Performance Exhaust

[GTForbes]

adam, you wont need a 3inch system till your pushing 400 ponies, it'll work against you.

[Leeky]

it'll work against you.

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I wouldn't have said so, on a turbocharged car the bigger the better is the rule. My new exhaust system is going to be 3" turbo back with a 5inch exit.

[adamgt]

it'll work against you.

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I wouldn't have said so, on a turbocharged car the bigger the better is the rule. My new exhaust system is going to be 3" turbo back with a 5inch exit.

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Car came with the exhaust on it. Anyway, i will be pushin over 400 by next summer

[GT4 BOOSTER]

it'll work against you.

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I wouldn't have said so, on a turbocharged car the bigger the better is the rule. My new exhaust system is going to be 3" turbo back with a 5inch exit.

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dont you need a section 2.5" to stop turbo problems or a restrictor plate somewhere.

[daktari]

Depends on the Turbo & other mods really i think.

[Bibbs]

it'll work against you.

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I wouldn't have said so, on a turbocharged car the bigger the better is the rule. My new exhaust system is going to be 3" turbo back with a 5inch exit.

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dont you need a section 2.5" to stop turbo problems or a restrictor plate somewhere.

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I think the restrictor is to stop boost creep ..

It's go so many variables it's hard to guess if you'll have issues.

The thing that makes me wonder about all these massive exhausts, if the Zonda has 500+bhp, a race spec engine and has 4 tiny peashooters, are these 4" pipes *really* needed?

[GT4 BOOSTER]

it'll work against you.

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I wouldn't have said so, on a turbocharged car the bigger the better is the rule. My new exhaust system is going to be 3" turbo back with a 5inch exit.

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Car came with the exhaust on it. Anyway, i will be pushin over 400 by next summer

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putting new internals in are you ??? pistons and things

[Sketchy]

With a CT turbo and a full 3" high flow system i.e. turbo back, chances are you WILL get boost creep. :ffs:

If you keeping the cat on and just changing the exhaust you should be fine, but you'll also be leaving the most restrictive part of the system in place and hence any changes to the exhaust will only produce minimal power increase.

It's all to do with the pants flow on the stock wastegate, it needs back pressure to work properly, also there some disscussion that the turbo bearings need back pressure to sit properly and stop oil leaking out.

[Leeky]

yeah if you going up to 400ponies your gonna need forged pistons.

Im planning on getting a 2.2l hks/jun stroker kit as it provides you with all the things you need to go up and above 400bhp.

Can someone tell me exactly what boost creep is? fancy name for hitting fuel cut?

[mikeb]

Can someone tell me exactly what boost creep is? fancy name for hitting fuel cut?

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It's when the boost level is out of control (i.e. a highly undesirable situation).

The wastegate relieves excess air from passing through the turbo, and is controlled to regulate max boost (e.g. 1.2 bar or whatever). Unfortunately, when toyota designed these turbos, they were economical with the capacity of the wastegate. When the wastegate is open the exaust gas is divided between two possible paths (turbine wheel or wastegate), and it will generally want to follow the path of least resistance. The stock exhaust creates enough extra resistance to make the wastegate the more efficient route. Having an exhaust that is too big can make the turbine path more efficient than the wastegate, the boost increases, more air flows in and hence out of the engine creating even faster turbo speeds in a downward spiral effect. The wastegate is wide open but it is ineffective at regulating the boost pressure.

If you are lucky, you will hit fuel cut and it will save your engine (unless you've got a totally blanking FCD). Otherwise, if you don't notice the excessive boost on a gauge and lift off the throttle your engine won't last long.

[adamgt]

Yep.. im gonna do the lot. Got some good prices on HKS cams too. :D

[Leeky]

Ah right, can you not just fit a bigger wastegate to prevent this?

[Sketchy]

Ah right, can you not just fit a bigger wastegate to prevent this?

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It is possible to weld the internal wastegate shut and fit an external wastegate which would cure the problem but if you going to all that effort you might as well get a new turbo as well.

It is also possible to have the stock wastegate ported to help eleviate the problem, which is a bit of a pita in itself. However it's not just the size of the wastegate that causes it, it the whole wastegate design.

Due to the twin port exhaust housing, it is difficult to create an effective flow path to the wastegate exits, i've heard that people get the same problem with garrett twin entry designs, but none of the single entry turbo suffer this....

[Sketchy]

Also a word of warning on the 2.2l stroker kit. There is a lot of debate about the about of boring that can be done on the 3s-gte engines, to do with the wall thickness between cylinders 2 and 3, and proxcimity of the waterjacket to the cylinder wall.

Alot of 3s-gte tuners seem very worried to go above 86.25mm bore, due to the risk of cracking.

Alot of engine builders will tell you it's fine, but that's usually due to them being used to cosworth YB block with inch thick cylinder wall.

Fennsport use the stroker kit crank and rods with 86mm pistons instead of the 86.50mm one to create a 2.1L in the 'rolla.

There's currently talk of boring the block out to 90mm then fitting steel liners to the block to get round the problem, theres a thread about it on GT4OC for those of you who still have access, under modification section titled "Stroker Kit, overzised pistons ST205".