Originally Posted by 1BADCK
hi guys, i have a 1995 gmc seirra with the tbi l05 engine and a 4l60e trans i think. its time for a new motor and i was wondering what my options are as far as a motor swap goes be it keeping the tbi are going carberated. i am looking to make around 350 horse at the flywheel. any info greatly appreciated. thanks zane
This is easy to do and keep the TBI which is a lot simpler than getting into fuel injection changes or conversion to a carb. The first going to a TPI system for example, while these systems offer some real horsepower they also offer some new adventures in systems design that can get really expensive if you not a do-it-yourself systems guy. Going to a carb is simple till you realize the instruments in the dash and the tranny run off the computer and the engine's sensors, while there's ways around that, none of it's cheap nor simple.
The 95 is fighting two really big anti-power issues and none of them is particularly the TBI. These issues are the cam which is somewhere beyond mild and the heads which are swirl ports. You will also want headers and duals even it means twin cats if you need to get past a SMOG check.
For a cam, you can go to the Edlebrock 3702 flat tappet with 194 degrees and .398 lift on the intake and 214 degrees and .442 lift on the exhaust measured from .050 inch lift with a 1.5 rocker. This does not require a new chip, but I think with all the changes I'll propose a new chip would optimize them for best performance. The 3702 cam is not too far timing wise from the old 300 horse 327 cam and is a considerable improvement over that thing GM laughingly refers to as a cam in the TBI engines which has about 30-40 degrees less duration. The exhaust on the 3702 holds open longer than the old ....929, 327 cam to accommodate the impact of catalytic converters in the exhaust system. The 327 also ran 10.5 compression which on today's gasoline there's no way to get to, but there are modern heads that make for that, getting more power on lower octane.
For a head selection the original Vortec is a good and inexpensive choice as these things go. If you use the Edlebrock 3702 cam, n o changes need be made to the Vortec head to force it to accommodate greater lift and better springs than it comes with. You'll need a TBI to Vortec intake which GMPP and Edlebrock both come to your rescue. The Vortec head is a solid 20-40-60 horsepower increase depending on the cam and compression. Mild cam and compression picks up 20 so that's about what you'd see just strapping them on your existing engine. With the 300 horse style cam and running the compression up around 9.5 you'd see about a 40 hp increase, which is where your engine would be headed with my recommendations. With a wild cam and another point of compression you'd see a peak of 60 ponies, but you've got to rev higher and give up some bottom end torque to get it, not to mention that now the existing TBI is out to lunch without a bigger TBI and new chip. The Vortec heads and intake have no exhaust heat crossover which if you lived north of the Mason/Dixon would require you figure out how to heat the mixture in winter. But the problem you will ihave s an EGR exhaust source. Both the GMPP and Edlebrock intake has a place to mount the EGR but the source of gasses has to be plumbed externally. Just weld a bung in a header tube to accept a fitting. Then connect that fitting to the one on the intake with a length of tube.
Piston selection plays into what you can get out of the head. You want to select a D shaped dished piston. The dish is sized/selected to control overall compression ratio. The flat portion opposite the dish closes very closely to the head's squish/quench deck which makes a very energetic mixture that burns fast and clean, which lets the engine tolerate compression around 9.2 to 9.5 without detonation problems. While I think this is more fitting for 92 to 94 octane unleaded, depending on which you can get. There are people who run these things on 87 or 89 and claim good results.
Getting to the exhaust, this needs long tube headers and duals with a cross over. This perhaps doesn't add that much power but preserves more of what the engine makes. Even if you have to put cats on it, just move them up to the end of the collector to keep them comfortably hot, put an H crossover from collector to collector and mount the O2 sensor in the crossover so it will see an average of what's coming out of the engine. I'd come down to a 2.5 or 2.25 inch pipe off the cats, run that to a decent pair of mufflers and go out back with a 2.25 to 2.125 tail pipe. I'm trying to choke the engine a little on any one side a little so the engine is forced to pump a little exhaust thru the crossover to expose the O2 sensor to a real mix of exhaust. Do this even if you don't run cats. In that case move the cross-over off the collector to the head pipe but keep the O2 sensor in the cross-over pipe.
If you just have to have more CFM there's a couple ways to go, one is an open spacer under the existing TBI, this lets both sides feed off the total volume. An injected engine doesn not have the same negatives that doing this to a carbed engine has since there is no signal on the venturis to screw up. Another way to go is a bigger TBI, Holley or the 454 engine with TBI are sources of a 670 CFM monster, but this will require a chip change to correct the fueling.
An outfit that did a lot with performance TBI especially for trucks is TPIS, there on the web, these guys can aim you exactly where to go with parts and have done a lot of camshaft research with these engines and have some hot stuff. http://www.tpis.com/index.php?module=chip
You can always build a stroker with all this stuff strapped on top. But there's no reason why you can't build a TBI 350 engine into the range of 320-350 or more horsepower and still have a civil engine.