Big block 400

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snookstalker
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Big block 400

Post by snookstalker » Wed Nov 23, 2016 12:49 pm

My dad has a big block 400 out of a '72 Pontiac Grand Prix that's been on a stand in his garage for probably 20 years. Ran perfect when it came out of the car. Curious what yall's opinion of this motor is and if it would make a good airboat engine. Seen some good boats with the small block 400, but don't know much about the big block.
Thanks for any input!
Dan

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scottyroll
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Re: Big block 400

Post by scottyroll » Wed Nov 23, 2016 1:14 pm

I've never heard of a big block 400, maybe it's a 396 big block?

If it is a 396, it's definitely not a desired airboat engine.
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glades cat
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Re: Big block 400

Post by glades cat » Wed Nov 23, 2016 2:45 pm

Cool. A different power plant.
As always, measure the crank end play. .003-.009
I would run conservative RPMs and use an oil cocktail with high zddp. The Branch mix of Rotella T 15w-40, Comp Cams additive and Lucas oil stabilizer. It will help the thrust bearing issues if running direct drive.
Seen all kinds of car engines used. You can put a prop on most any engine...where there's a will, there's a way. Get a decent hull that will float the payload safely, put a composite prop that you can adjust and rig it up direct. For more push...and with additional funds, you can also run it through a gear box and rig accordingly.
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snookstalker
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Re: Big block 400

Post by snookstalker » Wed Nov 23, 2016 4:17 pm

If I was to utilize this engine, it would not be direct drive as it would be to replace my current direct drive 500 Caddy on a 14' Combee. Just not sure if it would be worth the effort. The old Caddy does pretty good (well, it will again once I replace/repair the crank!)

Edit
For 1967, Pontiac introduced the 400 cu in (6,555 cc).

The '400' V8 was essentially a bored-out (+.060) 389 with 4.120-inch (104.6 mm) bore and 3.75-inch (95 mm) stroke 400.4 cu in (6,561 cc). It replaced the 389 in 1967 and remained in production through the 1978 model year. The 1979 cars with a 400 had an engine produced in 1978.

The 400 was a popular performance option for many of Pontiac's cars. The 400 produces a good balance of low-end torque and higher-RPM power when used with a four-barrel carburetor or other high-airflow components.

In 1967, the cylinder head design was improved for all engines. The valve angle was reduced from 20 degrees to 14 degrees for better breathing. 1967 was the last year for closed-chambered heads. The "670" head was a 1967-only casting, and the last PMD head to have a closed chamber. Pontiac went to open-chambered heads in 1967 to improve power, engine breathing and reduce emissions. The valve size increased as well, to 2.11" intake and 1.77" exhaust valves on high-performance heads. Low-performance and two-barrel applications got 1.96" intake and 1.66" exhaust valves and pressed in rocker arm studs.

SWAMPHUNTER45
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Re: Big block 400

Post by SWAMPHUNTER45 » Wed Nov 23, 2016 7:29 pm

Time to fix that Cadillac !

snookstalker
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Re: Big block 400

Post by snookstalker » Wed Nov 23, 2016 9:19 pm

Yea yea...I know Eric! Starting to get into my busy season at work, so I'll have some $$ to work with. :angel4:

Olf Art
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Re: Big block 400

Post by Olf Art » Wed Nov 23, 2016 10:47 pm

Love me some GM 400 small blocks ..... I'd love to find a cache of some somewhere in a warehouse, still in the crate. As a DD motor on a light 13' boat one of them would be killer.
I'd throw some roller rocker arms and an MSD ignition at it and run it till it dropped.
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Deano
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Re: Big block 400

Post by Deano » Thu Nov 24, 2016 2:48 pm

snookstalker wrote:I have a very heavy 4 seat 14' Combee DD 500 . . . . Will go most anywear with just me on it, but have to be careful of sticky grass and black mud if loaded up. I love it. Criuses very nice and can haul a ridiculus amount of camping gear.
If your intent is to stay DD, that 400 won't have a chance acting like a healthy 500.
Given a gearbox to go with it; that would most likely be an improvement.
Just as easy to change the stand for a box as a different DD.
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Re: Big block 400

Post by SWAMPHUNTER45 » Thu Nov 24, 2016 3:49 pm

I know that it's been a bummer waiting Snook, but if nothing else see if Steve will rework the crank for you. Some guy on here who was eating up a few thrusts said he had one fixed for $125 recently, but I don't know exactly what your plans are with the old engine. If you need info PM or text.

The 542 is a beast, you really should try to get up on a day during the week and take a ride before I put the 520 on it and start that engines break in process. Maybe Blu or I could talk Mr Branch into coming along that day too. I think he raced Oldsmobile and Pontiac back in the day. That 542 idles like a direct drive but stand on the gas and it comes alive. Had a guy up in Cedar Key grab us at the ramp. He said I don't have a clue what that engine is on your boat but it roars...lol

Ironically it sounds a lot like an old Pontiac to me.

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Re: Big block 400

Post by Olf Art » Thu Nov 24, 2016 10:46 pm

Deano wrote:If your intent is to stay DD, that 400 won't have a chance acting like a healthy 500.
It will if the boat is light, and it'll burn a lot less gas.
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Deano
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Re: Big block 400

Post by Deano » Fri Nov 25, 2016 2:05 pm

Well in this case, the fact of the matter is that it is not a light boat.
His own assessment was that, "I have a very heavy 4 seat 14' Combee . . ".

Olf, I have a great deal of respect for you and your opinions. Still, mine are different on those two points.
The prevailing presumption that a 500 Cadillac can't be fuel efficient is largely a myth. And after having a Gran Prix with that 400 in it as a kid, I seriously doubt that it would be any better when toting the same load. It was thirsty; although I will readily admit I did not spend the same amount of time and/or effort toward that end.

I agree with Glades Cat in that any different engine on an airboat is extra cool. :thumbleft: Hell, if a 460 Ford wasn't such a heavy pig and was as light and torquey as a Cadillac I would run one. Sadly that ain't the case.
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Olf Art
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Re: Big block 400

Post by Olf Art » Fri Nov 25, 2016 3:47 pm

Deano wrote:Well in this case, the fact of the matter is that it is not a light boat.
His own assessment was that, "I have a very heavy 4 seat 14' Combee . . ".

Olf, I have a great deal of respect for you and your opinions. Still, mine are different on those two points.
The prevailing presumption that a 500 Cadillac can't be fuel efficient is largely a myth. And after having a Gran Prix with that 400 in it as a kid, I seriously doubt that it would be any better when toting the same load. It was thirsty; although I will readily admit I did not spend the same amount of time and/or effort toward that end.

I agree with Glades Cat in that any different engine on an airboat is extra cool. :thumbleft: Hell, if a 460 Ford wasn't such a heavy pig and was as light and torquey as a Cadillac I would run one. Sadly that ain't the case.
Your points are well taken ..... we never argue. We just discuss. :thumbleft:
I always thought it would be fun to build a little two seat rig using a flat 6 Porsche engine. Different is always cool.
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