What to do with a 75 400 SB? - Team Camaro Tech
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post #1 of 16 (permalink) Old Apr 12th, 15, 05:52 AM Thread Starter
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What to do with a 75 400 SB?

So a buddy of mine picked up a (well rusty) late 70s monte to strip parts off of. There was what looked like the original 350 engine still there, car had 85K miles. Engine ran fine, no smoking, so a took it for my 51 truck project. Now I had always planned to make a 383 out of a 350 for the truck. Looking at the engine closer and decoding the numbers it is a 1975 Chevelle 400 SB (175 hp ). So I had always heard 400s had cracking problems.

I want to pull a small trailer with the 51, so I need the torque. Should I keep the 400? Or stick with the 383 plan (I have a 2 bolt 350 block as well).

I am not that knowledgeable on 400s, so what will wake it up from the 175 hp? I always planned to go with a squarebore EFI on the engine. What else to do?

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post #2 of 16 (permalink) Old Apr 12th, 15, 05:57 AM
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Re: What to do with a 75 400 SB?

Simply put, I would go ahead with the 383 plans. That 400 rated at 175hp (smog) would not be worth a rebuild IMHO. Just my .02

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post #3 of 16 (permalink) Old Apr 12th, 15, 06:50 AM
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Re: What to do with a 75 400 SB?

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Originally Posted by KevinW View Post
I want to pull a small trailer with the 51, so I need the torque. Should I keep the 400? Or stick with the 383 plan (I have a 2 bolt 350 block as well).
A 383 is just a small bore 400. I've run several 400's with no problems at all, and if you want torque the 400 is the way to go. The horsepower rating from the factory has nothing to do with anything here if you are going to put the same dollars into the 400 that you would into the 383.

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post #4 of 16 (permalink) Old Apr 12th, 15, 07:03 AM Thread Starter
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Re: What to do with a 75 400 SB?

Doing a little reading and the stock torque is 305, not too shabby I don't want to touch the internals yet (need $$ for the trans). So the EFI, headers and some electronic ignition should give me a few more ft/lbs. I am not a high reving kinda guy, going with a 5 speed and a 3.73 rear gear (I think) should help some. Just need to find a 400 flywheel cheap , has a flex plate on there now.

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post #5 of 16 (permalink) Old Apr 12th, 15, 07:23 AM
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Re: What to do with a 75 400 SB?

Good decision to keep. If it ain't broke, don't fix it.
It will serve you well, keep it cool and it will work.

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post #6 of 16 (permalink) Old Apr 12th, 15, 07:32 AM
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Re: What to do with a 75 400 SB?

Sometime in the 70's they went from gross HP rating to net HP, which I assume to be flywheel vs rear wheel hp - your 400 is likely a bit more powerful than 175 hp based on the earlier method


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post #7 of 16 (permalink) Old Apr 12th, 15, 07:35 AM
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Re: What to do with a 75 400 SB?

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Sometime in the 70's they went from gross HP rating to net HP, which I assume to be flywheel vs rear wheel hp - your 400 is likely a bit more powerful than 175 hp based on the earlier method
265 Gross.

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post #8 of 16 (permalink) Old Apr 12th, 15, 07:42 AM
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Re: What to do with a 75 400 SB?

The majority of the 400 blocks were built during the smog era and were never meant for very high horsepower output or high rpm usage, so a lot of the production blocks are not very good castings. Can you build them, sure..... If completely rebuilding a 400 compared to a 383, I'm going the 383 route. It probably would be cheaper too.

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post #9 of 16 (permalink) Old Apr 12th, 15, 07:43 AM Thread Starter
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Re: What to do with a 75 400 SB?

265hp/305tq sounds like I can live with the 400 Keeping it cool will be a bit of a challenge though. AD trucks have small radiator space and if you go thicker it reduces the space between the rad and front of water pump (on v8 conversions). I will have to measure very carefully and make sure I can get an electric fan in the gap.

thanks!

Donny, I never planned on rebuilding this engine, since it was a good running one, I was just going to clean it up and run it. Then build the 383 in the future. But now with the 400, I may keep it in there longer and do some test towing. If it does not hold up, I can always go back to the 383 plan.

I still have a way to go to fix the rust on the 51 and get it back together


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post #10 of 16 (permalink) Old Apr 12th, 15, 07:56 AM
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Re: What to do with a 75 400 SB?

Makes perfect sense now Kevin. Keep the 400.

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post #11 of 16 (permalink) Old Apr 12th, 15, 08:20 AM
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Re: What to do with a 75 400 SB?

Had a 400 (4 bolt) in my 74 Blazer...ran good (stock with a cam)
Went to a 406 (2 bolt) with a 230/230 Comp cam and stock heads...much better.
Added a better set of heads....nice
Added a bigger cam...nicer
Installed in the Camaro...low 13's
Bigger cam, little head work, mid-low 12's
More cam, better heads, and mid-low 11's
That motor (406) used a Eagle crank, stock 350 rods, and 377 pistons. Turned 7500 rpm at the track, had around 100 passes, and still ran great....now in a buddies car still runs great. low 11's
Don't let the rumors scare you...400's are great motors when done right.
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post #12 of 16 (permalink) Old Apr 12th, 15, 09:33 AM
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Re: What to do with a 75 400 SB?

No replacement for displace ment...I had a solid roller 383 that was awesome in My Camaro...made lots of power and torque...

Went to a 400 build, and this thing not only has more street manner, but is far better than the 383...

nothing against a 383, but I definitely prefer the 400...

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post #13 of 16 (permalink) Old Apr 12th, 15, 09:34 AM
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Smile Re: What to do with a 75 400 SB?

400's were choked by smog emissions terribly in the 1970's. A different set of heads, and it should be a night vs day difference.

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post #14 of 16 (permalink) Old Apr 12th, 15, 09:40 AM
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Re: What to do with a 75 400 SB?

I ended up with a similar story. Bought a 350 car and it turned out to be a SBC 400.

Did a little research and found a lot of guys make big reliable power with the 400s.

Did a 406 added Alum heads and it turned out great. Better then 383s for sure

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post #15 of 16 (permalink) Old Apr 12th, 15, 11:38 AM
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Re: What to do with a 75 400 SB?

You would be surprised how many 400s were bored to 406 and ran on dirt tracks. Those old "truck motors" won more than a few races.

Since you are keeping the engine as is for now, just don't have extremely high expectations at this point. With the right upgrades, they make excellent power, as already stated.

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