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Old 12-11-2004, 11:08 AM   #1
G.Subramaniam
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Default Throttle body boring by TWE ?

Throttle Body Optimization
Optimization and boring helps to compensate for the flow deficiencies of the stock intake manifold and complements flow improvements made through cams or porting or the addition of a pressurized intake.

Optimization

Includes:

Disassembly and cleaning
Back Throttle Shaft Modification
Machining of the top of the shaft
Throttle Plate profiling of leading/trailing edge
Reassembly
Price: $199

Boring & Optimization

Includes the above plus:

Boring of the Throttle Body
*Fitting and installation of larger Throttle Plate
Re-machining of the Throttle Body Inlet Taper
*Warning; this involves removing the top layer of the shaft and will weaken the shaft, however, many factory throttle bodies come with this type of shaft direct from the factory.

Price: $499

Flow Bench Testing Results

Throttle Body
Flow *CFM
Gain *CFM
Price

Stock
435.7
0
$0

Optimized
476.5
40.8
$199

Bored & Optimized
514.5
78.8
$499

-------

Assuming normal atmosphere is 14 psi
the $199 job increases airflow by 10%, 1.4 psi
and the $499 job increases airflow by 20%, 2.8 psi

In the forced air kits, generally 1 psi = 10 whp increase

Would the same rule apply to this throttle body work

In addition, when increasing air flow by 20%, would stuff like Wallbro fuel pumps etc be necessary
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Old 12-11-2004, 01:30 PM   #2
RS_to_WRX_swap
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Quote:
Originally Posted by G.Subramaniam
-------

Assuming normal atmosphere is 14 psi
the $199 job increases airflow by 10%, 1.4 psi
and the $499 job increases airflow by 20%, 2.8 psi

In the forced air kits, generally 1 psi = 10 whp increase

Would the same rule apply to this throttle body work

In addition, when increasing air flow by 20%, would stuff like Wallbro fuel pumps etc be necessary
---
That rule (never heard of it, but sounds reasonable) would never work like that on a N/A car. their isn't a chance in hell a optimized TB would give you 14whp, or a bored tb would give 28whp. Just because you increase the flow of one part by %20 dosn't mean the whole motor will flow 20% better. Improved throttle bodies are so far up on the modification ladder, there are so many other mods that will give a better bang for the buck. Optimizing TB's is something i have done on my past two cars. I could tell very little difference, i DIY and would never pay $200 for that service. I doint think you wound have to have a better fuel pump. but one would benefit from tuning, mostly with the bored tb.
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Old 12-11-2004, 06:27 PM   #3
Kevin Thomas
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RS_to_WRX_swap is right in that you shouldn't expect to the whole motor to flow 20% better based on one mod.

However, if you want to go all out, do the mod and test the results. I haven't seen a lot of information about bored throttle bodies here from personal experience. Expect to see a few post about what Cobb Tuning had to say about throttle body boring and it not being worth it, etc.

TWE may be pricey but they have experience with these things, especially subaru specific stuff. You can go with RC Engineering if you are looking to have it done cheaper (between $200-$300).

If you have the facilities, after getting this mod done, test it for yourself. Go to the track, dyno or wherever and share your results.

Don't have tunnel vision and let the throttle body be the end all. It may help compound other mods like a freer flowing air filter, slightly wider intake diameter and/or wider air flow sensor like this pic....


That's a dyno plot of a Dodge Neon with an RC Engineering throttle body. Look at how torque was gained throughout the powerband. Yes, the Neon has additional mods as well so they probably are contributing to the gain. It is what it is though and that was the before and after result. Go for it!
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Old 12-11-2004, 08:15 PM   #4
G.Subramaniam
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What is the website of RC Engineering ?
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Old 12-12-2004, 03:33 PM   #5
Kevin Thomas
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Quote:
Originally Posted by G.Subramaniam
What is the website of RC Engineering ?

http://www.rceng.com/

You aren't going to see any custom throttle body information though. You have to call or email them. I learned about them doing throttle bodies from reading Sport Compact Car articles in the past.
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Old 12-14-2004, 01:38 PM   #6
Section 8
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Put a vacuum sensor/gauge in your manifold, and run the car WOT with the filter off and see what the gauge reads as your manifold vacuum. It will only ever get to 0 PSI with a "perfect" intake. When you do it with the filter on, you will se that the vacuum probably rose. THe flow rates that you suggested would be making up the differecnce between how much vacuum you have and atmospheric pressure assuming that the TB is what is causing the restriction in the intake tract.

A percentage of whats missing not a percentage of the maximum.

You will have to do something about the manifold before the throttle body.
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Old 01-13-2005, 02:30 PM   #7
G.Subramaniam
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Has anyone used RC Engineering Throttle body boring and what was the improvement ?
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Old 01-13-2005, 05:29 PM   #8
Matt Monson
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There is a reason Cobb stopped offering this service. The intake manifold still isn't going to flow any more than 240cfm. The TB will flow more, but the air will still slow back down through the manifold. Don't waste your money...
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Old 01-14-2005, 01:17 AM   #9
Kevin Thomas
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Quote:
Originally Posted by Matt Monson
There is a reason Cobb stopped offering this service. The intake manifold still isn't going to flow any more than 240cfm. The TB will flow more, but the air will still slow back down through the manifold. Don't waste your money...

Hey Matt,

Is there a reason why the same thing doesn't (or seem like it doesn't) take place when you add an aftermarket intake to an N/A Subaru? I mean, once someone adds a freer flowing air filter and/or smoother intake tubing bends, the air should still slow down once it gets to the intake manifold.

Perhaps part of the gain is not just with increasing the cfm of air but reduced engine pumping loss. I dunno!
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Old 01-14-2005, 12:15 PM   #10
Matt Monson
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Kevin,
I can gaurantee you that the stock intake plumbing on an RS flows nowhere near 240cfm. Maybe half that if you are lucky. Plus there is a pisston of turbulence as well...
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Old 01-14-2005, 12:34 PM   #11
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My experience with adding a bored out TB to an NA engine is that it gives the throttle a real on-off feel. As soon as you touch the pedal, a much larger amount of air is allowed in thus giving you the feeling that you've opened the throttle a lot more. its like flooring it all the time. Unless you remove other restrictions in the intake, that's the only change you will notice.
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Old 01-14-2005, 12:38 PM   #12
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I wouldn'T go for a throttle body until everything else is optimized. i don't think the TB is a major source of restriction on the EJ25...
on my previous car, I bored the throttle body on a lathe, and build custom throttle plate. the engine was a gm 60 V6 3,1, and the car was a corsica (similar to cavy Z24 and other J-body) Most of the J-body enthusiast were according to say that the TB was restrictive, and a lot were paying a bunch of money to get modified one. stock bore was 52mm, I bored it to 56mm. this is a 16% increase in area. plus, even if the lathe finish was already smoother than stock, I polished it. combined with 3" intake and a cone filter, the engine stopped pulling at 5500 rpm instead of 5000. gain in torque were noticeable at all rpm, but it's hard to say if it's because the engine breathed better, or because the engine was acting like if the throttle would be more open. So, in this case, it was worth 100$. maybe 200$ for the craziest people. never 500$.
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Old 01-14-2005, 12:41 PM   #13
G.Subramaniam
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Yesterday I took my car to Rallispec to pull off my throttlebody
to send off to TWE
I saw the throttle body up close
It is a hollow cylinder with a circular plate opened by springs
The cylinder has extremely thin walls and the opening is much much larger than the metal walls
Boring out the walls will only very very slightly increase the air cross-section

I am kind of skeptical, But I sent it off to TWE for stage 1
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Old 01-14-2005, 12:56 PM   #14
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What else have you done to your motor? Kinda seems like a waist of money, unless you have a pretty impessive list of mods, and you are running out of things to do!
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Old 01-14-2005, 01:08 PM   #15
G.Subramaniam
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CAI
Headers
Catback
Cams
Torque chip
Pulleys
Heads port and polish
Torque convertor
Fast shift kit
Suspension
Brakes
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Old 01-14-2005, 01:43 PM   #16
Matt Monson
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To each their own, but personally, I think that $$$ would be better spent towards a set of thin Cometics and a phase II EJ25 to bolt your heads to. Unless you bump your CR and redline at 8000rpm, that engine is never going to break 200@ the crank...
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Old 01-14-2005, 05:36 PM   #17
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Quote:
Originally Posted by Matt Monson
To each their own, but personally, I think that $$$ would be better spent towards a set of thin Cometics and a phase II EJ25 to bolt your heads to. Unless you bump your CR and redline at 8000rpm, that engine is never going to break 200@ the crank...
With his mods he should already be at 200 crank horsepower. I have same mods and I am at 204 chp with 112k miles on my shortblock. But I agreed upgrade block is next best thing.
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Old 01-14-2005, 08:35 PM   #18
G.Subramaniam
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At 200 hp crank
Many common parts get to be needed whether I swap in a short block or
do a super-charger or a wet nitrous
Fuel Pump, EGT guage, Air Fuel Guage, Knock prevention etc

Reddevil's supercharger does not need intercooler and essentially uses parts similar to high hp NA builds

Whats holding me off on the short block is I whether a high CR EJ 25 can co-exist with 50 hp wet nitrous
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Old 01-14-2005, 08:59 PM   #19
Kevin Thomas
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Quote:
Originally Posted by G.Subramaniam
Whats holding me off on the short block is I whether a high CR EJ 25 can co-exist with 50 hp wet nitrous
There's only one way to find out. Dcoty was/is going that route but things slowed down a bit. I don't see why it wouldn't work when some folks are running around with high boost on stock compressioned EJ25s.

I 'ran' around with a 60hp shot of dry nitrous and 5psi of boost (both intercooled and non-intercooled) for what seemed like forever. And this was on stock fuel injectors and a stock fuel pump. Go out and have some fun. Just monitor your EGTs with a sharp eye.
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Old 01-14-2005, 09:00 PM   #20
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Red Devil here.

OK, I didnt have an intercooler but I do now. I broke piston #4 once with too much boost and not enough gas. Then I rebuilt the motor, and before I tried heavy boost again, I installed the intercooler.

I have done NOTHING with my internals or heads other than rebuild the heads (so now I have slightly higher compression cause they were shaved a tad), and new pistons and rings. I am supporting my hp increase just with a bigger and better fuel pump, and bigger injectors. The pistons I am using are ROCK brand and are popular among DSM owners as they are cheap AND good.

I am putting down at least 150ish hp at the wheels which means I am at least 200 crank hp, maybe even up to 220. This is accomplished of course by the 6-9 psi of supercharger boost.

Off boost the engine is very strong but certainly no powerhouse.
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Old 01-15-2005, 01:03 AM   #21
Patrick Olsen
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Quote:
Originally Posted by G.Subramaniam
I saw the throttle body up close
It is a hollow cylinder with a circular plate opened by springs
The cylinder has extremely thin walls and the opening is much much larger than the metal walls
So that's what a throttle body is!

It sounds to me like you would benefit from learning a bit about how engines work. Having some technical knowledge will allow you to more wisely choose how to go about modifying your car.

Pat Olsen
'97 Legacy 2.5GT sedan
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Old 01-15-2005, 07:58 AM   #22
Kevin Thomas
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Quote:
Originally Posted by G.Subramaniam
Yesterday I took my car to Rallispec to pull off my throttlebody
to send off to TWE
So Rallispec is still working on people's cars? Who pulled off your throttle body there? I thought they were going to be just a distributor.
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Old 01-15-2005, 09:57 AM   #23
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They have a very long wait list
I dont know who pulled it off

Last edited by G.Subramaniam; 01-15-2005 at 09:57 AM. Reason: error correction
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Old 01-15-2005, 04:05 PM   #24
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Rev-Lab does throttle bodies too.
Before:



After:



Looks like quite a difference to me. Mine almost looks thicker than the one in thier before shot.
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Old 01-15-2005, 05:31 PM   #25
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I see the boring, but the improvement in cross-sectional area is so small. does it really matter ?
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