need help on engine rebuild

[Rylan]

Hey guys I am 16 and thinking about rebuilding a 87' 350 TBI and I want to keep the stock fuel injection but i want to put in the biggest cam i can without having trouble. Or is there a better way to get more power I am planning on getting headers. Thanks

 

[1987 GMC Jimmy]

A mild hydraulic flat tappet cam would be an improvement, but the head design and the air intake capacity of the TBI unit are the two big restrictions. If you wanted to go all out and complement your cam swap and headers, you'd want to find a different set of heads. Aftermarket, pre-TBI (depending on the casting number), or Vortec are all better. You'd also want to figure out a better TBI system. You could either do a 454 unit or get a modified SBC unit that's been bored and has heavier injectors. I don't know how far you want to go or how much money you have, but you'd need to do more for a noteworthy power gain. I'd say you'd liberate about 30 hp with the headers and gain no more than 20 with a mild cam swap using factory everything else, give or take.

 

[4WDKC]

A cam swap wont be a simple fix for this engine the tiny cam, poor intake and head were all designed to worked together. You will need to replace heads,cam and intake if you are dead set on keeping a sbc in the truck, find yourself a running 350 vortec engine to rebuild. It already has the benefit of hyd. roller cam and you can still drive the truck while rebuilding the engine. Later you can swap the engine in and adapt the TBI to the vortec.

With what you will spend rebuilding the sbc, cost of heads, cam and intake you will be well into the cost of a complete LS swap. So the question becomes which do you want to do?

 

[Honky Kong jr]

Put a set of 3.73s or 4.10 gears no hp gain but it will feel like it.

 

[Rylan]

50 hp is about as much more as i want so i could put in a mild cam and headers and shouldn't have any trouble right?

 

[4WDKC]

50 hp is about as much more as i want so i could put in a mild cam and headers and shouldn't have any trouble right?

A new cam lets in more, more air requires more fuel, the factory ecm can only "learn" so much before a tune is needed. Basically any cam worth the swap will require reprogramming the Atari like ecm.

 

[Rylan]

How do you reprogram the Atari?

 

[Honky Kong jr]

How do you reprogram the Atari?

He was referring to its antiquated design when he called it an Atari ECM. What gears are in your truck?

 

[yevgenievich]

tbi without programming is probably only good for additional 20-30hp at most. Unless you get in to programming (https://www.moates.net/) or have someone else do it, there is not much to do with tbi. Especially on budget. Side note, there is a Vortech TBI Supercharger Kit for sale on thirdgen.org for $800. He has a chip for it as well. I wanted one but can't use it because of the 4l80e and do not want to mess with programming, but it might work for you.
https://www.thirdgen.org/forums/eng...arts/748888-vortech-tbi-supercharger-kit.html

 

[CSFJ]

50 hp is about as much more as i want so i could put in a mild cam and headers and shouldn't have any trouble right?

And the overall horsepower gain that you will see is not as simple as adding the 2 proposed figures together. To see a maximum gain on any modification, the rest of the system needs to be operating as effectively as possible to support it. Like 4WDKC stated above, if you put in a bigger cam, you'll need to upgrade the the computer map to provide more fuel. You would also need to address ignition timing, and you already mentioned that you plan to run headers. Are they going into new pipes, or are you planning to hook them to the existing exhaust system?

 

[crazy4offroad]

A bigger cam requires bigger compression. Swapping to Vortec heads with the smaller combustion chamber will gain you a little but I doubt if it will be over 9:1. Also Vortecs require a different intake, more expense. Swapping pistons from dish to flattops will give a nice bump in compression, making a larger cam happier. At the same time your cam selection can't have more lift than your heads can handle. Swapping to the 454 TBI is a good way to feed it more fuel/air but I think you're still going to be limited to a relatively mild truck/rv cam, too much overlap and the ecm will pitch a fit. Some of the worst sounding, popping, backfiring engines I've heard were from a person trying to run a cam too big for the compression stock pistons/heads can make. All they really wanted was that lopey sound but had no performance gains worth mentioning.

 

[OkieFishMan]

If it were me, I'd ditch that TBI stuff, throw on a 600 cfm carb with a performer intake, slap on some used vortec heads, stuff a mild cam in it, add headers, and the drive the hell out of it.

 

[Honky Kong jr]

A bigger cam requires bigger compression. Swapping to Vortec heads with the smaller combustion chamber will gain you a little but I doubt if it will be over 9:1. Also Vortecs require a different intake, more expense. Swapping pistons from dish to flattops will give a nice bump in compression, making a larger cam happier. At the same time your cam selection can't have more lift than your heads can handle. Swapping to the 454 TBI is a good way to feed it more fuel/air but I think you're still going to be limited to a relatively mild truck/rv cam, too much overlap and the ecm will pitch a fit. Some of the worst sounding, popping, backfiring engines I've heard were from a person trying to run a cam too big for the compression stock pistons/heads can make. All they really wanted was that lopey sound but had no performance gains worth mentioning.

Not to mention needing higher valve seat pressure with a bigger cam meaning new springs as well. Yes you can shim springs to get more seat pressure but not an ideal way to go.

 

[4WDKC]

www.gearhead-efi.com if you want to learn how to tune the ecm yourself. But in all reality your still looking $100 cam, $100 gaskets, $150 ish tuning software. Tuning will depend on you to do some of the leg work as mail oder tunes usually leave alot room for improvement on these ecms. Heads are $600+ (new), gaskets, $150-$300 ish for intake.

 

[Honky Kong jr]

www.gearhead-efi.com if you want to learn how to tune the ecm yourself. But in all reality your still looking $100 cam, $100 gaskets, $150 ish tuning software. Tuning will depend on you to do some of the leg work as mail oder tunes usually leave alot room for improvement on these ecms. Heads are $600+ (new), gaskets, $150-$300 ish for intake.

A set of 4.10s and done lol way cheaper
Gearing the best band aid for lack of HP