I just recieved my latest issue of High Performance Pontiac, and to my (thankful) surprise, they actually did a tech article on a third gen Trans Am. Basically, they covered the very basics of bolt-on upgrades which includes headers, catalytic convertors, catbacks and AFPRs. They took a bone-stock 350 TPI and equipped with Hooker 2055s, a Magnaflow cat, a huge 4" Mufflex catback with a 4" Spintech muffler, and a Holley AFPR. After installing all the parts and doing some simple tuning, the Trans Am went from a baseline 180 RWHP and 245 ft/lbs RWTQ to a decent 194 RWHP and 257 ft/lbs RWTQ.

The article mentions some small details that I thought were interesting. The first thing was the already well known issue with Hooker's 2055 headers and their tiny ball flange openings after the collectors. They enlarged enough to flow adequately without detremental effect on the sealing properties of the flanges. The article states that the 2055s were designed like this to keep the velocity of gases flowing in small cube engines (like 305s) but the 350 in the article needed more than the tiny openings could provide. Personally, I don't know whether or not this is true, but when I also enlarged the openings on my 2055s before installing them on my 305 as well. It seems pointless to have a 3" y-pipe when the collector ball flange gets narrowed down to just under 2" before it even hits the y-pipe itself. Anyway, they opened it up and had plenty of tubing left for a good seal.

Next, the article talks about port matching the headers to the gaskets. The article actually goes into detail about the disadvantages of not portmatching the headers to the gaskets, explaining how it is not only a restriction, but can actually reduce the effectiveness of headers by creating a backwards pulse of exhaust gas as it hits the right angle of the header exhaust port. It made a lot of sense to me, but it's something I didn't even consider before installing my 2055s and I definately don't have the patience of taking them off my car now to do some minor port matching only to see minimal (in any) gains. However, in the future I will remember to port match the headers with the gaskets to avoid any potential decreases in exhaust flow, and consequently decreases in power.

Finally, one particular part of the article that caught my attention was the fact that once the headers were installed, the car actually lost torque (although gained HP) and the powerband became a lot more curved compared to the baseline dyno. They consulted Bruce Hawkins (the owner of the one of this site's sponsors, Hawks Third Gen Parts) about what might be going on, and he suggested that the installation of the headers was actually creating a lean condition since it reduced so much backpressure from the exhaust. Sure enough, after using the Holley AFPR to increase fuel pressure, they increased the torque of the car by 12 ft/lbs over baseline and got another slight increase in HP. The article mentions that the powerband was much flatter than it had ever been as well.

So, this got me thinking. Stock for stock, a pathetic LG4 exhaust is creating a lot more backpressure than the comparitively beefy L98 exhaust, especially with the tiny tubing it uses compared to the L98's stock 3" tubing. Therefore, doesn't it only make sense that the AFR of our anemic LG4 cars would be even more out of whack? Is there still more power to be had after installing headers on LG4 engines by changing the amount of fuel the carb delivers by changing the rods, the hangar, and ect.?

I've never had my car on a dyno, and I don't know how to check what my AFR is precisely either. Obviously, the car that HPP tested and everyone else's cars are very different as well. But logically speaking, doesn't this idea at least make sense? I'm all for getting every last bit of power out of my car that I can, and this idea is something that didn't even occur to me until I read this article. If anyone has some kind of input or experience with this, I would love to hear it... especially if it results in more power gains for my car!

 

Generally speaking, stock rods/hanger are pretty anemic, anyway. So, they need to be tuned up even with stock exhaust.

I've thought/wondered about the rods/hanger thing with regard to reducing backpressure and changing altitude. What I've concluded is it isn't an issue. This is consistent both with my experience and with the theory. My experience was that the same rods/hanger that made the stock LG4 run better for me were just fine when I installed the 2055's, ported World 305 heads, and Crane 2050 cam on the 305. And, those same rods/hanger were fine when I put the 350 shortblock w/ZZ4 cam with those previous parts used to upgrade the 305. And, fine when I went from 5800' elevation to 1500' elevation.

This is the theory: The AV system is a mass air flow system. The rods/hanger pull out of the fixed jets as a function of mass air flow. Whether backpressure is reduced, flow capacity increased, or altitude changes, doesn't matter with regard to the rods/hanger tuning - because with increased air mass flow, the rods are pulled up more, increasing the fuel flow proportionally. That's my theory, anyway. (This would be true until the point when the AV fully opens - rarely happens with 350's, extremely unlikely to happen with a 305.)

FWIW, I did the same mods to my 2055's as you are saying the mag did. They must have seen my posts regarding 2055's on the Exhaust forum. . .

 

Also FWIW, I asked Holley why they had that tiny hole in the collector. Their response was it is the ensure good sealing to the y-pipe. Further, they said it isn't an issue because the exhaust gases have slowed down by the time they get to the collector. To which I say,

 

When you have your carb all together, and running right, you can do some runs at the dragstrip, then swap rods/hangers and see if it goes faster. Generally, fastest is best (duh )
You can also do a WOT run using the secondarys, then check your plugs. Best combined with the speed test at the track.

 

Good information. Thanks.