Ok, so, granted we can get our hands on MHI hotsides still. However the song is getting old in that the divider's will keep-on-crackin. FP's got some interesting builds out now on their SS housings. FP54 vs UHF. Which spools quicker, and would either one even be in the same ballpark as a 71 in order to get away from MHI's.

 

The MHI housing goes quit a long time before cracking. The one on my red went 25k hard miles with track use at 500whp, then ate all the **** that went through it (piston and valve chunks) when the motor blew up and it didn't crack.

I'd go to a turbo kit with a Gseries turbo before going to a single scroll "stock frame" turbo. The G25-550 would be super responsive.

 

Well I have 4 hotsides here that would disagree lol. Would love a Gseries, but that's a "do I spend 5k for a turbo kit or 5k for a dry sump" question. Why is everything so many damn K's at this level lol.

 

Do you log EGTs?

 

This.
And are you running gasoline or E85?
Also, where/how bad are they cracked? A small vertical crack in the divider isn't the end of the world. They can be run quite a while like that without issue. Hell, FP will even still machine them.

 

They USED to machine them back when they weren't available. Now they're back to rejecting the simple vertical cracks again. 100 octane, never above 1080 C's mid summer usually. The issue is duration at that temp, the thin divider is a matter of time in these cases. Yes it still runs "fine", but this isn't a grocery getter. When it's tuned within 1hp of my class limit fresh and new, we can't have any degradation since I'm already ~10hp behind due to AWD points.

 

1080*C is super hot, hotter than acceptable (1950*F). Example, the Mar-M turbine (higher temp rated than inconel) and stainless turbine housings used in/on the Gseries turbo's are rated at 1050*C.

You need to work on your EGT's, they are simply too high. What boost, timing, and AFR are you running? Any reason you're not running E85?

 

850-900 normally, it only gets around 1080 on a 100 deg day when you're sucking in hot humid air for 45 mins. That was last year, I have since used a different stock manifold, different tuner, etc so I dunno what it is now. I usually shoot for 11.6-11.7. You can't use the stock fuel tank on e85, simply not enough volume. Would need in the range of ~20+ gallon tank to do that. None of the surge setups are FT3 certified, and even once you did go that route, you'd need to recert every 5 years.

 

Your target AFR is lean. You should be targeting a 10.8 running gasoline for hot laps.

 

That's pretty rich for back straight 4th, that'd be more for TT and 93 octane. If I ran that rich I'd be out of gas with 10mins to spare in the race, I barely get done with 1/8 as it is. It depends really on the gas you use, real race gas likes it lean much like E85 does.

 

Your EGT's and cracked turbine housings say otherwise.

Race fuel doesn't lower EGT like ethanol, and still tends to need the richer AFR. Even with Ethanol, we only run a low 11 for road course use, 11.1-11.3.

 

I have run my car in the 11.3-11.4 range on track for years. In monitoring EGTs during tuning, I've actually seen higher EGTs (920+ C) when running high 10 AFRs than mid-11s (high 800s/low 900s) -- all on 93 octane. I attributed the higher EGTs with richer mixtures to more unburnt fuel making it into the manifold and then combusting there. So, potentially lower cylinder temps with richer AFRs but higher exhaust temps hitting the hot side (though not necessarily the combustion chambers and exhaust valves). Am I wrong?

 

Getting cooler as you go leaner like that generally means not enough timing.

 

How much interest is there in a twinscroll stainless housing for FP turbos?

 

If you could nail the design, prove reliability, and keep the price reasonable then I think demand would be high. Even more so if/when the MHI housings disappear again.

Getting to that point could be difficult, though. I'm assuming there's a reason that FP hasn't tried it themselves yet