CT458 vs CT358 what would you choose?

[jogi730]

@ jogi and all,

when you are driving off boost on lower revs with a smaller turbo and a bigger turbo, does that make any difference?

When im driving around with up to 0bar boost or 0.5bar boost at most, does it make any difference the size of the turbo?

Im asking this,because if you have seen from videos i have put up here, that is what i get already with the 3071R.So since repo and justin can give me a turbo that spools basically the same as 3071R and give me more than 80hp more than what i have now, why not go for it?

Also when off boost however the car goes,depends on how lightened the moving parts are,since basically it is like being a natural aspirated car.Of course other factors come into play,like compression cams etc.

My whole idea is for the turbo to be able to produce the amount of power im after with spooling before 4000rpm and with boost less than 2bar. The amount of power im after is 500hp but with a headroom as well.Justin seems to think that the 358 is capable of that. The 458 came into play as the main difference is giving even more headroom for improvement and minimal spooling differences.

By the way, repo was giving me the option of CT355 for 'easy'500 hp but possibly with 2+bar which i prefer not,and even if that is possible (which i dont doubt) it doesnt leave any room for improvement. As i explained,this will be the permanent turbo choise for me as improvements and further steps will not be taken.SO i want to have a good range power without stretching the turbo.

You are making the same mistakes I did. As some people have said, bhp is a pub currency but means little in reality. DJones has 450bhp, b ut his car is mad up to 100mph. I had same with my t34.Sure the t61 was a brute from 4k rpm, but as Darren says he would have been away before I even hit the power.
That's why initially R/epo suggested a 355 for me but has since changed to a 350, a turbo still capable of 500bhp (as achieved by clients cars).
Do what you will, but just be warned and don't be unhappy with results if it doesn't work.
Chris

[Jamo]

The smaller turbo You use to get the power, the larger the powerband

Biblical quote

[A80Avant]

...and the higher boost you need to achieve it as well,right?

Djones car wont probably need any more hp anyway because it is very light as well. If mine was 1400Kg tops, i probably wouldnt change turbo either.In a car weighing 1700+kg though... thigs are differenct.YOu can still have a 500hp with good driveablility car..

Main reasons for changing the 3071 are:

1) surging down low brings spool later
2) can get a similar turbo (as far as spooling time) and more hp.

I understand the concerns of getting a ridusucly big turbo that would spool from 5000+rpm and that is not what i want to go for.

It is just that comp has so many options that makes a choice difficult. Sure the 355 can get 530hp with 1.9bar. I believe that. When i ask about the spooling differences with the 358 the answer is minimal. If the 355 can get that number and spool from 3500rpm on OEM inlet manifold as repo has stated in other threads,then im definitelly going to be happier to have the 358 which will give more power if i want to in the future, spool <4000rpm on reverse inlet manifold and OEM cyl head.+ that turbo may be able to make the same amount of power on 1.7bar perhaps(?) even better for my liking.

Then the question arised when the 458 and 358 again had very minor differences. These are not turbos that are going to be in a completelly different powerband from each other. It is not comparing GT3071R and GT35R for example. It is more like comparing a GT3076R with a GT3076R and a Gt35 compressor housing more or less.

Nonetheless, i want to thank you again for all the answers! they do help into the desicion making prosess!

[jogi730]

Well good luck and I hope you get the car working just as you would like.
However, I would give you one final warning - Justin at CT will have very little knowledge of turbo's in Audi engines. Repo on the other hand has fitted these units.
Look forward to seeing results whatever you fit though.
Cheers
Chris

[A80Avant]

repo is even more positive on spool times and hps from justin as far as the turbo's capabilities so bottom line is that when jade tests his 358 i will have a better view of what they are capable of.

I respect repo's work and abilities but it is always good to have more information! (hence this thread as well!!)

[porkkis]

I'd say 58/58 0.63 will surge too. Of course impossible to say for certain and even harder without comp maps, but I just have a feeling...

As i explained,this will be the permanent turbo choise for me as improvements and further steps will not be taken.

Haha

[A80Avant]

i know what you mean,but im hopeful!

will it surge as much since it is not ball bearing?

[Bram]

CT355 it is Vasilis. That would be my next choice of turbo.

[QuattroFever]

Knowing how much you seem to want the power I'd say go for the larger of the two and if you don't like the lag then build a stroker

More sound advice in that than probably realised.

[S2central.net]

FWIW - I would take Repo's advise on this... he's built more 500hp +++ engines than most of us put together. The quote about smallest turbo for target power is spot on... Only 'gotcha' is that implies higher boost levels - If Repo has evidence that can be done reliably at 1.9bar or 2bar on this turbo (with the right cams and EM) then I wouldn't worry.

A 500hp target on a heavy RS2 is gonna need plenty of torque in the low and mid range to make it anyway pleasant to drive in normal traffic and such.

[A80Avant]

guys, 560Nm of torgue that i have now on the rs2 from 4000rpm is not at all bad. The 355 can do that 530hp with repo's exhaust manifold (not the SQ) which has better flow, and on 1.9bar.SO is it possible that the SQ will be more restrictive hence less boost or ignition timing to avoid EGTs hence less overall power?

On a race engine a turbo can perform it's best no doubt.But on engines built to last long,it might be slightly less.

Besides, 355 and 358 have the same turbine impellers (i think) and different compressor wheels.Otherwise they are the same. Lets see how jade does on his engine...I believe that the 358 can have a quite wide powerband as well.

[GazzaG60]

id take the advice of those who know. i know a fair bit about turbos but the likes of repo and killa who i speak to have forgotten more than i know.

they have seen and studied the turbos through the years and have a proven track record on making turbo engines work well.

the comment regarding turbo size that jamo said is biblical most cetainly is. the best turbo for the job is the one that gioves the widet powerband at the chosen powerlevel. turbos are about compromise after all.

i too have been looking at new turbos. i like my precision 6152 but would like a wider powerband and more efficient top end so may change for one of the new precision billet range.

i will agree with comments regarding on/off switches. this is more prominent on smaller turbos. bigger more lethargic ones tend to inch the power in until high up the range creating a nice easy transition to boost. most drivable but not great for zipping cars in traffic. in real world terms a car has pulled a lenght on me then in boost i pull back 5. if that car is a well sorted one id be on catchup. this was always more evident with my Corrado G60 (supercharged) v's the subarus.

[Billman]

I hear all these months such nice things about these CT turbos but dint see any dynos yet! Is something out there???

if i have the money for this and time i will drive mine also to a dyno to see what it makes with the small hx40.

[Rocco]

Vasilis and are you thinking in the gearbox stress??


how many nm´s of torque can be enough for break and destroy the Stronger RS2 gearbox??


i am sure that in the ARV´s more than 550nm will be critical surelly...

[A80Avant]

CRB gearbox has been tried on with cars of 700 and 800hp and loads of torgue.I dont fear that there will be a problem there