Turbo choices and why

[Manic172]

As you all should know by now I am building a mk1 race car.... well you do now any way.
Right it's coming to that point soon of engine and turbo spec.
Rough spec is rods 8.5 cr pistons. Catcam cams and pulley. Posted and polished head bigger inlet manifold . Over sized inlet and exhaust valves. Etc etc.
But turbo I am a bit lost on.. Do I go k04 hybrid... garret been told the g25-660 is worth it's money. Or even the 550. Or is there another
Please throw your ideas and reasons out there. And what you running and why you like and dislike the set up or what you would do to improve it.

 

[Leon20vt4]

Okay so I know a lot in this area of bigger turbo choices... I need more information from you first and I can give you some recommendations and reasons why.

Budget for turbo what would you like to spend and then what is your absolute maximum ... just the turbo nothing else

What HP and TQ do you want?

What will your rev limit be?

E85? Meth? 100?

Different turbos will give you different power bands in the rev range. What kind of peer and are you looking for? 2000-6000 or 3500-8000?




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[Manic172]

Looking for a useable 350-400bhp. Running normal super unleaded. Not worried about budget. Just not going stupid money on a name . Don't want lay or loads of lag.
The car is raced for any thing up to 2 hour endurance racing.
Thinking about 2000-6000 rpm so not excessive wear on the internals.

 

[Leon20vt4]

Have you already gone 8.5 CR?


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[Leon20vt4]

And does the motor already have all of that done?! Because you’re building a motor that sounds like you’re shooting for 700-850+ HP


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[Manic172]

Nope nothing done yet just making lists buying parts. Wanna make an enginnethat can easily do the 350-400 with out straining it and pushing it when raced.

 

[Leon20vt4]

Nope nothing done yet just making lists buying parts. Wanna make an enginnethat can easily do the 350-400 with out straining it and pushing it when raced.

These 20v engines we have actually flow rather well! In my opinion for your HP goals under hard abuse for the track don’t need everything on your list.

You can utilize the money in other areas.

For 350-400hp you only need rods on the street. Now since you’re tracking the car I would do this list below. It’ll be plenty durable and flow great.


*Upgraded Rods (IMPORTANT rifle drilled)

*Upgraded Pistons (just for security... stock pistons can hold 500hp all day)

*Supertech Intake and Exhaust Valves

*race bearings

*ARP bolts or studs everywhere you can use them

*Baffled oil sump

* Oil cooler

AGU large Port head and intake mani (much cheaper alternative to porting, and you don’t even need large port at your hp and redline goals)

Upgrade intake mani (when you want to... not necessary for your HP goals)

You don’t need larger cams at your hp and rev limit if you want to change them go with NA intake cam only help with larger turbos no good for small or stock turbos.

You don’t need valve springs unless you go above 7500rpm


Of course you can do it how you wish brotha it’s your car and your project! Just trying to save you money where you don’t need it. Now if you told me you want to go 600+hp later for the track then I would understand the excessive build up. Long story short our engines are actually pretty good and just need some strengthening. The only time larger porting and more airflow etc is necessary is above the magical 500-550hp mark. If you’re underneath that you really only need rods, exhaust valves, ARP bolts and studs for daily driving and for track add on some forged pistons, intake valves, bearings.

Next post will be turbo information for you


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[Manic172]

Yep ie Eiffel rods will be ordered. Got baffled sump. Manuel cam belt tensioner. Supertech +1mm inlet and exhaust ordered. Along with new supertech valve guides and seals .Not sure what make pistons to go for.. wossner cp or some thing else.

 

[Manic172]

Will be ARP head stud conversion. Big end main ends, flywheel got carbon fibre belt cover coming. Looking in to msd ignition coil pack with lead conversion. And running on omex 600 ecu

 

[Leon20vt4]

You do your own tuning?

Also 350-400 at crank or wheels?

Sounding to me like a “properly specd” GT2871R will be your go to turbo. Especially if you do a large port head and mani.

A properly setup GT2871R with a .64AR is capable of 450hp there are a few variations you have to make sure you get the 450 capable version.

This turbo will give you that low RPM boost and little to no lag you’re looking for. If you go to a 3071r you’ll be moving that power band up higher in your rpm range.


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[Leon20vt4]

You do your own tuning?

Also 350-400 at crank or wheels?

Sounding to me like a “properly specd” GT2871R will be your go to turbo. Especially if you do a large port head and mani.

A properly setup GT2871R with a .64AR is capable of 450hp there are a few variations you have to make sure you get the 450 capable version.

This turbo will give you that low RPM boost and little to no lag you’re looking for. If you go to a 3071r you’ll be moving that power band up higher in your rpm range.


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450-475 max crank hp


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[Leon20vt4]

So take a read at this... 100% relevant sorry for posting from another forum, but it’s relevant info to this topic.

https://forums.vwvortex.com/showthread.php?4600369-What-is-for-me-...GT2871R-vs.-GT3071R&amp=1


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[Leon20vt4]

Stay 9.0-9.5 compression ratio to keep the lag away you don’t need 8.5 you’re not running 40psi, 100octane will be fine at that compression ratio.

I like weisco pistons myself but any high quality brand will be great no questions asked.

Large port head AGU
Large port upgraded mani
GT2871R .64ar
9.0-9.5cr
22psi (1.5bar) by 3200-3500 for sure and will pull hard all the way to 7500rpm

Here is the turbo part number I believe will be the perfect turbo choice for you. But I would give Garrett a call and ask.

Part number: 836026-5021S


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[Manic172]

How comes your saying the gt28 over the gt25. From what I have read the 25 is smaller but has bigger capability. I know the gt25 is external waste gate so need manifold and waste gate etc.
I know bigger all about turbo so all I am learning is by reading but I know not to believe all I read lol. So this is why I have so many questions .

 

[Leon20vt4]

You mean for example g25-660? Etc?


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[Manic172]

Yeah sorry the 660
It's got a higher bhp capability and guessing more modern technology is a little smaller so less weight hanging on a manifold etc. Just wondering

 

[Leon20vt4]

Don’t get me wrong if you have the money the g25-660 is an amazing turbo. But it’s nearly 2x the price of the Gt28.

And for your power goals it’s overkill.

Now if you want the baddest turbo for small displacement engines up to 650+hp and to future proof your car then it’s the turbo to get.

But if you’re goals are 400hp and you don’t want to spend 2k just for shits and giggles then go with a gt28


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[Manic172]

Really stupid question but what's the difference of the gt25-550 and the 660. Apart from the displacement.
Trying to find on line if it just the hot and cold side impellers or is there more to it. As the 550 would be good enough.
Then with a good manifold. 3.5 down pipe. Then 3" system. Think it will be on song.

 

[Leon20vt4]

Really stupid question but what's the difference of the gt25-550 and the 660. Apart from the displacement.
Trying to find on line if it just the hot and cold side impellers or is there more to it. As the 550 would be good enough.
Then with a good manifold. 3.5 down pipe. Then 3" system. Think it will be on song.

Definitely a question for Garrett give them a call Monday and just ask the difference between 550 and 660


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