I have a question. Here is my ported TBI.
https://www.thirdgen.org/techbb2/sho...t=ultimate+tbi
What, exactly, is the effect of radiusing the bore walls? Does this increse flow or what? I've got a lot to learn about TBI but I really love it's concept. Also when I did this porting, the motor was pretty much stock. When I put it back togeather I added the Turbo City FI spacer...Little SOTP difference.

 

In theory yes it does increase flow. Your smothing th path for the incoming air. The argument seems to be exactly how much it helps. Guesses are any where between .5 and 5 HP.

 

Ok! That was fun to read! And I have to say very informative. Really! I love the tech stuff! Now, my question is, I have a stock "92" Firebird, 5.0 and is this mod on my TBI going to help me?

Much respect given!
dnot67

 

Some food for thought. Using basic CFM calculators, a 305 CI Engine at 6000 rpm needs:

450 CFM at 85% VE
530 CFM at 100% VE

I doubt any of these engines are pushing even 85% VE at 6000 rpm, so considering the flow numbers of the stock TBI's and the air demands of the engine, I'd say GM didn't do too bad at selecting the throttle body size.

 

Correct, it's not air flow limited like people thought in the past. Things that keep the TBI slow are as follows; heads, exhaust, cam, emissions calibration. Change those things and you'll be fuel limited... bump up fuel pressure and start tuning at the track or find some way to measure ACTUAL performance.

 

Per David Vizard's book on carbs & intake manifolds (I forgot the exact title), in one chapter he shows the effects of having, or lacking, a radiused transition inlet on airflow in a runner. A velocity stack is one example of a radiused air inlet on a pipe. This also applies to the inlet bore on a carb or throttle body.

IMS he showed that conical tapers are no better than just a straight tube. He also showed that any amount of radiusing helps the airflow by a few percent, and up to 5% can be had by a generous radiused air inlet.... i.e. rounding the bores. The highest number was 5.5% IIRC, and that seemed to be a limit based on the number of different shapes he tried.

So on a 500 cfm TB (or on a TBI that has injectors), you could expect as much as 25 cfm (5% gain from 500 cfm). This isn't a huge gain, but it is a free gain. If the engine were properly tuned, you would (in theory) likewise gain an extra 5% increase in power. BUT --- if the engine isn't tuned to cope with the extra airflow, or if you aren't close to max-ing out the airflow of the stock unported TB/TBI, then the gains will be less or even nil. That's why some people who do the mod to the TBI get very little reward for their effort.

HTH.

EDIT: rounding the edges of an air inlet bore is also done during flowbench testing, by using buildup of clay into a smooth radius. If the radius isn't included, the airflow is always less.

 

cant you lose torque when boring out the TB and not the rest of the intake?

 

As long as the rest of the intake remains the same, the torque shouldnt change that much if you bore out the tbi.

As far as radius goes, a lack of radius will make the bore look 'smaller' as the air will seperate from the surface since it wont be able to make the sharp turn.

 

did you use a dremmel with a grinding bit to do that?...i thought i read that someone recommended wearing a mask when grinding down the castings....why?...b/c of sparks or smell?

 

To cut off the ridges, you'll probably want to use a high-speed cut-off wheel with the dremel. But, once the ridges are off, a grinding wheel or sanding drum is great for taking down the imperfections, nicks, and high or low spots that the cutting wheel made. And after that, use some sandpaper on all the areas that you cut/grinded and make it all smooth.



It was probaby one of my post that you read about wearing a mask. The reason is because of all the metal particles that starting flying around when your cutting/grinding. After a couple of hours my throat got really scratchy from inhaling all those tiny bits of metal. Although, as long as your in a well-ventilated area (I wasn't ), you shouldn't really need a mask.

 

that does not sound good...I'll try to be carefull if i do it

 

I just realized something. When I was referring to a mask, I was really referring to those cheap painter's respirators, like this:


After I reread my posts, it sounded like I was talking about a full-face mask.

 

Goggles are a must also. A small metal shard in your eye, is not a fun way to spend an afternoon. Driving to the emergancy room, with one eye closed is not fun either...ask me how I know. ;-)

 

Thanks Kdrolt, I posted something simlar to that one of the 50 or so times this thread has come up.

The throttle shaft grinding is probably one of the most flow improving mods, thats a direct impediment to air flow. Its easier if you can disassemble the unit and do the shaft with plates attached seperately.


I wanna see someone with hard data on what happens to the fuel from a tbi unit once its in the plenum at high rpm because it sure does not behave like fuel coming out of a carb. But real data is hard to come by around here. Ive posted data logs of my setup with both carb and tbi... somethings going on beyond what I can log which includes WB (except for small fluctuations of AFR at high rpm)

anyway if you guys would do some back to back testing with your tbi setup vs a properly tuned carb you may see the same thing. Maybe its my manifold combo.

 

Something such as shown in this graph (see attached). Note what happens once the RPM exceeds 5,000 (50 on the Y axis). The X axis is in hours:minutes:seconds.

RBob.

 

RBob..........what kind of software is that datalog chart from?

I don't remember seeing one like that before.

Thanks.......DM

 

The data was collected with a Lockers setup (17 frames of data a second), then a section of it was imported into Excel. From that I used Excel's graphing feature to get what is shown. I did cut a section of the graph out and pasted the legend back in. The second gear portion made the pic too big to post.

RBob.

 

Kool.........I forgot that you were the "Lockers Master".

That is the kind of information all of us need that are "trying" to tune with a C3. Besides the speed I see Wide band, spark advance and some kind of pulse width?

Sorry to get off thread but when I seen the graph and info I thought that it was

DM

 

So what did you find that was causing the high RPM breakup?

 

DM91RS, the brown line labeled sbpw is the injector pulse width. The use of 'sbpw' is a lousy name. Notice how high it goes during the initial throttle stomp. That is the AE. The code I use has the AE as synchronous pulses, not async pulses as the stock code does.

BMmonteSS, sure did, fixed it too.

RBob.

 

What was the cause?

 

LOL I have a sneaky suspicion that the "fix" is set to be released very soon. At least that's what I'm hoping for.

 

Yep Rbob, just like that


makes the car run like caca


cool to hear you found the fix. I sold off my tbi stuff cause of it.

Wish I had the time and skills to figure out stuff like you do.

 

Excellent work, if so!

 

You of all people should know that it will cost you next to nothing to get that stuff back. Hehe, that is, at least until RBob's code gets released, then I foresee everyone jumping on the TBI bandwagon because of it.

Liberate yourself from Vader and the 'Darkside' Pablo (you're Grand National), and come back home to TBI (insert Yoda's voice)...

Again, RBob, excellent work! Who would have thought such an exciting time (first Ben73's mid 12 second run, and now RBob's work soon to be released) for TBI would be on the horizon...

 

just thot id add some more to this thread and a pic of my modded air cleaner, as you know TBI's suck from the sides so getting the air filter as close as i could to the base of the TBI was my goal, all also add this about cutting the ridge i doubt it picks up any HP, weather or not it does, it does increase throttle response,

all also add, some data for you guys

The following airflow tests were performed on the University of Northwestern Ohio's SuperFlow SF600 Flow Bench. All CFM values are corrected for airflow at 28 inches of water.

Stock 4.3/5.0/5.7 2bbl TBI complete -- 574.1 cfm (dry)
Stock 4.3/5.0/5.7 2bbl TBI w/o injectors -- 584.7 cfm

 

NFS.........what diameter filter is that? Looks stock size.

DM

 

its a stock air cleaner for 96 pickup

 

Alright, i have a 1988 5.7 chevy Truck engine in my 88 camaro, and its rebuilt it has the TBI of course, I have a very very powerful low end but after 65 It sucks and i read about the spacers and what not, and then grinding alittle bit around the edges to create more air flow, Now, I dont know what PPG means, idont know what the diffrences from a lo3 to lo5 or lg1 or any of that, id like to learn, because i really like to tinker on cars! but anyway i get 24.0 MPG i just calculated that out today and would like to gain some more HP cause right now it really bogs and rattles in the engine somewhere when its at 3/4 to WOT when trying to pass and it takes awhile for me to pass someone going 45- 50mph. anyway. can someone tell me what the best thing to do is? Which is probably "Leave it alone!!!!''

 

if you like to tinker then go for it, you want see much power but the thorrtle well be more responsive...

 

so what should i do? Both Spacers? or the grinding around the barrels?

 

It sounds like to me, you have a problem with the tune. So your not going to see any major improvment modifing your TB. You need to find out whats rattling. Are you still running the stock 305 chip? knock sensor? injectors? if so, thats where you need to start. You can still get decent milage because the ECM has a good bit of self learning built in, but all that gets ignored once you go wide open throttle.

Do some searching on swaping in a 350, if you still have questions post in one of the many 305->350 threads or start a new one.

 

Whats the point of porting it??? if your still restricting air?? get a K&N Filter it will make a difference

 

everything makes a difference,

 

How restricting is the stock TBI intake manifold ?

Is it even worth switching to a Performer manifold .. or are the gains marginal ?

 

i would have to say yes its worth it, the stock TBI intakes dont cut it, aftermaket is a much better pick, if i had my Edelbrock Performer RPM off the car i could compare the 2, HUGE diffrents

 

My thought was the difference between stock TBI and Performer manifold not being that tremendous .... considering one can get carb intakes flowing better ... problem is... not enough manifolds out there that have the EGR fittings



What I was getting at was... isn't one of the big reasons the Performer has been able to sell ... that it's still quite low .. so it fits underneath the stock hood ?

 

i think its a tad bite taller, infact i know it is i had to get a smaller air fillter....

 

hey im swapping my Lo3 tbi, for the GMPP 350/330 HO
If i kept my throttle body and bought one of those 30 psi regulators that they used on the 454s and raised my fuel pressure, and then put in a walbro 255 fuel pump. Would that be enough to run that motor the right way, or should i buy a whole new throttle body system, if so which one?

 

I would tune it with the stock TB unit and once you have that handled then swap in 7.4L unit with larger injectors. 55 lbs injectors at 28 lbs FP will support 320 HP at 90% DC. I have an Aeromotive FPR and it supporrts high FP or low FP based on spring supplied. Not sure if topdownsolutions has a spring that will handle 28 lbs. The GM spring from 1995-1996 7.4L TB will. But where to find one?

 

after reading all the discussions is the ultimate TB mod a big foot or lochness or is it for real is it worth the work would a TB off a 454 help me more

 

deffinately. Do not switch the 454 throttle body. not needed. ultimate tbi and adjustable fuel regulator and you'll be fine. tbi spacer not needed, injector spacer isnt a bad idea though. but before I did any of this. I would do a header and exhuast swap.

 

anything bigger then 50mm on mild 350 is a waste of time.and or money.

 

I think holley projection is a better flowing manifold but the edelbrock is a easy replacement

 

Yeah if you want to keep and use the egr and pass visual. only option is the performer tbi manifold really. if that wasnt the case i'd be running the perfomer rpm manifold with adapter. but im lazy and dont wanna change stuff every 2 years to pass emissions testing.