FAQs: Exhaust Manifolds
1. Which is the best exhaust manifold for the small-block Chevy engine?
We have tested various exhaust manifolds for the small-block. The stock 2 1/2” Corvette “Ram Horn” manifolds are about 10 horsepower better than any other manifolds. When CNC Modified, the 2 1/2” Corvette manifolds and Tru-Ram manifolds are at least 20 horsepower better.
The second choice are the 2” outlet “Log” manifolds, but only the “Log” manifold from the late 60’s. The “Log” manifolds from the late ’60’s have larger runners than any of the later model manifolds off the new trucks. We tested several types of the later model truck exhaust manifolds and found that the cross-sectional areas were 10 to 20 percent smaller than the early ’60’s logs.
We have a CNC Modified “Log” manifold that will produce 11 more horsepower than stock “Log” manifolds. The modified “Logs” will still be 10 horsepower below the CNC modified Corvette manifolds.
2. I can’t fit the 2 into 1 exhaust system on my car the way it is shown in your catalog. What is the next best way to run the system.
The “over the top” design of the 2 into 1 system is the easiest to install and a good way to keep the system from contact with the trailer and the race track. While over the top installation is generally easier, running the exhaust pipes under the car will produce the same increase in horsepower as long as the pipes are connected into one of our collectors.
When building your system remember to keep the primary pipes as short as possible. Our systems are designed around individual 90 and 45 degree bends, which are 12” long. Do not use more than 72” of pipe on each side. Three horsepower will be lost for each additional 12” section beyond 72”.
Unequal length primary pipes will not hurt power. Our tests have concluded that variations in primary length have no adverse effect on power when our 2 into 1 collector is used. Primary pipes which are equal in length, or as close as possible, are preferred but in some applications this is just not possible. So, if your pipes going into the collector are not equal, it will not hurt the engine’s performance.
If you are not running a muffler, run a minimum of 12” of secondary after the collector. Adding more length has no effect on power. In other words, “We’ve run 1 to 6 feet of secondary pipe and noticed absolutely no power difference.”
In most cases we suggest the purchase of the part #171 style exhaust system for your application. In this kit there is an assortment of pipes to get you going on your system. Since all cars are a bit different, you may have too many pipes or you many need more pipes; you will not know until you start to put the system on the race car. If you purchase our part #171 style system and have too many pipes simply return them for a refund. We also have pipes in stock for immediate shipment.
3. My rules or my chassis do not allow me to run the 2-into-1 system. What is the next best system to run?
One of the biggest mistakes racers make is not allocating adequate resources — both time and money — on the exhaust system. Do not ever just hang a couple of old pipes on the manifolds and go racing.
In cases where you are not able to run a 2-into-1 collector do the following:
a. If you are restricted to a dual pipe system, each side should be 45” to 55” in length, equal on each side and run a balance tube the same diameter as the exhaust pipe.
b. Always use mandrel-formed pipes. A mandrel formed pipe will not be “kinked” in the middle of the pipe radius. Most pipes bent in muffler shops will be kinked. All of our pipes are mandrel formed.
4. Will the 2-into-1 Collector work with headers?
While the 2-into-1 collector was originally designed for cast iron exhaust applications, it will work on headers, also. In most header applications, expect to gain 5 to 10 horsepower. As with cast iron manifold systems, it is usually not possible to get the pipes from the header collector to the 2-into-1 collector equal in length. We have found that having a variation in these pipes will not effect power.