383 Compression
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
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From: Mesa AZ
383 Compression
I have a 383 with 997 , 76cc. 1.94 heads. I want to install new dart 2.02 heads, 64cc. How much will this increase the comp ratio? Will it be too hi for 92 pump gas? I currently have 9.5 comp ratio. Will they give me enough performance increase to be worth the swap?
[Modified by chadman, 8:58 AM 7/24/2002]
[Modified by chadman, 8:58 AM 7/24/2002]
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: 383 Compression (chadman)
I would think it will bump it up to above 10.5 which will be borderline detonation depending all the factors that cause det: oct rating, gas quality, timing, cam overlap etc.
Safety Car
Joined: Aug 2000
Posts: 3,711
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From: San Antonio TX
Re: 383 Compression (chadman)
Thick head gaskets (thick as in beyond the normal crush thickness of a composition gasket...say around .040 or so) are not always beneficial when trying to address a detonation problem. They can kill the quench area, which would actually decrease your engine's detonation resistance.
If you know that you have a calculated cr of 9.5, just change the input of the CC volume and re-compute. If you're currently going by an advertised ratio, then you're probably shy of that 9.5 number.
If you know that you have a calculated cr of 9.5, just change the input of the CC volume and re-compute. If you're currently going by an advertised ratio, then you're probably shy of that 9.5 number.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: 383 Compression (chadman)
Here's where to go to figure it out for yourself.
http://www.smokemup.com/auto_math/compression_ratio.php
My 383 is 10.84 C/R with 64 cc and it runs fine on 91. I wish I would have went with 11.3 or so. Your cam type and valve events really determine what static compression ratio is fine to run with a certian octane level.
http://www.smokemup.com/auto_math/compression_ratio.php
My 383 is 10.84 C/R with 64 cc and it runs fine on 91. I wish I would have went with 11.3 or so. Your cam type and valve events really determine what static compression ratio is fine to run with a certian octane level.
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
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From: Mesa AZ
Re: 383 Compression (Paul 75 L82)
Actually I haven't run it yet. I bought it with those heads, I'm dressing it up and thought about swappin heads before the install. Thinkin 2.02s fully ported would be a good change. The others are probably fine, I guess enough is never enough. The builder said desktop dyno put it at about 380hp and 422 ftlbs torque.
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Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: 383 Compression (chadman)
You could choose a higher cc head. I am not sure what Dart offers but I have seen 67, 70, 72 ,74 and 76 cc heads by other manufacureres so you got choices. Like gkull said, a cam can drop you actual comp a lot so factor that in. 10/1 seems to a very popular comp ratio and I have it also in my 383 with alum heads. My current 350 is 8.5/1 and it runs nicely on 87 which saves me some $. Funny thing is that have seen a lot of dyno info and I am suprised how relatively little is gained by bumping comp as opposed to the bumb in gas $. Just one more thing to consider.
[Modified by Fevre, 1:28 PM 7/24/2002]
[Modified by Fevre, 1:28 PM 7/24/2002]
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: 383 Compression (chadman)
Also curious as to why a small block to replace your big block? Are you going to replace your springs? Your car might sit to high with the small block. I assume you are bagging your BB for future re-sale value.
Thread Starter
Racer
Joined: Dec 2000
Posts: 422
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From: Mesa AZ
Re: 383 Compression (Fevre)
My car had a small block when I bought it. It sits just fine. Ride is stiff tho. I was planning to go big block, but got ripped off by engine builder who went bankrupt. Now can't afford the swap. Maybe later. Got a good deal on the 383. In truth, probably more than I need.
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: 383 Compression (chadman)
I remember your thread now. Unless you are going to tear it down and inspect everything, you might want to run it as is to make sure it holds together. I had piston go bang and it caused $400 worth of clean up on my new alum heads. :( New heads can wait. Might be spirited enough for you as is anyways. Good luck!
[Modified by Fevre, 3:07 PM 7/24/2002]
[Modified by Fevre, 3:07 PM 7/24/2002]