Hello all, I have a 68 Cutlass S convertible with the original 350 2bbl #5 heads 2speed trans. Car has 140,000miles and motor is starting to smoke and use oil. I would like to have it rebuilt to have more low end pep, no racing, just a cruiser, about 5,000miles/yr in town and some highway. What would be a good compression piston, cam, intake, and carb if I stick with the 2speed trans? What if I switch to a TH350 or 200-4? Thanks for any advice!

 

Switching to a TH350 or 200R4 will give you more pep due to the lower gearing. The 200R4 will also have an overdrive which is what I plan on doing to my car. If that is not enough then you can look at increasing power with a rebuild.

 

Thanks 455man, but it's time for a rebuild on the motor. I'm looking for some input on a good rebuild plan if I stick with the 2speed and also for going with a 3or4speed.

 

I'd do the same build no matter which transmission you use.

Pistons will be the key item for getting decent compression - you do not want to use the generic "350 replacement" pistons found in most kits as they have huge 24cc dishes and are .020" or more short on compression height. This results in a compression ratio below 8:1 in most cases.

Your heads likely have combustion chambers in the 66-70cc range, so you need the piston dish to give you about 9:1 to 9.5:1 compression ratio, depending upon the camshaft grind that will be used.

For the cam, something with around 204-210 duration @ .050" would likely be good for a street setup.

For a strictly street cruiser, maybe 9:1 and a 204º duration cam. There are many ways to do this, though, so you need to determine exactly what you want out of the engine and how it is going to be used.

 

Thanks Fun71. What if I went with Speedpro 2320F flat top .030 over pistons, Elgin E-976P cam (.449/.473 - 204'/214'), performer rpm, and slightly modified 800cfm quadrajet, Would this combo work?

 

Using some assumptions below, I ran a compression calculator and got 9.9:1, which is high for street use to begin with, then with a short duration cam like that it will likely have too much cylinder pressure to run on pump gas.

Bore = 4.087"
Stroke = 3.385"
Combustion chamber volume = 68cc (guess - must measure to verify what you have)
Head gasket thickness = .040"
Head gasket bore = 4.250"
piston-to-deck clearance = .020" (guess - must measure when assembling the engine using the pistons you choose)
Flat top pistons

Changing the above to 6cc dish pistons such as the L2321F and the CR = 9.3:1, but I'm not sure if you can still find these pistons.

 

Just fwiw . I built a 350 reusing the stock pistons (14cc) and using a shim gaket and milling the heads kept compression around 9to1 . I used a comp 260h cam . Edelbrock intake , full length headers , x pipe , hei distributor , 600 cfm edlebrock carb , with a th400 and a 2200 stall , with 3.73 gears it went 13.86 through the mufflers at the track. The car ran super smooth on the street . The th400 will eat some hp had i gone with a th350 i would have picked up a few tenths . Personally for a few more bucks i would go with the probe pistons.

 

The L2321F .030 over are available at Summit for $400. If I could get by with the minimum deck and head milling what would be a good cam to run?

 

It all depends. How your heads cc , and all that because with the flat tops you will be around 10 to 1 compression or 9.3 to 1 etc etc. Lots of variables at play.

 

This should be a sticky, i have seen you post it a thousand times!

His engine has 140K on it, VERY unlikely the stock pistons can be re-used. And, the 14cc dish pistons are not readily available. Another option is the flat tops and #8 heads (or Pro-Comps, if you can afford them) CR will be right at 9 to 1. The Probes are nice, but 3 cc might not be enough to get the Cr down where you want it, unless you go with a thicker head gasket. Lots of variables, for sure.

 

L2321F is a good piston. with stock heads you should be at 9.5:1. That's the piston I used when I built my 350. They are little cheaper on ebay. ebay link
Talk to Mark - cutlassefi here on CO, he can set you up with a good cam.

 

Thanks everyone, your experience is very valuable. I think I'm catching on to the whole compression calc thing and how important it is to be accurate. Does anyone have a list of different brands of head gaskets with thicknesses?

 

The Probe are a much better piston BUT have a taller compression height. That makes the compression high despite the 3CC dish. The Felpro head gaskets are .041" thick, Rocket Racing has .028" thick and M+J Proformance has .011" shim gaskets. Expensive Cometic gaskets can be had in nearly any thickness up to .150". That cam is a generic grind. I am assuming it is exactly like the Edelbrock Performer cam. It will work OK with 9.5 to 1 or lower but is mild.

 

There aren't many piston choices available unfortunately. With older small chamber heads you end up with CR that is either too high or too low it seems. Since your goals are so modest, one option is to just get the shitty big dished pistons but deck the block, mill the heads, and use a thin gasket to get your CR in the high 8's to very low 9's.

Of course you can always get custom pistons too!

 

I agree with all of the above. $360-ish for the pistons is not bad and they would give you a good compression ratio that would be useable with a wide range of camshaft profiles. And Mark is a good resource for getting a cam that will work well for your intended application.

Once you have the compression and camshaft defined, I consider all the other stuff such as intake, carb, exhaust, ignition as "tuning" refinements that can work for either wild or mild choices.