Bluem

8.5:1 low comp. rotors ,what are the pos+ of runing
low comp rotors????????????????????????????????

20B Junkie

More boost?....

maxcooper

The lower compression is attractive for high boost safety. Keep in mind that they weigh more, so you'll need new front and rear counterweights. Or a different flywheel if you aren't running a light flywheel.

They are probably less prone to "denting" with the lower compression and greater mass, which is a plus. My stock rotors were dented when I had my engine rebuilt at 92K miles, used only with the stock turbos at 11 psi most of the time, never more than 13 psi. The denting may have been the result of some ignition retard (hot track days + lean + J&S installed), but I worry about it sometimes with my current single turbo setup.

-Max

Bluem

does power change by runing them with higer boost
and how much are they

JBC

I am guessing you are referring to the 8.5:1 rotors in the 1987-88 model of the 2nd gen turbo. It's funny that I have never really heard this question before. I would guess that this would be strictly for a track driven car because power off of boost would be down but it would allow you to run a few pounds more on pump gas. Maybe someone familiar with the math could calculate how much. I bet mazdatrix or racingbeat sells them. Probably about 500-600 bucks apiece.


I remember reading an article on Turbo Magazine awhile back profiling Kieth Ta's supra. He had built the engine and lowered the compression to 8.0:1. I think he made something like 750-800hp on pump gas with his twin T-66's. But I haven't really heard lowering the compression discussed on this board. I think improvements were made in the rotor design from the late eighties to when the 3rd gen was introduced which is why this has never come up. Most of the quick drag cars don't have a problem running high boost on the stock rotors which is another reason.

Bluem

i read something a wile ago that low comp. rotors are used for race cars...

T88Kid

Denting on the rotors is cuased by detonation. This is why I went with lower compression rotors on my motor rebuild.

Mario

T88Kid

If I am not mistaken T2 rotors are better than the rotors on the 93+ cars. They are also lower compression.

Mario

20B Junkie

what the? Really.......huh

SPEED_NYC

iTrader: (3)

I thought I was the only one. My FD has 88 TII low comp rotors that have been lightened and ballanced. I also had them cut for use with 3mm SE seals.
ppl say that you will loose power off boost, but i dont really notice this. as for increased weight, you can always have them lightned by machining away material from the rotor sides. besides, for drag racing having a little more rotational mass never hurts. this is why most drag racers (except me) use stock flywheels instead of lightweight ones.

I use a light steel flywheel from racing beat, because the stock 88 TII flywheel is TOO heavy for my tastes. It is like 10lbs heavier than a stock 93 one.

Mercury

I was thinking about goign low compression rotors on my next motor because that will allow me to run more boost on 91 octane.

This also got me thinking... what if when the RX8 hits the market w/h its hight compression rotors, all someone has to do is find a way of making low compression totors for it. Then you could turbo charge it. This would alow mazda to release a reliable car... and allow the tuner to do some amaizing things with it as well...

680RWHP12A

low compression rotors allow for less chance of detonation, not more power... thats why in 93 the compression ratio went up to 9-1 from 8-5 ... the low compression cars were slggish, down on power off boost and were often hard to start due to low compression...I have tried both and the only difference i noticed was with the higher compression[9-1] the car had better throttle response and used slightly less gas,on the other hand with the low compression rotors[8-5] you could rur slightly higher boost on pump gas without detonating....I have never seen dented rotors, to do that something serious has to be wrong..... Abel Iberra uses the 9-1 rotors with 30+ pounds of boost and he dosn't dent them! One last thing, to get the same power out of a low compression motor you have to run more boost to make up for the lower compression engine so ultimatly wich engine can make more power, seems obvious to me......

RETed

maxcooper is right - the Zenki FC rotors are less prone to damage (i.e. denting) from detonation.

Abel Ibarra has already done his homework, so he has detonation under control.&nbsp Those who are still trying to "perfect" their tuning of very high power (500+ hp) rotary engines would like the fact you don't have to throw the rotors away after one incidence of detonation at 20+ psi.&nbsp All the Japan tuners running big numbers usually run these rotors for their durability.



-Ted

Bluem

**** it im buying a subaru wrx and will buy a rx7 for
drag racing only im from Puerto Rico some good tunners
out here like "siguel" jose torres(siguel racing)=$$$$$$

680RWHP12A

sigul geys my respect..... and he uses 9-0 rotors!!! 7-0 @ 195........ he's the ****!!!!! why go pistion when you could go rotary!!!!!!!!

maxcooper

Here's what my dented rotors looked like (scroll down):
http://www.mazdatrix.com/faq/boost.htm

-Max

Kurgan

I've had both kinds of rotors in my T2. My most recent 13bt had 8.5:1 rotors. I would not do it again. They are down on power in the lower rpms (as well as the higher ones, but not as noticeable). It takes them longer to spool a larger turbo (not HUGE, but I was using a 60-1). You can theoretically run more boost on a the lower compression rotors, but I think the trade off for more lowe end is worth the 2 psi extra that the 8.5 rotors would give you.

My 20B has 9:1 rotors in it and I plan on running around 13 psi with the stock twin. This winter, when I upgrade the turbo system (haven't decided on either dual 60-1 turbos or a single Garret GT42), I'll run 20 psi at the track, maybe 25 if I go with the GT42.

E6KT2

I will trade my 8.5's for 9.0's. They're still in the engine so no pics, yet. I want a little more low end and a higher redline vs. the increased rotational mass of my 8.5's.

680RWHP12A

find the right tuner and you wont have to worry about making less power .... and denting rotors...if the factory can do it then somebody else can........do you think they only boosted 12psi,,,, i dont think so .... the factory techs know alot more than you know!!!!!!!!!!

maxcooper

I am not quite sure what you mean here, but I am sure the factory engineers know more than I know, and I am also sure they had different goals to shoot for in tuning the car. I am not saying 8.5 rotors are the way to go: I had the choice and chose 9s again, in fact.

There are some hard facts about compression and IC engines that are worth figuring out. How much more boost can you run? How much power is lost off boost? I'd be interested to hear some answers to these questions that included numbers. At least with those answers you'd have a good explanation behind a choice one way or the other.

-Max

RICE RACING

Here is a really good source of information.

1988 F1 turbo F1 car, Honda engine ran 2.5 bar (abs) around 21.75psi (gauge boost pressure) they ran a compression ratio of 9.4:1 to get the best power from the engine while not suffering detonation on a lean mixture, read 14.7 to 15.0:1 !!!!! In some racing conditions to increase racing fuel efficiency.

This was done on a blend of pump gas and Tolulene in this state of lean running with a hot charge temp they got the best BSFC with "reasonable race power while still no suffering from detonation.......sure it is on race fuel but I will draw you to the fact that the fuel measured no more than 100 octane on the RON std test.

I settled on 9.0:1 rotors for my rotary engine for the reasons of best efficiency and power in the 1.5 bar boost and below range, I have run my car only ever on 98 octane (RON) pump gas and with water injection, on my dyno run in which I made 472rwhp (around 566 bhp) I ran my car as lean as 13.7:1 with no signs of detonation, on a charge temp of 45deg C, with a hotter charge temp the A/F goes to around 11.5:1 or richer for saftey margin, my engine on 9.0:1 comp is very fuel efficient, it is a daily driver so this was a high priority for me, I week in week out get 400km to 50lt of fuel (city driving) wich is around 22mpg or 12.3lt to 100km.

I think that 9.0:1 is a real good compromise, and with water injection I have been able to use 1.5bar boost while still have a very efficient engine, even when compared to a piston engine of similar output.

Just what I have experienced.

Kenku

Actually, it was 84% toluene with the rest being heptane, which was just there to supress the measured RON without actually, in practice, doing much. Which is a bit farther from pump gas... but Formula 1.

... and the only reason I know this is because I always use that engine as an example in technical discussions.

RICE RACING

I was not going to get too "technical"

Excellent to see another member with a good knowledge of history, did you know they test three different blends of fuel in that engine, I have the exact ratios of Tolulene somewhere in my Files. They managed VERY good BSFC figures, a marked improvement over the 4.5bar engine the year before, mainly due to the higher compression ratio allowed by the lower boost limit set by the FIA. Typical of Honda though they never released exact timing specifics for best power, just MBT or detonation limit !! LOL

Kenku

*snicker* I guessed that you were holding off, really. I don't know about the development blends unfortunately; just the final results.

Hm. Now I have to wonder what various fuel blends they were sticking in the Schnieder Cup racers of the late 30s would actually do in terms of resistance to detonation. I mean, I know they worked incredibly well at the time but... of course, on the other hand, they weren't worried at all about BSFC, as evidenced by how incredibly pig rich the "ultimate" blend burned.

... but that's even farther into history. And my notes for that are at home.