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350TBI to 454TBI 1988 Suburban

Greg Ducato

Greg Ducato

1/2 ton status
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Mar 26, 2010
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Location
Weatherford Texas
Well guys, I have been trying to love my upgraded 350TBI engine but it just doesn't have the grunt required to move around this big heavy Suburban, and fuel economy since the gear and tire swap has dropped to 10mpg. I could live with the milage if the power was there, but on a hot day with the A/C blowing, I am still losing MPH going up long inclines and the merging performance is less than stellar.
I have purchased a nearly complete 1988 454 TBI engine to build to replace this small block and will be putting the small block into my 51 Willys wagon instead of the 4.3 V-6 ( why have two underpowered 4x4's?) Plans for the build are an Edelbrock top end on an otherwise stock, quality built, short block. I already have a modified 454 Throttle body and injectors and an Edelbrock TBI intake from a previous project. I plan to use the Edelbrock 454 TBI Aluminum heads and a TBI friendly cam,and Thorley headers into my existing 2 1/2 dual exhaust system.
I would appreciate any comments on this package from those with experience with these components or this conversion. I would also appreciate any experienced advice on cam selection for more power while still keeping the computer happy. I am building this more for low end grunt than top end pull, the heads are probably overkill but the wieght savings appeals to me as does the slight compression bump. Any wiring issues, fitment or mount pitfalls or any suggestions or help will be appreciated. I used the search engine and picked up a few tidbits but thought I would ask for the most up to date info.
 
Forget keeping the computer happy IMO. Build the engine to the specs you need, and make the computer work with it. The PROM MUST be tuned to make sure that you are getting as much power as you should be, safely.

My dad swapped the TBI from an '89 454 Suburban into his truck. Only mods were headers, Edelbrock intake (came with the injection stuff) and a "computer friendly" cam. That setup needed 20% more fueling than what the stock setup was providing. Not only that, it needs more fuel pressure, as those ECM's have a flaw (correction: limitation) that only allows so much fuel to flow. Without bumping up the pressure, he has hit the limit of fueling in the ECM, which is dangerous when doing something with a decent load.
 
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Yes, and with TBI once you start messing with fuel pressure, you get into a loop where the PROM must now be tuned to make sure the engine isn't running rich under certain conditions, and so on.

I might suggest spending some time over at gearhead-efi.org and learning about what other ECM's could be substituted for what you have. I assume that is a 1227747 ECM, or service replacement for it. As I recall there is at least one other TBI ECM that can be used that doesn't have quite the same limitations, and has more functionality than the '747.

The early TBI BBC's didn't use a knock sensor. IMO while not a necessity, it is a nice "just in case" to run one, since it was done factory, just not on the early stuff, and should be fairly simple to add.
 
Oh and more! Do you have autozone down there? I haven't borrowed it yet, but their fuel pressure test kit appears to have the adapters to use it with TBI.

It's a very good idea to make sure that the fuel pressure is at 13PSI...GM spec is 9-13, but they need to be at 13 to run their best, at least stock. The regulators are somewhat a pain to modify for more pressure, but not that technical to do.
 
I have an adjustable regulator and gauge on the 5.7 now, running 12.5 psi. I had planned to install the same set up on the 7.4 so I could dial in the fuel pressure required.
 
Definitely a good call...we didn't have an adjustable FPR OR a gauge, so it was trial and error. I apparently didn't shim the spring enough, fueling didn't change much. Not as much as the motor needed. Needs to come back apart to adjust further, although it's not THAT difficult to get the stock regulator out and apart.

Would be far nicer to be able to adjust it and watch your fuel pressure I'm sure. :)
 
Do yourself a favor and go with a single 3" exhaust, it will build more low end torque than a 2 1/2" dual set-up.
 
4X4HIGH said:
Do yourself a favor and go with a single 3" exhaust, it will build more low end torque than a 2 1/2" dual set-up.
Click to expand...

Thanks, too late though, already switched to a full dual system from the Thorleys back. I did like the sound and response of my old 3 inch single system though, but it needed repair and while I was at it I thought the duals might be a better choice for the larger displacement engine I was anticipating using.
 
You know your milage will not get any better with a BB?

You could get more power from the SB with a tuned chip...
 
I have a generic chip in the truck now, didn't notice any real difference. The truck runs about town very well and has plenty of pep, but cruising out at 70 mph it has trouble maintaining speeds on steep uphill stretches even with no passengers or gear. I think it is simply a matter of aerodynamics versus available power. Right now we are at 2300 rpm at 70mph in overdrive with the 4.56 gear and 33's and milage in combined driving hovers around 10 mpg. I don't mind the mpg so much but want enough power to pull hills with the A/C running and the truck loaded for a trip. If you could burn me a chip to do all that with my current small block I could probably fall in love with you:D
 
Since you mention generic chip, are you then running premium fuel?

All the (crap) aftermarket chips I'm aware of bump timing up, which requires increased octane and lowered coolant temps (both band aids for a bad tune) to keep the motor from knocking.

It *could* be, if you aren't running premium, that under high load as you describe, you are running into the knock sensor, retarding timing, and thus experiencing low power.

Mark will agree, a properly tuned chip wouldn't have those issues. I know if/when I run into the knock sensor on my truck (still not tuned correctly), I lose massive amounts of power as timing is pulled.
 
Good points, I run 89 octane and a 180 degree thermostat, engine runs super cool even in the hot summer months. I will try a tank full of premium next go around, shouldn't take me too long to burn through the 30 gallons I have in there now. I would love to try a custom chip if I knew someone who could help set one up for me.
 
We've read many generic chips and some have as little as 6 insignificant changes and none were worth $150. Guys would be really pissed if they knew how bad they were ripped off! Some custom tunes we have seen are a joke!

*Disclaimer! I'm not accussing anyone, there are some tuners out there that actually sell good stuff!*

I can always start a guy off with a chip tuned for the engine. But without a data log that is all it is, a starter chip.

Greg if you have a laptop? Get a cable for about $55. TunerPro RT free to try and the best $39 you could spend to watch your data and read codes. I wrote the files for it and they are free. Do a data log and we will look it over, tune you a chip and prove this point once and for all. Actually I'd rather have a data log with your stock chip so I know the starting point. I could read your generic chip and show you what was done for the money.

dyeager535 have I ever helped someone get a good tune?

Really getting tired of people getting ripped off, maybe I'll get a vendor status here and start giving CK5 brothers something worth their money!
 
cool! thanks for the info. I will be out of town till next week but will check into that when I get back. Even if the 350 doesn't work out I'm sure the 454 will need some tuning love.
 
Nope, never a good tune Mark. LOL

From what I recall on thirdgen.org, most of the chips simply increased timing enough that knock was a real issue, hence the cooler t-stat and premium fuel. That's not how to make power.

My buddy has a stock '90 'burb, and I don't think that thing lacks for power at all. He drives his vehicles harder than anyone I know.

If I was going through a gen 1 SBC that was already TBI, I would go Vortec heads, headers, and probably leave it at that. Of course with a good tune.
 
dyeager535 said:
From what I recall on thirdgen.org, most of the chips simply increased timing enough that knock was a real issue, hence the cooler t-stat and premium fuel. That's not how to make power.
Click to expand...
There are all sorts of tricks to get more HP. Problem is you loose something else. Doesn't matter if it's a track car but how would you like to gain 30HP and give up 40% MPG even if you drove nice on street?

Or do it right and get better drivablity, pick up some MPG all around, add 10% or so on freeway cruise and add 30 HP. All while keeping turn key truck that drives better then off showroom floor.

I just did a TBI truck with new motor, Vortec heads, aluminum intake, cam @.050 218 intake and 224 exhaust, long tubes and duals. Needed 18.5 PSI to handle estimated HP. Starts on a cold morning and drives like a new truck same as if it's warm on a hot day. Was fun truck to drive while doing WOT fuel with the Wide Band 02 sensor. :D
 
Well, the 454 is in place and running as of friday the 10th. Put about 140 miles on it over the weekend in various driving conditions.
I ended up staying with the cast iron "peanut port" heads and about 9-1 compression so I could use a mid grade of fuel. I used the Comp Hydraulic Roller , "EFI Friendly" cam with 112 degree lobe seperation, 485 lift on intake and exhaust and 210/220 duration at .050 lift. She idles nice and smooth and has a good strong pull. We are running the Edelbrock TBI intake, a 454 Throttle body with enlarged throttle bores and plates, matched injectors, adjustable fuel pressure regulator ( 14psi), Thorley Tri-Y headers and the same 2 1/2 inch dual system with crossover tube and Hemi Turbo mufflers. I ended up staying with a built 700R4, fortified for the new engine, switched to a 241 T/C from the 208 and had the driveshafts rebuilt with 1350 series joints out back and new joints up front. Overall it was a pretty straight forward swap once all the parts were located.
I tried to use as many stock type installation parts as I could to lessen the chance of not being able to replace something later down the road. I ended up using the 747 computer and 5.7 harness, sensors etc. and lengthening it as needed to reach some new sensor locations. I have a generic chip in the computer as of now I am not entirely sold on, but it should get me by till I can get some break in miles on it and find a better tune.
Overall I think it was worth effort and expense to me to make the conversion, I actually find myself lifting off the throttle on some hills and grades the truck would lose speed on before so that I keep to the speed limit or from rear ending the guy in front of me. I still have some small items to tidy up but so far I'm diggin it.
 
Sounds like a sweet build! :waytogo:

You have no idea what that motor will do until you data log and tune a chip for it.
:woot:
 
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