Are the extra CIs worth in Boosted Applications?

[Nazman]

Ok Folks,

There has been lots of debate lately on the question of: are the extra CIs worth in a boosted application?

For example: 284CI vs ~302CI Stroker, 304CI Big Bore or 322CI Big Bore Stroker

Some say that it does not matter, just up the boost, others (me included) will say the more CIs the better.

Well, I build these two Turbo Consumption Chart for Modular 284 and 322CI BB/Stroker just to see if the extra CIs were worth the dollars and here is the data and my findings. Take it for what is worth. Again, just wanted to see it in paper and the final decision its yours!

So, here its.

The first chart is a 284CI (.020 over) Modular, and that followed by the 322CI Big Bore Stroker....Sorry, no Stroker chart as of right now, but will do one soon and add to the madness.

I utilized the following factors:

85% Motor Efficiency
130F AIT
Intercooled

They are all the same for the two charts. HP is rated “at the wheels”.
Boost level from 10-25PSI and 3000-7800RPMs.

284CI Modular @ 85% Efficiency, 130AIT, Intercooled, Power "at the wheels":

322CI Modular @ 85% Efficiency, 130AIT, Intercooled, Power "at the wheels":

Some of the “analysis” at the most “common” PSI and “a realistic” RPM point:

-284CI @ 6500RPMs
AVE HP X PSI = 39.63
HP @ 10PSI = 513.7
HP @12PSI = 555.3
HP @ 15PSI = 611.7
HP @ 18PSI = 680.0
HP @ 20PSI = 721.6
HP @ 25PSI = 825.6

-322CI @ 6500RPMs
AVE HP X PSI = 44.93
HP @ 10PSI = 558.8
HP @12PSI = 629.6
HP @ 15PSI = 700.3
HP @ 18PSI = 771.0
HP @ 20PSI = 818.2
HP @ 25PSI = 937.1

Now, it’s time for discussion! Lets hear it!

Naz

 

[Nazman]

Some FYI in case you have no idea how to read the charts:

Top Row = PSI (Boost Level)
PR = Pressure Ratio (This is the ratio between the inlet and outlet pressure of the turbo's compressor)
RPM= Engine Revs Per Minute

So, you look for the RPM level you want, then move right and look for the PSI you want and it will give you a value. This value is Multiplied by 10 to get the "theorical" HP.

Naz

 

[AntiHeightPunk]

i didnt understand one part of that till the summary
sounds good...more proof i need the 324ci
btw does john do custom cams too?

 

[Nazman]

Here is how these charths are utilized with a Turbo map.

From the turbo maps we can find out lots of very usefull information. Like with the diferent applications (ie: CIs) how the Turbo would behave and how it will come into the power band, if you are going to be in the man or even off the ma, if you could be surging and efficiency of the turbo!

Lets use the common T76 Turbo as an example:

T76:

So, here is what we can read starting at 3500-7000RPMs on a 284CI Motor at lets say 15PSI:

3500RPMs
~332.6HP
2.2PR
*Just off the map at the surge limit -Starting to "Spool Up"

4000RPMs
~380.1HP
2.2PR
*Right in the middle of the 70% efficiency island. Making power, spooled.

4500RPMs
~427.6HP
2.2PR
*Right at the edge of the 78% efficiency island. Making power, should be fully spooled by now.

5000RPMs
~475.1HP
2.2PR
*In the middle of the 78% efficiency island. Making power, fully spooled.

5500RPMs
~522.6HP
2.2PR
*In the middle of the 78% efficiency island. Making power, fully spooled very close to 62,000 inpeler (SP?) RPM.

6000RPMs
~570.1HP
2.2PR
*Near the edge of the 78% efficiency island, moving towards the 75% island. At or very near 65,200RPMs.

6500RPMs
~617.7HP
2.2PR
*In the middle of the 75% island. Still at ~65,200RPMs.

7000RPMs
~665.2HP
2.2PR
*Right at the 75% efficiency island, at about 68,000RPMs.

7500RPMs
~712.7HP
2.2PR
*At the 70% efficiency island.

The T76 would be right at home at 15PSI on a 284CI motor. The higher the boost, the more power it would make but it will cost you efficiency in the higher RPMs (motor). So at 20 PSI @ 7000RPMs (for example) ~777.2HP, 2.2PR but it will be just off the map at 58% efficiency. That means that the AIT temps would be SICK high but the same PSI at 6000RPMs would be right at 75% efficiency island making about 660HP.

Now, lets do the same with the 322CI motor:

3500RPMs
~377.16HP
2.2PR
*Should be "Spool Up" at about 65% efficiency. Making power.

4000RPMs
~430.9HP
2.2PR
*Fully spooled at the 78% efficiency island. Making power.

4500RPMs
~484.8HP
2.2PR
*Right in the middle of the 78% efficiency island. Making power.

5000RPMs
~538.7HP
2.2PR
*Just off the 78% efficiency island @ ~76%. Making power, fully spooled.

5500RPMs
~592.6HP
2.2PR
*Right at the outher edge of the 75% efficiency island. Making power, right at 65,000 RPM.

6000RPMs
~646.4HP
2.2PR
*Moved back inside the 70% efficiency island at about 73% efficiency at about 67,000RPms. The turbo is loving it!

6500RPMs
~700.3HP
2.2PR
*Rigth at 70% efficiency, doing about 70,000RPMs.

7000RPMs
~754.2HP
2.2PR
*Just of the 60%efficiency island, out of Turbo doing ~70,000RPMs.

7500RPMs
~808.0HP
2.2PR
*Off the 60% efficiency island (off the map), at about 57% efficiency at 74,000RPMs.

The T76 would be right at home at 15PSI on a 322CI motor up-to 6800RPM or so, after that, the Turbo is not enough but it would be a SICK set-up for athe street with very quick spool and mid-range. The higher the boost, the more power it would make but it will cost you efficiency in the higher RPMs (motor). So at 20 PSI @ 7000RPMs (for example) ~881.2HP, 2.2PR but it will be off the map at probably >50% efficiency @ 80,000+RPMs. That means that the AIT temps would be SICK high. At the same PSI 6000RPMs it wold inside the 60% island at about 61% efficiency making about 753HP.

Naz

 

[brkntrxn]

Makes sense to me, Carlos. Common sense says that a smaller motor will have to up the boost to have the same power as a larger bore motor. In an extreme example just think about how much boost you have to had to 281ci to equal a naturally aspirated 460ci motor.

I think a better questions are these (once you have defined your horsepower goal):

- What is cheaper, building a smaller cubic inch engine to handle higher boost and a blower to produce high boost OR building a larger cubic inch engine to handle lower boost?

- Which combination is cheaper to maintain in the long run? Stress the smaller engine with higher boost (and the blower) OR stress the larger engine with a longer rod throw and larger bore?



-284CI @ 6500RPMs
AVE HP X PSI = 39.63
HP @ 10PSI = 513.7
HP @12PSI = 555.3
HP @ 15PSI = 611.7
HP @ 18PSI = 680.0
HP @ 20PSI = 721.6
HP @ 25PSI = 825.6

-322CI @ 6500RPMs
AVE HP X PSI = 44.93
HP @ 10PSI = 558.8
HP @12PSI = 629.6
HP @ 15PSI = 700.3
HP @ 18PSI = 771.0
HP @ 20PSI = 818.2
HP @ 25PSI = 937.1

 

[Nazman]

Hummmm, I figured that we would have lots more post/coments on this subject since we had lots of "talk" in regards to this subject.

Ill say that the 322 or even a stroker will be worth it over a 284CI.

Just look at the summary on the first post

-284CI @ 6500RPMs
AVE HP X PSI = 39.63
HP @ 10PSI = 513.7
HP @12PSI = 555.3
HP @ 15PSI = 611.7
HP @ 18PSI = 680.0
HP @ 20PSI = 721.6
HP @ 25PSI = 825.6

-322CI @ 6500RPMs
AVE HP X PSI = 44.93
HP @ 10PSI = 558.8
HP @12PSI = 629.6
HP @ 15PSI = 700.3
HP @ 18PSI = 771.0
HP @ 20PSI = 818.2
HP @ 25PSI = 937.1

~90HP Gains @15PSI
~95HP Gains @18PSI

Or look at 25PSI with 284CI vs 20PSI with 322CIs

Making about the same HP with 5 less PSI, that that is quite a bit, given the AIT tems, etc. Plus, achieving the same or higher power levels at less RPM.

Naz

 

[Nazman]

Makes sense to me, Carlos. Common sense says that a smaller motor will have to up the boost to have the same power as a larger bore motor. In an extreme example just think about how much boost you have to had to 281ci to equal a naturally aspirated 460ci motor.

I think a better questions are these (once you have defined your horsepower goal):

- What is cheaper, building a smaller cubic inch engine to handle higher boost and a blower to produce high boost OR building a larger cubic inch engine to handle lower boost?

- Which combination is cheaper to maintain in the long run? Stress the smaller engine with higher boost (and the blower) OR stress the larger engine with a longer rod throw and larger bore?



-284CI @ 6500RPMs
AVE HP X PSI = 39.63
HP @ 10PSI = 513.7
HP @12PSI = 555.3
HP @ 15PSI = 611.7
HP @ 18PSI = 680.0
HP @ 20PSI = 721.6
HP @ 25PSI = 825.6

-322CI @ 6500RPMs
AVE HP X PSI = 44.93
HP @ 10PSI = 558.8
HP @12PSI = 629.6
HP @ 15PSI = 700.3
HP @ 18PSI = 771.0
HP @ 20PSI = 818.2
HP @ 25PSI = 937.1

Yes, exactly what I was talking about, just missed your post.

 

[bsmith782]

It seems like common sense. Bigger motor more HP. Now that we have efficiency/power/CI numbers lets put some $ numbers in the mix. I think that the last part of the equation is the most important to mose ppl.

 

[Nazman]

In an extreme example just think about how much boost you have to had to 281ci to equal a naturally aspirated 460ci motor.

Just for giggles....a theorical 460CI motor @ 85% efficiency could support:

~533.9HP @ 7000RPMs (at the wheels)

It will take a 284CI ~9.5PSI @ 7000RPMs to make the same power.

It will take a 322CI ~3.1PSI @ 7000RPMs to ake the same power.

Naz

 

[Nazman]

It seems like common sense. Bigger motor more HP. Now that we have efficiency/power/CI numbers lets put some $ numbers in the mix. I think that the last part of the equation is the most important to mose ppl.

We all know that, but the argument goes further than that.

Boost vs CIs vs RPM vs Durability

Lets utilize some advertised Modular Performance prices for a short block:

"Stage II" 284CI Short Block
-$3299.00
*You must supply your own block and crank

Big Bore/Stroker
-$5857.00
*Boss5.0 Block Included
*New Crank Included

So, that is a price diference of: $2558.00

By keeping it simple, the 284 is lots cheaper but if you do the right math, its lots closer than you may think.

With the BB/Str you get the Bad to the bone Boss Block and new Crank.

If yor stock motor is running, you could sell the short block as a running unit or sell the Block and Crank and make some cash there. Lets say you could get 500 bucks for the Teskid block/Kellogg Crank, that would bring the additional cost down to ~2058.00 which is still quite hefty.

So, what do you do?

Do you rather go with the 284 at the cost of extra boost/RPM or make same power at lots less boost @ less RPM, or the much, much, much more TQ and response that the 322 would provided?

More coments?

Naz

 

[bsmith782]

322!

 

[Double"O"]

the answer is in your charts mang

more cubes FTMFW!!!!

 

[Nazman]

the answer is in your charts mang

more cubes FTMFW!!!!

I know what the answer is (for me).

Just wanted to settle the argument.

Naz

 

[Double"O"]

I know what the answer is (for me).

Just wanted to settle the argument.

Naz

there should be no argument the phrase "there is no replacment for displacment" was coined for a reason!

 

[bent99]

Nice research and info. I used to roll a dart blocked 331 fox body jamming 17 psi down its throat. That car made 678 rwhp and was street driven for 4 years. Now I drive an 01 cobra ,fully forged and not a single upgrade besides the forging. Never messed with a turbo yet. I should though.

 

[Scout238]

i just breezed through stuff... but what about CR?

 

[bent99]

There was an article in muscle mustangs about that exact point. In the end the higher compression engine made much more power under boost then the lower compression engine. It will take a delicate (well more delicate) hand on the tuning for sure. My dart blocked 331 was 8.0 : 1 . Could have been more power for sure but with how much street driving the car saw I was happy. Good point

 

[olgreydog7]

The more power the motor makes without boost, the more it will make with it. That being said, I don't know if I would do it. Just cause of teh cost. Now, if I was building a motor for racing, I would do it in a heartbeat. For the street, you can get plenty of power at moderate boost levels, so it's not worth it. On street tires, what is an extra 40 hp (@10psi) when you are already over 500? I'll tell you what it is, smoke.

Man would I love to get drunk and talk tech with you guys.:beer:

 

[Nazman]

Man would I love to get drunk and talk tech with you guys.:beer:

Drunk? Why?

Next time you are in San Antonio come over and we will have a few brews and talk some junk!

 

[Nazman]

i just breezed through stuff... but what about CR?

That is a whole can of worms! lol!

There was an article in muscle mustangs about that exact point. In the end the higher compression engine made much more power under boost then the lower compression engine. It will take a delicate (well more delicate) hand on the tuning for sure. My dart blocked 331 was 8.0 : 1 . Could have been more power for sure but with how much street driving the car saw I was happy. Good point

As Ben stated, there is lots of power and responsivines (SP?) in extra CR!

As a rule of thumb, there is a ~3% Power gain for each point in CR, so it has to be ~the same or more in a FI system.

So, if you make a theorical 500HP @ 8:1CR, the it should be around 515+@ 9:1CR. Not just that, but the motor will be SOOOOOOO much responsive.

Naz