Reducing Turbo Lag

[discopotato03]

54mm GT28 turbine trying (hard) to turn 76mm TO4S 48T compressor . Garrett do not give this turbo a glowing review on their turbobygarrett site (under products) . I'll have a look and back in a tick ...

[discopotato03]

From their site the maps look like this , though the turbine map should vary with different compressors at this site it does not .

So you have ~ 21.5 lbs of exhaust flow if it has the .86 a/r exhaust housing or ~ 18 lbs flow if it has the .64 a/r housing . The energy recovered by an efficient 54mm turbine has to try and muscle a 76mm TO4S dinosaur compressor wheel that has the capacity to pump 49 lbs of air in its .70 a/r TO4S cover . That cover by the way if used on a GT35R can pass 60+ lbs of airflow and approx 75 lbs on a TO4R/Z so way overkill for 49 lbs .

If you look at the compressor maps for the GT2860RS and GT2871R 48 trim they show 35 and 38 lbs of flow from a 60 and a 71mm compressor in a .60 a/r TO4B cover .

The point of all this is that more modern compressors are far smaller than the dinosaurs for adequate flow and the comp covers or housings are more compact as well . The GT28 turbine is a high speed device as are the GT series compressors , the fact that they work together at high rpms means they compliment each other . The TO4S compressor from the GT2540R or GT2876R as Garrett now calls it is way out of step technology wise with its GT28 turbine . It has reasonable airflow for its size and trim but pumps it volume because it is big rather than efficient - for its airflow . It doesn't need high revs to work but the GT28 turbine does so this is where they fight each other and the result is boost lag .

The Garrett site said - best suited to unique applications , not recommended for general performance applications .

I don't know where you go from here , your compressor wheel and cover are the problem so its a case of change them or change the turbo to get better response .

Probably not what you wanted to hear , why those turbos are on the market at all beats me .

Cheers A .

Edited February 18, 2006 by discopotato03

[noakespg]

If you got a custom exhaust manifold made up that would feed the exhaust gasses into the turbo quicker it should, in theory, make it spool up quicker. Has anyone got any experience with this?

[discopotato03]

The problem is that the higher your make the gas speed the closer the tube or duct is to its maximum flow . Engines don't care where the restriction is but the result is the same .

Cheers A .

[dbo]

Yeah not really what I wanted to hear but a good informative insight none the less..

I suppose unless anyone else has some other input i'll be looking for a turbo upgrade?

[Drift_Mulisha]

There's no need to upgrade your turbo, just come down an exhaust housing size to 0.64 & u will be far better off. As much as the GT25R doesnt look good on paper I have been impressed buy how it performs so far in the real world.

[Slide]

NOS is the only cure for turbo lag.

Its like panadol day/night comes in a blue or white capsule and gets rid of your headache quick smart :lol:

[discopotato03]

NOS only really helps a turbo thats large in relation to an engines capacity . If the combinations problem is a tiny turbine and housing gas merely helps it destroy itself sooner/faster .

Cheers A .

[mokompri]

first thing i would try to find out is if:

A ) this characteristic is normal for this turbo, on this engine or

B ) its abnormal for this turbo/engine combo to get this sort of lag

i had a lag issue on my sr20det car that had a gt2530 turbo, i was spooling early on in the range, but would take 5K rpm to hit 1bar of boost.

after ALOT of fiddling around it was found that the wastegate arm didnt have enough tension on it, so when the pressure built up in the exhaust housing, it was opening the wastegate early and causing a sort of wastegate creep. unplugging the vacuum line from the wastegate didnt affect it because the pressure opening the wastegate flap was in the exhaust housing itself, not from the vacuum feeds positive pressure.

so in saying all that, check that the wastegate arm has tension on it, if its an adjustable arm, give it around 1-1.5cm of tension. disconnect the vacuum line from the wastegate, and give it a run. if boost response is better, then you are in category B, same as me, which is easy fix. if not then follow the advise given on this thread, specially get your tune checked out !

after i fixed this issue on mine i started spooling earlier and hitting 1bar at 3.3k rpm WITHOUT a tune

Edited February 21, 2006 by mokompri

[dbo]

Cheers for all the info.. I'll have to ask around and find out if anyone else is running a GT25R on an RB20 like me, and find out if it is normal behaviour to be so laggy..

[spmir1]

don't complain kids

i own a current model celica.

try driving one of those or a vtec.

think of the positives... better fuel econmony whilst driving conservitively under boost.

[Guilt-Toy]

LOL....Ok

But i never even get near 5,500rpm in day to day driving. so i suppose when i hear bottom end i think the rpm you are pulling in traffic

When you are up the thing, who really cars what your bottom end is like, its only in day to day hustle and bustle when i need to shift back to 2nd at 45km/h to get past a car i curse the RB20

Looks like you have just taught yourself a lesson about the benifits of a rb30det. My 3 litre can overtake cars at 45km'h in 4th or 5th gear off boost.

[dbo]

I use to work at Hinterland toyota, so I got to drive the Sportivo corolla's and the celica's with the VVTL-i, so I know what you mean.. But this is alot worse than waiting for the valve lift just to kick in... i'm talking absolutely gutless off boost... I honestly think if I raced a sportivo corolla and started off boost, it could take me out :|