Larger turbo at SAME PSI make more power?

[SS/GNX]

Will upgrading your turbo, say from going from a stock turbo running 21lbs of boost, then moving up to a larger turbo (CPT-61 BB in my case) make more power at the same boost levels? Please explain your reasoning.

I'm just curious if my recent purchase was worth while. Will it pull harder and make my ETs decrease provided equal traction? If I'm not going to gain anything out of it, then maybe I will exchange it for some ported heads or something! I dont want to have to run extremely high boost to meet my goals, cause I dont want to blow my engine.

Thanks!

 

[stagemonster]

with a larger turbo you will move a larger voulme of air. so you might even make more power at less boost. volume is the amount of air your moving and boost is just a measure of restriction. the more flow (cfm) you have the more power you will make.

 

[turbodave231]

First off, Running a higher boost won't "Blow your engine". Detonation is the killer. Making power without detonation should be your #1 goal. I've seen plenty of stock engines run over 30 psi boost with zero detonation and suffer no ill effects.

Every turbo raises the temperature of the air it compresses. That is unavoidable and that is why intercoolers (aftercoolers) are used. Smaller compressors impart more heat into the air when they are operated outside their efficiency range. A larger compressor can move the same amount of air and impart less heat into the air than a smaller compressor operating outside it's efficient range. How do you know where any given compressor's efficient range lies? Compressor Maps.

Inlet heat is a killer for two reasons: Density and Detonation. High air inlet temps (manifold inlet temps) decrease air density (and power) and increase the likelyhood for detonation (bad things happen).

Removing restriction in the intake tract (ported heads and intake manifold) allows you to make the same power level at a lower boost pressure with less detonation. How? The same amount of air is delivered at a lower temperature.

Dave

 

[callmeebryan]

You dont make power because of pressure. You make power because of the amount of air being forced into your engine. Pressure is just a by-product of that airflow. Boost pressure is really showing you how inefficient your engine is , because its all the air that cant make it into your engine.

A larger turbo will move more air at the same speed as your stock turbo, but the trade off is that it takes more energy to spool up. You may even make more power at less boost with a larger turbo vs the stock one.

 

[bison]

A larger turbo will make more power if the engine can use the extra air. So you will have to run more boost and or rev the engine more. You have to be able to tune it also. The stock turbo is out of breath at 4800-4900 on a 231ci at 22-23psi.

 

[SS/GNX]

Thanks for all the replies so far.

Doesnt sound like the bigger turbo was a waste.

I know detonation is the killer, its why I have a frount mount, alky, and wideband controller with the MAFT Pro. Keeps a nice fat AF ratio for me.

I purposely tune a little on the fatter side to keep it safe, but with more boost, I just assume that means more compression on the cylinders and therefore more strain on the factory internals.

I can assure you I wont have the balls to run 30 psi, but maybe 24?

What do you think is SAFE (provided no detonation) You can still have failures to components without detonation... The weakest link always goes.
It could be head gaskets, I could crack the crank shaft in half... neither one I really want to happen.

I need this motor to last me at least 3 more years.

Thanks again for the input, the more the merrier.

 

[bison]

Thanks for all the replies so far.

Doesnt sound like the bigger turbo was a waste.

I know detonation is the killer, its why I have a frount mount, alky, and wideband controller with the MAFT Pro. Keeps a nice fat AF ratio for me.

I purposely tune a little on the fatter side to keep it safe, but with more boost, I just assume that means more compression on the cylinders and therefore more strain on the factory internals.

I can assure you I wont have the balls to run 30 psi, but maybe 24?

What do you think is SAFE (provided no detonation) You can still have failures to components without detonation... The weakest link always goes.
It could be head gaskets, I could crack the crank shaft in half... neither one I really want to happen.

I need this motor to last me at least 3 more years.

Thanks again for the input, the more the merrier.

The weak link is the main caps with zero detonation. Ive hit 31psi a couple times with mine on the stock bottom end. On the 133mph pass it was 28.5psi. Its a crap shoot though. Im about 150hp over the safe limit for the stock bottom. I never detonated this engine even one time though. 125mph at 3600lbs seems to be the safe limit where you can run it and run it and it wont break if the tune is good,

 

[Roc87]

What do you think is SAFE (provided no detonation)

I have a non BB PT61, and have been pushing 28# into my GN for quite a while. I had a non-progressive alky kit on the car around 115k miles and got up to 25# (With a PT51), switched to Razors progressive around 140k miles (And the PT61) and that's when I got to 28#. Is it safe? Probably not, but with no detonation, it hasn't broken anything (But a tranny or two )and it sure is a blast to get to the track and with nothing but an air down of the DRs run an 11.8

 

[bison]

I have a non BB PT61, and have been pushing 28# into my GN for quite a while. I had a non-progressive alky kit on the car around 115k miles and got up to 25# (With a PT51), switched to Razors progressive around 140k miles (And the PT61) and that's when I got to 28#. Is it safe? Probably not, but with no detonation, it hasn't broken anything (But a tranny or two )and it sure is a blast to get to the track and with nothing but an air down of the DRs run an 11.8

At 115mph trap speeds your not even close to the threshold of the stock bottom end.

 

[Roc87]

At 115mph trap speeds your not even close to the threshold of the stock bottom end.

Yeah, but the stock heads and high altitude aren't helping . I had figured if I got a nice set of heads, then the bottom end would be done for (Before seeing your sig) how many miles were on the longblock when you changed heads?

 

[bison]

Yeah, but the stock heads and high altitude aren't helping , and I figure if I get a nice set of heads, then the bottom end would be done for:frown:

Altitude wont really matter at all. It will just take a little more compressor wheel to make the same power. Altitude doesnt effect blown engines any where near as much as an NA engine. If you corrected my 133.46mph pass to sea level vs. the 800' i ran it at it is only about .2 mph more. So it would take about 4000' to lose roughly 1mph. So only about 15hp at the same boost pressure vs sea level. Thats it. If your not on the edge with the turbo then it would be even less loss. Your about 150hp away from even having to think about breaking the bottom end. It will take a lot more than heads to pick up 150hp. It will take heads, rpm, and boost. Just keep the detonation out and you will have no problems turning up the boost. Around 143k on mine before i switched heads.

 

[KL Mallender]

Intake "Boost" pressure divided by exhaust "Backpressure" = Turbo Efficiency
Not all Turbos created equally, err, built equally, err Used Equally- yah that's the ticket -"Used". Once you get touched by good boost you will learn quickly that comparing "Boost" numbers is as relevent as a 3/4 cam and a liars poker game, mine's bigger :biggrin:

Kevin.

 

[Turbo6Smackdown]

You don't have to run it fat. You got a front mount and alky. Leaner is meaner. If you have a wide band and a power logger, you can get some good tuning goin on. Nice and accurate. With that (and heads of course) a bigge turbo is NEVER a waste. Though, make sure you have an rjc plenum plate in there. Keeps her nice and even.
Though, with all that stuff on there, do you have the brace kits, engine tie down strap, better shocks/springs, boxed control arms, gauges, scanmaster etc etc?

 

[bison]

Intake "Boost" pressure divided by exhaust "Backpressure" = Turbo Efficiency
Not all Turbos created equally, err, built equally, err Used Equally- yah that's the ticket -"Used". Once you get touched by good boost you will learn quickly that comparing "Boost" numbers is as relevent as a 3/4 cam and a liars poker game, mine's bigger :biggrin:

Kevin.

The problem is about 99% of the guys on here run 3 bolt setups. This makes it nearly impossible from a performance standpoint to get a pressure ratio that is anywhere near ideal for a performance application. Even with this restriction heads up racers have gone well beyond the intended hp range of the 3 bolt turbos. Ive heard reports of over 70 psi backpressure! Not going to happen with out external CO2 to hold the gate shut. What the hell is a 3/4 cam? Do they leave some lobes off so its only 3/4 there? Like 9 vs 12 lobes? Im good as long as she said i had a bigger one:biggrin:

 

[KL Mallender]

10-4 Bison :biggrin:

Kevin.

 

[Bent6]

The funniest thing to me is when people (especially ricers) talk about how much boost they run or when magazines spec a turbo by it's "max psi". Many think that the more BOOST the more power and that simply isn't the case. It's all about getting the highest VOLUME of air into the engine in the most EFFICIENT manner possible. All turbos have a sweet spot ie- compressor map for a given engine - anything above that is just generating heat. If it were all about boost, we could just put a stage block in it and weld the wastegates shut.