15 replies to this topic

[italikko]

I just wanted to ask if there is any valid information around.

 

I can not decide between gtx2867 gen 2 with tial housing 0.86 and gtx3071 gen 2 with tial housing 0.82.

 

My goal is to have less lag possible.The lower the heat generated the better.

I want to go above 370 bhp using less boost available.The engine has forged internals,big cams and flowed head.Static compression is 9:1.

 

On paper the 3071 goes on full boost 400rpm later but i would like to hear from someone that used these setups before.

Is there any considerable lag that compromises the street driving?The car is going to be a fast road and occasionaly track day car.

Thank you,

[Nev]

For a real world example, on my engine (which you need to understand has a very special cylinder head) with an old Gen1 GTX3071R turbo, I get the following results:

 

10 PSI = 480 HP

24 PSI = 520 HP (but an extra 150 HP in the mid range).

 

If you are buying Gen2 Garrets then I'd suggest using a GTX2867 - it will spool about 300 RPM faster than the GTX3071 and blow nicely up to about 7200 RPM. Also it will easily make the power you want.

 

Depending on your engine's max revs, you could consider a GTX2871 - this would suit a very high revving engine (up to 8000 RPM) as the compressor is large enough to flow at the higher revs.

 

I think you'd be pleasantly surprised by the lack of lag, especially if you stay with OEM cams that promote lots of torque at low RPM. Mine doesn't really suffer from lag, more that it suffers from lack of torque (relatively) under 3500 RPM. But if you stay with OEM cams and valves, then this won't be such a problem for you.

 

Good luck.

Edited by Nev, 14 October 2018 - 12:44 PM.

[italikko]

Thank you so much for your answer.

 

I have driven an opel astra opc which is the same as the astra vxr.

The car had the 3071 gen 2 with custom headers and external waste gate.

It had lot of lag and was not pleasant.Full boost around 4500 rpm.From 2000-4500 was lethargic,Then the turbo came in and began to wheel spin.

 

I suspect that the ecu map and setup was poor.

 

Do you have a boost map to show me?I am curius to see.

If the difference is just 300 rpm then i could go with the 30.

At what rpm do you see 10psi?

[Nev]

From memory 10 PSI is there from about 4000 RPM.

 

If you stick with OEM cams + valves etc and the smaller turbine then I think you'd see 10 PSI from about 3500 RPM. 10 PSI is plenty really, you just need to be sure its there all the way to the red line.

 

Are you building a new engine presumably? What's your spec for CR? Mine is very low (just 8.25:1) - I'd suggest you aim at about 9:1 and use less boost and better petrol (I wish I had in retrospect), you'll get a flatter longer torque line then and the engine will be very responsive from about 3500 to 8000 RPM, which is a massively wide power band to stir the gears in.

 

I do have some old boost maps from a different dyno, I will try and find them...

 

Edited by Nev, 14 October 2018 - 01:21 PM.

[Nev]

Here are some old dyno plots to give you an idea. This was with a rather poor map. It shows 4 different dyno pulls (at 4 different boost settings). Since then I have a stand alone ECU and better mapping and the dip around 3500 RPM is not so noticable now.

 

 

 

 

 

 

You need to take the power + torque figures with a pinch of salt, as I think the dyno over-read by about 50 HP.

Edited by Nev, 14 October 2018 - 01:31 PM.

[italikko]

It is the stock z20Let rebuilded from scratch.Fully forged bottom with balance shafts removed.The head has some work on it from a very respected tecnician here in Greece.The camshafts are custom made at the limit of the hydraulic followers.They give their best from 3000 at about 7500 rpm.Oem valves.

 

The car is going to be driven hard on the Greek mountains,on the alps and will do some track days around Europe.

 

I really don't care about numbers.I want real usable power all over the range,low to none lag low temperatures.

The reason i consider the 3071 is that it should give lower iat at the same presure.

Garrett says that the difference is 300 rpm penalty for the 3071.I should be sure about that because i dont want to find my self on a situation with little to no boost before 4000 rpm and the suddenly a big torque explosion.

 

I see that on 3000 rpm you go with nearly 5psi of boost which is very low.

From 3000 rpm to 4000 rpm you engine gains nearly 130 hp.

Is it drivable indeed?What rear tyres you have?

I have 245/40/17.

[Nev]

The car is going to be driven hard on the Greek mountains,on the alps and will do some track days around Europe.

I expect heat will be a big issue for you IMO, need to spend a lot of thought on oil + water rads.

 

I really don't care about numbers.I want real usable power all over the range,low to none lag low temperatures.

If you get the GT28 then drivable powerband from 3700 to 7500 is wider than most OEM 4 pot engines.

 

The reason i consider the 3071 is that it should give lower iat at the same presure.

Yes, GTX3017 will give slightly lower IATs, I have exceptionally low IATs (@ 10 PSI), even on really hot summer days the max I ever saw in 8 years was 45 degrees C. I've driven flat out at max RPM on a track (ambient about 22 degrees) and IATs only reached 39 degrees.

 

Garrett says that the difference is 300 rpm penalty for the 3071.I should be sure about that because i dont want to find my self on a situation with little to no boost before 4000 rpm and the suddenly a big torque explosion.

If you want 10 PSI before 3500 RPM I'd suggest the GTX28, based on the way my engine responds.

 

I see that on 3000 rpm you go with nearly 5psi of boost which is very low.

Yes, it's relatively low, the car feels sluggish (compared to full power). My cams and big valve and low CR all affect this as I tried to explain. If you are trying to drive fast however, there is no reason for your revs to drop < 4000 RPM though, so it's a "non problem" in the real world.

 

From 3000 rpm to 4000 rpm you engine gains nearly 130 hp.

Yep. Take a look at my current (low boost (10 PSI)/torque) map though, the old one is missleading. This one is very smooth indeed, straight line power (even to 8000 (which the plot doesnt show)).

 

Is it drivable indeed?What rear tyres you have?

On the lower torque map it is very drivable and "feels" really low powered. It feels very NA like, the mapper pulled massive amounts of ignition in the mid range to stop that "shove" feeling most turbo cars give you. Rear tyres are only Federal RSRs, V70a is best for grip but too expensive and only last 2000 miles.

 

I have 245/40/17.

I'm on 285 rears.

 

Edited by Nev, 14 October 2018 - 02:15 PM.

[italikko]

Thank you so much.

Appreciate you kindness.

[TFD]

Mountains sound like lowdown torque is needed. Like Nev said, I would suggest a gtx2867 with a .64 housing for faster spoolup and an external wastegate for better boostcontrol. That would be my setup for 350-400hp.

2871 with .86 housing is laggg...
Furthermore, your cams are playing a roll in spoolup. More duration will reduce lowdown torque/spoolup, so be carefull what hardware you are combining.

Goodluck!

[mafumoto]

Don't forget the manifold plays a big part in lag

Longer runners increase lag pushing the spool range further up the revs

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[italikko]

Thank you for your help.

 

My exhaust manifold it is from klasen.

 

[scw02102]

I cant comment on these turbos on a VXT but have regularly driven the GTX3076R and most reports say how its not that laggy etc... Maybe for a big turbo it isn't too bad but in real life I personally find it takes too long to come on boost for the road. I assume the 3071R will be similar. Yes these turbo make big power but under 4k not much happens. Im guessing the light weight VXT will help this and should pick up better at lower rpm.

Overall Im saying don't read too much into technical data from the manufactures, listen to the boys above with real life experiences. 

 

Standard small turbos just pick up and go, bigger turbo have next gen crap stamped on them and yes in results may be better but on the road it takes that bit longer than any small turbo so be warned on the road can be annoying. 

 

 

 

[Doctor Ed]

Don't forget the manifold plays a big part in lag

Longer runners increase lag pushing the spool range further up the revs

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yeah.. no

[mafumoto]

http://www.enginebas...be Headers.html

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[Doctor Ed]

yeah, no

[iram]

from my experience my GT28-65 HTA with a tail housing and external wastgate spools like a bastard starting at 2600 , on it at 3000, loaded gun at 4000 keeps climbing and no drop off into the red zone!power when i want it ,how i want it with the ecu! cant see why more bhp/torque later is beneficial!   went 65 as to be even more driveable  id say 500 rpm earlier on the charts to a 67!  and way more earlier than a 3071 if your overlapping dyno graphs!  real life cant comment! and cant comment on the klasen manifold effects!