87350IROC

iTrader: (2)

Are these better, bigger than camaro throttle bodies?

RMK

They use the same throttle body.

87350IROC

iTrader: (2)

thats a shame, i have one and i though it may have a bigger bore

D Stroy H8

Port and polish it... =\
But i thought bigger TB's were only necessary upwards of 450+ horses. It really makes me laugh - my friend owns an alero, and guys on his board have 60lbs fuel settings and 62mm TB's... all of this on thier 3.4 liter engines SFI. lol.

SHO350

Bigger throttle bodies can help throttle response.

89 Iroc Z

When you supercharge thoese 3.4's and 3.8's they sure will move. Their not bad engines when talking about V6's, you can pump a lot power out of them.

D Stroy H8

No doubt. I am not in anyway putting down a six cylinder car trust me - I used to drive one =)

However, the people I referenced to were doing these mods (62mm TB, 60lb fuel) have nowhere near the requirements for such modifications. Granted, maybe justifiable with a blower or something seriously making large increases in output... it's ridiculous.

2000 Alero GLS
3400 V6
Cold air intake
Borla Catback exhaust
Ported upper intake plenum
62mm TB <- ludicrous
58lb fuel pressure <-equally ludicrous

see my point?

Jza

How do you figure that's ludicrous? Those aren't twin 62mm bores, are they? Stock is like a single-bore 57mm TB. And comparing the fuel pressures used to our cars is like comparing a TBIs FP to a TPIs FP. You just can't compare two different systems like that. A more accurate way to compare would be percentages, like 10% higher pressure, or 10% larger bore..

Anyway, there are better places to find improvement than the throttle body, so that at least is ludicrous [spending tons of money on a billet TB for little or no improvement]. The stock throttle body is hardly a restriction. I'd focus more on the smoothness of the intake tract, etc.

scorp508

As the others have said, the TPI Corvettes have the same 48mm TB as the F-Bodies. I'm sucking through my stock 48mm right now and making about 388hp at the moment and should be around 400-410 or so after tuning. You could get it bored out to a 52mm if you wanted to, but I don't see the need unless you are going to be with a 383 or larger engine. Look at GM's crate engines, most come with a 48mm on them.

As far as better throttle response with a larger TB, I'd like to see the truth in that.

Jim85IROC

iTrader: (2)

Don't hold your breath. In addition to quite often slowing a car down, a bigger throttle body will create a sluggish throttle response. I suspect that it's due to too much air at throttle tip-in. Tom Keliher and GMHTP or CHP or some magazine tested his car with a 58mm throttle body. Tom had a fair amount of minor mods at the time, and his car slowed down with the bigger throttle body.

Guest

A bigger TB will definitely make the throttle response WORSE not better.

scorp508

Yup. I just wanted to see him try to prove it.

Ed Maher

Depends what your definition of throttle response is. A 58mm TB at 70% throttle opening may move as much air as a 48mm at 100% opening. A bigger TB is like having a faster foot, you can have more air with less movement. Unless you need the extra flow though, in essence all you get is less useable throttle range.

scorp508

It will let same amount of air in sooner, but you are also letting the air in through a larger opening therefore reducing the overall incoming velocity of the air.

Ed Maher

Damn good thing that the TB is the smallest part of the system, even if it's a 58mm on a stock plenum. I'd sure hate to be counting on velocity through the TB to aid in velocity in my intake considering that once the air passes through the TB it hits the big open plenum and loses all it's velocity anyway. Or that before the air sped up to go through the TB it was also going slower in the wide open intake tract. The TB bores are far too short for the incoming airstream to have any appreciable inertia to have a real scavenging/manifold filling effect.

I'm not arguing that big TBs are a good idea. But i can't place merit in the velocity through the throttle bores theory for the reasons i put above.

Jim85IROC

iTrader: (2)

Ed, if you put a 1050cfm Dominator carb on a mild 350 and jet it appropriately, what happens? How's throttle response?

Ed Maher

Hey Jim, what does a carb due that a TB doesn't?

I'll save you the trouble. Carbs rely on the velocity of the incoming airstream to FUNCTION. If your carb is too big for the application, then the venturi doesn't work and fuel is not metered properly.

A FI TB only passes air. And i say again, immediately after the TB, the orifice of the plenum is so much larger that any velocity through the TB is lost. (yes this is still a venturi, but its still not responsible for metering or mixing the fuel so who cares)
The function of the plenum is to buffer the airflow to the runners so that each runner doesn't have to pull it's air supply from the TB instantaneously. If high velocity in the TB was such a good idea, why not extend the concept and make the plenum as small and streamlined as possible so that each runner can have an even higher velocity of airflow available.

So if you don't need velocity in ther TB to mix and meter fuel, and the velocity is not in any way aiding the VE of the engine since the air slows down immediately after the TB anyway (and was going 'slow' before it got to the TB too don't forget), exactly why do you want high velocity in the TB. There are other ways to explain why SOME cars slow down after putting a bigger TB on then by some half cocked excuse like velocity. Like the pump shot needs (which is defined relative to throttle movement) are now completely off since a completely different amount of air is passing per throttle opening.

Guest

Ed, before you try to use physics and whatnot to explain it, why dont you try it? I can assure you that if you swap from a 48 to a 58, you will lose "throttle response", even if you mess with fuel and timing. Using a carbed vehicle as an example is perfectly fine, it does the same thing for the same reasons a FI car loses some throttle response. You could step on the gas as lightly as you want to, its still the same deal... the throttle response is not the same.

Ed Maher

All i am debating here is velocity through the TB as it relates to throttle response. If i had the money and the free time i'd take you up on your offer and get a 58mm TB and spend the time to tune it.

Yes i know that some people lose throttle response. And i also know some people slow down. And i also know that there is more in play then velocity through the opening into a plenum from which the engine feeds.

And carbs are a very very poor analogy to a dry PFI TB in my book. Carbs lose throttle response because the mixture and it's distribution suck when the airflow through the VENTURIS falls off. And once the mixture is a little bad, then combustion degrades, so the exhaust degrades. And the next intake stroke degrades, so velocity falls off worse, and then the engine stalls out (or at least sputters for a few seconds until it manages to get things going again)

Please will someone tell me how in hell velocity through the TB affects cylinder filling and i'll eat my crow and smile. If the best example anyone has is a carb, then i stand content that you're just grasping for straws and that some other factor is causing it but velocity sounds cool so it must be it.

Ed Maher

Ever wonder why they make different venturi styles for those nifty high dollar carbs. Could it be to adapt the carbs fuel metering characteristics to the airflow of the engine. Like if you want to run a dominator on a 350 you would want relatively small sensitive venturis/booster whereas if you tryed to run those boosters on a big block you would end up with trading some pinched off airflow but be able to run relatively less pump shot since the main fuel system would catch up so quick.

Ed Maher

When you first tip the throttle plates in, the air in front of them is barely moving. Now try not to get lost.

Bam, WOT from closed.

-Small TB car. Needs X airflow. Has Y orifice to pull through. Velocity is going to be proportional to X/Y

-Big TB car. Still needs X airflow. Now has 1.25*Y (arbitrary number) to pull through. Velocityis reduced for the same flow( X/(1.25*Y) < X/Y )

NOW.

Given that before you open the throttle plates the air in front of the TB is barely moving, and will have the same velocity (idling airflow/apperture will be too similar to not be the same for this example's purposes)

Now, the small TB car needs to accelerate (uh oh) the air it needs to breathe to a higher velocity than the big TB car. So the big TB car moves the same amount of air more quickly than the small TB car (unstated assumption above, X airflow is all the engine can use, and a small TB can flow it, and a big TB is no help)

Yes, absolutely the big TB will have less velocity. And amazingly enough even for an engine that was previously maxed out on airflow, a bigger TB will still completely alter the speed with which that air makes it to the cylinders, because the air column doesn't have to accelerate as much. Which yes, i can easily understand would cause a hrottle response problem without extensive tuning to compensate. Might even need to change things that aren't in an editor that are buried in the code as assumptions about airlfow properties.

However, i cannot fathom why more airflow more quickly would in and of itsef cause a throttle response problem just because it isn't moving as quickly through an arbitrarily picked point in the airstream. The air is moving slower on both sides of the TB. And for the purposes of this example, the velocity is identical on both sides of the TB with both TBs (well except for the transition region, where the big TB has more velocity after the TB more quickly than the small TB, but steady state, they are the same)

Now considering that the small TB engine has to work harder to get the air moving than the big TB engine (accelerating a mass to a velocity requires energy, less velocity = less energy. There is no free lunch, that energy comes from the intake stroke), why would the big TB necessarily have worse throttle response? Needing to waste less energy, and wait less time for the air to be available is a bad thing? Or do you just need to tune the engine to adapt.

Jza

The correct answer to this post was brought to you by:
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RMK..

RMK

:sillylol: :sillylol: :sillylol:

Ed Maher

ooooooo...touche'