ITB sizing for worked g180w

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BackToTheGem
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ITB sizing for worked g180w

Post by BackToTheGem »

I'm looking at fitting either bike or 4age 20 valve throttle bodies to my g180w. It will be approx 10.5:1 cr, headwork, cams, a nice set of 4:2:1 headers and 4 coil ignition.

Looking at these throttle bodies I'm wondering if they may be too small for my build. I'm looking at 42 - 45mm throttle bodies which would be roughly the same sort of flow as 45-48mm webbers. The engines they come off are around the 170-180bhp mark - I was hoping too make more like 150-170 hp @ wheels.

Does anyone know if there's much headroom from stock power figures in any of these throttle bodies? Heavily worked g series twin cams seem to often run twin 48mm webbers so I'm thinking the 45mm throttle bodies should flow around what I need but the 42mm throttle bodies may be marginal. On the other hand the 42mm throttle bodies would probably make the engine nicer on the street compared to the 45's.

I've read MGOTD's build thread a few times over now - lots of very good info but I'm aiming for a different power level with my twin cam.
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Post by MGOTD »

4age 20v Silver tops run 42mm throttles and make 120hp@8000rpm, 4age 20v Black tops run 45mm throttles and i haven't seen a dyno for one but should be enough flow for your car, if not you could look at getting some 48mm EFI hardware throttles etc and they will bolt straight to a twin weber manifold (like bad 44u has). I plan on running my qaud setup on a wild 1.8 once i get the 1.8 built.
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Post by BackToTheGem »

Cheers mate. I might look for some 45mm black top 4age throttle bodies. The bike throttles look nice and I can get them in 45mm but those silicone joiners they use that make them so damn easy to mount can't be good for flow (I read where bad44u said he tried them on his trumpets and lost 20-30hp). The iacv setup on the 20 valves looks a lot nicer too. Are you running it on yours? I've spent a bit of time playing with silver tops (dad runs one in his clubman) and they do idle nicely and drive well at low speeds.
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BackToTheGem
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Post by BackToTheGem »

Oh and EFI hardware gear looks the goods but probably a bit more $$$$ than I'm wanting to spend. I'm also wanting to raise my ports a little and run an angled inlet like you did, the twin cam already has a pretty direct entry to the valve as standard so I don't think I'd need to raise the ports or angle the inlet quite as much as you did though.

Still that's something I'll talk about with my engine builder
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Post by MGOTD »

nah not running the iacv on my car i had to cut the original manifold up because the spacing is all wrong for g series engines because the ports aren't evenly spaced and there where a few mods required to the throttle linkages because of that too.......If you look at the ports on a 20v they have massive angle one of the other benifits of an angled inlet manifold are clearance for brake booster and master, with straight runners like i have the throttles actually foul on the brake booster.
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Post by redzone (coxy) »

45mm throttles will be ok for that power level, 48 would be a bit boggier at low rpm but will give u more top end potential
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Post by BackToTheGem »

Cheers Coxy.

Guess it's go 45mm and save a few dollars but restrict outright power potential or spend up and go 48mm.

Do you think the 48mm throttle bodies would be that much boggier down low - enough make the car bad to drive on the street? It's far from a daily driver but I don't want an absolute pig either.
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Post by BackToTheGem »

I found some flow figures for DCOE style throttle bodies.

40mm - 34kw
45mm - 40kw
48mm - 48kw

So I guess that means approx 136kw / 160kw / 192 kw @ engine for each of these sizes before they become a restriction.
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Post by F3ARED »

The things to watch out for with all of the 4AGE quad throttles is the port shape is not perfectly round - its more of a kidney shape. More noticeable on the 45mm versions.

What would you say if I told you i knew of 48mm plate-style [similar to Weber flange] throttle bodies that had the exact same center-to-center measurement as the DOHC head?

Ive already done the headscratching for this, just need to start putting my DOHC together...
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Post by archangel62 »

This thread is awesome.

BackToTheGem - Coxy mentioned above that the 48's *will* make it boggier down low. I think I'll be going for 45's on my EFI G180W street car.

I wonder how much difference runner length would make? Or where to put the injector in the runner? Orrr, if the 4AGE kidney-shape would cost any power.

I googled 45mm throttle bodies, and these are the first I've found:

http://www.efihardware.com/products/12/ ... mm-to-50mm

Not sure if they're the going rate, or a bit pricey, but they look awesome. My only thought is that they're designed to bolt directly up to a DCOE flange, and therefore have stuff all runner length. The injectors would be basically pointing at the valve, too. Still, torque would be good, and they'd have the flow for RPM too. Perhaps it'd come down to having a high quality injector with a good "mist" spray.

Any thoughts on these from the gurus?
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Post by F3ARED »

The Efihardware/injection perfection throttles ARE an awesome piece of gear, but are definately NOT worth the money. To give you an example, the 'secret' throttle bodies i mentioned above cost between 250 to 400 for 3x pairs of throttles - 6 throttles in total. Not to mention they are ALOT more compact and easier to mount if you dont have a weber style manifold...

The kidney bowl shape does cost a small amount of power, however its not the throttle body itself that doesnt flow, itll be the transition from kidney to round [to suit the ports] that hurts it. That, and the biggest disadvantage with these is the scene tax they attract. I dont think ill be paying 500 odd for 42mm throttles when I just contacted a bloke to buy his 48mm throttles...and he has them advertised for 250!
Not sure if they're the going rate, or a bit pricey, but they look awesome. My only thought is that they're designed to bolt directly up to a DCOE flange, and therefore have stuff all runner length. The injectors would be basically pointing at the valve, too. Still, torque would be good, and they'd have the flow for RPM too. Perhaps it'd come down to having a high quality injector with a good "mist" spray.
You dont want too much runner length anyway. Yes in theory it helps the fuel and air mix better on the way down to the valve, but if you have a close look at the standard Isuzu EFI manifolds you'll notice that the injectors are seated, and angled, pretty much straight into the valve anyway. If your tuning for torque or top end, changing the trumpet length before the throttle butterfly helps.

In terms of injectors, a good mist is what you always want.
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Post by BackToTheGem »

[quote="GeminiCoupe"]What would you say if I told you i knew of 48mm plate-style [similar to Weber flange] throttle bodies that had the exact same center-to-center measurement as the DOHC head?[quote]

I think I'd say that sounds pretty damn awesome (I'd love to know more about them if it's not a secret)!! Are they off a bike or car?

The DOHC has 85mm bore spacing doesn't it?

Agree with the "scene" tax on the 20 valve stuf - it's doubled in price the last couple of years. That's the main reason I was looking at bike gear (closer to $250 for a set of 4) EFI hardware gear looks nice but at $1500 for a set of throttle bodies they're a bit over the top. Especially when I'd still need injectors, a TPS etc.

For the runner length I was going to try to keep it as short as possible (probably just enough room to mount an injector) so I can get the butterflys as close to the head as possible. For my trumpets I plan getting as long as I can fit in the engine bay - optimum length would more than likely be far longer than I can fit anyway.
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Post by BlueGem »

GeminiCoupe wrote:The things to watch out for with all of the 4AGE quad throttles is the port shape is not perfectly round - its more of a kidney shape. More noticeable on the 45mm versions.

What would you say if I told you i knew of 48mm plate-style [similar to Weber flange] throttle bodies that had the exact same center-to-center measurement as the DOHC head?

Ive already done the headscratching for this, just need to start putting my DOHC together...
They're not off a nissan are they?
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Post by F3ARED »

All im going to say is they definately arent GTiR items.... :lol:
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Post by redzone (coxy) »

What u have to remember with sizing throttles, is that you look at a car like elky's drag twin cam, running 40mm dellorto's with 32mm chokes, it is only breathing through a 32mm hole, so even a 40mm throttle will be a massive gain.. 45mm throttles will be a massive improvement over 45mm webers etc. 48mm throttles flow a LOT of air. 45mm throttles will probably still be a little boggy at low rpm..
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