how rare is factory AC?

[Mike C]

There were no high performance high compression big blocks in the trucks. The only real difference between the 396 and 402 is a .030 overbore. And on the GMC trucks, they list the big block as "400" on the SPID. Same motor. The combination of pistons and combustion chamber dictate compression ratio. Closed chamber heads used different domes than the open chamber but the were all 8.5:1.

I just built a 390hp 427 for my '69. It's also a '69 from a 'vette. 512 2 bolt block and 290 101cc heads. Should be right at 10:1 with the SpeedPro pistons that are the stock replacement spec. I have a second 427 with the same pistons and a set of 781 heads that should put the motor at 9.3:1 because of the 118cc chambers of the later open chamber heads.

Originally Posted by 71CHEVYSHORTBED402

You know if that had the heads with larger ports? The heads are 10:1 compression, while the 402 is 8.5:1. At least those are the numbers I recall.

Those are in strict terms. For all I know some 402s had the larger heads & vise versa. That and I'm all ears if someone knows better. The guy who built my engine (1993) explained this, and sold me the heads off a 396. He said my heads had been gone through & were toast. I always questioned that. There was only 99K on the truck when it threw a bearing. Sure built a great engine though. Supposedly the best in the area, I can't argue that.

[s10mk]

It seems like most of the big block trucks discussed in this thread had automatic transmissions. Was that the preferred way to order a big block truck?

[cooperhw]

Originally Posted by Haru

Looks familiar

nice.

I am usually not much of an original guy, but when you find one like ours that's all there, well, that changes things. For me at least. Last thing on earth I want to do is cut this one up or rip out that big block.

[cooperhw]

Originally Posted by hdff

My '71's spid shows 396 which was a 402(gm was slow on changing spid language) 4 season ac and power steering on a short fleet. When I got it the ac needed some work but it's workin now!

Beautiful truck.

[71CHEVYSHORTBED402]

Originally Posted by Mike C

There were no high performance high compression big blocks in the trucks. The only real difference between the 396 and 402 is a .030 overbore. And on the GMC trucks, they list the big block as "400" on the SPID. Same motor. The combination of pistons and combustion chamber dictate compression ratio. Closed chamber heads used different domes than the open chamber but the were all 8.5:1.

I just built a 390hp 427 for my '69. It's also a '69 from a 'vette. 512 2 bolt block and 290 101cc heads. Should be right at 10:1 with the SpeedPro pistons that are the stock replacement spec. I have a second 427 with the same pistons and a set of 781 heads that should put the motor at 9.3:1 because of the 118cc chambers of the later open chamber heads.

If you're saying only GMC shows 400, I have two 402 Chevy that show 400 on the SPID. I know little about engines, but I understood heads do contribute to compression. That or perhaps they provision for more compression? Is it possible high performance heads came on a Chevelle and such?

On a side, that license plate number is a fluke. Considering they use letters as well, what you figure the odds? It's another reason I chose not to destruct the truck.

[71CHEVYSHORTBED402]

Originally Posted by s10mk

It seems like most of the big block trucks discussed in this thread had automatic transmissions. Was that the preferred way to order a big block truck?

I'd say so. Seems most 1 ton work trucks would be on a stick. An uneducated guess.

Originally Posted by cooperhw

nice.

I am usually not much of an original guy, but when you find one like ours that's all there, well, that changes things. For me at least. Last thing on earth I want to do is cut this one up or rip out that big block.

Original is my goal. During my tear down I've learned I bought an unmolested truck. That's until I and acquaintances put our hands on it. Only thing missing was the heat stove. I've had the truck a long while. One of the challenges was to ID the wire/hose clips. With board help and research I'm now comfortable with the layout. Turns out I saved all the clips less a few. But that's why I bought the 72 The build "half" on the 71 should be simple. Nice to know how these came off the line, and I'm nearly there. This message board made it possible.

[Mike C]

Just saying my experience with big block trucks are just GMC's. Not sure how Chevy did that.

The heads and the pistons together determine the compression ratio. And there was never a higher compression big block in a 67-72 chevy truck. At least from the factory.

70 was the first year of the open chamber head in production (69 ZL-1 had open chamber aluminum heads if memory serves) but only on some engines (hi perf 454 for sure) but I think it was 71 before the 402 Chevelle got the open chamber heads and I think the truck soldiered on with the closed chamber until the arrival of the 454 in 73. That was why gross power outputs were lower in '71 and then the net power measure in '72 really dropped the numbers.

Either way GM spec'ed it with no dome closed chamber or small dome open chamber, compression was 8.5:1 for truck 402's.

But in the 40+ year history, what's on the truck and what came on the truck but not be the same...

[dirt_dobber]

My 67 in high school had AC - and the 72 that I sold 14 years ago also had it - I miss both of them... getting the urge to get another one...

[71_402]

Sorry to butt in on conversation but was wondering if one might be able to say values on a big block AC truck? A few months ago I bought a 71 long Cheyenne, factory 402, turbo 400 trans, factory AC (everything is there, just not working at the moment). I bought it from a friend and really enjoy the truck, I am just curious as to what values a big block goes for as opposed to a small block? I don't see (in my area) a big difference in pricing

[RenoKeene]

All depends on total package, condition and personal preference.
The deference between long bed big and small blocks might not be much but the deference between short bed big and small blocks is about 150%
See attached..

[71_402]

Wow that is a beautiful truck! Mine isn't near that condition. Mine isn't restored, it's patina'd and mostly solid....rockers are shot, but other than that, in good shape. Definitely wouldn't bring the money yours would! I'd have a hard time parting ways with it so I guess value doesn't really matter, just something I was curious about. I've seen a few big block trucks in my area that have been LS swapped and it didn't make sense to me of why you'd want to do that to a rare packaged truck

[tristan]

Here's another 1971 BB with AC. It's a SWB Cheyenne too. It's currently in storage, but the original white/ochre/white/ochre paint schema will ride again some day after I finish my other project. One of the great rarities of the C/K-10/20 world.

[71_402]

I wish mine was a short bed, I really like the stance of those! That last one you posted looks great! Here are a couple photos of mine

[71_402]

Okay let me try this again....Im having a hard time posting pictures on my phone, so switched to work computer

https://www.flickr.com/photos/151065...posted-public/

https://www.flickr.com/photos/151065...posted-public/

https://www.flickr.com/photos/151065...posted-public/

https://www.flickr.com/photos/151065...posted-public/