throttle body upgrade?

[Nevin]

Well, like the title suggests, I'm curious if there are any throttle body upgrades. I would assume that there is nothing "off the shelf" but I'm wondering if anyone has ever gone to the trouble to bore out the stock throttle bodies and put in larger butterflies. Plus, I haven't looked too closely yet, but do the butterflies sit striaght up and down, or are the plates an ellipsis? Also, what IS the diameter of the stock TB's?

Just curious, because I'm planning on doing some work on the intake side of things to help the motor breathe a little easier. I'm planning on sending a spare intake manifold to Extrude Hone to have them polish the inside, and I'd like to see if I can get ahold of a set of phenolic spacers.


Anyways, just curious if anyone has looked into this yet. I realize that they are already generously sized for how big the motor is, but maybe there is an improvement to be had.

If no one has looked into this yet, I would spearhead something myself to see if we could get something done.

Thanks for any help!

[YourConfused]

got a price from Extrude Hone on doing the intake yet?

[Nevin]

got a price from Extrude Hone on doing the intake yet?

I just emailed them the other day, and I'm waiting for their response.

I don't really care how much it costs though, I just want it done. I don't think I've heard of anyone doing it on an SVX yet, but I know it's shown worthwhile gains on other cars. I think if I did phenos, IM, and something with the TB's (possibly also extrude hone) and an intake like myxaplyx, I think I would have some noticeable gains.

[svxfiles]

The throttle body twin intake throttle plates are 60mm and capable of flowing 900 CFM*.
Our 202 CID engines can only flow 420 CFM at 100% volumetric efficiency
at 7200 RPM.

That said, there are some slight gains to be had, at least theoretically, with some mild porting/port matching.

However, depending on your applications, the exhaust is where you should look.

* Paraphrazing Terry McClain in The Subaru SVx FAQ.

[Nevin]

Ok, yeah I figured that they would be more than enough. Seemed like plenty of throttle body for our small motor. Anyways, that's good to know!

I'm still planning on checking out extrude hone though, and seeing how that turns out, and doing before/after dynos.

If it works out how I'd like, I see they do group buys, and I would be willing to organize one if there was enough interest!

[svxfiles]

When I checked with Extrude Hone they wanted, what I concidered to be a huge amount for their services.:o
And I pass their place on my way to Pgh!
Another Racer also spoke with them and decided against going that route, but we both went with ceramic coatings and Outlaw Engineering phenolic spacers.:)
Tom

[Nevin]

I have a set of outlaw spacers on my probe, and I absolutely love them, and I saw in your signature that you had some, so I at least figured they were an option. Looking at their website, I don't see the SVX listed, so can I get something through you Tom, or should I just email them?

[YourConfused]

"we both went with ceramic coatings and Outlaw Engineering phenolic spacers"
Are there specific reasons other than $ for this decision?

[svxfiles]

I have a set of outlaw spacers on my probe, and I absolutely love them, and I saw in your signature that you had some, so I at least figured they were an option. Looking at their website, I don't see the SVX listed, so can I get something through you Tom, or should I just email them?

If you speak to Sean at outlaw he can hook you up.
you only need to decide whether you want all five spacers or just the top three.

[Nevin]

If you speak to Sean at outlaw he can hook you up.
you only need to decide whether you want all five spacers or just the top three.

Is the 3rd the throttle body spacer?

[svxfiles]

"we both went with ceramic coatings and Outlaw Engineering phenolic spacers"
Are there specific reasons other than $ for this decision?

Everyone who is on a budget has to make decisions.:(
It was much easier for me to port and coat the intake manifold than to pay about $200 or so to "hone it".
And when I was done with it it mached.
Throttle body to manifold.
Manifold to stacks.
stacks to ports.:)
I know that the ceramic coating with the spacers lowered my intake manifold temperatures.
Many people have felt my intake manifold and can vouch for how cool it was.:cool:
As I remember Extrude Hone wanted about $300.00 to do both exhaust manifolds, the honing that is, and that was approaching the parts bill, of my headers!
I wish I had unlimited funds and time, then I would have had Burns Stainless built my headers.
For about $2000.00:o
Not the labor, just the parts.
Tom

[svxfiles]

Is the 3rd the throttle body spacer?

Yes, and the fourth and fifth are for under the stacks.

[SVXRide]

FYI,
You get the inside of the intake and stacks glass beaded when you have the thermal coating done as they put the pieces in a giant vibrating tank for the final "finishing" stage of the coating. So, +1 for everything OT has said in this thread!:cool:
-Bill ("Father" of the intake thermal coating mod;):D)

[Nevin]

I just figured that I would get the outside of the manifold coated and get the inside honed. While glass beading certainly wouldn't hurt anything, it wouldn't make things nearly as smoothe as the extrude hone process would.

Also thought about getting the outside chromed. That would just look flippin' sweet.

[svxfiles]

I just figured that I would get the outside of the manifold coated and get the inside honed. While glass beading certainly wouldn't hurt anything, it wouldn't make things nearly as smoothe as the extrude hone process would.

Also thought about getting the outside chromed. That would just look flippin' sweet.

Why dont you take a walk through my locker.
Engine pictures shows the silver ceramic coated manifold. and there are three sections on porting, plus several on the Outlaw Engineering phenolic spacers.:)

[Boxersix]

I'm not personally fond of the extrude hone procedure and it's "benefits". We've used it a few times on different motors and did not gain anything appreciable that makes the cost of the process worthwhile. I too agree that ceramic coating the intake plenum will yield greater results. Doing so has for me in the past on many aircooled 911's

Second a perfectly smooth surface doesn't help flow any and actually hurts it in some cases due to the loss of the boundary layer(layer of air that "sticks" to the inner walls) Air flowing across a perfectly smooth surface vs a boundary layer has greater friction, this has been proven time and time again. Adding the ceramic coating inside the manifold would most definitely yield a better surface than the super rough OEM surface, but not as bad as going with an extrude hone that damn near polishes the inside. I think it's one reason why the extruded hones DON'T make any appreciable power, at least in my experiences.

And finally, I'd leave the TB's alone. They'll flow more air than the motor could ever really need right now. Only thing I'd ever change would be to convert from a butterfly setup to a flatslide valve setup to eliminate the air obstruction of the butterflies and shaft at WOT but even that's going beyond what most would ever really use. :)

[Nevin]

Ok Tom, went through your locker. I think I will just contact Outlaw and have them make me a set!

Also, to others who have responded, I'm definitely not trying to say "I know it all why hasn't this been done before?" More like I just haven't read anything about it on here and I wanted to know if it was worth it. Thanks for everyone's response so far! They are appreciated.

[SVXRide]

Second a perfectly smooth surface doesn't help flow any and actually hurts it in some cases due to the loss of the boundary layer(layer of air that "sticks" to the inner walls) Air flowing across a perfectly smooth surface vs a boundary layer has greater friction, this has been proven time and time again. Adding the ceramic coating inside the manifold would most definitely yield a better surface than the super rough OEM surface, but not as bad as going with an extrude hone that damn near polishes the inside. I think it's

From a fluid mechanics perspective, you actually want a slightly rough surface on the intake side to "trip" the flow and get better mixing of the air-fuel. Smoother on the exhaust side is okay.

-Bill

[Boxersix]

From a fluid mechanics perspective, you actually want a slightly rough surface on the intake side to "trip" the flow and get better mixing of the air-fuel. Smoother on the exhaust side is okay.

-Bill

Exactly. The optimum surface prep is around a 400grit comparable. Just enough to optimize a good boundary layer for velocity and turbulence level for atomization :)

[Nevin]

So wouldn't it be good then to have the intake itself as smoothe as possible to increase velocity,and then leave the "stacks" with the factory finish since that's where the injectors are? Seems like it would help smoothe airflow until the point where are and fuel mix and then the extra velocity would create extra turbulance and increase combustion effeciency.

[Boxersix]

So wouldn't it be good then to have the intake itself as smoothe as possible to increase velocity

Not really, as the smoother the surface the less of a boundary layer you have. This of course has a fine line you need to follow as obviously if it's too rough then you're just messing with flow and are right back to the beginning. For example, when I port heads they all get a final blast finish in the port with a 4-600grit(pending head material) after all the port and sand work has been done. I have shown people at my shop with a CNC ported head with two ports, one polished and one 400 grit soda blasted with the blasted port having a higher velocity than the polished port on my flow bench. This is of course on the intake ports. Exhaust ports just get ported and sanded as a boundary layer there makes minute effects in exhaust velocity.