IS 350 performance upgrades? - Lexus IS Forum
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post #1 of 6 (permalink) Old 02-27-2011, 11:50 AM Thread Starter
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IS 350 performance upgrades?

What are the limiting factors for performance? I was asked to build up an IS350 and would normally put a turbo on any car I build. So what problems do people run into?
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post #2 of 6 (permalink) Old 02-27-2011, 07:37 PM
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What are the limiting factors for performance? I was asked to build up an IS350 and would normally put a turbo on any car I build. So what problems do people run into?
Mainly the fact it's cheaper to buy an IS-F than it is to make an IS350 equally fast.

There are no forced induction kits sold for this car in the US market.

12:1 compression and 0 aftermarket engine management options is a killer. (the compression much moreso than the engine management stuff honestly). Ditto the complete absence of any aftermarket way to lower the compression of the engine... anything you did there would be custom and fraught with additional other issues.

In Japan they do sell a couple supercharger kits. You're looking at $7000-8000 for about 40-50 horsepower there...and they're not bolt-on for non-JDM vehicles....
(the TOMs kit requires a JDM ecu... and the HKS kit requires shaving the water pump, some wiring changes, etc).

Nobody bothers with a turbo kit because a supercharger kit is cheaper (and still too expensive to make any sense for the relatively little power produced) and the engine likely can't handle more than 7-ish psi reliably with that compression ratio and the stock fuel system.


In short- if someone bought an IS350 to modify it for significantly more performance, they bought the wrong car.
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post #3 of 6 (permalink) Old 02-27-2011, 10:23 PM Thread Starter
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There are absolutely no piston or rod options? Can the stock pistons be shaved, modified, anything to lower compression? Thicker head gasket? I've modified a ton of heads and found virtually none that can't be ported...it seems that if you were interested in lowering compression then with a combination of different tactics getting it to a manageable 10:1 has to be possible..
Are there no stand alone systems just for the engine management for the IS? It's a lexus...the engine can't handle an extra 200 hp without blowing up?
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post #4 of 6 (permalink) Old 02-28-2011, 08:04 AM
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There are absolutely no piston or rod options?
Off the shelf? Nope.

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Originally Posted by Wowow09 View Post
Can the stock pistons be shaved, modified, anything to lower compression?
The pistons are a very specific shape to accomidate the stratified fuel charge and the direct injection system... you'd be taking your chances on not destroying the engine by trial-and-erroring any change in shape without having the engineering background to know exactly why they are the specific shape they are currently.

Here's a CL quote on this:

Quote:
The piston crowns have a patented shape which works with the DI programming to create a stratified charge effect. Changing the dome of the piston will mean lots of trial an error unless you can get someone with intimate knowledge of how the piston dome needs to be shaped to help with your project. Unfortunately, that guy is an engineer at Lexus in Japan. Best of luck with that one.

Finally, this is an aluminum block with thin iron sleeves. It would make a lot of sense to hydrostatically test the bores before doing anything else to determine what the maximum allowable cylinder pressure is before the bores go into permanent deformation from being over-pressurized.
Not saying that can't be done, but unless you get really lucky your first try it's going to cost a ton more than having bought an IS-F instead would. (even then it won't be cheaper unless your labor is totally free and you can do all the machine work yourself)


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Thicker head gasket?
Also a bad idea on this motor... discussed here:
Club Lexus Forums - View Single Post - alright guys i decided to go turbo

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Originally Posted by Wowow09 View Post
I've modified a ton of heads and found virtually none that can't be ported...it seems that if you were interested in lowering compression then with a combination of different tactics getting it to a manageable 10:1 has to be possible..
Again, I'm sure it's POSSIBLE.

it would just be entirely custom, require some trial and error likely going through a few motors in the process, and just makes no economic sense.


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Are there no stand alone systems just for the engine management for the IS?
There weren't last anyone checked... it'd need to run 6 DI injectors and 6 port injectors, and tie into the CANbus system (and the half a dozen other encrypted ECUs that all talk both to, and through, each other)... now if you just want to run the motor and don't care about everything ELSE in the car working properly, you likely have options... but again not ones that are less expensive than buying an IS-F instead.... and the ECU problem won't fix the compression.... (and if you didn't care about the rest of the car working might as well just put a 2JZ in there... with a few hundred hours of wiring you can even get most of the factory systems to work with it... not all, but most...)

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Originally Posted by Wowow09 View Post
It's a lexus...the engine can't handle an extra 200 hp without blowing up?
At 12:1 compression? (11.8 for the 350, 12:1 for the 250)... with no added fueling or any way to manage any of it? nope.

A couple guys have run 6-7 psi on a supercharger mostly successfully... and a couple guys have run 85-100 shots of nitrous on race gas without blowing anything up (well, I think the guy with the 100 shot got a little transmission slippage... which suggests the tranny will break even if you get the motor to hold 200 more...) but that's about it....

(and one fella who was running like 7.5 psi on a supercharger was running out of fuel at higher rpms, seeing AFRs north of 13)

Last edited by Knightshade; 02-28-2011 at 09:12 AM.
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post #5 of 6 (permalink) Old 02-28-2011, 09:07 AM
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As per the above your best bet maybe the HKS kit,...very expensive, unless you can source one used: HKS350 does it again! Living up to the title.. - Club Lexus Forums

'06 Tungsten Pearl IS350,...with battle wounds and scars,...almost new.
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post #6 of 6 (permalink) Old 03-04-2011, 09:36 PM Thread Starter
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wow - well thanks for the feedback...guess its a no go...
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