by Larry Paulick in the April and May 2004 RootesReview
The Tiger exhaust system in its stock form is adequate for the stock motor. If you would like the car to breathe better, or if you have made changes to the intake manifold and carburetor over the stock system, then you need to really build an exhaust system to match the intake side. We all know that the engine is just an air pump and so if changes are made to one part, then the other parts must be adjusted. Think of the intake and exhaust as a coordinated system. What goes in must be able to get out. New manifolds, carburetors and tube headers are very common in Tigers.
The problem is that the exhaust pipes must pass through holes in the body X-Frame that limit their size. On a stock system, with a 1-3/4” diameter exhaust, the pipes become even smaller by crimping to go through this passage. I have a 1990 Mustang 5.0 L engine with a Edelbrock F4B manifold, the LAT-1 option, with a 600 CFM Double Pumper Holley that requires an improved exhaust system.
The exhaust system, described here, consists of Rick’s Headers that have been coated by Jet Hot, 2-1/4” diameter exhaust pipes, an “H” pipe after the headers and Flowmaster mufflers. A revised exhaust pass-through in the body allows the Full 2-1/4” diameter exhaust pipe to run the full length of the car from header to exhaust tip.
Intake and Exhaust System Considerations
Here are some things I have learned over the years of reading car magazines, especially with dyno tests, which are the real test for any change. Size your carburetor to your engine size and maximum rpm. My carburetor is just over the top at 600 cfm. With tuning, it has not hurt performance.
Select your intake manifold for your anticipated rpm range, i.e. idle to 5,500 rpm, or 2,500 to 6,500 rpm. This will determine how your engine and carburetor match. Manufacturers like Holley and dealers like Summit can help you size your carburetor and manifold for your engines size, rpm range and transmission type. I called Edelbrock, and said that I had a Tiger that weighed about 2,400 pounds, had a 5.0L engine, stick trans, and I did not want to go much past 6,000 rpm. I still have the stock cam, even though this engine has a roller cam and now roller rockers.
Funny, I told them I had the old F4B manifold and they said that was still a very good manifold, good from about 1,200 rpm to 5,500 rpm. That “made my day”, as I was ready to go to one of their other manifolds. I liked the old manifold, and it really fit within the rpm range of what I wanted.
Decide on an Exhaust Manifold
The stock manifold is very restrictive and never intended for performance. Even the very pricey Tri Y LAT-27 headers were reported to add little to hp and torque, according to the Book of Norman. I purchased a set of headers that Rick, of Sunbeam Specialties, supplies. They are quality 16 gauge metal, of a more modern design, and with a little adjustment, they fit the Tiger.
Coating the headers with a long lasting coating is a worthwhile added expense. I chose Jet Hot, for lots of reasons, but there are other good coatings available, so you decide. The choice was really a no-brainer. The life of the headers is extended significantly, which is important if you have ever had to change headers. Also, over the life of an uncoated header, it not only rusts internally, or what looks like rust, but is really metal fatigue. What this does is slow down the hot gasses, and over time not only reduces the life of the header metal, but reduces the hp and torque up to 5%. Bummer. I paid as much for the Flowmaster mufflers and headers as the Jet Hot coating, which was about $250 over the cost of the headers, but for the above reasons, I went that way. Besides it looks nice, and I hate rust. You can paint with HTP (High Temperature Paint) but they just don’t have the properties of these coatings.
An added H Pipe connects the two exhaust pipes and does several things. First, it increases the torque at lower speeds, and secondly, it reduces the db level, or noise of the exhaust system over the entire rpm range. How much? Well most articles say it will increase torque about another 5-10%, and lower the db level by about 5%. That sounds good to me, and the added cost in a new system is not that much more. By the way, the only place the H Pipe will fit conveniently is not too far after the headers, which is the optimum location for an H Pipe. You should put a connection on either side of the H Pipe in case you want to remove the engine and transmission without a complete removal of the exhaust. The same applies to the muffler system.
Why 2-1/4″ pipes? Bigger is not always better. Look at the various web sites for mufflers such as Flowmaster, Borla, etc. and read the magazine articles. You will find that for at least my 302 cid engine, and at my rpm range, 2-1/4″ exhaust pipes are optimum. For your Tiger, it will probably be between 2″ and 2-1/4″ diameter.
The idea is to keep the exhaust gases hot and flowing. 3″ diameter pipes look great, but they hurt performance. The exhaust pipe materials available are uncoated steel, aluminized steel, and stainless steel. The prices go up dramatically, as well as the longevity of each material. The front part of the exhaust, after the headers, including the H Pipe get enough heat that they do not suffer from the dread of most exhaust pipes, which is the acid in the water that collects in an exhaust system. This acid will eat a system from the inside out. The muffler does collect acid water, and the only way to reduce the problem is to drill a 1/8″ hole in the lowest part of the muffler to drain the acidic water. The performance is not affected, and muffler life will be increased. The exhaust pipe after the muffler also collects the acidic water, as it is the coldest part of the exhaust. Therefore it is prone to rust out the quickest. I used aluminized steel from the headers, including the H Pipe to the muffler, and polished stainless steel pipes after the muffler. I recommend that you use stainless steel bolts and clamps. The cost of the Custom Exhaust System including custom mounting tabs in stainless steel, rubber mounting isolators and installation was $450. Is It worth It? ell, all of this theory is good old hot rod science. The system looks good and I will not have to change the exhaust system for many years.
I used Flowmaster mufflers. They are well designed with thick materials, and really deliver what they say in the way of performance. You want the largest muffler you can fit, to reduce noise. Because of the short overall length of the total exhaust system, you can either cut down on noise and performance with a restrictive muffler, or choose the largest muffler with good performance characteristics. Loud mufflers wear you out real soon on a long trip. The Flowmaster #42451 just fits as far as size, and has very good performance characteristics. Cost is about $65 per muffler (in 2002). They now have a TriDelta muffler that is supposed to be marginally quieter, is the same size, and just about $20/muffler more expensive.
Required Body Modifications
This frame exhaust pass-through design allows a true 2-1/4″ diameter exhaust pipe to pass through the frame without crushing the exhaust pipe. A number of years ago, Dale Akuzewski did an article, where he took a 3″ diameter electrical conduit pipe, crushed it into an oval with a minor axis of about 2-3/4″. This is a very good idea for three reasons:
- First, you can run a true 2 1/4″ exhaust.
- Second, you actually strengthen the frame in this section. The pass through area is cut out to fit the electrical conduit, with a die grinder, and then, the front and back, are continuously welded. This provides a stronger section than the original design.
- Third, it eliminates the open part of the frame that is open to the elements, collect water,
and can rust out.
Rear wheel performance on a Dynojet Model 248C Dynamometer, with no tuning and just the muffler system installed for a base run was 196 hp and 250 #-ft of torque. Assuming a 20% loss for trans and diff, this equates to adjusted figures at the flywheel of 245 hp, and 313 #-ft. The final rear wheel engine performance, after dyno tuning, yielded 237 hp and 277 #-ft, or 296 hp and 346 #-ft at the flywheel. The torque curve is very flat, with approximately 245 #-ft at 1,800 rpm, and dropping to 250#-ft at 4,900 rpm. A stock 1990 EFI Mustang is rated at 225 hp at the flywheel. The Dyno guy said that the Mustangs he does normally have about 185 hp at the rear wheel, if they are in top shape and with some modifications already done to the engine. The Mustang engines also have more accessories running than a Tiger.
Good Luck with your project.