Quote:
Originally Posted by BunkerJ
When you're talking about the safety of the engine, we have two concerns: throwing a rod (as a result from a broken rod bolt) and blowing the piston ring. The former is going to happen when either car is operating at a high, consistent power delivery (Track use) and the torque destroys the hot, weakened bolts. We aren't sure how much the stock bolts could take from use just on a strip or street use, but I'd garner to say that it's within 100lbs of the track cars that pushed 350 and threw rods left and right. The other is due to too high of pressure in the cylinder. We've had what, two guys now that have overboosted (JB4) into the 25 range and rings in one or multiple cylinders were destroyed.
You have to be sure you differentiate between lb/min and psi here. Pressure is pressure. 22psi in a small turbo and 22psi in a large turbo both exert the same amount force here. Now the difference in flow rate or CFM, is the difference. At 22psi, the smaller turbo could be pushing only a measly 30lb/min of air and fall on its face in the higher RPM band due to a low air velocity and not being able to keep up with requirements of the car. To make up for this, you can spin the turbo faster to increase PSI and hope to push more air into the cylinders, but as you push it out of its efficiency range, the charged air temp rises and you lose density and overall air volume. On a bigger turbo pushing 22psi, you could be pushing 50 lb/min and thus be making more power due to a higher volume of air. The deficiencies of the smaller turbo become advantages of the big turbo, just like how the advantages of the smaller turbo become the disadvantage of the bigger turbo.
So, rjdnyy224 , your last statement is correct that a larger turbo here is delivering more consistent power in the higher RPM range. Does it shift the power curve at all? Depends on the turbo. MHI/Dinan and similar will likely not shift it. They are "bigger" turbos, but not like what you'd think. They're still Twinscroll and spin up just as quick as the stock turbo, it just operates more efficiently in the top end. Swapping in this turbo isn't going to change your boost on the same tune, as I've already logged this and there are no differences there. Hunter and I have also seen this difference on the street. Back when we were rocking the same parts and tune, I had my turbo replaced with MHI. I initially thought it was generating more lag but turned out to just be an adaptation thing. We later (safely and legally) raced each other from I think a 40 roll. He still took off ahead in the beginning, but I'm going to say that it was from AWD + some quick honking  ; however, the entire way up was me creeping up on him and by 90-100, I was eclipsing him. Now, his AWD contributed to that factor as well but my creep wasn't that grand before in previous races.
So, I think the only other point I saw in here was regarding the torque curve. In the end, you're only going to want to shift it if you're putting in a turbo that spools quicker and making bigger numbers. BM3 thankfully has a reduction in boost by gear, and that would easily solve it. You could work with your tuner to shift it also but the turbo itself isn't going to shift it until you get to a bigger one (and I mean much bigger).
Also, the MHI turbo is rated for 32psi but good luck, have fun.
I think that's it. Please tell me if I missed something. It's 7:30 and I'm still drinking my first cup of Joe for the day. |
So 'bigger' turbo, MHI/Dinan, which is what we were talking about in the first place, won't make more boost on the same tune, and won't significantly shift the power curve, it will just flow better, push more air (by volume not pressure) into the cylinders... It will also remain efficient at higher rpms. All that meaning it won't practically be any safer than the stock turbo. Right?
So what kind of power increase do you think you'd see going from stock to MHI sticking with BM3 OTS Stg. 2? It sounds like it won't be all that much.