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Old 06-20-2010, 06:15 AM
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What all can be done to chevy TBI engines to gain more power???

ok if you have 350 tbi engine, what can you do to it with out messing it up, if you put a cam in it you have to stay with one that will provide enuf vacume for the tbi?? or what about flat top pistons?? would this be beneficial?? anybody got anything on this, id like to hear it,,, thanxxx........

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Old 06-20-2010, 11:47 AM
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Here`s what I did to my 4.3 TBI. The list is long.
Block bored .030 Decked .010
Rotating assembly balanced.
Speed Pro Hyper 4 valve relief flat top pistons 1.560 comp height. .015 down in bore at TDC. Stock Rings. .030 thickness head gaskets, .045 Quench distance.
Stock Swirl port heads, 68cc chambers, clean up ported. Fearra 1.94 necked down valves, 30 degree back cut. Springs, locks, retainers to match cam.
Isky Hydraulic roller cam. Computer compatible. Duration @ .050 .204 In. .209 Ex. Lift: .450 In. .465 Ex. Milodon double roller timing set.
Comp Cams Magnum Push Rods. Crane replacement Roller tappets.
Comp Cams 1.6 ratio roller tip rockers.
Edelbrock performer TBI intake.
Stock throttle body, full ported. Fuel Pressure Bung, Adjustable fuel pressure regulator with vacuum compensator. TBI pod spacer.
Venom Injectors. K&N air filter.
MSD spiral core spark plug wires. MSD Blaster coil.
Stock exhaust manifolds. Dual exhaust into turbo mufflers.
5 speed manual transmission. Ram clutch, pressure plate.
3.42 gears. Positraction.
Stock chip. But I plan to get a better chip for it in the future.
It has explosive torque and tachs very quickly. It pulls hard until about 4300.
A vast improvement would have been Vortec heads, which I also plan to add later. It gets excellant mileage. It pulls my 21 foot Gambler bass boat with ease. Cruise torque is high, and you have to be careful, you`ll look at the speedo and your doing 50, you look again seconds later your doing 65.
I wanted something that had a lot of torque in a small package that got excellant mileage, and that`s what it is. It`s a 92 chevy silverado step side regular cab. It was costly to build, that`s one of the negatives.
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Old 06-21-2010, 05:42 PM
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The TBI engines are a well-matched package; low compression, poor head flow, tiny cams, computers that don't adapt well to vacuum changes, and modest-flowing throttle bodies. There is no one magic thing holding them back.

if you just want a few more ponies, go with headers. If you really want to make some extra juice, it will call for a comprehensive package - heads, intake, more throttle body flow, more compression, more cam, and a computer that can handle it all.
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Old 06-21-2010, 06:34 PM
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Originally Posted by gofastz
ok if you have 350 tbi engine, what can you do to it with out messing it up, if you put a cam in it you have to stay with one that will provide enuf vacume for the tbi?? or what about flat top pistons?? would this be beneficial?? anybody got anything on this, id like to hear it,,, thanxxx........
Actually quite a bit can be done, but totally insane is not easily nor cheaply achievable.

The heads, if this is a truck engine, are the infamous Swirl Ports they are a prime limiter of performance as the vortex generator within the port provides a significant impediment to mixture flow above 4000 RPM. As usual the common replacement for these heads are the L31 Vortec, but there are other modern versions out there both at GMPP and from the aftermarket. The L31 head requires a bolt pattern and port positon specific intake which as intakes go is a bit pricey. These can be had from GMPP or Edlebrock. Both force you into an external plumbing of the EGR system and parts to do this are available in both places. This is because the L31 Vortec head does not have an exhaust transfer passage. The L98 head from the late 1980's thru 1991 makes a good choice and will accept your current intake, these are easily found on Ebay. They are good for about a 20 horse boost on the swirl port where the L31 Vortec is good for about 40, but you'll need a new intake for the Vortecs.

The TBI engines are very limited by their cam, the OEM product hardly qualifies for the definition on "camshaft". The sensitivity of the sensors limits the cam to about 215 degrees duration measured at .050 inch lift, with about .45 inch lift total, with an LSA of 110 degrees or more. A bigger cam than this kills the manifold vacuum to where the MAP sensor just isn't good enough to relate the subtle flow changes into substantial fuel and ignition changes that go with the low vacuum readings of a big cam. The Edlebrock 3702 is designed to take the TBI engine close to its limit with TBI on top. This isn't a bad cam, it is very close to the cam used in the 300 horse 327 but with more LSA at about 112 degrees to keep the idle vacuum up for the TBI.

The factory 1-5/8's throttle bore TBI flows around 440 CFM which is a bit small for a 350. The 454 TBI engine came with a bigger 1-7/8s throttle bore unit and Holley has several 2 inch versions rated at 670 CFM.

The piston is an integral part of the combustion chamber. If you're doing a full up rebuild a D dish piston and a thin head gasket is the way to go in order to control overall compression for best power and mileage at about 9 to 9.5 with a cast iron Vortec head and about a ration higher with an aluminum head. The D dish keeps a flat portion on the piston to oppose the flat squish/quench step of the head, this optimizes these functions where a round dish piston with the additional space between the squish/quench deck and the true position of the crown floor diminished these functions making the engine more detonation prone regardless of compression ratio.

As usual duals with headers on the engine and low restriction cats and mufflers on the other end help power and economy.

Such a set up will require a custom chip for the engine, try these sites:





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