rotaryPilot

Hi all,

After running a lot of track drag races I came to the conclusion that my car seems to have some power issue.

To be more specific in a track and controlled environment I raced more than 6 times against a similar powered car. In detail the race included 2 RX-8 192ps 5MT. However my car was always behind at least 2 car length. Further, we even changed cars ( I drove the other RX-8) and the results were the same. Always my car no matter the driver was behind by 2 car length. We have even checked our tire pressures our fuel load and both cars are 100% stock. The difference was apparent when both cars were running with 4th gear and above 100Mph.

The difference in cars is that the faster car has 7000miles in odometer whereas my car has 26.000 miles in odometer and I have never changed spark plugs. So as my check list in order to find the power issue will be the following things:

1) Spark plugs: Mazda says to change in 37.000 miles and I have 26.000 I have not changed before
2) Coils: Although there is no sign of burnt coils or drivability issues I think I must check
3) Catalyst: Ι have visual inspect it at 18.000 miles and there was no problem. There is not any drivability issue (the car revs fine, no check engine etc)
4) Fuel Pump : No issue again here but I do not know anything else to check
5) Compression: Although an RX-8 with low compression seems to run very good with no power issues I have never checked my car’s compression and I will perform a check.


Additionally my car revs very good and DOES not feel underpowered. As a rough estimation it seems that my car is about 10 horse power under the other car. What do you people think about this case? Do you think that I should check something else that the list above?

Thanks

Brettus

iTrader: (2)

put in premix at 100:1 then go out and try again - would love to hear the results .


so these are both 5 speed 4 port rx8s ?

rotaryPilot

Sorry for my ignorance but what is premix 100:1 ?

Yes both are 5 speed manual 4 port

rotary crazy

re-set the ECU drive it hard for a while before trying againg

check your air filter

StealthTL

iTrader: (1)

Premix means to use some two-stroke oil in your fuel.

100:1 means a ratio of 100 parts fuel to one part oil, so 500ml for a 50L tank.

S

chetrickerman

that is a lot! i second checking the air filter. i think it is suffocating the engine, cause at 100 mph speeds, the engine should have a lot of air flowing in

rotaryPilot

Thanks for your answers guys.

All the drag races have performed with a drop-in K&N filter and I count 5K miles without having cleared it. So I believe that it is not an air filter issue.

What do you think about having done 26000 miles with the same coils and spark plugs? I strongly believe that my plugs need a change but I cannot draw any conclusions before changing them.

Also I suspect a broken cat only because I have 26000 miles on it. The problem is that apart from visual inspect it I do not have any strong evidence of broken cat. No cell , no strange metallic sounds, and the cabin temp was always high.


I have heard that lower compression does not affect the performance. Is this true? I will have a compression test but this is something later on my list.

StealthTL

iTrader: (1)

Personally, I would reset the computer then clean the MAF sensor, it could have K&N oil on it.

S

rotary crazy

check the MAF sensor, reset the ECU, spark plugs,and check the compression

rotaryPilot

checked the MAF sensor and it seemed very clean. I only cleaned the temp sensor which had some dust on it. I made a reset ECU and drove hard for some miles.

I think that next thing will be spark plugs and coils.

What about the compression? Many people claim that low compression the car runs pretty good (until you can start it then it runs good). Anyway compression test is on my list also.

eviltwinkie

Low compression means something is up with your engine...when searching for used RX's you want to see the compression test and verify its not too low...

You generally avoid the low ones...if that tells you anything...

Haze

26K miles you need new spark plugs IMHO. Mine seem to be spent at about 20K

rotaryPilot

^

How did you find out you needed spark plugs at about 20k?

rotaryPilot

I had checked my car at idle with an OB2 scanner and I noticed that the catalyst O sensors graph values tend to fluctuate. However, I checked my friends car and the O sensors graph values tend to be stable. Do you think that maybe the fluctuating values of the O (lamda) sensors mean something?

otakurx

I am having similar issues, but seem farther along. I have all described plus a real rough idle (somtimes idles close to 1k because it shutters too much any lower), still starts well. Also has gone from 22mpg at the beginning of last week to 13mpg now. Now I had something similar and it was plugs so I swapped them out. I am thinking it is the same thing again. My question now is there are 2 different sets shown on sparkplugs.com, the stock ones and some hi-pref ones. Which would be better?

Stock NGK's or the Hi-Pref Denso's (says they are for racing)

ManicMechanic

To, rotaryPilot, Check your compression while you have the spark plugs out, it will save time later. Coil packs on the 8 are a high failure item, however not at your milage (first time for everything). If you are tight with the other drivers, swap coils and see if it makes a diff. Have you checked your oil level lately, what weight are you running, what kind?????? Royal Purple has been proven to give a Chevy 350 (stock) an eight hp gain at 3500 rpm. I never ran my car on a dyno, but I feel the diference, however subtle it may be. 5w-20 weight is recogmended in the latemodel RX-8s, It just feels smother than CastrolGTX that I was running in the past. It's expensive at $7.59 a quart, but it's cheeper then coil packs!! Try it first!! By the way don't go 6,000 miles between changes, I don't want to read your post about a blown engine, unless it's done with a supercharger!!! Cleaning the MAF is a good idea since you are running a K&N, you should throw it away and go back to paper!!

ManicMechanic

About the two sets of sparkplugs, you need both sets. Put the stock plugs it the engine, and swap them out at the race track, then swap the stock plugs in for the ride home! Spark plugs will last longer if you rev it under load to at least eight grand every time you drive it, yes every time. By the way 13.5 MPG is the best I've ever done.

otakurx

I normally average 22mpg, I got 19mpg when I got it exactly a year ago with the stock plugs in (15k miles) changed the plugs to 3rd gen RX-7 plugs at ~42k miles and started to see a consistent 22mpg (after a short drop to 15mpg). Now with it down to 13mpg I am looking at trying the NGK RX-8 plugs again (now at 65k miles) The K&N filter brought me up to 20mpg and smoothed the idle out (put in at ~30k miles) I checked it 2 oil changes ago (~ 59k miles) and it looked pretty clean and everything was clean behind it. I have been thinking about the coil packs but not sure yet (since they are so expensive).

Note: I used thicker washers when I put the 7 plugs in the 8 to makes sure nothing rubbed.

Note: Yes I know I have put 50k miles on her in one year.

ManicMechanic

I thought the carbed rotary was an A12. I don't know much about the RX-7s except for the engine #s, 13B was fuel injected.

shaunv74

I'm not sure why you guys think coils are expensive. They're abour $30 each at the dealer. Not much more than spark plugs. If you have an '04 with the original coils definitely change them to the new part number. Make your changes 1 at a time to see what makes the difference.

And oil shouldn't make that much difference. I do agree with pre-mixing when on the track. But if there's something wrong than you're just covering up the problem. It could be also a plugged cat. Take it to the dealer and have them physically inspect the cat. by unbolting it and looking inside. It can still go bad even though there is no CEL. Make sure they check it and verify visually that it is not plugged.

nycgps

iTrader: (1)

I vote for change your plugs.

Then add some premix.

chetrickerman

change the coils to a new part number? what part number is that? and why?

otakurx

Both the 13B and the 12A had a carb on the, just different years. the RX-7 never saw a carbed 13B from factory tho.

rotaryPilot

Ok I understand that some things have to be checked out in order to be certain about the problem. As I said my list has the following

1) Coils, Spark plugs and compression test. I think it is not bad to change coils and plugs having 26.000 miles on my car. I am not sure if compression is responsible for the low performance because I have heard that even low compression RX-8 do not lose in performance.
2)catalyst. Yes I will visual inspect it.

I guess that if 1) and 2) are checked and everything is ok the only thing that remains is fuel pump.

Concerning my oil I inspect the level very frequently and I use only the MAZDA suggested Dexelia 5-30. I know that the American specs RX-8 use 5-20 but the European specs use 5-30.

zoom44

if you have a sligth compression loss adding oil to your fuel (pre-mix) will help th eengine SEAL better improving the compression and therefor the power. try the premix then retry the races. BUT have someone take the Catalyst off and visually check it inside first.