boost

Turbo and Supercharger discussion
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By Butterzz
- Wed Feb 02, 2011 8:46 am #236632 When compressed air from a turbocharger enters a cylinder, you're getting more compression per stroke then in an N/A engine. The 'effective' is the compression ratio after the the air has already been compressed by the turbo, and is now being compressed by the piston.

For example, my D16A is 9.8:1 compression stock, but when im pushing air compressed at 8 psi (at peak boost) my compression ratio jumps to 15.13:1.

The 15.13:1 is the 'effective' compression ratio.

PS - Awesome tool.

By AutoXCivic
- Wed Feb 02, 2011 3:38 pm #236660 It has more to do with the volume/pressure of the air in the cylinder than with the psi coming from the turbo. Simply because 8 psi on a t25 is not the same as 8 psi on a t4. The CR has to do with how much the air is being compressed above and beyond atmospheric pressure. When you used forced induction you are in essence pre-compressing the air. This creates a multiplier that has to be factored into the CR calculation.
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By beerys95lx
- Wed Feb 02, 2011 5:51 pm #236666 so how high is the min. Cr in the effective side before I'm running race gas, because the highs i want to go is 93 octane

By Butterzz
- Wed Feb 02, 2011 7:01 pm #236671 To my knowledge there isn't set brackets as to when you need to up your octane. The rule of thumb is; the higher the octane level, the less chance of pre detonation.

And your A/F ratio also plays a part in your chances of predetonation. If you're injector latency isn't set right and you're leaning out, you'll detonate whether you're running race gas or not.
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By beerys95lx
- Wed Feb 02, 2011 7:18 pm #236674 how much boost do you thing i can run on a freshly rebuild d15b7 bottom end with y8 heads and pistons.
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By teal_dx
- Wed Feb 02, 2011 8:23 pm #236680 it all depends on the turbo you're using. I'd get a set HP amount in mind that your setup is built to handle and then pick an appropriate turbo for your goals.
You can always adjust the boost at the very end when you're tuning :thumb:
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By beerys95lx
- Wed Feb 02, 2011 11:28 pm #236707 ok ya i get that but i don't really know how much the d15 bottom end can handle does anyone know?
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By teal_dx
- Thu Feb 03, 2011 3:32 am #236751 you mean D15b7 right? (from above)

The D15b7 rods are pretty much a joke. I wouldn't push them past 180 HP - on a good tune - if you're keeping this as a safe driver. If you don't mind blowing it up, then shoot for 200+

Lots of other factors come into play like mileage, tune, driving style ... there's no set HP number that the bottom end can withstand. Some last longer than others but it's usually those tiny D15b7 rods that are the culprit.
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By beerys95lx
- Thu Feb 03, 2011 4:31 am #236761 so would i be better to get a d16 and rebuild it with h beam rods but what else should i do to it to make it more turbo friendly. i like to make around 300hp but still be able to daily driver?

By AutoXCivic
- Fri Feb 04, 2011 3:31 pm #237058 Currently RC autoworks has a deal with a hungarian company to bring some custom length USDM d15 rods to the US. You might try contacting them. Also FJDistributors has a started testing on their own custom length USDM d15 rods and those should be ready later this year. These are going to be the only budget minded d15 rods available for the time being. Currently your only other option is Crower which sells a set of forged stock length rods for $700ish a set.


These custom length rods are meant be used with the famed vitara pistons. With the stockers the pistons sit above deck. These custom length rods bring the pistons so that they sit about even with the deck. If you don't mind running 8:1 ish CR then that is a way you could go. I've pretty much given up on the idea of building my d15 because I want to maintain my 10:1 CR with boost, and there's currently no time frame on cheaper forged stockers.

By AutoXCivic
- Fri Feb 04, 2011 3:34 pm #237060
beerys95lx wrote:so would i be better to get a d16 and rebuild it with h beam rods but what else should i do to it to make it more turbo friendly. i like to make around 300hp but still be able to daily driver?


Easier ... yes. Better ... maybe. Turbo friendly is all in the tune. You can make 300whp on a stock head easily. Getting a turbo cam (with some aftermarket valve springs), and some port work will make it easier. You can have a milder tune. 300 whp daily driven is fairly easy on a D.
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