judder at low rpm, only seems to be 5th and 6th, any ideas?

[arron1995]

my stage 1 cr170 acts weird when in 5th and 6th, if the revs are lower than 1400rpm and i put my foot down the car judders/vibrates quite bad, it only seems to do it in these 2 gears, if im going uphill i have to drop it down into 4th for it to pick up properly, is it just because the rpms are too low?

[Stevey Y]

1 hour ago, arron1995 said:

my stage 1 cr170 acts weird when in 5th and 6th, if the revs are lower than 1400rpm and i put my foot down the car judders/vibrates quite bad, it only seems to do it in these 2 gears, if im going uphill i have to drop it down into 4th for it to pick up properly, is it just because the rpms are too low?

Hi I think you have answered your own question, revs are to low, might well be worth checking the hydro bushes on the engine mounts they are prone to failure around 100k.

Steve.

[cliffcoggin]

I have no idea what a stage 1 cr170 is, but if it is a tuned engine then Steve is right, the revs are too low. Generally the more tuned an engine is, the smaller the power band. Most road cars are designed to deliver power over a wide rev range for maximum flexibility, but if you modify the engine for more more power you sacrifice some of that flexibility.

[arron1995]

On 9/6/2021 at 9:29 AM, cliffcoggin said:

I have no idea what a stage 1 cr170 is, but if it is a tuned engine then Steve is right, the revs are too low. Generally the more tuned an engine is, the smaller the power band. Most road cars are designed to deliver power over a wide rev range for maximum flexibility, but if you modify the engine for more more power you sacrifice some of that flexibility.

cr170 is just an abbreviation for the common rail 170bhp (125kW) engine, it is stage 1 but i lost the dyno graph, after looking at some other dyno graphs it seems every tuner starts the run at 1800rpm so makes sense.