Ok so I heard a rumour that the MK2/2.5 could only handle 8-10psi of boost as it is fitted with weaker con rods. After a bit of digging around and a phone call to a very helpful Mazda parts department they confirmed that my MK2.5 VVT has the exact same con rods that the MK1 has up to 1995 and all MK1 1.8’s along with all MK2 1.8’s.
I doubt the pistons would be of different construction so it looks like the myth is busted.
I believe its due to the VVTi and the engine running higher compression. So boosting too far will bend the rods easier on a mk2.5. I was in a boosted mk2.5 on Sunday down at Mazda HQ, he is running 240 BHP, but it’s the torque that can bend the rods. So you have to be very careful, his has been boosted for 6 months now, and seems stable. But I have been recommended not to go above 220 BHP on standard internals. Obviously a lot has to do with the age and condition of the engine in the first place.
So it’s not to do with the construction of the rods, and more to do with the compression on the mk2.5 engine that means it is more prone to bending rods. I am no expert, but I have asked a few garages that specialise in turbo builds and this is what I have been told so far.
I hope that helps.
Hi
I read your comment about weak con rods on the 2.5 I am running MP62 Supercharger just setup with ME221 250 BHP no problems at all hope this helps the rumours.
Regards Bruce
Nice when posters get back to those who try and advise is’nt it?
Apologies for not responding I didn’t mean to offend anyone. I have looked into it further and found that most mk1-mk2.5 share the same Conrods. The compression ration was upped in the 2.5 to 10.1 I think. Anyway after a few more mods including am me221 ECU I have discovered that my engine is down on compression running at around 160 psi per cylinder and not the 182 psi Mazda claim meaning my power is way down at a terrible 127bhp. Due to the low milage of the car I’ve put this down to glazed bores. I have since purchased a spare engine that I will rebuild with turbo spec internals and fit that at some point.
I may then either build the original engine to the same spec or just replace the rings and have the bores honed.