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PRND21

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Discussion starter · #1 ·
Ok, so who out there is rocking some numerically low rear end gears? Not because they are factory and you are broke but wish you had 3.73’s or 4.10’s.
Also, I know you big block guys are in a different worlds as far as gearing. I’m talking about you experienced small block guys that specifically chose 3.08, 3.15’s, 3.23’s and so on….


383 stroker here. All forged and internal balanced. 10.5:1 compression AFR 195 heads. 230/236@50 110lsa 550 lift 1.6 rockers Comp Cams xr282hr cam. Headers, Edelbrock performer rpm air gap, Holley 3310-2.

Plenty of timing. 18 initial, 36 all in at 3000. 14 vacuum.

TH350 with a 3000-3500 stall. It’s a high multiplication unit or hard hit. Nice and loose.

3.73 gears

My highway cruise is my last issue with this tuning.

I have a whole post dedicated to my 3310-2 carb running rich at 3000 rpm’s on the highway at 70 mph. AFR’s are perfect at all other conditions. Idle, off idle, cruise.

I also have a whole post on my temps creeping up at sustained 3000 rpm cruise. All other driving conditions are perfect.

I don’t want a manual or overdrive auto or a gear vendor unit. Too expensive and I love this reverse manual valve body th350.

My only option is 3.08 gears. That will put me at 2500 at 70 mph with a clean 14:1 AFR.

I believe these carbs were never meant to cruise at 3000. Back in the day, the speed limit was 55 mph and after that, overdrive came out.

3.08 gears will solve my issues on the highway.

Also. I have no traction in 1st gear. It’s basically useless, so this may be a better deal.

Any thoughts? Experiences?
 
#2 ·
PRND21 said:
Ok, so who out there is rocking some numerically low rear end gears? Not because they are factory and you are broke but wish you had 3.73’s or 4.10’s.
Also, I know you big block guys are in a different worlds as far as gearing. I’m talking about you experienced small block guys that specifically chose 3.08, 3.15’s, 3.23’s and so on….


383 stroker here. All forged and internal balanced. 10.5:1 compression AFR 195 heads. 230/236@50 110lsa 550 lift 1.6 rockers Comp Cams xr282hr cam. Headers, Edelbrock performer rpm air gap, Holley 3310-2.

Plenty of timing. 18 initial, 36 all in at 3000. 14 vacuum.

TH350 with a 3000-3500 stall. It’s a high multiplication unit or hard hit. Nice and loose.

3.73 gears

My highway cruise is my last issue with this tuning.

I have a whole post dedicated to my 3310-2 carb running rich at 3000 rpm’s on the highway at 70 mph. AFR’s are perfect at all other conditions. Idle, off idle, cruise.

I also have a whole post on my temps creeping up at sustained 3000 rpm cruise. All other driving conditions are perfect.

I don’t want a manual or overdrive auto or a gear vendor unit. Too expensive and I love this reverse manual valve body th350.

My only option is 3.08 gears. That will put me at 2500 at 70 mph with a clean 14:1 AFR.

I believe these carbs were never meant to cruise at 3000. Back in the day, the speed limit was 55 mph and after that, overdrive came out.

3.08 gears will solve my issues on the highway.

Also. I have no traction in 1st gear. It’s basically useless, so this may be a better deal.

Any thoughts? Experiences?
Click to expand...
These cars were not designed for 55MPH freeway speeds. That speed limit started after the oil embargo in 1973 that pushed gas prices up. I drove my '68 El Camino from Northern California to Los Angeles and back at 70MPH. It had a powerglide and 3.55 gears so it was cruising at over 3K for several hours.
 
owns 1969 Chevrolet El Camino SS396
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#4 ·
You may have more than 2500 RPM at 70mph, depending on how much slip there is in your converter. I have 3.07's and I run at 3000 RPM at 70 mph with a 2000 RPM converter. That's about 10% slip. According to many opinions that's too much, and I agree, but according to the manufacturer it's in normal range and according to online reports that's typical of that manufacturer. I used to have 2.73's with a stock converter and 3000 RPM would be at 75 mph.

That said, 3000 RPM at 70 mph is not even noticeable. Once I get up to 75 mph, and definitely 80 mph, it does start to get annoying.

I agree with not going to a different transmission. While many have done that successfully, it would likely be opening a huge can of worms.

If you have no traction in first gear with the 3.73's, then 3.08's will probably be fine for acceleration. Personally, I like to be able to roast tires from a stop or even a slow roll -- if I want to -- but spinning at anything above that is a waste of rubber, money, acceleration, and handling and begs a numerical reduction in gears. Fishtailing in second may impress people waiting for the bus, but it does nothing for performance.
 
#5 · (Edited)
With a loose converter like you said you have, if you put in numerically lower gears, you will be pushing harder on the converter. I don’t think you’ll be seeing the same RPM drop benefit as your calculations.
 
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#6 ·
454 BB limping in here with 3.31’s. I’ve ran 4.10’s in a 496 before. Not my jam spinning 3K rpm’s at 60mph. My 3.31’s are way more than enough for my previous 454. A new MJ 467 is on the way. Yes I’m going to keep the 3.31’s. I prefer spinning around 1800 rpm at 60mph.

In a small block world I believe the 3.73’s are the ticket. If that’s not enough your build/engine is lacking.

All my thoughts are on manual tranny’s though.
 
#8 ·
Back when I had a 383 I ran 4.56 gears with a Turbo 400! Now I have 4.10's with the .060 over 396. Have driven it down to Ocean City Maryland several times at 3+ hours at 3000 RPM. I have a 2 core copper/brass radiator (high efficiency core) with no cooling issues. I will hopefully soon be installing a TKX 5-speed so the overdrive will solve the high RPM highway issue. Finally after 40 years of owning the car it will see an overdrive.
My 69 Camaro SS350 had 3.08 gears and a turbo 350. It was a good cruiser, but I would not say it was fast.
 
#9 ·
I’ve got 3:08s with a 468 and run 275 60 15’s and at 70mph it runs around 3krpm. To be honest I’d probably be happier with a 350ish gear.
 
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#10 ·
Can you fit a taller tire to see how that affects your cruise rpm and a/f ratio? GM did make a 3.23 for 10 bolts. I have a 3 .42 in my 454 C10 but it sees no highway. It won't see the road at all with no a/c until the temps drop 20 degrees at least lol.
 
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#13 ·
If you are just worried about AFR, have you taken some main jet out? I would drop the main jets and if you like the results, open up the PVCR's to compensate.
 
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Discussion starter · #14 ·
Yeah man. Tried all that. Lower main jet does lean out the 3000 rpm cruise. Upped the PVCR. Added a 10.5 PV. Even then, lean jet means super lean moderate acceleration. The small MAB helps keep the curve flatter but in or der to keep a decent moderate, non PV, acceleration, I have to keep it at 72. Honestly, 73 jets give me the crispest strongest acceleration. But then cruise is like 12.8.
 
#15 ·
What size rear tires do you have? I'm running 3.08s with 26.5" tall tires, a Richmond 5 speed ( 1-1 fifth) and 70 mph is 2750 rpm. Of course there's no slippage either. I'm actually thinking about going to 2.73 or 2.56.
 
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Discussion starter · #16 ·
I’m running 28 inch tires. That’s good info regarding your locked clutch. I guess I’m skipping a lot more than I thought.

this 9.5 inch torque converter has a #0 pump and 082 stator. High multiplication and mid range coupling. It’s a neutral pump. Should slip but not too much.
 
#18 ·
PRND21 said:
Yeah man. Tried all that. Lower main jet does lean out the 3000 rpm cruise. Upped the PVCR. Added a 10.5 PV. Even then, lean jet means super lean moderate acceleration. The small MAB helps keep the curve flatter but in or der to keep a decent moderate, non PV, acceleration, I have to keep it at 72. Honestly, 73 jets give me the crispest strongest acceleration. But then cruise is like 12.8.
Click to expand...
That's pretty fat for cruise AFR. Wide open peak power you want 12.8. For cruise you should be around 14.7.

At part throttle cruise your converter should only slip by a couple percent. At full throttle it will slip more. My car has 3.50 gears and a 30" tall tire with a 6K stall converter. At cruise it only slips a couple percent.
 
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#19 ·
BBC 454 I just switched from 3:73 to 3:07 due to highway RPM. I am very happy with the cruise feel on the 3:07. I still have plenty of torque to blow the tires loose.
I am currently using a poor excuse for a 2800rmp stall torque converter. I will be switching to a 2800-3000 RPM FTI one.

I am not going to drag race and just like the thumbs up while cruising around with the AC kicking on high.
 
Discussion starter · #20 ·
does it still feel fast?

Yeah man. I can burn rubber in 2nd gear all day with this converter and 3.73 gears and 28 inch tires, so I figured it would be ok. My converter is on the cheaper side, so I could upgrade to one that couples a little harder with the same stall.
 
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