Dapper Dan

iTrader: (28)

Ok im having a little problem here. I just got my new motor broken in and
started tuning my pump gas map. Im hitting 330 load and then it drops all the way to 170.
Ive fixed all my boost leaks and my boost is holding solid. Ive done a compression test and its just under 200 across. Im running a gt35r and a gm maf. Do you think it could be the maf giving me these problems? Before this motor my load would stay pegged till 9000 rpms. Any ideas would be great.


-nick

Q15H

iTrader: (5)

That is expected behavior. As RPM increases - for the same airflow - load will drop.

Load = ( airflow ) / ( RPM *2 )
(since there's two rotations per intake cycle)

Typically load will very closely follow your torque peak.

Remember that load is the amount of air per cylinder charge. So if you had 2000 #/hr (33.3 #/min) airflow at 3000 RPM, that same airflow at 6000 RPM would be exactly half. (33 #/min is roughly ~300-330 HP.)

If you are attempting to "flatten" out the load values in the higher RPM range, you will need to drastically increase the boost levels as RPM increases to get more airflow (which is not always proportional to boost pressure).

Dapper Dan

iTrader: (28)

That makes sense, I just dont remember it dropping off like this before. But then again its been a while.

l2r99gst

iTrader: (2)

Load is dropping off way too much, assuming your boost is holding steady.

Did you do anything with the MAFT? Is it zeroed out?

Q15H

iTrader: (5)

Post some logs. Include RPM, corrected MAF value (in airflow, not in volts), and the ECU's calculated load values. Hopefully you saved some from "before"?

Dapper Dan

iTrader: (28)

Thats what I thought, Im using the same maft settings I was using on my old motor.

Give me a few minutes and ill have one up. I dont have any from before anymore tho.

But any ways my load is acting really funky now, im only hitting mid 200s

Dapper Dan

iTrader: (28)

Dapper Dan

iTrader: (28)

My airflow should be much higher

Q15H

iTrader: (5)

Your recorded airflow values are reasonably flat from 6K to 9K so while RPM climbs ~33%, load also drops off about the same amount so the calculations (by the ECU) appear to be very close.

Yes - you need more airflow in the upper RPM range. If those airflow values are in pounds per hour, your airflow seems lower than I would expect. How much power is this engine making? That airflow (again if the values are in #/hr) is just a bit under 300.

Dapper Dan

iTrader: (28)

I dont know how much power im making but something isnt right for sure. My car just feels like it has no top end.

The last time I was at the 1/8th mile track I ran a 7.3 @ 96 mph on low boost and 7.1 @ 101 mph on high boost.

l2r99gst

iTrader: (2)

You sure you didn't change the MAFT settings due to bigger injectors with your new motor or something like that? What is your boost during that pull, from start to finish?

Since you are using a MAFT/GM MAF, I would suspect the issue lies there.


Q15H - the airflow numbers are Hz, not any mass airflow.

Dapper Dan

iTrader: (28)

yes im positive I havnt changed anything, I just started trying to tune it today. Everything on the motor is the same as before its just built now.

boost is 26-27 all the way.


Im going to see if I can find a new gm maf and see if that helps

Evo8Emperor

iTrader: (12)

Do you think maybe because its a fresh motor with perfect compression, leak down, etc. That its making better power and maybe you need to just lower the timing and see if that helps ?

I swear I went through I similar situation. But it could also be your maf so maybe not.

But good luck.

Dapper Dan

iTrader: (28)

I definitely don't think thats the problem, My old motor had perfect compression too tho btw.

Im leaning towards the maf or MAFT. I should have a new Maf tomorrow to throw on and test out.

GST Motorsports

iTrader: (8)

No way on earth a 35R at 26psi is only flowing 1800hz. That is less than a stock turbo at full song.

I would take the MAFT off and just run straight MAF to see if it changes.