Its cool RageRace. It does sound like the high comp might be better for a daily driver. I just know that when it comes to the track its all about more power.

Maybe we should start are own rotary magazine, we could test ?'s like these. This would be an awesome article, higher a credible builder to build us two engines for the same car. Same everything just different rotors, then tune them for max HP and find there 1/4 mile times. THE ROTARY TIMES

 

Here it goes....

All 13B rotors

Year - Comp - Weight(lbs)
74-78 - 9.2 - 11.58
84-85(GLSE) - 9.4 - 11.58
86-88 N/A - 9.4 - 10.04
86-88 Turbo - 8.5 - 10.04
89-92 N/A - 9.7 - 9.54
89-92 Turbo - 9.0 - 9.54
93-95 FD/Turbo - 9.0 - 9.54

I have personally used 8.5, 9.4 and 9.0 and like the 9.0 the best......lighter and easily run 18 psi on pump gas.
The 8.5 will run a bit more but don't rev as fast.

In my Turbo2 I noticed I made about the same hp with 9.4 with ~2 psi less over the 8.5 but there's many other variables.
The higher you go on compression you will need to run less timing and boost....simple rule !!!

Hope this helps..
JD

 

Excellent information Boostn7.

So you say the 9.0:1 are best overall that you've run. But say for a high HP street/drag car, how would 9.0:1 comp rotor compare to 8.5:1? Is better, or worse?

Again, this thread has lots of great info. Some mod should sticky this.

 

Im actually selling the 9.4 Gsle to get the 9.7 91' N/a ones. Has anyone personally witnessed or have alot ofd experience with changing just the rotors compression and have any records or testimonies of the results. Thanks to Boostin7 for the compression ratios

 

Correct me if I`m wrong, but I thought that on engine with low comp rotors/pistons the turbo will have to compress more air into the engine to get the same boost pressure,as on the same engine with high comp rotors/pistons..?
This is because of the low comp engine has got lager volume inside(ccm of the engine + the ccm of the combustion pressure) than a high comp engine.
So on a low comp engine you will have more air compressed in the combustionchamber at let`s say 15psi than you will on a high comp engine.
More air means more fuel, and that means more power.
So why does an engine with low comp need higher boost to make the same power as the same engine with high comp.
I thought the power would be lower off boost and higher when on boost on a low comp engine compared to a high comp engine..?
Can anyone explain this for me?

Cheers
Ronny

 

One more thing, how much boost can you safely run on pump gas (here in Norway we can get 98 octane on every fuel station) using 8,5/1 rotors, the rest of the engine is a steetported T2 S5 with a kkk k27 turbo?

Cheers
Ronny

 

Can RX-Rotary, Crispeed, Rice,Ernie, (or who ever else is knowledge with 500hp+ cars)etc chime in on this debate please.
JT

 

i am not understanding why there is SUCH a debate. what is the big deal to just use the 9.0's? if the debate in your head is saying because of 2 PSI of boost or so is going to cause you to run a lower HP rating, why not turn the bost up a bit? if THAT causes you to run out of the turbo's efficience range, maybe you need another turbo configuration.
the S5 n/a rotors *will* work. there is a VW bug localy w/ them in there running good on them, but i believe they were used due to being the only thing he had available. runs S6 stock twins at 18lb of boost also...
as stated before by John D, you wont need as much advance if runing higher comp rotors. me personaly, i had a S4 TII and had similar results as John D. the motor revs much quicker when FD rotors were swaped in. not sure exactly what it was about it, weather it was the comp ratio or the weight, but it felt (in a way) as if a lighten flywheel was added.
this debate can probobly go on forever. its like back in the day the two schools of thought on tuning n/a motors on the cheapest gas you can find, or on good gas with more advance....
and for the record, i do not have a 500rwhp sheet under my belt, but i can offer a little bit of input. also, if/when i do, i will most likely keep it to myself.

 

whats the difference between the 89-92 Turbo and the 93-95 FD/Turbo rotors
nothing i have read mentions a difference but here in Australia they are a different price???

 

I have been running the 8.5 (S4) at 22 PSI on pump gas and water injection on a 62-1 turbo.
I am planning on throwing a S5 Jspec in there, using the same system.
Do you think I will need to decrease my boost?

 

89-91 turbo II rotors and FD rotors are identical weight and compression......but FD rotors come with bigger selection for bearings and outer surface are completely CNC machined including the compression pocket making them identical vs the 89-91 ones which are cast(pockets).

RXtasy1: YES....at least 2 psi....you should be about same power levels with more power off boost

OK...let's understand static compression....
Simply the ratio of the chamber volume @ BDC(biggest volume while port is open) to the volume @ TDC(smallest...). So, if there's 80cc @ BDC and its then compressed to 10cc @ TDC then we have a static compression of 8.0:1.

Now, to make more power we need to increase cylinder pressure and burn more fuel.....one way is to raise static compression or increase it via boost resulting in increasing the effective compression.
Effective compression=((boost psi/14.7)+1)*engine compression.

Engine with 9.0 compression running 14.7 psi and a 8.5:1 comp engine running 16.5psi will have about the same effective compression (~18:1) and same overall power......difference will be in the power curve. The 9.0:1 engine will be more efficient off boost with better throttle response as well as better gas mileage.

Does the 8.5:1 motor have higher potential for hp??
On the extreme side of a full race motor..YES
The fact that its able to contain more volume is very minor but at higher boost levels it will be an advantage.

Hope this helped
Later,

 

I have a set of good 13B -rew rotors for sale. If anyone is interested in them, email me at Jrbjag@yahoo.com
Best,
John

 

bump for good info

 

bukp for good info

 

anyone have any opinions on what would be the best street and circuit(not drag) set up? I am planning to go with 9.4 rotors but have 8.5 and 9.7 laying around. THe engine is going to be used for circuit/track (still not drag) and street. The owner of the car wants the engine to last a decent amount of time but is not unrealistic with his engine life expectations. He is looking at a little over a year. I have not built a High Comp Turbo motor and am curious as to how long they tend to live?

 

How long the motor lives depends on how good the builder is. Assuming the engine builder knows what he is doing, and doesn't go too radical on the ports (sufficient corner seal ride, water passage-to-port area, etc.), then it is all left in the tuning.

How much horsepower is he owner looking for? This question is almost always how you will determine what to use to build the motor.

 

bump

 

im kind of new to the the whole comp. comparison but recently i have talked to a friend that has his GSL-SE 9.4's in his FD lightened by RB and tells me his off boost response with a T04R from HKS is actually the best response for his set up. my question is would there be any noticable difference with lightening any rotors for a street application and would you see that difference in a dyno graph since there is less rotational weight to move and better response?

his setup:
GSL-SE rotors lightened by RB
HKS T04R turbo upgrade with HKS R-Type intercooler
mild intake/exhaust port polish
3" downpipe with 3.5" exhaust
APEXi Power FC
720cc primary and 1000cc secondary( don't remember if they were at 100% or not)
3.90 final drive ratio
running 93pump gas with 104 octane boost
boost for the street is set at 5 psi(for fuel economy) and when racing is cranked to 25psi

if i remember correctly the dyno graph showed that with 25psi he made 520hp w/ 470-80 lbs of torque. but can't remember at what rpms he made it though

 

Something doesn't look right whether that's 520bhp or rwhp. With a 720/1000 injector combo, there is no way he has enough fuel unless he has his injectors stuck open and is forcing fuel in through upped fuel pressure.

I would like to see a dyno graph.

 

Any thoughts on the renisis rotors in the REW?
being that light with high compression would be nice

 

I am installing my new high comp turbo engine on Tuesday and will be tuning with Steve Kan on Saturday. I'm in Cali so we can only readily get 91 octane. We will not be tuning for dyno queen numbers but only for how I drive it daily and at the track (same setup).
The car is a daily driver and sees open track events at least once a month (when it runs ).

The eninge:
Built by Pineapple Racing
Large street port
Series 4 NA rotors (9.4 compresion ratio)
3mm ceramic apex seals
Series 5 plates
Series 6 rotor housings
Series 5 lim
Series 6 uim
GReddy fd tb elbow/ modified
No smog equipment or cats
3" dp

The turbo:
Garret T04R compressor cover w/
T4 non-divided turbine housing .96 A/R P-Trim

I also have an Aquamist 2d system to cool the charge some.

I have no idea what the power will be like but will let the thread know when we're done.

 

any updates???

 

WHEN is somebody going to make a set of 10-1 comp. ratio rotors, but manufactuerd from titanium 5.5 lbs. each ! now thats an idea come on GUYS think ahead of the box not out of the box. RON

 

Not going to work biggest issue is expansion rates and galling.
Any updates on the renisis rotors?

 

Turboed 10:1 Compression rotors in an S5 FC? Hell, twincharged 10:1 Compression rotors in an S5 FC?