O.E. 5.7 Vortec CPI intake with 16197427 PCM ?

[pmkls1]

Well, as with many projects, this project MAY not progress any further I'm afraid. I just bought a '99 GMC Sierra 1500 this evening and am undecided as to which vehicle will stay and which will go. I picked the truck up with some minor body damage and moderate rust damage for a paltry $800. It actually runs and drives and I have yet to discover any abnormal mechanical issues. I am going to perform a thorough inspection tomorrow and determine the overall condition and viability of it being a daily driver. As long as it appears that the rust is repairable and no major mechanical issues exist I'll keep the truck and sell the firebird and my hoard of parts. If not, then I'm going to part out the truck and scrap it. Either way, the reason for buying the truck was to make a little money. If I end up selling the car, the project may not be completely dead as I would need to get it back running and driving again to sell it for a decent price. I still think the fastest way to get it running decent is utilizing the factory intake so I may still at least put the car together and tune it well enough to sell. If so, I would still be able to gather some info about how well using the combination works as it seems it may be a first.

[pmkls1]

Sounds like the biggest issue is the stock exhaust manifolds, followed by the factory L31 cam. Neither allow you to make over about 270-300 HP. The peformer rpm and 670 CFM TBI are good to ~6,000 rpm and well over 400 HP if you have the fuel to match.

The 91 Formula I am working on has "810" TBI heads on a Vortec 350 short block and a stock L98/9C1 cam. Even with the OEM intake manifold, oem 305 TBI, and factory dinky exhaust manifolds it does not fall off until around ~5,500.

Yes, the exhaust manifolds are a big cork even on the stock 305. There are also some different exhaust manifolds for the 3rd gen F-bodies. The low output engines like the LG4 and the L03 only have 2" outlets, but the TPI engines and possibly the L69 had larger outlets at 2 1/4" IIRC. I may be wrong about the size of the outlets on the performance versions, but they are indeed larger. Even having the larger oem exhaust manifolds on my car would help out with the breathing. That is all besides the point though as I was just saying that I didn't expect or need that many RPM's out of the engine for now. Like I said, with the fairly tall gearing I can have plenty of fun in the low to mid RPM range with the torque of the vortec in a "light" vehicle like my car. The hot rod stuff was always intended for the next engine as this was meant to be a semi-temporary setup just to replace the original 305 that was on it's last leg. I have spent far more money on making the engine work in the car than I did on the engine itself. The engine was a core out of a truck that we put a brand new crate motor in and the core charge on a NEW L31 is $100. A reman engine has a way higher core charge than that, but since GM is still making brand new L31 motors they have no major need for old blown up cores. Anyway, I am just rambling on now and I have to get to inspecting my truck so I can decide which vehicle goes and which one stays. I love my firebird and have owned at least a half dozen of them, but money talks and especially so for someone that is unemployed and considering disability like myself.

[Hog]

I think you are correct about the 2 1/4" exhaust manifolds for the TPI/IROC-Z manifolds.

peace
Hog

[Fast355]

Yes, the exhaust manifolds are a big cork even on the stock 305. There are also some different exhaust manifolds for the 3rd gen F-bodies. The low output engines like the LG4 and the L03 only have 2" outlets, but the TPI engines and possibly the L69 had larger outlets at 2 1/4" IIRC. I may be wrong about the size of the outlets on the performance versions, but they are indeed larger. Even having the larger oem exhaust manifolds on my car would help out with the breathing. That is all besides the point though as I was just saying that I didn't expect or need that many RPM's out of the engine for now. Like I said, with the fairly tall gearing I can have plenty of fun in the low to mid RPM range with the torque of the vortec in a "light" vehicle like my car. The hot rod stuff was always intended for the next engine as this was meant to be a semi-temporary setup just to replace the original 305 that was on it's last leg. I have spent far more money on making the engine work in the car than I did on the engine itself. The engine was a core out of a truck that we put a brand new crate motor in and the core charge on a NEW L31 is $100. A reman engine has a way higher core charge than that, but since GM is still making brand new L31 motors they have no major need for old blown up cores. Anyway, I am just rambling on now and I have to get to inspecting my truck so I can decide which vehicle goes and which one stays. I love my firebird and have owned at least a half dozen of them, but money talks and especially so for someone that is unemployed and considering disability like myself.

Understandable, just hated to see you put a ton of money into something that is only marginally better.

The LG4, L03, LB9 single cat engines all used the 2.0" manifolds. The L69, LB9 dual cat, and L98 cars used the 2.25" manifolds. The Y is even more horrible than the manifolds.

[pmkls1]

Well, I guess that if I didn't have as many problems with my particular configuration then the improvement would only be marginal if any. But, I have had nothing but trouble with the car ever since swapping in the engine and some of that is due to something I did long before that. Shortly after I got the car I replaced the fuel pump with a Walbro 255lph high pressure model anticipating a swap to mpfi. Since this was my first TBI vehicle I didn't realize that the flow and pressure capabilities of the fuel pump would be too much for the TBI unit to handle. No matter what I did with an OE style regulator I was unable to get the pressure below 20psi at idle. I went to an OE style billet housing and set it up with a manifold vacuum reference and set the base pressure to 30psi. At idle and high vacuum conditions the pressure would drop down to arount 22psi. I had intended to and did begin running E85 as soon as I was comfortable with the car. Since I was using E85 I never had many issues with the fuel pressures I was running due to the increase in fuel demand. Once I swapped in the vortec things went south because I wasn't going to run E85 until I had gotten the tuning right with gas first. Needless to say I was never able to get the tuning right and had also suspected many components were bad so I did the ECM swap and replaced any suspect components. And that leads up to the present where I still have problems with drastic rich to lean swings under part throttle cruising causing lean surges and such. I am so tired of messing with the TBI setup I was ready to just throw an OE intake on it to get the car to drive normal again.

That being said, I only spent $40 on an entire intake setup with throttle body, sensors, pigtails, etc at the junkyard. Even if I need to replace some sensors the cost will be negligible unless I have to buy a new injector spider which is still not bad at ~$230 from amazon. I could easily spend that much on injectors or a throttle body on the TBI setup so compared to the $60 it cost me to replace the spark plugs every few months because of the damage that the rich and lean conditions were causing I am really not spending much on it. Like I said, performance wasn't my goal, driveability was. And the car has hardly been driveable since last spring so I was willing to do just about anything to make it run right. I know how stock Vortecs are supposed to run and the one in my car hasn't come close ever since I put it in the car. Just FYI since you aren't familiar with my ongoing plight, even though this was a core engine I put it on a stand and replaced the heads, inspected the entire engine internally, replaced the oil pump with a high volume pump, replaced the oil pan with an 8qt pan, replaced the timing chain with a heavy duty single roller piece, and installed all new GM gaskets including the rear main and valve stem seals. So, I know that I started with a good engine and the only components that are suspect are the lifters which I am in the process of replacing due to some bleed down issues. I also had to do away with the factory Y due to the oil pan. The front section of the exhaust is fabricated from 2 1/4" pipe that is routed in a similar way to the Y on an LT1 car and it connects to a typical 3" intermediate pipe that runs to a Flowmaster that has a single 3" inlet and dual 2 1/2" outlets. I personally fabricated the entire exhaust system except for the intermediate pipe. So, the manifolds are the biggest restriction because even the custom 2 1/4" Y isn't that restrictive.

[pmkls1]

Now for the bad news. I have decided to keep my new truck so that means that I will be selling my firebird and my collection of parts. That doesn't mean that the project is completely dead though. I am going to keep the parts that I need to install a V8 into the S10 and I intent to use a vortec 350 with the OE intake and a 427 PCM. I don't know how long it will take to continue the project though because I am going to rebuild one of my engines before installing it. So, bottom line is that the project will continue but it may be a while before it does. So, we will still see how things work out but it may be a while before that happens.