Compare the compressor inducer size, turbine exducer size, & housing size (ar size) of the two. When you're not sure go with the bigger one it will be easier to make power and have less back pressure on the head. The top-end power is where the fun is. These new bigger turbos are usually very responsive at 3000 rpm and above.

 

What kind of ratio would I be looking for comparing the two’s inducer and exducer sizes? Thanks! I believe the A/R are actually equivalent between them.

 

Hi all! I have seen a lot of information on the G25-660/25-550 turbos and they look very promising. I have the opportunity to purchase a G30-660 at a discounted rate new and was wondering if anyone is running one? I was hoping to find out what the spool time was like, is it super slow? My power goals right now are 380-400 hp with stock internals and stock fuelling (with E), however I want to build my motor and upgrade fueling in the future. Is the 30-660 overkill and will the spool time make it feel too sluggish? Thanks!

Ethan

I went with a BNR3071 (.72 ar)because it'll make mid 400's easily with supporting mods (fueling). It only scarified a few hundred RPMs on the spool time over a BNR2867, but made more power with less effort. Its my bottle neck now as I am built for and want just over 500whp, and Im prob 480-500 range right now. I guess the goal is to KNOW what power level you really want. I was going for 400whp...then 420whp...then 440whp...then figured wtf i built the engine due to breaking it around 410'ish whp while it was stock internals, and now with the HPFP and Injectors, my turbo is the limit at 500whp at most (Ill eventually dyno it soon). I think there are YT videos comparing the 550 vs the 660, and the turbo will have the same characteristics on any platform (i think it was on an STi if i recall).

Ive eyed the 25-550 because it would have the breathing room to get me over 500, which is my current and final goal (100% I just want to hit 500 mark). But since everywhere advertised that my BNR71 could get 'up to 500whp', and I dont know if Im quite there with all the supporting mods, that 550 may not easily get to the 550 if thats your end goal. My recommendation based on experience is do not go over 400 whp on the stock engine like you mentioned (big turbo, RS injectors would allow you to get there). Even with a well maintained, very clean engine at 100k miles, it was too much for the rod in cyl1 and I was doing 3rd/4th gear pulls and never ran it over redline or ran it hard in higher gear at lower speed. It was simply the limits of the rods (cracked, bent, caused the ringlands to melt into the cylinder wall and allow oil by). The BNR also is a pretty simple swap and for the cost, a great turbo. The latest version Bryan (with BNR) has yet to release, will net over 500 adding upgraded internals. I think it'll be "V3"? Im likely going to swap to that since it'll be an out/in kind of swap..maybe just a slight tune revision by JST. Otherwise, I may swap in the 25-550 which costs more and will require a bit more work over the BNR.

 

so what I’m hearing is likely it may be better to future proof with the larger option since my HP goals are north of stock internals and would put less strain on the turbo when I have those built internals.

 

I’m also only at 68,000 miles, but I know sometimes that just doesn’t matter.

 

Yea a 0.72 ar is in the middle range. It also depends on the turbine exducer size. ARs range from ~0.64-1.05 maybe higher or lower these are some I've worked with. I've had 0.64 that spool extremely quickly and a 1.05 that spooled fairly quickly due to a smaller exducer but flowed a lot up top due to less back pressure.

Yea a 0.72 ar is in the middle range. It also depends on the turbine exducer size. ARs range from ~0.64-1.05 maybe higher or lower these are some I've worked with. I've had 0.64 that spool extremely quickly and a 1.05 that spooled fairly quickly due to a smaller exducer but flowed a lot up top due to less back pressure.

This is what garrett has to say about the inducer and exducer, could you help me decipher these numbers? Thank you!!

 

for comparison.

 

Id go g30-660 personally...

 

I’m inclined to agree, but what’s your reasoning?

 

If your goals are 400hp, the 660 series is overkill. The G25-550 will have plenty of room at the top to get you your 400hp and will retain the same (or very similar) responsiveness as the OE K03.

JST tuned my G25-550 and it exceeds OEM boost levels by 2600 rpm’s. I’m also running the ArcEnemy downpipe with the latest version of the Junit’s elbow.

JST thought the downpipe and elbow were contributing factors in enabling the G25-550 to have the type of instant power as the K03 yet still have all the up top power.

This is a link to JST’s thoughts on the G25-550 tune he put on my car.

If you’re going to build your engine and go 500+ horsepower, the 660 is a better turbo compared to the 550.

 

So I changed my mind and ended up going with the G25-550 with the downpipe, that quick spool is too enticing.
How did you like being tuned by JST? I’m waffling on who to go with.

 

So I know I’m not who you directed the question to and I don’t have a G25-550 but I gotta say I think you’ll be hard pressed to find a bad review about Brian at JST.

For me it was his reasonable pricing, his knowledge and the fact he actually cares about the platform, and what really was telling to me about his character was his willingness to answer my many questions and concerns about tuning and big turbos prior to me even going with him.

im sure you’re probably tossing up between him or edge likely especially now that monster tuned is out of the picture. The truth is neither is a bad choice. I have also learned a lot from Edge’s videos he has posted about the platform.

 

So I know I’m not who you directed the question to and I don’t have a G25-550 but I gotta say I think you’ll be hard pressed to find a bad review about Brian at JST.

For me it was his reasonable pricing, his knowledge and the fact he actually cares about the platform, and what really was telling to me about his character was his willingness to answer my many questions and concerns about tuning and big turbos prior to me even going with him.

im sure you’re probably tossing up between him or edge likely especially now that monster tuned is out of the picture. The truth is neither is a bad choice. I have also learned a lot from Edge’s videos he has posted about the platform.

Thank you for the insight, I will probably end up going with JST since I see he puts out quality work for an affordable price (nearly $120 less then edge for the same parameters that I want).