Car stops pulling @ 7k. 50+lb/min

[cjridert1]

Looking for advice:
Car feels like its doing real good power 4-7k, but I see lots of guys getting way more rpms. I have: Stage 1 buschur head, 272s, SMIM (homemade, pic attached) as well as .55 BEP housing - looking for where the car is choking. Im looking at headwork and larger cams, but what I have should be pulling past 7k I would think? This is ~30psi and 15* of timing.

 

[cjridert1]

SMIM on bottom of page here; couldnt figure how to transfer it over

 

[1gDSM4g63]

Unless it's the tuning, your head unit with the Crower 272s is good. When I had an unported head with my HX40 69 lb/min the powerband never ended or at least til 9000. Maybe the 52 lb/min turbo ends at 7000.



You mean this?

 

[cjridert1]

Yea thats the pic. Setup is a bit different, but same intake mani. What cams were you running? turbine a/r?

 

[cjridert1]

Liklihood that a .70a/r housing would fix the problem?

 

[1gDSM4g63]

I'm using the T3 BEP .70 a/r and BC 280 cams, but if you're using the T3 BEP like it says in your profile that it is .70 a/r not .55 a/r and the Crower 272 cams doesn't choke at 7000. Plus the Burschur stage I head unit is not ported, but that shouldn't matter.

The 52 lb/min turbo may not have the broad powerband range.

 

[dsm-onster]

^^^ The bolton housing with the same hx40 turbine wheel you have doesn't choke at 7K either with that big hx40 setup you have (which is very nice BTW). You just will have faster spool and less pumpgas power. Yes it will choke more than the .70 housing when the hx40 is being pushed to the limit. You ll need more boost for the same power and still have a powerband that will drop past 7500rpms (if you really care), but that's only if you really push the turbo. The 70a/r housign is a GREAT piece, but not really neccesary for a 600whp hx40 build at all, no matter what rpm you want to run at. If it takes 8K to see 65lb/min with your setup, then the turbo will be there to deliver it. And the bolton hx40 can certainly do 65lb/min easily. 700whp hx40??? then yea, get the bigger housing. More power at lower boost???? then yes, that .70 a/r housing is ideal. Still spools pretty good.

You there have the makings for hellatios results!

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Cody! Congratulations on that airflow. I've NEVER seen someone log much over 53lb/min with a bolton housing and an hx35 turbine wheel. But you're pulling 56.5lb/min in 2nd gear! at 25psi! Boost IS falling off. Are you sure you have enough WG spring? If so then you certainly are seeing the full potential of a bolton housign with that smallish hx35 turbine wheel. Its really looking like a good match for the fastest spool for the most power.

I think you might be right about the smaller turbien housing. But still, you see your highest airflow, that 56.5lb/min, at 7750rpms. That's not bad and well over 7K. Doesn't look like it's really dieing up top. I've seen similar curves all over the website and other boards. Limited flow past 52-53lb/min is why I don't recommend wasting the extra money or time hunting down a 7blade 60lb/min hx35 when you're going to use a bolton configuration with the hx35 turbine wheel (hx40 turbine wheel is a whole different story. You however are seen quite a bit more than 52lb/min.

But first let's get the details of your hx35 turbo in here:

Which blade count is the compressor? There's also a 54mm 8blade inducer hx35. Do you have that one? The most common hx35s are the 56mm 7blade and 8blade units. But several I've seen that have the regular silicone coupler compressor outlet (not vband copressor cover outlet) have the small 54mm inducer. To see 56.5 lb/min out of this compressor with the bolton housngi would be . . . just nuts!

 

[cjridert1]

Its a .55a/r with mitsu outlet t3 inlet. 7 Blade hx35 off a 2001 I believe. I dont have the #s handy, but I remember compressor being 56ind 79exd (memory dependent, sorry). I ground the Vband off the compressor outlet and welded a 90* aluminum 2.5" elbow on. The 56lb/min may be falsely elevated, boostest is a few psi higher than my gm3bar and I think airflow values are calculated off boostest values? My mechanical gauge was higher than both.
Waste spring is a 14.7/blue. The car pulls really well 5-6.5k or so, but really asks me to shift at anything over low 7ks. In third, I am shifting right about when it starts to fall off.

 

[dsm-onster]

I think you're fine with your smaller 38mm gate with a 14psi spring at 27psi spike then. I don't see that blowing upen. But it's possible. I'd try another spring if you can. See if you can hold boost better from 5K to 7K. Can you get more boost out of the turbo just turning the MBC up? Or have you tried?

After than, then it looks like youre showing us how far a bolton hx35 can go in the flow department. If you can get an accurate calibration done, we can see exacty where things are going flow wise.

 

[cjridert1]

I think you're fine with your smaller 38mm gate with a 14psi spring at 27psi spike then. I don't see that blowing upen. But it's possible. I'd try another spring if you can. See if you can hold boost better from 5K to 7K. Can you get more boost out of the turbo just turning the MBC up? Or have you tried?

After than, then it looks like youre showing us how far a bolton hx35 can go in the flow department. If you can get an accurate calibration done, we can see exacty where things are going flow wise.

Yea, boost has been up more (up to 31-2ish); dont have those logs handy. Pump gas started knocking a bit past 30. Is there a way to calibrate airflow past 2400hz? If #s are important, maybe convert hz to lb/min?
Ill see if I can find a spring somewhere and give it a go.

 

[dsm-onster]

LOWER the 2400hz slider . It will affect all hertz numbers past that.

 

[JayRolla]

Yea I was going to say his calibration is off. Im planning on the 8 blade hx40 in the bolt on and expecting to flow what he is, . But I will be on stock cams.

 

[dsm-onster]

Woe! think about it. Your boostest is ONLY accurate when VE is 100%. That doesn't mean your lb/min airflow is inaccurate. lb/min airflow is directly calculated from maf hertz and baro and inlet temp. If you have a maft then it is based soley on the maf hertz with the other data clamped to make the actual airflow calculation accurate (otherwise the ecu can't meter the fuel properly). Calibrating the maf and usign the boostest number only works from 5-5500rpms. You have to extrapolate the graph after that.

Point is. . . I doubt the VE of your motor is at 100% VE at 7500rpms even with the cams and smim upgrade. No way. When VE is below 100% boostest will read high for a particular airflow. Since the motor isn't pumping 100% of it's potential, the airflow makes the link estimation protocol think more boost is there than there really is. . .

 

[dsm-onster]

To confirm my above post. . . Looking back at your boostest vs. your actual boost from 5K-5.5K, you're boostest is only about 2psi above actual boost. That's not a bad % difference at 30ish psi. That means your airflow numbers are likely rather accurate

At 5500rpms in 3rd gear (the best gear to log in and correct the maf with), you are at 28.5psi actual and 30.6psi boostest and 3500Hz raw (<=). Using Jeff's MAf calibration page, you can see that you need to move the last maf compensation slider down a little less than 5%. That's all. I suggest moving the second to last slider down 2% to make the compensation graph look more smooth.

You should now be logging 54ish lb/min in 2nd gear. That gear seams to be showing the highest airflow in your case.