LOOKING FOR SOME FEEDBACK ON SWAPPING THE STOCK THROTTLE BODY UNIT ON MY 305 TPI TO LET IT BREATH. I FIGURE MORE AIR IN AND A FREER BREATHING 3" EXHAUST KIT WILL BE A SIMPLE WAY TO SQUEEZE MORE POWER BEFORE I TRY ANY MAJOR MODS. (IE HEAD WORK, INTAKE RUNNERS ETC)

GIFF

 

A new throttle body on a stock engine is going to slow you down. Don't waste your money.

 

The LT4 puts almost 300 horsepower to the rear wheels. It uses the same 48mm throttle body that your 305 uses. GM's new Ram Jet 502 is a 500 horsepower big block. It uses the same 48mm throttle body that your 305 uses.

For $350, you can buy something that will actually matter, like a good set of headers and a y-pipe or a cam swap.

 

For sure.
If you want to improve the throttle body, go ahead and purchase a throttle body foil and install it - that'll actually gain some marginal power rather than lose some marginal power. =\

A foil will allow more CFM as far as flow goes where as the adverse effects of larger throttle bodies has been discussed to death, do a search if you're curious. Last note on the foil - don't expect a brand new hot rod after you install it =). It's marginal improvement at best.

To be a little long winded (to late), I'd suggest making a cold air intake to pair up with the new foil, this'll make more marginal power =D

im done.

 

The foil is pretty worthless too, but at least it costs less. I saw flow-bench numbers that showed a throttle body with the air foil flowed a whole 12 cfm more than a stock one.

 

Got mine on sale from SLP for like $22. That isn't too bad for 12 cfm. I say take it where you can get it (especially if its cheap).

I DO concur with Jim on the TB though. I'm thinking the only way you could use a larger TB is if you have a 383 or 400 that is putting out 500 or so ponies. Then it may help...some.

 

The foil makes less turbulence in the TB. That’s where the improvement comes from, not really because it flows more.

 

Whatever it is the foil does - it can't be argued that it's completely worthless. It does help a tid, and that's exactly what Giff is going for here: a tid more power.

 

Sounds like the larger throttle body is a waste...that's why i'm asking here and not just plunking the jack down w/out any thought.

thanks for the feedback.

giff

 

whoa...I was planning on an Edelbrock twin 58mm TB For my 400HP 383... I can get it for $250...

the stock 350 TB wont be much differant?


dang... Looks like I was just saved $250 by you bastards....heh

 

I don't believe that the turbulence is the issue at all. As soon as it gets into the plenum whatever happened previous is negligent. The plenum is a reservoir for air so that all 8 runners have adequate air. Air through the plenum is like throwing a hot dog down a hallway. There's plenty of room and by the time the air gets to the runners, the turbulence from the throttle body is negligent.

 

I don't think you're taking into account the velocity at which this air flows...
Volumetric Efficiency is the name of the game with the air foil. If air is turbulant and radical, it isn't as dense...If the air is being pulled through the TB effictively, the volumetric efficiency of the upper plenum is raised because the air is more smooth, dense and cool.

Fast air is colder than slow air...or perhaps cold air is faster than hot air... either way, a proper air foil is worth the buy for the VE increase reguardless of your modifications...

 

Took the words right outta my mouth 88. =D

 

I understand that, but I still feel that the plenum will negate any effect from the throttle body. If the car had 8 individual throttle bodies on short runners that directly fed the heads, I'd agree 100% with you. Even on a carbed car I think this can make a difference because the plenum volume is very small, but on a TPI car I just don't think it's an issue. The air is going to slow down dramatically when it gets into the plenum because of the huge volume. Each runner will then draw from that.

 

The way I understand it is that air isn't being PUSHED into the throttle body...(unless you have some sort of forced induction. It's being SUCKED in from the cylinders through the heads, lower intake, runners, upper intake and throttle body.
Picture that airflow in your head and try to tell me a smoother, more aerodynamic throttle body isn't effective.

The efficiency of the air flow is imperitive! An entirely smooth airstream is much less congested...which is more dense...and hense more powerful...



Since the air is being sucked in very quickly, the atmospheric pressure in the upper intake plenum is higher than the air in the engine compartment, isn't it? (I'm really not entirely sure about that so I should really shut up...but I wont...)...how is the possible without forced induction? My understanding is that the vacuum in the cylinders is so demanding, that it pulled excessive amounts of air in due to the velocity at which it flows. SPEED of air is the key to high pressure and high availability of air in the upper plenum at any given frozen moment of time.

Since I'm getting into areas I don't entirely understand, I've got a question for more seasoned car freaks...
How the HELL, do you get a VE of over 100% in a car without a ram air or any type of forced induction (N/A) ? I've heard numbers of up to 110% are possible?

 

Nope. Lower than atmospheric pressure = vacuum. Higher than atmospheric pressure = boost.

You can't.. You can get damn close but it's not possible. Forced induction can get VE over 100%, but the overall mechanical efficiency is still sub-100%. Otherwise we'd have the fabled perpetual motion machine and free power for the whole world.

Yes, airflow efficiency is important, but as it pertains to throttle bodies, it's moot point because the throttle body is not the bottleneck!!!. Find the bottleneck and make that bigger or better.

 

 

well as far as airflow through and engine it is all change in pressure from point a to point b. pushing air vs. pulling air, doesn't matter, the pressure change is what counts, that is what is causing the air to move in the first place.

I keep reading people say upgrading the TB is worthless. I change mine and noticed a worthwhile difference, about 10 gps of air on my scanner as measured by the MAF sensor at 5000 RPM @WOT. Then there are the analogies that said engine/car made XXX HP with a stock 48mm TB. Ya the car did that with a stock exhaust system as well. Would you recomend to him not to replace the exhaust as well? what about the cam or heads? How much more of a gain would the other engine make with a less restrictive TB?

area:
duel 48 mm TB: 2.80 in^2
duel 52 mm TB: 3.29 in^2

ratio of area 52mm/48mm: 1.175:1 ==> 17% increase in area

for a stock engine with no intake work I would stay with the stock TB. For a engine with intake work I would upgrade the TB. I have no experience with the 58mm TB but they have 46% more area than a stock TB so you would have to move a lot of air for them to be effective. Plus the TPI plenum is not that great at cleanly moving air.

 

Thats not true. Many High $$ builds will acheive 102% to 105% VE at certain points in the powerband.

NA

 

Ok, here is an easy way of lookin at this. If you get a larger TB then you should porth the in's and out's of the plenum, then get a set of runners to match, then you can port the intake in and out's, then a set of heads prolly ported too, and a good exhaust to go with it. There you have it. The induction system is able to fully benifit the new TB. Unfortunately you 1. just modded your motor around a $350 TB (or $250), with about a grand in parts and time. and 2. do you know for sure that the displacement, and internals you have will need all that air? Its like an 850 cfm carb and a tunnel ram on an LG4.

You can save face by keepin the stock TB, and do all that was listed. the smaller TB will help you keep some low end after you open up the rest of the motor.

BTW, and air foil must do something. Why else do the aftermarket TB's have them already molded in?