Theres a funny thing called a restrictor plate on speedway engines.. which limits airflow and cuts several hundred HP.

 

Yes, you've discovered the hole in the maccaroni. Now, do you thing you can tell me the size of the openings on the restrictors and how much CFM does it equate to? And how much power do the engines make? This is why I brought it up, so that the thought of 670 CFM being the restriction for the 360 HP limit be dismissed.

 

I still have the stock injectors in my Cross-Fire ( 62 + 66 lbs/h ).

I measured 300 rwhp and that calculates to 360-370 hp on the crank. I already touched the hp limit for the 2 * 90 lbs/h injectors according to this ...

That was with an internally stock engine, stock TBI's and a stock ( non-ported ) intake and 10 psi of boost. At 10 psi boost the progressive fuel pressure regulator increases the fuel pressure to 23 psi over the injector.

360 hp is NOT the limit with 90 lbs/h injectors.

( I still have to start tuning too )

 

"Reducing horsepower with restrictor plates, NASCAR Winston Cup Series race cars use Holley 750-830 CFM four-barrel mechanical secondary venturi carburetors. "

"Smaller bore holes restrict air and fuel mixture creating less horsepower. The restrictor plates limit the amount of fuel and air mixture to the engine. The result is less air, lower engine revolutions, less horsepower and, therefore, lower speeds. The standard carburetor used today has 1-9/16 venturi (holes) and the restrictor plate has venturi of 29/32 of an inch." (a reduction of 40% or 450 CFM (750) and 498 CFM (830)

"The plate reduces the engine power from 750 horsepower to 450 horsepower, depending on the size of the hole used on the plates."

Several quotes from Google...

Airflow is not the problem. Its a lack of consistant fuel delivery. TBI is restricted mainly because of the injectors and design charactoristics of the injectors not airflow. (i believe) Yes you can crank up the pressure but that is a band aid at best and reading what Grumpy has posted, the stock code can't correct at idle the increased pressure.

Joby..very nice ride, but having 10# boost changes things

Anyway to each their own, just love how because someone wants to do "insert idea" thats different from the mainstream that others seem to need to jump straight into jackarse mode to tell them that they are fools for trying. Bet Grumpy heard lots of that when he decided to fiddle with ECMs so long ago...jeeesh, Bob

 

Not really ...

The boost only affects the air-flow, not the fuel that can be deliverd thru the injectors. If my stock injectors can deliver fuel for 360 hp then they can deliver it wihtout supercharger too, if they get the same fuel pressure.

 

Joby,I guess your fuel delivery system is stock too(fuel pump,etc). Besides we're talking n/a.$1300 is not that bad for the holley setup.You get everything from ecu to hardware.That is a good deal,much cheaper than an intake,tb,injector upgrade.This post needs to be moved or locked.The design limit of the tbi fuel delivery system should be a topic on the tbi board.It seems like peedy puff wanted to pick a fight w/ grumpy this is all .This guy can't even respond to logic.Check his posts he just floats in here to see if someone agrees w him.He's just got more nays than yays and don't like it,come on mod lock this sh*t.

 

Let me get this straight. 360-370 HP out of a blown 350. With 10psi of boost on it. And you're giving advice on the accuracy of fuel metering?

And you wonder why nobody takes you guys seriously. 360hp is a mild NA 350 build, you don't even need fancy heads or expensive roller cams to make that number. If you need a blower to make that number then i would say that TBI seems more fuel limited than ever. You can't tell me airflow is your problem with 10psi of boost, so something must be keeping you from making power.

 

Thanks joby for the empirical evidence to support your statements. Nice to see that for a change.

 

Correct, However I am guessing you are using a FMU or a boost referenced AFPR to increase your fuel as boost increases. So yes you can get more fuel from your injectors, hence your stated HP. Again if I understand what Grumpy posted is, yes you can increase FP for more fuel at WOT but the idle goes to crap because the code can't lean out the extra fuel. So I am assuming that 360 HP is the max HP a typical TBI can supply without going to junk. Just how I see it, cheers, Bob

 

did you even bother to find out if his longblock is bone stock or not? or did you just feel like being an *** right out of the gate?

 

Pablo, whos the ***? JoBy has already stated his motor is stock. So if this is directed at me please...... Bob

 

saturn

I have a problem with that. See, for that to be the case, the larges injector (90 lb/hr) would have to be right on the verge of going async fire at low speed even on stock applications. Hell in the early 90s GM offered a 502 for truck apps tbi injected that put out like 325 hp and over 500 foot pounds of torque. The fuel pressure on that engine was vacuum regulated I might ad from like 10 psi idle to 18 psi. . How did GM manage that without going async down low especially on the low vacuum areas. Even if say it was just within limits to do what gm asked it to do, when have we known GM to build something that was JUST enough to do the job on so many different levels..

FYI Im not trying to "challenge" anyone. Id just like to understand more about how and why things work the way they do

 

that was NOT directed at you saturn that was directed to Ed Maher. I actually appreciate your eloquence and level headedness on this post

 

Thanks Pablo, I didn't understand where that was directed.. Poor Ed lives with finish line first syndrome, which is fine but does come across rather crappy at times.

Anyway for grins I ran some numbers using RC Injectors calc.

http://www.rceng.com/technical.htm

For 360 HP, with 2 injectors, BSFC of .4 and 80% max duty cycle and 20 pounds pressure, it shows that 138 lb injectors are needed.
There must be something I am missing, a difference between multiport and tbi injector construction, as 90 lb X 2 calcs to 175 HP.
cheers, Bob

 

Am I missing something here? Joby is running CFI, so that is 2 TBI units which equals 4 (90lbs?) injectors... right?



So, if according to your calculation, he should be making 360HP/4 = 90HP per injector...

 

Let's look at the facts when I measured 360 370 hp ...

* The stock 84 Corvette is rated 205 hp

The mods at the time:
* ADS Superchip and 180F thermostat it came with.
* New exhaust with full length headers and removed cat.
* no EGR
* no AIR pump
* K&N filter

Those are the only mods that could affect the hp when N/A.
I estimate that they are worth max 10-15 hp over stock.

To make the supercharger installation work I did the following mods:
* Vortech supercharger.
* Progressive fuel pressure regulator (FMU).
* 1992 Corvette ( LT1 ) fuel pump.

I increased the power from 205 to 360 ( >75% ) without even removing the valve covers or the intake. It is with STOCK TBI's and non ported intake.

Increasing power by 75% over stock without changing ANYTHING in the engine is not that bad ...


What I said in my previous post was that I got 360-370 hp from the stock 62 / 66 lbs/h injectors without tuning the ECM. Then 360 hp is NOT the limit when using 90 lbs/h injectors. I did change the fuel pressure and the fuel pump, but I used the stock injectors.

 

The CFI uses two ONE bbl TBI's ... That adds up to TWO injectors.

 

As I said that was with 23 psi fuel pressure. To raise the fuel pressure I had to use an LT1 fuel pump and a progressive fuel pressure regulator (FMU).

 

Well JoBy you have a fine example of how to overcome tbi's limits.That burnout on your page is baddd @ss too,I love it.But this post has turned into "how to overcome the 360 hp limit.

 

Hasnt this post gone to the dogs....

Nascar and CFM and HP cant be related to a TBI setup to come up with a max HP rating unless you are building a race car. That 450hp is somewhere around 7500RPM. If you wanna rev your engine that high on a street car, well go right ahead.

I think some people here need to stop 'theorizing' solutions to their problems, and just start trying things, whatever they may be. You obviously dont want to take someone else's opinion when it disagrees with your own, so go try it on your own then. Make your own set of rules, and stop worrying about everyone elses.

 

Well I figured out the why 90lb didn't add up. I missed that they fire twice as often.

So running the calc, 90 lbs, .4 BSFC, 80% DC, 10 PSI X 2 injectors shows roughly 175 HP.
Now since they fire X2 we have twice the fuel for a given amount of air adds up to 350 HP at stock pressure and N/A max.

Now increasing FP will give gains at WOT but injectors of this size dont respond well to very short PW. cheers, Bob

 

That calculator is setup under the assumption the injectors you are using have been flow rated at 43.5 PSI (where RC's injectors are rated), not the TBI 10psi. It shows what size RC injector you need based on your rail pressure. Its poorly setup IMHO.

360hp @ .5bsfc and 80% DC requires 2 113lbs/hr injectors or 8 28lbs/hr units.

The so called 80lbs/hr 17112560 injector flows 75lbs/hr @ 10psi and will deliver 113lbs/hr @ 22psi.

 

Max, I don't mean to point you out, but if NASCAR and CFM and yada yada yada has nothing to do with solving the problem then what has your post done? The NASCAR examples were given because people were saying you can't make HP with only a 670 CFM limit. Period. Read the posts thoroughly and it was already stated that those engines were a whole other animal, but only to be referred to as what can be done with little airflow (about 450 CFM as Bob quoted). On to the next question from Pablo however about the 502. Well, 325 HP and 500 TQ can be achieved a whole easier with more cubic inches and less rpm and is a whole lot easier to tune. Problem is you guys are working with 150" less displacement and the only way you can overcome thit is by spinning it higher which means a compromise. Is that "theory" acceptable? You are correct Max, what needs to be done is action and not talk but again, that was already stated too. I will say it again, I am a PFI fan but I am following this thread because I like to learn not like to watch people bicker. If the solution is found I would like to know it.

 

While I agree with you about absolute limits, I dont think anyone here in this post is building an all-out race engine with a TBI setup. I think they are trying to make a powerful street car, in which case going to that high of RPM's makes no financial sense unless youre Donald Trump or Bill Gates.

I threw the book out the window myself and just started trying things a while ago. Sometimes, ya gotta do it.

Anyway, I've wasted enough bandwidth here. I'm surprised this post is still here to tell you the truth.

 

enough with the hot air please max


yes i see what you are saying hector which brings me to another question..

i imagine the "off" time for an injector is just as important right?

so would it then be true that 325 hp at 4500 rpm is easier to achieve than 325 at 6000?

like say we have an engine that requires the same afr all the way up and the same amount of fuel needed to fill each cyl all the way up the rpm range

basically im saying the engine would have the same pulsewidth all the way up... it would seem to me the only thing that would have to change is the amount of off time the injectors have.. it would shorten as rpms increase? right?


im still ignoring the whole aspect of just using more injector whether that is pressure induced or just a larger one physically

but just at first thought id guess the higher the rpm the hp is made at the more injector you need so you can maintain the off time?

edumacate me please

 

lemme try wording that differently

take engine a

makes peak power at 3000 rpm and has x for vol. efficiency at that rpm and say to do that it needs 4 msec of injector pw. Well TBI fires twice per rotation. At 3000 you have what? 20 msec for one rotation? So im guessing that injector fires.. holds 4 msec.. then shuts off for 6, then fires again, then shuts off for another six


engine b makes the same power as engine A but at 6000 rpm and has the same x for vol. eff. at that rpm so it needs the same amount of pw.. 4 msec crank rotation time is 10 msec, halved from 3000
injector comes on for 4 msec.. takes a 1 msec rest, then fires again and takes another 1 msec rest.

If i have this right then just rpm can overload injectors and put you at 100% duty cycle...

right or wrong? let me know

 

oh damn i forgot hp is is torque multiplied by rpm im just thinking of torque

then again maybe not cuz i did say VE in my example

 

brain worky on this.. be back later

 

All the answers to who what why are here in Grumpys post.
Also JoBy has confirmed this tho its not obvious. Yes he has been able to acheive 375 HP with stock 60ish Lb injectors, with increasing FP during BOOST. Hence hes making more power at WOT but FP returns to stock at idle and he maintains a decent idle. So is the Catch-22, increase FP for more power at WOT and lose idle quality or keep FP near stock and have a good idle and lose WOT power. Pablo is on the right track. With TBI firing X2 and having less time to fire as RPM increases along with the characteristics of "X" injector frankly TBI just dosent have the time or fuel volume to surpass 375 HP without some sort of assistance to increase FP as RPM increases and decrease FP to maintain idle. Now..how to do this without boost I think is the direction TBI'ers need to look. Just my .02. cheers, Bob

 

SATURN5,

Well spoken!

 

so you are saying that if you can get to 360+ hp earlier than say 4000 rpm you could make more than 360 at higher rpm?

I would post my further theories but im busy doing . again, LOL!!
(redeisgning the pod, been done with the tbi for almost a year. )

actually my wrist is swollen from playing too much golf, so its tough to type with a severe carpel tunnel syndrome flair up.

I still think we need to move this to the tbi board. so i can moderate it LOL.

but i do appreciate the editing so far. Thanks guys. seriously.

 

If you can use a pressure reg that is boost operated then it is possible to use vacuum to operate it as well. It would take some design work but could be made cheaply enough. All that would be needed is a cyclinder, piston and spring. The spring would give the vacuum line going to the reg a false boost signal when the vacuum in the intake dropped to near zero, then during normal cruise or idle the vacuum from the manifold would overcome the spring and return the pressure back to a preset pressure.

manifold vac < -[~~I ]- > pressure reg

I know this is crude but it has it's perpose.

Steve

 

Steve is right!

This is how I have the regulators set:



Blue is the fuel pressure the stock regulator wants to maintain.
Pink is the fuel pressure the progressive 2:1 regulator wants to maintain.

Both the regulators raise the pressure by restricting the flow in the fuel return line. They are in series so the regulator the wants to have the highest fuel pressure 'wins'. The resulting fuel pressure is the dotted yellow line.

By adjustring the spring presure in the stock regulator I set the fuel pressure at high vacuum ( idle and cruise ).

By adjusting the spring presure in the progressive regulator I can move the point where the it 'takes over' and starts to raise the fuel pressure.

I set that atmospheric pressure because then the stock chip is correct for idle and cruise. And I only get extra fuel under boost.

If I would increase the spring pressure so that it intersects at -5 instead then the fuel pressure would be 5 psi higher at atmospheric pressure. No boost is needed to make this work.

This is what my progressive regulator looks like:

 

well wait a minute now dont get too excited kids. We allready have something that can do the same thing, a vacuum referenced regulator (i actually have one on my car but there is no vacuum connected)

the only thing you ccould do is tune WHERE the fuel pressure comes up at on the fuel map

run one vac reg infront of a static reg. Set the static reg to where its higher than the vacuum reg at idle but as vacuum decreases the vacuum reg soon takes over boosting fuel pressure closer to 100 kpa rather than immediately.

I see problems with this though it would screw your pump shot all to hell allthough i imagine you could get it to work but it would make your table act like one that started off small and took a huge jump at the high end of the spectrum instead of a smoother curve that an always on vfpr would give and secondly you still have the low rpm area where the only problem that has presumed is that the injectors will go async

hell, what is the problem with running an always on vacuum reg, gm did it.. Ive searched around different sources and have come up empty handed trying to find info on the subject (diy archives included allthough its a mountain of material im sure there is a needle in that haystack somewhere)

 

btw i thought about it more and while hp needs rpm as a variable not just cyl filling per revolution. Torque on the other hand.. well.. i dont know how that is calculated exactly but as far as i know it isnt

and what happens when you move the torque peak up the rpm range, you move hp up the rpm range.

 

Pablo, I think the problem comes with the large injectors in that, as you stated, the injectors would go async at idle. The other problem may be finding the correct spring that would alow a low enough pressure for idle and a high enough pressure for WOT. Then on top of everything you have a cam that won't pull enough vacuum at idle to keep the ecm from adding more fuel. Now we have another problem to solve. Nothing is easy, but if it was, well you know, everyone would be doing it.

Steve