BergerZ28

I have been thinking about the next mod for my Z and Im thinking I will go with a throttle body. However im not sure with which one to go with. Right now I have an slp cold air intake, longtube headers with the ory, and a 160 degree thermostat. Should I go with a 58mm or something smaller?

borninatransam

iTrader: (4)

holley twin 58mm ftw. im sure youre not stopping here with you mods so why not go ahead and do more than is necessary. and before anyone says that it will hinder performance, show me proof and i will believe you.

97bowtie

iTrader: (1)

Your money would be better spent elsewhere, as the stock 48mm TB is plenty to support your power level.

JUICED96Z

Holly 58. I got mine used on here for $300 shipped.

LT1MAN

iTrader: (6)

get a torque arm and lower control arms. they are very cost effective.

always faster

iTrader: (6)

To max out a 52mm tb you need 500-525hp so a 58mm would be too much...

A 52mm tb is gonna you very little hp but gonna give you a better throttle responce.Go with a ported stocker from mjblund on ebay(his also a member on camaroz28.com).It cost less and your not gonna have any common problkem found on aftermarket one like idle trouble or buttefly not closing all the way.

My 2 cents

LT1MAN

iTrader: (6)

i agree with always faster. but if you want to buy at 52mm tb, i am actually selling my 52mm ported stock throttle body. it was professionally ported and rebuilt i did not do it myself. i put it on probably 10,000 miles ago. ill sell it for dirt cheap. pm me if interested.

buffman

iTrader: (9)

bigger TBs are more worthwhile than some of you think

David Vizard wrote an article where he tested several throttle bodies. His site is gone or I'd link it here. Anyway, he concluded that as long as the flow through the throttle body did not exceed 180 feet per second (I think that was the number), the pressure waves generated in the plenum could shoot back out through the throttle body into the intake pipe, effectively making the intake tract part of the plenum. Exceed this critical number and you wound up with a net pressure drop inside the plenum.
What does that mean for us? Well, it means that the stock throttle body has an opening of (pi r squared x 2) 3620 sq. mm or .039 square feet. The engine needs 161 cubic inches of air (0.09 cubic feet) per rotation, assuming 85% volumetric efficiency, so

.086 cubic feet ÷ .039 = 2.21 feet per minute velocity per 1 rpm.

180 x 60 = 10800 feet per minute (critical velocity)

10800 ÷ 2.21 = 4887 rpm

The stocker is good to about 4900 rpm before you start to see a performance hit. Redline on the stock engine is 4800, so this makes sense. (b-body LT1)

The 52mm throttle body calculates out ot about 5800 rpm, and the 58mm TB calculates out to about 7200 rpm.

These are just rough estimates based on an assumed volumetric efficiency. As your individual engine's volumetric efficiency changes (ported heads, cam, etc) your critical rpm is going to fluctuate.

The thing to keep in mind is that these numbers are only critical on an intake that is too small for the engine. Expanding the plenum beyond a critical volume (I don't know how to calculate what that would be) is going to reduce the effect of the throttle body on horsepower loss.

Looking at it another way, you can avoid buying a big intake (Lingenfelter) buy slapping a big throttle body on the car instead. It also explains why the intake manifold on the ramjet 502 is so freakin' huge - it saved them from having to develop a new throttle body as well.

seawolf06

iTrader: (8)

Also keep in mind to go larger than 54mm, you're going to need to port your intake manifold openings. I wouldn't recommend anything larger than 52mm until you go with a cam or heads. You can get them from ebay or the guy above if you want.

People also have reported several recurring problems with the aftermarket throttle bodies working with the stock base.

Captainofiron

iTrader: (1)

Well said Buffman. I was about to say something similar sans calculations, but you beat me to it. Nice.

BergerZ28

So them a 52mm would prolly be a good choice since im looking to go with a head/cam combo sometime in the near future. I dont want to get wild, I just wanna have a little more punch than what I have now. But thanks for the advice.

lt197formula

iTrader: (6)

With your current mods I would look into a cam, headwork, roller rockers, suspension parts or gears because as your car sits the stock throttle body is still plenty adaquate. Yes you can get one and I would suggest an AS&M 58 (just picked one up and damn is it nice) but the power won't really be seen until your engine has more aggressive modifications.

Edit: Just saw that you're going to go with a h/c combo soon, just hold off until then and get a 58mm because you will have to have your intake manifold portmatched to fit a 58mm, doesn't make sense in going with a 52mm to me with a h/c setup.

Captainofiron

iTrader: (1)

Yea just go for the Gold and get a AS&M MonoBlade 58mm, its not that much more than other brands 58mm TBs

97bowtie

iTrader: (1)

This is the key to your argument, as the stock intake/TB isn't too small for a bolt-on setup. The stock intake/TB flows enough air to support full bolt-ons and even a mild h/c setup. The only way you're going to gain anything with a larger TB is if the 48mm TB is a restriction, which it isn't at this guy's power level. The TB is there to do one thing, flow air and as long as you can get as much air through the TB as required by the motor, the TB isn't a restriction.

This is an age old debate, and it's going to vary with your application. My point was simply that the thread starter was asking about a bolt-on setup, and IMO, his money is better spent elsewhere as the TB isn't a restriction at his power level.

I'd like to dyno my car with the 58mm TB, then swap a 48mm TB onto the car and do back to back pulls. I think, even at my power level, the difference would be pretty small (5-10 peak HP I'd guess). It's possible the 48mm TB wouldn't be a restriction at all. There are guys running low 11s N/A with 48mm TBs - but that's not to say they wouldn't run quicker/faster with a larger TB.

$.02

BergerZ28

My car isnt tuned yet, around how much power would you think I am making and how much power could the stock tb support?

96capricemgr

iTrader: (1)

YOU are missing the point. Buffman is saying the intake MANIFOLD plenum volume is small, think of the plenum as a reservoir most engines have a larger "resevior" when compared to displacement. The small resevior can get depleted upon the sudden demand of a cylinder, the larger TB allows it to draw more directly minimizing the pressure drop in the resevoir/plenum.

The TB/intake do not see steady flow, rather peaks, and the flow between those peaks is simply trying to even out the pressure.

Yes there are people making massive power on 48mm TBs, for one a TB is a progressive restriction not an on/off switch where it will only make X number of hp, they can also do things like increase plenum volume, heard of a few people cutting the tops off LT1 intakes to accomplish this. More than one way to skin a cat.

GIZMO

iTrader: (8)

You need to be making a bunch of power to need more intake volume than the stock intake. Same goes for the stock throttle body. Spend your money on a cam and valve springs.

97bowtie

iTrader: (1)

I'm not sure that I said enough for you to determine whether I'm missing the point or not.

I suspect the reason some of you guys are feeling better throttle response is because the larger TB will allow more airflow with the same change in TPS/angle of the throttle blades.

Might you gain a couple HP with a 58mm TB on a bolt-on setup? Maybe, maybe not, but a couple HP gain would be about the maximum gain. On the same token, why not chop the intake and add plenum volume and slap a monoblade on the bolt-on setup. Hell, why stop there. Why not throw a sheet metal intake on the bolt-on setup. That would only set you back $2k or so and gain you another few HP. Get my point? Most people at his power level are interested in dollars/HP, and a 58mm TB on a bolt-on setup is going to give you very minimal gains (if any gain at all) for the money spent. If this guy is after the most HP for his money, a cam package or N2O would be a much better investment. If he's after buying neat parts to throw at his car which might show VERY minimal gains at his current power level, then that's his choice. IMO, it comes down to where is the money best spent, and at his power level, a TB isn't the next logical step and I think many share this opinion. We don't have to agree with each other, it's his money and to each his own.

If you're going to buy a bigger TB for your bolt-on setup, you might as well throw a larger MAF and a Hypertech Power Chip into the mix as well. You might pick up 6-8 HP for around $1k.

I'd suggest reading this thread, there are some very knowledgeable people posting in this thread:

http://web.camaross.com/forums/showt...+throttle+body

Here's a quote from Injuneer:

"I can tell you why an oversize TB won't help. Just because a TB can flow more air at a given pressure drop doesn't mean it will cause more air to flow into your specific engine. Air flow is determined largely by the heads and cam. The TB is simply there to act as a "valve".... allowing the engine to run at less than 100%.

Yes, if you had a severely undersized TB to start with, you would choke off the amount of air that can flow into the engine, but put a grossly oversize TB in place of a correctly sized TB, and it isn't going to magically make the engine demand/flow more air.

A measurement of flow means nothing if it isn't accompanied by a pressure drop. Pressure drop is roughly proportional to the diameter raised to the 2.5 power. Once you reach a certain point, the reduction in pressure drop is negligible. And the only thing that is going to change the amount of air filling the pistons is the pressure drop in the air inlet track. A fraction of an inch of water isn't going to alter volumetric efficiency any appreciable amount.

As a point of reference, when we first set up my engine, we used N-alpha programming, where fuel is essentially determined by throttle position and rpm. At 77% open, the 58mm TB was flowing about as much air as the engine needed. In effect, the engine could have made the same amount of power on a 52mm TB. Going larger did not cause the engine to flow more air, or make more power.

I can't tell you why Craig is saying the 58mm is costing you power because you have an A4. I doubt that the velocity of the air through the TB bores is of major significance, since the volume of the plenum relative to the volume of the runners should effectively decouple the TB from the runners. I "think" that's the case... can't prove it for the specifics of the LT1 plenum.

But the idea that putting a larger TB or a larger MAF sensor or a larger CAI magically makes your engine flow significantly more air is a popular misconception. The increase in flow is proportional to the reduction in pressure loss, relative to full atmospheric pressure.... a few 1/10th's of an inch H2O from an oversize component means virtually nothing."

buffman

iTrader: (9)

And I do agree with that. $200+ for a bigger TB at beginning mod levels can be spent elsewhere. I was merely trying to state that there's nothing wrong with slapping a bigger TB on a LT1

97bowtie, I did read that linked, post, boy a lot of arguing going on over there.

Some other info I've read states if you are producing over 2" of vacuum @ WOT, you have an intake restriction. I suppose one could measure vacuum and if you have more than 2", start looking for restrictions in the intake tract.

LT1MAN

iTrader: (6)

i would guess 280rwhp/310-320rwtq