350 300-350hp recipe ? - ClassicOldsmobile.com


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Old February 12th, 2018, 07:08 AM   #1
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350 300-350hp recipe ?

Starting the homework on what it will take to build a 350 olds to a streetable powerhouse.
is 350 asking to much, will it become a tempermental beast.
What is a fair number for a mild ,can live with it daily if needed power out of these.?
I'll be fine with an honest 300hp if it has a nice fat torque curve to it..
yes it be easy to just dump a 403 or a 455 in it , but I already have a 489 gas hog.
The 75 350 is listed at 8.5to 1 but knowing gm it really is lower than that.
What are the limits on the valve train /rocker set up?
Sorry used to chevy's..
plan on a hyd roller cam unless they are super big $$$, my bbc solid was over 1000.00 cam and lifters..


opinions welcome.
Ideally I'll find another 350 to build as I drive my car.. but assume for this that it was the engine and heads from a 75 cutlass.
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Old February 12th, 2018, 07:36 AM   #2
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My project 350 build should be done and dynoed in the next couple of weeks. Iron heads, flat tappet cam and the new Mahle piston yielding 9.4:1. Should be a pretty typical build.
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Old February 12th, 2018, 08:11 AM   #3
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Originally Posted by cutlassefi View Post
My project 350 build should be done and dynoed in the next couple of weeks. Iron heads, flat tappet cam and the new Mahle piston yielding 9.4:1. Should be a pretty typical build.
9.4 to 1 nice, my crate vortec 350 ramjet cam and 1.6 rockers, edel intake and headers made a solid 336.7hp.. I doubt I'll get out of it as cheap as I did there,3000.00 bucks - the carb
the pistons cast or hyper (still cast) or a forging

Last edited by midnightleadfoot; February 12th, 2018 at 08:14 AM.
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Old February 12th, 2018, 03:48 PM   #4
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Fyi

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Originally Posted by midnightleadfoot View Post
9.4 to 1 nice, my crate vortec 350 ramjet cam and 1.6 rockers, edel intake and headers made a solid 336.7hp.. I doubt I'll get out of it as cheap as I did there,3000.00 bucks - the carb
the pistons cast or hyper (still cast) or a forging
You'll need to budget double that for the same hp. Owning an Olds is not cheap.
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Old February 13th, 2018, 06:45 AM   #5
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Mahle's pistons are forged and Mark quoted 6K for the complete motor, so Dave is very accurate.
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Old February 13th, 2018, 08:10 AM   #6
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Originally Posted by olds 307 and 403 View Post
Mahle's pistons are forged and Mark quoted 6K for the complete motor, so Dave is very accurate.
IIRC (only glossed over that thread)
That engine is a flat tappet cam.. iirc.
I was thinking hyd roller.. but don't know olds, and what that require up at the valve, rockers, other than shorter push rods..
first olds. valve train look to be of a non-adjustable type stock.. but again. not sure still learning the olds engine . no idea if that has to be all changed to go roller? or what is the limit with a flat tappet with it's set up..
Totally green here and need as much knowledge before I start this project.
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Old February 13th, 2018, 08:46 AM   #7
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Keep reading up. There's also a good build index over at realoldspower.com.
Olds parts tend to cost more - not as many suppliers, not as much demand.

In the end it's a GM engine, so there's nothing crazy going on.

Roller cam adds ~$600 to the build cost. Check head to pushrod clearance closely. I goofed on that and have a nice noisy self-clearancing setup at the moment....

Intake to head seal is a PITA, especially since Edelbrock apparently doesn't verify anything anymore. Expect to cut the intake, use fiber gaskets, check carefully. But everyone has an opinion on this.

Valvetrain is fixed, so picking your fix for that is a big step. Comp has roller-tip stud mount rockers. The rockers and hardware are good - but get poly locks and throw away the pushrods that come with the kit. Or get the Harland Sharp 5016's. Ignore HS's application list - use the 5016 for any Olds engine.

Cam guidance is similar to a Chevy engine, except the typical Olds exhaust port is pretty bad, so most Olds builds have more duration on the exhaust that a non-Olds build.

The stock heads can be reworked to be OK with some basic porting. Nothing surprising there. You can run the Edelbrock heads on the 350 (they bolt right on!), but getting the compression ratio back to a decent place is a lot of work.

The block will almost certainly need to be decked. Most aftermarket pistons are shorter than stock, and common aftermarket head gaskets are more than twice as thick as stock.

Lower end part selection on the 350 is pretty limited. I'd take a long look at the stuff Mark (cutlassefi) is helping to bring to the market.

Use the 350 diesel oil pan gasket (felpro OS30471C) - it's cork with metal core. Also use a Ford real seal instead of the stock rope - I use Felpro BS6141. There's not much point buying the name brand engine rebuild gasket kits because half of it is junk. The olds vendors can put together a kit for you.

Assembly is mostly normal except for a few key things:
Check crank thrust carefully. Thrust is on #3, sometimes that cap isn't happy.
The oil galley plugs are unusual. The front right has a squirter for the timing chain. The rear left has a squirter for the distributor. The plug kits do not have holes, and the kits do not include the front plugs. The plug kits will have some extra unused plugs also, so don't be alarmed.
There's a "slinger" that goes on the crank snout just inside the timing cover. It's actually a cover to limit how much oil hits the front seal. Not catastrophic if you forget it, but it's a good idea to put it in there.
The cam needs the fuel pump eccentric regardless of whether or not you're using a mechanical pump. It keeps the cam pin in place.
Bearing notches in the rods point towards the cam - not the oil pan rail.


Olds engines are torque happy, but run out of air pretty quick due to the head layout. So focus on low RPM torque and make use of that in the drivetrain rather than 6500+ rpm HP. A 227/233 (with good exhaust) or 227/237 (with stock-ish exhaust) duration @ 0.050 is a good place to start looking. Will idle decently around 700 to 800, vacuum will be a little low for power brakes but not crazy.
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Old February 13th, 2018, 09:00 AM   #8
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Originally Posted by oddball View Post
Keep reading up. There's also a good build index over at realoldspower.com.
Olds parts tend to cost more - not as many suppliers, not as much demand.

In the end it's a GM engine, so there's nothing crazy going on.

Roller cam adds ~$600 to the build cost. Check head to pushrod clearance closely. I goofed on that and have a nice noisy self-clearancing setup at the moment....

Intake to head seal is a PITA, especially since Edelbrock apparently doesn't verify anything anymore. Expect to cut the intake, use fiber gaskets, check carefully. But everyone has an opinion on this.

Valvetrain is fixed, so picking your fix for that is a big step. Comp has roller-tip stud mount rockers. The rockers and hardware are good - but get poly locks and throw away the pushrods that come with the kit. Or get the Harland Sharp 5016's. Ignore HS's application list - use the 5016 for any Olds engine.

Cam guidance is similar to a Chevy engine, except the typical Olds exhaust port is pretty bad, so most Olds builds have more duration on the exhaust that a non-Olds build.

The stock heads can be reworked to be OK with some basic porting. Nothing surprising there. You can run the Edelbrock heads on the 350 (they bolt right on!), but getting the compression ratio back to a decent place is a lot of work.

The block will almost certainly need to be decked. Most aftermarket pistons are shorter than stock, and common aftermarket head gaskets are more than twice as thick as stock.

Lower end part selection on the 350 is pretty limited. I'd take a long look at the stuff Mark (cutlassefi) is helping to bring to the market.

Use the 350 diesel oil pan gasket (felpro OS30471C) - it's cork with metal core. Also use a Ford real seal instead of the stock rope - I use Felpro BS6141. There's not much point buying the name brand engine rebuild gasket kits because half of it is junk. The olds vendors can put together a kit for you.

Assembly is mostly normal except for a few key things:
Check crank thrust carefully. Thrust is on #3, sometimes that cap isn't happy.
The oil galley plugs are unusual. The front right has a squirter for the timing chain. The rear left has a squirter for the distributor. The plug kits do not have holes, and the kits do not include the front plugs. The plug kits will have some extra unused plugs also, so don't be alarmed.
There's a "slinger" that goes on the crank snout just inside the timing cover. It's actually a cover to limit how much oil hits the front seal. Not catastrophic if you forget it, but it's a good idea to put it in there.
The cam needs the fuel pump eccentric regardless of whether or not you're using a mechanical pump. It keeps the cam pin in place.
Bearing notches in the rods point towards the cam - not the oil pan rail.


Olds engines are torque happy, but run out of air pretty quick due to the head layout. So focus on low RPM torque and make use of that in the drivetrain rather than 6500+ rpm HP. A 227/233 (with good exhaust) or 227/237 (with stock-ish exhaust) duration @ 0.050 is a good place to start looking. Will idle decently around 700 to 800, vacuum will be a little low for power brakes but not crazy.
Thanks.. Yes rather a torque happy over spin it hp engine..
I normally tap oil galleries for screw in plugs, but good to know about the plugs lack of holes..
Not a fan of roller tip only rockers, good to know about pushrod to head clearance, but I normally check this, had to open up my vortec heads because of that.


I always wondered if the olds 260 diesel block was as beefed as the 350 one.. The devil inside of me, thinks a gas 260 with a turbo and 307 heads might be a fun ride, and good on gas..
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Old February 13th, 2018, 12:08 PM   #9
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Good info, but a couple of corrections.
The HS 5016 is better suited to the Edelbrock style heads. Stock heads are better suited to the 5003.
To run any of the aftermarket aluminum heads on a 350 simply just entails cutting the heads to the desired cc. They have plenty of meat in that area.
All oil galleys are already tapped, just have to install the right plug in the right hole. However you will have to use an electric fuel pump��.
Olds engines are “torquey” only because of smallish ports, which is also the reason why they don’t make the power or turn the rpm of other similar size engines in stock form.
The new Mahle piston I brought to market is about .015 taller than most other aftermarket pistons. That makes it more compatible to stock replacement head gaskets. I did that on purpose.

Last edited by cutlassefi; February 13th, 2018 at 12:13 PM.
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Old February 13th, 2018, 12:33 PM   #10
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The devil inside of me, thinks a gas 260 with a turbo and 307 heads might be a fun ride, and good on gas..
307 heads are pitiful for breathing.
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Old February 13th, 2018, 05:24 PM   #11
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307 heads are pitiful for breathing.
Not only that, good luck in finding a 260 diesel block, most seem to be replaced with a 350 diesel under warranty. But there is the 75-76 solid main gas 260 out there. Also many shops have installed the center exhaust guides too tight and valves have stuck and caused damage. I believe the spec is .0028" needed for the center exhaust valves due to the large center exhaust crossover ports.
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Old February 13th, 2018, 05:34 PM   #12
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Originally Posted by cutlassefi View Post
Good info, but a couple of corrections.
The HS 5016 is better suited to the Edelbrock style heads. Stock heads are better suited to the 5003.
To run any of the aftermarket aluminum heads on a 350 simply just entails cutting the heads to the desired cc. They have plenty of meat in that area.
All oil galleys are already tapped, just have to install the right plug in the right hole. However you will have to use an electric fuel pump��.
Olds engines are “torquey” only because of smallish ports, which is also the reason why they don’t make the power or turn the rpm of other similar size engines in stock form.
The new Mahle piston I brought to market is about .015 taller than most other aftermarket pistons. That makes it more compatible to stock replacement head gaskets. I did that on purpose.
Also the long and fairly small intake runners and the flat 6 degree valve angle also contribute to that strong torque curve. I also find a lot of part throttle timing, easy on the factory 70's and 80's low compression stuff, improves seat of the pants acceleration.
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Old February 13th, 2018, 06:31 PM   #13
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my engine makes about 370 hp and I spent 3500 carb to oil pan. I used., used stuff ( good shape ) . Car runs low 12's. Its on the lighter side of things about 3300 with me in it.
Its sweet simple and there are some many used sbo parts out there it can be done. I might add is still a heavily street driven car. Its driven to the track and back and used to get groceries and everything in between. I've hauled lumber in it.

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Old February 13th, 2018, 07:56 PM   #14
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my engine makes about 370 hp and I spent 3500 carb to oil pan. I used., used stuff ( good shape ) . Car runs low 12's. Its on the lighter side of things about 3300 with me in it.
Its sweet simple and there are some many used sbo parts out there it can be done. I might add is still a heavily street driven car. Its driven to the track and back and used to get groceries and everything in between. I've hauled lumber in it.

https://classicoldsmobile.com/forums...-i-do-now.html


Ya, I'm sure it can be done for less. that 6k just nice to know what you are in for If you needed a bunch of stuff.
I'd assume most 350 heads you are doing guides. and if using the earlier heads exhaust seats.
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Old February 13th, 2018, 07:57 PM   #15
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307 heads are pitiful for breathing.
Well.ok see I'm green on the olds, haha. so 350 heads lol
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Old February 13th, 2018, 08:00 PM   #16
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Originally Posted by olds 307 and 403 View Post
Not only that, good luck in finding a 260 diesel block, most seem to be replaced with a 350 diesel under warranty. But there is the 75-76 solid main gas 260 out there. Also many shops have installed the center exhaust guides too tight and valves have stuck and caused damage. I believe the spec is .0028" needed for the center exhaust valves due to the large center exhaust crossover ports.


On junkyard crawls I've seen 2, and when I say seen, I'm going by the emissions decal under hood.. I couldn't tell if it was a 260 or a 350. This was when I was hunting for a hydra boost unit for my SS.
Just thought it be an odd build that be super cheap.. lol.
I sometimes have twisted ideas..
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Old February 13th, 2018, 08:23 PM   #17
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On the 350 heads pretty much treat anything used unless proven as a core. Yeah guides will be needed more than not. My heads just have 2.07 in. and 1.63 ex. with the bowls opened up. No other common mods like heat riser filled and the divider welded.

But I would agree 6k would be a pretty complete build from a builder.
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Old February 13th, 2018, 08:46 PM   #18
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Mild cams, cast low compression pistons, and the stock heads and intake and headers, with the quadrajet are not temperamental, and can be a good 13 second street terror. Did it almost 50 years ago. Stock BBO heads and aluminum intake, and more cam plus a Holley 500 two barrel went 12s in an Omega, and all this at almost 4000 feet.
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Old February 14th, 2018, 06:51 PM   #19
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Ya, I'm sure it can be done for less. that 6k just nice to know what you are in for If you needed a bunch of stuff.
I'd assume most 350 heads you are doing guides. and if using the earlier heads exhaust seats.
Oldsmobile heads aren't mush like the chebbie heads, no hardened seats required.
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Old February 15th, 2018, 01:45 PM   #20
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Oldsmobile heads aren't mush like the chebbie heads, no hardened seats required.
ok, why? hardened from factory?? back before unleaded gas?
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Old February 15th, 2018, 01:49 PM   #21
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ok, why? hardened from factory?? back before unleaded gas?
My 455 from around 1970 never had a problem............so something is different
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Old February 15th, 2018, 05:05 PM   #22
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ok, why? hardened from factory?? back before unleaded gas?
71 and up were induction hardened but basically is gone after the first valve job. I think Chebbie thought any sort of hardening wasn't necessary, think all their flat cams in the 70's. I think the cast iron is just a better hardness, it just isn't an issue even on the 60's heads.
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