Wastgate question?

J

jpward

Guest
Was wondering what would be the highest pressure you could run with an internal wastegated turbo?

.. and if you go for larger turbo say GT3076R the fact it blows more would suggest you need less pressure for same over all flow rate so would that mean that you would be able to get away with an internal 5 bolt housing rather than have to go to the expense/bother of getting an external setup? :?

Ohh and can someone explain in layman's terms how to read a compressor map all these surge line, pressure ratio, Vs CFM hard to work out the answer to my question.


Thanks 8)
 
P

pulsarboby

Guest
not too sure tbh jp but think that with an external wastegate, it would be more reliable as its not in direct heat from housing so would be less likely to crack (as normal area round internal wastegates do).

dont know about performance difference between the two, but that would be the main reason i would use an external wastegate, assuming i wanted one that is.
 
J

jpward

Guest
I was thinking if you were only going to say 1.8Bar would it be necessary to go to the bother of buying a good wastsegate say Tial £250 and then new manifold at £300 plus new turbo elbow £200 soon ads up if say 1.7Bar was recommended limit you could live without the .1Bar for the extra hassle if i am making sense?


Ohh Bob any word on O2?
 
Trip

Trip

New Member
I was wondering the same thing myself. I just ditched the T3 GT3071R and just ordered a T25 type GT3071R from the states. I still have the 38mm Tial wastegate at hand.

Its either I block/shut the internal w/g with a spring and weld a flange on the manifold to accept the external w/g, or just use the internal w/g. i will be running 1.8bar.
 
A

ashills

Active Member
ive stuck with the 3071 again on new car as we think the 3076 will get the same performance due to the restriction of the T25 flange and internal waste gate design
the flow map reading is very complicated to fully understand (i only have a rouh idea about them kieron has a good idea )
but when u look across the graph at lbs of air this can give an idea of bhp that turbo COULD flow on a perfect engine
ie a gt35 will flow 62lb of air and on a well built engine thats optimized it should do arond 620bhp
but u have to also look at the exhaust side of the turbo as to how that will affect the spool up and if that will hold the compressor side back from making its full potential power
 
campbellju

campbellju

Moderators
Staff member
jpward said:
I was thinking if you were only going to say 1.8Bar would it be necessary to go to the bother of buying a good wastsegate say Tial £250 and then new manifold at £300 plus new turbo elbow £200 soon ads up if say 1.7Bar was recommended limit you could live without the .1Bar for the extra hassle if i am making sense?
Click to expand...
The issue with a wastegate is not the boost you run but the capability of the turbo. On an internal wastegate, if it can't bypass the air away from the turbine fast enough then the turbo will spin up too fast and overboost on the compressor side (surge). You see it less when the turbo runs higher boost.

On my 3071 and a standard elbow I never had boost surge as the elbow was giving a physical restriction to the turbine. Once I moved to a 3" elbow (recommended) I understood what people had been talking it about. Boost controller and mapping will have a big affect on how much surge you see and how it affects the driveability of the car. I did a few things and in the end at 1.4Bar it sounded like train but was smooth. At 1.8Bar the issue was reduced but still present at times.

Since my engine is dropped I've removed the exhaust housing and ported the w/g to 29mm. This should help with the surge, I'll say how well it worked once I find out myself.
 
J

jpward

Guest
campbellju said:
The issue with a wastegate is not the boost you run but the capability of the turbo. On an internal wastegate, if it can't bypass the air away from the turbine fast enough then the turbo will spin up too fast and overboost on the compressor side (surge). You see it less when the turbo runs higher boost.

On my 3071 and a standard elbow I never had boost surge as the elbow was giving a physical restriction to the turbine. Once I moved to a 3" elbow (recommended) I understood what people had been talking it about. Boost controller and mapping will have a big affect on how much surge you see and how it affects the driveability of the car. I did a few things and in the end at 1.4Bar it sounded like train but was smooth. At 1.8Bar the issue was reduced but still present at times.

Since my engine is dropped I've removed the exhaust housing and ported the w/g to 29mm. This should help with the surge, I'll say how well it worked once I find out myself.
Click to expand...
Thanks Jim, porting sounds like a great new idea how big is the standard port and how much can you get away with taking off? ( as in do you need say 2mm min for the disc to seal properly or is it not an exact science?)
 
P

pulsarboby

Guest
jpward said:
Ohh Bob any word on O2?
Click to expand...



have the car in now jp but someones coming to see the engine running on thursday, so dont want to remove it untill the lumps sold, which will hopefully be thursday. then il get it in post to you;-)
 
campbellju

campbellju

Moderators
Staff member
@JP 25mm as standard an extra 2mm all round removed leaving about 1.5mm to seal. I've seen others go to 30mm but I didn't want to take the risk.

Edit: I don't think its a new idea, its quite a common problem and this is the cheap ass solution :) I did get the work done professionally for £20 to make sure it was accurate. Stumo took a grinder to his and it looks okay too.
 
Last edited:
K

Keira

New Member
ashills said:
(i only have a rouh idea about them kieron has a good idea )
r
Click to expand...
reading compressor maps is abit like understanding a woman, unless you know how they work its a fooking waste of time :lol:
 
Trip

Trip

New Member
Keira said:
reading compressor maps is abit like understanding a woman, unless you know how they work its a fooking waste of time :lol:
Click to expand...
Now I see why you are more familiar with maps then, You do understand yourself right ? :lol:
 
Trip

Trip

New Member
How to determine Pressure ratio (Vertical value on compressor maps):

(Gauge-PSI + Absolute-PSI) / (Absolute-PSI - Restrictions)

So i want to boost my engine to 26psi(~1.8bar)
Restrictions are any airfilter restrictions and altitude difference since absolutePSI is 14.7 as sea level. I will use 0.5psi as combined

(26+14.7) / (14.7-0.5) = Pressure Ratio

40.7 / 14.2 = 2.87

So now I know what my Pressure Ratio is. 2.87

-------------------------------------------------------------

In order to get the Ib/Min(horizontal value on compressor maps) i first need to get CFM(cubic Feet/min)

I need the following
Engine Size (L) = 2Ltr
Volumetric Efficiency (VE) = 88%
RPM = 7800
Pressure Ratio (PR) = 2.87

(L x VE x RPM x PR) / 5660

(2 x 88 x 7800 2.87) / 5660 = 696.1CFM

Easy way to convert CFM to Ib/min is to multiply by 0.07

Ib/min = 696.1CFM x 0.07 = 48.72

-------------------------------------------------------------------------

So now I know
Ib/Min = 48.72 @ 7800rpm
Pressure ratio = 2.87 @ 7800rpm


This was just an example and all formula's above are taken from a book about Turbochargers. Also the VE of every engine is different.
 
J

jpward

Guest
Trip said:
How to determine Pressure ratio (Vertical value on compressor maps):

(Gauge-PSI + Absolute-PSI) / (Absolute-PSI - Restrictions)

So i want to boost my engine to 26psi(~1.8bar)
Restrictions are any airfilter restrictions and altitude difference since absolutePSI is 14.7 as sea level. I will use 0.5psi as combined

(26+14.7) / (14.7-0.5) = Pressure Ratio

40.7 / 14.2 = 2.87

So now I know what my Pressure Ratio is. 2.87

-------------------------------------------------------------

In order to get the Ib/Min(horizontal value on compressor maps) i first need to get CFM(cubic Feet/min)

I need the following
Engine Size (L) = 2Ltr
Volumetric Efficiency (VE) = 88%
RPM = 7800
Pressure Ratio (PR) = 2.87

(L x VE x RPM x PR) / 5660

(2 x 88 x 7800 2.87) / 5660 = 696.1CFM

Easy way to convert CFM to Ib/min is to multiply by 0.07

Ib/min = 696.1CFM x 0.07 = 48.72

-------------------------------------------------------------------------

So now I know
Ib/Min = 48.72 @ 7800rpm
Pressure ratio = 2.87 @ 7800rpm


This was just an example and all formula's above are taken from a book about Turbochargers. Also the VE of every engine is different.
Click to expand...
Thanks Trip I have those Formulae myself but still doest get me a short answer :lol:
 
K

Kev@Apex

New Member
We ran a stable 2.0Bar on one of our older S13's, with CA18DET.
It was running just over 500bhp, with an internally wastegated standard position GT3076R.

3071's seem to be prone to creep, so do benefit from being used in external wastegate configuration to help control the boost sufficiently.
 
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