I have a 1969 cutlass with a 1977 olds 350. It is rebuilt (stock except mild cam and flat top pistons, comp about 9:1). It has a turbo 350 transmission and a type O open diff with 2.56 gears.
I know this is not the best engine year. It runs OK but would like more power. What are my options?

 

Change the rear end gear, 3:42 with 200-4R transmission if you like to highway cruise.
it will wake the car up.

 

A higher numerical gear ratio is all you need to wake up your car. A 3:42 or 3:55 ratio or something like that. You will use more gas however!

 

As both Tuffnut and Tj have stated a much more aggressive gear will really wake her up. 3.55 and you will feel a significant difference. 0-60 gets reduced by 1/2 a second on a 1 point move under these circumstances.

I likely have your same stock gear. It performs so inadequately in performance tests, I am better off leaving it in 2nd gear. But I don't recommend doing that without a properly functioning tachometer. She is turning 4800 rpm in 2nd at 90 mph vs 3100 rpm in 3rd. When going in drive it shifts so late in a run it slows down forward progress. Its power versus weight versus length of race works completely against itself stock. 3.55s and she will spin 4300 rpm at 90 mph in drive and she fires through each gear that much quicker.

Still want more oomph on top of that, long tube headers will give you a 20 horse pop. But can be challenging and high maintenance.

P.S. the 77 350 will be fine as long as you don't ask it to do to much, you should be fine in that department.

 

Exactly what 69CSHC has said.
If your torque converter is stock it holds you back with anything larger than the stock cam, but gears in the 2.xx range severely slow you.
Since you have increased cam and compression - I'd hope you have headers already, if not that is your next step for sure. I've used headers for over 49 years and you gain torque and horsepower thru the complete range - it's a necessary part of the package for gains!
Use a quick advance kit in the distributor also, this will also be a must!

 

4:11 gears, 2600 rpm stall speed converter, great for coming off the line or street light ..shift kit in the turbo 350, for a great feel, you could also shave your heads to boost the compression some.

 

As above. Sounds like you have a nice, easy to live with mild SBO build, so the best way to wake it up is by ditching that 2.56 gear. Go to a 3.23 or 3.42 if you don't want to spring for OD, or for more of a kick in the *** while maintaining cruiseability, a 3.90 or 4.11 plus 200-4R. With those gears plus the 2.74 low in the 4R a super high stall converter should not be a necessity, whereas if you don't go for the OD a little more stall speed might be helpful.

 

You have a weezy motor. Don't ask too much from it or it will bite you. Ask me how I know! Your set up isn't made to go fast. If it were me I would just enjoy the car. It will NEVER be fast.

 

Air in-air out as efficiently as possible.
Super tune what you have.
Air intake...high flow manifold & air filter
Air out...exhaust. Mandrel bent dual exhaust with high flow mufflers. Headers could be your friend...or not.
Optimize the 3 timing events (ignition super tuning---> base, centrifugal, total)
Optimize the carb idle, off idle, and WOT circuits.(Carb super tuning).

Once you have taken everything above to its limit, now start installing parts...converter shift kit rear gear cam.

 

Thanks for the feedback.
I would like to change the rear end gearing but finding type O stuff is not easy.
What other rear ends will fit easy?

 

GM 12 bolt.

 

Yes, if it's from a '68-72 A-body it should be a (wait for it) ... bolt-in. In fact, Canadian F-85/Cutlii came from the factory in Oshawa with Chevy 12-bolts in '68-9.

 

The stock stall is pathetic, about 1600, only good for the stock cam. Even a 2000 stall will wake up your car off the line. If you do a ton of high speed driving, going to 3.42/3.55 gear will seem awful. Even a stock stall, around 1900 rpm from my experience 2004R overdrive with a working lock up converter will run nearly the exact same as your current 2.56 rear on the highway with a 3.42/3.55 gear. With the better 2.74 first vs your current 2.52 first and a 1 to 1 rear gear ratio multiplication is truly the best of both worlds. Your motor being very mild, the 2004R will only need minor upgrades outside a proper rebuild to survive. Literally the only mods to install one is BBO/TH400 emergency brake cables, a way of controlling the lock up torque converter and making sure your current carb works with the throttle valve cable that controls shift points. That is it, a very easy swap. Mine performed fine with the factory 2.78 gears and 25" tall tire. I did 1/4 block one wheel peels thanks to a 2350 stall, 2200 to 2500 rated stall. I did have a 88 Cutlass with a factory 2004R and 2.56 gears. Factory 205/70R14 short and equally short 245/60R14 tires. With the stock 1900 stall and stock 83 Olds 307 swapped in, very lazy. With a 204/214 cam 403 with a 2400 stall, 2000 to 2600 rated, launched hard and went flat with a horrible single exhaust. Shorty headers and 2.5" dual exhaust gained everywhere. As said full length headers and 2.5" exhaust will make a noticeable difference. Good luck.

 

You can defiantly use an A-body ten bolt rearend, but use the one out of a chevy for best parts availability and the least expense.
You don't want to back into a BOP rear and be in the same boat.
On the other hand ; Quick Performance shows an Olds type O Eaton posi, ring & pinion, and bearing set for $990.00, not a bad price! Their options are either 3.42 or 3.90. The 3.90 with a 200R4 would be a rocket in first gear take-off, but just the 3.42 with your th350 would be a huge help!!

 

Agreed !

Bluecutlassconvertable fellow members have made great points pro and con. But when desiring a little more. These basic mods are essentially a must try for our type of rides. It will increase the fun factor at a minimum.

Assuming base setup this is the basic go to list, tried and true for 350s.

2bbl to 4bbl conversion
single exhaust to dual
highway gear to performance gear
long tube headers

That final step as 68post so emphatically pointed out is as good as any basic mode could be. Below is the idealized beneficial gain of swapping in long tube headers over log manifolds.

A 3700 lb Cutlass Coupe that touches 200 hp runs a 15.4 in the 1/4 mile.
A 3700 lb Cutlass Coupe that touches 220 hp runs a 14.9 in the 1/4 mile.
(Performance results come via a performance calculator. Where weight vs horsepower has an absolute outcome.)

As you see when fine tuned the benefit is also a 1/2 a second reduction in ET.

If that's not enough to quench the thirst, time to really start spending some bucks.

 

There are aftermarket gears, 3.42 and 3.90 that fit with the Yukon aftermarket posi or a factory 3.08/3.23 carrier. I just put in the Yukon posi, grips really well with used 3.08 gears in my 70S. Either the 12 bolt chebby from 68/69 or 71/72 10 bolt is the cheapest to build and bolt right in. But there is driveshaft differences plus the cost of buying the rear, especially if different gears and posi are needed. It can quickly equal or surpass the more expensive parts the Type O takes. It cost me about a grand doing it myself. Nothing is cheap these days.

 

Thanks again for the info.
It has a 4-barrel carb and dual exhaust and high flow mufflers.

 

Some pictures

 

Nice looking car!

Lots of good suggestions above. FWIW I’ll add mine, basically parroting much of what’s already been said.

3.23 -3.42 w/ 3 speed AT. (If you ended up swapping to Chevy axle 3.31/3.36, at 3.55 starting to push most folk’s comfort envelope) >> $1200-2500

3.73/3.91/4.11 in combo with OD AT. (200-4R being nearly a bolt in swap, along with some peripherals) >> as above + $2k-$4k for trans & details

Full Length Headers, can be grafted to present exhaust >> $500-1k

Ignition Recurve Optimization >> pocket change

Comprehensive Carb Tune Optimization. >> varies widely, maybe $300-$400 to buy A:F gauge, weld in O2 bung, tuning kit + lotsa trial & error (labor)

Gears will make huge difference, even more so if springing for OD trans swap. Realize that gears best present around town & secondary road driving, with a trade off on open highway. OD trans lets you have your cake & eat it too. Headers will make a noticeable improvement, best results coming in conjunction with ignition & carb tuning.

Those are the relatively simple, best bang for the buck improvements, some still requiring substantial bucks. After these, it gets more involved.

​​​​​​….

 

Wow... Nice ride

 

Blue Cutlass , the pictures of your car / the rims are Olds Super Stock / 5 x 4 3/4 . If you change to a 12 bolt Chev diff , would that not be a 5 x 5 bolt pattern ? if yes , then would not fit the Super Stock rims .

 

I never knew this. I put in a 12 Bolt Rear made by Moser. My wheels fit. Huh.

 

Parroting with further clarity is always a good thing !

Yes it is !

1977 Cutlass Coupe 350 TH350 2.41 rear, Car and Driver = 18.4 @ 75.7 mph.
A 1969 Cutlass S convertible 350 ST300 2.78 rear, was also a 18 second car ...

Potentially reducing ET by 4 seconds with your mild cammed 350s proposed combination, and along with bccan's tried and true suggested mods is a no-brainer.

 

NO, Chevelles, Camaros, Monte Carlos all have the 4 3/4 bolt pattern and use the 12 Bolt Axle. 5 on 5 was used in the larger bodied vehicles

 

Well, that explains things.