mates gota rebuilt rb25det runs like shit (gotta base tuned megashit ecu) anyway it smokes like a dog and not rich smoke oil smoke so he tested the compression and told me it hit around 135 per cyl ,i thought that was low (even tho im not a skyline person) then he tells me it was a cold test so i told him to get it to op temp then retest .100-110psi across all six now i know that aint right ,but then again it is a recent rebuild and maybe the rings havent bedded yet ! .any more RB knowledgeable guys have anything to say about thoses numbers!
sorry about my spelling
pollymay,
Oct 5, 8:00pm
that or his basetune is so bad he blew out the ringlands
Bedding in the rings means thrash the pants off it, however I wouldn't do that on a basetune so catch 22
chook90,
Oct 5, 8:43pm
I'd be doing the compression test myself - cold at that. There are many reasons for oil smoke in an RB and rings are just one of them.
thegravelracer,
Oct 6, 7:52am
yes well ive heard bad things about the chap up north's base tunes in the Mega squirt or better known as mega shit . i have seen the comp results my self and compared it to a very similar setup on another rb25det and the other engine was putting out 150 psi so . im guessing the ringlands are gone burgers
pollymay,
Oct 6, 9:07am
Megasquirt is a great system if you know how to use it, worlds better than messing with a stock ecu. However if you have not a clue you will blow your car up.
intrade,
Oct 6, 9:30am
how was it rebuilt! new rings on worn boors! or propper machined and then honed boors with new rings and pistons!
thegravelracer,
Oct 6, 9:45am
propper machined and then honed boors with new rings ,re machined crank and new mains,journals ect but re used pistons and rods
ceebee2,
Oct 6, 10:39am
!Turbo fault, head gasket leaking but to name a few. I do not rely on compression testers as they are notoriously unreliable depending on age. Their only practical use is measuring any differences between cylinders rather than the actual reading.
I use the cylinder leakage tester which is far more indicative of where any leakage is occurring and the % loss between cylinders is also accurate. It may even bubble up through the radiator if the gasket is blown /leaking into the water jacket for e.g.
thegravelracer,
Oct 6, 12:59pm
I agree iwth you and disgree ,our dyno tuner has used them and will use them but hates using them .As for re mapping a stock ecu i only have experience with crome and other honda data-logging setups (bre for tuning Crome for smoothing and i swear by it .id never go out and buy a cheap setup like megasquirt or ever pay the way with link when the older eprom tuning works brilliant
1ollie,
Oct 6, 3:40pm
For starters try another tester as they can play up or be of low quality, it should be in the 150-180psi sort of range ideally but I have seen a few RB's with numbers around the 120psi mark and they went fine with no problems(not rebuilt of course though) or as ceebee2 said do a leak down test as that will give you a better insight. It is very hard to say with out know the whole story from start to finish as there can be many variables with whats(and how its) been done. What was the motor like before rebuild like was it going fine! as you say reground crank which makes me wonder why it needed that!, has it got an after market turbo!, is the person who did all the work skilled and reputable etc! as normally you can just give even a tired smokey RB a freshen up like what you have described with no problems like I have done many and seen many more done and how was the car ACTUALLY driven with this "base tune"! as one persons definition can be different to another persons as you could imagine.
1ollie,
Oct 6, 3:51pm
Now this is just my honest opinion and I am sure some people will disagree with this part of what I will say but throw that piece of shit ECU in the bin they are a waste of money and time! there is a reason why 90% of the reputable tuners in NZ wont touch them and why you so so so often hear of people removing them for one reason or another and installing a Link or other such ECU! with a RB25DET you are far far better of buying a 300ZX ECU and getting it chipped/re-flashed with Nistune or a similar tune as the factory ECU's are a very powerful and good item when done right and for less of the same price as a Mega shit you would be silly not to!
thegravelracer,
Oct 6, 4:29pm
Everything you mentioned here is spot on IMO ,this is my freinds build not mine as stated im willing to have a go at niztune as im sure it wont variy much from other programs i have seen (BRE ect) and iv heard good things ,
We have used the same comp tester on a almost identical setup on a rb25det and 150(ish) on all six so we have ruled out damaged or faulty tester im betting its just a shit rebuild or over hone or something now
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