Alright, I have tried searching, but didnt find anyone with a similar situation to my own. I have a 1991 Trans Am GTA, LB9 305 TPI Speed Density car. I am planning on upgrading to a 350 L98. I have found one for sale locally but it is a 1989 L98. Now, since my car is a speed density setup, and the motor I wanna buy is a MAF setup, I am gonna have to choose one or the other. I would just swap out all my TPI stuff onto the long block of the new motor, but this motor comes with a fully ported intake setup and has Edelbrock runners, 24lb/hr injectors, BBK throttle body blah blah blah. So I want to keep the TPI parts really. Is there anything I can do to keep my speed density setup but still use the ported TPI parts? Or am I going to have to swap EVERYTHING including the harness, ECM etc to the MAF setup (the motor I am buying does not come with this stuff so I will have to buy it separately).

Option 2, are the Edelbrock runners for an 89 MAF setup the same as the 90-92 SD setup? If so I could at least keep those and maybe port the plenum myself, and pickup an aftermarket base somewhere. Also, would the injectors swap over too? I have read that the '89 MAF cars did not have a cold start injector in the TPI setup.

 

im facing this same issue right now due to i bought a basket case 92 trans am. But from what im gathering 89 was only year that you can use parts from on a SD car like runners and lower manifold. the upper plenum is special to the SD cars due to have a special vacuum port layout on the rear passenger side for the MAP sensor.

you should be able to just swap out the MAF plenum to the SD plenum and then go get a chip for a l98 SD and should be all set

ALSO! you need the MAP L98 KNOCK sensor! it isnt the same as the maf.....least this is what a handful of people have told me so far.

 

That would be awesome actually, because the plenum is probably the easiest item to port as far as matching it up to the Edelbrock runners. Replacing the knock sensor, I can also live with, same with the PROM (I knew I'd need that anyways). Thanks for your input.

 

id switch to MAF, better for prom tuning anyway IMO, faster response time and atleast theres an abundance of parts.

Plus that motor is already pretty built as is
but thats just me lol

 

i think that you could just swap upper pleneums

have you bought the motor already

if so just take both pleneums off and compare

 

Nope I havent bought the motor yet. Waiting for payday :P

 

Shift06: I think that there is not much to be concerned about. Your computer is a speed density computer. The major difference in electronics is the MAP vs MAF sensor. Simply install the MAP sensor from your 305 engine onto the 350 engine (or reuse the top plenum from your 305 setup which should contain the MAP sensor).

Buy & install in the computer an aftermarket Eprom chip for a '91 or '92 350 speed density car. You need this new Eprom chip mainly because of the fuel injector size, even though its probably for 22#/hr injectors, not the 24s.

And you might have to replace the knock sensor. Check with a Chevy dealer or part store for part numbers; see if they are the same or not.

Also, while you are at it. Install an AFPR (adjustable fuel pressure regulator). This will give you a little bit of tuning capability.

 

I'd keep the speed density and swap the rest. You will need to use your plenum though as well as have a custom chip burned for the engine, injectors, mods, etc. Should be a fairly straight forward swap. Neither setups have a cold start injector. 89-92 TB's are the same so your cable should connect. Good luck!

 

Lb9 and L98 tpi engines use the same base, runners and plenum stock. You can swap all of your tpi parts from the Lb9 to the L98. The L98 will use 22 lb injectors, while the Lb9 uses 19 lb injectors. The ecm doesn't know what the engine size or injector size is unless you burn a new chip to tell it. If you put the 22 lb injectors in with the L98, it may be pretty close, since the injectors are sized to the engine and the injector setting for 19 lb injectors in a 305 may be close to the settings for 22 lb injectors in a 350. Make sure you use the knock sensor out of the 350 with the 350. The knock sensors for 305 and 350 engines will not interchange.

 

Thanks guys.

@ doc,

The motor comes with an AFPR already installed, plus I have a NIB BBK unit I never got around to putting onto my 305.