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Author Topic: Compression Ratio 1986  (Read 192 times)

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edberry78

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Compression Ratio 1986
« on: December 26, 2017, 17:02:32 »

I read here that in 1985 the compression ratio was increased to 9:1 under specs on the police cars. Did they do the same on regular cars? Just trying to figure out the compression ratio on my 1986 model (318).
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lsm360

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Re: Compression Ratio 1986
« Reply #1 on: December 26, 2017, 18:41:00 »

Yes, an '86 318 was 9:1
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DobaMark

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Re: Compression Ratio 1986
« Reply #2 on: December 27, 2017, 06:17:05 »

I read here that in 1985 the compression ratio was increased to 9:1 under specs on the police cars. Did they do the same on regular cars? Just trying to figure out the compression ratio on my 1986 model (318).
Only the 2bbl engines had the increased compression. 4bbl police car engines did not see the increase in compression.
The increase in compression came with the high-swirl heads and a switch to the Holley 2bbl, as well as a recommendation for premium gas. The changes were likely driven to meet increasing emissions and gas mileage requirements. The police cars were not subject to gas guzzler laws. The civilian cars were.
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Derekb

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Re: Compression Ratio 1986
« Reply #3 on: December 27, 2017, 06:58:23 »

under the valve cover would have casting 302 for the high compression heads
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edberry78

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Re: Compression Ratio 1986
« Reply #4 on: December 27, 2017, 08:53:38 »

Thanks, fellas!
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lsm360

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Re: Compression Ratio 1986
« Reply #5 on: December 27, 2017, 12:00:32 »

Yes I should have been more clear. The 2 barrel cars went from 8:7 to 9:0. Thanks Mark.
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80 Lebaron Coupe

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Re: Compression Ratio 1986
« Reply #6 on: December 27, 2017, 13:37:50 »

4bbl police car engines did not see the increase in compression.
What was the CR for these 4BBL engines to handle the 360 heads?
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lsm360

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Re: Compression Ratio 1986
« Reply #7 on: December 27, 2017, 17:20:12 »

What was the CR for these 4BBL engines to handle the 360 heads?
I think it was 8:5 but need to look in my Chrysler Police Encyclopedia to be sure and I'm goofing off at work right now.
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DobaMark

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Re: Compression Ratio 1986
« Reply #8 on: December 28, 2017, 05:52:48 »

I think it's even lower, like 8.2 on the 318-4 engine.
The earlier 318-2 was 8.5.
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lsm360

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Re: Compression Ratio 1986
« Reply #9 on: January 04, 2018, 10:28:27 »

Encyclopedia says 2 barrels got 9:0 and 4 barrel cars 8:4 with the 360 hp heads.
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Re: Compression Ratio 1986
« Reply #10 on: January 05, 2018, 11:43:37 »

Encyclopedia says 2 barrels got 9:0 and 4 barrel cars 8:4 with the 360 hp heads.
One would think it should be the other way around considering the 360 heads drop the CR 1 point.
IE: 9:0 would be 8:0 with the 360 heads. and 8:4 would be 7:4.
7:4 doesn't seem like enough to get out of its own way.

Maybe I got the info wrong from here, and the point is from the bottom end, like 8:4 would be 8:3 with the 360 heads.
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lsm360

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Re: Compression Ratio 1986
« Reply #11 on: January 05, 2018, 17:37:54 »

It explains it in the Encyclopedia, sort of anyway. Can't say I know enough about heads, the burn, etc., to understand completely. Wish I could scan and post.
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