I have access to a 454 TB for $15. I have a decent 305 about to be put together...Ported 416 heads setup for high lift cam + 1.6 rockers, Lt1 cam, Torker II intake, Headers, open pipes, open air cleaner. I've been told that the 454 TB is too big for the 305. But shouldn't that extra air be a good thing? Just add bigger injectors and get a chip custom tuned a few times right? Has anyone run a similar setup successfully? Thanks.

 

Do a search for 454TBI and you'll find quite a few post with a lot of great info. Trust me, this has been brought up before!

Bruce (90RS305)

 

A 454tb is waaaay to big for a 305, so you need to let me buy it for future use. No really though you might have some problems with to much air at slow speeds. Do a search on (snflupigus)+(454tb). He used to run a 454tb on his 305. He goes into pretty good detail on the problems he had.

Steve

 

The 454 TBI is a perfect match for that engine. However (!), you will need to get into chip tuning to get it to run correctly. This is true even if you stay with the stock TBI. So hang over the DIY PROM board for a bit, read up on posts there and here about tuning the TBI setups & ECM and go for it.

Here is a TGO link to a writeup that Traxion put together, a decent into:

https://www.thirdgen.org/newdesign/tech/promintro.shtml

Only question I have is that you mentioned a high lift cam then the LT1 cam, is it the LT1 cam you used or another?

RBob.

 

For $15 buy that throttle body as fast as you can! Even if you don't use it now you can use it later or sell it on ebay for somewhere in the $200 range or more I'm not sure what they go for now.

 

Sorry, I meant that I would be using 1.6 rockers to get extra lift out of the Lt1 cam. It should be around .480 or .490 right?

 

That's OK, I was just wondering. The LT1 cam will be on the easier side to tune. Not sure of the LT1 cam specs myself, I am sure that they have been posted here though.

RBob.

 

.477 .489

 

If that tb is a perfect fit then anyone running a 350 needs a tb off a 540tbi engine.

RBob I believe you and Grumpy could put a roots blower on a Honda Trail 70 and make it run in the 13's. :yourock:

Steve

 

a 305 at 5,000 rpm needs less than 400 cfm at 100% ve. ours will need even less. A stock tbi is easily capabe of supplying that.

 

Actually it was low 14's, the air drag was killing it on the top end. . .

RBob.

 

I come up with 441 CFM @ 100% VE and no restriction across the TB. At 6,000 RPM the flow is 530 CFM. A 454 TBI flows 670 CFM with a drop of 1.5" Hg across it. A performance street engine shouldn't run more then 1" drop with a maximum of a 1/2" drop desired.

gunz4life2 isn't running an LO3 either. His is a decent combo, single plane intake, LT1 cam & 1.6rr, headers, ported 416 heads. . . I'd say a good 260 HP.

He would be killing two birds with one stone: air flow & fuel capacity.

RBob.

 

i turned up this thread:
https://www.thirdgen.org/techbb2/sho...ight=cam+specs

there are others out there in the ALLGOHERE thread is a link to another board. searching there old posts will turn up lots of info.

 

What formula are you using to determine that?

 

Determine what?

The engine airflow is simple math: 305 ci / 1728 = 0.1765 cf. 0.1765 cf. * 5000 rpm / 2 = 441 CFM. For 6,000 rpm subsitute the rpm term above an re-calculate.

The value of 1728 comes from 12 cubed, which is the conversion from cubic inches to cubic feet.

The HP is an educated best guess based on what the LT1's pump out, factored by ported 416 heads, 1.6 rr's, single plane and headers (no exhaust), open element.

The 454 TBI airflow according to the Holley manual (see AJ's info in the sticky) is 670 CFM @ 1.5 " Hg.

The 454 TBI injectors run from 75#/hr to maybe 85#/hr. At this point no one is sure.

As far as the drop across the TB this information comes from the Holley carburetor book, 1972, as recommended values to use.

RBob.

 

Our cars have no where near 100% VE. 441 cfm at 100% ve is only 374 cfm at 85% VE, which is probably close to where most L03's are. I do agree however that with his combo he probably has better VE so he will need the extra cfm, not to mention he will probably pull more than 5k. On most L03's though the 454 tbi would be a waste of time.

EDIT: I know what AJ says and that book says, but I talked to Holley directly and they assured me than the 670 tbi was flowed at 3HG. I have talked to turbo city as well who claims the stock 1 11/16 tbi flows 520 cfm and 590 cfm modified, at which they also assured me that was at 3HG.

 

I guess thats all the more reason to use a 670 or 454 tb on a modded 305.

Steve

 

It all depends on the setup. given that turbo city says their modified throttle body, which is basically an ultimate tbi modded one, flows 590 cfm at 3 hg that would be 417 cfm at 1.5 hg. going to a 454 throttle body would only be necessary if your 305 tbi needs more than 417 cfm, which 95% of them do not. Keep in mind also, VE matter a lot, and hardly any engines produce even close to 100% VE, so most likely you will need a lot less than the calculations say.

EDIT: If anyone knows what the actual VE is of a stock L03 I would very much like to know that.

 

VE is an rpm-dependent thing. VE usually peaks at the rpm for max torque. VE will be less at the rpm for peak power.

Stock LO3 rated at 255 fw ftlbs @ 2400 rpm (torque peak). That's 116.5 fw hp at the same rpm. Since an engine consumes approx 1.5 cfm per hp, then 174.8 cfm is needed to make that amount of power (or torque) at 2400 rpm.

Now using RBob's formula:

305 ci / 1728 = 0.1765 cubic feet (cf)

(0.1765*2400 rpm)/2 = 211.8 cfm if the VE were 100%.

So the VE at 2400 rpm is 174.8/211.8 = 0.825 or 82.5%

The LO3 peaks power at around 4200 rpm (170 fwhp), so that means 255 cfm is needed. If the VE were 100%, then 370.7 cfm would be needed. So the actual VE at 4200 rpm is 255/370.7 = 0.688 or 68.8%.

Summary:

the VE for the factory rated LO3 is 83% at the rpm for peak torque (2400 rpm) and 69% at the rpm for peak power (4200 rpm). I don't know how this compares to the bin values in the stock table for VE in the LO3 ECM.

As an exercise for the reader, repeat the above for a TPI engine of the same displacement (i.e. for the LB9).

Q.E.D.

 

hey rbob, where'd you come up with that figure?

 

i called holley after reading that "670 @ 1.5" hg" comment as well. the tech i spoke to said all 2bbl carbs and throttle bodies were flowed at 3" hg, not 1.5". also, that flow figure of 670 cfm, whether at 1.5" hg or 3" hg was for the holley throttle body, not the gm 454 unit.

 

yeap, exactly what they told me.

 

The figure being "A 454 TBI flows 670 CFM with a drop of 1.5" Hg across it."

https://www.thirdgen.org/techbb2/sho...hreadid=205713

RBob.

 

right. i read that and called holley. they said no, all 2bbl carbs and throttle bodies are flowed at 3" hg, all 4 bbl carbs and throttle bodies are flowed at 1.5" hg.

 

See data in this thread:

https://www.thirdgen.org/techbb2/sho...&highlight=cfm

Thius lists the test data on a single-bore 2-inch-diam TBI obtained 333 cfm when tested with 13.6" water (same as 1" Hg). This is a Crossfire TBI unit bored out to a larger throttle diameter. Two of these units, together, would give 666 cfm when using the same pressure drop. That's the flow equivalent of a dual-bore 2-inch-diameter TBI unit. The Holley unit is a dual-bore TBI having 2-inch-diameter throttle plates.

So based on the test data (as obtained from the CF Vault, by Ken73), it might seem that Holley is being conservative by rating their big dual-bore TBI unit (the "670") as flowing only 670 cfm at either 1.5 or 3.0 inches Hg, because Ken73s test data shows that the throttle-area-equivalent flows 666 cfm at only 1" Hg. I will add that the Crossfire TBI units always have radiused transition bores on the top side and that adds as much as 5% to the flow. The Holley unit lacks them, so it makes sense that the Holley wouldn't flow exactly as well; rather it would need a larger pressure differential to make the 670 cfm number.

If you were going to do your own flow testing, with your own flow bench, it makes sense to try to place the test data on a level playing field.... so that you would know how much extra airflow (and hence possiblt power) a 4v carb would make on a given engine when replacing a 2v carb. If you test at 3.0" Hg (3 inches column of mercury movement as measured by pressure taps below the carb and above the carb), a "vacuum" that represents the pull of the engine on the 2v carb, then it stands to reason that the pull on the 4v carb will be a lot less because there is nearly double the throttle area. So it is customary to reduce the pressure differential (or column height) on the flowbench when testing a 4v carb as compared to a 2v carb. Likewise, it also makes sense to do the same when comparing a 4-bore TBI unit to a 2-bore TBI unit.

If the flowbench has a big enough vacuum source, you could still test at larger column heights with the 4v carb (or 4 bore TBI) but it makes little sense to do so, because large pressure drops across the carb/TBI means that the frictional flow losses will be a lot higher.

FWIW the formula of new_cfm = old_cfm*sqrt(inches_new/inches_old) is only valid when the flow is incompressible (flow speed is small compared to the speed of sound) and the Mach Index is well below 0.5. These two items probably demand non-turbulent flow as well... so don't get too excited by trying to work the math formula -- because it's probably not accurate for large pressure differentials (large inches Hg). Reynold's number is probably at work here, but I've been away from that stuff for too long to remember.

HTH, FWIW.

 

OK, so then the 2" bore 454 TBI flows 670 CFM at 3" Hg. Everyone agree?

Good. Now lets go back to the very first post of this thread and decide whether Mr. gunz4life2's engine with ported 416 heads, LT1 cam /1.6 rr's, single plane manifold and open headers requires a 2" bore 454 2bbl TBI or not.

I said that it was a 'perfect match.' Others disagreed. Full circle comes back to: yes, it is a perfect match.

Well. . . Whats the verdict? Time to ante up folks.

RBob.

 

in 1989, hot rod magazine did a project called "f-notes". they got over 300 (flywheel) hp out of a 305 tbi. figure 10% driveline loss for a manual trans and you're at about 270 rwhp.

they got those numbers with a stock throttle body and 350 injectors. they didn't even do the ultimate tbi mods. the company that did the work was traco engineering. they're now defunct, but i tracked the former owner, jim jones down. he's now head of engine development for reeves callaway.

he said they tried a 454 throttle body on the car, but there wasn't a lot of difference in peak hp. they did notice the throttle was a lot crisper and drivability was better with the smaller throttle body. the ets were actually a bit better with the 454 tbi unit because the wheels didn't spin as much, but the mphs were virtually identical. they went back to the original throttle body.

if you're going to go with a 350 or bigger, i'd say definitely go with a 454 or holley 670 tb. the one thing that is positive about working with a 305, though, is that it doesn't need as much air as a bigger engine.

there's a guy in texas who bores 305/350 throttle bodies out to 15/16ths.

http://users3.ev1.net/~thor10/tbodytest.htm

i believe this will be more than enough for even the most extreme 305, and it's a direct bolt on. no brainer. i don't believe you'll need it, however, till you get really deep into the mods. as far as the combination gunz4life outlined in the first post in this thread, i don't believe that little lt1 cam and 416 heads will ever need a 454 tbi.

 

OK, so you are as guilty as everyone else. Quoting other peoples work with a touch of . . . nothing. Hmmm . . . Well, since I've run both a 2bbl 1-11/16" bore TBI and a 2bbl 2-1/16" bore unit, I'll stand here and state flat out that a mild build SBC can use the flow of a 2" 2bbl TBI. This is from direct experience, not voodoo magazine science.

The shame of this whole post is that gunz4life2 is probably still wondering what the heck he should do for induction. Gunz4life, go with the 454 TBI and tune it. You won't be sorry.

RBob.

 

The answer lies in simple math. use the above calculations to find out what your motor needs. I bet it wont need the 454 tbi.

 

Im far from being as educated as you guys on this topic but I have been reading of the amazing stuff people are pulling off with tuning, and seeing that article was written in 89'.....I just think tuning has come a very long way in the last 15 years, and that w/ some patience I think the 670cfm would come out on top. And as far as comparing his set up to an lo3, about the only thing he has in common w/ an lo3, is his method of induction, and the 305.

my $.02

 

I'm with RBob on going with the 454 unit. That's a decently built 305 and the extra airflow couldn't hurt especially for that extremely low price Gunz4life found it for.

 

man, i hate it when they start this insult junk. are you really so vain that you have to attack me just because i showed you were wrong? .....

well mr. direct experience, you've been on here for half a dozen posts swearing that 454 tbis were 670 cfm because of one wrong post someone made months ago. one phone call or a simple search on here could've cleared it all up for you. not only were your facts wrong on the cfm, by the way, but it was a holley throttle body, not a 454. also you keep referring to "a drop of 3" hg across it" or "a drop of 1.5" hg across it". do you have any idea what you're talking about? and what the heck are you trying to say with this? "A performance street engine shouldn't run more then 1" drop with a maximum of a 1/2" drop desired. " do you understand what's being discussed when people mention " hg?

your "statement of fact" on a mild build sbc being able to utilize the flow of a 2"tbi is way too broad. you understand that a 400 sbc will require more airflow than a 350 sbc, and a 350 sbc will require more airflow than a 305 sbc, don't you?

and "vodoo magazine science"? do you have any idea how many trans am races and even championships engines built by traco engineering won? have you ever heard of a callaway corvette? are you seriously suggesting that the director of engine development for reeves callaway, a man with more experience building high performance engines than 95% of the people in this industry, a man who built a 300 hp 305 tbi 15 years ago doesn't know what he's talking about? most of us can't duplicate that today, even with all the improvements in head and cam design since then.

are you one of those people who sneers at cars written about in magazines because they're envious, can't duplicate the results, or both? let me give you a quick tip .... those formulas you're talking about? every one of them is based on cfm at 1.5"hg. they're totally meaningless unless you have that figure. even if you did, do you understand that the space shuttle's engines probably don't operate at 100% ve? the very best you're going to get out of virtually any street engine is around 85-90%.

just because you aren't willing to take the time to research or understand the figures and terms you so pompously toss about doesn't mean others don't. don't go attacking people just because they disagree with you.

here is the bottom line. a 305 with mildly worked over 416 heads and an lt1 cam (do you know how mild that cam is?) is not going to need more air than a stock throttle body can provide. even if you could tune it to run, you'd see a loss in driveablility and throttle response with it. i almost bought a 670 holley from a guy on ebay last week who'd put it on his 305 camaro with world products s/r torquer 305 heads, lt4 hot cam, performer rpm intake, burned his own chips, etc., etc., and so forth. he was selling it because the car ran better with the stock tbi unit with 65lb injectors. flat ran better. drove better. had more torque. ran better times at the track. i guess he's wrong, too.

i don't profess to be an expert on any of this. what i am is a guy who researches things thoroughly before he shoots his mouth off. look into it.

 

it's not just a question of tuning, and it's not a problem restricted to fuel injection.

too much air is just as bad as too little. actually, worse. if you have too little air, the car will run fine till upper rpms, where it'll "nose over" as it runs out of air. you'll never notice it in everyday driving. too much air kills low rpm performance and torque. you see it every day.

check the tpi board or talk to any knowledgable 4th genner. lots and lots of guys go to 58mm throttle bodies and regret it because they flow too much air.

my favorite car of all time was a chevelle running a 400sbc, "camel hump" heads and one big *** cam (5.10 lift/3.10 duration). we spent months trying to get it to run with an 850 double pumper. drove like crap, ran worse. couldn't break out of the 13s. changed jets so many times i could do it in my sleep. nothing.

borrowed a friend's 780 single pumper and was amazed. drove fantastic and picked up 3 tenths in the 1/4 mile with no jet changes. bought a 750 double pumper, dialed it in and ended up over 7 tenths faster than it had been with the 850. even better, it had crisp throttle response with absolutely no bog or lag and much better gas mileage.

watch holley 670s or 454 throttle bodies for sale on ebay and email a few of the sellers. you'll regularly find people who put them on 305s and couldn't get them to work. bigger is not always better. these 305s don't need anywhere near as much air as a 350, much less a 383 or 400.

 

Do you think RBob has been hanging around Grumpy too long? I don't want to side with anyone BUT RBob has been at this awhile and he does know his way around an ecm or two. There is a possibility he may have been able to tune it to get the driveability and performance out of it (454tb) that everyone else can't seen to do.

When I get my engine in my RS this summer I'm going to drive up to RBob's house and let him tune it for me.

Steve

 

you know what? he may very well have been able to get it to work. that's not my problem with him. first, he states an opinion, then challenges people to disagree with him.
____________________________________________________

I said that it was a 'perfect match.' Others disagreed. Full circle comes back to: yes, it is a perfect match.

Well. . . Whats the verdict? Time to ante up folks.

RBob.
____________________________________________________

ok, so i do. then he makes it personal.

____________________________________________________

OK, so you are as guilty as everyone else. Quoting other peoples work with a touch of . . . nothing. Hmmm . . .
____________________________________________________

that's uncalled for. especially from a moderator.

you know, i love this board. i've been on here just over a year and am often amazed at how much great information and helpful advice i've gotten from it.

that said, though, there are some things that suck. for example, *** help the poor newby who dares go on the diy prom board and ask what the few experts who dominate that forum deem to be a stupid question. his or her buns will be bar-b-q'd so fast they won't know what hit 'em.

even in the tbi forum, which is my favorite, almost every newbie question is now hit with a "do a search" response. when did this become an experts only forum? have the moderators forgotten how they learned everything? heck, if i don't want to read a post, i don't read it. it's easy. why is it such a terrible offense to ask a question that's been asked before? how will anything new be learned if people are always directed to old posts instead of encouraging discussion and debate? perfect example? do a search on slp 1 3/4" headers on a 305. over and over you'll see people stating they're too big, they'll kill bottom end torque, etc. well, i'm here to tell you it's not true. i know. i put them on my car, then put my car on a dyno. i saw a bigger increase in torque than i did horsepower. my car spins now where it bogged before. the next time i see a post with someone asking that question, i'll have an answer that you won't find in the old posts.

worst of all, people who are knowledgable are tolerated as they abuse people whom they deem less knowledgable. if rbob truly is an expert, then one would think he'd be here to teach and debate, not attack and humiliate. he's not the only one. it's one thing to have the occasional 14 year old come on here and have at it, but rbob and grumpy are two examples of people who believe their knowledge gives them the right to be jerks. *** help the poor sucker who dares disagree with them or worse yet, prove them wrong.

in my opinion, the fact that rbob is given the priviledges of a moderator makes it even more intolerable for him to act that way. i've seen threads shut down for flames, why is he allowed to do so with impunity?

i come here to learn, discuss and debate, not tolerate abuse from insecure, power mad jerks who don't have the self esteem to tolerate disagreement from others.

 

 

Alright guys lets please remain on topic here. There is a lot of good information in this thread and I'd like to see more of it. I know you guys can do that for me. Thanks!

Bruce (90RS305)

 

Something to think about: if gunz4life2 were to have asked whether he should go with a 2bbl carburetor or a 4bbl carburetor, what would have been your response? (yes I realize the proper response is neither, stay with the TBI).

RBob.

 

that'd be simple. carbs don't have a computer making constant fuel and spark adjustments. if you had a big 2 bbl and a small 4 bbl which flowed the same amount of air, i'd think the 4 bbl would be more drivable because it runs on the primaries during normal driving with the additional airflow coming into play only at or near wot. it also has an accelerator pump for an extra shot of fuel when it's needed.

one of my first cars was a 69 mustang 351w 2bbl. i didn't have a lot of money, so when i came across a holley 2bbl, i decided to save the money over going with a 4bbl and try it out. i believe it was rated at 500cfm. not sure, it's been a long time, and now i know that, whatever it was rated at, it would be at 3"hg.

anyway, some time later, i came across a deal on a stock 4bbl intake and a 600 cfm fomoco 4bbl carb. after putting it on, i was amazed to see that, not only was it much faster, but it drove much better and got much better mileage (when i kept my foot out of it). i worked after school washing cars at a ford dealership at the time. the mechanic there i asked about it told me the improvement in everyday usage came from the fact that the primaries were only around 250 cfm. always made sense to me.

you've just hit on another reason why you can't compare 4bbl airflow to 2bbl airflow, whether carb or fi. even though the computer is making constant adjustments, you only need max airflow at wide open throttle. having all of it at lower rpms and part throttle conditions creates big problems. that's why holley recently made it's commander 4bbl throttle bodies progressive ... to solve driveability problems. according to the tech i spoke with, they've been wanting to do it for some time, but only recently developed the commander software to the point that it could handle progressive airflow.

i would love to have a progressive, 4bbl throttle body that i could keep emissions legal. i think it's a shame that gm never built one. the only way i see to get one now would be to go with a complete commander system and a piggyback harness to allow the factory ecm to continue to control the emissions while the commander ecm controls everything else. that harness alone costs over 750, then there's the cost of the commander system. no way i'm going to put that kind of money into a wet injection setup when there are a number of mpfi options that would only be marginally more expensive.

i know people are modifying the boards in their ecms to drive additional injectors, but that's way over my head, i don't think any of them have perfected it and i don't believe any of them are progressive. i'd think variable airflow would create a slew of issues that our ecms just aren't equipped to handle.

 

Interesting response, so you would have him go with the 4bbl, right?

As far as comparing a big 2bbl TBI to a big 2bbl carb is like comparing apples and peaches. A carb operates on an entirely different principle then a TBI unit. A TBI does not require airflow to pull fuel from a venturi.

With a TBI unit the ECM regulates the amount of fuel injected. So lets say the engine is at 1800 RPM and the throttle is open 25 %. Since we have a big TBI on there this is enough to to supply enough airflow for 100 KPa manifold pressure. The ECM will supply X amount of fuel in response.

Then the driver pushs to go pedal to the floor and and the throttle is now open 100%. The manifold pressure is still 100 KPa. And heres the good part: the ECM is still supplying X amount of fuel. The same amount. Not more, not less, the same.

Why, because the ECM knows the manifold pressure and the volumetric efficiency of the engine. And even better is that this isn't a carb that is having trouble metering the proper volume of fuel due to the low air flow through it.

How much experience do you have with modified engines and big TBI units?

RBob.

 

thats a good response RBob, many people try to compare TBI to a carb, when the only way they are similar is that the put the fuel into the plenum, and not into the intake ports people often forget that the one big downside to carbs is that the rely on the vacume pulses to determine the fuel needed. that is why dual planes give better low RPM drivabitly on carbed cars, because it isolates those vacume signals per bank. TBI on the other hand doesn't need those signals. what it needs is a pressure drop across the TB to allow to the air to flow through (we all agree that the pressure diffrence is what causes air flow, i hope). wether a 2" bore or a smaller bore, really makes no diffrence. at part throttle, if there is a pressure diffrence, air will flow. the ECM will determince the ammount of air the engine is using, at that certian pressure diffrence, and RPM. and inject it. as long as the VE tables are tuned correctly, the mix will be right. and the engine will be happy. but with a bigger TB, you have the bonus of more airflow where need it. high RPM, WOT blasts.

 

i'd recommend a 4bbl carb, but certainly not a 4bbl throttle body for a 305.

yes, i understand the differences between the way a carb operates and the way fuel injection works. it was you, not me who brought carbs into the picture. i have no idea why you went there.

regardless of the differences between how carbs and efi work, you absolutely can have more airflow than the ecm can compensate for. going back to the tpi/lt1 example, you frequently see people upgrade to 52mm, 56mm and even 58mm throttle bodies from the stock 48mm (at least, i believe that's what the stock tb is). the 58mm throttle body has been shown time and again to be too much for less extreme engines.

at the most basic level, an engine is an air pump. it moves air in, it moves air out ... with some explosions in between. how much air is absolute, and is controlled by a number of factors .... all finite. cubic inches of displacement, valve size, how far those valves open and how long they stay open, etc. rpms factor in, too. the higher you rev, the more air you need. obviously, i'm simplying to the extreme, but the point is that the airflow needed to produce max power at max rpm is much greater than the airflow needed for daily driving. even though there are great differences in the way carbs and wet efi work, the leading aftermarket manufacturer of throttle body injection has switched to a progressive 4bbl tb as the most efficient way to address the compromises required to achieve max power and great driveability.

when i spoke of wishing there was a way to use a progressive 4bbl tb and retain emissions, i meant for the 400 i intend to go to at some point. there's no way i'd need that much air for a 305. coming full circle back to the poor guy whose question started all of this ....

* the stock throttle body flows enough air to support his combination. he only has 305 cubic inches, 58cc combustion chambers, a mild cam and 1.94/1.5 valves. the project done by traco engineering i mentioned earlier had more cam and better flowing heads and still saw no improvement in mph with the 454 tbi. if it had made more power, mph would have been up, so the additional airflow was wasted at wot and hurt the car in daily driving.

* if you do a search on here, you'll see thread after thread posted by people trying to make 454 ot holley 670 tbs work on a 305. most give up and go back to the stock unit. there are reasons for that.

* airflow aside, getting a 454 tb to work in place of the stock unit with our ecms is an exercise in frustration. again, don't take my word for it, do a search. if he ever did get to the point where he needed more airflow for his 305, he'd be better off having a stock tb bored out to 48mm. his linkages, tps, iac, etc would all bolt up as stock.

 

So you have no experience with TBI systems on modified engines, correct?

RBob.

 

I believe those reasons are that most people that swap on those units figure they can gain some power by just putting the bigger unit on, which isn't entirely correct. If they were to put the bigger units on and tune them properly and then tune the VE tables in the prom accordingly I think they would see the gains they were looking for in the first place.

A modified 305 is going to benefit from larger bores if tuned correctly. If these 305s didn't gain power from gaining more airflow by whatever means then why do so many people do the Ultimate TBI mods? All they basically do is increase airflow to the engine. If this increased airflow is not needed then why do people pick up MPH in the 1/4 from them? That's just my view on it; any time, when working with fuel injection, tuning is the key to success. The engine has to be tuned in with all its components to get optimal power.

 

that's correct. and your point is?

 

I just want to add that I bolted a 454 TBI on a totally stock 305 and it ran fine, until you got over 1/3-1/2 throttle. at that point it totally flooded the engine. otherwise it ran great. I don't claim to know much else about it, just that I tried it.

 

In response to: So you have no experience with TBI systems on modified engines, correct? (RBob)

Yes, as I expected, another 'expert' that speaks from the orifice of flatulence.

Lets put some additional reality into this thread. If you observed this data what would you do?

Some additional information: The MPH is just that, the RPM is just that, the VE% is from the VE table at that rpm/load, and the TPS% is just that.

The first data line is at key on, so Map is Barometric pressure.

Hmm, I see an engine at 4375 RPM, 100% TPS (WOT!), and manifold pressure at 95 KPa. That is 8 KPa down from barometric.

Having driven this vehicle I can state that by 4800 RPM the engine was dead, no more acceleration. Flat as the plains of Kansas.

So, what would you do? Stay with the 1-11/16" bore 2 bbl TBI (as is with the data)? Or go with a larger TBI? Maybe you can explain how that much pressure differential across the TB affects the output of the engine.

I also challange you to telling us what you think is under this 1-11/16" TBI. Has to be a 406ci monster. . . right?

RBob.

P.S. the data presented in this post is real. It is from data logs that I personally collected.

 

BronYrAur, I'd like to borrow a phrase that you stated and highlight it:

any time, when working with fuel injection, tuning is the key to success.

Everything you stated is true. However, this statement is the part that I think too many miss. Thank you.

RBob.

 

My combo is a good example of poor tuning hurting performance. 15.50 @ 93.

 

once again, you make personal attacks.

i have no intention of taking your "tests". i've never presented myself as anyhting more than an enthusiast who's been researching the issue and has opinions based on that research. you were the one sneering at magazine projects and making personal attacks.

as far as your expertise is concerned, as i recall, you were the one insisting that 454 tbis flowed 670 cfm @ 1.5" hg and attacking me because i pointed out that you were wrong.

don't play childish games, don't try silly tests ... if you've gotten a 454 tbi to work on a 305 ... put up.