I had a compression test done today on my T-Rex and the results look good. 1st pix is front, 2nd is rear. Any opinions on this?
Overall good figures.
I notice there is a rather large discrepancy in the rear rotor, namely between the 7.9 and 8.8. A sign of uneven wear imo...
Rear rotor is going, although saying that, how many miles has the engine done? It takes a bit of time for everything to run in (like piston rings on a rubbish piston engine)
The car stood unused for a few years which a reading was taken in 2010:
7.8, 7.7, 7.6 front
7.8, 7.6, 6.8 rear
I understand the engine was rebuilt at 61,370 miles in 1999. And rebuilt again at 89,764 in 2003. It had many services and loads of oil changes in between too. The car also spent a little time in Spain until 2010 when it went straight into UK dry storage.
The mileage at the moment is late 97k, I had the oil changed twice very recently (between 300 miles) as I was advised to do this due to the long storage and to ensure no contamination.
Perhaps the compression improved after I had a few small mods done recently like a new intercooler, racing beat air flow unit, k&n etc...
Was told by Dave that these readings are as good as new and the odd lower compression reading is not a worry as there was a pefect technical reason behind this which he explained but at that point I kind of got lost :rolleyes:
It seems very good results and that what counts :evillaugh
Did a dyno on the car yesterday and noticed the stock ecu seemed to be reducing the boost after 4500rpms, up to 4500 it was boosting .8 but as revs went higher it fluctuated a lot and downwards to a low .3 at the high rev end. The engineers will check all the relevant sensors to ensure they are fine but meanwhile I bought a R.E. Amemiya Redom type \'B\' ecu which should help. I chose not to go for apexi at this time due to my car having only a BPU and a decat. Once this is done hopefully on friday or monday I can take it back for a re-run on the dyno.
By the way the descrepencies on the compression readings is according to Mazda are well within tolerence levels and in a nutshell the variations are due to very slight imbalances. Apparently rotors are balanced at factory and graded something like A, B and C. Pairs can be matched like A and A or A and B but not A and C.... I think this what I understood and as it got more technical I then got lost.
An A and a C rotor can be paired together. In fact a C will go with any other rotor as it is in the middle of rotor weights from A to E. On a rebuild they should not be more than two away, but for a really good engine it is best to try to get the same weight of rotors.
The low compression on one face will be a side seal gap being slightly bigger than the rest. Nothing to worry about.
Beware of a chipped ecu, they can run more boost but run lean as they are running higher octane fuel in Japan and can get away with it.
Regards
Carl
Oh and the boost dropping off is caused by something other than the ecu as the stock ecu runs at 10 psi,then drops to 8 psi on the changeover to twins turbo operation at around 4-4500rpm then back up to 10 psi again to the redline.
The issue is likely a solenoid failing or an air leak in one of the vacuum hoses.
Regards
Carl
Hi Carl,
Many thanks for your explanation and you can see why I got lost!
Betwwen idle and approx 4350 rpm its 0.8 bar
4350 - 6000 rpm its 0.6 to 0.4
6000 - redline area its 0.35 to 0.4
Lots of horsepower (217) till roughly around 4000 then it fluctuates up and down a bit all the way plus dropping a little closer to redline.
I will mention what you think it might be. I know the vacuum was checked and that was ok. Many thanks again.
Good news, all high power restored. There was something left unplugged somewhere in the engine bay..... hmmmmmm, what I cant remember but who cares as my t-rex is back! Right I will re-dyno it soon....
^^^^result :) ..... look forward to seeing the updated / revised dyno figures.... :)
Thanks, me too. I am thinking of taking an engineer (Dave) with me and we do an interesting test: dyno the \'stock\' ecu, then dyno the \'re amamiya\' ecu and then dyno an \'apexi\' ecu (tune it too). This way we get to see the results for all and I stick with the most appropriate.
By the way I remember what the problem was; the air pump was unplugged! Why I dont know :Hammer
There was a very small water leak spotted and the guys at the moment are fitting a new gasket just to be safe.
Quote from: rx7.eu;811658Thanks, me too. I am thinking of taking an engineer (Dave) with me and we do an interesting test: dyno the \'stock\' ecu, then dyno the \'re amamiya\' ecu and then dyno an \'apexi\' ecu (tune it too). This way we get to see the results for all and I stick with the most appropriate.
By the way I remember what the problem was; the air pump was unplugged! Why I dont know :Hammer
There was a very small water leak spotted and the guys at the moment are fitting a new gasket just to be safe.
I hope you are using mappers that have experience with Rotaries. Could be an expensive day if not. When running and tuned well they can be strong as hell I can testify to that but they do not put up with any mistakes.
What the man above me said! Don\'t make a costly mistake!
Also how can you get a higher compression when the car has been stood for a while, ie in 2010 you had readings of 7 and then in 2012 you had readings of 8
:xconfused:xconfused :xconfused
Quote from: Rzla;811673Also how can you get a higher compression when the car has been stood for a while, ie in 2010 you had readings of 7 and then in 2012 you had readings of 8
:xconfused:xconfused :xconfused
Lots of oil
Thanks, fully aware of the risks, guys have 30 years combined experiences and know what they are doing.
Was told its not unusual for compression reading differences as it can be due to a number of factors. Perhaps back in 2010 it had old or not so good oil whereas I recently had it changed twice in a space of 300 miles using the best mineral oil, plus adding a better air intake perhaps also contributed. I am not an expert in the whys here, perhaps someone who works on rotarys can contribute to the possibilities here? i do know the car was also stored a year before it came back to the uk and the owner then rarely used it plus was driven gently (slowly). Perhaps the engine rebuild around 9000 miles ago is also contributary, so perhaps it is only starting to run in and being run hard a few times over the last week has also helped.