I spent last night porting the hell ouf of my holley TBI unit I think you guys would dig what I did. Ill get some pictures up

basicaly i ground down the throttle shaft, the heads of the screws, knife edged the leading edge of the throttle blades, radiused the inlets to the throttle body, trimmed down those big aluminum chunks that seem to be there for no reason but to just center the aircleaner, and, i ground on the bolts on the perimeter of the bores

Another thing i noticed that Ill bet you guys will notice too is that the holley TBI unit does not go to WOT. I thought my eyes were decieving me so I checked every which way and sure enough the unit is cast on the safe side of things i guess to keep from going too far. I ground on the casting where the tab strikes to keep it from going completely open and now the blades open all the way. IT was actually a surprising amount that they had to go.

Ive run into a snag though, the injectors dont seem to want to fire during crank except but for a moment when i let off on the key and there is no power to the starter but the engine is still turning ill get one spray or two. I managed to get it started and it idles and revs up just fine (SUPER RESPONSIVE, i forgot how responsive compared to the carb) but once i shut it off it wont crank up again because of the same problem. I think the injectors are gummed up and need alot more voltage to fire than what they are getting during crank. I have em sitting in some carb cleaner right now hoping that does the trick.

I love fuel injection, the idle is soooo smooth, the AFR is rock steady, and the response from the pedal is so crisp. Cant wait to get it up and running.

If i cant get these injectors to work does anyone have a spair pair of injectors they would part with on the cheap? dont really care how big so long as they are atleast 305 injectors.

 

ive got some 305 injectors from my 89 formula 305 tbi.

 

I'll have to check my holley TBI and see what you're talking about as far as the WOT goes. I may have to do the same thing you did.

As far as the injectors go, I have a set of 57pph Delhi injectors I'd get rid of for cheap. They spray perfect, I only replaced them because I went with 85pph injectors. All you would have to do is order a new style injector pod, I think it goes for about $80. You can get it through orielly's or auto zone or where ever special order.

 

well i dont think the injectors are bad anymore, i think it has something to do with the way power is going from my ignition. It seems like if i move it to the crank position the fan shuts off (is this normal?) and Im pretty sure this coincides with the lack of injector fire. I played with the key and cranking it a bit and it seems like if its cranking and i just let off to where the poer comes back to the fan the injectors will fire but the car is no longer cranking so it wont start. STarts cold like this though, have to sort of nurse it

 

the fan shutting off during cranking is normal. the way everythign is wired almost every thing shuts down during cranking because the starter is such a large draw. check your oil press sender. I know a guy with a tbi truck that had a similar problem. the ecu won't fire the injectors on start up until it sees oil press. that is why tbi's have to crank for a sec before they fire.


Zac

 

dammit what are you doing sitting here on TGO go get some TBI times!!

 

well the car wont start unless its cold and it takes alot of finagling , poses a problem that, and there are no roads to Gtech here on so i have to wait till next weekend for the track at the earliest

 

Should have radiused the leading edge.

Radius the leading edge, knife edge the trailing edge.

 

ok poor choice of words its not quite a knife edge but i trimmed it down

 

where are the pics pablo? I have been waiting for you to put the tbi back on for a while now. I hope you can get everything worked out and get some times soon.

 

Well, I checked my holley tbi, and it goes to WOT no problem. Maybe the older style holley's came with the restriction

 

you sure you looked real close? Its hard to tell if you just look down the bores but you can see it with the tbi off and looking at the blades from the side sticking up through the bottom. Youll see they arent a perfect 90 degrees. I never noticed till I had it off. Maybe they did make a better casting though

No pics yet, sorry, working 55 hours a week makes it hard to do much except but on the weekends

 

I'll have to check again next time I have it off, but the blades looked completely verticle with it on there.
So far, I have rounded the openings of the bores, smoothed the injector pods, added an injector pod spacer, and polished the bores, blades, and pods. I left most of the adapter plate cast however for better fuel mixture.
I plan on filing down the throttle shaft and screws that hold the blades in place. Are there any more mods you recommend to the tbi Pablo? Should I leave the adapter plate as is, or polish it up too?

 

I found the same problem with mine after I had it bored out to 2.2 inches. I stumbled across it when I was smoothing out the entrance to the bores. Don't know if it was related to the modifying process or not. Mine is the GM 454 TB. I have a couple of spare stock 454 TB's and will check those to see if any of them exibit the same problem.

Bill

 

I dont know which adapter plate you have but if its like mine which is just a plate of steel then youll want to bell mouth the openings on the manifold side of the adapter. It helps fuel move to the sides along with the air since air can make turns easier (see david vizards book on carburetors and manifolds) Maybe it helps atomize or vaporize fuel too since small area to large area with the same flow means high pressure to low pressure like how clouds are formed. I didnt do as much as i would have liked on mine because the plate is steel and it takes years to grind on. I rounded the edges mostly.
I wouldnt leave the casting rough, I dont see any carb spacers rough or bottom halfs of carbs left rough for that purpose. It would seem to me that the rough walls would basically decrease the cross sectional area of the throttle body.

As for the throttle shaft, you can thin down the areas around the screws to pretty darn thin and the shaft stilll remains surprisingly strong. You have to be carefull with the threaded part though because the threads dont actually start till well into the shaft (there is like a threadless beveled portion like .065 deep before threads start) I didnt take down the areas around the threads as much.. just touched em a little bit but basically went around them shaping them up to present as little an obstruction as possible.

 

Can you expliain why? Got any pics of what you are talking about?

 

what he is talking about is basic fluid dynamics. I dont know all the details why and I wont pretend to know but having a really sharp leading edge on something is a bad idea. Take a look at the shapes of airplanes and airplane wings. I think it has to do with a sharp leading edge requiring air to hit it directly straight on, if not it just acts as a ledge and vortices form on the other side. Since TBs dont have perfect laminar flow, nor do airplane wings, (i dont think anything does) a sharp edge vs a rounded edge loses since air can turn around a rounded edge easier (stick to it closer)

The reason for the sharp edge on the back is that the air isnt hitting the blade from the front its just letting the air slide off like a wing. Creates lower pressure, pulls that boundry layer of air closer to the blade especially since it was probably pushed far outward by stuff ahead of the trailing edge, increases flow area area.. stuff like that


*Disclaimer, a dude with a 1.4 college GPA wrote this so use at your own risk

 

I POSTED PICS OF MINE A WHILE BACK. he is right though basically you round off the bores at the top to radius it. knife edge means just that if you look at the edge of a knife they taper off its a little thicker then it gets real thin it poses less restriction to do it that way. i would take some more pics but i sold my ported throttle body to another guy on the site here. i also polished the body so it looks all shiny...

 

I bought 92rsV8's TBI and it looks very nice. I have my old one to compare it to so I can see everything that has been done to it. If you do a good job like he did it almost looks like it came from the factory like that.

 

so wait, let me get this straight, If I do the same thing to my TBI like pablo will I get the smoothness, quick response like him? if so, tell me. My tbi in my camaro is bone stock, I havnt done squat to it.

 

As for the radius the leading edge, knife edge the trailing, i beleive its because there should be no abrupt changes in the surface of the throttle blades. Having a knife edge on the leading portion will introduce a corner on each side where the edge makes the transition to the main face of the throttle blade so *laminar* airflow would have a tendency to seperate around the corner. Introducing a round or some other smooth transition will allow for realativly large radius' that the air can easily follow. One thing for sure is that you can bet your bottom dollar that the flow is very high reynolds number and, as such, is very turbulent so the overall benifits are probably debatable since the airflow is already quite turbulent and not really following the surface on a small scale.

The smoothness and the quickness are from the good state of tune and AFR's that the fuel injection systems have. If you want to get into prom burning and/or tuning you can probably make some real improvements. As for the throttle response of a properly tuned tbi with a realativly small cam, its nothing short of amazing. Really saved me today when a ***** almost broadsided me. Naturally, I nailed the gas and my 350 instantly wisked me to saftey.

Oh, BTW, pablo, did you ever find out what was wrong?

 

where can I get a kit to re-assemble my tbi unit? anyone know?

 

DriftaGMCamaro "where can I get a kit to re-assemble my tbi unit? anyone know?"

Autozone, Advance Auto, Pepboys, Napa... U name it... There about 35-45$ depending where u go. I get a nice little discount on all that junk so I couldnt tell u the actual price just a round about price.

 

check the new chevy high performance. they did a "blueprint" rebuild on a tbi unit. it was obviously simply their doing an advertiser "a solid", but at least a magazine printed SOMETHING about a tbi f-body. i damned near fainted.

 

yeah I read about that. FINALLY something about tbi systems, but they mentioned about drilling on the side and putting in a washer to fill in the gap, is that really necessary?