HRHohio

Hi guys, with all the boost going on, I was wondering what order was on restrictions of airflow into a boosted motor (LS1, LM7, LQ9, LSx, etc).

What I mean is, when boosting, where will the bottlenecks be? Is it the Throttle Body? The Heads? The Intake? And what is the order. I'm looking for where the backpressure is caused.

For example, what I'm looking for is:
1) LS1 78mm Throttle Body - Cross Sectional Area= xxxcc = XXX Total CFM
2) Heads/Cam - 280 cfm @.600 lift = XXX Total CFM
3) Intercooler?
4) Piping
5) etc.

Not sure I'm conveying correctly what I'm looking for.... essentially wanting to know your thoughts on what to prioritize when designing a system. Where to look to flow say 800rwhp at the lowest psi. For example, if the restriction is the heads/cam setup, would it make sense to upgrade the LS6 intake to something bigger if the heads are causing the bottleneck? Vice Versa, if stock heads flow enough, would the money be better spent with bigger intake manif and TB? Where are the bottlenecks in the system?

Obviously 800rwhp on a 6.0 will be different than a 4.8, so lets just say with a stock displacement LS1 motor to standardize it all, for the sake of argument.

Thoughts???

Thanks!

Wnts2Go10O

iTrader: (12)

thats really something that is setup specific. to figure it out u need the correct tool.

HRHohio

Yeah, I realize that each setup is different, that's why I was kinda going after a stock LS1 motor, untouched.

What tool?

gnx7

iTrader: (28)

stock LS1 style TB has been in the 8's
stock heads have been in the 8's (with upgraded springs)
smaller bores don't allow as big of valves
stock LS1 rods beyond about 650rwhp are going to bend eventually
LS2 rods (2005+ engines) seem to be holding 900rwhp+ before bending

2005+ 6.0 shortblock, L92 heads with better springs, LS3 intake, 90mm TB
upgraded cam, bigger injectors and properly sized turbo...... should put you in the 8's.

The turbine wheel in the turbo seems to be the biggest factor in back pressure simply because it can't move enuf exhaust for a given engine size. Make sure your turbo is properly sized for your setup.

71 chevy

iTrader: (18)

here is my non-traditional take on this:

the number 1 bottle neck is , wait for it, the stock shortblock.

ie, you can take a stock short block, put the best flowing heads,intake, and throttle body on it, AND YOU WILL MAKE LESS POWER than if you took a built shortblock, and put the worst flowing heads, intake, and tb on it. why, because you can raise the boost to compensate, and you can raise it past where the stock shortblock would have kaboomed.

the number 2 logical restriction is the fuel. if you are running a fuel that forces low timing, you are killing potentially 3 digit hp vs if you ran the right fuel and aggressive timing.

things to think about.

LS6427

iTrader: (2)

Stock heads are the biggest killer in airflow on a stock engine. That's why a good head/cam/tune package on a stock cubed engine can net an additional 150+ RWHP.

.

The Alchemist

iTrader: (19)

Actually I think the stock heads flow quite well, hence why you see massive gains when people swap to a big camshaft.

Take a stock car, swap the heads, and you'll get about 20-30rwhp. Take the same stock car, with stock heads, and do a cam swap, and you'll get upwards of 50-60rwhp.

Packy

iTrader: (11)

I still use the stock throttle body and stock 241's with dual springs, stock lifters, and pushrods. They seem to flow well enough for my application. I feel that in most FI builds the exhaust is the major restriction. If you are going for big power and trying to run 8's or 9's maybe stock components are not the answer.

HRHohio

All of this is GREAT info to think about guys. I appreciate the comments. All well received!!!

What I'm hearing is basically that stock components like TB, Heads, and Intake can all be "forced" to work by swapping in a better flowing cam and simply upping the boost. That is... until one reaches the maximum potential of the stock shortblock (650 rwhp ish... ). Also, using a turbo with a higher flowing exhaust turbine to allow the LS motor to breath is key in reducing backpressure on the exhaust and therefore on the motor which improves performance.

As for fuel, I'm running the snow methanol injection system with a 30/70 meth/water ratio. Not experiencing any knock (via hptuners). My tuner has it pretty safe in timing because he knows it's stock bottom. E85 really isn't a practical option for me (Fuel not readilly available, system not built for it, etc.)... for now. But I definitely understand the benefits of running E85.

Side question: If I'm running a 44mm wastegate on a small turbine turbo, would upping the size of the wastegate (Say to a 60mm) reduce backpressure on the system and make it perform better? Would this make a difference in performance? Keep in mind that I am not experiencing any boost creep, however I am peaking my hp at 5100rpm on the dyno and I can feel the power fall off after 5100rpm on the street and through the traps.

So do you think the smaller wastegate size (without boost creep) has anything to do with peaking early on my hp/tq curves?

Thanks again for the input everyone.