I do not know how you can gain 150 cfms from not changing the bore diameter at all. I agree you can change the cfms just at off idle, but the overall cfms..... ??? The only way I can see this have an effect is forced induction having positive pressure on the outside of the TB and smoothing the outer walls eliminating any turbulence....if any ever existed.
The seat of the pants feel can be explained by changing the characteristics, like at 5% throttle you have increased the airflow to what it would have been per say...15%. Your increasing your throttle opening ratio basically....not in any way altering the amount of air flow though it.
If you want to properly port the TB , have someone laser some new blades a few mm bigger, bore the TB and then you will have a larger TB.

 

What effect could be had/felt on a blown ls1 @ 7psi or so???

 

WOW once again,....an AWFULL lot of "EXPERTS" can be eh,...... not so correct. There IS simply TOOOOO much information out there to say they do not do anything. You will not get 20 r.w.h.p.!!! But you will see an improvement over the "stock" T.B.,...especially in the Torque curve. Oh,....ya,.....Torque is what WINS races,.... horsepower is for posers. Why don't you look at some of the professionals here's just a few....... http://www.ls2portworks.com/ Cory is just on the other side of the "sound" from Seattle, and http://www.s2performance.net/home2.html cory at LS2 port works ported my LS6 intake manifold and he has on of the cleanest shops you will ever see. the other gentleman is I think in Texas and when I spoke to him he impressed me right off. When Thomas Wong @ Portland Or .,....one of the best tuners ANYWHERE is impressed with the work anyone does,.....IM, impressed!!

 

when you ported you are increasing the diameter by 5% which make over 10% on the area, plus when you smooth it you decrease the loss of pressure therefore the flow increase quite significantly

 

No, im talking about the port jobs people do that do NOT increase the diameter, but just smooth the outside.
Also air doesnt blow in the TB, it is drawn through. No one seems to grasp this concept.

And just because a place advertises they do alot and they also sell them... doesnt mean they actually do anything. They tell you they do so you buy them.

 

First mod I ever done on my vette and ta. Cutting the ridge out in front of the blade seems to really help the throttle response.

 

You dont have to increase the TB blade size to increase how much air a stock TB can flow. By removing material in the right places and adding material in the right places you increase flow by improving the efficiency (due to a better shape) of the part in question.

I built a fixture to test all this good stuff on my flowbench because I wanted to quantify the gains I made porting my stock TB while my car still had a factory sealed longblock with bolt-on's (LS1 6 speed with a stock LS1 cam). At the time my car just had headers and a cold air box and a few other small items (LS6 intake, X-pipe, etc.) and I saw a gain of almost 5 RWHP swapping out the stock TB for one of my ported units putting me solidly in the mid 340's RWHP at the time. My only surprise was the total gain because the SOTP increase felt triple that due to the better throttle response etc. While a small gain like that is better than a poke in the eye, the drivability increase and snappy throttle are worth the price of admission in and of themselves.

Also, when you make something more efficient to flow more air (not just bigger) it means you have increased the airspeed (due to that parts more optimal shape) which always pays dividends in an internal combustion engine.

Its like having a stock head with a 2.02 valve compared to an AFR 205 head with a 2.02 valve. Virtually the same size port....the same size valve which the air passes thru, but you have an increase of 70+ CFM stepping into the better head and a bunch more power after you do the swap.

A stock 78mm TB is very poorly shaped out of the box.....one look at it can tell you that without having to have a degree in fluid dynamics.

And Im not trying to sell a thing....just pass along some information in a field I am very versed in.

Tony

PS....I would be all over that forum members TB for $90 if it is a quality ported piece with the void filled with epoxy. It will feel like the best $90 you ever spent.

PSS....A 78mm TB blade in a straight un-restricted tube would probably flow close to 1000 CFM. By changing the shape of the TB housing and addressing how the airflow hits that TB blade you are simply getting it closer to its theoretical optimal peak.

 

they did mine and increase the diameter.
if you look at a throttle the passage before is smaller than the butterfly.
Mine now is the same

 

It would take longer to explain the priciples of fluid dynamics than I have here. I did work in and around air flow benches at GM for 10 years, so I do know from wence I speak.

Entry and exit conditions do greatly effect air flow regardless of whether the air is being "pushed" or "pulled". In reality, it's the same thing: Just a pressure drop from the inlet to the exit. Adding a blower and increasing the pressure will effect the conditions within the orifice (Reynolds number, etc.) but will not greatly change how the airflow reacts to entry and exit conditions of the orifice.

Air doesn't like sharp edges or changes in diameter without carefull consideration of the transitions.

A good comparison is a properly shaped venturi vs. a flat plate orifice. Both may have the same cross sectional area, yet the flat plate will have a huge pressure drop and the venturi will have almost zero.

What would actually happen in your drawing is that the air entering the smaller passage would see the edges and form turbulance which would in effect close off the effective diameter of the passage.

Again, not saying that a ported throttle will help a stock engine. Probably take some engine mods to draw enough air to make a difference. That's one question I'm trying to get answered without doing the flow bench work myself: On my 390 rwhp LS1, how adequate is the stock throttle?

 

Tony, Great info, thanks. What pressure drop are those figures at? I would assume the 4bb norm of 1.5 inHg, but sometimes people go back to the old 3 inHg standard.

Thanks

PS. Is there a thread anywhere showing what mods are worth it?

 

I did AFR 205 heads and G5X3 cam this winter, kept the stock TB, and had it bench tuned (awaiting dyno tune ) - car ran alright, but it was rough

Last week I added a Vararam B2 and a Shaner Ported throttle body - I didn't change anything else (except different oil pump - ie: still waiting for dyno tune) and my car runs NOTICEABLY smoother and I think more "crisp" throttle response -

 

Thanks everybody for your input.

Excellent and informative thread

 

Just bolted my Shaner S2 Performance Throttle Body on and WOW a noticable "seat of the pants" improvement in performance. Throttle response is definately much crisper and the car pulls harder. The 1st to 2nd gear shift breaks the tires loose now where it didn't before. Initially the car wanted to idle fast but I did an idle re-learn and all is normal now.

This mod, IMHO is a fun, quick and easy way to pick up a few RWHP. It is well worth the bucks.

 

Definetely a good mod if the port job is done by an experienced expert technician such as Tony who makes a living doing R&D on high performance engines. There are some people out there who port that are no more than a butcher and know nothing of shape, only size. I feel that is where much of the bad press has come from

 

AJAY,

I asked the question if an 80MM BBK was worth it and guess what some said yes and some said no.

I did not mentioned 90MM bacause I have not yet done H/C.

Went on and did it anyway, glad I did.

Money well spent!

 

 

It's all about CFM.
If you round the ridge just before the throttle plate, you will improve flow, this is the most important area, this is improved flow with the same size throttle plate.

I did my TB and although I did not add expoxy to the large open area, it did help.