Best turbo for a stock VVT block that's getting forged in the future?
 

Hey guys,

New to the forum, but I've been lurking for a while. I've been a bit lucky recently and got handed an opportunity to get a rather large discount on a turbo kit (T25 flange)

Question is however, what turbo should I go for? I've had a few on my mind and I don't mind paying a bit of a premium if it saves my ass in the long run. I've currently got the following turbos shortlisted. 280whp is probably the most I'd ever want out of the turbo once I build my block, preferably 200 whp before I start modifying the internals.

BorgWarner EFR 6258/6758 - I personally opted for a 6258 initially, but the kit manufacturer said that the 6758 is a far better turbo. My worries with the 6758 is that it might blow up my block down the road. I like these for their supposed fast spooling. (Drove a NB 1.8 with a TD04 and that was lots of fun, but it did lack a bit of power)
Garrett GT2554R and Garrett GT2560R - Tried and true on MX5's, but I heard the 2560 doesn't spool as fast as a 6258 and the 2554R isn't quite up to the task of 280whp once I go built
Garrett GBC20-300 - Suggested as an alternative by the kit supplier, but journal bearing is off-putting. Worried about how these spool. Can't really find much about them online either
Pulsar G25-550 - Knockoff Garrett, not sure if I'd want this.

What are your thoughts? Anything I'm overseeing? The 6258 is the one I'm still leaning the most towards to as I'm afraid a 6758 will straight up murder my block even at tame settings. Pump gas here is 98 octane (93 US) - Magic corn juice doesn't exist here unfortunately

I'd go with a GTX2860.

Spools a little slower than a 2560, easier on the rods on a stock block as long as you keep boost reasonable (<10psi or so?), tons of overhead for when you go forged.

The 6758 is a larger turbo, so it'll spool just a bit later, so technically it's safer for a stock block. Tune any turbo smartly, and you won't have any issues blowing up your block. You can run the EFRs are low as 4-5psi with the correct wastegate preload.

Not going to comment directly on choice of turbo, just say that having bent a set of rods on a 140rwkw (MSM) IHI turbo with a supposedly safe tune, build the motor sooner rather than later, before the rods make the decision for you.

Like you I was planning for the future, but the future came and bit me on the bum before I was ready.

(FWIW I am currently running the Pulsar 2860 clone, 190rwkw on a 'running in' tune)

I I'll keep that one in the back of my mind. It's been mentioned by others before too.


Would this mean getting the lower boost actuator in order to get that to work? I'll be honest, I'm not too knowledgeable on the EFRs other than hearing people sing praises on them.

Rods and pistons are next on the list, it's just that I'm getting the kit at a 1500 eur discount and with free fitment.


While I've got the thread up here, I suppose I might as well ask another question. Originally before I got this opportunity thrown in my face, I was thinking of supercharging the NB. I still want to keep the driving dynamics of an MX-5 with a snappy throttle response and a linear power delivery. With that in mind, which turbo would be the best based on the choices above?

And that's a perfect example of how to bend your rods, small turbo making peak torque quickly. I too have bent rods with a MSM setup. If you install a 6258 or 6758 and tune the EBC for max spool, you're going to have a bad time. Run wastegate only with very little preload, and you can run the turbo on a stock motor for a long time.

This is me - stock motor EFR6258 running wastegate pressure with low preload (~7.5 PSI on average). 5 years of track days and not blowed up yet (knock on wood).

EFR 6258 on stock BP4W rods and pistons. Low pressure wastegate can with minimal preload and EBC. 2 years and going (knock on wood).