Originally Posted by bfhduh
i have a 79 350 turbo 400 in a 91 s10 and i want more top end power out of my stock setup. Now i do have a set of vortec heads edelbroc intake and a new carb. now is this going to be good enough to improve my top end or do i need to add a cam to the equation and if i need a cam do i need to replace the stock springs and lifters. this is my first build and i am doing it by myself so anything u guys could add to help me out would be really awesome. like i said i am pretty impressed with my 0 to 60 it is a sreaming little truck stoplight to stoplight but i want more!
The cam is at the heart of the engine's relationship with power output. Not that it works alone, the compression needs to be high enough to match the cam, things like Vortec heads and exhaust headers work better with more cam. That's to say that Vortec heads bolted to an ordinary smog era, Gen I, 350 pickup engine with no other changes to cam and compression will pull the power up by 15-20 horses. But working with a better cam, the power addition from the Vortec head can look more like 40 to maybe as much as 60 when the cam, piston crown shape and compression optimally come together; this being on top of the usual 30-40 horse increase from going to say a Comp XE-268 in place of the OEM truck cam. With a D dish piston to get a flat top like surface under the head's squish/quench step and a D shaped dish under the valve pocket to keep the compression ratio in line with what the fuel octane will max tolerate even when pushed by a high degree of squish/quench.
Long tube headers are better at making power than shorties, that is when the individual tube length of more than 20 inches shows a significant power addition compared to slightly shorter lengths. If you are using shorty headers some of this can be recovered by running a long collector, say about 36 to 40 inches and terminating the collector with an H-pipe and large, though unbaffled, muffler. This will do much to make a shorty work more like a long tube header. The total length of shorty and collector would be about the same as long tubes and collector to achieve this.
Duals on an S10 are difficult to pull off do the space limitations and the gas tank location but I like their look. Sticking out the back they just PO Beemer and Audi drivers something awful, they just have to race you. This does make a large diameter single pipe look attractive but that limits using a large resonator to terminate the collectors due to space limitations under the cab. A common solution I've used is true duals, I've modified the factory tranny cross member by welding two of them together to get a cross member with a hump for the exhaust on each side. This buys some clearance to the roadway when lowering the suspension, not much mind you and you'll have clearance problems with the emergency brake cable, I usually make some guides so the cable isn't cutting through the exhaust pipes every time the parking brake is used. The left side routing uses a mandrel bent 90 degree turn just behind the cab angled up to the right to meet next to the right side pipe that makes a straight up 90 bend. Then with another pair of 90's angle each pipe into a pair of mufflers that hang from the original muffler bracket under the bed. From there I route over the rear axle then drop down and align to bring the pipes out one the left side and the other to the right under the bumper or valance panel. I typically use 2-1/2 inch pipe for the collector, 2-1/4 for the H pipe, a resonator similar to the Vibrant 17930 as a termination box on each side. I reduce the pipe diameter after the terminator box as the gases are giving up energy and temperature at this point which contracts their volume so to keep the velocity in the pipes up I drop through a 2-1/2 to 2-1/4 adapter to the 2-1/4 pipes going the rest of the way out to whatever the muffler choice is hung under the bed. Keep in mind that for the most part the exhaust system is simply something that is designed with the intent of loosing as little power from the configuration the engine had on the dyno. The second function is to get the headers to pull on the intake system during the cam's overlap to boost the amount of mixture in the cylinder to a density greater than normal. This is a variable function that comes and goes at different RPMs. This is a typical configuration used for 350-400 horse street driven 350 or 383 power plant. For competition these dimensions can be increased by a quarter inch or more. For emissions testing where required the termination resonators are replaced with cats.
A 350 with Vortec heads even with the deep dish pistons a 79 originally came with by replacing the OEM truck cam with something like the Comp XE262, modifying the valve guides to accept more lift, using long tube headers, an Edlebrock Performer RPM intake with a suitably large carb from 650 to 750 cfm; this motor should be able to make 380-390 horses on an engine dyno. With the addition of 1.6 rockers, this combo should break into the 400 zone. With D dish, hypereutectic pistons that hold the compression about 9.5 to 1 with this cam, the engine should start pushing into the 415-420 horse range doing this under 6000 RPMs. This is a reasonable street performance 350, which will feature high reliability, long life and decent operating habits.
The problem with the S10 will be the rear axle. The 7.5, even with a girdle and shock proof oil combined along with spinning the tires as a means of pressure relief on the ring and pinion will take the shock loads way down, but at 400 horses off the crankshaft that axle may still prove to be too light for the task. The S10 axle is very narrow, about the only thing that fits without a huge amount of work is the older 8.8 inch Ford Explorer axle. This is a very sturdy piece that will easily take the power. It hits the spring perches dead on but is about 2 inches wider for the 92 and earlier and 4 inches for the 93 and newer. This is not the same axle as the Ranger which is less strong than the Explorer. The wider track requires an offset wheel similar to those of the mid 90's Camaro/Firebird, these will put the tire inside the wheel well. The hub will need to be plugged and redrilled for the Chevy bolt pattern. Explorer's pre 95 use a 10 inch drum brake, the 95 and up is a disk.