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I had a leftover unanswered question from the intake manifolds thread:) http://www.supraforums.com/showthread.php?s=&threadid=32090&perpage=40&pagenumber=2

Why exactly is an engine limited in running a certain #psi? Like most people don't run over 30 or so psi on a stock supra engine. Shouldn't boost limitations be determined by the intake manifold, ic piping, throttle body, etc. instead of the engine because these are the places where the air is being built up.
 
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What makes you think it's a mechanical limitation at all? The reason most people don't run over 2.0 bar is because the vast majority use the VPC and it's 3 bar MAP sensor.
 

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Walser said:
What makes you think it's a mechanical limitation at all? The reason most people don't run over 2.0 bar is because the vast majority use the VPC and it's 3 bar MAP sensor.
Ahh, that clears alot of stuff up. Its just that sometimes I see stores and stuff saying you should build your engine before going above 28psi. Guess they're just trying to make money
 

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Walser said:
What makes you think it's a mechanical limitation at all? The reason most people don't run over 2.0 bar is because the vast majority use the VPC and it's 3 bar MAP sensor.
One more question, If someone had a fully blueprinted small-medium sized turbo, like say a sp63 that would work decent at around 35-40 psi, then could someone run like 40 psi on the stock block as there wouldn't be a hp limit on the engine with only a sp63?
 

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racing fan said:


One more question, If someone had a fully blueprinted small-medium sized turbo, like say a sp63 that would work decent at around 35-40 psi, then could someone run like 40 psi on the stock block as there wouldn't be a hp limit on the engine with only a sp63?

I had a SP63 and added nitrous to the 32 psi I was running without a problem. The boost spiked to 39 psi and, like Darren commented, the VPC was not able to compensate for the extra air with the fuel. Engine went lean, and bent 3 rods and found one of my pistons basically in the oil pan.

Does that help answer any of your questions?


stephen
 

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element217 said:



I had a SP63 and added nitrous to the 32 psi I was running without a problem. The boost spiked to 39 psi and, like Darren commented, the VPC was not able to compensate for the extra air with the fuel. Engine went lean, and bent 3 rods and found one of my pistons basically in the oil pan.

Does that help answer any of your questions?


stephen
yeah, So basically you would have been ok running exactly the smae thing but with a stand alone?
 

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element217 said:



I had a SP63 and added nitrous to the 32 psi I was running without a problem. The boost spiked to 39 psi and, like Darren commented, the VPC was not able to compensate for the extra air with the fuel. Engine went lean, and bent 3 rods and found one of my pistons basically in the oil pan.

Does that help answer any of your questions?


stephen
This doesn't make sense. If an engine goes lean you would melt valves/pistons. You shouldn't experience any bent rods (of find pistons in the oil pan!). Rods bent when there is too much forse pushing on them, such as would be the case if you're running 39 psi + NOS.

Also I thought that the usual rule of thumb limitation for a stock Supra motor of ~30 psi comes from the fact that above that psi stock valve springs will no longer be strong enough to operate effectively. Still some people have successfully ran over 30 psi on the stock motor, but it is not common.
 

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$upraMan said:
This doesn't make sense. If an engine goes lean you would melt valves/pistons. You shouldn't experience any bent rods (of find pistons in the oil pan!). Rods bent when there is too much forse pushing on them, such as would be the case if you're running 39 psi + NOS.

Also I thought that the usual rule of thumb limitation for a stock Supra motor of ~30 psi comes from the fact that above that psi stock valve springs will no longer be strong enough to operate effectively. Still some people have successfully ran over 30 psi on the stock motor, but it is not common.
Severe detonation(brought on by runing lean) combined with nitrous can and has bent rods(I've done it myself)
 

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$upraMan said:
This doesn't make sense. If an engine goes lean you would melt valves/pistons. You shouldn't experience any bent rods (of find pistons in the oil pan!). Rods bent when there is too much forse pushing on them, such as would be the case if you're running 39 psi + NOS.

Also I thought that the usual rule of thumb limitation for a stock Supra motor of ~30 psi comes from the fact that above that psi stock valve springs will no longer be strong enough to operate effectively. Still some people have successfully ran over 30 psi on the stock motor, but it is not common.
Detonation (which is caused by running lean) causes very large spikes in cylinder pressures, which put extra strain on the rods and rod bearings, as well as pitsons.
 
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I don't think running real high boost on a small turbo is the way to go. First off, smaller turbos won't be able to hold high boost levels to redline. Second, they will be spinning well out of their efficiency range at that boost level and not making much more power. A better way would be to get a larger turbo and run a moderate amount of boost.
 

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Walser said:
I don't think running real high boost on a small turbo is the way to go. First off, smaller turbos won't be able to hold high boost levels to redline. Second, they will be spinning well out of their efficiency range at that boost level and not making much more power. A better way would be to get a larger turbo and run a moderate amount of boost.
but then you get lag:( ... the tradeoff of turbocharged cars
 
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