Has any one experianced Torque groan at low revs during Wot in fifth and sixth gear?
And has anyone found a cure to prevent this.

 

In short, nope

 

What boost are your running and ftlbs if you don't mind me asking?

 

1.9 and 520

 

Never heard of it, what is it?

My old UK MY00 Turbo with 2.5 hybrid and 6 speed STI box ran 1.6 to 1.7 bar on some turbos big enough to need the bell housing grinding or rotated.

Heads would lift, and once cracked a ring land from very brief det on standard pistons which couldn't take the strain.

Gearbox shift linkages were trouble.

 

Hmm was told today by a very well known mapper that this is quite normal on 2.5 Sti especially on hatch.

 

Apparently it when there a lot of torque produced at low revs in high gears it transmits a vibration that's felt through the car. But disappears over 4k

 

Anybody else ever heard or experienced this?

 

is it called being in the wrong gear at the wrong time.............

 

Sounds like compressor surge?

 

It's not compressor surge boost would be fluctuating if it was.
And on the low boost map the car pulls fine in the same revs so nothing to do with being in the wrong gear.

 

Is the problem from the engine or drivetrain? Is it a resonance, an imbalance, a structural twisting?

Surely for a 2.5 we are talking over 3000 RPM before it can build sufficient exhaust gas flow to spool a sufficiently large turbo enough to produce significant (eg over 500lbft) torque outside the artificial confines of an engine or chassis dyno where the engine speed can be locked no matter the engine output?

 

You must keep the Revs up in the upper gears with the 2.5 esp with higher torque , in that no labouring , I can't put mine in 6th till at least 65-70 , anything below 2500 rpm in 4th or higher is a no no ,

 

Just to add , I suffer also & as shrecksta says if I'm pottering around & go into 4th ( wrong gear) ha ha , I'm subjected to the car giving me its disapproval big time

 

That to me sounds quite compromised as a road car. I guess you're happy with that, but the joy of making brisk, quiet/subtle, part throttle progress is lost. Some of the best cars I've had make fantastic acceleration at 2000-3000 RPM at part throttle and can be short shifted. I don't think the driver should be able to floor the throttle above 1500 RPM in a high gear and have to put up with nonsense from the vehicle.

 

Driving around off boost the throttle is mainly feathered ,
MDV Billet on boost isn't a compromise as the first 3 gears are short , 4th your making speed , 5th license alert shift into top around 140 , smooth as silk , just like the runway

Even as a standard 2.5 running a 43 or 48 there is nothing below the 2500 rpm mark

 

Interesting... Mine will quite happily potter about in 6th at 1500rpm iirc that's about 42mph... Will also do it in 5th at same revs..obviously lower speed..

Maybe it's just a 'hatch' thing...?

 

Yea no doubt mickey is your car stock running a 48 ?
I have every reason to believe it will run, but you won't get a sniff from that turbo that low down .. But saying the question was asked about torque loading on the car . How does yours fair up ? Any , none little etc & what's your figures & spec

Regards

 

No.. Mine is a hawkeye so was running a vf43.. However I had some work done just before Christmas including a T36 turbo mapped to 448bhp and around 455 torque.. Was the same RPM-speed-gears before and after new turbo..

 

Well all I can say is I'm astounded to see a Hawk running torque at that figure plodding along in 6th at 42mph , again im not hear to discredit anyone .
Mine won't do it , wasn't built to do it , so fair play to you

 

No problem with mine 520T/490hp

 

Ha ha , luv it must have built my 5 5 wrong

 

Yeah I can see where you went wrong just from that picture.
Your oil filler cap isn't on straight
Nice bay

 

Cheers
Changed a few cosmetic things since this pic , also added grimmspeed spacers & junked the lateral 4 bar sensor & solenoid for perrin plug n play ( wich I should have done from the off ) the MD321V Billet works fantastic , I wanted the car to be a standard location turbo from the off . The engine is due a overhaul next spring when my attention will be fitting cosworth heads

 

splendid bay

 

its a shame your not closer as I would have taken you for a spin.. sadly its not something I could put in a picture or even a vid..

 

IS this like a excessive vibration, like when laboring an engine, but at a higher rpm?

Normally most 4 cylinder vibrations should cancel out by 1500rpm, this is caused by the gap between firing pulses. Its what ALL four cylinder engines do. IMO by 2000rpm everything should be gone.

There's lots done by car manufacturers to dampening it; Flywheel/clutch issues, crank pulleys, engine mounts, gearbox mounts, prop shaft mounts, diff mounts, sub frame mounts, rubber weights on driveshafts and floorpans to add dampened mass etc. Basically anything that involve balancing the engine or that bolts a rotating component to the chassis. If the rubber has gone bad, it allows too much movement and allows vibration to resonate. If they've been replaced with polyurethane, then that may not provide enough dampening.

Yamaha even make a damper for the chassis which is fitted to some JDM STi scoobs, whether it works and what frequency of vibration it dampens (i.e engine or road vibration, or maybe both) though I don't know

I'd have to say if this meant I had to keep above 3000rpm all the time even when cruising, I'd quickly get peeved off with driving that car everyday.

 

Yea , that's a valid point Ali , as most my mounts have been replaced , c frame gone replaced with summit brace , lighter flywheel , pulleys etc etc ...
Sure I get what your saying , I can happily sit at 2500 , but your right , as an example
The cars drivability is determined by how the driver knows the car & it's characteristics...
Not by how the drivability of the car stands from a showroom perspective

Regards

 

Ps
I suspect the flywheel plays a decent part in the conclusion

 

Dual mass flywheels certainly play a part, so switching to solid would make a difference.

I think Subaru call theirs a "flex flywheel" works on the same same principal though.