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Old 04-15-2012, 10:51 AM   #1
bvaughan
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Default Compression Ratio on Turbo Engine

What do you think is the best compression ratio for an all out turbocharged race car (drag racing). I have heard a lot of people are in the 10 to 10.5:1 range. I am running about 9.5:1 now, but I am building another engine for next year.
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Old 04-15-2012, 11:37 AM   #2
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Default Re: Compression Ratio on Turbo Engine

9.5-9.7 on gas and 10.5-10.7 methanol. This is a sliding scale based on cuin and turbo you are allowed to run. If boost is limited CR is usually raised some to compensate. If you have a turbo on the large side and tons of boost available then on the lower side of numbers. Other things influence the CR as well and without all the info on the setup these are just general statements and nothing specific for your setup.
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Old 04-15-2012, 11:37 AM   #3
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Default Re: Compression Ratio on Turbo Engine

We are at 11:1 on E85
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Old 04-15-2012, 11:42 AM   #4
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Default Re: Compression Ratio on Turbo Engine

im running 9.7:1
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Old 04-15-2012, 11:57 AM   #5
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Default Re: Compression Ratio on Turbo Engine

Good points. I am looking to run rs275. The class is limited to 76mm turbos. I am at 408 CID now, but I am going to build something max effort around 350 CID for next year. I want to run as much boost as possible at that CID. I am guessing I could make 20-25 psi with 350cid. I want to run more compression to make up for the low boost.
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Old 04-15-2012, 01:23 PM   #6
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Default Re: Compression Ratio on Turbo Engine

I run 9.8:1 338sbf 93 with meth 19psi
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Old 04-15-2012, 02:36 PM   #7
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Default Re: Compression Ratio on Turbo Engine

Quote:
Originally Posted by bvaughan View Post
The class is limited to 76mm turbos. I am at 408 CID now, but I am going to build something max effort around 350 CID for next year. I want to run as much boost as possible at that CID. I want to run more compression to make up for the low boost.
I'm not real smart, but I'd start with the compressor map since that is the limiting factor and build based off that. You may find broader power and/or more reliability from different combos that max a particular turbo.
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Old 04-15-2012, 05:52 PM   #8
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Default Re: Compression Ratio on Turbo Engine

11:1 or more gas or alky. Compression is your friend.
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Old 04-15-2012, 06:04 PM   #9
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Default Re: Compression Ratio on Turbo Engine

Some of the guys seem to be running big cubes 400+ with the little 76mm. They are running in the 5.30 to 5.50 range. I figure they must be making good low end torque for better 60 ft times. The class is 1/8th mile. I figure the compression could be helping build boost on the line better.
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Old 04-15-2012, 07:17 PM   #10
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Default Re: Compression Ratio on Turbo Engine

I would look at the BW 76mm that you can he with a 1.50 A/R and max the cuin for this hot side. Im guessing it may be larger than 350cuin.
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Old 07-04-2012, 12:28 PM   #11
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Default Re: Compression Ratio on Turbo Engine

What's the max anyone has run on pump gas on here?
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Old 07-04-2012, 02:47 PM   #12
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Default Re: Compression Ratio on Turbo Engine

Max effort limited turbo....

12:1 maybe more. Static compression means jack anyway. Its all about dynamic.

Personally seen 30psi on a motor thatll crank 200....Another person told me they put 50psi on an engine that cranks 240.....And i believe it.

As long as you arent octane limited.... More is better.
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Old 07-04-2012, 02:58 PM   #13
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Default Re: Compression Ratio on Turbo Engine

I'm at 10.5-1 on our gas 509bbc at 28-29psi boost
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Old 07-04-2012, 02:58 PM   #14
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Default Re: Compression Ratio on Turbo Engine

Quote:
Originally Posted by RDY4WAR View Post
What's the max anyone has run on pump gas on here?
E85 is allowed in the class. I would go with 10.5:1 or so.
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Old 07-04-2012, 03:01 PM   #15
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Default Re: Compression Ratio on Turbo Engine

I have seen upward of 14:1 on some pretty ridiculous cars. Of course, this narrows the tuning window quite a bit, but if it's a max effort, why not go all out? Of course this would be on methanol.

Myself, I will be building a 10 or 11:1 street motor to be run on E85. Off boost the higher compression will make the car less lazy to respond, on boost, it will just make it a handful!
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