I havnt been able to find hp numbers from a highcompression rotor 13b, I'm in the middle and just looking to see how much 10 psi on high compression rotors over low will make roughly.


Running 4x550cc stock turbo and aem fic for fuel / retard timing. Stock tmic and yea, fully gutted so, if u have any idea or any numbers let me know thanks!

 

you need to be more specific.

10 psi on stock turbo ? or 10 psi on a gt42r is very different.

high compression, you mean s4 NA rotors ( 9.4 ? ) . This wont yield alot more power vs a 9.0 , but will yield better response and out of boost driving.


If you want an answer, look at a similar 13bt setup , it will probably be the same .

It will come down to the tune as well the few NA turbo setups ive seen locally always run very rich and pull a lot of timing to be on the safe side, yieldind a fun car, but not the highest per psi.

There was a turbo na a few years back in ottawa, ran a custom twin turbo system ( 2 x gt20s I think ) , and then a S4 turbo. I believe it was around the 200-220 hp at 10 psi on a haltech. ( safe tune and beefy ignition system ) .

 

I made 362whp at 10psi on a BNR turbo and 9.4 rotors
Practically built boost just passed idle...

 

6port 13b 4x550cc stock s4 turbo , innovate wide band and aem fic6 for tuning , hope'in to push out 220whp ish with a solid tune.

 

Our 24 Hours of LeMons FD makes 331 at the wheels with S4 NA rotors, a half bridgeport, and an Ebay Chinaspeed T04B $150 turbo. 10psi.





I am a convert - the response is so much more crisp. When my street driven FD needs a rebuild, I'm going high compression.

 

That's pretty awesome!

 

When the time comes I'm rebuilding my 13B-REW with 9.7:1

Higher compression is good, more compression = more work released from the same amount of fuel, less internal EGR, hotter EGT = better spool, better transient response because the engine naturally makes more power.

It might only be 2-3% increase but it comes with no downside other than being more highly strung. People love porting for its 20% increase but think about all the downsides that come with it.

More compression and more boost are basically the 'no downside' ways of making power.

 

so with the higher comp rotors, would there be a safe boost/hp limit? Say with a mid size 35r turbo or similar?

 

I think the downside is that you can't safely run as much boost and/or ultimate power.

Low end you'll see the benefit (I've got the S4 NA rotors in mine) but if you plan on pushing over 2 bar you might want to reconsider...

 

2 bar is way more than most rotary owners run tho no?

 

Yes there is a downside, you definitely can't run as much boost on pump gas, I decided to switch back to low compression rotors mainly for the reason I can run much more boost on pump gas


My car made 362 at 10psi with 9.4cr
And made 342 at 9.9psi with 8.5cr
So only a 20hp loss between high and low compression rotors but I can run 8-9psi more with the low compression rotors on 91oct and that will make up more than that 20-30hp difference

 

The way to view boost versus compression is total effective pressure.

So (10 psi boost + 14.7 psi atmospheric) * 9.7:1 compression = 239.59 psi when compressed

People say they run around 20 psi on 9.0:1 compression, or is it 23? I'll use the lower one.

(20 psi boost + 14.7 atmospheric) * 9.0:1 compression = 312.3 psi before ignition

So lets find what boost level would have the exact same characteristics on higher compression rotors.

(Y psi boost + 14.7 atmospheric) * 9.7:1 compression = 312.3 psi before ignition
(Y+14.7)9.7=312.3
(Y+14.7)=312.3/9.7
Y+14.7=32.2 (rounded from .19587)
Y=32.2-14.7
Y=17.5

So for the same characteristics in the combustion chamber:
17.5 psi boost @9.7:1 = 20psi boost @ 9.0:1

You just have to decide if the slightly lower peak power will be offset by the different driving characteristics of an 7.8% increase in compression ratio.

 

Pretty much. If I ever get too much extra money burning holes in my pockets I may get a spare set of s4 NA rotors and have them lightened/clearanced/machined from 9.4 to 8.5 then balanced

Higher compression rotors are great for getting extra power in N/A motors for the same reason that they ARENT great in boosted applications.

 

But does the higher compression move the dyno plot left if you will? It seems if it improves off boost power it should also increase spool. I personally wouldn't mind the peak power decrease in trade off for lower rpm torque.

I wish there were dyno sheets of very similar cars but the only difference being the compression of the rotors. I'd be interested in the power curve vs. the peak number.

 

If your willing to go e85 seems like a no brainer way to make big hp at big psi/cfm

 

I would prefer higher compression rotors also because I have low hp goals, and want as much response as possible