|The Goodwrench Quest Part II|
This article was taken from the October 1999 issue of Chevy High Performance magazine. This is the second of a eight part series.
Budget horsepower in the name of this game. If you followed the exploits of our GM Goodwrench budget 350 provided by Scoggin-Dickey Performance Center from last month, then you know that we pumped a few steroids into the stock OEM combination in the form of a set if headers and and Edelbrock Performer intake. In this configuration through mufflers, we made a respectable 265 hp and and even stronger 350 lb-ft of torque. While that's not bad for a couple of simple bolt-ons, we're not nearly satisfied. We know this pedestrian 350 is capable of much more power.
The simplest path to increased power is to methodically remove the restrictions that prevent the engine from breathing more deeply. We started that process last month with the headers and intake. Now the cork in the system was the cylinder heads. While we could just bolt on a set of better heads (which we will do next month), we thought we'd first try improving the existing cylinder heads. This was also the cheapest way to go.
Our first step was to remove the cylinder heads and do a little measuring. Chevy claims the engine squeezes a mean 8.1:1 compression, but somehow, in a fog of mathematical befuddlement, we claimed last month that the Goodwrench motor measured 8.4:1 compression. We were wrong. After we rechecked our ciphering, Mr. Goodwrench proved to be much lazier. The actual compression figures out to be a menial 7.8:1! Based on this complacement squeeze factor, we decided that increasing compression and improving airflow would be a good idea.
Flow To Go
As you might imagine, stock 1.94/1.50-inch castings are weak when it comes to air flow. In the name of budgetary restraint, we decided to stick with the stock valves so we could evaluate the effect of the porting. McKenzie Cylinder Heads in Oxnard, California, performed the cylinder head porting for this story, but per our instructions. Todd McKenzie spent very little time on these heads. Better yet, you can duplicate this work yourself with little more than a porting kit from Standard Abrasives, a small air compressor, and a hardware store 1/4-inch die grinder. The plan was to perform a simple pocket port job that would generate the most results for the least effort.
If this is your first attempt at cylinder head porting, you may want to practice first on a junk cylinder head, While the work looks intimidating, it really is easy to do. In fact, once you get comfortable, the hardest part is to stop working after blending the seat area 1 inch past the bottom of the valve seat. The key is to stay conservative and not hog out the port in search of more power.
Another area worth investigating is back-cutting the valves. Flow bench testing has proved that placing a 30-degree back cut on both intake and exhaust valves improves the low and mid-lift flow of both the intake and exhaust ports. This back cut is placed just inside the 45-degree face of the valve and acts much like the three-angle radius of a valve seat to improve flow. The 30-degree back cut can be accomplished by any competent machine shop and will improve cylinder head airflow even if pocket porting is not included. We have found that back cutting both the intake and exhaust works, but McKenzie decided to back cut only the exhaust side for this test.
Before the heads were reassembled, McKenzie also treated them to a simple milling operation that reduced the chamber volume from 76 cc to 73 cc. The effort was aimed more at ensuring that the deck surface was flat than at attempting to dramatically increase compression. However, we also decided to eliminate the stock GM compression gasket that measured a stout 0.039-inch thick in favor of a much thinner 0.015-inch thick gasket from Fel-Pro.
After measuring everything again and doing accurate ciphering, we came up with a slightly better 8.4:1 compression. While this is hardly killer squeeze, we figured every little bit helps.
While all the theory supports these efforts, the only way to know for sure is to test these stock heads before and after and report on the results. Typically, pocket porting is worth around 20 hp, with most of the power gains seen above 4,000 rpm. While we did improve the torque, as usual the bulk of the improvements occurred above the 4,000 rpm mark. Keep in mind that all we did for this first test was yank the heads off, do the pocket porting, and stuff them back on the Goodwrench grist mill. From lat month's best numbers of 265 hp at 4,400 and 350 lb-ft of torque at 3,600, the combination of the pocket-porting work and the compression ratio increase pushed our Goodwrench Quest 350 to a solid increase of 26 hp at 5,300 rpm. The cork was now the miniscule camshaft. It was time for a hotter cam.
The stock cam was downright wimpy, (see the Cam Specs Chart) and now that we had a set of cylinder heads that were up to the task, it was clearly time to take advantage of the heads with more duration and lift. There's always a tradeoff when swapping camshafts. The stock cam produced a smooth idle but didn't make great power. The Comp Cams Xtreme Energy 268H cam we chose bumped the duration at 0.050 inch by a massive 30 degrees on the intake side and 28 degrees on the exhaust. Even more amazing is the lift comparison, where the intake valves now jump 0.094 inch higher and the exhaust gains 0.079 inch!
After we installed the cam, we turned Duttweiler loose on the dyno and pushed the Goodwrench 350 to a thumpin' 336 hp at 5,300 rpm, with peak torque jumping up to a killer 377 lb-ft at 3,800 rpm. These are excellent numbers for a basic 350 with a few simple modifications.
Are we satisfied
with the power? Hardly. We've pumped it up from a measly 236
hp to a righteous 336-a massive 100 hp over the bone-stock baseline.
Next month, we're all set to try a set of Corvette L98 aluminum heads from
GM Performance Parts, and then we're going to pocket port them to see what
they can do. After that, we've got a set of those trick iron Vortec
heads to try. And then maybe a bigger camshaft and then....well,
even we haven't gotten that far yet.