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Discussion Starter · #1 ·
Well I have been meaning to work on my intake manifold for a while now. I need to install my intake air temperature sensor for my engine management. So, I pulled out my spare manifold for sone drilling. While i was at it I decided to take a close look at the stock manifold and throttle body compared to my upgraded Porsche 70mm throttle body. The plastic of the stock manifold is actually ~70mm. Yes, the Porsech throttle is a better fit dimensionally than the OE Volvo part. This means the stock 65mm throttle body extends into the intake a little with a sharp edge. I wonder why Volvo designed the intake for a 70mm throttle but then installed a 65mm. A 33% reduction in flow area if im doing the math right in my head. Its not like its really a difference in cost on a manufacturing level. This being an electronic throttle its also not an issue of throttle resolution since the throttle responce can be tuned in the ECU. Perhaps this is the same throttle as the 2.4?

Thoughts?
 

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Discussion Starter · #3 ·
Interesting. Maybe the lip helps with turbulence and fuel mixing. Or maybe they just went to the psrts bin.
 

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I think that there were other reasons for it.

Usually the restriction is somewhere else inside the manifold, you can put a 100mm TB on it and it will still only flow as much as 50mm or in this case 65mm due to what is past the TB... in terms of restrictions.
I think engines are so optimized these days that the days of big old V8s with huge intake runners and a tiny TB or CARB are gone. In those days you can jsut upgrade the TB and flow more air therefore make more power but in those days they also had to deal wtih emissions so they choked them up to achieve the government goals.

You can try going to a bigger TB and see what happens. on my T5 i doubt it will see much difference that can be felt. Could be good for 2-3hp if that but since its boosted it probably wont make a huge difference that is measurable.
 

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Discussion Starter · #5 ·
So you're saying the intake manifold or head is at choke flow and a larger throttle body will make no difference other than loosing reponce at the top end right? You could see that with a cylinder pressure transducer. Anyone want to send me a few grand for a spark plug pressure transducer? ;)
 

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When we were upgrading the 2.0 and 2.2 Ecotecs with the 2.4 Ecotec throttlebodies on the Chevy Cobalts, it did allow for a lot more potential for HP building, but really only added about 5 or 6 without more significant upgrades. With a forced induction setup, other than tuning the ECU to the new TB, if they drop in, it will allow more air to hit the 4 and 5 cylinders, but you're not going to see a huge change in power. If these guys had problems with breaking rings in the 4/5 cylinders due to header tubes and heat issues like the cummins do on 4/5/6 cylinders, I would say it would be worth it, but unless you're going to put in a new turbo, intake, exhaust, it's probably not worth the money for anything other than throttle response.
 

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Perhaps the max tq curve is why - max torque peaks at a pretty low level, especially for a turbo engine. Smaller intake helps move air volume at lower rpm, but limits at high rpm.
 

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Discussion Starter · #8 ·
You are right mercdude! I did sone reading and the numbers on hipermath.com give me 55.7mm for a low VE engine and 64.1mm for a high VE engine. Guess I should not have bought this 70mm throttle body. Looks like I would not really gain anything and may actually loose some driveability.
 

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With the stock manifold and stock intercooler piping, an upgraded throttle body really doesn't make that much of a difference because the air is still being restricted elsewhere.
But with everything else upgraded, the stock throttle body then becomes the restricting part, so 70mm makes a noticeable difference.

I have a lot more get up and go with the Porsche throttle body. WOT is a complete beast and you really feel the extra bit of air coming in.
 

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Discussion Starter · #11 ·
With the stock manifold and stock intercooler piping, an upgraded throttle body really doesn't make that much of a difference because the air is still being restricted elsewhere.
But with everything else upgraded, the stock throttle body then becomes the restricting part, so 70mm makes a noticeable difference.

I have a lot more get up and go with the Porsche throttle body. WOT is a complete beast and you really feel the extra bit of air coming in.

Since I have both I may need to do back to back dyno pulls to prove this. The math doesnt show much benifit to the 33% more flow area. I think it is tricking you because it appears that you a are getting more power because you get more flow change for a given % open. But, what is actually happening is that you are hitting your maximum flow through the throttle body sooner. So instead of reaching full flow at 100% open you reach full flow at say75% open and the last 25% has very little effect. So in essence your control range is reduced. You may gain a couple of HP but you loose driveability. The numbers show that a 65mm bore is just about right. Now, the throttle is kind of a poor design because the rod goi g through the middle is too thick. So, it may be that 70mm has a reduced flow area more similar to what a well designed 65mm bore should be. From the math it tells me a bore of 65mm is just a hair larger than we need with a 2.5L regardless of boost. But if you subtract the area taken up by the actuator rod, the throttle body total flow area may indeed be too small on the 65mm unit. I will take a few more mesurements to confirm before botheri g with a dyno. I suspect the 70mm units total flow area is closer to what the 2.5L engine actually needs given that you are saying you did indeed make power gains with it. Again if this is just a butt dyno the larger throttle would FEEL more responsive but actual WOT HP would not be much different.
 

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Before/After dyno would be great. But are you still using the stock intake manifold?

I bought my TB with absolutely not expectations for improved performance, it was just a great price. But the butt dyno and side by side pulls with friends, my car is just faster than it was before. Honestly, at partial throttle, I don't notice any difference, it pulls just about the same and feels the same around town. But WOT and the car has a noticeable difference; but this is entirely with my setup. The only stock part (excluding turbo) still in line from the cone filter to the lower manifold was the throttle body.
 

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Good stuff here.

Just to be clear: area of a 65mm circle = 3318.31mm^2, area of a 70mm circle = 3848.45mm^2. That's a difference of 530.14mm....or 15.97%.

I have the 70mm TB on a nearly stock engine....it made no difference. Why do I have it? Forthcoming plans...
 

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Discussion Starter · #14 ·


My bad Doc. I forgot to use R. Anyway, assuming the rod is about 8mm across here is what the rough numbers come out to. As you can see on a 2.5 L engine. It just doesn't look like there are gains with this unit.
 

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Discussion Starter · #15 ·
Yes, I have the stock intake... for now. I really wanted to see what I could do with it before upgrading. Also. I refuse to pay the ridiculous price they charge for the aftermarket ones. Ill be welding my own up. Budget $150 max.
 

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I'm eager to see what kinda numbers you get from the dyno, can i request that you fab up a bigger charge pipe (2.5" or3") as well as your work on the intake, my welder wants 150$ for the charge pipe and 250$ to do the intake plenum I'd like to know if that's worth it before delving in.

As for the throttle body I just wanna be able to say I have a 70mm Porsche throttle body when I'm going over my mods list lol

I'm not nearly as savvy as you, mniwt and doc but I'm wondering could you dremel down the rod to be thinner during WOT? Would a that allow smoother airflow?




"Embody god... Then go crazy"
 

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Haha, ironic timing for them to publish that article. I was beginning to wonder when it would get posted.

Now I'm really curious to see the before / after dyno.
 
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