Larger throttle body

warrior · Post by **warrior** » Wed Dec 19, 2012 4:40 pm

I am wanting to get a bigger throttle body for my supercharged car. Any one had any sucess with one? There are plenty of larger ones availble but I am wondering how hard they would be too fit. Buying one looks like a cheaper option than getting the original bored out and I think they can only go 2.5mm bigger anyway.

punkoutnz · Post by **punkoutnz** » Wed Dec 19, 2012 4:43 pm

They already run a pretty large throttle body, you would have more restriction in other parts of the engine (notably the head) before you'd ever need to even consider upgrading the throttle body. In fact I'd go out on a whim and say unless you're pushing 350+hp you wouldn't even need to consider upgrading a throttlebody on a B6 engine.

warrior · Post by **warrior** » Wed Dec 19, 2012 6:35 pm

Thats not what everything I have read says. They all say with a supercharged engine a larger throttle body makes quite a improvement. They say it is a weak link in any supercharger setup.

SLYDIT · Post by **SLYDIT** » Wed Dec 19, 2012 8:04 pm

warrior wrote:Thats not what everything I have read says. They all say with a supercharged engine a larger throttle body makes quite a improvement. They say it is a weak link in any supercharger setup.

grain of salt anyone...what makes a supercharged car any different from a 250HP turbo car? absolute waste of money. the head flow is the restriction and then after that its the super high inlet temps that limit HP on a SC car.

Post by **jif** » Wed Dec 19, 2012 8:37 pm

hmm.. isn't a SC throttle body under vacuum ?

http://www.musclemustangfastfords.com/t ... ewall.html
It should be noted that throttle body sizing and maximum flow is less critical on a blow-through (centrifugal supercharger and turbo) application than a draw-through (positive displacement).

On 19 December 2012 20:04, SLYDIT <horsepower@mx5forum.co.nz (horsepower@mx5forum.co.nz)> wrote:

warrior wrote:
Thats not what everything I have read says. They all say with a supercharged engine a larger throttle body makes quite a improvement. They say it is a weak link in any supercharger setup.
grain of salt anyone...what makes a supercharged car any different from a 250HP turbo car? absolute waste of money. the head flow is the restriction and then after that its the super high inlet temps that limit HP on a SC car.

------------------------
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Mad Kiwi · Post by **Mad Kiwi** » Wed Dec 19, 2012 9:02 pm

Not sure where you are reading to say "everything" but i'm guessing turbo and SC are the same or similar requirements in the TB area and I have never read anything about limitations other than them failing and the butterfly screw going through engines....in very rare cases (constantly high revving 7200+ race engines...).

warrior · Post by **warrior** » Thu Dec 20, 2012 10:03 am

Guys, there is a HUGE diffrence between a turbo and a supercharged car. The turbo car runs the throttle body AFTER the turbo so the air going through the TB is pressurised.

A supercharged car runs the TB BEFORE the supercharger so the air going through the TB is NOT under pressure.

Think of a straw, the turbo car is forcing (at whatever PSI is it running) air through that straw but a Supercharged car is just breathing through that straw so it makes sence to make that straw bigger so more air can get in dosnt it?

So a larger TB makes a very big diffrence.

Have a look at all the supercharer kits for the commodores, mustangs, and even the new larger supercharger kit for the mx5, they ALL have larger throttle bodies, and this is for a good reason.

It is quite simple really.

warrior · Post by **warrior** » Thu Dec 20, 2012 10:07 am

p.s , I have spoken to TRACKDOG racing, Moss motors and read it in Keith Tanners high performance MX5 book that this is the case also. And all three of these places do not sell larger TB,s so they have nothing to gain in telling me this.

tomtikki · Post by **tomtikki** » Fri Dec 21, 2012 9:10 am

I've noticed the TB fitted before the supercharger on a cpl of builds, whats the deal?
I mean if the TB can handle it after the turbo why can't it handle it after a SC?
Im sure it has been done for a reason by people much smarter than me but still it seems odd from a laymen's point of few...

warrior · Post by **warrior** » Fri Dec 21, 2012 11:34 am

It comes down to be able to make the car idle correctly, very tough to do with the TB after the supercharger

warrior · Post by **warrior** » Sat Dec 22, 2012 2:39 pm

P.s a turbo car runs a blow off valve, a supercharged car does not

WideOpenThrottle · Post by **WideOpenThrottle** » Sat Dec 22, 2012 8:12 pm

warrior wrote:P.s a turbo car runs a blow off valve, a supercharged car does not

Mine doesn't have a BOV and i have been told many times by reputable sources that under 15 psi not really necesary to have one.

warrior · Post by **warrior** » Sat Dec 22, 2012 9:10 pm

Sorry maybe I should have said a bypass valve. Here is the reason why superchargers have the throttle body after the supercharger and why a larger throttle body is worthwhile. "Because of what happens to the pressure in the intake system when you close the throttle. Unlike turbos, airflow cannot reverse backward through a fixed displacement supercharger. This means when you close the throttle under boost, theres a huge pressure spike in the intake and you can actually blow an intercooler apart. A large bypass valve may be able to solve the problem on a supercharger but nobody has been able to implement it well" quote from Keith Tanner.

WideOpenThrottle · Post by **WideOpenThrottle** » Sat Dec 22, 2012 10:24 pm

I dont have a bypass valve either....this performs the same job? as a BOV except it releases pressure back into the system before a turbo while a BOV generally vents to atmosphere although they can be recirculated like a by-pass valve i believe.

If a supercharger has the TB before it then does a vacumm arise once the throttle valve is closed? so no need for a BOV or by-pass valve whereas in a turbo its the opposite and you have pressure which if too great needs to be released..

If your SC is able to pump more air with a bigger TB then surely you need to increase the size of your whole intake tract as well.
Also you need to give thought to the 'Ram-effect of' faster air through a smaller tube can be better than to too big a tube with slower moving air.

So what i am trying to say is match pump to best airflow speed.
My set-up is so much nicer for having smaller IC tubing as i have matched turbo out-put...its all been a very experimental learning curve for me.

warrior · Post by **warrior** » Sun Dec 23, 2012 12:04 pm

As I said before you can Not compaire a turbo TB with a supercharger TB

warrior · Post by **warrior** » Sun Dec 23, 2012 12:16 pm

Oh and yes you are correct, the rest of the system is 65-70mm and the TB is about 55mm with a butterfly in the way so it is a lot smaller.

warrior · Post by **warrior** » Sun Dec 23, 2012 2:24 pm

You are also correct about the "ram affect" but the air going into the TB is not being rammed in that is why there is a need for the larger TB

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Dec 23, 2012 2:46 pm

Next obvious question...is it the mx5 TB or a TB that came with the SC?

If it came with the SC then it may be of a size thats already at its most efficient in relation to the out-put of the SC so to go bigger might not create any increase in power!?

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Dec 23, 2012 2:59 pm

Also ....what size is your exhaust?.....no point in trying to force more air in if it cant escape!

warrior · Post by **warrior** » Sun Dec 23, 2012 3:12 pm

Exhaust 2.75 inch all the way through

warrior · Post by **warrior** » Sun Dec 23, 2012 3:15 pm

It is a jackson racing kit so it uses the standard TB but the inlet hole to the SC in bigger than the standard TB

warrior · Post by **warrior** » Sun Dec 23, 2012 3:17 pm

I,m not sitting here saying with a bigger TB I am going to get another 20-30hp but from what I have read and from what I have been told it is worth upgrading to a bigger TB, and at about $200.00 for a larger one its not a heap to pay if I get another 5-10hp out of it

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Dec 23, 2012 3:28 pm

I'd be surprised if its more than 5hp.

warrior · Post by **warrior** » Sun Dec 23, 2012 3:55 pm

We will see.