Top speed problems
 

can anybody help me ? I attempted to see the top speed of my 2004 231PS yesterday and it was pulling very well up to 135 when i changed into 6th , it gave me a few more mph and seemed to stop at 140mph only doing 6500 rpm maybe 7, (was trying to watch the road aswell lol) I have read threads on ecu speed restrictions and i have also read that you should just keep pinging it in 5th to achieve top speed. My friend was tailing me to check speed in his supercharged jaguar (monster !) and we both agree that the car shouldn't pull the way it does to 135 and not have any more left.............is it restricted ? should i of kept it in 5th ?...............is it fucked ?............Please help

drag, wind resistance, friction, tires, type of road, altitude, humidity, ambient air temperature.


read.


And i am going to turn a cheek and assume that this is being done on a track.

Add overall engine health etc.
I don't understand these threads anyway, top speed an useless method to determine a car's health.
Of all the straights i did i passed 170mph on just one (Doettinger Hoehe...) and it was scary as hell to say the least.

Yes i understand that conditions may affect performance , but not by 15 to 20 mph to get the reported top speeds. And i am not trying to determine cars health either. I am a petrol head who buys a sporty car to put it through its paces and top speed is important to me. Test was done on local abandoned airfield where top speed is achievable in any car, so very safe. going back soon to try holding it in 5th, if it goes bang then so be it. For the money we pay for them we can just buy another engine and still be spending less than a lot of other sports cars lol

I know for a fact that you lose speed by shifting into 6th. Keep it in 5th and you should see better results. I hope your not doing this on the streets because that would be extremely reckless

What if you have lost 15% of your power because of poor engine compression and weak coils?
My results don't matter much since i have different gearing and a modified car but still i have seen many rx8 reach 250ish km\h in a long enough straight.

Thanks bse50 , a power loss seems to be the most appropriate answer. I was hoping someone was going to tell me that it may have been ecu restricted but never mind. My dad owns a garage and i myself have a decent knowledge of all engine matters , apart from the rotary. Is the anything internally that can be replaced after wear and tear, rotor tips or anything like that. I think i'll go and get it dyno'd asap and try a compression test , also can you get uprated coils ?

Apparently you have a lot of catch up to do on these boards.
Good things to do anyway:
Cleaning the MAF\Iat sensors (and throttle body). Fresh plugs. Check the catalytic converter and engine compression.
Coils tend to fail, a quick search here will tell you why and who produces viable solutions.
Premix.

You can't just replace the "rotor tips" (apex seals) to restore compression. Rebuilding an engine is much more than that unfortunately.

Thanks again , my Dad said he checked compression when it flooded once and was all ok (i've just spoke to him) It had new plugs 12 months ago (i work at sea so this was actually only about 5K). I'm going to go and check the other things you mentioned now and booked in for a dyno run at 3 O'Clock so ill pass on the results. Thanks again , your a star :-)

Was the compression test performed with the appropriate tool? Using piston engine testers is not that good.

Dyno results are in. At around 6500rpm the 'dsc off' light disappeared and the skid and abs light came on. The mechanic said the engine note changed so thinks that the dsc was not letting the car perform correctly. At the same time as the lights came on the curves take a nose dive and then only recover slightly to 180 bhp. Just before the dip at 6000rpm curve shows 135 bhp and 160 torque. I have tried to compare this to other rx8 club members curves and seems a little low at the 6000 mark although everyones curves take a dip at the same time as mine theres recover, mine is more like a plummet than a dip. The good news is that he said engine sounds lovely and upto the lights coming on car is performing well with a lovely straight power line rather than a curve you see on most cars. Do you think i have a dsc problem or a related sensor problem ? this is the exact rpm when when car stopped pulling in 6th at 140mph last night !

Smart shops dyno the cars with the controls off... :)
The "dip" may be normal or be a stuck or rattling\not properly functioning intake valve (check its solenoid in case).
180bhp may be normal or on the low side depending on several factors like dyno calibration, coils condition etc. PM Charles R. Hill about the coils... ask Arnie or Shifty how they like theirs if you have any doubts ;)
Stock rx8s dyno anything between 180 and 200is bhp. Dyno error can account for up to a 5% difference so there we go again. A compression test is usually the best and safest way to see how the engine is doing.

The dsc was off but seemed to turn itself on at the 6500rpm area. It seemed like it could never be fully off ! The mechanic said without the dip was looking good for a lot better result and said that there was definately something preventing the car from 'using' all of its power , just like the dsc does ! He insisted that the dip was a result of the skid and abs lights coming on. Is there a way to completely turn the controls off rather than just the dsc button ? I'm going to get some new coils for it and check the other things you mentioned. I cleaned the MAF sensor before i went to the dyno. I have read a few other comments about ignition problems causing low readouts on power so coils seem logical , is there a way to test the ones on or just have to bight the bullet and get new ?

How To Dyno The Rx8
Seems you need to pull the DSC fuse in order to completely turn it off.

Getting the hang of these forums now. found all the answers i need on coils etc , thanks bse

There are 2 steps to turn the dsc off.
A not so subliminal message reads: click the link in my sig, lol :)