I guess what I meant to say was....this all sounds good on paper but I have yet to see it applied and the results. I have seen several try, including myself but have never seen anyone go any quicker than 13.20.

 

ok, i'm no expert, but i've been trying to figure out just how many cubic inches and horsepower tbi could support since i bought my formula in january. i definitely want to "look before i leap" and know what i'm doing before i start making changes.

please correct me where i'm wrong.

as i understand it, airflow is what limits the cubic inch/max rpm factor, while fuel flow limits horsepower, which makes this two separate issues.

first, cubic inches/max rpm:

Engine Size (CID) X Maximum RPM / 3456 X % Volumetric Efficiency = CFM needed

so, a 383 with a redline of 5500 and using a VE of 85% would look like this:

383 X 5500 / 3456 X .85 = 518.019 CFM

now, that formula is for cfm @ 1.5" HG and 2 bbl tbis are flowed at 3" HG. the formula for converting flow ratings at 3" HG to 1.5" HG is:

CFM @ 3”HG X 70.7%

using this formula, a 670 holley would flow 473.69 cfm @ 1.5" HG (670 X .707). not enough.

735 cfm @ 3" HG = 519.64 cfm @ 1.5" HG, so that's the minimum you'd need.

the biggest 2 bbl tbi i've found is the big throat 2.2" bore tbi:

http://www.454ss.com/gallery/JimD/JimD_TBI.htm

i don't know what it's cfm ratings are, but i don't think they get any bigger. if this doesn't do it, i don't think anything will.

the second issue is how much horsepower can tbi flow enough fuel to support. the formula for that is:

(HP @Flywheel X BSFC) / (# Of Injectors X Duty Cycle)

so, 400 hp with as bsfc of .45 and a duty cycle of 90 would need:

(400 hp X .45) / (2 injectors X .9 duty cycle) = 81pph injectors.

if you go back to a bsfc of .5, it would call for 90pph injectors.

using that formula, a 400 hp 383 seems doable with a big throat tbi and 90pph injectors. the limiting factor would seem to be airflow, not injector size, as you could raise the fuel pressure on those 90pph injectors to get more fuel flow.

you could also address the airflow issue by setting the engine up to make max power at a lower rpm. going from 5500 to 5200 rpm drops the cfm requirement from 518.019 to 489.832. since a 670 holley flows 473.69 cfm @ 1.5" hg, you'd definitely be in the hunt, wouldn't you?

 

The applied results are proven as far as pressure goes. Jon runs at 28 psi. I run at 22.5psi. No problems whatsoever with the injectors.
And you cannot look at time slips as a means of determining power. Trap speed is by far a better means of deturmining power. Proven. Suspension work (currently none) and slicks, An exhaust that actually flows, and more prom tuning and I promise you I will be a twelve second car w/ a 2bbl TBI. My 60' times of 2.3-2.4seconds just doesn't cut it right now.

 

Exactly. The injectors WILL flow enough, but like you said, the airflow is still limited, and peak hp needs to be at lower rpm. That is why I'm using 1.5 roller rockers instead of the 1.6s. Once I get a 4bbl on there, 1.6s will be in the works as well. Good explanation sean.
Man that deep throat cost a lot to fab up! Too much imo

 

Perhaps I didn't dedicate enough time and effort to it, keep up the efforts and I am sure you will keep us posted. Good Luck,
Don>>>

 

Thank you Don. That is the hardest part with TBI-it does take time and effort, especially when venturing into new territories and power levels. It can be fun when the results pay off, but very frustrating in the attempts to get there. My main goal with the 2bbl TBI is to deturmine how far it will go naturally aspirated and hopefully help any others trying for performance.

 

have you thought about going with a vacuum adjustable fuel pressure regulator? that way you get the extra fuel pressure only at wot.

 

Thank you for the suggestion sean. I have actually thought about it. My only problem is that I would need to fab up my own as the only one I know of is for the gm unit. I know jon made his vacuum holley regualtor referenced, and I have a general idea on how to do it. I just need to get my hands on a holley diaphram for the regualtor. I'm using a gm one right now, and unfortuantly it doesn't seal the one place I could stick the vacuum line(kinda weird to explain).
I ran winaldl yesterday-for the first time since the track. I made my best times by upping the fuel pressure to 22.5psi and adjusting the timing-so I left it there. While it helped my WOT extremely, it also killed my part throttle. At idle, my blms are at 90!!! Cruising rpm blms where anywhere between 100-120!!! Ouch!!
I knew I was running rich due to my plugs and always smelling like exhaus, but d@^%!. Oh well, maybe my milage will increase a mpg or two once the blms are nearer to 128

 

On the same note winaldl note, I some how managed to get knock counts even though I am running a dummy sensor away from the engine rapped in electrical tape!!!! Over to the electrical board I go, but if anyone has ideas I would appreciate the help. I don't hear any detination either.

 

the only reason a lot of guys go to carb isnt becuase they are unwilling to learn how to tune fuel injection but it is just much more cost effective....for the price you paid for your holley throttle body you could be making prolly 100hp more with that motor.....yes gas milage and reliability may not be as good but in order to get that much power with fuel injection youd need a steath ram setup that can feed enough air....a 4bbl tbi isnt cheap either...i know the complete 4bbl kits to convert to muliport fuel injection or whater(which most of the 4bbl ones are) are $2000+.......most guys would rather just buy a demon or something for 500 and take the 1500 and buy a new interior or something

 

Wow, this is probably going to get the post closed, but oh well:

BeNnYBooPy,
You are a FREAKIN' RETARD!!!!!!!! This post has nothing to do with carbs. It is for those who want to use TBI on there cars. I have already stated that, and for a time there, I thought you carb guys actually understood that. But hey, why would you, you guys don't even grasp the simple consept that we aren't living in the stone age anymore, and that there are some of us that need and/or want to keep fuel injection for a number of reasons including emissions, reliability, and driveablity.

Let me explain enlighten you as to what a dumba$$ you are:
Hmmm. My Holley TBI cost me less than $300 brand spankin' new. The only way I'm going to make 100hp with $300 is if I purchased the cheapest nitrous kit available.
hey, you do have a slight clue of what's going on...... ....wait...I was wrong-you don't have a clue. First off, how do you know how much power my engine is capable of? Wait, you don't because you simply describe it as "that much power". It is a pretty well known fact that a 2bbl TBI can support 350-360hp by purely doing the math.
Hmmm...now let me see, $300 for my holley, or over $2,000 for a stealth ram..... Are you going to buy the stealth ram for me BeNnYBooPy? I didn't think so. So sit down and shut up. Once again, your ignorance on the subject is beyond belief. A Holley 900cfm TBI runs just under $800 new. Expensive? yes, but not $2,000+. However, besides the external injector driver board(<$20), there is nothing more you need other than a chip.

So say I spend $500 on a performance carb because I'm a moron and can't deal with computers. I rip the computer out as you guys say. But d'oh!! Now I have to go spend $200 on a noncomputer controlled distributor. Double crap!!! I have to spend another $50 on a coil as well. Oh, and in my ever so cost efficient swap to carb, I need a fuel regulator as well, another $30. So now I'm at $780 as opposed to $820 for TBI. Sweet! I'm $40 dollars ahead!! Well, at least for a couple of months until that gas costs add up and eventually make my swap to carb not as "cost efficient" as all you carb guys told me it would.

The fact of the matter is you guys need to stay on your board instead of coming over here and trying to voice your opinions on something you know nothing about.
And when I do have a 4bbl tbi on there, and it is outperforming any kind of carb I could put on there, I can promise you that I will NOT be posting on the carb board on how everybody should swap to fuel injection. I am not such a low life that I would go over there and disrespect people on there efforts, unlike you carb guys that come over here.

 

ouch

dude, this is a pretty good thread ... lots of good info. i get your frustration, but if you flame that hard, it just gets the thread shur down.

 

Yeah, I know. It just really disappoints me. There was good discussion going on only to be interupted once again with carb jiberish. We really need a sticky or something at the top of the board to maybe help prevent these debates from ever happening, and hopefully help focus on what we're supposed to-TBI and TBI performance.

 

Yeah guys I'm liking this thread there is a good discussion going on between all the carb bs. Just try to ignore stupid posts by completely ignorant and uninformed people like this bennyboopy. Let's all just ignore any posts like that and move on forgetting that they even exist within any threads on this board.

 

the bottom line is any tbi f-body running 13s is a good thing. seeing how he got there and how he goes further is an education for those of us not as far down the path as he is.

the next time someone rags on tbi, ask 'em how many 2bbl carbs are running 13s. comparing a 4bbl carb to a 2bbl tbi is like comparing apples to oranges. earlier, someone said if gm had made 4bbl tbis, no one would be saying anything. i couldn't agree more.

i have a buddy with a pretty serious 454 chevelle. he had his rpm air gap plumbed for mpfi fuel injection, dumped the demon carb and put on gen vii dfi and picked up 123 rwhp. no other changes. since it was the same intake, there's no question that this is a direct comparison between carb and efi.

the truth is, efi makes more hp than carb. carbs are definitely cheaper, but you can bolt a gen vii, stealth ram or mini ram on virtually any carbed car and pick up serious hp as well as mileage, reliability and driveability.

tbi was not meant for performance. my 305 tbi was the lowest hp v8 chevrolet or pontiac made that year. the only thing going for it is it's what i have, and it's cheaper (and smog legal) to tweak it than it is to swap to something that really excites me. besides, i like the idea of seeing what i can get out of it. the fact that so few people run tbi, that parts and information for making it faster are so scarce is what's attractive about it to me. it's the same thing that made me put a 401, a 4 speed and a ford 9 inch in a gremlin and beat all the camaros and mustangs 20 years ago.

 

lol..geeeeeeeeez....sorry if i offended you by mentioning carbs. just so you know i have a tbi car too. lol..i totaly get why youd wanna keep tbi, i was just wondering why you didnt choose a different type of induction like carb or tpi for that much more performance oriented motor. I believe that guys can get lots of performance outta tbi, it is just a lot less friendly on a motor like that compared to tpi or carb and will prolyl take 5 times as long to get it working as good. Dont take any of this as an offense but i view it kinda like building wild 305's. it can be done, just takes a lot more effort for less.

 

just out of curiosity, those of you running 30psi+ on the injectors, cant they go bad at that kinda pressure seeing as how they were meant to work at lower pressures? does itmake it harder to tune fuel and timing curves when the pressure is that high?

 

I'm running 28psi on Holley's newer delphi injectors and they're fine. They spray an even cone and at the higher pressures I noticed a lot better cone without any dripps (at idle).
The injectors aren't wimpy saturated, they're peak and holds so they can handle a lot of abuse. They have been tested up above 50psi without any failure but who knows how long it was run with that kind of pressure. As for GM running higher pressure, they do. Just before the end of TBI in 95 there were cases of systems opperating in the high 20's I think even low 30's.
Now to address your "tuning", yes, it must be modified. In the eprom you need to recalculate your injector constant so the ecm knows how large the injectors are. There is no sence in fudging this number, it doesn't hurt your injector on time for higher engine speeds. All it does is make the ecm's alogorithms more accurate for desired AFR. Another advantage to running higher pressure is that your accel enrichment goes up. The "pump shot" is injector on time, it has nothing to do with your injector constant or bpw. So by increasing the fuel pressure and changing your injector constant you will be adding more pump shot. See how that works? That's only if nothing else is touched in the calibration code.

 

hey r90camaro--

i live in kc, and have been to kcir many times. I have raced once or twice with my l98 but im waiting to get my 383 stroker in as well!!! all i need is heads, and im getting vortecs, . as soon as those are on its drop in time!!! what color is your car?? when do you usually go up to kcir??? I want to see your car, maybe i could get some help or suggestsions from you! and vic versa!! well let me know, seeya round

Check out my new site!! i have the motor pics, on my irocz menu

http://weshopkins.tripod.com/iroczman

check it out im gonna put more pics on!!!

 

My car is going to use the ltr setup, but tbi is cool, if the times are good then you must be doing somethin right, i think with some sfcs and mabe some torque arms youd really lower your times.

Do you get traction ????

Hey not to mention, i work at oreillys and get big discountss at 12 different stores in the area.

 

Well, I haven't made it out there for a while now. I usually try to hit the track on wednesday nights, because friday's are just too packed. Anyways, I'm the only black RS I've seen out there. You'll know it's my car if it has a z28 grill and messed up paint job. I usually go with my buddy w/ his teal '96 SS. You'll definetely have to let me know next time you're headed out there, I've finally gotten some of the bugs worked out, but unfortuanlty my radiator is shot, rear end is whinning like a b!t(h, and my rear right brake needs adjusted-it's pretty stiff when up on the jacks.
As far as traction goes, all I can say is argh!!. I'm running 255/60/15 street tires in back, but honestly I was making better '60 times with the bald 215s I had on there. I either spin like crazy, or bog hard of the line. I have poly bushings and the Spohn adjustable torque arm and that's about it, and I'm pretty sure the angle is mess up on the torque arm. Now I am really afraid of adding traction hearing the rear end whine like it does.....It's just one problem after another I tell ya.
Hmmmmm work at oreillys.....Maybe you could get me a deal on a 4bbl tbi Just let me know when your headed out there and best of luck with the engine buildup.

 

ttt