Turbo restriction

[mgbond]

Gave the car (GTO) to a different garage for some final mapping for drivability and cold start.

It was also interesting that the car didn't make the same power (same dunno make) as previously mapped. At 1.2 bar originally it was 419 and after he has done some fine tuning it will probably just hit 400. Which I'm happy with.

However, he did note that from 1 bar to 1.2 bar there is not much of a gain. I have the ST200 plenum and upper inlet which are both bigger and my CC pipe work is bigger (and that is rated to 650 anyway). I have a pro alloy IC.

So, what could be constricting the gain, I'm guessing I'm probably pushing the std turbos. Would this be the reason?

Are they not the same as a std GTO3 turbos?

On an interesting note, he was impressed with the CC on general running on the dyno inlet was 20deg and on full boost pushing it inlet never went above 35 deg. The fan they had at the front of the car was almost as big as me. Lol

Bondy

[supaniga]

Hi bondy ,have you got 2.5 down pipes or 3.0. I noticed the hole on my 2.5 turbo elbow flange was alot smaller than the 3.0 litre so made my own out of 10 mm stainless plate and re-welded the 3.0 litre downpipes to them

[mgbond]

My exhaust is not std it's a Haward and Scott so I assume its a bigger bore. Simon might be able to help there.

[2.5bluenob]

Bondy the 2.5L turbos are not the same as the 3.0L ones.
2.5 turbo's are made up of half T2 and half T25 parts,
3.0L turbos are T25.
I think you have done the right thing with the smaller turbos as i like how responsive they are!
My car has had the original 2.5L turbos then i changed to T25's then upgraded T25's and now Gt28rs.
And for me personally i loved the kick the smaller turbos gave rather than the more gradual power of the larger ones but the larger ones give more high end power.

[mgbond]

2.5bluenob said:

Bondy the 2.5L turbos are not the same as the 3.0L ones.
2.5 turbo's are made up of half T2 and half T25 parts,
3.0L turbos are T25.

Mine are std, so do we think they are at their limit. I will eventually get GT25s but just interested if I'm at the limit?

[2.5bluenob]

mgbond said:

Mine are std, so do we think they are at their limit. I will eventually get GT25s but just interested if I'm at the limit?

I would have thought so. that's good power on standard turbos.
Have you tried running more boost?

[mgbond]

That's my point. I'm being told running more boost isn't really adding anything extra. So for 400 ill probably be close to 1.2bar. But 1.1 will probably be only 10bhp less. Kind of indicating I'm at the limit.

As long as its nothing else then I'm happy with that until I upgrade.

[andygtt]

sounds logical that your turbos are the limiting factor.... I'd run it on the lower boost and upgrade to GT25's when you can afford it, pushing the turbos that hard is not going to be good for them and an extra 10bhp isnt going to be that big a deal... Also going for GT28's would be pointless on a 2.5 as you can make close to 600bhp on GT25's so all you will loose it low down power.

you going to le mans?

[mgbond]

Cheers Andy, that's what I thought. It will only be mapped to 1.2 and I turn it down to 1bar anyway as that's all I like to run.

Unfortunately I'm not going to Lemans, I've had and got booked a few jollies this summer and ill probably get castrated if I had booked any more. It's probably a good idea I help Jayne with the wee one every now and then. Lol

[anonymous-user]

Despite what you might read on t'net, turbo's aren't a free lunch! They have an "efficiency" associated with them, and hence, if the higher pressure ratio required across the compressor and turbine move the turbo into a significantly lower efficiency operating point, then the slope of the "power vs airflow" curve will fall. Added to which, your combustion system, in terms of spark efficiency will also at some point become limiting (i.e. you have to retard the ignition timing to avoid detonation or Pmax) and the engine simply cannot realise the extra power potential from the extra airflow. Before you modify/change your system you need to plot your WOT operating line onto the compressor/turbine maps to see where you currently sit (very difficult for the turbine, as you don't know the wastegate bypass ratio generally speaking)

[Adrian W]

Max_Torque said:

Despite what you might read on t'net, turbo's aren't a free lunch! They have an "efficiency" associated with them, and hence, if the higher pressure ratio required across the compressor and turbine move the turbo into a significantly lower efficiency operating point, then the slope of the "power vs airflow" curve will fall. Added to which, your combustion system, in terms of spark efficiency will also at some point become limiting (i.e. you have to retard the ignition timing to avoid detonation or Pmax) and the engine simply cannot realise the extra power potential from the extra airflow. Before you modify/change your system you need to plot your WOT operating line onto the compressor/turbine maps to see where you currently sit (very difficult for the turbine, as you don't know the wastegate bypass ratio generally speaking)

So if I stick GT28rs's on my car it wont make more power then

[anonymous-user]

Adrian W said:

Max_Torque said:

Despite what you might read on t'net, turbo's aren't a free lunch! They have an "efficiency" associated with them, and hence, if the higher pressure ratio required across the compressor and turbine move the turbo into a significantly lower efficiency operating point, then the slope of the "power vs airflow" curve will fall. Added to which, your combustion system, in terms of spark efficiency will also at some point become limiting (i.e. you have to retard the ignition timing to avoid detonation or Pmax) and the engine simply cannot realise the extra power potential from the extra airflow. Before you modify/change your system you need to plot your WOT operating line onto the compressor/turbine maps to see where you currently sit (very difficult for the turbine, as you don't know the wastegate bypass ratio generally speaking)

So if I stick GT28rs's on my car it wont make more power then

I was primarily commenting on the fact that during the mapping "more boost" didn't make a lot "more power", rather than commenting on the optimisation of any particular turbo "matching"!

However, in all cases, understanding the operating conditions of any current hardware BEFORE you splash out a load of cash on new shiney bits is a good idea ;-)