The myth of low CR with high boost

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The myth of low CR with high boost

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Honda Civic >> Your Ride >> Nitrous, Super Chargers, & Turbos >> The myth of low CR with high boost

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The myth of low CR with high boost - 5/21/2006 4:43:17 PM

Fiirkan

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ok so i have been hearing recently that in order to use high boost on supercharged application(i am assuming that this implies turbos as well) with honda engines you need to rebuild to a lower compression ratio. but it has just come to my attention, that this is in fact false. i was reading in my Honda tuning magazine this week, and found a letter from someone who wanted to supercharge a B16A, and Hondatuning told that that it is not always necessairy to run low compression in a boosted motor. and they then go on to explain that the myth of using low compression originates from the days of old school muscle cars with horrible piston and chamber designsthat were pron to detonation at low boost levels with average compression. With Honda motors we have the luxury of some of the best designed heads in the world, and it is ok to run 10-11:1 compression ina welltuned supercharged motor. honda tuning actually supercharged a stock TypeR integra not too long ago, and the stock ITR has 11.5:1 CR. and it is infact ok to run 12 psi of boost on a 10:1-11:1 CR on a stock motor. and you would even be able to use forged pistons if you want, and retain that high CR and then increase the boost even more... I for one found this imnteresting. and hope that it answers some questions for people too

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RE: The myth of low CR with high boost - 5/21/2006 4:53:40 PM

Street Sniper

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I read that too and found it very interesting, but you better have a fat wallet if you want to run 12psi on 11.5:1. I also think the low compression theory is far safer for the daily driver.

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RE: The myth of low CR with high boost - 5/21/2006 4:57:15 PM

Chips

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So, this is not so much a myth as merely not as true anymore? That's what seems to be the case in my mind. I really don't understand enough about CRs and turbos to really make a distinction, but from what you said, it seems you can run boost on high CRs, just not as high or as safely as on a low CR. Is that right?

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RE: The myth of low CR with high boost - 5/21/2006 9:13:20 PM

riceburner700

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yeah i saw that to but what octane gas were they using....?

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RE: The myth of low CR with high boost - 5/22/2006 1:22:35 PM

Kappa22

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quote:

ORIGINAL: Chips

So, this is not so much a myth as merely not as true anymore? That's what seems to be the case in my mind. I really don't understand enough about CRs and turbos to really make a distinction, but from what you said, it seems you can run boost on high CRs, just not as high or as safely as on a low CR. Is that right?

Partially. But these statements ultimately have more to do with how big the turbo is (i.e. how much air it's moving) than with psi. PSI looks good on paper, but think of it this way: you can blow 10 psi through a straw, but you're not moving any significant air volume. Now, a T-60 blowing 10 psi is probably going to be moving over 550 cfm depending on the trim... The tune also has a huge impact on how well a high-compression engine can handle boost.

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RE: The myth of low CR with high boost - 5/22/2006 1:27:46 PM

Berzerker

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Yea if you retard the **** out of it to stop detonation your counteracting the gains you would get from compression. Its a fine ballance and one that needs to be explored for your particular application.

Berz out.

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RE: The myth of low CR with high boost - 5/22/2006 2:21:00 PM

larsenracing

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I agree with the first statment. Im many cases you are better off funning a lower CR when running a higher boost level but with a lower CR you will be loosing Torque and we need more torque in a honda than what we have so my suggestion is to run a higher CR and a lower psi on a honda. Then your boost will pick you up at the higher RPM's when you are at full spool. take for instance a Top Fuel Dragser runs like a CR of 6.8:1 with 32PSI of boost because they have pleanty of torque because they are a big block V-8. Good luck.

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RE: The myth of low CR with high boost - 5/22/2006 2:24:15 PM

Nail I3unny

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thats more or less what i was trying to say in another thread about a week ago. you can run fairly high CRs with decent boost fairly reliably...but it depends on the turbo, internals, and tune you have in the car.

theres a GSR that has a couple videos on StreetFire thats running an 11.5cr on 12psi from a vortech supercharger and 93 or 96 octane. thats a really good example in favor of the argument that you can run high psi on high compression.

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RE: The myth of low CR with high boost - 5/22/2006 3:08:48 PM

Chips

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Ok, so in a nut shell, high CR = torque and high boost = hp? I know there's more to it than that, but that's the general idea? So if I were to (hypothetically) take my d15b7, throw on a y7 head to raise CR, and boost it, I'd be good to go so long as I get a tune and use ARP bolts? If so that may be a good direction for me.

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RE: The myth of low CR with high boost - 5/25/2006 10:29:06 AM

larsenracing

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Go for it but if your not going to use upgraded pistons and rods dont go above 5-6PSI on that setup and if you do have them I wouldnt go above 11-13PSI, anything above that on a honda you better stake the block. You will need an upgraded ignition & fuel system (pump,injectors,risenrate FPR) and i would upgrade the cams and exhaust. Any boost on a honda i recomend running a front mount IC. Good luck.

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Post #: 10