EFR 6258 or 6758
 

Hey Ladies,

I'm about to choose a turbo for my car, but not 100% sure what to go for...

My car is mainly used for circuit racing and entry level time-attack, so probably key to keep power levels linear as possible

My current plan is just to +T the thing, no built motor run low boost, till the the forged motor is built (still a few months away), then turn it up a little and start playing around with E85 (doing preparation for that now).


Recommendations, flames welcome

EFR9180

Did find an awesome post by Soviet on the 6258 and 2758 with dyno graphs...
https://www.miataturbo.net/dynos-tim...e2/#post939044

This is a comparison that has been extensively hashed out. If you want much over 300 whp, go 6758. You'll have lots of headroom with a slight penalty in spool/response. If you don't need more than 300whp, no reason to go 6758.

Assemble all the parts required. Buy the turbo last based on how much money you have left or after you've thought long and hard about what you just asked.

quoted for truth, minus the crossed out part

I forgot, both the efr6x58 turbos cost the same.

In terms of drivability how drivable is a BP on 9.5 compression with a 6758?

Questions are getting quite silly now

Indeed.

It's not like this is some .86 A/R T4 turbo from 1992.

There are videos and Dyno plots and driving impressions all over this forum. Aidandj, savington, that other guy... And more. Just, go read about it.

Are you asking pre or post ventilating the block?

Good luck OP

/unsubscribed

I went with a 6758 and love it, coming from a 2560 @ 17psi I would say I found the spool is (as expected) slightly slower with the EFR but only just. The V-Band interface makes any exhaust side work a piece of cake. I would say if you are going to run e85, you should get some good injectors though. In my case I went with Injector Dynamics 1300cc which were made specifically for corn. Gives me a nice stable idle and plenty of DC% left at 20psi on the EFR.

Thanks @Der_Idiot, more in line what I was after :D

Bumping an old thread sorry. What if you're spinning to 8500-9000 rpm?
I was thinking the .64 may really choke the motor at higher RPM. I'm going with a custom manifold anyway, so I was thinking Twin scroll 6258, if that still gets choked then twin scroll 6758

6258.

In the end I went with the EFR 6258, partly because there was no 6758's in stock :P And I figured if it doesn't fit, I'll sell it and go bigger. But it will do just fine for the next year, while I finish my spare motor.

Both turbo's have the same 58mm exhaust housing so in my opinion if you're worried higher RPM spool you need to go bigger. I can't comment if these run out of puff at that RPM, mine is till in a box :giggle:. As for twin scroll, you gain a wider range of operation, but you give something up too and that is the amount it can flow, normally thats why you can go slightly bigger with a twin scroll exhaust housing, then there is the manifolds, no off the self item for Miata's that I'm aware off.

My two worthless New Zealand cents :2cents: