Port and Polish
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Lexus Test Driver
Joined: Sep 2007
Posts: 1,097
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From: Dallas
Port and Polish
Anyone thought of getting the intake manifold or throttle body ported and polished?
I know for many cars this is a relatively cheap and beneficial mod.. you guys think any power can be made by doing this with the IS350?
A mod like this maybe be only beneficial to people considering some FI like nitrous.. im not really sure though
I know for many cars this is a relatively cheap and beneficial mod.. you guys think any power can be made by doing this with the IS350?
A mod like this maybe be only beneficial to people considering some FI like nitrous.. im not really sure though
Without doing this to the heads, it's a complete waste of time. The biggest gains are in the last 1/2 inch of the intake ports. Everything up to that is pretty much dependent on that part being done first.
It's the most likely place to fix the power limits we're seeing. Intakes don't get much of anything, throttlebodies for drive by wire are typically already bigger than what you'd have seen in years past because the computer can do what you mean, not what you say. So, the biggest opportunity is in getting the flow through the ports in the head optimized along with ensuring the rest of the engine's critical measurements are exact. When the heads are off, you can zero in on what the factory couldn't afford to do right the first time.
Lexus Fanatic
Joined: May 2007
Posts: 11,030
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From: Windward, Oahu
lol... i remember the days of porting a T3 head/18R-G head then matching the intake for dual 44webber IDA's AND dont forget to match the exhaust port too 
... hours n hours with the dremel, those were the days 
... hours n hours with the dremel, those were the days
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It should be noted not all heads are created equal at the factory. Lots of things can go wrong in the manufacturing process that cause a perfectly good stock head to be unsuitable for porting or any other high performance work. Core shift in the casting process is one of the most prevalent things you'll see on a stock head that make it mostly useless for modifying unless the shift is slight and you're planning on oversized valves.
Still, a basic street port will signficantly improve low lift flow and broaden the powerband. Just don't expect to put full race heads on a street engine and have it work well. Get the work done that makes the most sense for the use profile you envision. An engine is a symphony of parts and pieces. That's why it takes a TUNER to get the best music from your symphony.
It's not possible to accurately predict without full knowledge of the piece we're working on. Maybe 5% maybe 25%. Depends on a LOT of factors and what other things we address with the heads off.
As I said, if there's core shift and the seats are not even close to concentric with the ports you might be able to make a good fix and get a huge improvement. You might also not be able to do much of anything if it's so severe you'll never be able to get rid of the step between the seat and the port. I've got a couple of Mitsubishi Evo heads I'm working on right now, and they're so poorly cast it's hard to imagine how anyone ever got big power out of them (boost does make up for a lot) with any efficiency. I've seen 2JZ-GTE heads that were nearly perfect from the factory, and others that had a full millimeter step because the seats were installed so off center is was hard to imagine. Each head presents a different potential, so, starting with a good head will allow the most extreme changes for the largest impact, and the worst heads will barely even clean up to perform as well as a good stock head.
As I said, if there's core shift and the seats are not even close to concentric with the ports you might be able to make a good fix and get a huge improvement. You might also not be able to do much of anything if it's so severe you'll never be able to get rid of the step between the seat and the port. I've got a couple of Mitsubishi Evo heads I'm working on right now, and they're so poorly cast it's hard to imagine how anyone ever got big power out of them (boost does make up for a lot) with any efficiency. I've seen 2JZ-GTE heads that were nearly perfect from the factory, and others that had a full millimeter step because the seats were installed so off center is was hard to imagine. Each head presents a different potential, so, starting with a good head will allow the most extreme changes for the largest impact, and the worst heads will barely even clean up to perform as well as a good stock head.
Last edited by lobuxracer; May 24, 2008 at 11:23 AM.
Lead Lap
Joined: Jul 2006
Posts: 430
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From: TX
And with core shift there's always a chance you could cut into a water jacket. My friends that cnc LSx heads talk about some kind of cool things. One is where they port the intake port from the intake side and then the same port has to be done from the valve side. There is a little ridge where the cnc machine doesn't quiet reach each other. If the ridge is not hand finished they get 7cfm more flow at full lift than if it is finished. But if they don't grind it out everyone thinks they were being lax and missed it. So they finish every one and people get a head that flows less but looks prettier!
And with core shift there's always a chance you could cut into a water jacket. My friends that cnc LSx heads talk about some kind of cool things. One is where they port the intake port from the intake side and then the same port has to be done from the valve side. There is a little ridge where the cnc machine doesn't quiet reach each other. If the ridge is not hand finished they get 7cfm more flow at full lift than if it is finished. But if they don't grind it out everyone thinks they were being lax and missed it. So they finish every one and people get a head that flows less but looks prettier!
