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One main concern in power production with forced induction is effective compression. Effective compression is the sum of the motors static compression, plus the additional compression added by the forced induction tool. A B18C1 (also B16A) motor will have a higher effective compression than a B18B motor will, on the same boost...therefore, pound for pound, it will make more power.

The next argument that people usually bring up is that a higher compression is bad for turbocharging. Well, if you understand the concept of effective compression, then you should understand that this statement is entirely incorrect. A higher compression engine makes more power in NA form. So, why do you turbo guys think that a lower compression turbo motor makes more power? Does that make any sense when you really think about it? A turbocharger is a power adder? So why deplete power that was there to begin with? The answer I usually get to that is "So I can run more boost!" Well, sorry to rain on your parade, but more boost does not always equal more power. Check out this mathematical example of effective compression:

A motor with a 10.0:1 static CR boosting 10psi
10psi/14.7psi = .68
.68 + 1 = 1.68
1.68 x 10 = 16.8 effective CR

A motor with an 8.5:1 static CR boosting 10psi
10psi/14.7psi = .68
.68 + 1 = 1.68
1.68 x 8.5 = 14.28 effective CR

Now tell me who is going to make more power? The higher CR motor, or the lower CR motor?

So, maybe add more boost to the lower CR motor, right? Wrong...

A motor with an 8.5:1 static CR boosting 13psi
13psi/14.7psi = .88
.88 + 1 = 1.88
1.88 x 8.5 = 15.98 effective CR

Now you see, even adding 3psi of boost, still does not equal the effective CR of the higher compression, lower boost motor.

Effective compression is not the only advantage of the B16A/B18C1 either. The B16A/B18C1 has a stronger, better flowing cylinder head. It can rev much higher, making it that much more effective, and it flows great to handle all of the extra volume. The block has oil squirters to help support the bottom end assembly at high RPM. It takes more than a valvetrain upgrade to make a B18B safe at 8k. The higher compression also aids in spooling the turbo faster too.

Both motors have similar tolerances though. Both motors pretty much top out at around 350-400hp on stock motors, very well tuned. The B18C1 will make it far more efficiently for you though. It takes less boost to do so, it has more safeguards...and the bottom line on any Honda motor is tuning. If it is well tuned, you will be set. That goes for both motors. YOU ARE A FOOL if you think for one second that just because your B18B has a lower compression, you can substitute that for proper tuning.

A lot of people like to lower their motors compression when they build their motor. I used to think it was a good idea before I understood about tuning, and the positive aspects of compression. In the mathematical representation below, I will show you how a low compression motor must boost more to equal the output of a higher compression, lower boost motor:

Motor: stock B16A2 boosting 7psi.
Static Compression Ratio: 10.4:1

((boost psi / 14.7) + 1) x motor compression = effective compression

Stock motor (10.4:1 CR) on 7psi:
7psi/14.7psi = .47
.47 + 1 = 1.47
1.47 x 10.4 = 15.288 effective CR

Built motor (9.0:1 CR) on 7psi:
7psi/14.7psi = .47
.47 + 1 = 1.47
1.47 x 9 = 13.23 effective CR

You will lose 2.058 points from your effective compression ratio, this translates to a significant power loss.

In order to gain back that power, you have to do this:

Built motor (9.0:1 CR) on 10.5psi:
10.5psi/14.7psi = .71
.71 + 1 = 1.71
1.71 x 9 = 15.39 effective CR

Add 3.5psi to what you were boosting before, and you should be able to make around the same power as before, granted you haven't done any other kinds of modifications port/polish, cams, etc...

As you can see, considering all things stay equal (bore/stroke/cylinder head/etc...), you must add 3.5psi to make the motors perform similarly. You just spent about $2,500 to build your bottom end, and make your car slow.

By now we all should understand the positive aspects of compression, and how when teamed with the faster spoolng turbo, more efficient output, better flowing B-series VTEC cylinder heads, better low end spool time, stock oil squirters, higher redline, etc...you should see that turbocharging B-series VTEC motors is clearly not dangerous, and highly adviseable. I love a good turbo B16A!
 

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Damn man! Great post!
I'm actually in the process of putting together an engine right now and a friend of mine is hooking me up with his old turbo kit.

Originally, I was designing my engine to run high amounts of nitrous with a 11.0 compression ratio, but I'm dropping it down to 10.0 now by having the chambers opened up in the head. I was actually worried that 10.0 would still be too much, but my builder assured me that 10.0:1 compression, with 8 psi of boost on 91 octane fuel will be ok on 91 octane pump gas, after we tune it on his shop's dyno.

From what he tells me though, I shouldn't run too much higher than 10.0 compression with 8 psi of boost on pump gas, because it'll increase the risk of detonation. On race gas though, the fun begins :D
 

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-=Zeqs=- said:


From what he tells me though, I shouldn't run too much higher than 10.0 compression with 8 psi of boost on pump gas, because it'll increase the risk of detonation. On race gas though, the fun begins :D
Probably not, unless conditions are bad, in my opinion. If it is a cool/cold day out, you should be fine. It is incredible how much weather can effect your motor, when it is turbocharged. If it is hot as shit out, then you should know to take it easy. I have run 10.4:1 on 15psi with pump gas, with no sign of detonation...hehe, a lot. If it gets bad though, just retard your timing, and take it easy.
 

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There are more sides to it. I just like to hover around that aspect of it...because I think it is important for street cars, and that is all I care about. If I were writing for fully built race cars, the article would be totally different. Temperature, octane, and timing come into play also, but I don't mention them, because I like to think that most readers have enough sense to know that already...

You don't take a stock/higher compression motor, drive hard when it's 110 degrees out, use regular 87 octane, and advance your timing...hehehe. :p
 

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Discussion Starter #8
MatT3T4 said:

You don't take a stock/higher compression motor, drive hard when it's 110 degrees out, use regular 87 octane, and advance your timing...hehehe. :p
Nope. :D

I am in the process of putting my turbo on.
I am going to run 10psi on my stock b16 with engine management. (91 Octane)

Think that's wise?
 

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Ryan Autry said:
Nope. :D

I am in the process of putting my turbo on.
I am going to run 10psi on my stock b16 with engine management. (91 Octane)

Think that's wise?
Is that all? :p

You'll be fine. Just pay attention to your car. I know it sounds corny, but if you become one with your car, you will know exactly what is going on with it. Seriously. I could turn on my car, and hear things that shouldn't sound like that immediately. I could drive her, and feel variations that weren't there before, no matter how minute they were. I've run 18psi, untuned, with 270cc injectors...hehehhe. RIGHT before I built my motor, we ran it up to like, 28psi or some shit...and made a bunch of passes. OH MY GOD. I cannot even begin to tell you how fast it was, and it still didn't blow, even though I didn't care, because I was on the street next to the shop it was being built at...lol.

Anyway, you can safely run that boost, no problem, just make sure you listen to your car. ;)
 

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fucking sweet hatch by the way...

i have a new project too:


I'll probably end up doing a turbo B16A also, but not until I have another daily driver. If all goes well, I hope to have a Honda Element sooner or later. Anyone seen them? FUCKING BAD ASS!!! A lot of people don't like them now, but YOU HEARD IT HERE FIRST, I think they will be a big hit.
 

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Discussion Starter #12
MatT3T4 said:
fucking sweet hatch by the way...

i have a new project too:


I'll probably end up doing a turbo B16A also, but not until I have another daily driver. If all goes well, I hope to have a Honda Element sooner or later. Anyone seen them? FUCKING BAD ASS!!! A lot of people don't like them now, but YOU HEARD IT HERE FIRST, I think they will be a big hit.
Thanks.

That looks like a nice little project you have there. :cool:

Good luck with it.

Honda Element are cool in my book. :cool:
 

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Your math is a little off, but the idea is good

First of all, you would multiply your compression ratios

You would multiply the compression ratio of the turbo time the compression ratio of the engine

For an ideal gas

14.7 psia air (atmospheric) fed into a 10:1 engine would have a cylinder pressure of 147 psia at the end compression stroke

When running 10 psig of boost to a 10:1 engine would have a cylinder pressure of 247 psia at the end of the compression stroke or 1.68 x 10

For the same engine effciencies, the more air and fuel you can put through an engine...the more power you make. Because of practical limitations, there is going to be a maximum amount of boost you can run on a given engine. Decreasing the compression ratio, allows you to increase the amount of boost you can run, consequently increasing the amount of air you deliver to the engine.

However, by lowering the compression ratio, you reduce the thermodynamic efficiency of the engine.

For any given engine, there is going to be a boost vs. compression ratio that is going to produce the greatest amount of power for that engine.

So its very possible that reducing compression ratio and increasing boost could make more power. In fact, when you're starting with an engine originally designed for NA, I would say more often than not it will..to a certain point.
 

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WeaselGSR said:
Your math is a little off, but the idea is good

First of all, you would multiply your compression ratios

You would multiply the compression ratio of the turbo time the compression ratio of the engine

For an ideal gas

14.7 psia air (atmospheric) fed into a 10:1 engine would have a cylinder pressure of 147 psia at the end compression stroke

When running 10 psig of boost to a 10:1 engine would have a cylinder pressure of 247 psia at the end of the compression stroke or 1.68 x 10
Neither my math, nor your math are off...we both arrive at the same number, we just use different entrances.

Everything is a give and take. You take some of #1, then you have to give some of #2, and vice versa.

The aim of this article is to those who have posed the question of whether they want to build their motor, or leave it stock.

Here is the deal, and I will explain it with a hypothetical situation:

Johnny Smith has a 2000 Si. Stock motor, nothing done to it. Johnny wants to turbocharge his car and make around 320hp. Conventional knowledge says that Johnny MUST build his motor, thereby spending close to $4,000 just for the motor itself, then add $3,200 for a turbo kit, and another $1,500 for fuel and spark, and then $1,200 for engine management...don't forget $200 for a dyno session. Johnny just spent close to $10,000 building his motor and turbocharging his car. Don't forget about hidden costs, maintainence, gauges, electronics...etc.

Now Johnny has a fully built motor, and his car is fast.

But wait...little does Johnny know that his stock engine can sustain that amount of power indefinitely, should it be well taken care of and properly tuned. It's not hard, it's not taboo. Subtract the $4,000 for the built motor, and add maybe $250 for a spare B16A shortblock, should you get overzealous one day and blow your shit.

Now, all of us who have had, or who have a POWERFUL street Honda know, that anything more than 300hp is somewhat poinless on the street. Traction limitations are rampant at that stage. So what is the point of making 550hp boosting 32psi on your 7.0:1 motor, when my little 260whp Civic will leave you in it's dust (as you leave yourself in tiresmoke), at the stoplight?

I write my articles, and base my tech around street enthusiasts. If I were writing for another aspect, my articles would be different.

Stock compression (otherwise known as high), is your best bet for the street. Not only does it afford you a more even powerband, power coming in earlier and faster...but in reality, it isn't even that high. If stock Hondas were running at 12.5:1...then yeah, we're breaking the rules, but the stock compression is not high. It is ideal. Far more efficient for a streetcar, than a low compression engine is. If it's hot as hell out, just make sure you are using high octane (you should regardless), be careful...don't get overzealous...and if it comes down to it, back down the timing a bit.

I have had two stock/high compression turbo setups, and there was a reason that my car was king of the valley I live in, lol...sounds corny, but it was true.
 

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B16A has a compression ratio of 10.4:1 and the B18C5 has a compression ratio of 11.0:1. Scary.

Isn't Turbonetics designing a kit for the Toyota Celica GTS which has a static compression ratio of 11.5:1?
 
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