Tim305

I am trying to get to between 300 and 350 hp out of my 69 olds cutlass 350. I have been reading a lot of these threads and first off I'm impressed by the knowledge out there and secondly I'm confused a bit by the tech stuff and a few of the abbreviations. I'm going to state my goals and background up front. I am 62and recently retired. I have helped my brother restore a 57 mga. we tore the engine apart had the machine shop work done and reassembled it. So I have some knowledge of engines however that was a very basic engine. I bought a 69 cutlass convertible that was about 80 pct restored. It has a 2bbl carb. The exhaust was converted to duels. The engine is a 69 350. It was rebuilt by a college auto shop class about 3000 miles ago prior to my buying it. I'm looking to use it as a cruiser like I did back in high school. Enough hp to light up the tires a bit but not a dragster. The book says this 2 bbl should be putting out 250 hp. With a 4 bbl it's 310 and the performance engine 325. I assume that's with dif heads. How accurate is this? If it's accurate I should be able to get where I'm going with a Eb rpm intake and a 4 bbl swap with some good headers right? Or do I need to go with a new mild cam heads and tork conv?

joe_padavano

You assume incorrectly. All 1969 350 Olds motors used the same #5 head castings with the same 64-ish CC chambers. Olds varied compression with different pistons. Your 2bbl motor has large dish 9:1 pistons. The 4bbl motors used pistons with smaller dishes and 10.25:1 CR. The 325 HP W-31 used flattop pistons with 10.5:1 CR. Note that these are nominal design values. As-cast heads typically had slightly larger than spec chambers and would need to be milled to achieve blueprint numbers. Similarly, these numbers assume the factory steel shim head gaskets. The more common blue FelPro gaskets today have a thicker compressed height, which will also drop CR slightly.

Cams were also different among these motors, as were valve sizes on the W-31 motors. Each of these differences makes up for some of the HP difference, and the mods really need to be done together to get maximum advantage of each.

Tim305

I didn't think it was going to be that easy it never is but I was not sure what the real difference was. So what would be the easiest way to get to say 325 hp?

Octania

Sounds like you need
flat top pistons [W31] or at least the 10.2 small dish pistons
more cam [consult the experts here for specs after your CR and etc. are known]
larger intake valves
then
Your intake and headers and higher stall converter

Of course if you are doing all this in front of a 2.14 final drive gear you will still be disappointed in the performance. Start with what gear you have or can obtain.

MDchanic

Honestly? Install a 455.

You can certainly get that from a 350, but you will need pistons, possibly machine work (who knows what the shop class did), a cam, intake, probably headers, but for the same money you can do the same stuff to a core 455 and get more power.

In the end, it's up to you, we have folks here who enjoy doing great things with 350s, but if your question is, What is the easiest way, that's it.

- Eric

redoldsman

I would say start with the 4 barrel, maybe a set of headers and then change the rear gears to something like 3:23's. None of that would be wasted unless you go to a 455 later. After you make those changes, see how happy you are with the performance. The 350 is a great engine and I guarantee it will spin the tires. I agree with Eric, if you are looking for lots of torque and hp, start with the 455. It all depends on what you are looking for.

Octania

Best bang for the buck is probably final drive gears, assuming you have at best a 3.08:1 open rear end. Maybe a 2.73 or even 2.56. If it's a Funday Driver, go for as much gear as you can stand on what highway driving you do. 4.33:1 is a bit extreme, I can attest from experience. 3.42:1 or 3.73:1 are better if you EVER need to go on the highway.

You might find that you are done right there, and don't need to go to another intake, carb, headers, etc.

Tim305

I have the o type rear. I don't know the gear but I'm sure it's in the 2:56 2:73 range open. I've been trying to find new gears like a 3:42 but not having much luck I'd like to also go posi.

redoldsman

You are not going to have much luck on the type O rear. Brian Trick (olds507) on this board can fix you up with a complete rear end. He is a great guy and does an outstanding job. I know he had a 3:23 posi recently.

hookem horns

Don't worry about actual HP if it's a hobby cruiser, a 350 SBO can be plenty peppy if not worried about winning races. First, make sure it's tuned properly, especially the timing. You already have dual exhaust so add the 4bbl. May not really make the car faster but who the heck wants a 2bbl on a muscle car . Seriously consider gears before internal engine work and a 3:42 is a good compromise for off the line performance while not bad on the highway.

hookem horns

Also, what transmission is in the car now? Many '69 2bbl cars came with the 2 speed jet-a-way (junk-a-way). A TH350 is a tried and true upgrade but lots of folks on here recommend the overdrive 200-R as well, especially if you do a lot of highway miles.

Fun71

Uh-oh. You need to find out what pistons were used in the rebuild.

The commonly available "factory replacement" pistons are the '71-'72 deep dish cast pistons that also suffer from being too short on compression height. This means your engine may have as low as 7.5:1 compression ratio, so there is no way you can get 300+ horsepower with that configuration.

Tim305

I thank you all for this information. I am planning on starting from the back and working forward. I want to go with a posi and a 3:42 gearing,( probably can't find it but if not I'll do the c clip even though I don't see how that little clip can keep the axle in ) funny you should mention the tranny. First thing I noticed was the P R N D L in the speedo was a little off. Then I noticed that the tranny felt like it was shifting 3 times. Would that not be a P R N D L S? The previous owner said the transmission was rebuilt the same year as the motor. I may have the th350 in it. The engine runs very well and seems very strong. I guess engine wise I'll just slap on the 4bbl and a Mallory distributer and call it done . Why? Same reason back in 1970 when I came home with a 69 firebird first thing I did was tore off the exhaust stuck on cherry bombs and shackled it up. My dad just shuck his head but nobody back then kept them stock unless they were over 30. I love the sound when I put my foot in a 4 bbl.

Tim305

Can I find out what piston it has by having a compression test done?

rcrac3r

To true. Due to an error on my part, & not knowing there were different types of dished pistons in SBO's, my rebuild ended up with the stock low compression dished pistons. Have to wait for the "car budget" to replenish before upgrading pistons. At least we can drive it the way it is, isn't to bad for performance.

Koda

You can fiber optic camera down the spark plug hole and look at the piston.

Fun71

Not really. The type of camshaft used has a large impact on the cranking compression (pressure), so it's difficult to determine the compression ratio based on the compression test readings.

If it's shifting 3 times, the you are probably right about that.

Allan R

1. PRNDL is the indicator display for a 2 speed Jetaway trans (M31) It was one of the 2 optional transmissions for the 350 back then. The standard trans was a column mounted 3 speed MT The other one is the M38 which is the TH350. If the dash of your car is original the M31 is apparently what your car came with from the factory in 69.

2. PRNDSL (not PRNDLS). The S is nomenclature for 'Super' range in the Olds manuals. Basically the same as second gear. All the TH350 and TH400 cars came with the PRNDSL on the shift indicators. You would not want to sling your tranny through L to get from D to S. Aren't you glad you don't have one of the early GM's that had the shift set as PNDLR?


1969 PRNDSL


1969 PRNDL (with speedminder option)


1970 - 72 PRNDSL

droptopron

Technically a turbo 350 would shift twice 1st to 2nd & 2nd to 3rd.
if you take a look at the pan the 350 looks like a square with one corner cut off. I think the Jetaway is more rectangular. A turbo 400 looks like Texas.

Performance wise I would start ripping down the engine if it runs good or discarding it for a 455. Get some gears & see how it feels to you. keep your eyes in CList. Maybe you find a good deal on a rear. Keep in mind if you go with a Chevy rear you'll need to change the driveshaft too.