Originally Posted by Hittman
Wondering if some of yall could help me out. I have heard that if you have a TBI 350 that you can install a HEI distributor to get more power and make it run better. Need some input on the wireing and what to do. I have a HEI distributor but no sure what needs to be done or if its better. Thanks
The answer here would be no. The modern era of automobiles including pickup trucks starts about 1986 with the introduction of what's called On Board Diagnostics I or (OBD I). This is a Systems Engineering approach to the dual requirements of lower emissions and increasing fuel efficiency. This is unlike the patchwork gadget add-on approach of the late 1960's up to the mid 1980's. OBD I starts down this road of everything under digital management by a computer, this includes your 1989's speedometer which looks for all the world to be an old fashion cable driven mechanical (analog) speedo. It isn't what it appears to be it is in fact a digital unit that uses a Digital to Analog (D to A or D/A) converter to drive the needle. The connection to the transmission is a wire bundle not a rotating cable in a jacket.
The distributor receives its base timing position from the computer, as it does for the advance curve. Unlike the mechanical/vacuum distributor that has one mechanical curve and one vacuum curve built in that is dependent upon RPMs and manifold vacuum thus having no adjustment for what would be the best curve for how hard the engine is working and in which transmission gear. The digital system is reading engine power demand and torque loading on the output shaft to pick an advance setting for the ignition as well as fuel flow for the injectors based upon the power demand. Further the ignition system is listening for detonation or preignition with a sensor that will reduce the timing advance just enough to prevent these events from damaging the engine. In this age of hyper-eutectic pistons and very edgy cooling capacity this is vitally important to prevent costly damage to the engine and transmission.
As time has come forward the Rocket Science of Systems Integration has hugely increased with the advanced system adaption industry wide in 1996 with OBD II and we are now moving beyond this to higher levels of complexity. Going, going, gone are the days of the shade tree mechanic. These modern vehicles require mechanic's with at least a 2 year automotive technology degree and many dealer shops keep a graduate engineer in automotive systems either on staff or on call. These highly integrated systems are how modern cars are delivering 30 miles to the gallon and 300 or more horsepower. Where today's lowly V6 Mustang will have the original "Bullet" 390 FE block Mustang for lunch any day of the week and twice on Sunday.
The news isn't all bad for OBD I truck owners, there's power to mined from a TBI, Swirl Port 350 if you know where to hunt. Setting aside your 350 since 1989 is getting rather old and may need a major overhaul to restore it even to its original power output; there are things that can be done to really wake this motor up. The two big power limiters to this engine are the camshaft and the cylinder heads.
The original camshaft has barely 170 degrees of duration and less than .4 inch lift at the valve. While TBI likes a lot of manifold vacuum which a short cam supplies, this can be pushed a good 20-30 degrees without getting into serious reprogramming of the computer chip. Edlebrock sells a cam part number 3207 made specifically for TBI engines ahttp://www.edelbrock.com/automotive_new/mc/camshafts/locator.php?part_number=3702&submit=go
The timing and lift on this cam are pretty close to the old Chevy "929" cam of the 300 horse 327. So it's a pretty big wake up call to your OEM 207 hp, 350.
Now you’re not going to get 300 hoses out of the TBI 350 because the Swirl Port heads and the fueling capacity of the TBI wound permit that much. The Swirl Port head is a huge limiting factor, the swirl vane adjacent to the valve guide boss limits flow to a peak RPM of about 4500. The solutions vary from porting the vane out of the existing heads or getting a set these passenger car heads you would need part number 10125377 to use your existing intake with the 72 degree bolt angle to the heads. The p/n 10125377 head can be made from castings 14096217 or 14101083 but these also make a head with the pre 1986 bolt angle of 90 degrees (p/n 10159552) to the head these would not fit your intake without a substantial modification to the existing bolt hole angle in the manifold and having to either re-spot face the bolt-head pad or making an angle adapter so the bolt-head lies flush to the surface its clamping. These heads are a cast iron version of the aluminum Corvette L98 head; these should take the engine to 250 with the Edlebrock cam. The L31 Vortec head of 1996 and up really wakes this engine up with a 20-30 hp gain over the L98 style head landing about 270 to 280 hp. This is the outside limit of your TBI to crack 300 horses’ takes a 670 cfm TBI with 88 pound injectors and reprogramming the computer with a new chip.
Installation of the 3207 cam and a set of cast iron L98 heads can be accommodated by installing an adjustable pressure regulator to the TBI you have. This isn't as clean as a new chip and won't get you past an emissions test if that's a requirement, but it'll be pretty good certainly comparable to a carburetor in accuracy.