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Discussion Starter #1
What's everyone who has experiance's take on compression on a turbo'd car ?? Since i'm getting Hondata, i'm thinking of upping my compression when I rebuild.

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when i rebuild my engine im planning on going with high compression and lower amount of boost. i was thinkin of around 10:1 cr. when i rebuild. but before i rebuild im gonna get a hondata 3 or 4b. so this way i can run lower amount of boost with equal cylinder pressure if i was running a low cr. on higher boost. plus better driving around town.
 

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when boosting, compression matters to an extenct. if you have a higher cr, all that matter is if the car is tuned right. without good tuning, it doesnt matter if you have high or low cr. however, lower cr allows for more errors in tuning.
 

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yes. lowering to cr is just a safety for poor/bad tuning. give you a larger margin of error, before you fuck up your engine. i plan on going full blown dfi or hondata 4b, along with a fairly high (10:1) cr. keeping the boost low and tuning up to par.
 

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You'll make more power by lowering the compression and upping the boost.

You gain 9-10hp for every extra psi of boost, while upping the compression 1 point only nets you a ~5% increase.
 

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GTwannabe said:
You'll make more power by lowering the compression and upping the boost.

You gain 9-10hp for every extra psi of boost, while upping the compression 1 point only nets you a ~5% increase.
so run more boost on a higher compression motor.
 

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st00pid

whats your take on higher compression + lower boost or high boost and lower compression. I have read that higher compression and lowerboost make more efficiant hp.
 

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Yes, in the perfect world it'd be great to run AvGas with 12:1 compression and 15#'s boost, but that ain't gonna happen.

What I'm saying is that on 93 octane you'll make more power with an 8:1 motor at 18psi than a 10:1 motor at 8-10psi.
 

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Lower Compression

Unless you have gobs of $$$ to put into your engine and a signed contract with the Devil guaranteeing that you will never lean out. Low compression will be the more reliable, safer power way to boost.

Check out this post

http://www.turbo-kits.com/honda_detonation_management.html

It will tell you all about Detonation Management...
 

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Physics....

The physics favor lower compression. If you think about it, it makes perfect sense. Lets think of two theoretical turbo motors with the same displacement. Now one is low compression and one is high compression. Both have the same EFFECTIVE or final compression ratio. That is, once the piston has completed its compression stroke, both motors have the same volume of air. Which will make more hp?

The lower compresion motor has the advantage. In the high compression motor, more of the compression is done in the cylinder/combustion chamber through the motion of the piston. This causes heat. Lots of it. In the lower compression motor, the same volume of air is moved, but more of it is compressed and put into the cumbustion chamber via the turbo. This results in a cooler initial charge because the air is not as hot. It has been compressed more effciently (slowly) and has been intercooled before going into the cylinder. Cooler initial charge for the same volume = more hp. Can't argue with physics.

Now, for a street car, there is a trade-off. The lower the compression, the less hp before you are on boost. But, you get more peak hp. Its all about balance in street motors. A turbo race motor will have really low compression because they never really run it off boost, except to stage. A daily driver will want higher compression so that the car is not a complete pig in traffic.
 

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Discussion Starter #12
I'm sorry for Posting this than not responding for a week...Vegas Rocks !! I'm running 9.5 rgt now. I'm resleeving the block and considering boring it to 84mm and upping the compression to 11 : 1 or so... What's everyone think ?? Anyone know what displacement a B18c would be with 84mm bore ?? The reason I posted here is because no one responded to my question in that post...
 

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A B18C1 with 84mm pistons will yield 1932cc of displacement. 11:1 can be done, is there any reason why you want the cr so high?
 

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Dr Drew said:
I'm sorry for Posting this than not responding for a week...Vegas Rocks !! I'm running 9.5 rgt now. I'm resleeving the block and considering boring it to 84mm and upping the compression to 11 : 1 or so... What's everyone think ?? Anyone know what displacement a B18c would be with 84mm bore ?? The reason I posted here is because no one responded to my question in that post...
Thats a mean ass motor..thats hella power..
 

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Discussion Starter #15
I'm thinking of upping the compression so I can get more outta the motor. It will be completely 'built' after I resleeve. I'm ordering Hondata this week. So, tuning won't be a problem. I think I pretty much have everything I need for a sick motor. I'm also thinking of ceramic coating the pistons for a better thermal heat barrier to help reduce the possibility of detonation. If been asking questions for a while now. I guess it is time act. Thanks for the help peeps.
 
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