Snip by BadDog
Cool, your truck sounds like the perfect candidate for TPI. TPI is built for low end grunt, and is not built for high end horsepower at all. Infact, it'll run out of steam at 4800 rpm on a typical small block. However, the low end torque, and driveablity is unbeatable.
First question though, what are the specs on the cam in the 350? For your TPI to run well, you really need to make sure that your lobe seperation angle is at least 112 degrees or above. Anything less than that, and you'll run into some major idle issues. An LSA of even 110 degrees will allow enough valve overlap that the exhaust will have fresh air introduced into it, which will cause the 02 sensor to detect an extreme lean condition, and cause the ECM to run full enrichment in an attempt to compensate.
That is extremely tough on your engine, as it washes cylinder walls, causes fuel vapour blowby filling your oil with gasoline, and fouls everything with carbon.
Everything else should be pretty happy with the TPI. It'll provide a ton of grunt for towing, and playing on the rocks. It might suffer a bit in the mud, due to the lower red-line, but she'll have excellent street manners (no more cold start bogs, tough starting etc)
Ok, now that I've asked my question, here is a bit of a tutorial about the various sensors that are specific to this truck. We'll cover each of the various sensors / systems that require you to modify your truck, but stuff like the temperature, throttle position, manifold air temperature sensors, idle air controller, etc that are just plug and play, we'll leave alone.
1) 02 sensor -- Your 02 sensor is absolutely critical to the proper closed loop operation of your truck with TPI, but fortunately, its pretty easy to install. How it is installed depends on if you are running manifolds, or headers.
With headers, you'll need a heated 02 sensor that is installed in the collector down below the truck. Make sure you install it on the top of the collector, so you don't shear it off on a rock or something. The reason for a heated sensor is becuase they need to be made very hot before they will start sending data back to the ECM, and being in a header collector, the exhaust gasses have had the length of the whole header pipes to cool down already, which is more than enough to get the exhaust too cool to get the 02 sensor working.
With manifolds, there are two different options. First option is to install a set of EFI manifolds, which have the 02 sensor bung already cast and tapped in the collector. Second option is to buy a 02 sensor bung much like the one you'd use for headers, and install it an inch or two below the collector in your exhaust pipe. If you have manifolds, a heated 02 sensor is not a requirement, but can be desireable if you live in an area where it gets really cold in the winter, as it will get your truck into closed loop faster.
2) Knock sensor -- The knock sensor is used by the ECM to detect detonation. It is specifically tuned for the sound pinging, and when it is detected, the ECM will automatically retard the timing until it is no longer detected. The knock sensor is very easy to install. You simply need to use an impact wrench to remove the coolant drain plug on the driver's side of the block, which is located on a raised boss just above the oilpan, near the center of the engine block. You then apply a liberal amount of anti-seize onto the knock sensor, and thread it straight in.
3) Mass Air Flow Meter -- The MAF is used by the ECM to detect how much air is being consumed by the engine, so it is able to accurately determine how much fuel needs to be placed into the engine.
Becuase of the nature of the beast, a MAF is considered a far more leniant system when it comes to engine modifications. You'll be able to get away with a rough 10% change in your engine (who knows how that number is calculated, but thats the generally accepted percentage). Hooking it up can be a pain, but there are various different options available.
The trouble arises when you try and run stock ducting. The ducting runs basically straight into the battery on the passenger side of the truck, and is just a general pain in the butt. So, the various options include buying an LT1 cold air intake duct for a MAF system that runs to the driver's side, or building your own ducting out of 3" tubing of some sort, and just slapping a cone filter on the end.
However, no matter how you route it, you need to make sure that your MAF is going to be in a position where it isn't gonna be getting shaken around a bunch, or exposed to excessive dirt, mud, or any water. These three things will kill your MAF pretty quick, and those things are not cheap at all. They'll cost you a good 200 for a good new one.
Air ducting is often the sole reason for people switching to speed density -- It was definitely my reason!
4) Cold Start Injector -- This little guy is used as a bit of a makeshift choke. It is opened by a switch on the front of the TPI intake, and remains open until the coolant reaches a certain temperature. To hook it up, you simply need to introduce an ignition controlled 12 volt source to the system. It needs to be on both while the ignition is in the on position, and the crank position.
5) Vehicle Speed Sensor -- This sensor is often overlooked by guys installing EFI. They feel it is either too costly, or too difficult to install. However, that is not at all the case, esspecially in these trucks, and esspecially with MAF TPI. The newer 83ish through 86 trucks use an optical speed sensor that is bolted to the back of the speedometer to generate a 2000 pulse per mile VSS signal for their cruise control systems. If you take one of these speedometers, and install it in your 74 (will require modifications of the cluster housing, and you will have an orange ringed speedometer that only goes to 85 mph), then you have the exact signal that you need to feed to your ECM.
If you are like me, and wanted to retain the 100 mph, blue ringed speedometer, there are two possiblities.
First possiblity is to get the newer speedometer, swap the 100 mph speedometer faceplate onto it, and have it re-calibrated at a speedometer shop to read accurately on the new scale, or you can do what I did, and find a 100 mph speedometer that was shaped in such a way that I could retrofit the speedometer sensor onto the back of the 100 mph gauge. It required a hole cut in the back, the two magnetic plates painted chrome, and the cup painted black. You'll understand once you get it all apart.
6) Upper Rad Hose -- You'll soon find after getting your TPI that the stock thermostat housing is this tiny little thing that points straight forwards. What I did was find myself a thermostat housing off a 4.3, which had the perfect angle to aim the hose to the driver's side, and back just a touch. Mr. Gasket also carries a chrome version of this thermostat housing. I then found an early 80s Crossfire injected Camaro (dual throttle body injection) which had the perfect radiator hose. I hear some of the 3.1 powered buick cars also have a good rad hose to use as well. The hose sends the coolant way around past the fan, and looks real good.
7) Electric Fans -- If you are planning to run MAF, you have to install electric fans onto your truck. The ECM will control when they are turned on and off, so no worries there. Again, tons of options for fans. Either you can get a set from a early 90s Taurus with a 3.8 in it, a Windstar with the 4.x engine, or you can buy aftermarket, or even just do what I did, and get the two biggest fans you can get onto a single rad from the junkyard. I wound up using a fan from a 3.8 V6 Buick, and a fan from some tiny 3-4 cylinder mid 80s Chevy Nova. Between the two of them, the entire rad is covered less a half foot by one foot space down by the lower rad hose. The 3.8 fan is huge, and should be able to cool the engine fairly well, but I put the Nova fan on as a sort of a backup, which is controlled by a temp switch in my engine head.
and finally
8) Fuel system -- This is probally what you'll have the most difficulty with. You need to install an at least 50 psi fuel pump to feed your TPI engine properly. To do this, you've again got a few options.
First option is to install an inline fuel pump, and use the existing fuel tank. You'll want the inline fuel pump as close to the fuel tank, and as far below it as you can possibly get it. Inline pumps like to be gravity fed, and hate sucking on fuel, they do really well pushing it though. Doing it this way, you will require new hard line fuel lines, or high pressure fuel injection rubber hose and fittings, along with an in-line fuel pump after the pump, and before the fuel rail.
Second option is to replace your existing Blazer tank with an 87+ Blazer tank. It will then have an in-tank fuel pump, which you can replace with a TPI car in-tank pump, and use the fuel lines from the K5 for the TPI system. The TBI fuel lines are the same fitting as the TPI lines, so if you are able to extend them somehow, you can bolt the TBI fuel line system from the 87 Blazer straight to the TPI fuel rail, and just change the fuel pump. The existing TBI filter will work plenty fine
I personally took the second option for my TPI pickup, and I wouldn't look back. Far cleaner fuel line install, and the in-tank pump is very quiet compared to the inline pumps.
Now, this has just been a very quick run over what you'll need to do. Get yourself onto
www.thirdgen.org and do a bunch of reading there, those guys are experts on TPI, and if you don't mention that it is going into a truck, they are generally very helpful (lots of the guys there are purists, and don't like to see TPI slapped onto other vehicles, lol)
www.chevythunder.com is also a very good source of information, and will have pictures of most everything I described up above.
If you've got any other questions about specific components that you need to install, feel free to post here, or PM me, and I'll do my best to answer your question, I've got a ton of pictures from my TPI build. These projects require a lot of reasearch, and do take time. So don't give up, its well worth it in the end!
