Thinking of changing turbo housings....

[Flapjack]

I've been talking with Jim at THP for the past few days, in regards to the difference in spool time now that I'm back on 91 octane (coming from E85). With the ethanol, the turbos were pretty much fully spooled around 3400rpm. Of course, that was with with 7psi only. Now, I'm hitting 7psi around 4000rpm, and not hitting 12psi (what the EBC is set to) until 5500rpm or so. It's really hard to tell without logging boost (working on that), but those rpms should be pretty close.

My engine is an built MMR 5.4L 3v with twin Garrett 61s. The exhaust housing is .82 and the wheels are stage 5. After talking with Jim, I'm considering going to a .63AR and keeping the stage 5 wheels.

I have not had the car dynoed with the new engine/heads, but I'm guessing I'm somewhere between 600-650rwhp. I made 547 (corrected, Colorado Springs, 6500ft) on E85 on the stock engine. I ran low 13s on street tires at Pueblo, but I was also having a MAF issue I didn't know about until now. The car feels much, much better... but I haven't had it at the track since and probably won't until Oct 27th. If I do the housings, it'll likely be a winter project.

Thoughts? The car is primarily street, which is the only reason I'm seriously considering this. I thought about a WOT box, which would probably resolve the longer spool time at the track, but honestly, I only make it out a few times a year. Nitrous is not really an option for me, as I have enough shit under the hood as it is, and really don't want to add another power adder. I will probably keep the .82 housings in case an E85 station pops up closer to my new house.

Here are some other pertinent info on my build:

- WGs springed at 7psi
-- Currently at 12psi with EBC, waiting on 13psi springs from THP
-- No plans to run more than 12-13psi until Spring
- RGR stage 3 heads, w/turbo cams
- JPC intake
- TR6060
- 3.73 gears
- McCleod RXT
- MT DRs (haven't run them with the turbos yet)

 

[19COBRA93]

I know it's a little different, but on my THP twin turbo 03 Cobra, I swapped from twin 67's (which were just massive overkill) to much smaller 54mm turbos with the same exhaust housings, and my full spool (10lbs) went from 5500 rpm down to 3500 rpm. I gained 150 ft/lbs of torque at 4000 as well. lol. The difference was like swapping from a centrifugal blower to a roots blower. And went from "I hate this doggy piece of shit" to "I can't stop driving the shit out of this car!"

 

[one eyed willy]

I'd go to the smaller housing! I run that .82 housing on my single turbo....I'm at 17psi before 3000 rpm.....

 

[Flapjack]

I know it's a little different, but on my THP twin turbo 03 Cobra, I swapped from twin 67's (which were just massive overkill) to much smaller 54mm turbos with the same exhaust housings, and my full spool (10lbs) went from 5500 rpm down to 3500 rpm. I gained 150 ft/lbs of torque at 4000 as well. lol. The difference was like swapping from a centrifugal blower to a roots blower. And went from "I hate this doggy piece of shit" to "I can't stop driving the shit out of this car!"

You've got me sold. My biggest concern everything I've read, and even Jim say, is that the larger AR makes more power (less restriction). The converse obviously being that more restriction makes less top-end power, but spools quicker. I'm sure I'll lose some top end power, but I'll be reaching my desired boost much quicker. Jim says with that housing/wheel, I'd still be able to run up to 30psi or so, which is more than I'll ever need. I can see me running no more than 20-25psi. I'm not sure where my limit will be with pump gas, but I'm sure it'll be somewhere closer to 20psi... if that.

I'd go to the smaller housing! I run that .82 housing on my single turbo....I'm at 17psi before 3000 rpm.....

Awesome. Hopefully the twin 61mm/.63AR/stage 5 combo will be closer to 3k than 5k rpm! Looking back, the .82AR was great for E85, but not for gas.

 

[Flapjack]

New housings are on order. Thanks, Jim!

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