Atr43ss-2 Prototype Initial Tune 250rwkws 18psi<2500rpm, Stupidly Responsive

[Harey]

But the exhaust housing is the reason for the awesome response. If you change the exhaust housing to a larger unit then you loose response.

Remember dynos are done in 4th gear. Not everyone needs a turbo that will pull to redline in 4th gear, your talking lock me up speeds on the street. 2,500rpm full boost in 4th gear would roughly correspond to 4,500rpm in 1st gear which is a big difference. I know dynos are done in 4th gear due to the 1:1 gearbox ratio but it can be misleading for someone wanting a responsive street turbo.

This thing pulled to redline HARD in second gear, third gear was good but did loose some torque.

If you want something to pull hard to redline in 4th gear then it cant be as responsive as this. The 3071 and 3076 are the turbos if you want the most response possible for 270-300rwkw. But if 250-260rwkw is enough, then something like this gives you fantastic response.

Stao also took me for a spin a few weeks earlier with a 3582 wheel and a 0.82 housing. Yup the dyno sheet will show the turbo making big power to redline in 4th gear but there was basically no boost in 1st gear.

Edited May 10, 2010 by Harey

[Harey]

seems like this thing would drive like a V8 haha.

i think its near impossible to have a turbo be as responsive as this and make decent top end.

the small rear housing will refuse to hold high boost at high rpm, therefore peak power at 5,000 odd.

but peaking at 5,000 i think seems a waste of the revving nature of the RB.

truly a street turbo; lots a power in the early rev range, but with no top end.

would be interesting to see how you go with boost control.

Remember peaking at 5,000 is in 4th gear, in lower gears it will peak higher. Trust me it uses the revving nature of the RB in 2nd gear

I agree it will be interesting to see how they go with boost control.

[Trozzle]

on the street, I rarely find myself about 5000-5500rpm. 6-7k ish when I wind the shit out of it up a hill in second....but really, I find the fun street driving to be ripping 3.5-5500 rpm in second and third (speed limit permitting) to be the best.

[Harey]

on the street, I rarely find myself about 5000-5500rpm. 6-7k ish when I wind the shit out of it up a hill in second....but really, I find the fun street driving to be ripping 3.5-5500 rpm in second and third (speed limit permitting) to be the best.

This thing slams you in your seat all the way to 7k in 2nd gear. 3,500-5,500 is still very strong in 3rd gear.

[Granthem]

for what it's worth the stock turbo looks like;

160km/h = 5714rpm = 195rwkw

170km/h = 6074rpm = 189rwkw

the stock turbo seems to peak at 5700rpm ish

and the prototype seems to peak at 5000rpm ish

this is based on my stock turbo tune

neither is right or wrong just offering data

i think a 33 GTST with that powerband would be pretty sweet on the street

its a good 50rwkw ahead everywhere in the power band so it should be shit hot

Slightly offtopic -

I dont get this. Something is different with my cars box or diff. My car on the dyno in 4th @ 175km/ph is on limiter. And limiter is 7000rpm. Power FC says its reving to 7k, as does the tacho, but the speed doesnt indicate it is (with stocko gearing anyway).

Harey ran into this problem when plotting my car in his turbo comparison thread... I cant work it out.

[Dale FZ1]

But the exhaust housing is the reason for the awesome response. If you change the exhaust housing to a larger unit then you loose response.

This thing pulled to redline HARD in second gear, third gear was good but did loose some torque.

I think it'd be interesting while Stao is testing gear to actually fit the larger A/R housing if possible, and try that. If it truly makes 18psi by 2500rpm with the 0.63, then a 0.8 housing shouldn't see the bottom end weakened dramatically.

It would be awesome to see this setup hold 250rwkW across a range eg. 5500-6500rpm than hit a peak and fall away. That would make sense if bottom end response only fell away by 200rpm.

[Tangles]

the bolt-on .73 ar rear avo skyline IW-housing would keep all-out response but up the power in the higher rpm area

[Harey]

I think it'd be interesting while Stao is testing gear to actually fit the larger A/R housing if possible, and try that. If it truly makes 18psi by 2500rpm with the 0.63, then a 0.8 housing shouldn't see the bottom end weakened dramatically.

It would be awesome to see this setup hold 250rwkW across a range eg. 5500-6500rpm than hit a peak and fall away. That would make sense if bottom end response only fell away by 200rpm.

Yes I think a 0.8 housing will reduce the bottom end significantly!

Yes of course if would be great to have more constant top end without sacrificing much bottom end but thats not generally how turbos work

[Harey]

the bolt-on .73 ar rear avo skyline IW-housing would keep all-out response but up the power in the higher rpm area

How would it keep its response and gain top end power. Surely a larger housing will loose some response for the gain in top end power...

[zebra]

If the turbo is choked than a larger rear housing "can" help boost response.

[R31Nismoid]

How would it keep its response and gain top end power. Surely a larger housing will loose some response for the gain in top end power...

Housing changes don't have as dramatic effect as you are making it out to be is why.

A minor up in A/R might be all it needs.

Totally depends on the wheels combo's and everything else.

You cannot just make a blanket statement saying "X" will hurt substancially when we have NFI what wheels are being used, restriction being encountered and so on.

[Harey]

If the turbo is choked than a larger rear housing "can" help boost response.

Ok I have never seen that before but I am not saying it cant happen. It would want to be seriously choked.

I used many small exhaust housings and yes ones that do choke quite badly that still increase response.

Edited May 10, 2010 by Harey

[Harey]

Housing changes don't have as dramatic effect as you are making it out to be is why.

A minor up in A/R might be all it needs.

Totally depends on the wheels combo's and everything else.

You cannot just make a blanket statement saying "X" will hurt substancially when we have NFI what wheels are being used, restriction being encountered and so on.

Housing changes do have a dramatic effect from my experience. Stao mentioned it as well when we were talking.

I believe it is quite reasonable to make a blanket statement that using the same turbo and a larger exhaust housing will reduce response.

[Dale FZ1]

Housing changes don't have as dramatic effect as you are making it out to be is why.

A minor up in A/R might be all it needs.

Totally depends on the wheels combo's and everything else.

That's my point exactly. I get the feeling that the turbine housing is choking, so bigger cross sectional area may have a minor effect on what is an absolutely stonking bottom end, and allow the top end to flow.

Speculation only, and I'm sure Stao has/is considering it all.

[R31Nismoid]

Housing changes do have a dramatic effect from my experience. Stao mentioned it as well when we were talking.

I believe it is quite reasonable to make a blanket statement that using the same turbo and a larger exhaust housing will reduce response.

It will alter the response - not one person is arguing that.

What people are arguing is your statement of 'signifigantly'. It is largely impossible to say that without knowing the full details as i said earlier.

I've seen guys move to a larger rear housing with 500rpm or so alteration. That in my book is far from signifigant given they have been able to attain 1500rpm extra power band (as an example).

1000rpm+ would be signifigant, however a minor rear A/R change will not have a 1000rpm+ alteration regardless.

That's my point exactly. I get the feeling that the turbine housing is choking, so bigger cross sectional area may have a minor effect on what is an absolutely stonking bottom end, and allow the top end to flow.

Speculation only, and I'm sure Stao has/is considering it all.

+1

Indeed speculation, but a few of us (including yourself) have seen similar before so it's reasonable grounds i reckon

Stao will know the full details either way and it would be very interesting to see what a slightly larger rear A/R will actually do.

[zebra]

I would rather have an extra 50-60hp in the last 2000 revs than make 18psi at 2500rpm...the engine can only swallow so much air, so it would be interesting to see how badly it surges at WOT and low revs.

[Harey]

On a different note are there any rules to apply between boost reponse in 1st, 2nd, 3rd and 4th?

For example if this turbo makes full boost at 2500rpm in 4th, what is the response in 1st, 2nd and 3rd?

Same for say a GT3076 which makes full boost by ~3500rpm.

Because I am sure a lot of people hear "full boost at 2500rpm" and think wow 2500rpm in every gear thats fantastic!

[Harey]

It will alter the response - not one person is arguing that.

Indeed speculation, but a few of us (including yourself) have seen similar before so it's reasonable grounds i reckon

Stao will know the full details either way and it would be very interesting to see what a slightly larger rear A/R will actually do.

Tangles is arguing that it will alter the response:

the bolt-on .73 ar rear avo skyline IW-housing would keep all-out response but up the power in the higher rpm area

Nowhere did I say that it would not be great to see some tweaks to see what is possible, its a great start.

Edited May 10, 2010 by Harey

[Harey]

I would rather have an extra 50-60hp in the last 2000 revs than make 18psi at 2500rpm...the engine can only swallow so much air, so it would be interesting to see how badly it surges at WOT and low revs.

Thats fine, go out and buy a GT3076. This turbo is designed for street response. Yeah 18psi at 2500rpm in 4th gear but in say 1st gear your talking about ~4500rpm. If you are trying to use a turbo on the street legally then an extra 50-60hp at the top of 4th gear isnt an issue.

It is great to have different turbo options for different people.

Edited May 10, 2010 by Harey

[paulr33]

Slightly offtopic -

I dont get this. Something is different with my cars box or diff. My car on the dyno in 4th @ 175km/ph is on limiter. And limiter is 7000rpm. Power FC says its reving to 7k, as does the tacho, but the speed doesnt indicate it is (with stocko gearing anyway).

Harey ran into this problem when plotting my car in his turbo comparison thread... I cant work it out.

this is based on my car which is normal GTST manual

4.11 diff gears (i assume stock?) with active lsd (stock)

RPM = (SPEED / 28) * 1000