TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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The posts in this thread have been edited and a link as been added to the ultimate TBI section of the "new to TBI thread" at the top of this forum. Thanks NEEDforSPEED!
Last edited by ShiftyCapone; 06-10-2004 at 02:04 PM.
i think im going to try to port this as far as i can, its off the car and i keep thinking i can take more off of it... hmmm im going to do the shafts next.... maybe today....
Originally posted by NEEDforSPEED i think im going to try to port this as far as i can, its off the car and i keep thinking i can take more off of it... hmmm im going to do the shafts next.... maybe today....
Don't knick the sides of the wall. I do not even bother with the throttle shafts because of that risk. You are not going to pick up any significant cfm from that as you do the casting wall.
Originally posted by NEEDforSPEED now that i think of it will that even help porting it more, or well the incomeing air be hotter becuz the unit wont be abile to disapat heat as well?
Hotter because you removed that little bit of material? Actually the fuel cools our TBI units and they are almost always cool to the touch when running. The next time you fire up your car feel the TBI unit after a few minutes.
This guy knows his stuff... and his parts work. Just read the article on his main page.
Unless you live in California.
Sheesh... I was considering a power plate after reading the information on that site but it might be just like the spacer I have. THAT mod can't possibly effect my emissions that much, can it?
yea id like to buy one thats already ported and stuff and install it... and give mine as a core.... (*** i wish i could do that)... i want to do that fuel pressure regulator mod but i have no idea WTF im doing... if i had some pics and some one to help me id feel better with porting and playing with TBI's
my baro at key on/engine off is 101-102, at 6200RPM with my motor combo, the MAP readings are still 101-102Kpa . . . with my stock TB, And I feel pretty safe is saying that I have probably have a significantly larger Air demand from my engine, than most poeple with 305 TBI's do.
I would be really interested to see someone who actualy has results showing any real power gain from all this grinding on the throttle body.
dewey u just confused me.. lol... more details? slower and smaller words... lol... im jp... but i really have no idea what that ment...
"my baro at key on/engine off is 101-102, at 6200RPM with my motor combo, the MAP readings are still 101-102Kpa . . . with my stock TB, And I feel pretty safe is saying that I have probably have a significantly larger Air demand from my engine, than most poeple with 305 TBI's do. "
Is my engine (305 with Ultradyne racing cam 206/216) needs to be shifted over 6k to take advantage of the powerband, the longer duration, and high RPMs mean my motor needs more air, than say a stock LO3.
When I data log, my map readings are the same as if my car is sitting is still, which means the sensors are not measuring any lack of air. So I see no reason why a motor that needs less air, would need a bigger TB than I have, when my car is getting all the air in needs (according to the sensors.)
Well, if i thought to myself, the map sensor is giving me the same readings when the car < edit > is running < /edit > as it is standing still, I'd think my sensor was setup wrong or i can't data log at all.
The map sensor should be measuring manifold air pressure which should definietly be below atmospheric (the engine is a air pump and air pumps dont work well with no vacuum on the intake) so your data logger is logging the barometric sensor as shown by it's reading of sea level air pressure at standard temp (or a bad map sensor). The baro sensor is what the map uses (i believe) and carbed motors use to measure the atmospheric pressure. The atmospheric pressure would definitely not change if you started your car up, but manifold pressure most certainly would. So your data does not reflect the map sensor readings at all. The only time they approach 1 atmosphere is when you are at WOT and you have a very free flowing intake setup, which is not what you'd have at < 1k rpms.
So, either your data logger is logging a barometric sensor, or you dont have the map sensor hooked into the manifold, or you dont have a working map sensor, or you have a really bad vacuum leak. Pick one, but in any case, your data is misleading you.
Porting the TB will definitely make a difference as the engine's air requirements can certainly be hindered by less than ideal air flow. Not necessarily the volumetric requirements of air, but the speed at which it comes. Of course, on bad heads, porting the TB wont help, because it's much less of a bottle neck, same goes for the way the TB gets it's air. You're only going to get the performance of your least performing link.
You just totally missed what Dewey was saying. Trust me when I say Dewey knows what he's doing. Yes his map sensor shows all kinds of different readings at part throttle. At full throttle he is saying that he has no restriction between the heads and the TB. The reason why he knows this is his MAP sensor does not see any vacume at WOT. The rule of thumb on a carb is anything more than 1.5" of vacume is a restriction. I converted that and it equals out to betwean 4 and 5 KPA which a metric measurement for vacume. So Dewey has no restrictions whith his TB. In order to prove that this mod does make more power you need to take a motor that can move enough air to pull vacume at WOT then swap to a ported TB and see if it decreases the vacume.
I'm running a luke warm 350 with a 454 TB and I get about 1-2 kpa drop at upper rpms. So I would say my motor would be a good canidate for this test. Unfortunately I don't have enough time to get a stock TB or test this theory. If any one wants to send me a stocker to test, I'd be more than willing.
No one is bashing this mod. It's a great mod because it's free, and it gives you an excuse to rebuild your TB. I just wouldn't go spending alot of money on it since there are so many other places to get more bang for your buck.
__________________ It's just a two barrel truck motor.......sorta
Originally posted by Dewey316 ...I would be really interested to see someone who actualy has results showing any real power gain from all this grinding on the throttle body.
I'd love to see it too. I think you'd find that he may have an suspension problem. You've essentially killed the direct port entry and any possible venturi effect that may help the fuel mixture at the injector.
The engine is pulling vacuum, just not any longer at the throttle body, due to it no longer being the restriction (throttle plates open). Indeed, the pressure at WOT would be near barometric pressure. I misread your statement about actually reving the car to WOT, after testing it off.
You're right though, the TB doesn't need to flow any more air but you'd also have to. But lots of people stand by injector spacers helping mix fuel in TBI's, and so porting the TB would have the same purpose. Not much gain for all the work, but you can't argue with your numbers. Without forced induction or a new engine you wouldn't require more air than the stock TB provides.
the spacer and porting are 2 diffrent mods. Moving the injectors higher abover the manifold floor, could help keep fuel attomized. I myself have not seen any reason for porting the TB until you start pulling WOT vacume.
I use an injector spacer because it gets my spray patter above the throttle plates and lets the fuel run down the side of the bore at idle. The shearing action of the fuel and air rushing around the throttle plate atomizes the fuel. Thats another reason to tune for the least IAC counts you can, it gets more air going through the TB at low speeds helping atomization. I dont' think this porting is going to do anything to the spray patter, all the porting is way above where the fuel hits the TB walls. Throttle bodies don't have any venturi effect since the walls are strait up and down. If you look at a carb they neck down just above where the fuel is pulled in. TBI doesn't need this because the fuel is injected.
Fuel pressure will do more for fuel atomization than any thing.
The spacer does help the mixture, but primarily it helps the suspension at WOT by increasing the distance to the floor of the intake. When the mixture hits, some of the fuel will precipitate right out and puddle onto the floor of the intake. This is why some people run with turtles in the manifold.
As for the possible venturi effect... The venturi effect happens because fluid pressure drops as the fluid speed increases. If you force a fluid (for example: air or water) down a tube with a narrowing in it, the fluid will move faster through the narrow part. When it starts to move faster the pressure drops. This concept has been recently applied with superb results in new exhaust products, the most prominent of which is the merge collector.
That said, I do believe there is a venturi effect incorporated into the design of the TBI unit. Maybe not much, but it's there, you can see the port neck down to the inner diameter of the bore. That would be a decrease in the 'tube'. It will help the fuel stay in suspension better and improve the overall mixture of the fuel and air. A TBI injector does not perform, IMNSHO, what you would call 'good atomization' of fuel. If that were the case we wouldn't have such high pressures in other injectors to improve the atomization, would we. Atomization isn’t jack if the fuel does not stay suspended.
I have the late model delphi injectors and the atomization isnt too bad. Its not really a spray but rather a fog of very small droplets at high DC. Although it really doesnt mean squat since the bores are large and the airflow has to make a 90 degree turn when it hits the floor of the intake.
Um... no. That's like saying if you're running a carb you could always benefit from a larger one, or that you could always benefit from larger primaries. Just not true, as a good example go over to gen tech or tpi and ask about bigger throttle bodies.
Originally posted by stuckatcuse If you're running FI, then you can almost always gain from a ported TB.
Gotta be more specific. For TBI no, MPFI, most definatly yes. More area less pumping losses = more power. The perfect drag car would have a break away throttle body that would be yanked off the manifold after the car's been launched... cut the ignition and have large brakes .
Really though, TBI is a funny beast. It likes things you wouldn't expect in a performance engine, like warm intake manifolds and offset throttle body (2 barrel directs air and fuel in funny ways at part throttles).
TBI is a funny beast. I need to post some of my new data logs with my WB. Very interesting stuff. Fuel suspension is a problem with tbi.
The TB's I've inspected had strait up and down walls with no taper other than going bellmouth at the top. Take a good look at a carb, the bore necks down a good .25". There's no reason for a venturie effect with TBI. The reason it works so well in exhaust is that it keeps the velocity of the gasses up when they merge in the collector.
Sure, I was going to wait till I had time to post the data logs to go along with it. I was tuning my pumpshot trying to get rid of a nice puff of grey smoke I was getting when I would blip the throttle. The WB was showing a way lean spike when I was first hitting the throttle. Just like you would expect to see if you didn't have enough TPS pump shot. Which was odd considering the puff of smoke. I was able to tune that down pretty easily, but the funny thing is my afr went peg rich at 10-1 for a good second or two after I wold blip the throttle. This was happening even before when I had the lean spike. It would stay rich even after the throttle was closed and the PW had droped. My theory is that this extra fuel was the fuel that was puddled or stuck to the intake walls. When I would blip the throttle the air velocity would pick up and start pulling this fuel off the walls. I tried tuning this out, with all the MAP accel pump taken out it was still doing it and was about undrivable once the rpm's were up and the motor didn't have this reserve of gas on the runner walls. If you get the rpm's up first and burn off this extra fuel the motor acts fine and I get a pretty stable AFR when I blip the throtlle.
I'm not blaming TBI for this problem. Just wet flow induction of any kind. My particular combo has very low velocity at idle. The RPM intake combined with the BBC TB, and the fairly lumpy (for FI) cam really slows the air through the TB. With a smaller TB I don't think this would be such a problem. Right now I'm idleing at 700 rpm. I think I'm gonna try to raise this a bit and see if it helps.
Originally posted by BMmonteSS The TB's I've inspected had strait up and down walls with no taper other than going bellmouth at the top.
That bellmouth would be the part of the tube that necks down. That would be a venturi. A very similar, if not exact duplicate, 'bellmouth' is found on small engine carbs (see below). Yes, I'm familiar with carbs, I've rebuilt a few in my time, the venturi there is designed to draw fuel out of the jet requiring a bigger velocity change, however, that does preclude a venturi effect on the TBI. Look at the overall design of both the enty port and the injector basket. Reasons abound for these things, they weren't thrown on there because they look cool.
Think of it like this, if you had negligible velocity going by the injectors, particularly during idle when there is very little, how well do you think the fuel would suspend?
Hey NeedforSpeed, good job on the port job.. do a search for "Turbo City TBI".. back when i had TBI i bought a Turbo City ported one, i have pics posted and you can see how far they grinded them out and put bigger butterfly's on. the throttle response was A LOT better, especially when i was using a K&N plus the extreme lid.
Originally posted by Red Devil Um... no. That's like saying if you're running a carb you could always benefit from a larger one.
*edit for shoddy grammar.
Depends on the intake manifold design. With a single plane, each cylinder has access to 2/3 of the total cfm capability of the carb/tb. With a dual plane, each cylinder has access to 1/2 of the total cfm capacity.
__________________ 90 454SS; TBI 496. Best to date: 12.42 @107, 1.63 60 ft.
Think of it like this, if you had negligible velocity going by the injectors, particularly during idle when there is very little, how well do you think the fuel would suspend?
Again, we fall into comparing TBI to carbs.
A carbed engine relies on engine vac to draw the fuel in.
TBI sprays the fuel in; it doesn't rely on engine vac.
The I in TBI is for injection
This is the main reason TBI works well on single planes.
Yea if you say so (injector is a jet now?), anyway, that may be all well and good but injection does not mean suspension. If you can't wrap your head around that, think of the cute little bumps you guys find in the intake tract of your heads above the valve.
I guess I give up. My last suggestion would be to go get a few books on fluid dynamics and intake and exhaust design and do some reading. :shrug:
you are missing the point of the venturi on a carb.
rember, as the velocity increases, the pressure decreases (all your fluid dynamics readings should have taught you that.) It is that low pressure zone created by the high velocity in a venturi, that pulls the fuel out in a carb. TBI does not need that effect. all a venturi would do in our case, is create a bottle neck. Remeber, TBI is not a carb, it acts somewhat like TPI in alot of the requirments (in this case, you will notice port injection doesn't need a venturi to function, neither does TBI). Don't fall into the trap of trying to compare TBI to some sort of computer controled carb. It is fuel injection, the only diffrence is the location of the injectors.
My point was, and still is this. If there is no pressure drop across the throttle body, what am I going to gain from making it bigger?
Originally posted by Dewey316 You know what is interesting about this....
my baro at key on/engine off is 101-102, at 6200RPM with my motor combo, the MAP readings are still 101-102Kpa . . . with my stock TB, And I feel pretty safe is saying that I have probably have a significantly larger Air demand from my engine, than most poeple with 305 TBI's do.
Originally posted by Dewey316 My point was, and still is this. If there is no pressure drop across the throttle body, what am I going to gain from making it bigger?
A bigger TBI has lower wall velocity which equates to less friction (yes compressibles also have friction). This in turn free's up horsepower.
Venturi is so over-rated. The "venturi" isn't important, the design of a venturi is to lower the pumping losses. Any time there is an expansion of area (cross section) there is a pressure drop. If you understand this then you know that the fuel going through the "small" bores on a TBI into a plenum is the same thing as it going through a carb. The reasons carbs use nice pretty venturies is for idle and throttle responce, those 2 things are taken care of with the electronics in our case.
Va, let me clarify, the only comparison to a carb that I am trying to draw is the shape of the chunk of metal. That's it. I learned how to work on cars using FI, carbs came later. Fluid dynamics etc. I learned in school and on my own thereafter, that is what we are discussing, not carbs.
Dewey, I'm not missing the point of them on a carb, you just aren't reading my posts in context. I'm saying there is one incorporated into the TBI. I didn't say it was vitally important. It is mainly there for the same reason the swirl port is in the heads. I think I intimated toward that earlier.
Jp is on the righ track mostly, but one addendum, in a carb, the venturi do not have much to do with idle. The idle jet is typically after the butterflies.
I think wher we are getting confused with the "venturi" reference is on what scale we're talking . I think Dewey and I are talking on a scale of from one end of the TB to the other. This is a carb in this Ruff sketch.
The carb has a very pronounced venturi, while the TB is nothing more than a nozle that smooths the incoming air into a smaller opening. I think your talking in a much biger scale as in the world then the TB acting like the "neck" above and then the manifold being the other larger opening.
World
...TB
Manifold
In both respects the velocity of the air is accelerated through the smaller section and a pressure differential is made. I agree with JP that the added wall area of a bigger TB will probably free up some pumping losses, but not alot compared to a system that has so much restriction that it pulls a vacume in the manifold because the TB is a restriction.
