350 build
September 6th, 2018, 09:28 AM
#1
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Join Date: May 2015
Location: Whittier California
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350 build
Hey all, I'm getting ready to rebuild my father's 1970 olds cutlass convertible (w25 option) can I get some recommendations on pistons and cam?
it's the original motor, and he wants to keep it looking that way if possible, but he would like a bigger cam and maybe some headwork, so stock iron intake, quadrajet, stock exhaust manifolds, stock exhaust, th350 with stock converter and stock rear gears, I'm guessing 2.73. Power brakes. He would also like it to run on 87 octane.
he had the thing rebuilt about 10 years ago and he has put maybe 10k miles on it, it has allot of blow by coming out the breathers, and after a compression test it has 1 cylinder at 50psi and all others 185-195psi. I believe when they rebuilt it they re-used the stock pistons and probly changed the rings. They also put in a (262 cam)not sure on the other specs.
he was always disappointed by the power it had but he did like that it ran on reg 87 gas.
any recommendations on a good cam and pistons?
it's the original motor, and he wants to keep it looking that way if possible, but he would like a bigger cam and maybe some headwork, so stock iron intake, quadrajet, stock exhaust manifolds, stock exhaust, th350 with stock converter and stock rear gears, I'm guessing 2.73. Power brakes. He would also like it to run on 87 octane.
he had the thing rebuilt about 10 years ago and he has put maybe 10k miles on it, it has allot of blow by coming out the breathers, and after a compression test it has 1 cylinder at 50psi and all others 185-195psi. I believe when they rebuilt it they re-used the stock pistons and probly changed the rings. They also put in a (262 cam)not sure on the other specs.
he was always disappointed by the power it had but he did like that it ran on reg 87 gas.
any recommendations on a good cam and pistons?
September 6th, 2018, 10:44 AM
#3
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Join Date: Feb 2013
Location: Phoenix, AZ
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Factory rear for a 1970 Cutlass would be an O-Type, and that rear doesn't have a 2.73 ratio. The standard no-cost gears were 2.56, but optional gears were available. You should probably verify what the rear gears are prior to deciding how to build the engine so that you get the compression and cam that will work well with the gearing.
Using factory high compression (10.25:1) pistons would make running 87 octane more challenging than something in the mid-9 range.
Using factory high compression (10.25:1) pistons would make running 87 octane more challenging than something in the mid-9 range.
September 6th, 2018, 11:02 AM
#4
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Location: Whittier California
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Factory rear for a 1970 Cutlass would be an O-Type, and that rear doesn't have a 2.73 ratio. The standard no-cost gears were 2.56, but optional gears were available. You should probably verify what the rear gears are prior to deciding how to build the engine so that you get the compression and cam that will work well with the gearing.
Using factory high compression (10.25:1) pistons would make running 87 octane more challenging than something in the mid-9 range.
Using factory high compression (10.25:1) pistons would make running 87 octane more challenging than something in the mid-9 range.
September 6th, 2018, 12:16 PM
#5
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Location: Ft. Wayne, IN
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2.78 was an available Type-O ratio. That's what mine had. There is a 2-character stamp on the axle tube that will tell you what is in it, or you could change the fluid and check the numbers on the gears directly (or estimate by jacking up the rear and rotating the driveshaft and counting revs of the tires or visa-versa).
September 6th, 2018, 12:23 PM
#6
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Location: Braceville, Ohio
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Even a 3:08 gear will wake it up a bit but still be able to cruise at 65/70mph no problem. Probably a stock rebuilt with a small RV cam would be the best without opening up a can of worms. Dual exhaust of course. Jmo
September 6th, 2018, 01:34 PM
#9
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September 6th, 2018, 06:03 PM
#13
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Location: Central Fl
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Abd don’t minimize the differences between the Speed Pro and Mahle pistons. They’re night and day.
September 6th, 2018, 06:12 PM
#14
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Location: Whittier California
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70 cutlass convertible
350 4v OEM ram air w25
2.56 gears, th350, stock stall
only real upgrade is the 2.5" exhaust system, but it's still 2" coming out of the manifolds.
I can port the heads of it's worth it.
Last edited by redbaron442455; September 6th, 2018 at 06:19 PM.
September 7th, 2018, 04:35 AM
#15
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Join Date: Dec 2006
Location: Melville, Saskatchewan
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The stock stall is a killer. I have a 9 to 1 350 with slightly better than stock heads, Cutlassefi''s mild 214/214 custom cam, stock stall TH350C, had the stock TH350, same result and 2.78 gears. It also has a RPM intake, headers and dual exhaust. I can barely spin tires off the line but picks up OK at speed. I had a 2004R trans my daughter ran low on fluid with 2300 stall converter. I could lay rubber for a 1/4 block. Needless to say a 2004R is going back in with the slightly better first gear and the same 2300 stall flash converter. It really made a big difference.
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