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94 TBI 350 with a rod knock Refresh time

tanman_2006

tanman_2006

Just a farm kid...
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Seiling, Oklahoma
Ok so my little flatbed step child has decided to try the life of a comedian by way of knock knock jokes.

It has a pretty good case of a rod knock on the passenger side. I have a 1990 Tbi 350 with a little over 200k on it that I bought as a parts truck on the same deal as the 94 c3500 came in.

What should I do to freshen up the other motor while I have it out and am swapping them?
 
If the other engine is out of a 1500 or light duty 2500, it is actually a different engine. It will work, but it has higher compression, slightly different heads, and will be a 2 bolt main VS the 4 bolt main that 8600 GVWR and over got. As to freshening it up, replace the pan gasket, put a rear main seal in it, I would yank the heads and do a valve job and update the valve stem seals to the 1 piece PC seals instead of the stock umbrellas, put a balancer on it, and make sure and replace the TBI base gasket. Check the timing chain, but the stock chain in them was pretty sturdy(they get loose and noisy, but I haven't heard of one failing). The rest is just basic maintence. And if it came out of a 1500 or 2500 light duty, you will also have to swap the TBI unit, EGR valve, EST module, knock sensor, and EGR solenoid. Theres quite a few differences between the 8500 and under GVWR, and 8600 and over GVWR engines. They're subtle, but there none the less.
 
I will be using my 8600 gvwr heads, intake, and Tbi. Didn't realize there were that many differences. Guess I better keep my old engine and rebuild it since it should be a 4 bolt main.
 
So I assume the heads off my C3500 will be a different compression ratio than the k1500 heads. Or is it in the pistons?

I don't tow with the truck much so it's not a big concern, it's mostly just loaded with tools and drive point A-B.
 
The difference is in the pistons. The heads have different valves and exhaust seats in the 8600 gvwr +. 8500 and down is supposed to be2 bolt main while 8600+ is 4 bolt main. That said, my neighbor just had a 2 bolt main 8500 and under long block put in his 88 R30 because GM discontinued the 8600+ 4 bolt main version. He reused his intake, tbi, and egr system. It runs pretty good, actually has some good kick to it as they rated them all at 210hp, but the 8600+ did it with 8.8:1 cr while the 8500- did it with 9.3:1 cr. You can tell the egr system isn't spot on with the compression ratio change, but overall it runs real nice. He tows on flat land and isn't in a hurry, so that's why he opted for the 8500- engine since the 4 bolt main was no longer available.
 
I found one of my half ton heads had a spark plug cross threaded in while I was compression testing. This is where the head question stems from.

I have also considered dropping a 454 with matching Tbi and prom if I find one for the right price. A 454 would probably be better for what I might end up doing with the truck
 
Since you already have a high pressure pump, that's an option. You would have to add in a knock sensor to the drivers side as the 4.3l and 7.4l in 94-95 used 2 knock sensors. If you found one from a 93 or older, then I believe it only used 1 knock sensor. Only problem is I believe 94-95 used a different ecm than 93 unless it came with a 4l80e. GM was funky in there ECM choices from year to year, and in many cases they used 2 or 3 different elECM's in the same year depending on how it was equipped. The manual trans trucks seen the most variations.
 
Does the knock sensor run directly to the ecm? One wire and a pin doesn't sound that bad.

I know there were a couple variations of the 454. What is the best and what will make decent power?
 
For the knock sensor it can vary from year to year, and even depending on which trans you have. Some use the EST module, while the same exact year with an auto won't. For the most part by 93 GM had done away with the external EST, but with a manual trans some kept it until 95. For TBI engines they are all pretty much the same for power output from my understanding. They were all peanut port heads that flowed the worst of any stock from what I've read, and I believe they made very little more HP than a 5.7L did, but they did have more torque. I would probably go with a 93 or newer, but if it was mine, I'd keep the small block, build a 383, port the heads, port the intake, ultimate TBI mods, adjusteable fuel pressure regulator, set of headers, and call it a day. You could even buy a set of the hybrid vortec heads that use the 87-95 intake and slap on it. But that's me.
 
I thought you didn't like the TBI mods and bigger fuel pump with adjustable fpr?

I wanted to raise compression a bit in a 4 bolt main 383 with vortec heads and a a small cam that made good power 2000-3000 for towing.
 
tanman_2006 said:
I thought you didn't like the TBI mods and bigger fuel pump with adjustable fpr?

I wanted to raise compression a bit in a 4 bolt main 383 with vortec heads and a a small cam that made good power 2000-3000 for towing.
Click to expand...
I said I didn't like running the vortec pump, but instead the 94-95 454 pump. As to the adjusteable regulator, that is fine so long as you keep it within reason. Some factory regulators are adjusteable while others aren't. Theres nothing wrong with setting the pressure up to around 14, but much beyond that on the low pressure injectors has been proven to cause issues. And I've run the TBI mods on most of them I've built. It's running the 454 throttle body that can cause you alot of issues.

The VORTEC heads are counter productive to bottom end pulling power. The stock TBI swirl ports make more torque than most any other head in the 2000-3500 RPM range, almost competing with big block territory. There's a few cams out there you can run on a stock tuning TBI without to many issues, but they don't take well to bigger cams without tuning. And compression is a slippery slope. 10:1 is about as high as you want to go if you're going to work it hard. GM went for 9.4:1 for the vortec, and even for the 383 truck crate motors. Depending on your cam selection it can be fine, to low, or pushing it to high as you also have to look at dynamic compression ratio due to pumping losses from overlap and duration. The stock TBI 5.7L engine ran OK, but the few I've done all would surprise you at how strong they ran afterwards. They can make some SERIOUS off idle torque with proper head porting(and I'm not talking hog em out for flow, I'm talking proper improvements to let the swirl work).
 
Closer to 10:1 is all I'm looking for.

I see your point on the TBI heads, I just don't know where to send then to get good port work and not a full hogged out port job. If I tow it's usually in 4th with either 4:10's or 4.56's so 3000rpm is about the sweet spot
 
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