more gear in third and forth.
 
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