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History question about 307

3558 Views 10 Replies 5 Participants Last post by  ReagansRollsRoyce
GM used Olds 307s on a lot of its cars in the 80s, except Chevies (and Pontiac Parisienne, too, no?) that had the Chevy 305.

We all have pros and cons about the 307.

Does anyone here know why GM chose to use the 307s rather than just run all the cars on peppier Chevy 305s?

Was it a cost issue, a quality issue, did 307s get better mileage, or what?
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As far as I know, Pontiac went with the 305 because of the death of the Pontiac V8 in 1981 and the close similarities between Pontiac and Chevy. Had a 305 in my '85 Parisienne, great engine! I know the Olds V8s survived long enough into the 80's and stuck with Buick and Olds, why Cadillac ever ended up with the 307 is beyond me.
I always refer to the 307 as the "Y" motor since that was it's VIN designation in the 80's.
The only real drawback is the 1/4 mile of vacuum hoses that go to everything.... that and the carbuerator!
They were solid engines though. I saw one come in with a piston broken off and stuck in the top of the bore with the rod flopping around in the cylinder. It was still running like a new one!

Chevy made a 307 for a few years in the early 70's but they were junk.
That's why they quit making them.
No, don't get me wrong, I love the 307. I don't drive particularly fast anywhere so I find it perfectly adequate for my needs. I also think its smooth and very quiet.

I was just wondering why GM chose to have two different V8s on its RWD sedans in the 80s considering that a lot of the aspects of the cars were pretty similar. Since it was the post horsepower era I was just surprised that GM didnt cut costs by going with 305s or 307s in all of the cars rather than mixing it up throughout the RWD model lines.
GM divisions used to be far separated for years.
During the late 70's they started swapping powertrains between makes and models. There used to be a time where you knew an Olds engine from a Buick engine, from a Chevy engine. During the 90's everything just blended together and now they make engines. The only ones that are for one carline are pretty much the Northstar engines. Everything else is in any car they want to put it in.
As with most things automotive I suspect that the bottom line was really the bottom line. Meaning, the decision was driven by money.
At the End of the 70's GM had probably what.... half a dozen engines with displacements right around the 300 mark. And how many different small blocks?

I didn't see the decisions being made, but I sure saw the results of the changes. Frankly I think it's better the way it is now, with one 3100, one 3400, and several variants of the small block in car and truck lines all based on the same design, using the same special tools.
It sure makes my job easier I'll tell you that.

I suppose I am not really answering your question but it's an interesting topic.
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307's were made to share block bore and ring tooling between the 3.8L "A" Buick V6 and the Olds V8.

the 307 Chevy was leftovers from the 283 and 327. 307 Chevies were notorious for wiping camshafts. Very poor oiling.

283 3.75" bore, 3" stroke
302 4.00" bore, 3" stroke
327 4.00" bore, 3.25" stroke
350 4.00" bore, 3.48" stroke
307 3.75" bore, 3.25" stroke
305 3.74" bore, 3.48" stroke

Oldsmobile Engine Specifications:

CID YEARS BORE STR. Jrnl. Mains Conn. Piston
..............................................Rods Dia. Rod Comp. Ht

260 1976-82 3.5 3.385 2.12 2.5 6.0 1.615
260 1979-80 3.5 3.385 2.12 3.0 5.886 1.770 (Diesel)
307 1980-86 3.8 3.385 2.12 2.5 6.0 1.615
330 1964-67 3.938 3.385 2.12 2.5 6.0 1.615
350 1968-80 4.057 3.385 2.12 2.5 6.0 1.615
350 1978-85 4.057 3.385 2.12 3.0 5.886 1.770 (Diesel)
403 1976-85 4.350 3.385 2.12 2.5 6.0 1.615

(swiped from the Olds FAQ
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GM started putting 307's in the B-cars in 1981. The Chevies stayed with the 305 until about 1987, when they got either the 307 or the 305. The wagons all got the 307 starting in 1987, I believe.

I think it depended on the plant they were built in. The cars that were built in Arlington all got the 307. The Chevrolets and Pontiacs that were built in Willow Run and Oshawa Ontario got the 305. The Canadian built cars got Canadian emissions and did not have 3C. They were much cleaner. I have a 1985 Caprice built in Oshawa, and it is a joy to work on compared to the 307 Y in my '86 Fleetwood.

In 1985, Parisiennes were all built south of the border. All the 1985 Parisiennes I have seen have the 307. Previous to that, the Parisienne was a specifically Canadian car and built in Oshawa. The 1982-84 Parisiennes resembled Impalas at the back with a Caprice grill and Pontiac emblem and Pontiac specific trim.

My theory was iut was a matter of logistics at to what car got the 305's or 307's. I think only the Chevrolet was built at Willow Run whilke the balance of Pontiac, Olds and Buick, plus the wagons were built in Arlington.

But, there is always an exception to leave us all scratching our heads. I work with a guy that has a 1987 Caprice with the 307 and Canadian emissions. That is no 3C. I have to run the VIN to see what plant it was built in.

As a note, the Oshawa Ontario plant switche to FWD A-body production in 1987. That ended B-car production there for good. This palnt built all Canadian market Chevrolet and Pontiacs there since the 20's.

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:hmm: Hmmm, my 85 Pari had a 305, and I'm sure she was built in Canada.
Hmmm. Interesting. Do you still have the VIN anywhere? If it starts with a 2 it's Canadian built. That would explain the 305.
A friend of mine has an '85 Parisienne with a 307.

1981 VIN's and up. 1980 and down didn't have the 17 digit VIN's.

guidematic said:
Hmmm. Interesting. Do you still have the VIN anywhere? If it starts with a 2 it's Canadian built. That would explain the 305.
A friend of mine has an '85 Parisienne with a 307.

When did they start building Broughams in Arlington.

According to the VIN on my '87 it was still built in Detroit.
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