350 to 400 swap... Worth it?

[Sam71395]

hello all, Sorry this is not square body related, this is pertaining to my 69 chevelle, and it has a mild built 350 in it, i just acquired a mildly built 400 small block, both are good engines. I'm just wondering if the extra 50 cubes is it worth the swap. I guess I'm just a little afraid to pull the engine on a car that was recently painted, but if its really worth the swap i will, and really be careful. thanks in advance

 

[GTX63]

Is it worth it? That depends on what it is that you want.
Are you trying to shave a few tenths off a quarter mile time or?
There was a point in my life where I was trying to claw every 5 HP out of a SBC I could find. Now, I build my motors with dependability and longevity in mind. Most are mild street builds that are strong enough to get out of everyone's way in traffic and back up that lumpy lope at idle.
400 Chevy motors, in my own experience dating back to when they were still making them, tend to run a little hotter because of the thinner webbing.
I guess you need to fill us in and what you are looking for?

 

[Ricko1966]

@GTX63 is right on,depends on what you're trying to achieve,if the goal is to go faster and be reliable,sell both engines and swap in a mild 454.

 

[Rickf]

There is no substitute for cubic inches.

 

[Sam71395]

Is it worth it? That depends on what it is that you want.
Are you trying to shave a few tenths off a quarter mile time or?
There was a point in my life where I was trying to claw every 5 HP out of a SBC I could find. Now, I build my motors with dependability and longevity in mind. Most are mild street builds that are strong enough to get out of everyone's way in traffic and back up that lumpy lope at idle.
400 Chevy motors, in my own experience dating back to when they were still making them, tend to run a little hotter because of the thinner webbing.
I guess you need to fill us in and what you are looking for?

I have heard that about 400s running hotter, the one i have has aluminum heads and i have an aluminum radiator, so cooling shouldn't be an issue. I guess what I'm looking for is a relatively fast street car that is reliable. I have heard some people say that the hp/tq potential from the 350s doesn't come close to the 400s potential, i'm wondering if that is true or just hype.

 

[Ricko1966]

I have heard that about 400s running hotter, the one i have has aluminum heads and i have an aluminum radiator, so cooling shouldn't be an issue. I guess what I'm looking for is a relatively fast street car that is reliable. I have heard some people say that the hp/tq potential from the 350s doesn't come close to the 400s potential, i'm wondering if that is true or just hype.

It's a math problem 1hp per cubic inch,not an unreasonable figure 1hp per cubic inch out of a 350 would be 350 hp a 400 would be 400hp a 50 hp gain a 454 would be a 154hp gain,one more thing you wouldnt have to breathe as hard on a 454 so best of both worlds. Power and reliability. I know people are going to say you can build a little motor to be faster than a bigger motor. Not really true an equally built 350 will not beat an equally built 400. That's why people build 383s cheap horsepower. Personally I've built a 355 that beat a 383 pretty good the man was very surprised. But the Motors weren't equal,I was zero decked, I had good heads a bunch wrapped up in my valve train. If my 355 had been built like his 383,no doubt he'd have taken me. The fact that your 400 has aluminum heads would lead me to believe it's got good heads on it. What heads are on each engine? Is either engine zero decked?

 

[GTX63]

I have heard that about 400s running hotter, the one i have has aluminum heads and i have an aluminum radiator, so cooling shouldn't be an issue. I guess what I'm looking for is a relatively fast street car that is reliable. I have heard some people say that the hp/tq potential from the 350s doesn't come close to the 400s potential, i'm wondering if that is true or just hype.

Both engines being equal, it isn't a night and day difference. More like 10 am to 2 pm. The 400 is a good motor, maybe not quite as durable or forgiving due to the thinner block material. The 400 is also externally balanced, so flexplates/flywheels/balancers do not interchange.
Again, if you are trying to max out the potential, a 400 might suit you; if you are just looking for a stronger boost to what you got, you can do that to your 350 without pulling the motor.

 

[Sam71395]

It's a math problem 1hp per cubic inch,not an unreasonable figure 1hp per cubic inch out of a 350 would be 350 hp a 400 would be 400hp a 50 hp gain a 454 would be a 154hp gain,one more thing you wouldnt have to breathe as hard on a 454 so best of both worlds. Power and reliability. I know people are going to say you can build a little motor to be faster than a bigger motor. Not really true an equally built 350 will not beat an equally built 400. That's why people build 383s cheap horsepower. Personally I've built a 355 that beat a 383 pretty good the man was very surprised. But the Motors weren't equal,I was zero decked, I had good heads a bunch wrapped up in my valve train. If my 355 had been built like his 383,no doubt he'd have taken me. The fact that your 400 has aluminum heads would lead me to believe it's got good heads on it. What heads are on each engine? Is either engine zero decked?

https://promaxxperformance.com/product/project-x-215-sbc-sold-in-pairs-copy/ heres a link to the heads on the 400, the cam in it is lunati's version of a 268 cam, It has not been zero decked, it has stock crank and pistons also. the 350 was rebuilt prior to me owning the car, it has stock heads and I believe the cam grind number is 262H from comp cams

 

[Ricko1966]

That 400 will wail on that 350,and maybe still some easy horsepower to be had. Depending on deck height head,gasket thickness and chamber volume. Just doing some quick math in my head, my guess is the 400 has at least 20 percent more hp. Good heads make or break an engine. The 400 already has displacement on its side, aluminum heads you can run more compression,and your 400 already has more cam.

 

[Sam71395]

That 400 will wail on that 350,and maybe still some easy horsepower to be had. Depending on deck height head,gasket thickness and chamber volume. Just doing some quick math in my head, my guess is the 400 has at least 20 percent more hp. Good heads make or break an engine. The 400 already has displacement on its side, aluminum heads you can run more compression,and your 400 already has more cam.

that is what i was thinking, the physics of making power are on my side, I guess the main thing for me is getting over the fear of pulling the motor on when it has been recently painted. I have pulled engines before no problem but never on somthing this nice

 

[mrdap]

It's a math problem 1hp per cubic inch,not an unreasonable figure 1hp per cubic inch out of a 350 would be 350 hp a 400 would be 400hp a 50 hp gain a 454 would be a 154hp gain,one more thing you wouldnt have to breathe as hard on a 454 so best of both worlds. Power and reliability. I know people are going to say you can build a little motor to be faster than a bigger motor. Not really true an equally built 350 will not beat an equally built 400. That's why people build 383s cheap horsepower. Personally I've built a 355 that beat a 383 pretty good the man was very surprised. But the Motors weren't equal,I was zero decked, I had good heads a bunch wrapped up in my valve train. If my 355 had been built like his 383,no doubt he'd have taken me. The fact that your 400 has aluminum heads would lead me to believe it's got good heads on it. What heads are on each engine? Is either engine zero decked?

No offense but you have a little math problem there.
Based on your theory, a 454 will be 104 horsepower increase over a 350, not 154 horsepower increase. And it's about 200 lb heavier, in stock form.

 

[MikeB]

What kind of heads does the 400 have? None of them from the factory had decent heads, with the possible exception of the 4bbl version used in the Monte Carlo for a short time.

You have to look at more that cubic inches to determine how an engine will perform. Performance-wise, a 350 with good heads will outperform a 400 with crappy heads every time. However, the 400 will make more torque at a lower RPM than a 350. That's why they were used in station wagons and trucks with high GVWR, but not in Camaros, Corvettes, Chevelles, etc. I don't think GM ever thought of the 400 as a platform for a high performance engine. Heck, I think a stock one made 400 lb/ft torque torque at around 2000 RPM, and probably stopped reving at 4000 RPM, if that high.

 

[Ricko1966]

No offense but you have a little math problem there.
Based on your theory, a 454 will be 104 horsepower increase over a 350, not 154 horsepower increase. And it's about 200 lb heavier, in stock form.

You are right I made a mistake in my math,sorry,let's do some more math. Yes the 454 is heavier let's use a 5000 pound vehicle as an example. A 5000 pound vehicle with 350 hp and 450lbs torque. A 200 pound heavier vehicle 5200 lbs with 454 hp and 550lbs torgue all else equal the 454 is going to out run and out pull the 350. That's why GM built Big Block Chevelles etc and big block trucks. The 200 lb penalty doesn't off set the difference in power.Im not meaning to create problems,but look at this real hard. People build 383s everyday. Why? They have a 350 block and can buy a crank. The added displacement makes more power.

 

[Donald]

I will make this short Yes, it is worth it, all the story's about 4oo's overhearing I have never had one overheat as long as you have a decent cooling system not a worn out clogged up mess. In fact, I have one sitting in my garage waiting for something to put it in.

 

[Sam71395]

What kind of heads does the 400 have? None of them from the factory had decent heads, with the possible exception of the 4bbl version used in the Monte Carlo for a short time.

You have to look at more that cubic inches to determine how an engine will perform. Performance-wise, a 350 with good heads will outperform a 400 with crappy heads every time. However, the 400 will make more torque at a lower RPM than a 350. That's why they were used in station wagons and trucks with high GVWR, but not in Camaros, Corvettes, Chevelles, etc. I don't think GM ever thought of the 400 as a platform for a high performance engine. Heck, I think a stock one made 400 lb/ft torque torque at around 2000 RPM, and probably stopped reving at 4000 RPM, if that high.

there's a link to the heads i'm using earlier in the thread, There 64cc aluminum heads with 215cc intake runners, with the stock pistons, the compression I was told should be in the mid nines.