To run a Carb or not?

[anwat]

OK, now I'm going to have to chime in. The stock fuel pump is about 75lph...isn't good for much more than stock. If you do any mods to the throttle body or change your cam much you're going to need to upgrade your fuel pump. The vortec pump is about 155lph, which is good for most anything you do to a 350. No adjustable regulators from GM, but those are the years that are easily modified. There are numerous write-ups on how to make the stock GM regulator adjustable, or you can buy one premade from rvmorsemachine.com. There are even springs you can buy and change out to increase or decrease the pressure to a set level. By far the cheapest way, but not adjustable without removing it and changing to a different spring. I would recommend getting the pressure gauge that attaches to the throttle body, also, can't beat it for convenience. Also, go to harristuning.com and read pretty much everything on his site regarding modification of TBI engines. He's got specifics on everything, and I've found what he says to be backed up by most every TBI owner and mechanic I've talked to. Thirdgen.org has a lot of good info, also.

You need to do some research before you start buying stuff and slapping it on there. Putting a big block throttle body on a 350 won't make it run like a big block. The injectors are going to cycle wrong, you'll have idle issues and no increased performance. The 350 injectors are fine with increased pressure and a change in the pulse width. Everything has to match, your tune on the prom, the intake, the throttle body bore, the injectors, the exhaust, and the problem child, the timing. Once you change the cam in a tbi, you're going to forever be guessing at the timing advance curve, since it's all controlled by the computer tune. It's more complicated than you would expect. Read up and save money! It's all been done before, you just need to decide what you want and find someone who had sucessfully done it.

OK, I'm done.

 

[HankScorpio]

OK, now I'm going to have to chime in. The stock fuel pump is about 75lph...isn't good for much more than stock. If you do any mods to the throttle body or change your cam much you're going to need to upgrade your fuel pump. The vortec pump is about 155lph, which is good for most anything you do to a 350. No adjustable regulators from GM, but those are the years that are easily modified. There are numerous write-ups on how to make the stock GM regulator adjustable, or you can buy one premade from rvmorsemachine.com. There are even springs you can buy and change out to increase or decrease the pressure to a set level. By far the cheapest way, but not adjustable without removing it and changing to a different spring. I would recommend getting the pressure gauge that attaches to the throttle body, also, can't beat it for convenience. Also, go to harristuning.com and read pretty much everything on his site regarding modification of TBI engines. He's got specifics on everything, and I've found what he says to be backed up by most every TBI owner and mechanic I've talked to. Thirdgen.org has a lot of good info, also.

You need to do some research before you start buying stuff and slapping it on there. Putting a big block throttle body on a 350 won't make it run like a big block. The injectors are going to cycle wrong, you'll have idle issues and no increased performance. The 350 injectors are fine with increased pressure and a change in the pulse width. Everything has to match, your tune on the prom, the intake, the throttle body bore, the injectors, the exhaust, and the problem child, the timing. Once you change the cam in a tbi, you're going to forever be guessing at the timing advance curve, since it's all controlled by the computer tune. It's more complicated than you would expect. Read up and save money! It's all been done before, you just need to decide what you want and find someone who had sucessfully done it.

OK, I'm done.

Uh yeah, I am doing research and I am not putting a big block throttle body on a 350.

 

[mrk5]

So how much cam is too much for a factory TBI? I am asking because I have a nice 454 to put in my K5 (zero miles) but it was built to be a carb motor. Carb is not an option for me. The 454 has an edelbrock performer cam with the performer 2 intake. I don't mind swapping the intake or running an adapter but I would like to not pull out the cam on a new rebuild.
Motor swap starting over here:https://ck5.com/forums/threads/200-k5.340114/#post-4078440
I am surfing the site looking for info on TBI with an older motor with a bit of cam.

There used to be cam upgrades for TBI trucks. Still only get the best results with a chip upgrade too tho.

As I remember it, it's all about the LSA, lobe separation angle. TBI doesn't like much LSA; can't remember if you want a small number or large number. I can't remember what the "safe" number is.

 

[folkenheath]

You're on the right track, although too much is probably too small of a number for LSA. The smaller the LSA, the more overlap you have and the harder it is for the EFI to compensate because of the intake and exhaust valves being open for too long at the same time mixes up the incoming and outgoing gases. If you have a larger LSA then you have less overlap and its more predictable and a flatter torque curve. A lower LSA is more peaky and will idle rougher. However, overlap is also changed with duration, if two cams have the same LSA at 112 for example, and one cam has 220 duration and the other has 250, the valves are open 30 more degrees and you are going to have more overlap with the same spread between the lobes. My app will calculate overlap from cam specs to compare different cams, overlap gives you an idea of how hard it is on the EFI, and also how rough the idle will be. Factory TBI is very limited here. Newer multiport systems are much more tuneable, and latptop tuneable aftermarket EFI is nearly unlimited.

 

[mrk5]

I couldn't remember if it was a small number or large number for the LSA. I edited my post so someone doesn't get the wrong idea.

 

[6872xtc]

Can’t say for sure on the BBC. I used the Performer Plus in a SBC and had to get a chip burned

@HankScorpio , I can tell you that the engine Bent is talking about ran pretty well in my opinion.

 

[beags86]

Uh yeah, I am doing research and I am not putting a big block throttle body on a 350.

You changed course? My buddy has 454 tb on a 355.
I never got into it with him. But it seems to run fine.

 

[dyeager535]

My Blazer is a '90 so it already has TBI, it should have enough fuel pump but I am going to check that both motors used the same pump. I have the correct 454 throttle body so that should help with fuel also. I also have the 454 ECU so that is covered but I bet I end up with a new PROM chip from Howell. I have a fuel pressure tester, I will get a base number from the 350 before I take anything apart. If all the '87-'95 trucks have the adjustable regulator then I should already have one.

As Anwat stated, the problem is the pump itself. My memory is horrid, but I want to say 350 and 454 used the same pump., and the limitation on TBI pumps is the lbh. They are just not rated very high. SOME factory TBI pumps can put out a bit more pressure than others. If you are lucky, bumping pressure up is possible with the existing pump (it's real simple... as a for instance, if it's running at 11PSI, and you shim the regulator spring with washers and can get it up to 12PSI, then you have some room to play with. If adding spring pressure doesn't help then the pump is maxed out already). If you have to replace the pump, you want excess capacity for sure. I remember shimming the regulator spring, but there isn't much room to play with...if a thin washer or two won't bump pressure up, you need another pump. If you shim the spring too much, you'll break the regulator housing. Don't ask how I know.

ECM's are the same, PROM different, having spares parts won't hurt though.

 

[anwat]

X2 on knowing about the regulator housing limitations. I broke two, then just bought the adjustable regulator from Morse. What I did to solve the pump issue is put the Vortec pump in, it's plug and play on the 90: Delco # 25163473, which will put out 155lph. Everything is the same as stock on the 90....hose size, plugs, plus it isn't as noisy as the stock pump.
There's plenty of pressure and volume there for either your GM or aftermarket TBI system.

My apologies...I missed the post where you mentioned you had a 454, so I was under the impression you were trying to frankenstein a 454 and a 350. My bad for not thoroughly reading the post.

 

[vandelay industries]

Carbs haven't been on cars and trucks since 1986. There is a reason for that.

An "outside" thought: i believe the 75 Cosworth vega was actually the first gm car to have electronic fuel injection. NOT the 76 cadillac seville as might be more commonly thought.

i apologize-----i'm into small chevys.

 

[dyeager535]

An "outside" thought: i believe the 75 Cosworth vega was actually the first gm car to have electronic fuel injection. NOT the 76 cadillac seville as might be more commonly thought.

i apologize-----i'm into small chevys.

And technically, some US GM cars had carbs up until 1990 (Olds 307), unsure about trucks, I know carbs are shown in the manuals into the TBI era, obviously on the higher GVW rigs. I have no idea how long carbs lasted on US, GM trucks. I'd expect no later than 1991. They must have been very uncommon, I don't recall hearing anyone say they owned an '87+ R/V truck that was stock with the carb.

 

[diesel4me]

Every so often I'd get a customer at the parts store I worked at in north central MA,that had a late 80's GM truck that was still carbed from the factory,a few still had point distributors and no EGR valve or catalitic converter too,(GVW over 8600 lbs)--all came from Canada and were purchased there originally..
I couldn't confirm with certainty they left the factory that way,but the owners swore the trucks were 100% original and unmolested..

It's weird how some other countries had different versions of the trucks & cars we are familiar with like Brazil,Austrailia..some of them were more advanced than what we could get here,probably due to emission laws..

 

[6872xtc]

I believe that the crewcab that Lawrence wrecked was an '89 big block with a carburetor. I was surprised at that when he got it, but I seem to remember some guys verified that it was available from the factory.

 

[imiceman44]

I believe that the crewcab that Lawrence wrecked was an '89 big block with a carburetor. I was surprised at that when he got it, but I seem to remember some guys verified that it was available from the factory.

Big block Chevy engines got carburetor in some applications, I know a lot of 89 RV engines with carburetor.
Also if I remember correctly 89 was the first year of a true TBI intake on the 454, or was it 90?
Before that it was an adapter on top of the intake

 

[Hogback Fabrication]

And technically, some US GM cars had carbs up until 1990 (Olds 307), unsure about trucks, I know carbs are shown in the manuals into the TBI era, obviously on the higher GVW rigs. I have no idea how long carbs lasted on US, GM trucks. I'd expect no later than 1991. They must have been very uncommon, I don't recall hearing anyone say they owned an '87+ R/V truck that was stock with the carb.

I had a buddy in college that had a '91 Cadillac Brougham with a 350 and Q-jet, stock

 

[dyeager535]

I had a buddy in college that had a '91 Cadillac Brougham with a 350 and Q-jet, stock

I'm going to double down on my statement. Olds 307 is widely accepted as the last carbed V8 GM offered in US passenger cars, and it was offered in the Brougham, up to 1990 when GM quit making the Olds 307. Then apparently 5L FI: https://en.wikipedia.org/wiki/Cadillac_Brougham

If there was a carbed, factory, commercially available GM car destined for the US market after 1990, that's the equivalent of proving a GM 12 bolt front axle existed.

 

[imiceman44]

I'm going to double down on my statement. Olds 307 is widely accepted as the last carbed V8 GM offered in US passenger cars, and it was offered in the Brougham, up to 1990 when GM quit making the Olds 307. Then apparently 5L FI: https://en.wikipedia.org/wiki/Cadillac_Brougham

If there was a carbed, factory, commercially available GM car destined for the US market after 1990, that's the equivalent of proving a GM 12 bolt front axle existed.

You realize that most 91 model year cars are built late 90, so that is the case here.
I bet if he looks up the build date it's 90

 

[dyeager535]

It has to be the model year (MY) certified by the EPA. Same reason converters were mandatory a specific MY, why CCC was across the board one year, why you could get X engine or Y trans or Z gear ratio one year but not the next., and so on.

Before emissions came on the scenes "one-offs" (leftover parts, rare combinations) could happen. In this case, GM would have had to certify a 1991 model year Cadillac Brougham with carb, Olds 307, and 200-4R through the EPA if that was ever to get into the general publics hands.

An emissions sticker would suffice as proof as far as I'm concerned, as that would show the carb and year.

Heres's an "apparently" rare '91 Brougham that shows the 5.7L (also apparently rare) TBI. Weird to me, in that the window sticker specs both the 5L and 5.7L, but both are FI: http://www.fleetofcads.com/Brougham91.htm

Here's the dealer brochure from that year showing the 5 and 5.7L TBI engines as the two available: http://oldcarbrochures.org/North America/Cadillac/1991-Cadillac/1991-Cadillac-Full-Line-Brochure/slides/1991_Cadillac_Full_Line-20-21-21a.html

I could certainly see someone having mistaken TBI for a carb. It still happens.

 

[TJ1978]

Bump.... forgot about this thread.. mucho info