Enlarged throttle body

[deadmau5]

I recently bought an enlarged throttle body (64mm, standard 60mm) after some positive reviews on the clio197.net forum. However, now I have fitted it whenever I go over 4000rpm the car goes into limp home mode and I get the message 'Check injectors'. When I restart the car it goes back to normal. No-one else with the enlarged TB has this problem and my knowledge of them isn't great. Does anyone know what could be causing this to happen? I made sure it is bolted on correctly and plugged the wire in securely.

[deadmau5]

FoundOnRoadside said:

Enlarged TB, more air getting in, engine runs leaner, worn out injectors can't supply enough fuel to compensate?

This sounds feasible. I'm on 58500 miles and I don't know if they've been changed.

[deadmau5]

Captain Muppet said:

FoundOnRoadside said:

Enlarged TB, more air getting in, engine runs leaner, worn out injectors can't supply enough fuel to compensate?

You think an extra 4mm of TB diameter will be enough to max out the injectors at 4,000rpm? It's not that (unless before the throtle went on it was already maxing out the injectors at 4,000rpm).

Throttle position sensor been disturbed at all? Or is it built in to the new throttle, in which case how did you check it worked before you bought it?

No the engine was running fine before.

I don't know if the TB was working before I got it unfortunately. I am going to try and get the parameters for the TB reset this evening then see how I get on.

[deadmau5]

Eggman said:

Sounds somewhat unlikely to me that (in the absence of other modifications) you would see much benefit from changing the throttle body anyway. Unless it'd a really odd design where the throttle body presents some kind of bottleneck.

Oversized valves I can see, but I suspect this type of modification is sold more on ease of installation than any very concrete benefits.

Personally, I would refit the original, see if the problem goes away, and if so, demand a refund.

They aren't sold by a business. A few owners had it done, found there was a benefit so a few more people had it done. The main benefit is more power lower down the rev range, which is where 197s typically struggle.

[deadmau5]

Max_Torque said:

deadmau5 said:

They aren't sold by a business. A few owners had it done, found there was a benefit so a few more people had it done. The main benefit is more power lower down the rev range, which is where 197s typically struggle.

sorry, but "b*ll*cks" !


At low rpm the throttle doesn't even need to open fully to support the engines airflow requirement without significant pressure drop. (in fact, it won't open fully until approx 4500rpm (to ensure a sufficently fast response for "torque downs" on TCS intervention)).

At peak power, a modern engine throttle body will be sized to a maximum pressure drop of approximately 1kPa. When you consider that daily varriations in atmospheric pressure can be 3 to 5kPa you'll see how small an effect that is.

If anything, all the change will do is make the "throttle map" a bit less linear. The large throttle will present a larger opening area for any given angle, and so all you have done is "shift" the pedal map a bit towards the closed end. However, at WOT, there is no benefit. So why would you "improve" the performance, but not at WOT. i.e. if you want full performance, then just floor the throttle pedal 100%!

Put it back to standard and stop F*cking with it !!!!

Sorry dad.

It is a pretty risk free mod as I can sell it on for the same price I paid for it if I so choose.

[deadmau5]

crocodile tears said:

Max_Torque said:

deadmau5 said:

They aren't sold by a business. A few owners had it done, found there was a benefit so a few more people had it done. The main benefit is more power lower down the rev range, which is where 197s typically struggle.

sorry, but "b*ll*cks" !


At low rpm the throttle doesn't even need to open fully to support the engines airflow requirement without significant pressure drop. (in fact, it won't open fully until approx 4500rpm (to ensure a sufficently fast response for "torque downs" on TCS intervention)).

At peak power, a modern engine throttle body will be sized to a maximum pressure drop of approximately 1kPa. When you consider that daily varriations in atmospheric pressure can be 3 to 5kPa you'll see how small an effect that is.

If anything, all the change will do is make the "throttle map" a bit less linear. The large throttle will present a larger opening area for any given angle, and so all you have done is "shift" the pedal map a bit towards the closed end. However, at WOT, there is no benefit. So why would you "improve" the performance, but not at WOT. i.e. if you want full performance, then just floor the throttle pedal 100%!

Put it back to standard and stop F*cking with it !!!!

sorry to break it to you, but I think this guy knows his st.

I guess I'll remove it and sell it then. Please inform me without telling me off next time

[deadmau5]

Max_Torque said:

davepoth said:

A bigger throttle body provides more power at full engine load

Once again, no it doesn't! It only "produces more power" (for which you actually mean "increases the intake mass flow by increasing the plenum density") if the original throttle was a restriction. Which on any engine made in the last 15 years, it isn't


Renault didn't just manage to squeeze 197 bhp out of their engine, and "not notice" that a 4mm bigger throttle would improve the output did they! Once the throttle is no longer the restriction, i.e. manifold pressure is atmospheric pressure (minus the intake system losses see below) then you could make it any size you like, or even completely remove it and the engine will not make any more power.


regarding intake losses, once again, modern engines are massively well designed here. Even with all the driveby noise regs and NVH concern, no OE accidentaly makes a rubish intake system any longer (they simply can't afford to). Typically the total pressure loss of the complete intake system is less than 3 kPa. Many people fall into the trap of not correcting for the dynamic component of pressure (which is transfered back to pressure as the air deccelerates into the plenum volume, usually with something like 98% efficiency or more). Measuring the intake pressure and only accounting for the static component can see what appears to be a large loss, but this is simply because at the measurement point there is a large dynamic component.

Having said all that, 99.9% of people "tuning" their car just read something posted online about "how X or Y mod massively improved some element of the performance" with no real data, and being posted by people with little or no technical understanding of their subject matter.


Now of course, it's your car, you can do what ever you like to it ;-)

(of course you have informed you're insurance company about the modification obviously !)

Thank you for the information.

I have now sold the TB already for the price I paid.

It's 197PS (194bhp) btw, but none of them actually make that figure.

[deadmau5]

fozzymandeus said:

Out of interest, (and I've read all the posts, so apologies for not noticing if it's been mentioned) but what was the original application of the modification TB? Was it intended for a larger displacement engine?

To achieve the specific output the 2.0 sport clio engine achieves it'd need a pretty enormous compression ratio and therefore a high air mass flow rate at full throttle anyway.

Most attempts to tune this engine I've seen have resulted in failure, somewhat O/T but aftermarket induction kits are a bit of a no-no in this application. When I bought my F1 it had some kind of K&N universal fit "cold air induction" kit fitted and all it achieved was lots of noise and a loss of linearity of torque.

I dunno. Great cars, sport clios, one of my favourites, but not a good subject for dubious modification. Just buy a VW and put some stickers on it instead

There are a few mods proven to give an increase in power but it's very expensive for relatively small gains.