im looking into working out a way to mod a pair of rotors for lower compression.
i think i want about 5.0:1 now if i was to just cut down into the combustion chamber on the rotor, making sure that all three faces were equal cc's, how far can i go before there will be problems?

now what i cant figure out is.... the overall rotor weight needs to be a certian weight so the counter weight will work. so i take s4 rotors down to s5 weight...
alright well how big of a window is there before the motor is off balence?
does the weight need to be dead on to the gram?

if one rotor face is not exactly the same weight as another due to my cutting it out.... if its just a very small aount off then it should be ok right?


clr sells the scalloped rotors that are also low comp... im just looking for low comp.

 

You need to do more research.
What you're proposing does not make any sense unless we're talking about 100psi boost on nitromethane?


-Ted

 

the clr rotors are low comp... they claim to have cars running 25psi on pump gas daily driven making 500hp.

im trying to figure out how to get a set of lower comp rotors.... how much lower is still a bit up in the air. but thats why im posting this. ill get ideas from you fart smellers.

 

8.5 from an s4 turbo not low enough?

 

You have no need for that low comp. It would need 20psi just feel Na

 

5.0:1, lmfao

 

ok well we have all decided that 5.0 is too low. thanks for offering your knowladge in a sociable way.

i have been doing more reading and searching. Many people seem to think that 8.5 s4 rotors are plenty low. Maybe so... but just for sake of argument where would someone get or how would someone make a lower comp rotor?
8.0, 7.5, 7.0,.... you guys know MUCH more then i do. Im asking for a open mind on this subject, even tho its not what your used to.

My thinking comes from a brain storm session with a local 240 guy that has is running a very low comp motor. His head gasket is thicker then i though possible. It was built to rely on the big turbo for power. he has some turbo i have never heard of before... some high dollar ball bearing one.
he tuned with high a/f and agressive timing when off boost and the car spools very fast. then normal target a/f and egt then on boost. Yes when off boost its gutless... but its so easy to get boost its not a concern. The low comp allows him to run 20 to 25psi on pump gas with not even a hint of knock.


When on boost this car revs and moves like a motorcycle. I have seen him walk 600hp beasts. The high boost makes the power... without it the car is less than n/a.

 

no need...8.4 is just fine
for a street car

see to make alot of power
you can't rely of Boost alone
your motor in N/A fashion should make 200+ to the wheels
and then add boost

 

I dunno what you're trying to do...

Basically you're just trying to scale down the compression ratio for more boost?
That's just crazy.

8.5:1 is just fine.
Hell, 9.0:1 are still okay, and there are many big boost engines making good power with 9.0:1 rotors.

IT'S ALL IN THE TUNING.

Dropping the compression ratio just to brag about big boost is a sign you don't know what you're doing when tuning.


-Ted

 

Look at the AEM NSX powerd Civic drag car

runs 6.5's in the 1/4 mile
and uses High Compression pistons
and runs those times with less boost then the 2JZ's in the class
relies on Motor Power not just boost

Listen to a interview
with Steph.P driver on the AEM car

http://www.speedsceneracing.com/Audi...ne05032005.wma

 

my goal is to make big power on pump gas

 

If that is your goal you are better off looking at water injection. Guys have successfully ran 25+psi boost on pump gas with water injection. And like RETED already stated it is all in the tuning. And your comment on the CLR motors well the reason they are making good HP numbers is that the rotors the way that they are cut give you power comparable to a bridgeport motor without the bridge. Therefore the motor is making more power than a comparable streetport motor and you put boost on top of that it is easy to see why they are making good power with those cut rotors. I will be sending a set of 8.5 comp rotors to CLR for future use and his pricing on the maching work is very well priced.

 

I remember seeing a factory race 13G turbo for sale in the 20B section. It was a full set-up using 7:1 CR on alchohol no intercooler.

13G parts are big $$$$

You could experiment modding rotors. The 8.5:1 will probably be the best starting point because of the relatively thick casting and low starting CR.

If it gets too thin machining the rotor face tubs you can try plasma cutting the tubs out and welding then in lower. If you put the rotor flat on a big heatsink and tig weld thin 1/8" beads in stiches from opposite sides w/ lots of time between welds for it too cool down it can be done w/ no measurable warping of the rotor.

A rotary specialty shop can balance each rotor then balance it to any full rotating assembly you provide.

A lot of work, but definitely possible- you should see what air cooled VW guys have to do for power cutting up heads, porting and welding it all together. You can do a lot w/ not much if you are willing to take the time. If you have to pay someone to do it- forget about it!!!

 

well if the limits on pump are 15 to 18 psi depending on who you ask... then lower comp rotors would push the det treshold higher. I have a t70 and would think that running 25psi on this turbo safly on pump would make up the loss of lowering the comp to say 7.5:1 and then some.
say i make 400rwhp on 93 at 16psi.. i lower the comp to 7.5:1 and only make 350 at 16psi... but now i can run more boost on pump gas right? so i up the boost to say ohh i dunno... 25psi. so now i make 450.. 500? on pump... woah. ill take it.

im trying to think out side of the box here...

whats the higest comp ratio would raise the knock threshold to 25psi on pump gas? seriously.

 

go ahead then
call racing beat and dish out couple grand for there custom casted rotors
or go to home depot and buy a dremel and get cracking...hehe

 

i was planning on it.

soooo we are back to the origional questions i asked in my first post.

what does a s4 rotor weigh and what weight do i have to get it to so the s5 counterweight will work. i im assuming that if i cut it down ill need to do it to a point to where i can use the lighter rotor CW.

what exactly is the weight difference? i searched for the weight of s4 tii rotors... and weight of s5 tii rotors... but after about 30 min of useless threads i gave up.


Im guessing the way to figure the comp of a rotor is to know the cc of the combustion chamber... whats the math to figure it out? how many cc is the stock s4 tii one?

 

http://www.mazdatrix.com/faq/rotorwgt.htm

 

http://www.mazdatrix.com/faq/rotorwgt.htm If you are going to be removing any material off the rotors you might as well get the whole assembly balanced. When I'm building a motor that is going to make some serious horsepower and see above stock rpm's I get the complete assembly balanced and I don't care if it's a complete matching assembly I still get it balanced. When you start short cutting things because of cost that's when your reliability drops dramatically.

Damn rotaryresurrection beat me by 2 minutes.LOL...

 

any guess on what the final comp ratio will be after taking exactly 1/2lb off each rotor to match the weight of a s5 rotor?

 

IMHO, low comp is the wrong way to go when looking for power. I raised compression in my high hp project, and i run 14 psi on 91 octane and 9.4 CR. dyno coming next week. its all in the building, tuning, and care you take of the car.

however, if you wanna do this, i wouldnt go lower than 7.5 CR, or you will have so little low end, you'll have to rev to 3 grand to build boost before you can move.

I figure you could get 7.5 pretty easy by TIG welding the compression faces and grinding them back into shape, without changing weight too much.

just my .02

pat

 

It's a helluva lot of work just to brag...
*sigh*


-Ted

 

i think making really high hp numbers on pump gas is worth bragging about... and fun to pwn the streets with.

im thinking of doing this while my motor is still good.. keeping the good motor un touched incase this dosent work out. If it is just a waste of time and i make the same power... or pop it trying to run 25psi on pump gas then i can put the stocker back in and tune to 15psi like a normal person.

 

This is a bad idea, J'. Stick with the 8.5:1 rotors.

Making big power on pump gas might earn some bragging rights, but I personally think it's just silly because pump gas sucks! It is HIGHLY UNRELIABLE from pump to pump!!!! Even if big power *is* made on pump gas, you can't run the kind of advance and aggressive timing on pump fuel like how you can on high-octane, leaded race fuel, like C12, C16, etc. You could net so... much... more... power .... with the proper kind of fuel for the job.

Keep it simple -- keep pump gas for low power and race gas for high power...

B

 

I'm not too sure about the highly unreliable part. I think that's been proven to be more overstated than is true.(Not saying your wrong so take no offense) As for being able to run more boost?? Boost is not power, Flow is.

 

No offense taken.

The issue I take with pump gas in its aforementioned 'unreliability' has to do with, I think, differences in vendors, their testing, their additives, as well as even simple mistakes made at the pump by the stinkin' truck driver that's delivering the gas. One other factor that makes me nervous is geography -- how much different is California gas as compared to, say, Texas gas? What additives are added in either state to try and conform to silly EPA standards?

It seems to me, overall that is, if you're buying a quality race fuel at $5+/gal, you're getting exactly what you're paying for -- it's reliable and guaranteed. That's where I'm coming from with all of this.

Besides, pump gas is still extremely volatile and it takes a chemical wad of soup in it to try and make it any better. Why risk a couple thousand bucks on parts and labour by trying to "brag" about using pump gas to make power? Even if it's do-able, I doubt it can be done reliably over and over and over again. Also, with race fuel, substantially more aggressive spark timing can be utilized to produce a heck of alot more power at the same boost as compared to pump gas.

I can appreciate the desire for people to try and make big power on pump gas, but it just sort of seems silly to me when you can dump 5-10 gallons of 117 leaded octane in, run a separate ignition and trail-split map, and crank out numbers well above 500rwhp with much less effort.

B