I'd guess this has been covered before but here goes.

90-91 LB9 TPI. I've fought this TPI system for a year now and I'm done with it. Just runs like Sh%^ most of the time. I've tested or changed the entire system and can find nothing wrong, all injectors are new all fuel pressures in spec. All sensors test good, No PCM codes, no vacuum leaks. Compression is 155 psi on all cylinders. Replaced Distributor and electronics, new PCM. It just studders and craps out unless its at wide open throttle. Its probably some wire someplace that's intermittent but I can't find it. This engine was transplanted into a 82 truck so the wiring is not the best job. (I didn't do it). It does run a bit better when it cold outside but even on 100+ degree days the water temp is always 180.

So, what is involved in replacing the TPI with a carb. I have a good 600cfm Holly but are the heads different on a TPI system or can I use any 'ol SBC intake manifold. Do I need to replace the Distributor & electronics to something else? HEI? Thoughts? Ideas? If I pull it apart I plan on installing a mild cam at the same time. Any gotya's in doing that? It has full length headers already.

It's just too undependable and in the end from what has been spent already going to a carb will be much cheaper. Look for a TPI system on Ebay..........

BTW its a 90-91 LB9 w/auto (700R4 I think, I'll have to look again to be shure)

Thanks
Doug

 

What intake manifold(S)year range will bolt up to the LB9 (305) TPI heads? I know I'll need an HEI ignition. Will I need a Torque Converter lock up switch, not sure on the 700R4. I know I'll need to change fuel pumps or get a regulator that has a return port. Throttle and Trans cable brackets? what will I need?. Does the LB9 have a Roller cam from the factory? If its a flat tappet I may change the cam to an RV cam but roller cams are too much $$$$

I'm not building a hot rod. I just want to dump the TPI and go to a carb for the least I can spend. I already have a good 600 Holly so that saves a few hundred.

I figured there would be lots of post or web sites about this but I can't find much on the LB9 engine. I know,Iknow put in a 350 but I don't have the money and just want to get it running descent.

Thanks
doug

 

Intake: any SBC will fit, 86+ have the center bolt holes the proper angle, older ones must be slotted with a drill

Lock up: yes, you'll need a vacuum lock-up switch. Emulate any carb car/truck that used a 700R4 or get a BTO kit

Fuel pump: Recommended to swap to a TBI pump or carb sender with no pump. Regulators can usually drop the 43psi down to the <10psi the carb wants, but the pump wont last as long as it should

Cable brackets: generic carb stuff from any parts place. Use TBI stuff if you're on a super tight budget

Cam: its a roller, price out a LSx stick before you complain about a $150 SBC roller cam

Same basic swap as any TPI, dont see the need to document every little engine, esp the ones no one cares about. If you're on a super tight budget, go find an 86-87 carb car in a JY and grab all the parts listed from it

 

Pocket, thanks a bunch. Since I have a good 600cfm Holly I'll use that. The intake is good news since their cheap. I think one of the summit HEI distributors will work fine with vacuum advance and they don't cost too much. I thought all the roller cams were $300-500 so its good news I can get one a bit cheaper, I'll need new lifters too. Which LXs would recommend? I'm not building a hot rod so something thats good from idle to 4500-5000 rpm with the best torque at around 2000-3000. don't care if it has loping idle a bit. As I said it already has long tube headers and No CATS. It would be great if I could get 225-275 HP out of it. Heads and bottom end seem ok with 150psi per cylinder

What is carb sender with no pump? right now I have an external fuel pump. I can easily replace that with a electric pump for carbs but what do I do with the return fuel line? Thought I needed a regulator that has a return port.

What is a BTO kit? sorry I don't know too much about auto tranny's. Am I correct that the PCM does not control the 700R4. guess I don't understand the TC lock up stuff.

Anyway you've been a great help, Thank you
Doug

 

i think he meant that lsx cams are alot more expensive. roller cams can be reused so look up an lt1 cam. fairly cheap and may be good for you. someone wanna chime in on if its a good idea or not? also search it. there is a s**tload of threads on the lt1 cam.

 

The comment was because LSx cam are ridiculously expensive for no apparent reason. A mild build on a budget points directly to the LT1 cam. Grab a used set of lifters too, make ok power for under $100

The fuel sender is the part attached to the top of your tank that the pump and fuel level float hang from. If your truck was originally carbed then dont worry about it, just swap out the inline pump for one carb friendly

Bow tie overdrives. They deal with alot of the old trans types like 700R4s and retrofitting them in places they werent stock. You want some sort of lock-up controller for your converter when driving on the highway. 700R4rs are partially electronically controlled, so you need to emulate the original functions. Unfortunately most of the carb cars were computer controlled, so the top gear switch was built into the ECM. EFI cars relied on the VSS to tell speed and high gear. Aftermarket kits are generally a vacuum switch and relay to tell high gear and commend lock-up. The trans itself is no electronic using a TV cable to control pressure for shifting. Lock-up is 100% electronic

 

Sorry I haven't done much engine work in many years so I'm not up on the mods lately. I've done a lot of research last weekend and I think I have a good grip on it now. The Truck has a EFI external fuel pump so it's easy to change to a carb friendly one. I saw lots of kits to take care of the TCC lockup. If I find a good used roller cam I'll try it but I think I'll just leave it alone. I read your comment about the LSx cam the wrong way, yes they cost $$$$.

Thanks for pointing me in the right direction
Doug

 

does the truck have a VSS and functioning park/neutral switch?

 

hey, I was just catching up on tgo and came across your thread. I am also in the process of installing a 90 350tpi. I was just wondering, did you switch out your fuel pump? My understanding is that the tpi needs the pump that supplies up to 50psi.

 

Well I'm going the other way TPI to carb. But yes you'll need a fuel pump that supplies 50-60 psi. The regulator reduces it to ~45psi. I'm not using the in-tank pump

 

OK, what is a TPI system worth? I'll have the TPI system,Upper & lower Intake manifold, all sensors that I have (most New). Injectors are new from Southbay Bosh III 19lbs. Distributor with new module & plug wires. New computer with Superchips ROM. Rebuilt fuel regulator. 60-70 PSI external fuel pump. Stock Roller CAM, Lifters & Pushrods, Timing set. All is off 1991 IROC - Formula LB9 305
wiring harness is extra ( I really don't want to remove it)

I just want to change to a carb setup. *NEW* = new in the last 500 miles

Thanks
Doug