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Strange S60...what gears to get?

11K views 71 replies 17 participants last post by  Geo71 
#1 ·
Getting ready to order an S60 for the Chevelle. Wondering what gear ratio I should pick...here is what is available:

Gear Ratio Selection
3.54 / 3.73 / 4.10 / 4.30 / 4.56 / 4.88 / 5.13 / 5.38

I'm currently running 3.90 in the 12 bolt....275/60/15 tire....4500 stall nitrous converter, 150-250 shot of nitrous.....Havent got to run the car yet with the 383 but it's in the car now. More strip than street....was thinking either the 3.73 or 4:10....

Thanks for any thoughts.
 
#6 ·
Shooting for 10.80 on motor....
 
#3 ·
Is the 650 the cfm recommended? What rpm do you think your going to shift at? The calculators can get you in the ball park. Ray is right gear to MPH.
 
#7 ·
No thats not the recommended carb, just what I had running on the previous 355. It's pretty small for this 383....going to get with jmarkaudio and have him put one together....thinking something like a 950HP would be good..

Probably shift around 7000 area....
 
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#8 ·
Have not dynoed it yet Ron. Hope to chassis dyno it sometime in the next couple months....
 
#5 ·
I would go for the 4.10.
You have good heads and a large cam and it should RPM if everything is right.
Between the 3.73 and 4.10 there will be about 500 rpm difference at 110 mph.

Math 336 is a given.
336 X Gear Ratio X MPH then Divide by Tire diameter = RPM Allow something for converter slippage.
10% would be very safe I would think.

With 28" tire and 120 MPH you would be 5900 rpm or so with the 4.10 then allow for slippage.

Still pretty conservative gear.
Your car is heavy and probably needs all the help you can give it.
Buddy borrowed my 3.70's for his 9" and 355" with the flat tappet 292H.

After about 2 weeks he wanted his 4.56's back.
I really like the 4.56 gear for the small block that see's 6800-7500 rpm.

But if you have issues with traction taking some gear out may help it.
 
#9 ·
Thanks Jeff...I'm going to work on the weight some, nothing too crazy just the basics....lighter wheels, fiberglass hood (need a bigger cowl anyway) that sort of stuff. The 4:10 was what I was thinking of going with...wasnt sure if less gear would be better with nitrous or not...just driving it around the 3.90's don't quite seem to be enough....but I also don't have alot of timing in it yet...need to get some better fuel first to be safe.
 
#10 ·
4.10 if more strip than street NA, you can always bring it down with a taller tire. On a large shot of nitrous maybe 3.73 or less.
 
#13 ·
I'm not sure if I can fit a taller tire under there...mine sits kinda low.
For a little nitrous motor, I would go 4.30 or 4.10. Nitrous makes tq, but still have wight and a small motor that needs some "help".
I wasn't sure with the nitrous...maybe the 4.30's wouldn't be bad...had 4.10's in my first Chevelle, but I think the tires were pretty short....

For a more strip than street and shifting at 7k I would consider the 430 or 456 . I run a 456 with 28" tire both on the street and the track, with a decent converter I go thru the lights around 7 k at 126.

Brian
How are the 4.56 on the street? The farthest I tend to drive is to Norwalk, bout an hour and a half give or take. I have a PTC converter that was gone thru and loosened alittle by a local guy...see how it works in a few months..
 
#11 ·
For a more strip than street and shifting at 7k I would consider the 430 or 456 . I run a 456 with 28" tire both on the street and the track, with a decent converter I go thru the lights around 7 k at 126.

Brian
 
#14 ·
I went over beefing up my 12 bolt and by the time I have the ford ends put on it, buy axles, pinion yoke etc it's not that much more to just buy the S60. Figure I can sell my12 bolt and cover a lot of it. The S60 is supposed to only be about 25 lbs heavier and going with a lighter , better driveshaft should even it out. I'm kinda planning for the future too :thumbsup:
 
#18 ·
With my old converter and 3.31's it stalled to 4000....when going to the 3.90's the stall dropped to 3800. New converter stalls at 4500 without spraying, should go up some with the nitrous I think...with 4.10's probably not much difference? Maybe the 4.30's would drop it some?
 
#28 ·
Do you think you would keep the spool? Never had anything like that.
 
#29 ·
Nice!

My car with 275/60/15 tire and 4.56's would run 35/3600 rpm at 60 MPH on the highway with normal 1-1 gear trans. Thinking about it as a street/strip car and the aid of the Nitrous, 4.10's would be my choice. My car with the 4.10's ran about 3/3100 RPM at 60 MPH. Nitrous off the line or going to a shorter slick could prove the best of both worlds. Looking at that option now with 770Hp BB and Nitrous in my streetcar now for this summer. My car should run "around" 9.40/9.30's NA.
I'm thinking either the 4.10 or 4.30 at most right now. Mine won't have that much power n/a, should be 550/575 somewhere in there once dialed in...don't think the nitrous will get used all that much...more for some once once in awhile. Time will tell :thumbsup:
 
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#33 ·
With my 355 changing the gears from 3.31 to 3.90 made no difference in et or mph. But I was able to use all three of my gears instead of just 1-2 which was nice. With only 280 hp to play with, cant expect too much. Used a 125 hp kit I borrowed which was a nice boost. We have a group of guys that go out on Fridays to the local tnt and grudge race for fun. First year was 12-13 sec cars...last year was 10-11 sec cars... this year alot of them really stepped up their cars... should be a few 8-9 sec cars. Going to be a fun summer! So yeah there will be some nitrous Friday nites...haha
 
#32 ·
MY 78 Nova busted 4 10 bolts before I stuck in a 9".
All my stuff gets a 9" easy to swap gears out and salvages are full of gears.

I ran a full spool in that Nova with 4.56 gears for 2 years as a daily driver, I worked 27 miles from home and I put a lot of miles on it. over 35,000 a year
Many times pulling the little Bayliner to the lake 160 miles away.
I also hauled scrap iron about weekly and it served trailer duty for that.

I did change tires when I went on those runs vs the drag strip tires.
I ran the 235-75-15 tires Good year wranglers are good for that.
They give easier going around corners vs the stickier drag type tires.
I had some uniroyal tiger paws 275-60-15 and 31" hoosier dirt tires.

I even had some 31-10.50-15 mudders when I took it hunting and fishing. Yes a 1978 Nova.

I had Datsun Z cars the 240 280 and 260 kind with inline 6's you get used to driving at 4000-4500 rpm on the highway.
R's do not hurt.. Look at a lot of your chevy boats on the lake 5000 rpm across the lake for 35-40 minutes.

I have been known to run 6500 rpm for many miles.. keep an eye on the oil as you can suck the pan dry if drainback is not optimum.. My ford van 302 would suck the pan dry at 4200 rpm.

When I want something set on kill I reach for the 4.56's, but like stated you could run out of R's
 
#35 ·
Going to a 9" is probably the least expensive route to go. I just hate the way they look. Still have it in my head to run some sort of posi in place of a spool...a buddy had a 67 mustang at one point that was full time posi of some sort. Squealed the tires and jumped up and down on turns...dont think I would like that.
 
#36 ·
Just trying to help. It seems you are trying to run fast, a 9 inch and S60 are not the way to go, they will both slow you down, combined with a 10 inch converter 10s NA will probably not happen, remember theres more to running fast NA than a stout engine.
 
#38 ·
I'm not really interested in the 9", just sucks they are so much cheaper to go with. I can see where the S60 is alittle heavier and must take a few more hp to turn. Not understanding what the size of the converter has to do with running faster or slower etc...never understood that part.

I know it will take some work to get the stars to align and get where I want it to be....I appreciate all the help, thoughts and info for sure. :)
 
#37 ·
George,

If you end up keeping your 12-bolt, (and IMO it seems like the best overall move), you might check with Jim @ JDRace.com over in Richfield. Me and two friends have done business with him and he's knowledgeable/good guy to deal with. His website kinda sucks, I'd suggest just calling him up.

-Dave
 
#39 ·
Yeah Dave, I wouldn't mind keeping the 12 bolt....this local guy is really good, but he's really busy and a big Mopar guy. So getting him to work on mine may not be that high on his list.

I will check out your guy too. Still have some time to get things done.

Took the Chevelle out for a cruise today :thumbsup:
 
#41 · (Edited)
George
I believe there is a calculator on the internet that will give you the Rearend gearing
needed to cross the 1/4 mile stripe at a certain RPM based on the Trans gearing

So you want to cross the stripe at just below your max RPM and after your engines best/highest HP at a/the applicable RPM

EG.
my Engine's max RPM is around 6,000 RPM
my Engine's max Trq Ft Lbs is 510 at 5,000 RPM
my Engine's max HP is 535 at 5,700 RPM

So I usually shift the TH400 at 5,750/5,800 RPM
cross the stripe in 3rd at/around 5,900RPM

I went the strongest Rearend that would last for me and how I use the car
Cruzin around city and Hwy Trips of 100 miles to relatives etc. plus the Track on sunny Weekends
a S60 from Strange
GM A Body Bolt In Fully Welded 360*Tubes / Mounts Installed & Raised 67 Spring Perches /
HousingEnds H 1135 11” Drums / 1350 PinionYoke / S/T Series 35 Spline Axles / ½” Studs /
Axle Bearings / True Trac(worm type) # OPRS02 posi / Standard Gear Set / U 1600 Steel Pinion Yoke(1350) /
LPW support cover # OPRS06 / Breather Vent / Filler Plug / Drain Plug / LucusOil /
Gearing Ratio 3.70 / Fully Setup # PRSA05
Strange S60 Rear End * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * With GM A-Body*Spring Mounts * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 35*Spline Alloy*Axles and*Trac-lock Differen

It was a easy direct replacement of the old 12 Bolt


The Rearend Gearing Ratio is something you have to decide with the TH400 that does not have OD
I went from a 12 Bolt with 3.55s to the S60 with 3.70s
as the RPM difference was only an increase of 200-300 rpms at Cruzin Speed
and gave me a little more go out of the Hole/Launch/first 60'
 
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#42 ·
Looks nice. How do you like the Trutrac? I've only ever had the reg eaton posi units....

With the current 3.90's and 28" tires my car crosses the line about 6000 (with the previous 355). I did a chassis dyno once with it...it was 280 hp @5100...300#ft at 4600 something like that. After a couple seasons of tuning ended up running the quickest shifting at 6500 1-2 and 2-3 which crossed the stripe at about 6000. That was with the old converter too...
 
#43 ·
Love the True Trac
smooth and quiet rear posi with no springs/shims to rebuild every so often

Me too on the reg posi in 12 Bolts
which I had rebuilt with new springs/shims
then fail/not work after only 2 yrs

I have had the S60 with the True Trac in the car since 2013 and everything working great
whether at the Track or out on the road Cruzin
I run 28" Tires on the Street and at the Track - M&H MSS001 (Rollout = 88.5)
 
#44 ·
Mid 2015 my buddy suggested the gear change to the 3.90's...We pull it apart and discover the axles are worn out, not a surprise since they were original. Get to looking at the posi unit and the inside of the housing was trashed. Good to find it ahead of it failing. So went with a new eaton posi and moser axles/ girdle cover. Its been a good rear ever since.
 
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#45 ·
You may not need to change it out.
You said your buddy is a Mopar guy.. My uncle was Mopar guy and has had some wicked stuff, He has passed away but the stories he had to tell.. He was a racer back many years ago raced against Petty and the others.

He had this old ford truck with big block and dual 4's and he broke three 9" rear ends.
Being a Mopar guy he installed a Mopar 8 3/4 rear end.
He said he never broke it.

Maybe if you need to upgrade... just saying your Mopar buddy would be thrilled.
 
#46 ·
Been doing a lot of research the past few day. Part of my reason for swapping the rear was not being able to find anyone to actually upgrade my 12 bolt. My local guy who is very busy must not really want to mess with it and has not got back with me. I tried to contact the guy in n Richfield with no response. So selling my 12 bolt and getting the S60 seems the path of least resistance and $$$.

Now talking with my Ford racing buddy that helps me a lot, he said to call Moser. Turns out they will work on customer stuff and if I get there by 8am it will be done by 2pm same day. They are only a couple hour drive. Looks like I will go that route. Have them put the ends on and weld the axle tubes and get the axles. Thinking 33 spline, 1350 yoke of some sort and will need to figure out what to do with the posi unit...maybe it can be upgraded for the bigger axles and reuse my 3.90's. Or better off with something else? Don't think I want a spool, but maybe that's the way to go...

More research time!
 
#49 ·
That was one of the ones I was looking at too. Now I guess the question becomes, how much race car can I deal with on the street as far as gearing goes and what series diff to buy....the online calculator seemed to lean towards 4.56 with trans gearing, tire size and rpm....I know I would hate that, but the car is more strip than street.

Probably not enough difference to change from the 3.90 to 4.10...
 
#48 ·
Sounds like you have a good plan George.
The only reason I go with a 9" is because I can fab it all in myself. I got many of them a few years ago for 65 bucks each.
The reason I went with a spool is because the clutch Posi units even rebuilt would only last me about 2 weeks on the street.

I drive my stuff hard and it hooks.
I would get in the gas and out and in and out. Loading and unloading is pretty hard on parts.
The spool for my race days was just more reliable and I set them up myself. the 9" is almost too easy.

My other Uncle ran a 57 chevy with BBC 600 WHP and a TH400 with 4800 stall. it had a 12 bolt and slapper bars he ran 4.11 gears and ran in the low 10s. high 9"s with everything right.
It weighed 3000 lbs and he tried 4.56 gears and it was slower.. ran out or R's before running out of track.

Never busted the 12 bolt and he had 33" tall Goodyear slicks.
Slapper bars were bent though.
So it hit pretty hard.
 
#50 ·
Yeah if I had something that was more of a full race car, the 9" would be a good way to go. I just think in an old school Chevelle the 12 bolt and even the S60 looks like they belong there.

From my limited street testing with the too small 650, it gets right up to 6500 like nothing. I don't think it would run out of motor with the 4.56....but may be more than I care to deal with....hope to at least score a trailer for some of the farther tracks...Norwalk is about as far as I care to drive now.
 
#51 ·
Too bad you do not want to keep the 12 bolt and 3.90
You could test that and then get the S60 with 456 and test that for ET and MPH.
Then go from there..
You are correct that you would be out less if you sold the 12 bolt.

Wonder if you could find a 10 or 12 bolt for cheap with a highway gear like 308. get that and swap it in when you want to just drive and drive.

My little 350 with 268H cam in my 3800 lb 57 4 door went 14.4 et with 3.36 gear in the stock 1957 rearend and I then stuck a 9" in to it and put it on the wheel dyno and lost 3HP the 9" has 3.70 gears now and the same ET at the track 14.4.

It was hotter outside but I really thought it would not matter that much.
Like 2 tenths quicker through the 1/8 mile,, just did not like the rest of the track.
You will not feel 390-411 swap and in fact many friends went for 370 to 411 and felt nothing said it was not worth the swap.

Yes a trailer is nice especially if you have the tune set on kill and are leaning on it really hard.
I pull my friends to the track many times ..then unhook the trailer from my car and race it also.

Decisions decisions.
I feel for ya. :)
 
#52 ·
Too bad you do not want to keep the 12 bolt and 3.90
You could test that and then get the S60 with 456 and test that for ET and MPH.
Then go from there..
Do this.
 
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#55 ·
Are you planning to run nitrous a bunch?? You said you figured running about 10.8's NA so I used 123 mph for a reference.

28" tire....3.90 gear.....6216 with 8% slip

28" tire....4.11 gear.....6551 with 8% slip

28" tire....4.56 gear.....7269 with 8% slip
 
#56 ·
For the bracket racing stuff no....for Friday nite fun most likely yes.

The guy that Dave recommended, I was finally able to get in touch with and have been going back and forth abit on some different options. He wants me to go with a spool and 33 spline axles. That limits the gear choices to 4:10 and lower....3.90 to 4.10 probably not much, if any, real difference.

Another option he suggested was to stay with my posi unit, gears, brakes and axles using cclip elims instead of the Ford ends.

I'm thinking the 3.90's would be leaving some on the table, but maybe not?

Waiting to hear back from the guy after I sent the last bit of info he asked for....then I should have some $$$ numbers to roll around.
 
#58 ·
Yeah looks like reusing my axles/ gears and such are out ( which I figured anyway, but worth a try)...so I think the ends are going to need to happen...he wants to go with 33 spline axles and spool too. Should know more tonite.
 
#60 ·
FWIW, I am running a S60 with 3.73 gears and tru-trac. compared to the cooperate 10 bolt posi with 3.73, it was night and day difference. No girdle cover for me. No problems and running high 11's.

I put my drum brakes off my old diff to the new one with no problems. Been running the S60 since 2008. weight wise, I think there 20lbs heavier than a 12 bolt. tru-trac is a great poi unit for a dual purpse car.

compared to other crate rear ends, bang for the buck you cannot beat the S60.
 
#61 ·
Ok got the details worked out for the most part. Spool, Ford ends and 33 spline axles, welded axle tubes...think I will just go 4 series with either 4.10 or 4.30's. Have to look into the wheel studs to see what It should be...1/2" good enough?

He mentioned that he could narrow the rear 1/2" on each side, is that something worth doing? I can fit my 295/50/15's with no issue now that I trimmed the fender lips a bit. They are on a 10" rim with 5.5" bs...my DR's are 275/60/15 on 8" rim with 4.5" bs. I'm going to need new wheels anyway I think for the bigger wheel studs. I had thought about going with the 295/65/15 which are the same height but a bit wider....don't really need the width but can't hurt. But also thought about the 275's on a 10" instead of the 8".

If it was narrowed wonder what that would do to the b.s.? Will have to do some reading and measuring.

So with the Ford ends, 33 spline axles and spool, what is a good disc brake setup? Some kind of stock swap deal out there? Or just go with some aftermarket deal?

Anyway get to yank the rear out this weekend and do a bit of driving!

Thanks for all the help so far!!
 
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