b18c5turbo

ok did a search and found this:

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.

is this making any sens????

fire7882

nice write up. i think i will have to agree unless someone else convinces me otherwise.

boostedsol

that was written by MaT3T4 on hondavision.com.

did you copy/paste that from hondalife.com?


anyhow it is a great write-up.

btw, that is a sweet setup you have there.

[Modified by boostedsol, 9:01 PM 9/27/2002]


[Modified by boostedsol, 9:02 PM 9/27/2002]

MatT3T4

I am very biased towards stock/higher compression setups...I am not a fan of lowering compression, anymore at least. If you can find any good facts to debate this, please let me know. I have studied this issue a crapload, and stand by the article 110%.

boostedsol

yup mat, im w/ you on that one.

Blaze45

word, i toatally agree, hands down please make this a stickey

Blaze

Quick 200k Mile Motor

yup, i remember that post.
Makes me think about the Ferrari F40 & F50

F50
11.3:1 compression
V12 4.7 litre
85mm bore x 69mm stroke
510hp @ 8500rpm
347lb-ft @ 6500rpm

F40
7.7:1 compression
V8 2.9 litre
81.9mm bore x 69.5mm stroke
478hp @ 7000rpm
425lb-ft @ 4750rpm

Quick 200k Mile Motor

ahh shoot! The F50 is normally aspirated.
sorry for the irrelevant post

tony1

I think it really comes down to the type of gas you are running. On 93 octane ulitmately you can make more power with 9:1 than 10:1. There is a point when you get detonation from compression. This point comes much sooner with higher compression. Of course it will take more boost with the lower compression, but you can safely run enough more boost to make more power. When you are talking about race gas or methanol, your theory applies. Not to mention the variances in octane from different batches of gas and the extreme summer heat. It's much safer for a street car with 9:1 and you can, on pump gas, make more power. You might think all the racers run super high compression turbo motors, but most really don't. You can make more power through boost than compression. The AEBS focus for example runs 7:1 and 50-60psi. These cars are even running 118 octane and there is still that point where the compression is to high. Bottom line, if there is not a limit on how much boost you can run, drop the compression a little and run more boost and make more power.

MatT3T4

The focus of this article was the every day street Honda, where 91-93 octane applies, and your average enthusiast knows when he/she should or should not be pushing it (in regards to ambient air temps.)

As well, "where" the power comes in to play is also a key issue. A lot of people are concerned with peak power, I'm not. Well, it's good, hehehe, of course...but it's no good if you make all of your power after 5500rpm. Stock compression, or slightely higher compression will afford you a more thorough distribution of power, meaning that the power will come sooner, and faster. Peak power is great for the track when you launch on slicks at 7000rpm...but on the street, sluggish starts suck.

MatT3T4

Good insights though, by the way...thanks for the response.

ImportReview

Good article....in theory..

But I am going to have to completely and utterly disagree, absolutely.

Because what is left out of the equation is:

Effeciency.

The dish piston is the most effecient piston you can buy. Period. The combustion chamber is wide open and flame travel is very very effecient, creating a very even burn in the center of the piston.

A dome piston is not nearly as effecient as a dish piston.

That is my argument #1

Argument #2.

Lower compression makes more HP at the same level of boost with pump gas (less than 94 octane).

I have tuned HUNDREDS of turbo cars....and the ones higher than 10.3:1 cannot take the timing...at all and are retarded WAY more than a dish piston.

Same boost, more timing the lower compression motor is going to kill the higher compression one.

take a look at this graph.

That is 9:1 Compression and using about 95 octane. The timing at full throttle under boost at 16 PSI is about 22 degrees. VS about 33 degrees stock.

Thats 11 degrees taken out...and the graph is still perfectly smooth.

If I added compression, and started this motor at 10.5:1 compression, I could not run nearly that much timing, and would have to reduce boost probably about 2 lbs. Which would make the graph about 40-45 HP less at the same timing.

Argument #3
Wear and Tear.
Not only is the 9:1 motor way more effecient....and has more timing in it using the same octane...which makes ALOT more power....the lower compression motor at the same level of boost is not being worn out as much.

14:1 VS 15.6:1 for example...

Which compression is wearing on your motor more? 15.6:1 for sure.

So, In conclusion...

With the 9:1 setup...you have:

1) more effeciency
2) more timing
3) AND less wear and tear.

And it makes MORE power at the same level of boost.

I learned all of this from experience, and from doing it for years.

We now have motors making 400+ WHP at as little as 13 PSI at 9:1 compression.

I think 400+ WHP @13 PSI is very very good, and I am pleased with it.

If we ever build a racecar....estimations would be it making 600 WHP at as little as 23-24 PSI.

On gas.

Jeff

MatT3T4

ImportReview, I would be interested in knowing the specs of the vehicles making 400hp on 13psi. Personally, I have been able to run 18psi plus on pump gas (92, before f'ing CA switched to 91), and stock B16A compression...without fail. I actually ran this setup for 1.75 years, before a freak accdent left two o-rings on my injectors broken. On top of that, I ran that through 270cc injectors (I know, I know). Once again...never a problem. My cylinder head gave way before the bottom end ever did. Stock B16A1 running a Mugen ECU hitting 9,000rpm all day every day. Gave the valve guide seals a working.

When I built the motor, it was horrible. I dropped from stock compression, down to 9.5:1. It was like turning down the boost to .5bar. I cannot remember all of the specs and settings, and I wish I could for this discussion...but that was my experience (with my own vehicle). Plenty of others with friend and shop vehicles.

The article applies to street cars...and choosing whether or not to build it. One thing that you must remember is this: the average street enthusiast DOES NOT have the resources that you do...and will not see the gains that you have, through what is most likely painstaking R&D, right?

ImportReview

Good one MatT3T4.

I understand the majority does not have the same resources. I was speaking on a "higher" budget scale. For sure.

With an FMU setup, you had no control really over your timing and lowering your compression, at the same timing that you were not detonating on before, would probably lose HP. Unless of course, you retarded your distributor alot.

B16A's are a different story because of their unique crank.

I am mainly talking about GSR's, LS/VTEC's, CRV/VTEC's that have a larger stroke...

B16 is the best turbo block dynamically, but not in HP numbers.

I posted that long essay on what I believe, my opinions.

I am betting some other shops will jump on my case stating I am wrong, and higher compression is better. Thats ok. Thats their opinion, which counts too.

We have a few cars making 400 WHP at 13 PSI. at 9:1 compression.

Its called Package 3 Turbo. I have 3 in the shop right now.

seems like thats all we do over here now. Build 400+ HP turbo cars. Its the craze right now.

Jeff

MatT3T4

Everyone has different opinions...and I like to hear all of them. You know what the problem is, that I notice EVERY time...and that I am fully guilty of? Not stating exactly which application we are talking about. I always write for street tuners, and I fail to make that clear a lot of the time. My apologies.

V-SPEC 1

That is a great info jeff! please tell us some more.

V-SPEC 1

I was about to purchaced a 10-5-1 compression pistons for my motor on my crvtec motor being built right now.

MatT3T4

I have been up since 2:30am this morning, so you have to bear with me as things are coming to me slowly... In regards to the above statement, back off the timing and stay steady with the boost. We've never had any issues with this. Once again I understand that every tuner has his/her methods, and in the end...most of us are coming up pretty fast, but I don't think that anyone has hit that one absolute method that is the be all, end all.

MatT3T4

hehe, oh yeah, wear and tear. ok you got me there ALMOST definitely. wear and tear is ALL on the driver, and you know that...

Ok, I've been awake for 22 hours. Good night.

Project_SOHC_EX

I found the article to be very informing just not to believing. If you compare the VTEC motors as compared to the B18a or B18b you will have to notice that although this motor does not have the high compression or for that matter better flowing head it's where this motor is making the power. A motor that revs high is not always going to win. One must remember that it is not about how much hp you make but where and how efficiently your car can make it. Well in that case the preferred choice would be the B18b it makes just about as much torque which is what we are after in these torqueless Hondas & Acuras.
Specs
B18B1
142hp@6300rpm
127ft/lbs @5200rpm
B18C1
170hp@7600rpm
128ft/lbs@6200rpm
B18C5
195hp@8,000rpm
130ft/lbs@7500rpm

As you can see the GS-R and Type R make 1 to 3 ft/lbs of torque @ 1,000 and 1,300 rpm's higher. Now in a race who's gonna get who first is gonna determine the winner. Waiting for that GS-R and Type-R to make that amount of torque all the way up top surely that car will lose. Just look at some of Direp's racing videos he kills car and that with an LS motor. THe B18b is not that expensive either as it's VTEC counterparts for one, and the statement of it costing a whole heap of money to get the B18b to be able to run safely @ 8k is not entirely true. The same build up you should do for the B18b you should do for the B18C1 and C5 oh yeah that doesn't excuse the B16. Improving the flow on a B18b is the same as it would be for the C1 and C5 engines. Go to http://www.Portflow.com and go to products check out how much they charge for a valvetrain upgrade and yes that does include pnp with a multi-angle valve job. Being able to lower the compression=more boost=more hp and torque. Now once again once it is all said and done it's who is going to get who off the jump you'll be waiting too long for that VTEC to kick in getting your *** burned while the "untrustworthy" B18b will be making it's power and torque 1000's of rpms lower. The last thing I will say is that although you can run the B18C1 and C5 to 9,000 after some mods you still don't need those rpms. Check out some of the members of HT with turbocharged cars and check out there posted dynos and see where they launch the car to redline they don't even use up the whole 9,000 rpms they usually use it up to 8,000 and then it doesn't make any more they cars usually top out some where around close to dont' quote me but I'd say around 7,500 so what the use of the extra 1,500 rpms? Exactly there's no need.
In the turbocharged game it's not how much hp and torque you make but where you make it on the powerband and how efficiently you can make it. Efficiency means=lower rpms.

shadowdawn

Only thing I know is stock for stock the b18b will make more TORQUE then a b18c with equal kits and boost level, I'm sure theres enough proof of that by just numbers people post of power they put down.

B18b (stock internals) + turbo = more torque
B18c (stock internals) + turbo = more horsepower

Who is it that always says hp wins discussions, tq wins races?

filetofit

The equation presented with regards to effective compression is misleading. Boost has to do with volumetric efficiency and compression ratio has to do with thermal efficiency. Mixing the two concepts is like mixing apples and oranges.


[Modified by filetofit, 8:20 AM 9/28/2002]


[Modified by filetofit, 8:21 AM 9/28/2002]

fire7882

At first i agreed with the theory that more compression was better, but then i got to thinking. Bear with me as i try to explain.

Motor 1
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

Motor 2
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

Each motor has the about same effective CR right, This means that there is the same amount of stress on the internals of the engine even though one is running more boost. Am i correct so far??

Since the combustion chamber is larger in the low compression engine, There is more fuel and air to combust. The more there is to burn/explode, the bigger the bang, the more power produced.

So the lower compression motor should make more power with the same amount of stress on the internals.
Is this making any sense????


[Modified by fire7882, 3:41 AM 9/28/2002]

filetofit

Like I said boost and CR are different concepts, one is volumetric (boost) one is thermal (CR).

fire7882

I think that is what i was trying to get to. Boost is read in the intake, CR is read in the combustion chamber. If you are running 100 lbs of boost and still have a low effective CR, the the fact that you are running 100 lbs of boost means nothing other than you have a big *** turbo. The reliability of the engine is still the same as that of a motor with a similar effective CR. Please correct me if i'm off base here.


[Modified by fire7882, 3:51 AM 9/28/2002]


[Modified by fire7882, 3:53 AM 9/28/2002]