Wanting to know if the L-98 aluminum heads will be a good choice for a 350 TBI engine? I am planning on installing a 1995 LT1 Roller cam in the engine, Edelbrock performer intake (With adapter to install TBI),Holley 670cfm throttle body,1 5/8 headers and new exhaust system.

What would the HP advantage be in using a TPI system over the TBI?

What would be the HP advantage be in using a set of Vortec heads versus the Aluminum L-98 on this TBI set up?

I have the computer  available for both the TPI and TBI systems at no cost.

Any help with this will be greatly appreciated.

David

David, the aluminum L-98s are an early attempt at a post  modern SMOG enginehead that can take advantage of electronic engine controls/FI. The heads are worth 15 to 30 hp over earlier smog heads and weigh between 40 to 50 pounds a pair less than cast iron, all this depends on whose doing the measuring. Their castings are a bit on the light side so they don't take to milling over .030 and .020 is safer. They also don't like big spring pressures from a structural point of view. If you run springs with 160/180 and up psi seat pressure these, heads will fatigue out pretty quick if expected to run on the street every day.

The iron Vortec is of course 40/50 pounds heavier but feature more modern ports and combustion chamber. Of course if your a student of combustion chamber design you'll quickly recognize that these Vortec or the  GT-40 heads from the Ford house have chambers are pretty similar to those used on the 1953-57 Lincoln, what goes around comes around I guess. Anyway the Vortecs will usually pull about 15 to 30 more hp against the L-98, again depending on whose doing the measuring, but they give up 5 to 10 ft pounds of torque on the bottom end. The cross over is about 3000 rpm. That's to say that one must match gearing to the engine's power profile to maximize performance. There is a factory aluminum Vortec which is often refered to as the Fast Burn head, this gives both the benefits of aluminum and the Vortec's porting and chamber for about 500 bucks more.

Both the L-98 and the Vortec improve compression which is needed with the LT-1 cam to recover some bottom end torque. The 58 cc L-98 looks smaller than the 64cc Vortec but one needs to remember that the L-98 requires a thicker composition head gasket compared to the Vortec which can run with the much thinner steel shim gasket. So the net chamber size, hence compression will be about the same. The Vortec is also a thin wall casting and doesn't take to milling any better than the L-98. It also needs some spring help and the top of the guides need machining for lifts over .420 to .450 inch, Some are reputed to accept lifts at .470 but I ain't seen 'em. So you have to watch this.

The cam is fine for a street engine the LT-4 HOT is a bit better but if you have to qualify through a SMOG test to get your vehicle license, it will be more difficult to get it to pass with either TBI or continous flow TPI.

Stock TPI and TBI probably are pretty close on top end power, but the ram effect of TPI will make the acceleration harder on the bottom end plus it does a better job of manging emissions. TBI is cheap and simple being basically an injection carburetor. It shares some of the carburetor's problems in terms of manifold icing (thus needs plenum heat, exhaust or hot water) and has cylinder to cylinder mixture distribution problems for the same reason as a carb. Which is stick the fuel in at a central location and hope for the best. However, in it's defense much work has been done to even mixture distribution out in manifold design so a hot rod manifold intended for a carb, will work well with TBI. Factory 350 TBI (1&5/8s to 1 & 11/16s throttle bore is only good for 500 cfm or so. You need the 454 TBI or the Holley 502-6 unit with a 2 inch bore and 670cfm if your going to run this baby into the 5 grand and up RPM range.

Bogie