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When I picked up my car with the new Stage 3 Toyomoto s/c in it... I was curious as to why it was able to run 18psi safely on pump gas (93 octane) when similiar turbo setups run 14-15 psi and run a risk of overboosting if they were to try 18psi.

My basic understanding of it is that when the boost is produced is the key factor... as we all know the s/c isn't producing 18psi from 4000 rpm-7000 rpm. It makes maybe 8 psi @ 4000 rpms and 18psi @ 7000 rpms, whereas a turbo kit with the boost controller set to 18 would spool to 18psi @ maybe 4500 rpms and stay there till redline. from what I understand, boost @ max RPM is the engine killer that limits turbos to 15 psi... if you try 18psi @ 5000 rpms you'll end up with a blown motor, but @ 7000 rpms 18psi is safe.

I've been told it has something to do with peak torque, or peak cylinder pressure @ xxx RPM, etc... but I'm looking for a more technical explanation of what's going on.

The other extension to the question would be: Why can't you make a boost controller for a turbo with a progressive increase... so you run 15 psi @ 5000 rpms but then let it increase to 18psi by redline? You'd get the "spool" ability of a turbo to make more boost down low while staying within safe limits, but benefit from the ability to run 18-20 psi in the higher revs and make more power (+ keeping the tq flat).


The first person who turns this into a s/c vs turbo debate is going to get slapped. :shame: I'm not trying to say one is better than the other... I want to a) understand my car on a more technical level b) learn more about options to improve the performance of turbos and c) share this info with yall.
 

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SUPERCHARGERS RULE AND TURBOS SUCK ASS!!!!!!! :lol: Especially yours John :p No, just kidding.... How has the Stage 3 been treating ya John? Got any good kills lately? :D
 

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heyitzkian said:
SUPERCHARGERS RULE AND TURBOS SUCK ASS!!!!!!! :lol: Especially yours John :p No, just kidding.... How has the Stage 3 been treating ya John? Got any good kills lately? :D
*SLAP!*

:lol: This is a tech discussion, I'll do a writeup on my car when I get a chance :D
 

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Compression allows for more boost. In the case of my car, and any other with the same hg/piston setup should be able run 17/18psi all day long. If you got the tt stuff put in then you would have a lower compression now due to the dished pistons as well as a headgasket. I imagine one, or both, were added to your car to allow for higher boost.

It is quite possible to run 18psi on 93 with a turbo or s/c. All cars make peak torque down low and peak hp up high. 5252 is the magic number where they cross and they always cross there. Look at any dyno ever.

I think you may be overthinking, or maybe I'm underthinking, the question at hand. WIth the appropriate compression ratio you can safely run more boost on lower octane fuel. 18psi is 18psi whether it is a turbo or an s/c. There are tradeoffs involved, but 17/18psi seems to be pretty safe. On the stock pistons, even with a hg, you are limited to 15psi @ 93 due to the pistons not being dished, thus a higher c/r.
 

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dasgalloway said:
The other extension to the question would be: Why can't you make a boost controller for a turbo with a progressive increase... so you run 15 psi @ 5000 rpms but then let it increase to 18psi by redline? You'd get the "spool" ability of a turbo to make more boost down low while staying within safe limits, but benefit from the ability to run 18-20 psi in the higher revs and make more power (+ keeping the tq flat).
I think that is possible with a remote control for the boost controller, I think greddy has it.
 

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Discussion Starter #6
VVTIS said:
dasgalloway said:
The other extension to the question would be: Why can't you make a boost controller for a turbo with a progressive increase... so you run 15 psi @ 5000 rpms but then let it increase to 18psi by redline? You'd get the "spool" ability of a turbo to make more boost down low while staying within safe limits, but benefit from the ability to run 18-20 psi in the higher revs and make more power (+ keeping the tq flat).
I think that is possible with a remote control for the boost controller, I think greddy has it.
So you have to turn a know as the car revs? :eek: Scary
 

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DarkStorm said:
Compression allows for more boost. In the case of my car, and any other with the same hg/piston setup should be able run 17/18psi all day long. If you got the tt stuff put in then you would have a lower compression now due to the dished pistons as well as a headgasket. I imagine one, or both, were added to your car to allow for higher boost.

It is quite possible to run 18psi on 93 with a turbo or s/c. All cars make peak torque down low and peak hp up high. 5252 is the magic number where they cross and they always cross there. Look at any dyno ever.

I think you may be overthinking, or maybe I'm underthinking, the question at hand. WIth the appropriate compression ratio you can safely run more boost on lower octane fuel. 18psi is 18psi whether it is a turbo or an s/c. There are tradeoffs involved, but 17/18psi seems to be pretty safe. On the stock pistons, even with a hg, you are limited to 15psi @ 93 due to the pistons not being dished, thus a higher c/r.
If it was compression alone (which would be achievable with a headgasket) why turbo cars with 8.5:1 only running 15 psi (stock pistons as you said, to answer my own rhetoric)?

Are there any examples of turbo cars with GTE engines/GTE internals running 18-20 PSI on 93 pump gas all day long?

If I want to run 18-20 PSI @ 5000 rpms with my current setup (GE block, GTE pistons) that wouldn't blow the motor?

And remember, 18psi is not the same on an s/c or turbo... because the turbo can make it from 4000-7000 rpms, while the s/c can only make it near 7000 rpms.
 

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dasgalloway said:
DarkStorm said:
Compression allows for more boost. In the case of my car, and any other with the same hg/piston setup should be able run 17/18psi all day long. If you got the tt stuff put in then you would have a lower compression now due to the dished pistons as well as a headgasket. I imagine one, or both, were added to your car to allow for higher boost.

It is quite possible to run 18psi on 93 with a turbo or s/c. All cars make peak torque down low and peak hp up high. 5252 is the magic number where they cross and they always cross there. Look at any dyno ever.

I think you may be overthinking, or maybe I'm underthinking, the question at hand. WIth the appropriate compression ratio you can safely run more boost on lower octane fuel. 18psi is 18psi whether it is a turbo or an s/c. There are tradeoffs involved, but 17/18psi seems to be pretty safe. On the stock pistons, even with a hg, you are limited to 15psi @ 93 due to the pistons not being dished, thus a higher c/r.
If it was compression alone (which would be achievable with a headgasket) why turbo cars with 8.5:1 only running 15 psi (stock pistons as you said, to answer my own rhetoric)?

Are there any examples of turbo cars with GTE engines/GTE internals running 18-20 PSI on 93 pump gas all day long?

If I want to run 18-20 PSI @ 5000 rpms with my current setup (GE block, GTE pistons) that wouldn't blow the motor?

And remember, 18psi is not the same on an s/c or turbo... because the turbo can make it from 4000-7000 rpms, while the s/c can only make it near 7000 rpms.
My car is a good example of one that can run 18psi all day long. There is another one at the shop that is capable of 20psi.
 

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Do you mean setting boost by RPM? My Apexi AVCR will do that.


dasgalloway said:
VVTIS said:
dasgalloway said:
The other extension to the question would be: Why can't you make a boost controller for a turbo with a progressive increase... so you run 15 psi @ 5000 rpms but then let it increase to 18psi by redline? You'd get the "spool" ability of a turbo to make more boost down low while staying within safe limits, but benefit from the ability to run 18-20 psi in the higher revs and make more power (+ keeping the tq flat).
I think that is possible with a remote control for the boost controller, I think greddy has it.
So you have to turn a know as the car revs? :eek: Scary
 

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dasgalloway said:
I've been told it has something to do with peak torque, or peak cylinder pressure @ xxx RPM, etc... but I'm looking for a more technical explanation of what's going on.
I assume this is directly related to the volumetric efficiency of a motor at different RPM's. That is, the engine will fill more of it's combustion chamber with A/F charge at 4000rpm and 15psi, then it can at 6000rpm and 15psi. Hence, with greater VE at lower RPM's, peak cylinder pressures are higher (therefore torque), and approach the limits of safe compression.
 

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Discussion Starter #11
DarkStorm said:
My car is a good example of one that can run 18psi all day long. There is another one at the shop that is capable of 20psi.
What do you have that allows that? Full GTE swap? GTE internals? Daily visits by Raul, the anti-detonation gnome?
 

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dasgalloway said:
DarkStorm said:
My car is a good example of one that can run 18psi all day long. There is another one at the shop that is capable of 20psi.
What do you have that allows that? Full GTE swap? GTE internals?
I'm still on the GE block, but have the TT rods and pistons. The dished pistons lower compression enough that I can run the additional 2-3psi without incident.

The AVC-R can also control boost based on gears, so you could potentially do 6psi 1st, 8psi 2nd, and then unload with 30+psi 3-5th (or 6th). :D
 

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Discussion Starter #14
TeCKis300 said:
dasgalloway said:
I've been told it has something to do with peak torque, or peak cylinder pressure @ xxx RPM, etc... but I'm looking for a more technical explanation of what's going on.
I assume this is directly related to the volumetric efficiency of a motor at different RPM's. That is, the engine will fill more of it's combustion chamber with A/F charge at 4000rpm and 15psi, then it can at 6000rpm and 15psi. Hence, with greater VE at lower RPM's, peak cylinder pressures are higher (therefore torque), and approach the limits of safe compression.
Interesting... I wonder when we say 18psi (measured in the boost pipe) that actually means 18psi (measured in the cylinder before each explosion). Or does the faster the engine turns mean that the cyls don't have enough time to get up to 18psi... so when I say 18psi I mean 15 psi @ 7000 rpms, and when a turbo says 15 psi they mean 12 psi @ 7000 rpms?
 

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Discussion Starter #15
DarkStorm said:
dasgalloway said:
DarkStorm said:
My car is a good example of one that can run 18psi all day long. There is another one at the shop that is capable of 20psi.
What do you have that allows that? Full GTE swap? GTE internals?
I'm still on the GE block, but have the TT rods and pistons. The dished pistons lower compression enough that I can run the additional 2-3psi without incident.

The AVC-R can also control boost based on gears, so you could potentially do 6psi 1st, 8psi 2nd, and then unload with 30+psi 3-5th (or 6th). :D
Ok good, so anyone with a GTE block or GTE internals should be able to run 18psi from 4000-7000 rpms everyday on pump gas without incident?
 

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Discussion Starter #16
DarkStorm said:
I'm still on the GE block, but have the TT rods and pistons. The dished pistons lower compression enough that I can run the additional 2-3psi without incident.
Also (this is from an AIM conversation with someone else), how does piston strength make it less likely that you'll detonate? That's tied to compression and boost, which can be controlled with the HG, and no matter what pistons/block you're using if you detonate enough it'll go bye bye. Nothing is invincible.

Hrmm
 

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Discussion Starter #17
Also, I'm asking more questions than giving answers... because I don't know the answers :D . I don't want anyone to think I'm calling them a liar, I'm just logically stepping through everything so I can understand.
 

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dasgalloway said:
Ok good, so anyone with a GTE block or GTE internals should be able to run 18psi from 4000-7000 rpms everyday on pump gas without incident?
As best as I understand it, yes, they should be able to. If I'm wrong on this, someone please chime in and say so.

For piston strength, stronger rods/pistons can take more heat/pressure. More pressure = more boost = more power. Wimpy rods/pistons can break on an n/a car just like they can on a f/i car. Carillo rods and JE pistons will enable you to run in excess of 30psi, where the stock rods/pistons really don't do well after about 20psi in my experience. With stronger rods/pistons, you can also run more rpms safely. Detonation can still occur, but light detonation is not as damaging to them because they are made of stronger materials. 30psi + 7k rpms + 15.0 a/f = death, even with a crazy setup.

Feel free to ask away. You're nearing the boundaries of my knowledge on this subject. I asked pretty much the same questions when they told me "by the way, you can run more boost now" when the tt stuff went in my car last year. I'm sure GTE and a few others have more insight on this than I do.

There's really good thread buried somewhere in go faster about compression ratios and boost. I think it made reference to the tt pistons being dished and lowering c/r, so it may be of some use.
 

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darkstorm that is correct, between compression and stronger rods and pistons can take a bit more beating , heat, light det.. Which will in the end allow you to run IMO 18-19psi safely, anymore is generally not a good idea even with the few like me who have 94oct available... Always the possiblity of getting bad gas and then you may get some knock/pinging at those higher boost levels. Besides if you got a nice set-up 18psi should dominate nearly anything that steps up to the plate :D




























if you do get beat you should be packin some c16 somewhere nearby anyways for those special occasions :thumblef:
 

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Doesnt matter, I creep all over the place :lol: . I just installed a HG well see if it will hold 10 psi any better then it holds 7 haha.

dasgalloway said:
Sentinel said:
Do you mean setting boost by RPM? My Apexi AVCR will do that.
Yes, interesting... how do you have it configured? For a constant psi throughout the RPM range?
 
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