softwarejanitor

I know the stock ECM needs to be upgraded if I want to have my throttle bodies bored to 2" and install TJ25 (68lb/hr) injectors. Which ECM should I get? The TJ25 injectors I believe were used in the 1990-1991 Caprice 5.7 and pickups with the 5.7 of that vintage. Should I get one from a Caprice or from a truck? Or would the ECM from a 1989-1992 Camaro/Firebird 305 be better?

What do I need to get to reprogram one of these things?

odxr

If you are going to reprogram the ecm it doesnt really matter-you are hacking into it to change the programming any way.You will need some kind of wide band o2 for data logging.Try this website www.moates.net I have not used or tried any of this but I have installed other aftermarkit efi systems after ripping out the oem system.In reality all ecm's are the same-just different software.

John A. Marker

I believe that the ECM's for the LT1's and up have to be programed with the VIN number....1st hurdle. Bigger TB would not be a issue. Why 68# injectors....these are much larger than "stock". Here is a list for reference:

FUEL INJECTORS: Stock Numbers –
From receiving cores back form customers I have sufficient evidence on what is in what. Here it goes.
l98 85 used a Bosch 24lb injector with a 36psi rail pressure net 22lbs.
l98 86-88 used a bosch injector 22 lb at rail pressure of 43.5 net 22lbs
l98 89-91 used a Rochester Multec 1 22lb at rail pressure of 43.5 net 22lbs
92-93 LT1 used a 22lb Multec 1 22lb at 43.5 psi
94-95-96 LT1 went to sequential injection and a 24lb Multec II at 43.5 psi
96 LT4 uses a 26lb multec 2 at 43.5 psi.
97-up LS1 uses a bosch design 3 24lb injector flowing at 55psi net 28lbs. These are also 12.8 ohm coils vs 15 on the SVO.
-FICINJECTORS


Normally you need to re-program or "custom tune" your ECM if you have changed out the cam or had other drastic changes done to your engine. If you have none of these then it is a waste of time and money. The bigger TB will not add HP....the stock 48mm TB on earlier Corvettes was good up to about 400 HP. Larger injectors will be the same...too much fuel and the O2 sensor and ECM will see a rich condition and pull fuel away.

Tom400CFI

^Stock injectors on a CFI are ~ 65pph. Remember, there are only TWO injectors. He's "upgrading" to 68pph which is basically worthless.



No it doesn't.

I ran a SBC 400, 224/234 cam, ported intake, bored TB's, headers/exhaust, 90 pph injectors, and other bits and pieces on the stock ECM/chip. You definitely do not need an ECM or even a tune for bored TB's.

FYI, bored TB's won't do squat on a stock or stockish CFI. Just so you know.


IF you want to change ECM's I'd think you could run ANY "TBI" ECM (the '7747 is a common swap, and it IS from a TBI Caprice, the TBI truck AND TBI Firebird), or any batchfired, Speed/density ECM.


.

corvettenorway

2"throttle bodies = no need to opgrade ecm ! stock injectors are 65 and 68ib/hr ! try to check your fuel pressure ! any other engine mods ? and read this http://www.dynamicefi.com/TBI_Fueling.php

softwarejanitor

Pretty sure that a TPI (L98) or LT1 ECM would be a bad choice for a throttle body system like CFI anyway since they are designed for a fairly different system.

I'm going to be greatly opening up the breathing through the intake manifolds, head and exhaust. That's the reason for having the throttle bodies bored out to 2"

CFI uses two throttle bodies with one injector each. Therefore you need much bigger injectors than a TPI which has 8 injectors. From what I've read some people use the SS454's TJ11 injectors which are 90lb/hr which I could believe might be overkill. The best I can find out about the stock CFI injectors the TJ12 and TJ16 is that they are in the 48-50lb/hr range, so the 68lb/hr injectors aren't a huge increase.

The CFI stock uses a TJ12 in the front and a TJ16 in the back. The 89-91 Caprice 5.7 used a pair of TJ25 in its dual injector throttle body, similar setup for 5.7 trucks of that era. All these TJ series injectors are made by Standard Products Corp a.k.a. SPC.

I'm planning on putting in a retrofit hydraulic roller cam, aluminum heads with 64cc chambers, 180cc intake ports and 2.02" intake/1.6" exhaust valves and headers.

It is going to need to be totally programmed from scratch, that's why I was asking. It is my understanding that the very primitive ECM that came with the L83 will not handle this level of mods very easily because they use an EPROM that requires UV erasing instead of a reprogrammable FLASH like the later units.

That's not relevant here since I'm planning on doing everything at once. From what I've read having the CFI throttle bodies bored to 2" (51mm) will make the net flow be about 700cfm (up from just under 500cfm at the stock size). 700cfm should not in my opinion be excessive for a 350 with intake, heads, cam and exhaust mods. 500cfm seems like it might be a limiting factor.

Anyway, I'm trying within reason to knock out all the major bottlenecks without creating any huge new ones.

softwarejanitor

I thought the TJ12 and TJ16 were lower than that, like 48 and 50lb/hr respectively... But now googling it I am having trouble finding anyone with the detailed specs. If you are correct then I guess I should consider the TJ11 90lb/hr injectors like used in the SS454 TBI.

Well, I guess I can try it with the stock ECM and if it doesn't work well then I can swap it.

This would be with either a Renegade or a fully ported stock lower intake. I realize that the stock lower intake is the major bottleneck in the stock system.

I will look for that one. It seems like they aren't horribly expensive used. The big advantage seems to be that they are FLASH programmable instead of using a UV EPROM which makes tuning easier.

softwarejanitor

Fuel pressure is O.K. with the stock 1984 pump but they have a reputation for being marginal with mods so I plan to put in a new 1985 style pump anyway -- it isn't that expensive and the original one is over 30 years old so it isn't a matter of if it will wear out it is more like when.

I'm planning on either Renegade or fully ported stock lower intake, retrofit hydraulic roller cam and link-bar roller lifters, double roller timing set, aluminum heads with 64cc chambers, 180cc intake ports, 2.02" intake/1.6" exhaust valves, 1.6 ratio full roller rockers, long tube headers into true dual exhaust with x-pipe and a Super 65k HEI with 8.8mm Accel wires.

If you are right about the stock injector specs I think I will go with the TJ11 90lb/hr injectors and have the throttle bodies bored to 2".

I'm hoping that all this should get me at least competitive with a lightly modded L98... in the 250HP range at least. So I hopefully won't have the slowest C4 in the local Corvette club anyway...

Tom400CFI

Why ask the question then?? The LT1 is a bit of a stretch due to an very different ignition system, but the L98 is fundamentally very similar to the CFI and it can work. In fact, I believe QWS on ths forum has already done that conversion.



Doesn't matter. It's already been done (massively ported intake) and then the addition of bored out TB's...didn't do one wit for power. Stock TB's are more than enough for a stock or stockish engine.



That's important...and a lot different than, "I know the stock ECM needs to be upgraded if I want to have my throttle bodies bored to 2" and install TJ25 (68lb/hr) injectors"...which is what you said in your first post.



The ECM in the L83 is just as "fast" and "advanced" as other L98 ECM's. I believe "69427" on this forum has hacked and studied the ECM in the '84 and made those observations. The problem w/the CFI ECM is that it isn't readily "hackable" and there aren't tools to interface with it. THAT is the primary reason why people switch to newer, more common ECM's.



probably not a limiting factor on the 350 that you're talking about. I'd bet that the intake will still be your limiting factor.



Probably, since you're doing cam and heads.



That is what I would do. That is what I DID with my 400, and ended up not needing ECM/Tuning. MY results were ~300 chp, stock like idle, great drivability and 24 mpg hwy. That was acceptable..."good enough". I used the 90 pph injectors and a vacuum referenced fuel pressure regulator from a marine application TBI to lower fuel at idle/cruise and it worked great. IF it hadn't worked out that way, THEN I would have proceeded down the ECM/tuning road.

softwarejanitor

Read the original quote again, I wasn't asking about TPI ECMs, I was asking about TBI ECMs. It was the person replying that mentioned the TPI ECMs and was asking about injector volumes related to TPI.

I just figured an ECM originally designed to handle 2 injectors in a TBI like the Caprice, truck or Camaro/Firebird TBI would be a better choice on a CFI than one for a TPI like the L98. The TBI ECMs are also dirt cheap on eBay.

I wouldn't consider the build I've laid out as "stockish" anymore. With the stock cam and large chamber small port/valve heads and restrictive exhaust I wouldn't be surprised that the TBs weren't the next bottleneck I'd run into. I'm trying to make sure the mods are well matched from top to bottom and knock out all the major bottlenecks at once.

[quote[That's important...and a lot different than, "I know the stock ECM needs to be upgraded if I want to have my throttle bodies bored to 2" and install TJ25 (68lb/hr) injectors"...which is what you said in your first post.[/quote]

Yes, but there is no reason to do that unless it was to support other more extensive mods -- I didn't think I needed to go into all that detail again.

As I said, one big difference is in ease of tuning because you don't have to UV erase an EPROM every time you want to re-burn it. That alone probably makes it worth doing.

500cfm for a carb would be a limiting factor on the build I'm talking about... Even on the mid 70s L48 smogmotors in C3s Chevy typically used a Q-Jet that was around 700cfm. For a carb on a moderately build 350 I'd go with at least a 650 if not a 750. But I don't know if that rule of thumb works the same with EFI.

O.K., sounds like the TJ11 90lb/hr injectors are the way to go. This is the kind of thing I wanted to work out before ordering any parts...

That vacuum adjusted pressure regulator is an interesting idea... It is my understanding that the stock regulator is in the rear throttle body and not adjustable at all. You don't happen to have any more references for the marine one do you? Otherwise it sounds like time for more googling.

softwarejanitor

Hmmm... now... if I do end up upgrading ECMs... the 7747 units seem to be selling $125+... the 6965 ECM as used in the 1989-1991 Caprice are selling under $50. Anyone know the difference and whether it is worth paying over twice as much for the 7747? The Camaro/Firebird 305 TBI ECMs seem to be somewhere between those two...

If the only real difference is the stock programming which would be erased anyway, it seems like the Caprice ECM is the way to go.

corvettenorway

those mods are in the 300 - 330 hp range cam spec.? my bored tb gave me more trottle respons ! pics. of my ported manifoil and tb in my crossfire album ! yes by me ! https://www.corvetteforum.com/forums...re-intake.html read this treat

TLS_Addict

I have a cross-fire car as well. What does a timing adjustment do for the car? As you know its out of breath at about 4k rpms. Haha

softwarejanitor

As I said I'm hoping for at least 250 HP so I can at least be competitive with stock-ish L98 Vettes... if I get more, great, but I don't expect it. The cam I have in mind is the Comp Cams XE270H. That is designed for retro-fit roller applications and is the most cam in that series that CC sells that they recommend for a car with stock converter and gears. It definitely should have significantly more breathing capability than the stock cam, especially when paired with 1.6 ratio roller rockers.

softwarejanitor

I've read that the timing is very conservative on the L83, but you would have to reprogram the ECM to change it... and that is why I was asking about what is needed to upgrade to an ECM that more mod friendly.

TLS_Addict

You can't adjust any timing with the distributor?

softwarejanitor

Not like you can with the computer. The ECM controls the advance curves, etc., on the newer ones, it isn't all centrifugal and vacuum advance HEI like the old pre-computer (1980 and older) Vettes.

TLS_Addict

Looks like the common practice to u hool nattery, unplug the brown wire, adjust timing advance to 10-ish, reconnect wire and leave battery unplugged for a while. Plug back in and no check engine code.

The 84 is nothing like the newer computer in that it is quite primitive with less finite adjustments and monitoring than later years, its why people upgrade the computer.

corvettenorway

mine can do 5200 rpms ported manifoil ,bored tb , koolblue filter , 1,6 rt , 14psi fuel , pressure, 12 deg.timing , lnew cat back , +++ next winther new ported heads and cam + paralell plumbing + 80 lb/hr injectors but it runs better than a 85 -89 modell right now

softwarejanitor

What is the part number for the 80lb/hr injectors? And you are running the stock ECM with bored TBs and the bigger injectors? That backs up what Tom said about the stock ECM being able to handle it... But I may still want to upgrade just to make tuning easier.