I'm trying to find something to prove or disprove the need for a 454 tbi...

Has anybody run the small TBI, then bored out their intake, put the bigger tbi on, and then gone back to the dyno?

Very interested too. I had a 46mm one built for me from the advice of this form. I was told to stay away from BB injectors. I have 68#'rs I am going to run at 25#'s to start and adj from there. I bought an EBL I hope it was worth it.

The issue is, what is the HP level of the engine? At the stock 160 (165?) HP, it won't make a difference. Change the heads, cams, exhaust, build the engine and drive-train, it is another story.

Need to match the air & fuel requirements to the expected HP level.

It is worth it. Just give yourself some time to learn the system and how to tune it.

The EBL Flash system was born out of the need to tune worked engines. And it does it well. Just need to learn tuning, or take it to someone that knows how to tune. The stock ECM is barely capable of being tuned past a stock engine. Let alone the stock TBI unit.

RBob.

yeah i do not know what is wrong with using the 454 injectors instead. i am doing that mod. myself. my holley tbi injectors arent cutting it. I dont know if I should just blast them up to 35 psi or run 454 injectors at a lower psi.

i do one thing then someone comes along and says no do this instead. gets me confused and makes me wanna go carburetor!

Check the MAP value at WOT. The lower it goes the greater the need for a larger TBI unit (or intake ducting/air-cleaner).

RBob.

Six of one and a half dozen of another. Do what works from your standpoint. If running the smaller injectors at higher pressure is enough to feed the engine, then no need for BBC injectors.

If you need to get injectors then go with the BBC ones at a lower pressure. Not sure why folks say to stay away from BBC injectors. I'm running a set now at 20 psi with a vacuum referenced FPR.

The biggest key to upping the injector flow rate via increased fuel pressure is the injector compensation values.

RBob.

From an email message from Walt Sherwin dated 8/25/03:

"17084304 is the stock (1990 - 1993 454) SS injector. The service part number is 17112560. It is rated at 75 lbs/hr of spec fuel, at 10.5 psig differential pressure. There was once a larger flowing injector manufactured and used in the early 80's, and in fact I have one that I've tested on the bench. The engraved number on top is RPD 17111784. It flowed around 80 lbs/hr, versus the 17084304, under the same conditions. However, you want to stay as far away as possible from those as the electromagnetics were terrible, they were quite sluggish, and beyond about 18psig they don't flow properly. There were larger alcohol injectors made for the Brazil market, but the last time I checked they were no longer available. Bottom line, stay with the 17084304 and crank the pressure until you get the delivery you need. I've run those puppies at 70+ psig fuel pressure !!!"

My experience with the 75 & 80# injectors parallels his, that's why.

But then again I run what some consider extreme pressure.

See I have no idea what the injector compensation value means. I guess their is something in the EBL I would correct? Im a total moron when it comes to that thing. And my reading comprehension sucks. I just add timing remove timing, add fuel remove fuel til it run's good enough to drive. And here I am debating on what I wanna do. I really don't wanna get rid of the holley tbi if I do not have too. It is already on there. Id rather just put a VRFPR inline and remove the holley one. Then run the BBC and deal with wiring up the IAC and all that stuff.

Well yes, that's common sense, but I was hoping to find the answer without having to pull the intake after the motor is in the truck to upgrade (if necessary). I am not running a crazy combo (LT1 cammed L31 with shorty headers) so I was hoping there was somebody out there like Fast355, dimented24x7 or one of those other guys who had some experience or testing with throttle bore sizes.

>> "See I have no idea what the injector compensation value means."

What we do is use the fuel pump voltage / injector offset tables* to compensate for the injectors slower operation under increasing pressure.

Injector offset is an PW addition to BPC as far as I know, and why it's effect is greatest at idle where it is a greater percentage.

*Edit: INJ-Injection Correction Offset - in the EBL .xdf tables.

http://www.dynamicefi.com/TBI_Fueling.php

Reading that should help some.

"Check the MAP value at WOT. The lower it goes the greater the need for a larger TBI unit (or intake ducting/air-cleaner).

RBob."




what number is considered low ? an is that at idle or wot ?

On a 340 HP SBC the stock SBC TBI unit wouldn't pass enough air. Engine power was dropping like a rock.

Changed to a bored (2+") TBI unit and the same engine would then go to 6K RPM without a hitch. MAP still drops about 8 KPa (2.4" Hg) from barometric at high RPM.

RBob.

The compensation values compensate for the amount of time it takes the injector to open. The fueling calculation provides an injector PW required for the amount of fuel. The compensations are required so that the injectors actually deliver that amount of fuel.

There is a PW offset table that is added to the PW. This makes up for the time is takes for the injector to start to open.

There is also a multiplier table, this value compensates for how long it takes for the injector to then fully open. It is a percentage of the current PW being added back into it.

As the fuel pressure is increased both of these tables need to be increased. As the injector is working against higher fuel pressure, it takes longer to open.

RBob.

Ah HAH! Thank you so much Bob! That tells me that I should reasonably be using a BBC TBI since I'll be in the same ballpark (slightly lower) power-wise. Bummer that I've already RTV'd the intake down, but at least the engine is not in the truck yet!

I already have a 454 TBI in the mail since I suspected this would be the case.

I guess it makes sense when you compare the throttle body bore size to a TPI engine making similar power.

I like to see 88-92kpa at the shiftpoint, this helps recovery immensely. I hope nobody expects to see atmospheric pressure on any running N/A engine, let alone a street engine. You don't want to rely solely on velocity, fuel in a vacuum behaves better anyway.

I believe100 kpa the engine is not running or stalled. I am 95-96 kpa/MAP but I am 1000 feet 7.4L TB .

interesting....
95-96 kpa at how many rpm? How many cubes is your engine? Heads/cam?

5800-6000 rpm .. 350 cid... Edel RPM heads 64cc ... 224/230 .05 114 LSA I pull higher kpa/map in second gear of four.

So I guess, based on 95kpa at 5800 RPM, we can say that the 454 TBI is big enough for a healthy-but-streetable 350. I feel like I've made the right choice now going bigger than the SBC TBI.

Thanks!

Well my buddy that has exclusively ran carbs and drag raced seriously years back says my 7.4L TBI is way too small. He believes a 750 Holley carb would provide large HP gains. He installed my top end on my car and does the serious mechanical repairs for me. He owns a restoration hot rod shop.

....but if your TB isn't holding back airflow, how can a Holley 750 give you much? How much intake vacuum is left at WOT at 6000 RPM in a similar motor with a Holley on it I wonder?

I agree unless there are other factors? Fuel distribution issues with TBI injection?

I think the TBI is rated w/o the pod on it? so a 670 TBI unit may only flow 620? Compare a 620 class carb with a 670 TBI may be comparable. something tells me the 750 series carb adds something to the equation. NASCAR had restrictor plates and carb last year. this year they are EFI with Holley TB units. I wonder if the Holley EFI TB's are larger than prior carbs in venturi area?