exhaust doser

[Rawze]

(12-05-2020 )JasonH Wrote:  my engine is ESN 79405155 and the turbo came off of ESN 79645840 both of which are 550's. Sorry about the strange messages I'm not very good with computers.

It being a 550, that 400 series is going to be restrictive and run out of steam and have too high A/R ratio trying to make the 38 psi that CM871 needs to make a full 550 hp. It would do good to support 450HP or so and only 35~ psi or so boost before becoming restrictive on that older 871 engine. What you seem to not be accounting for is the fact that a CM2350 does not need but only 32-33 psi boost to make 600+ horsepower due to its much higher cylinder compression ratio vs. the 871. - That is why the turbo is so much smaller. .. those 2350s do not need that bigger 500-series on them to make the same power as the older 871's did.

You put that 400 series on there your going to have issues. Either your not going to have enough boost for the power it is making, and 33-35 psi is going to make EGT's too high and cook that turbo ... or if you force its vanes closed more to make the 38+ required, then it will be restrictive at this high pressure and the engine is going to have higher than normal back-pressure on the exhaust manifold. This makes for more heat in the cylinders, it will labour against the higher than normal exhaust, taking power away from the flywheel. 37~38+ psi boost on a 400 series will also end up over-spooling that turbo for it to make it, killing the turbo after a while and or causing excess heat in the cylinders putting it at risk to crack a piston. -- That is what is going to be the result. The A/R of those 400 series turbos does well to keep after 33-maybe 34 psi boost on the isx. This is fine for a higher hp high compression ratio 2350 but not so good for higher HP on older engines.


If the engine were set down at 450HP, maybe 1650 torque, you could get away with about 34-35 psi boost and EGT's not be excessive. It would be in the ball-park range with it on the 871 ... Otherwise it is going to have issues.


Next Q. is WHY did the other turbo go out to begin with? -- Bad delete programming is notorious for shortening the life of the turbo significantly as well as the engine.