TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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I bought a Formula a while back as a weekend cruiser. First 3rd gen and first time working with TPI. I was looking into buying a plenum and aftermarket throttle body and doing some machine work on the plenum. I was also looking at some SLP runners and doing the same with them as well. It's the original engine and only has 67k on it so I don't want to do anything to it I can't easily put back to stock later on down the road. How well do these motors respond these kinds of modifications? Any snags to watch out for? I'm a machinist and welder in the Air Force so I plan on doing the work myself. Any good combos or bolt ons anyone can recommend?
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I've got the LB9 aswell. First thing i did was full exhaust (check vBgarage for full details)...I know it helped alot, doesn't pull down nearly as bad starting out in first. Im also getting a custom chip burnt here pretty quick, should add a few ponies.
Next thing is intake, hsr perhaps? vette 113 heads?
As with any engine; improve its efficency, get it running as good as it did from the factory and it'll probably wake up a fair amount. My car was very neglected (sparkplugs hadnt been changed in 10yrs, vac lines were cracked). So, replace all of your vac lines, the O2 sensor, Plugs, wires, cap and rotor (brass terminals on the cap), EGR and if youre dismantling the intake, the IAT is probably a good bet as well since youre in the neighborhood. I also replaced my valve cover gaskets and my catalytic converter. Car seemed to wake right up after that honestly. Oh I changed the fuel filter and added a bottle of injector cleaner to the tank. Lots of people have suggested Seafoam engine treatment...just make sure you point it downrange when you fire that car up, it makes a helluva smokescreen.
Oh if youre a fabricator in the airforce (thanks for your service) you could probably buy a bunch of J bends and weld up your own smooth factory style exhaust system. Mine came with a mandrel cat-back (with a flowbastid knockoff which I swapped for an aerochamber muffler).
good luck
Nate
you may want to look in to the restore stuff you put in the motor oil i put it in my 87 LB9 trans am it has more power and revs faster
98% of the oil miracle restore is just that.. Basically it is just an oil stabilzer it won't last and it's just a quick fix to an old problem. ... Unfortunetly, if you want more HP, it will starting costing you $$$.. From mild to wild.. Price goes up
i agree with nate get all the basics done first. plugs, wires, rotor, cap, and O2. then go with the exhaust.
If you're doing all the work; port work always will wake it up. when i put on my AS&M runner i ported the plenum and lower base to match. i didn't get track times but the seat-of -the-pants feel gave me a good kick in the but. oh and a fuel pressure reg is good to have to.
When I got the car, I went through and gave it a full tuneup. I also installed an adjustable Holley fuel pressure regulator. It already had replacement exhaust from the manifold back, but those log style exhaust manifolds look fairly restrictive.
First, a tune up with K&N air filter and check and replace any worn sensors (MAF, MAP, TIPS, ICM, EGR, etc.) and an oil change at this time with synthetic oil. You could consider a better distributor, coil and spark plug wires at this time if they are worn. Second, exhaust upgrades (ie headers and bigger and freer flowing exhaust). Third, a camshaft. Fourth, upgrade fuel induction (new injectors, adjustable fuel pressure regulator, throttle body coolant bypass, cooler thermostat and porting work. You do not need a bigger throttle body.) Fifth, new heads preferably done with fourth step. Sixth, new PROM chip.
The Mass Air Flow Sensor (MAF) TPI set ups respond very well to modifications. The Manifold Air Pressure (MAP) TPI set ups starting in 1990 are a little less responsive to modifications.
Last edited by BC GTA; 04-15-2009 at 04:05 PM.
Reason: throttle body coolant bypass, cooler thermostat
What about SLP runners and plenum with siamesed ports along with an aftermarket manifold? I looked at some Pacesetter headers, they look fairly easy to install assuming I don't bust a bolt . At some point I'd like to look into some aluminum L98 heads with roller rockers and aftermarket cam. I'm fairly new to TPI so I'm not 100% sure what combos work best. Luckily it's the high output 305 so it's fairly quick as it is. I replaced the MAF when it took a dump on me. The first thing I did when I bought it was go over everything, but it's in like new condition under the hood with no leaks anywhere. I run Mobil 1 synthetic in all my cars so that was one of the first things I did along with new plugs, distributor cap, wires, etc.
Well I would start by getting some hooker 2055 headers and y-pipe to start off. The stock plenum/runners flow more than enough for a stock 305. After headers I would look into cam/lifter kits, just make sure you ugrade your valve springs as well. Roller rockers wont hurt either. After the cam have somewhere like PCM4Less burn a chip to your cam specs etc etc. If your going to spend your time porting something, port the heads.
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1987 Sport Coupe, 2.8 MPFI, 700-R4, 3.42's, 50,000 Original Miles. Parting Out!!!
1989 IROC-Z, 355 TPI, RHS Pro-Torker's, COMP XE-256, 700-R4, Soon To Be Zexel-Torsen With 3.42's.
i agree with nate get all the basics done first. plugs, wires, rotor, cap, and O2. then go with the exhaust. 
. At some point I'd like to look into some aluminum L98 heads with roller rockers and aftermarket cam. I'm fairly new to TPI so I'm not 100% sure what combos work best. Luckily it's the high output 305 so it's fairly quick as it is. I replaced the MAF when it took a dump on me. The first thing I did when I bought it was go over everything, but it's in like new condition under the hood with no leaks anywhere. I run Mobil 1 synthetic in all my cars so that was one of the first things I did along with new plugs, distributor cap, wires, etc. 
