Twin HP expectations

just added twins to my 04.5 63/68 with .80 wastegated exhaust housing over a 476 with 1.32 housing it made 669hp/1100ish tq
previously it made 765hp 1500tq with an 369SXE on a steed speed 3rd gen manifold
the turbos were the only change except for the 24v manifold
any ideas why i lost so much power? or how to get it back?
was wanting to get to 800hp at some point.

Could be a bunch of things, correction factor, different day, different operator. Also, compounds have more drive loss than a single. Average power is probably way better.

Sent from my SM-G930V using Tapatalk

How does it feel driving it? That set should be alot quicker spool and stronger. Check your waste gate on the secondary. What boost did it make peak.

Is it a 476sxe, or a cheap $675 475? Flow wise, the 475 is very similar on the compressor side to the flow of a 369sxe, after factoring in pumping losses, I wouldn't expect a power gain, should be similar numbers but faster spooling and little bigger torque number. Assuming everything is tight and working properly, you might have a slipping tranny. If you dyno'd on 2 different dynos, then you might not have a problem.

it pegged the 80 psi gauge however the 476 only made 24psi i don't think it was much over 80psi because the next lower tune i have makes about 75psi

same dyno same operator

it does everything better except the dyno number

the 476 is the cheap one. a 475 with a 76 billet wheel upgrade

Sounds like you need to do some pressure ratio math. Primary boost looks a little low imo.

Those "476" and "465" turbochargers on the market can be a bit deceiving. Not sure why people thought it was OK to start marketing turbochargers based on bore size while the rest of the industry uses actual wheel measurements.

The 69sxe has a better flowing turbine and it was more than likely in a T4 housing I take it on that steed speed? If that is the case going to an entirely more restricted exhaust setup couple with pumping losses that will is referring to will definitely lower your number on the screen.

That aside, if it does everything better then don't get too caught up in the dyno number.

zfaylor said:

That aside, if it does everything better then don't get too caught up in the dyno number.

Click to expand...

x2
For street stuff, the area under the curve is the most important part, IMO.

Is there any dyno software that can easily spit that number out?

dieselpriest said:

it pegged the 80 psi gauge however the 476 only made 24psi i don't think it was much over 80psi because the next lower tune i have makes about 75psi

same dyno same operator

it does everything better except the dyno number

the 476 is the cheap one. a 475 with a 76 billet wheel upgrade

Click to expand...

I agree with Jlbayes, 24 psi from the atmospheric charger is a bit low, you need to open the wastegate more on the smaller high pressure turbo, this will retain more heat in the exhaust flow to drive the large turbo, it will also relieve some of the exhaust drive pressure at the small turbo and help with engine efficiency, help with high pressure turbo lifespan, and should make a noticeable power difference in the upper RPM range. On a heavily loaded dyno, we can usually make good power numbers with a tight wastegate on the high pressure charger but it needs to peak in the 2200 to 2400 rpm range before it chokes on exhaust. If the dyno load is moderate to light, you'll see better dyno numbers with a looser wastegate setting. In a real world driving scenario, the looser wastegate setting will make more peak power and upper rpm pull. The tighter wastegate setting will run cooler and tow better when fueling is cut back and you're making say 50 or 60 psi total boost vs max fueling setting that hits 80 or 85 psi.

Sometimes an in-cab wastegate controller is nice so you can play with it while driving and see for yourself what feels best, what runs coolest EGT wise, etc.